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I was recently asked how I would design a dedicated listening room to house a pair of Wilson Audio Specialties Alexandra XLF, Pipe Dreams 7 speakers, Magico’s M Project special editions, Final Audio Opus 204’s, CAT MBX Powered Speakers, Backes & Muller BM 100’s, Moon Audio Signature Titan II’s, Magico Ultimate III’s, Wisdom Audio Infinite Wisdom Grande, Kharma Grand Enigma’s or any of the real high end speakers out there? A number of our clients have such speakers and so it has become a specialization of ours to build rooms to house them. I asked my colleague Ali to interview me as I talk faster than I type. The following is my response to the inquiry.

Dennis: The speakers mentioned are all large speakers so you really need large rooms to put them in. If you have a large room to put them in, it’s not that big of an issue but for the new Sacred Ground Studio we’re building in Hollywood we have 9-foot ceilings and we have 7-foot high Pipe Dreams 7 speakers. So I think everyone realizes from our past videos that you have to match the speaker with the room size and we all know that the floor and the ceiling are two reflection points. They are the first ones that the speaker uses so to speak and it makes sense because that speaker is sitting on the floor and the ceiling is directly above the speaker. So these are reflections at the listening position that have to be dealt with.

Large speakers in large rooms are not a problem, large speakers in small rooms are and you have to take extra measures with the ceiling and work with the reflections off of that. With our North Carolina project we have 12-foot ceilings and 6-foot high Wilson Audio Specialties Alexandra XLF speakers so a 2:1 ratio, perfect. In Sacred Ground we have maybe 1.5, maybe 1.25:1, something like that so not so good.

Ceiling absorption required

We have to use absorption to treat those reflections because we can’t use diffusion. It’s too near in the field. We’ll end up creating more distortion than what we wanted originally or would have had originally so we have to use absorption. We have to use the right rates and levels. I’ve been preaching this for years and people are finally starting to understand that its the rate and level of absorption that’s critical, not just absorbing anything 100% all the time, like everybody else tells everybody to do.

Each part of the room has a particular need. Each part of the room has a particular time signature. Each part of the room has a particular pressure issue. They all have to be dealt with individually. Good quality sound is a combination of a lot of little things done correctly. If you don’t know those little things and you don’t do them correctly in the right order you’re never going to get good sound. So the bottom line is you have to follow certain rules, certain must-haves when it comes to acoustics. Big speakers in big rooms not too much of an issue but big speakers in small rooms you have to address the reflection side of it.

Ali: Okay. So, this is very important, what room dimension would you say not to go below this for these kinds of speakers?

Dennis: Well, it doesn’t matter who’s the manufacturer, it’s the speakers size which is critical. The room could care less who made the speaker. This is what always makes me chuckle when I talk to dealers because they go into 2, 3 minute dissertations on their speakers. How the engineer designed them, how they built them, how proud they are of them and that’s great I guess, but the room could care less who built them, the room could care less who designed them, it’s just energy for the room. It doesn’t matter whose name is on them.

So you really have to be cognizant of matching the speaker to the room size and volume. And it’s just size. The other variable you need to look at is the diameter of the low frequency drivers. If you have large drivers and small rooms, we know that that’s not good. If you have large drivers in large rooms, that could be good and bad. It just depends on other dimensions that you’re working with. So there’s no set rule, there’s no set way to say it. Does a 6-foot speaker fit into a 7-foot tall room? No. Does a 6-foot speaker fit in an 8-foot tall room? Sure, it can if you use the right rate and level of absorption.

If you gave the height dimension for speakers, you would come up with a number for each speaker. Maybe 4-foot, would be 6 or 7-foot high minimum, 8-foot high minimum. You have to put it together in a little chart and see, I have all these numbers in my head from experience. But it’s also dependent on the diameter of the driver. How much low frequency energy are we putting into the room that’s going to blend with the reflections.

Ali: Okay. So for anybody starting out with a dedicated room, what’s your kind of ideal starting point? I know you said in the past you want to be involved at the blueprints stage because it’s easier to move a line on a piece of paper than it is to move a wall. Do you recommend anybody with a dedicated room that they need barrier technology as well?

