Great Sounding Speakers

Have you ever heard anyone say that certain speakers sound great and others do not sound great? I am certain all of us in the audio business have heard this statement before. What goes into this statement and what does a great sounding speaker sound like. I think the real answer is somewhere between measurements and perceptions.

Hearing Test

The first measurement we could look at would be the hearing capacity of the listener. Does the listening have the physical ability to hear everything that the speaker can produce. Is the listener able to process that so important 500 – 3,500 range where all middle range information lies. Can the higher frequencies be heard or are they attenuated by aging of the listener. Assuming all parts are there and in good working order, we can now look at the speaker measurements.

Speaker Measurements

Do our speaker measurements glide smoothly across the frequency spectrum or do we have a 300 cycle bump because of the crossover. Is the cabinet resonances properly damped so we actually hearing speaker only sound as much as that is possible. Do all crossover points in each of our drivers work together so there is a seamless blend of middle and high frequencies.

Speaker Combinations

Is the low frequency bands properly balanced to mix and match with the middle frequencies. Or are we running smaller monitors that maybe go down to 50 Hz. and have no low frequency extension to them because of their size. Are we using the two smaller monitors in conjunction with a sub woofer. Is the sub woofer crossed and positioned correctly within the room in which it is placed.

Not One Size Fits All

Is the speaker the correct size for the room. Will it provide too much energy for the room to handle at average or higher sound pressure listening levels. If our listener thinks more is better, than having a six foot tall speaker in a room that is 7 tall, may cause sonic issues. Critical matching of driver diameter and number of drivers to room size is very important to sound quality perception of any speaker size.

Room Sound

When someone says that speaker sounds great, those words must be qualified by saying, “in this room” The room contributes at least 50% to the sound the listener is hearing. It is not just this speaker sounds great it is this speaker sounds great in this room. Low frequency resonances, speaker to room wall distance, listening position to speakers, and comb filtering from our room can set the stage for audible room sound in our mixes or playback presentations.

Room Size

Room size is critical. There is simply no substitute for selecting the proper ratio of height, width, and depth that will produce the least amount of low frequency resonances. Not only the amount of resonances but where they are located within the room. One must find these elephants and tame them through proper low frequency absorption techniques. Resonance blur and smear our presentations with excess energy that can smoother and blur our music presentations. A microphone placed in a room resonance may not “hear” any of the frequencies you want to record because the pressure level of the resonance is smothering everything you want to record.

Speaker Boundary Interference

Where is our speaker that sounds great located. If it close to a room wall surface, we will have condition occurring termed speaker boundary interference. The distance of the speaker to the wall and listening levels is a critical factor in determining room frequency response. If the speaker is placed too close to the wall, we can have low frequency energy levels increased at our listening position. If the listener like bass and the speaker/wall distances are more on the bass heavy side, he may consider that sound to be good speaker sound. Instead, It is bad room sound.

Near Field

If our speakers that sound great are set up in a near field set up, then we have less room reflections to deal with at the listening position. With less room reflections at our listening position, we have less room sound and more direct energy from our speakers. If a near field set up is used we hear mostly the speaker. Sitting and listening near field is a good way to really listen to a speaker. If it sounds great near field, it will probably be a great speaker.

Comb Filtering

Comb filtering is another room distortion that can cause our speaker and room sound to not get along at all. The problem with comb filtering is that you may not know that you have it. If you measured the room, you would know. The display of a comb filter looks like hash marks that resemble the teeth in a pocket comb. Comb filters hide and distort frequencies that are mainly located in the middle frequency range where most vocal information lies. They are a series of reflections between two closely located surfaces that get together and make their own sound.

Many Factors To Great Sound

If someone says that this or that speaker sounds great, we must make sure the listener can hear everything reproduced by the speaker. The speaker must also be able to reproduce all the energy required in a seamless and timely manner and presentation. The position of the speaker within the room and the size of the speaker to the room all can contribute to speaker sound quality perception. Speakers and the walls in the room can cause issues along with room size and comb filter distortions. These speakers sound great, must be followed by “in this room”.

One Sound Family

Our speakers and microphones are part of our signal chain. The microphone is at the very beginning of this chain and our speakers are at the other end. Microphones take acoustical energy and convert it to electrical energy and then we process this energy through our equipment. Our speakers then take this electrical signal and mechanically move to produce analog energy that our ears can hear. All of this connectivity ends when we place our speakers and microphones in our rooms.

Microphone

When we use a microphone in the recording process, we are continually dealing the sound of the room in which it is placed. Care must be taken to include the vocal or instruments information with the correct amount of room sound for a balanced blend of room and music. With vocals we want no room sound or a very small amount. With drum sound, we want the sound of the room. Room sound is usually not welcome in our recordings except when recording drums.

Drum Sound

Our typical drum room has high ceilings and is a larger room. It is a larger room because larger rooms produce a larger sound at the microphone positioned. Most recordings like to have a larger sounding drum. If the engineer gets the drum sound correct, everything else in the mix falls into place much easier.

