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Speaker Boxes Are Room Boxes

MikeSorensen July 5, 2012 No Comments
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Sitting In Your Speaker

When you are sitting in your favorite listening, home theater, or professional monitoring room, you are really sitting inside your speaker cabinet. It is like listening to a speaker from within a speaker itself. Speakers and the rooms we listen to the music they produce in have similar construction needs and methods.

Speaker Cabinet

A well designed speaker cabinet is very similar in construction and design to a listening room, home theater room, and professional recording studio. Both “boxes” must deal with resonances and raising or lowering them below or above the audible range. Stiffness, mass, and damping are the three main factors speaker designers work with to try and achieve a balance between vibrations produced by the speakers and the inherent vibrations produced from the cabinet. Speaker designers use stiffness to raise or lower the system’s resonant frequency to a point of inaudibility. Speaker designers use mass to damp high frequency resonances and lower the cabinet’s Q value. Damping is used to minimize the amplitude of resonances inside the cabinet particularly from the low frequency driver.

Room Cabinet

Room designers look for that balance by building a room that has the stiffness to deal with the vibrational energy interjected into the room enclosure by sound pressure waves the speaker box will produce. Mass is necessary for sound isolation and pushing the room’s resonant frequency out of the way of the critical listening frequency range we need to have for a balanced sonic presentation and to also compliment the stiffness of the room’s construction. Damping is critical to deal with any remaining energy that the mass and stiffness did not address. Remaining energy that is caused by room dimensions and the associated resonances that are inherent with any room volume ratios.

Magico Speakers

Magico is a speaker company that builds speakers the way one should build rooms. When you look at the design of their speakers, you see an aluminum frame inside the speaker cabinet. This aluminum frame provides the mounting platform for the drivers to secure to. They have a tension coupling system that clamps the drivers to the aluminum frame using a high torque, steel rod, fastening methodology that the end user can maintain strength on from the rear of the cabinet. The frame is the mounting system for the drivers and the speaker cabinet itself contains the rear wave produced by the drivers. With this combination of opposing materials that have opposing physical characteristics a reduced vibration environment is created.

Vibration Isolation

When one builds a listening, home theater, or professional recording studio, we must address the speaker cabinet as a vibrational producing device and as a sound energy injecting device into our small room acoustical environments. Vibrations from the cabinet itself must be isolated from the room structure which is the floor in typical home theater and listening rooms. In professional monitoring situations, we have to deal with monitor enclosures that are built inside of walls. Vibrations from our speakers must not be allowed to transfer to the room surfaces and set those surfaces in motion. Room boundary surfaces must have the necessary stiffness to minimize any sound pressure or speaker cabinet produced vibrations. We do not need our room surfaces moving and behaving like loudspeakers. Dealing with two channels of sound energy in a room is enough, thank you.

There Is No Substitute For Mass

Mass within our rooms is like horsepower in an engine; there is no substitute. One needs mass for damping of resonances within the room boundaries. Only mass will dampen low and high frequency resonances alike and just like in a speaker cabinet, mass will assist us in lowering the Q value of the room. The pressure within a speaker cabinet can reach up to 100 pounds square inch. Pressure levels in rooms can be high enough to make a standard
2′ x 4′ wall go diaphragmatic and start ringing. The proper amount of mass inside the room’s construction can have up to a 40% impact on reducing room surfaces vibrational levels and a similar ratio on overall room sound contribution.

Damping

Damping is critical for the reduction of any unwanted resonances produced within the speaker cabinet or room. Both a speaker cabinet and a room have a height, width, and depth that will by definition produce certain audible resonances. A speaker designer does not want those resonances to be heard along with the sound of his chosen drivers. A room designer does not want the resonances of the room excited by the speaker produced energy to be heard in the room. Room resonances can exaggerate certain sounds that fall within its modes and completely eliminate others. Low frequency resonances are the most difficult to deal with.

Stiffness

Stiffness in room construction creates a very unique “room sound”. I am building a room now using poured concrete and steel. Walls are 8″ poured concrete, We have a room 25′ W x 50′ L x 16’H with steel horizontal beams supporting the massive roof system. The roof system will have 18″ of top soil across the total roof surface dimensions. This room is stiff. It feels “stiff”. It feels strong and solid like a much smaller room. Stiffness in our rooms must be designed for and then built for, not the opposite way around.

Mass In Our Rooms

Mass is necessary to give us the material thicknesses to work with the vibrational and sound pressure issues that arise within our rooms. Low frequency wavelengths are long and thick. These are the most problematic frequencies when it comes to room resonances. These resonances need mass in the technologies we use to deal effectively with they strength. One needs a combination of materials and vibrational reducing technologies that can handle and deal with the amplitude these low frequency issues produce. Mass does cost more and take more space, but we know it works and we also know why it does.

Damping In Our Rooms

Damping is a critical tool in small room acoustic environments. The process and term of damping is applied to vibrations as well as reflections. Damping is used to reduce vibrational energy from the air into our electronic equipment. Damping is used to reduce speaker to room physical contact. Middle and high frequency reflections can be “damped” or manged with acoustical foam. Closed cell acoustic foam will produce a smoother absorption
curve than the popular, open celled, foams currently in the marketplace.

Speaker And Room Boxes

Speakers and rooms are really “boxes”. A speaker is a box that holds a driver or numerous drivers and lets those drivers produce sound energy into the room. The build of that box needs to address stiffness, mass, and damping which are the same issues a builder of acoustic purpose rooms will use.
a speaker box has a rear wave that the driver produces and sends to the box rear. A room has a speaker that puts out this rear wave and then some direct waves of its own and produces a certain sound.

Designer In Your Room

This is the sound of the designer in your room with your room sound added. This is why it is imperative to listen to any new speaker within your room. Your room contributes over 50 % to what you hear. Never but a speaker because it sounds good in the show room or looks good on the internet. You can’t look at room acoustic measurements and say, that room sounds good. Viewing and seeing are as different as hearing and listening. Anything that contributes over 50 % to anything has to be considered in any decision whether acoustical of financial. It is the designer’s way of showing you, through example, what his perception or at least close to it, is of what good sound to him should sound like. You must meet the designer at least half way and have a room that is built and designed using the same vibrational reducing methodologies as the speaker designer used in its construction and room voicing. It is the only fair thing to do.

If you agree with the new sound you hear in your room, you buy the speaker. If you don’t, you will probably buy another because of the new momentum you have just created with this new speaker project. Peter Gabriel said it best: “Once the flame begins to catch, the wind will take it higher.” Either way, mission accomplished.

MikeSorensen

I am a structural engineer as well as a master furniture maker. I design cabinets for low frequency, activated carbon absorbers. Connect with me on Google+

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