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Why Your Bass Traps Don’t Work

Brandon Drury —  July 5, 2011 — 16 Comments

bass traps

I’ve been behind on Pensado’s Place and I did some catching up the other night.

They had a super dooper acoustics dude on. His name is Thomas Jouanjean and he works at Northward Acoustics Engineering, the firm that built Focal’s facility for testing their monitors, among many other ultra high end studios.

If you can’t see this video head over to Youtube and watch it.

While I’m not exactly sure why, anytime they start REALLY hitting on super information that gets me excited, Dave Pensado tends to get goofy talking about the NBA. I’m all for goofy both before and afterward, but I guess I REALLY wanted to hear what this French dude had to say. Oh well, I’m not complaining. There were some HUGE points made in this video.

@26:40 Thomas Jouanjean talks about not using a high-pass crossover filter on studio monitors when using a sub, which lead to this discussion…. No High Pass On Monitors With Sub

@32:31 He starts to talk about the difference between using fiber-based absorption vs membrane based absorption. It turns out that 703 or Rockwool place right up against the wall does almost nothing for the low end.

DanTheMan brought up this very same concept in a really awesome thread on optimizing bass traps.

@35:20 He says that he wouldn’t recommend working with less than 4-6” thickness of Roxul/703. That’s not a breakthrough or anything, but I see a lot of people dabbling with 2” 703 when it’s clear that greater thicknesses are necessary.

@36:30 Dave Pensado asks what’s the lowest frequency a frame with 4-6” thick of rockwool/703 spaced 4-6” off the wall will absorb. It’s important to note that this is accepted as a bass trap in home recording land. Most people don’t even go this far with depth or air space from the wall.

Thomas Jouanjean says that the ¼ wavelength thing applies.

The home run came at TIME where Thomas Jouanjean said, “These systems based on rockwool or owens-courning [703] do not work so well under 100Hz”.

Going back to this ¼ wavelength busies. I’m not sure where you measure from. I’m assuming when dealing with a 4” sheet of rockwool that is 4” from the wall means we can call that 8 inches. If that’s the case we need to find a wave with a wavelength of 32 inches and that’s what we are optimally absorbing. I just came up with about 423Hz. YUCK!!! That’s not a bass trap. That’s a boxiness trap (not that we don’t need those, too).

Assuming 6” of 703 and 6” of air space from the wall, we are looking at frequency of 282Hz. YUCK!! This is when sacrificing 12” of space! Who can do that in their bedroom studio?

To get down to 100Hz we need more like 3 feet of space from the wall. That’s not gonna happen in any bedroom converted to a studio.

The most horrifying…
@41:36 Phil’s got a 7′ ceiling in his studio. Pensado asks, “A lower ceiling can sound good, right?” Thomas Jouanjeanrespondss, “No!” AHHHHHHHH!!!!!

Don’t Shoot The Messenger

While most of this info is not good news for the guy recording and mixing at home, it’s nice to have a lot of gray areas FULLY confirmed. Few people are in a position to say, “Definitely do NOT do X.” When it comes to acoustics. I think that makes this video insanely valuable and a good thing.

Solutions To Our Bass Trap Problem

There are still solutions to bass trapping. I’m talking real solutions that will work effectively without chewing up enormous amounts of space.

1 – Membrane absorbers
(See DIY Membrane Bass Trap Plans) Membrane bass traps by stretching “deadsheet” or even plywood over a sealed area with 703/Roxul stuffed inside. These have to be tuned specifically but they can absorb very deep frequencies without chewing up a ton of space in your studio. Also, they avoid the HUGE problem that occurs with an excessive number of broadband absorbers in the room. They reflect high end back into the room keeping the room from sounding “stuffy”.

2 – Commercial bass traps
With so much that can go wrong with a bass trap design, I’m starting to wonder if it just wouldn’t be CHEAPER to go with commercial bass traps. These guys have no choice. They need bass trap designs that go very deep but also are shippable.

Everyone seems to rave about the Real Traps. Ethan Winer is around here all the time and is extremely generous with his acoustics knowledge . I’ve never heard anyone complain about bass trapping and diffusor products.

3 – Helmholtz Resonators
Ever blown into a coke bottle? When you get it right, the entire bottle starts to “ring”. This is a Helmholtz Resonator that just happens to be tuned rather high. When tuned lower, Helmholtz Resonators can be very, very effective at absorbing low frequencies.

If anyone has any plans for Helmholtz Resonators, let me know. The only ones I’ve came across are in Alton Everest’s Master Handbook of Acoustics.

Conclusion

We should no longer call 703/rockwool wrapped in fabric and mounted 4”, 8”, or even 12” from the wall “bass traps”. They aren’t trapping a significant amount of bass. It’s time to move on from that model and push for designs that really do work in the confines of the home studio.

This means going to either go membrane, go Helmholtz, or go commercial.

Brandon

Saved Comments

EnSkorSang – 11-22-2011, 11:41 AM Edit Reply
Nice blog, that video is a real information gold mine (although pensado seems to make things a bit confusing).These membrane traps – so these things are basically the ‘bad’ version of bass traps (some inches of rockwool) but covered in plywood/’deadsheet’ ?