Speakers Smaller Rooms

Our speakers do not like larger rooms. Larger rooms require bigger speakers in order to produce the necessary amount of energy to fill the larger space.The larger the room, the more detail we loose in our sonic presentation. Larger rooms require larger drivers which loose detail as they increase in size.

Hardwood Floors

When we place our microphone in the drum room, we notice that our drum room would have hardwood floors and not much room treatment on the walls. Reverberation times would be higher than most rooms because of size and lack of absorptive room treatment. If the drum room had carpeting, it would probably be removed and any existing absorptive room treatment would be removed from the walls to increase room reverberation times.

Carpet On Floors

Our speakers do not like hardwood floors. Any hardwood flooring will produce reflections at the listening position and we do not want any reflections at our listening position interfering with the direct sound from our loudspeakers. Carpeting or some type of rug treatment over the hardwood floor is desired.

Find The Reflections

The microphone is our drum room likes reflections. Reflections represent the sound of the room. The time signature difference between reflections from our drum room wall and ceiling surfaces is the sound of the room size that the microphone wishes to capture. All of these reflections occurring at different time intervals all add up and contribute to the room’s total reverberation times. Different drum room reverberation times, produce different drum sounds in our mix.

Less Reflections Please

Our speakers have to be placed in an area of our room that is free from room boundary reflections. Our goal at the listening or monitoring position is to have the direct sound, the sound that travels from the speaker to the listening position in a straight line, reach our ears first before the room reflections. We want some reflections to follow the direct sound to add realism to our sound stage, but our goal is to hear more of the direct sound which contains the essence of our music.

Distortion Everywhere

We have distortion in our equipment. Some of it is wanted and self induced. The unwanted type must be managed and controlled. Our small room acoustical environments also have distortion. It is not electrically induced but it is distortion none the less. All room distortions are unwanted by their very own definitions.

Distortion Definition

The term distortion is a term that refers to a change from the intended designed for signal and the unwanted sound. Distortion is this difference. It is the change in the original wave form as it moves through the circuitry of a unit or though many units chained together. If the waveform is changed in such a way that it is flattened from its original bell shape, we call this distortion clipping because it “clips” the top of the waveform off.

Wanted Distortion

In our equipment their are two main categories that distortion falls into. Lets call it wanted and unwanted. Wanted distortion is sought after. We twist this knob or that one to try and alter the waveform to produce a desirable, unique, and different sound quality to an instrument or vocal. We can overdrive an amplifier with a guitar to achieve a certain guitar sound.

Unwanted Distortion

The unwanted distortion occurs when we have hum or static in our system. This unwanted distortion comes about because of the misuse of electronics in the signal chain. If an electronic circuit in one of our pieces of equipment sees a signal that it can’t handle and then starts to overload, we will get electronic distortion. We have all heard this with ground looping issues. The original waveform that was originally designed to produce by the equipment has been distorted through overloading the circuit.

Longitudinal Waves

Sound waves are classified as longitudinal waves. They oscillate or expand and contract like a caterpillar moving across the floor. This raising or lowering of the caterpillars body produces higher and lower pressure regions. Each of these pressure areas minimum and maximum have opposite polarity. The pressure on one side is increasing and the pressure on the other side is decreasing.

Room Modes

Our small room acoustical environments have distortions. Rooms have a certain dimensional ratio that produces room modes. These modes or resonances are the room’s way of reacting to certain frequencies or wavelengths. Certain room sizes like certain frequencies while disliking others. When a room modal resonance is excited, it can blur and smother other frequencies. A microphone placed in a room mode may “hear” some of the intended sound to be recorded, but may miss other frequencies completely.

Axial Modes

Room modes come in three main flavors. There are axial modes which are the resonances that occur between two parallel room boundary surfaces. Axial modes are the most powerful of the three forms of modes. Axial modes occur between the ends of our rooms, the sidewalls, and the floor and ceiling. There are also the associated harmonics that go with each fundamental resonance.

Tangential Modes

Tangential modes are half as strong as axial modes and occur between two sets of parallel surfaces. Tangential modes are formed by four traveling waves that reflect from four walls and move in a manner that is parallel to two walls. Even though they are only half as strong as axial modes the frequencies that they occur at along with their harmonic trails interfere with our middle frequency ranges where our vocals lie.

Oblique Modes

Oblique modes involve eight traveling waves that are reflecting from all six room boundary surfaces. They are half as powerful as tangential modes and half one fourth the energy of an axial mode. Axial and tangential modes give us the most difficulty when we are trying to manage them. If one treats for axial and tangential modes first, the oblique modes will usually become a non issue.

Speaker Boundary Interference Response

Our speakers and our room walls create another distortion. It is called the speaker-boundary interference response. This is a distortion that is produced as a result of the direct sound from our loudspeakers interlacing with the reflected sound from our room surfaces. This particular type of distortion occurs at lower frequencies more than middle and high frequencies.

Virtual Images

The room’s boundaries that are close to our loudspeakers create another speaker if you will. The sound leaves our speakers and strikes the nearest room boundary surface. That energy is then sent back to the speaker through reflections. This process continually repeats itself and we have the speaker producing energy and then all of these virtual reflected energies producing sound. Thus our sound at the listing position will be coming from our speakers and the room boundary interference “speaker”.

