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How Do You Stop Low Frequency Issues in a Small Room?

MikeSorensen March 7, 2012 5 Comments
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How does one stop low frequency issues in a small room? The short answer is that one does not stop low frequency or bass issues in small room acoustics. The best we can hope for from an acoustical design perspective is for minimization of the major issues and some patience and toleration of the others. The reason for this is basic physics.

Physics 101
A 40 Hz. wave is how long? A 40 Hz. wavelength can be found by dividing the speed of sound in feet which is 1,130 feet / second by the frequency we need to find the length of. Dividing 1,130 by 40 produces a quotient of around 28 feet. Therefore, a 40 Hz. wave is 28 feet long.

If we wanted to be absolutely sure acoustically, we need a room at least 28 feet long in every dimension in order to not have this long, low frequency wave cause any acoustical issues at our listening position. Unfortunately, real estate is expensive and having a room with a 28′ length, width, or height is a rarity. We need a powerful “sponge” to deal with these low frequency wavelengths.

Current low frequency products in the marketplace do not work for many reasons. Sometimes, a low frequency or “bass” absorber is an afterthought to an existing companies product line. They spent their monies on middle and high frequency control and left the more difficult design issues of low frequency absorption on the sideline.

Since they are marketing absorption panels, they need a bass absorber to round out their product line. I have seen companies even raise the definition of low frequency control to match their products poor absorbing performance. Some companies consider low frequency absorption to be at 400 Hz. Really?

Most low frequency absorbers simply don’t cut it
Most low frequency absorbers in the market place can be thrown over your shoulder and carried out of the room. How does one absorb enough low frequency energy to have a sonic impact in their products if one can carry it out by hand. How does one absorb parts of a 28′ long wave with a hand held device. The answer is you don’t.

One can change the design absorption frequency to match what the product actually absorbs at and call it a low frequency absorber, but the reality is that it is not a low frequency absorber. It is only marketing jargon that the uninformed will buy into and eventually purchase. after a brief period of use, they will still have low frequency issues.

Address the energy that falls below 100 Hz
Low frequency energy control requires a design parameter that addresses low frequency energy that falls below 100 Hz. It must have this design criteria firmly in line and focus if it is going to create a product that actually absorbs below 100 Hz. It must also absorb at a high rate and level at the most problematic frequencies found in most rooms.

These are the low frequencies that fall from 30 Hz. – 50 Hz. One can not absorb effectively at these frequencies with a product that is lightweight and small. The laws of physics will not allow for this no matter what the companies sale literature says.

In Summary

If you have any questions follow up questions on this subject please feel free to email me and I will be happy to help. Please message me at info@acousticfields.com. If you want to learn more about room acoustics please sign up for our free acoustic video training series and ebook. Upon sign up you will have instant access to the room acoustic training videos and ebook to help improve the sound in your studio, listening room or home theatre.

Thanks
Mike

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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5 thoughts on “How Do You Stop Low Frequency Issues in a Small Room?

  1. I am having problems due to other people’s sound systems. I guess that would be better termed hz frequencies or waves. There are 3 people that really enjoy their amplified bass. I can not determine their location. Rarely, if at all, does my body, floors and furniture enjoy a respite from vibration. It doesn’t seem to be coming from my closest neighbors. One person revs up the bass around 11 p.m. to the point I am shaken out of any slumber I am fortunate enough to grab. It is now affecting my health. I am a disabled widow. Since I do not know the location of this bass lover, how can I protect myself and get necessary Zzzzzzs? I understand people wanting to “feel” their music, but I don’t want to feel it in my home 24/7.

    • Hi Gloria,

      Low frequency energy < 100 Hz. is both air born and structurally transmitted. You must isolate from both. You need to localize the source and build a barrier between you and the source that will not only isolate from air born transmission but also from structural vibration. This is expensive and a permanent fix that requires structural modifications to any building. You will need planning and zoning approval from your local municipality. The most cost effective and easiest solution is to locate the source and get it to lower its output. I would start at looking at sources that are within 50' of your location. It appears you are in a multi family dwelling such as an apartment building. I would first speak to the management company and go from there. There are city ordinances that prohibit noise issues above a certain rate and level. You can easily document the frequency and amplitude of the noise with your phone for documentation purposes.

    • Hi Gloria, It appears you are receiving both structural and air born energy. Both must be isolated from by building a barrier that is thick, heavy, and very expensive. Locate the noise source. Start by looking at noise sources that are 50′ away or closer. Tell them to turn down. If they don’t comply, report the noise to management first and then local authorities. There are noise ordinances in place to deal with these situations.

  2. Is it possible to take inspiration from the fresnel lens (which fits a large into a smaller area), and invert it, to attenuate larger wavelengths into smaller ones for easier? Obviously it’s possible to create big water waves from small paddles, so could that be used to extinguish lower (longer) wavelength noise? If so, how would you do it, and how feasible would it be to make such a unit for smaller rooms?

    • K, Light and sound are completely different. It’s difficult to use light technology to explain lower frequencies. It does have some comparison validity for middle and high frequencies.

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