Dennis: No it just depends on their noise levels. Where’s the room going to be located? Are you next to a railroad track? Are you next to a manufacturing facility that runs all night long? Are you next to a racetrack? Where are you? You have to figure out what your noise levels are that are outside you room and which you have to work with. Maybe it’s noise within the structure yourself that you’re dealing with.

Why is this important? Because noise raises the thresholds that we seek to hear music within. Let me explain that to you. The quieter the room is, the more music you will hear. Now when you say quiet, it’s how much noise from external and internal sources are getting into your room? And you can measure that and do that with a simple, sound pressure level meter.

Put the meter in the room, turn it on, walk away or sit real quietly. Do that at different times of the day. You’ll begin to see patterns. You begin to see in the mornings, it’s 5 or 10DB noisier than it is in the evenings. The difference between those two numbers is an average. That average is called the noise floor. That’s the noise floor your music has to penetrate. The higher the noise floor, the more the music has to penetrate through it because our ears hear noise differently. Our ears hear that noise differently than it does to music.

Noise is all just grouped together. Like white noise and pink noise. All the frequencies group together. That’s kind of how our ears hear. But music has to get above that. So if we start by putting music on the floor of a graph, and our noise floor is a little above the X axes, and our threshold of hearing is a little above that, the music has to go through the noise floor, reach the threshold of hearing, and then be heard. So the less noise it has to go through, the lower those diameters and parameters.

Ali: I guess somebody spending a high end amount on speakers, we’ll assume they have a house and it’s more of an internal issue?

Dennis: Well, it could be the case. I mean, yeah, but then look at our Sacred Ground project, its right in the middle of Hollywood.

Ali: Yeah true.

Dennis: Right on a busy street. So what did we have to do with Sacred Ground? We had to install windows that had the proper barrier technology or sound transmission class rating to block the noise levels that we were experiencing. So I took some noise measurements over a two or three week period and we tried to get the high traffic noise levels and the low traffic noise levels and I think we were pretty successful. And then the next thing you do is look for the weakest link in the wall.

What’s the weakest link in a wall?

A window. Especially with a concrete wall like the one we’re working with so the glass would be the weakest link in the wall. Sound is like water. It will find the weakest link and it will pour through it. So you have to bring up the density or the sound transmission class rating of the window to equal the wall or the window becomes the weak link and all the sound goes through it or vice versa. It’s a two way door sound comes into. So you have to get all the densities of all the structures as close to each other as possible. You may have to add density to the whole wall. You may have to add density to all four walls. You may have to add density to the ceiling. It’s all about mass and density versus amount of noise level.

Air borne energy vibration acoustics

So think of what a barrier is. You have noise and you have yourself, the receiver. The quickest way to stop that noise is to put a barrier between you and the noise source. How thick the barrier is depends on the noise. It also depends on how quiet you want it. See? If it’s an office building you know there are certain thresholds of noise that are acceptable. There are certain thresholds that are not. So you just have to figure all these variables out and design for it.

Why do we always tell people to locate in quiet areas?

Because of the density and mass costs money. The higher the noise level, the more money you’ve got to spend. Look at that project we looked at yesterday, a multi-million dollar facility, office facility. Probably 20 to 30 million, I built projects like that. All glass and aluminum and glass conference tables. What are the two worst surfaces for sound? Glass and metal. But yet the whole structure is built out of glass and metal and they’re calling me and they’re saying we can’t hear anything. And when I looked at the pictures I go, really? Not so surprising. Who designed this? Whoever designed it, designed it for looking pretty not for functionality. So they have conference rooms where they are going to hold meetings with glass tables, metal doors and sheet metal ceilings.

Now here’s the great assignment that we have, make it sound good but don’t change the appearance. How do we do that? How do we make it sound good by adding obviously sound absorption technology, we don’t want diffusion, we don’t want to spread any more energy out. There’s enough money in the room going on with glass and metal surfaces. We don’t want to do that so we have to use absorption.