Comb Filtering

Comb filtering is another room caused distortion. Comb filtering is basically a reflection that interferes with our speaker direct sound. The direct sound from our loudspeakers is the sound that travels in a straight line from the speaker to our ears. It is the sound that we need to hear so we get our mixes correct. Reflected energy from our room surfaces contains all the room sound. We do not want room sound in our mixes, so we sit near field to try and take the room sound (reflections) out of our mix.

Comb Filtering Evil

When reflections interlace with the direct sound and we take a picture of this phenomenon, we see a series of peaks and troughs closely grouped together to form a “comb”, just like the device we use on our hair. You know the thing we use to keep next to our pens in the pocket protector. This comb filter does just what the name implies. It imposes its comb like teeth on our audio signal and can filter all of the clarity and definition from our music. A comb filter can also mask whole instruments or vocals, especially harmonies and rhythm sections.

Natural Diffusion

Sound that occurs in our lives that is not absorbed is reflected or diffused. Diffusion is everywhere in our world with sound bouncing and moving off all objects on earth. Our ears are specifically designed to deal with diffusion of energy and our ears localization systems work in a diffuse sound field. When we take a space of air and build four walls with floor and ceiling, we contain that air space and then we minimize the diffusion that occurs naturally in our world.

Diffusion Is Air

A diffuse sound field has “air” in it. Air is that space between each attack note. It is also that space where the note decays in. It is in the reduced and focused reflections from the walls that it works its magic. Diffusion takes a reflection and reduces it in magnitude without altering the signal’s phase or amplitude.

Our electronic equipment produces both unwanted and wanted forms of distortion. Bending waveforms does have its sonic limits. Unwanted distortions that are produced electronically are unwanted because they hurt our ears. Our rooms can also be a source of this acoustical pain. Reflections mix themselves up with the direct sound and then we have this dance of direct/reflected energy. It is a dance between the direct which is the music and the reflections which represent the room sound. If the dance gets to heated, we get comb filtering. Our room is a box and we must let fresh air in our box. One could tear the walls down or simply add acoustic diffusion to create more natural air.

There are many variables to room acoustic treatment. There can be even more variables to the application of the technology associated with room acoustic treatment. A step by step check list is needed. Just as a pilot goes through a pre-flight check list, we need an acoustical flight checklist before we can musically “fly”.

First Guideline

Choose the correct room size. Find the balance between height, width, and depth that minimizes all resonances that occur below 200 cycles. Remember, our room is a huge box of sound pressure. We need to have room size that has all room resonances spread out through the room. If you need to take an existing room and make it smaller to fit a golden ratio of room dimensions that spread resonances out, do it.

Second Guideline

Treat all low frequency issues now. Run a room modal calculation and find out where these rascals lie within the room. One has to take a measurement, move the measuring mic. and then take another measurement. Repeat this process every three feet around the room. One can actually map the resonance’s location and its amplitude. It takes awhile and a couple people to help do it, but it will be worth it. If building new, use a resonant cavity to control low frequency energy. If using an existing room, use a resonating panel type of absorber. A diaphragmatic absorber is a good example of a resonating panel.

Third Guideline

Isolate the room from outside noise. Insulate and isolate the rest of the world from the sound produced inside the room. Do not increase the ambient noise level of the universe. Keep all sound produced in the room where it belongs, in the room. keep all outside noises from getting into our mixes or playback musical presentations. Use barrier technologies to achieve sound transmission loss within or on existing structures.

Forth Guideline

Choose room building materials that will naturally produce a better room sound. Room energy that strikes a surface within our rooms takes on the sound of that surface. Sound strikes glass, one gets glass sound. You know that sound. That is the sound of your car stereo. Sound strikes wood, one gets wood sound which is smooth and warmer sounding. Some rooms are harder than others. A concrete room will have more reflectivity due to the harder surface of the concrete. A gypsum wall surface will flex slightly when compared to a concrete wall that will move much less and cause less reflectivity.

Fifth Guideline

Decide on the room purpose and use. A monitoring room has different acoustical goals than a playback or listening room. In a monitoring room, we need to keep the room sound out of the mix. We need to hear only the music, not the music and the room. In a playback room, we want to hear the room sound and the music. Our goal is to reproduce the original recording with all its accuracies and sometimes flaws. We want to manage the amount that we hear, but we want some room sound.

Sixth Guideline

Find the proper location within the room for your speakers. The distortion that occurs from the speaker/boundary is a source of acoustical distortion. Improper speaker positioning can boost some frequencies and bury others. Find the location that produces the smoothest frequency response curve. This position will be a certain distance from the front and side wall boundary surfaces.

Seventh Guideline

Reflection control must compliment room usage. If one is using the room for professional monitoring of recorded signals, then we must use a near field monitoring position to minimize side wall reflections. We also must absorption technologies for side wall reflections, so they do not interfere with the direct music sound from our monitors. Our monitors must be frequency response flat. If we are using the room for playback, we want a blend of absorption and diffusion on the side walls, rear, and front walls.

