acoustology_104 2 | Biblioteca audio auralex

competing manufacturer out there now that sells "traps" that are nothing more than 3" or 4" thick absorber panels that they

I will leave you all with one final preview: Auralex will be debuting many new products in 2004. Among them will be some

Resonators and Diaphragmatics and Couches...Oh My?

a panel such as plywood is rigidly affixed to the frame. This device will resonate like a drum. By themselves, these

the effect of widening the range of frequencies that are absorbed, but the actual absorption coefficient

you!!!

couches as treatment, click here. Other "stuff" can include:

actually absorb that frequency. Now, if you imagine a huge cola bottle, you can imagine a device tuned for lower

fantastic low frequency devices and packages. So stay tuned we haven't forgotten about your low end and neither should

answer all our e-mail.

Next month: What's that noise?

principle that a fixed membrane over an air space will resonate at a certain frequency. Usually, a frame is built and

concerning treatment. I would encourage you to contact us any time if you would like to discuss your LF alternatives. We

Large pieces of furniture. Items would have to be large enough to break up low frequency waves i.e., a

not work as intended. (This statement is based on an independent study of LF devices, the details of which are

usually required to make any sort of difference in the room. So many, in fact, that it is not likely you will

and the absorption will increase. Unfortunately, this tuning is a very tricky process. Many prefabricated devices will

build yourself will have to be tuned throughout the construction process to ensure nothing goes awry. This is

Miami.

Noy. If you are not a member of AES, this document will cost you $10. For members, it is $5.) Most devices you

have the space for them.

3. Stuff. That's right, "stuff"! Check this out: Couches can be fairly decent LF control devices. For an informal study of

opening, you can hear a tone being generated. If you have enough of these types of devices in a room, they will

decreases across this range.

instruct you to space 3" or 4" off the wall. Talk about marketing!)

devices. In other words, they are not tuned to any specific frequency. There are two types of tuned devices:

To absorb more than a single tone, they are often filled partially with sound absorbing material. This has

airspace with sound absorbing material and unlike the Helmholtz resonators the frequency range will decrease

A large open window or sliding glass door. This is, of course, challenging if you live anywhere north of

frequencies. The problems with these devices are as follows:

Open closet doors. This only works when the closet is filled with clothes or other "soft stuff."

available in AES Preprint number 5944 entitled Low Frequency Absorbers Applications and Comparisons by Dirk

desk chair is not a bass trap.

of the panel or the airspace.

There are several other ways to control low frequencies. Up to now, we have been talking about passive low frequency

2. Diaphragmatic absorbers (aka, "panel" or "membrane" absorbers). These devices are based on the acoustic

All of these Acoustology installments on low frequency control should help you make some very well-educated decisions

because dramatic changes can occur with the design frequencies with as little as 1/64" variation in the thickness

Based on this decrease in what is already a fairly low absorption coefficient, many of these devices are

1. Helmholtz resonators. The simplest example of a Helmholtz device is a cola bottle. By carefully blowing into the

devices are nothing special. Gyspum wallboard ("drywall") over studs has much the same effect. However, fill the