You all know what sound absorption materials look like out there. We have to put a lot of them in this room and not change the appearance of the room. How do you do that? Beats me. I don’t know. We’ll give it a go. But would it be any easier to spend 30 million dollars on something that you could listen to people speak in? That has speech intelligibility ratings to it? The goal for a conference room for a company is speech intelligibility. With speech intelligibility, you have to have better communication, better understanding. Isn’t that what its all about? All the meetings I’ve ever attended in my life, reluctantly at times it must be said, were all about communication and understanding. If you can’t hear what the person is saying, how can you have understanding? So this will be an interesting project hopefully we’ll get it and we’ll be able to talk about it as an example of what not ever to do. Never, ever, ever do this. And here’s what we have to go through to fix it. Now, it’s going to cost a small fortune to fix.

So what do we have to work with? We have the ceiling. You can lower reverberation times by putting sound absorbing material on the ceiling. Not flat against the structure. This is what people get mixed up with. Not flat. Surface area, hanging pieces so you have air movements on both sides of the pieces. You have two surface areas on a piece of our 2-inch foam. You have air movement on one side if you hang it and you have air movement on the other side if not secured flat to the wall. If you put it flat, you just have the one surface because the other surface is stuck to the wall. If you hang it, you get air movement on both sides which increases the surface area and why do we need a lot of surface area in this project? I think the room is 18,000 square feet. So we’ll run the calculations figure what to do but what we’re going to end up doing is hanging 50 or 60 of our large 55inch by 75inch pieces of our foam from the ceiling. Here’s an example of a project where they just spent millions of dollars and didn’t even consider acoustics.

So in your small rooms, spend a little time researching and planning and speaking with a professional like me who builds rooms all the time. In your small room rooms, spend a little time with noise because you’re going to spend a lot of time in your room. The lower the noise floor you can get in your room, the more music you’re going to hear at lower volumes. Lower volumes are always better, better for your hearing, better for your neighbors, better for a lot of things, sometimes better for your ears. So spend some time addressing that noise issue and it’s easy to do, it’s easy to measure. With the applications they have on smartphones today, you can measure it really easily. There are acceptable levels inside the listening rooms and there are ones that are not. If you don’t have those thresholds in your rooms achieved, for whatever noise reason, address the noise issues. Maybe it’s a fan in the air conditioning system. Maybe it’s a light buzzing. Maybe it’s a window that’s not sealed correctly. Could be a lot of different things. The smallest little hole, remember sound is like water, so the smallest little hole in something can let a lot of noise in.

Ali: You’ve said in the past that there’s a relationship between the cost of speakers and room treatment. So somebody spending $150K, $200K, $350K on a pair of speakers and then not taking the time to treat that room are not going to hear most of the music those speakers are capable of producing. What’s the disparity between what they’re spending and not hearing?

Dennis: Well you have to realize that speaker designers that have a top of the line unit, it’s a hundred thousand plus. I for the life of me do not see how a speaker should even cost that much. The components cost maybe five thousand. But anyway, if you’re spending that kind of money on a speaker obviously the goal is to hear everything because I’m going to assume that you have a pretty expensive amplifier to go with it. I’m going to assume your cabling is pretty expensive. So you’re on a mission for the best, you’re on a mission to get as much sound as you can and you’ve decided that it’s worth 6 figure investment to do that. No problem.

Just make sure your room is up to the task because if it’s not then you just might as well have spent five or ten thousand dollars for a speaker. If your noise levels are too high, if you’re not managing reflections correctly, if you’re not dealing with the unwanted low frequency pressure issues in the room correctly, if your speakers are not positioned in the room correctly, all of these variables decrease the amount of quality sound that you’re going to hear from that designer. Let’s put it this way, the more noise in the room and I don’t care what the source is, reflections, unwanted pressure, a tractor outside, it doesn’t matter, whatever noise is in the room, the speaker can’t compete with that. The noise will always win. Even in the quietest passages, and maybe more so in the quietest so you have to address the noise issues. So it just goes back to if you’re going to spend that kind of money and get that kind of resolution hopefully in a speaker, then your room better be up to the task of resolving that expenditure. Think of it as an investment. If I’m spending a hundred thousand dollars to get good music, what am I going listen to that music in? I’m going to listen to that music in a room which is essentially a box. Its not out in the countryside. So the room is going to influence what you hear and so a high resolution speaker like a Wilson Audio Specialties Alexandra XLF, a Pipe Dreams 7 speakers or a Magico’s M Project special edition, calls for a high resolution room.