Eighth Guideline

The rear wall of any monitoring or listening room must have two dimensions of diffusion. This is a minimum requirement. A two dimensional diffusor can be installed or one can use quadratic diffusion. The frequency range of the diffusor must be specifically designed for. Once that is determined, one must position both vertical and horizontal quadratic diffusors to achieve a two dimensional reflection free sound field at the listening or monitoring position.

Ninth Guideline

Use absorption as the ceiling treatment in a professional project studio that has lower ceiling heights. Our goal with our professional mixing environment is to keep as much as the room sound out of our mixes as we can. Ceiling reflection absorption technology employed on the ceiling will keep ceiling room sound as a minimum. Listening rooms need two dimensions of diffusion or a blend of absorption and diffusion.

Tenth Guideline

There are only three things that happen with the sound energy within our rooms. Sound energy is either absorbed, diffused, or reflected. To control and manage these three energies we use sound absorption and diffusion technologies to deal with reflections within our rooms. We use absorption technologies for lower frequency control and management. Lower frequency energy is not diffused only absorbed. We do not want to encourage it by using huge diffusors.

Project and Full Studio Elephants

I have been in over 12 project and full studios in the last few months and there is one issue that plagues them all. Each studio type has at least one room in a full studio and the whole room in a project studio that has some low frequency energy resonances. It is the lower frequency ranges that are the sleeping elephant in every room. Well, most of the time, the elephant is not sleeping but trumpeting always without much provocation. Our elephant usually lives in the 30 -100 cycle range.

Lots Of Music

There is a lot of musical information within this frequency range. It is the frequency range that plays the most havoc with our professional monitoring and control rooms. It destroys any balance in our listening rooms and can smother and blur everything with unwanted sound pressure resonances.

Saltmine Guitar

Bass, Toms, and Kick

It is also the most critical area for all of our energy from the lowest string on our acoustic or electric guitar, say around 80 Hz. Bass guitar follows in this same region with a start at around 35 Hz. Our tom and kick drums are also located in this neighborhood. Toms start around 50 Hz. with kick drums beginning at 30 cycles. These notes provide the track for the music train to run on.

Saltmine Drums

Air Guitar

All of these instruments provide the driving force behind and underneath our middle and high frequencies. Well, at least our middle frequencies. Highs seem to have a mind of their own. They make our feet tap and cause our hands to move, like they are playing a bass guitar even though we have no knowledge on how to do that. Low frequency notes in our music deserve more room respect than they currently receive.

Lets Go Hunting
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We have three “weapons” we can use for our low frequency resonance reduction. I use the word reduction on purpose. Room dimensions dictate the resonances that will occur and at at what frequency. Only changing room dimensions will eliminate a low frequency resonance. Unless you have a room with at least a 30′ length, you have no way with add on room treatment technologies to have a room that is flat down to 20 Hz. All one can do is manage or reduce the amplitude of the resonance.

Resonant Cavities

We have two, low frequency services at our disposal. We have resonant cavities and resonant panels. Resonant cavities are large devices and require a lot of surface area. They are a cavity that is calculated to have a certain volume that will resonant at a frequency that is low enough to absorb the resonant frequency. Resonant cavities are too large of a low frequency device for a project studio where space is critical.

Resonant Panels

Resonant panels are easier to work with because they can be free standing or wall hanging. They also can be designed and built to absorb a lot of energy in a small amount of space. They are built by using a sealed box that has a front panel or diaphragm that moves when sound pressure strikes it. This diaphragm movement slows the wave down as it moves into the cabinet.

Cabinet Fill Material

Inside the cabinet, it will meet an internal cabinet fill that is designed to absorb all the resonant activity within the cabinet. The internal fill material must also be able to assist in absorption of other energies other than existing cabinet resonances. If a proper material is chosen for the internal cabinet fill, one can achieve a large amount of absorption in a small amount of space.

Depth And Density

The depth of the cabinet and the density of the material used to build the resonant panel or cabinet are ones that need to be chosen carefully. There is an acoustical relationship between density and distance. The cabinet density or mass influences how low the absorber will go down to absorb. This is called the panels resonant frequency. Frequencies above the resonant frequency will be absorbed, those that fall below will not.

Diaphragmatic Absorption

Diaphragmatic absorption is another name for a resonant panel absorber. A diaphragmatic absorber has a front wall or diaphragm that moves in sympathy to the amount of sound pressure exerted upon it. It also has a cabinet and face panel that have a certain density or mass. There is a statistical relationship between these two pieces. The cabinet material density has to be greater than the density of the face panel by a certain factor.

Internal Cabinet Fill

The internal cabinet fill material must also be considered as a critical part into the total cabinet’s performance. It is the most important factor in determining the cabinet’s rate of absorption. The cabinet’s depth and density contributes to the cabinet’s achieving a certain resonant frequency. The front panel’s density and method of installation and construction go hand in hand with the cabinet’s resonant frequency.

SPL – Sound Pressure Please

Resonant panels or diaphragmatic absorbers work with sound pressure. They all need sound pressure to activate or resonate. They require it in order to perform. They perform well when the pressure is high and they work well in locations of the room where these higher amplitudes reside. Corners of our rooms and the intersections of the floor, ceiling, and walls are good high pressure areas. Try to distribute low frequency absorption around the room and not concentrated into one area of the room.

Both small and full room project studios suffer from low frequency issues. The frequencies from 30-100 cycles in our rooms contain a lot of musical energy that is necessary in our recordings and playback environments. It must be heard clearly and well defined. We can use a resonant cavity if we are building a room. However, for small room acoustics we must use a resonant panel that can be designed to achieve a certain resonate frequency above which energy can be absorbed. A diaphragmatic absorber is an example of a resonating panel. Rent a hand truck to position the diaphragmatic absorbers in place. They can weigh over 200 lbs.

TWICE-”Tablets Driving Premium Headphone Sales”

In an recent TWICE blog entitled, “Tablets Driving Premium Headphone Sales”, Dave Dunbar discusses what people look for when purchasing headphones to go with their tablets. Dave talks about price, sound quality, and fashion and how these three variables interlace with each other and enter into the decision making and ultimate purchase.

Line Item In Budget

Dave tells us in the article entitled, Tablets Driving Headphone Sales, that prices for headphones for tablets can reach $100.00. With the price of tablets around $400.00 that equates to 25% of the total purchase price that goes for sound. This is very encouraging to see. A customer is willing to spend a part of their budget for good sound quality instead of using the standard supplied ear buds

Better Sound Quality

It appears that individuals with tablets or even lap tops want a better sound quality in their audio signal chain. Well, I say its about time. The whole platform of tablets and laptops has been about the video presentation using text, stills, and videos. We have U Tube for videos, we send text for emails, and we attach still photos to our emails. All of these formats are video only and have audio as a secondary concern. Playing music through your computer speakers is definitely making audio presentation a secondary concern.

Need More Sound Conscious Consumers

It is good that sound quality is a consumer issue and enters in to their buying decision. We need a new generation of people that want good audio presentations. The more people that want it and purchase products that have it, the more demand for it that will be created. This demand will “force” audio manufacturers to develop quality sounding technology at a price point that fits into the tablet and laptop landscape. It will help consumers obtain better quality headphone products.

Another Hook Needed

Perhaps the video formats have all been worked out and manufacturers must look for new ways to attract customers. Now, we have tablets that are small and very portable. We even have cell phones or smart phones that can be used to play an instrument on. If a group of people are playing their phones, audience members can use their cell phones to show approval by selecting a “flame” application as if using a cigarette lighter in the audience. It also appears from the commercials on television, that one can even take a real time video of one’s mouth and voice approval or disapproval for the live music event by using our smart phone screen with a video of our mouth moving.

Younger Years

In my younger years, all of my friends and I were hi-fi enthusiasts. We all had our own two channel playback systems that consisted of a turntable for our source, an amplifier or more appropriately a receiver, and two speakers. Some of us had headphones, some did not. We had our systems set up into our rooms and back then basements. We would spend hours listening to music in these environments. It was a major event when a favorite group came out with a new album. Whoever had the money at that time bought the album and then we took turns listening to it.

Music, No Video

Music was always in our lives. Our hi-fi systems were our source of music and really our only source. Well, I guess we had a transistor radio to listen on. I remember listening to WLS out of Chicago. It was the most powerful radio station of the time and I think it was 50,000 watts or something like that. I remember listening to it all the way from Illinois to Florida heading to spring break in Panama City.

Sound Quality Back Seat

Today, sound quality definitely takes a back seat to video. Everything is about sight and not sound. It is a complete paradigm shift. Smaller and smaller the screens get and smaller and smaller goes the importance of our sound quality. The sound quality does not stand a chance with the speakers in our lap tops or smart phones. At least with headphones, one can control the sound quality level a little more.

Accessorize Accessorize

One could also accessorize with an external DAC. DAC stands for digital to analog converter. It take the digital recording data and converts it to an analog signal that our ears can hear and the headphones can process. Perhaps manufacturers could provide matching styles for the DAC and headphones. With the DAC, one can just use the smart form for digital data storage and then play this data back through the external DAC. The sound quality of an external digital to analog converter is always better than the ones in smart phones and lap tops.

Whatever the marketing strategy or hype, it is a welcome to see at least a partial shifting towards audio and in particular audio quality. If more people are exposed to good sound quality then perhaps audio still has a chance to compete with video. I do not think audio quality will ever run ahead of video but if younger people are involved with quality sound through headphones connected into their tablets then we have a new generation of music and sound appreciation. One can only hope.

Listening And Monitoring Rooms – 101

In our last narration, we discussed three major acoustical benchmarks that must be used in any listening or monitoring room environment. We discussed proper room sizes, side wall reflections, and low frequency resonances. In this discussion, we will focus on our reflection free/reflection minimized zone, comb filtering effects, and front and rear wall impacts on our listening or monitoring position position.