Ali: Okay and finally, you always say you need to get those low frequency and reflection issues under control before adding diffusion. Give you give people a sense of what diffusion would add in one of those well-treated rooms with those kind of speakers?

Dennis: What is diffusion? It is an acoustical treatment that’s designed to minimize the impact of reflections. What is absorption? It’s an acoustical treatment designed to minimize the impact of reflections. Both do the same thing. The way they do it is different. The outcome is different so you have to use the right technology in the right room position. Let’s deal with diffusion first.

Diffusion takes energies that strike it and breaks that energy down and spreads it out into smaller pieces of energy if you will. Based on the design of the diffuser, based on the frequency response of the diffuser, based on about six other variables but it takes this big reflection and breaks it down into a lot of smaller reflections. The amount of energy is the same. It’s just the focus or the strength of the energy is spread out depending on the position of a diffuser. You can spread energy out in horizontal, vertical domain so that’s what diffusion does.

Now why would we want diffusion?

What would be the purpose of taking a reflection off a flat surface and breaking that reflection up into a lot of little pieces. What does that do to our brains? Our hearing perceives smaller reflections as kind of a non-issue. A major reflection, a single reflected point back to your ear gives the brain the ability to localize. Blind people in rooms can actually hear sound and tell how far the surfaces are away from each other because they’re hearing has been developed. Average people can do that too.

So the brain has this really good ability to localize distance. Probably it served as well when we out hunting and pillaging or whatever we were doing back in the early days, but the bottom line here is it’s the localization that you’re trying to avoid in a room. You don’t want to hear that boundary surface. You don’t want to hear that back wall. You don’t want to hear it in a side wall. Those surfaces have to go away. Well, how can they? You’re in the room. They can’t go away. Well they can if they’re treated correctly.

If you’re using absorption, the right rates and levels for the surface area using diffusion, the right diffusion sequence for the surface area of the wall. What will that do for your listening in a room? It’ll make that surface acoustically seem like it’s not there. If you can’t localize the distance, let’s say the rear wall, if you can’t localize the distance of the rear wall, behind you, then your perception is there’s going to be more distance. So your perception is the room is larger and it’s all about perception.

Ali: Okay. So for those who haven’t been in a room with diffusers, how does that add to your experience and enjoyment of music? What does that do for the uninitiated? How does it make you feel?

Dennis: Well, we have all listened to music in our cars, and if you listen closely to the music in your car, you get a lot of energy in this very, very, very small space. A small space is covered with glass, well most of the time anyway. So you get glass sound on top of it. Small space, glass sound, lots of reflections. In a room, it’s larger, so you have more distance between you and the surfaces than you do a car so you have more spatial orientation if you will in a room because you have larger spaces to work with.

So the balance between the direct and reflected energy reflected off the room surface and the direct from the speakers changes dramatically in a car versus the room based on the size of the room. I don’t even know if there is direct energy in a car if you think about it, well not in my car, there’s none. So a larger room gives you more of the direct energy from the speakers. What is the direct energy from the speakers? It’s the purest sound. It’s the sound that doesn’t contain any room. It’s the sound that you want to hear.

So larger rooms give you the benefit of being able to hear more direct energy versus reflected energy and that’s always a good thing when it comes to music. So reflections and direct energy it’s always that balance, it’s always that synergy between the two that you go after and you strive for. And that’s what gets you closer to the music. There’s always this balance and it’s subjective in a lot of cases. How much direct versus how much reflected. It’s kind of subjective. I like more direct energy, that’s my preference. May not be the case for a lot of other people. I like to hear just what comes out of the speaker and not the room and that’s what I strive for.

In Summary

If you are planning to build a dedicated listening room please feel free to call me on 520–392–9486 so we can discuss your plans. Alternatively if you would like to fill in the information on this form, I can take a look at what you currently have in mind and we can go from there.


Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.

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