Reflection Free Zone

Our monitors must be set up in a way that creates a reflection free zone at the monitoring position. We must position our monitor speakers and monitoring listening position as the points of our reflection free triangle. The two left and right channel speakers form the two base points of our triangle and the listening position forms the point. Our acoustic goal is to slow all reflections down to a point where they do not have any sonic signature on the pure, direct sound from our monitors. This is what acoustic people call a reflection free zone.

Direct Sound

The direct sound from our monitors is the purest sound we can get at the monitoring/listening position. All of the music is in the direct sound without the room sound. The direct sound is the sound that comes straight at you from the speakers. The shortest distance between two points is a straight line and the direct sound travels on this straight line.

Listening Rooms

In our listening room environments, we want more of the room sound in our presentations. Our goal with our two channel playback systems is to try and recreate the original recording and its environment that it was recorded in. If it is a live recording in a small room, we want more room sound because that is what the music sounded like when it was recorded. In order to achieve this room sound, we allow more reflections in our presentations. We also may move the listening position back farther out of the reflection free zone triangle.

Wall Reflections

When wall surface reflections enter into and interlace with our pure direct sound, we get a different sound. The reflections represent the room and they interject their energy into the direct sound. We not only have reflections from the side walls which are the most noticeable. We also have reflections from the ceiling and front and rear walls. I guess we could even say that reflections from our console are part of room sound.

Comb Filter

Reflections from our console and any other physical object with the reflection free zone of our listening or monitoring position can create a comb filter. The best way to explain a comb filter response is to think about sound energy striking an object and then hitting another object. The reflections bound back and forth between these objects and create there own “sound” or rather cover or smother some of our sound energy. This phenomenon is especially harmful to our middle and high frequencies.

Signal Coloration

Comb filters can mask certain frequencies partly or completely. They can interfere with an accurate mix and result in a coloration to the mix on play back. We have to be careful with the console and any reflections that may bounce off of it into our ears. These reflections produce distortions that we hear and the less room sound in our mix the better.

Listening Rooms Comb Filters

In our listening rooms we have to be careful with equipment positioning and set up. I see a lot of equipment set up between the left and right channels. This produces a comb filtering effect when sound energy bounces off the equipment rack and back into the listening position. There is also a comb filter effect from equipment and the front wall. Energy can get trapped in this small space and produce unwanted coloration.

Cumulative Effect

One may not hear this isolated situation immediately but a series of these situations can add up to a noticeable sound difference in our presentations. If we have an equipment rack, comb filter going on and then another one with say a coffee table in front of our listening chair, the cumulative effect of both of these can produce audible distortions at our listening positions. One small one by itself may not be audible, but they do add up and are especially troublesome with our middle and high frequencies.

Control Room Front Walls

Our front walls in our control rooms are a source of reflected energy. The front wall will produce reflections from energy that is generated from our monitors. Remember, energy is generated from a 360 degree pattern around our monitors. Those front wall reflections bounce back to our monitoring position and mix with the direct sound from our monitors. Our goal at the monitoring position is to minimize these reflections because they contain room sound.

Front Wall Absorption Technology

Front wall acoustic treatment is absorption technology in our control rooms. We do not want any front wall artifacts interlaced with the direct sound from our monitors. Sound absorption technology is the preferred method to minimize front wall reflections in our control rooms. Don’t forget about low frequency issues in the front of our rooms. This is where our speakers are located, so we must deal with the speaker/room boundary issues that their energy produces.

Rear Wall Time Delayed Signal

The rear wall produces a time delayed reflection as it strikes the rear wall and then comes back to the monitoring position. This unwanted time signature from this rear wall reflection interlaces with our wanted, direct sound from our monitors. This rear wall reflection is full of room sound because depending on its distance from the monitoring position, it will also have a delay effect added into it.

Rear Wall, Control Room Treatment

Rear wall reflections in our control rooms can be dealt with using sound absorption or sound diffusion technology. Sound diffusion technology will take the rear wall energy and break it down into a series of smaller energies if you will which will not be so predominant at the monitoring position.
Diffusion is the preferred method for rear wall acoustic treatment because using more absorption may deaden the room too much.

Listening Rooms Diffusion

In our listening rooms, we want more room sound. We therefore treat the front and rear wall with sound diffusion technology. Quadratic diffusion can be used on both the front and rear walls to achieve a more realistic sonic playback presentation. We can position quadratic diffusors in vertical and horizontal positions that can generate a two dimensional sound field at our listening position.

Our control and listening rooms each have different acoustical objectives. In our control rooms, we minimize reflections at our mixing or monitoring position, so we can remove as much of the room from our recordings as we can. In our listening rooms, we want more room sound to add to the realism of our musical presentation. Each approach requires that the room be treated differently and that each room surface has a particular sonic impact on our final sound we hear in the room.

First Things, First

There are basic acoustic rules that must be followed when one is dealing with setting up speakers for two channel listening or monitoring. Sound energy from our speakers must be dealt with in many ways that are the same regardless of the end use of the room. In a listening room we have rules and with a monitoring room we have similar acoustical principle that must be followed.

Room Size

The first acoustic rule is choose a room size that has the proper ratio of width, height, and length. This is a priority because if one chooses the correct ratio of these three variables from the beginning we can minimize the number and amplitude of these pesky resonances. I know it is not possible to find larger rooms because larger rooms have less low frequency issues. Most of us have to make do with an existing room. However, we may be able to make the room smaller to sound better.

Golden Ratios

There are published ratios of room width, length, and height that lend themselves to a better acoustical environment. All of these “golden ratios” have one goal in common. They all use dimensions that when you run a frequency response measurement in that room with the proper dimensions, the lower frequency modal resonances are more evenly distributed throughout the room. This separation of room modes is acceptable if they are at least 10 Hz. apart in frequency.

Make Room Smaller

If you have a room that does not fit a golden ratio, then look to the next size room dimensions that will fit inside your existing room. A smaller room size can have a smoother frequency response. Find those smaller room dimensions that will fit into your existing room and change the room size to fit those smaller size. If you are moving only one wall to more conform to a golden ratio, make sure you use new construction materials with the same densities that the other walls are constructed with. Consistency in room surface densities is important when dealing with small room acoustic issues.

Sound Speed

Sound is an energy wave that is generated by an electromechanical device, a speaker. The sound waves and rays produced by our speakers travel at a given speed. It is this speed that we deal with when we are trying to find that balance between direct and reflected energy off of our side walls. The direct sound from our speakers is the sound that travels in a straight line from the speakers to our ears. The reflected sound is the sound that leaves our speakers and strikes the side wall closest to that speaker. Our goal is to balance those two energies together into a direct/reflected ratio that works for the room’s intended use.

Control Room

If we are tuning a control room, we know our objective at the mixing position is to have less room sound and more speaker sound. We want our reflections from the side walls, which represent the room sound, to be less than the amount of direct energy from the speakers. In fact, in most control rooms, we want only direct sound from our loudspeakers at our monitoring chair. No room sound in our mixes.

Listening Room

In hi-fi rooms where our acoustic goal is to recreate the original sound in the recording that the recording engineer put so much time into achieving, we want more of the room sound so that it more closely resembles the sound found as if live musicians are playing in your room. We need more of the room sound in our system presentations. Since we need more room sound for more realism, we will want more side wall reflections in our sonic signal at the listening position.

All Side Walls Are Equal

The only way to be able to effectively adjust this direct/reflected ratio of energy is to have side walls that are of equal distance from the left and right channels. Since sound travels at a given speed, we need surfaces that are of equal distance from the speaker, so that the speed of each reflection at the listening position is arriving at the same speed. This speed consistency from both side walls is much easier to manage than if one side wall is two feet farther away.

Low Frequency Resonances

Low frequency resonances in our rooms must be dealt with. All small room acoustical environments have some type of low frequency resonance that must be dealt with. Low frequency resonances smother and blur our instruments and vocals. Low frequency resonances can have amplitudes that are +20dB-30dB in strength. This is a huge unwanted guest in our rooms. It must be treated as a guest and asked to leave immediately. One must hunt each resonance down and treat the location within the room in which it occurs.

Resonance Interference

If our monitoring position or listening position is in one of these resonances, we will have to move. If we can not treat it by reducing its amplitude to a level that does not interfere with the task we are seeking at our monitoring or listening position. If we sit in a resonance or room mode, we can have certain frequency ranges smothered to the point we can not hear them. We can also have situations where the resonance exaggerates certain frequencies and makes them more predominant. A lower frequency resonance also has its first and second cousins in the form of fundamentals that we must also treat. The whole family of resonances must move out, so we do not have to.

Our first objective with any room that we are going to use for some sonic purpose is to choose a room size that has the proper ratios of room width, height, and length that will give us the smoothest, frequency response. We want to choose a room size that minimizes room resonances. We can even make our room smaller if those dimensions produce a smoother, frequency response and more evenly distributed room modes. Side wall to speaker distances must be equal. We must have consistency in distances to keep our reflections speeds the same at our listening or monitoring position. Low frequency resonances will only get worse as we interject sound energy into the room. We must treat them in the beginning with powerful low frequency absorption technology.

Living Roof-Three concludes our three part series on the Living Roof Project. Living Roof-Three focuses on the roof itself with the solar panels and garden. Consult Living roof-One and Living Roof-Three for more project details as the designer traces his thoughts and decisions through the project. A project that has been a dream project for years and years.

Electrical

My dreams of solar farming remained on hold until TEP (the local electrical utility) offered a program for residential PV installations up to 10 kW to receive a rebate for tying into the grid. I had long waiting for the economics to become practical. I signed onto the program and bought my Kyocera panels long before I was able to actually install them. It was ironic to have to store them totally covered in the yard for over 5 years.

Four Sections Of Solar Panels

Power On

They are just now producing power, and even though the utility rebate has dropped from $3 per watt produced to $.75 and I will be receiving only a fraction of what I could have gotten if our project could have been online sooner.This doesn’t particularly bother me since it got the ball rolling on our project. It is obvious to me though that the utility companies will have to accommodate individual power production and remove barriers to participation (i.e. making a profit possible rather than only offering credit) for consumers and allow them to become net producers of electricity. There are security issues, as well as economic reasons to open up these relative monopolies, so that citizens can participate in the power grid.

First Try

The first iteration of the building design utilized Zomework tracking panels in the building design but this proved quite impractical. The next design integrated the PV panels into the garden design with steel standoff pipes attached to Uni-Rac brand struts that are manually adjustable for seasonal tuning. I read that the efficiency of panels is decreased by high temperatures of roof environments and hoped to mitigate that by combining the garden, which cools roof temperatures dramatically and also provides plant shading.

Panels Chosen

Kyocera panels consist of 48 panels on 4 arrays on roof garden and 56 on porch awning fixed with a 32 degree angle. There is also a 2 SMA grid tied inverters. This is where the electrical grid is the “battery” and credit is given for power produced which is rated at 11 kilowatts. We hope to have enough spare production to power an electric car from a 220 volt outlet in the garage.

Desert Fish

Future Technologies

With future technologies in the pipeline promising energy storage innovations such as fuel cell storage, we are anticipating being able to generate and transfer power easily from home to battery to car, etc. If regulatory and utility hurdles were to be removed from home power production, where those who are now customers could become producers and broker their power the way the utility does across the national grid, especially beyond the 10 kW’s that TEP will sanction, I think that our energy independence and security would be assured.

Water

Water conservation is a survival issue here in Tucson where we have only 10” of rain yearly. Long term climate issues threaten future viability. Since moving to the desert in 1984, I have gained appreciation for the preciousness of this resource, beginning with using 55 gal. drums as storage and over flow for the washing machine and irrigating the plantings in our yard. This setup grew when I installed several 1000 gal. dough boy ponds and galvanized water troughs, stocked with papilla and floating plants.

Waste Management

Waste removal, a crucial factor for any population, became a valued resource, so we wanted to get the most out of it. We circulated the pond water into gravel filled trays planted with water chestnut and strawberries that breakdown the wastes and aerate the water. We then cycled it back into the pond. Orchards and gardens, planted near enough to benefit from the effluent, were robustly healthy, and I saw the system as something of an oasis on steroids.

Institutional Support

Much of this work was inspired by the work of The New Alchemy Institute (RIP) and the Environmental Research Lab at the UAunder the guidance of Carl Hodges. I constructed this with a minimal budget and was successful until too many fish were introduced to the system causing a population collapse and a plant fertilizer bonanza. This was a valuable lesson in maintaining balance. I have since lowered my ambitions in aquaculture to decorative ponds and waterfalls. We have had water features since moving to the Tucson desert and have found that running water is a crucial part of softening the desert’s heat and the urban noises.

Cistern Installation

The first major construction on this site was the burying of two 10,000 gal. concrete cisterns in the driveway area. I am glad that I had these “installed” first as the soil they displaced was easily larger than most backyard pools. They were engineered vaults, highway traffic rated, from Utility Vault, and came in pre-cast sections (6 total) that were craned into place and the lids buried. These proved their load bearing capacity many times over by the many cranes and concrete trucks rolling over them. They will have 6” drain pipes from the roof plumbed into a 500 gal. sand filter which will be piped into the cistern chambers.

Cistern Capacity

We figured that the cisterns could take in 6 months of rainwater which we could use in the landscape with minimal filtration and pumping. We also wanted to make it possible to use this water much more widely with greater filtration (ultra violet, activated charcoal, etc.) in the addition and beyond. The addition has dual plumbing where ever practical and a 20” industrial sized whole house filter will cover the system. The filter allows high flow rate and longer life than smaller ones and there are many options for the filter materials.

Living Roof

Gray Water

Gray water is gold, particularly in this climate with its sterile soil. I have always kept it simple with a hose and a barrel (which mitigates the flush of water from the washer) but hope to add greater flexibility and lessen pond and stagnancy problems by integrating a multi-zoned leaching system from the machine to several planting beds. This will be a variation on a gray water system Oasis Design (http://oasisdesign.net) which promotes many a dizzying array of alternatives for high tech pumping and filtration or gravity flow simplicity.

System Choice

I chose a system that would utilize the washer’s pump to propel the gray water 100 ft., downhill from the machine’s 3’ above grade outlet, into buried leaching fields surrounded by well mulched plants, especially bamboo. There are back flow preventives and other security measures to prevent contamination of the water line and the system can be monitored and flushed with city water periodically.

Hopes

I hoped to irrigate the roof with gray water but was dissuaded by the incoming water pressure and particularly by the contaminants in the water which would clog the engineered soil mix on the roof. There might be short term gain with this approach, but it would lead to clogged soil and drain problems eventually, so the Oasis gray water system was chosen. We are not ready to implement it at this point and I am preparing beds with mulch and composted materials which our pig, Zap, uses as a lounge on cooler days.

This concludes the three part series on our Living Roof Project. View Living Roof-One and Living Roof-Two for more details of the project start through the project finish.