Lance – 11-22-2011, 12:14 PM Edit Reply
Damn it! I literally just picked up a couple of bundles of Roxul Safe and Sound, 20 meters of Fabric and some 1 by fours to start making some broadband obsorbers and corner bass traps! I guess all I can do is make them twice as thick as I had origionally planned. 6″ instead of 3″

brandondrury – 11-22-2011, 01:36 PM Edit Reply
These membrane traps – so these things are basically the ‘bad’ version of bass traps (some inches of rockwool) but covered in plywood/’deadsheet’ ?
Sorta. That sentence could be taken the wrong way, but it’s my understanding that the membrane is tuned to absorb X frequency. It’s the front panel that does the real work, but having the fiber inside it improves it.In Recording Studio Design, there is a chart that shows Helmholtz Resonators with and without fiber inside. The with-fiber method (sounds like a cereal) was much more effective in the low frequencies. The tricky part is figuring out the exact thickness and dimensions.
pensado seems to make things a bit confusing
Mr Dave is being a tv host (mostly) and playing devil’s advocate. He’s trying to dumb it down for beginners, but guys in 101 stage aren’t watching the show. It’s guys like us who already have fancy preamps and such and are trying to figure out how to move to the next level. Then again, sometimes he seems legitimately confused with rather simple stuff. Other times he OBVIOUSLY knows his shit. It’s all the mystery that is Dave Pensado.
Damn it! I literally just picked up a couple of bundles of Roxul Safe and Sound, 20 meters of Fabric and some 1 by fours to start making some broadband obsorbers and corner bass traps! I guess all I can do is make them twice as thick as I had origionally planned. 6″ instead of 3″
You are lucky! You could have figured out that your bass traps are mostly useless 3 years from now after spending all that money AND doing all that work. This wasn’t a happy article for any of us. However, I’d rather get the truth out ASAP because no one was telling me that spaced roxul panels were a waste of time for solving 100Hz problems. Now we KNOW.My advice would be to dig deeper on the membrane front. That’s where the money is at, it seems. Brandon

Robert200 – 11-22-2011, 02:06 PM Edit Reply
I saw that interview last week… He really contradicts a lot of the generally held beliefs… I love Pensados Place but I do wish they would take a media lesson on when to shut up… a lot of times the guest will be talking and right when they get to the money line… the other two will pipe up with something and make the key sentence indistinguishable …. Regarding sound absorption and proofing… this stuff is supposed to soundproof a room… is you do the whole room and fill the cracks and air spaces… etc… Mass Loaded Vinyl, MLV for Soundproofing Your Walls and Ceilings I’m just wondering .. what would happen if you sandwiched a sheet of this stuff between 2 pieces of the 703 or the rock wool… maybe you wouldn’t need the 2nd piece… maybe you wouldn’t need any… just tack up a piece of this vinyl in a 2′ x 4′ frame…. … it gets back to absorption versus soundproofing… if this is for sound proofing… not sure how it would work in a bass trap scenario….

Robert200 – 11-22-2011, 02:14 PM Edit Reply
I forgot to add this… a lot of good information on the options for acoustically treating a room….

Soundproofing 101 – How to Soundproof Your Room’s Ceiling Walls and Floors

Lance – 11-22-2011, 02:47 PM Edit Reply
You are lucky! You could have figured out that your bass traps are mostly useless 3 years from now after spending all that money AND doing all that work. This wasn’t a happy article for any of us. However, I’d rather get the truth out ASAP because no one was telling me that spaced roxul panels were a waste of time for solving 100Hz problems. Now we KNOW.My advice would be to dig deeper on the membrane front. That’s where the money is at, it seems. Brandon[/QUOTE]

I agree 100 percent. I am glad I was able to catch this article and video before I started building today! Now I think I will start with building smaller broadbands to handle first reflections, and continue to research bass traps. It was definately a little dissapointing, but very informative!

doug hazelrigg – 11-22-2011, 03:44 PM Edit Reply
I’ve never thought of 703 as a bass freq absorber, mostly HF reflections. In my studio,
I use regular 2×2′ Auralex panels to attenuate reflections, and the triangular corner traps
do a decent job of absorbing bass accumulation. Also, using non-ported monitors helps.
But after a certain point, it’s just best to know your room and your monitors

retrogradeorbit – 11-22-2011, 08:40 PM Edit Reply
As a graduate physicist I just want to chime in and work on some of these perceptions. Yes everything he says is technically true. Yes the quarter wavelength applies (this is because the wall must be a node, and your first wave antinode is 1/4 of the wavelength into the wave). If you were doing the calculation you’d use the middle of the trap, not the front face. So 4 inches of rockwool, 4 inches from the wall puts the center at 6 inches from the wall, which is by my calculations (using speed of sound to be 346 ms-1) a frequency of 567Hz!!

That being said, this calculation determines the place of *optimal* efficiency. Such a trap will have maximum attenuation at this bottom frequency. But there is a bandwidth to its attenuation. It’s not like 567Hz is absorbed and 566Hz is left untouched. The absorption will continue all the way down to 0Hz, but with lessening attenuation. Think of it like efficiency. Placing such a trap catches 567Hz extremely well. 500 Hz very well. 300Hz ok. 200Hz somewhat. 100Hz a little bit. 50Hz a smidge. etc. The absorption band is like a curve with its maximum at the 567Hz point. That curve into the LF improves with spacing from wall, thickness of panel, and density of rockwool.

So things to avoid is placing them right against the wall. This places them in the nodal point of the waves and pushes that curve way out. So all your low frequencies are untouched. And the second thing is making them as thick as possible, as this increases the absorption coefficient for low frequencies. But I think to say we should stop calling a decent slab (say 5 inches thick) of dense rockwool (say 100 kgm-3) a good distance (say 4 inches) from the wall a bass trap is wrong. They _are_ bass traps. They _are_ taking out bass frequencies. Maybe not as much as say a helmholtz resonator tuned to a low frequency would, but they are taking low frequencies out. Maybe they should be called low-mid traps as they take out even more of this!

You can prove this all to yourself by removing all such bass traps from your room and measuring the room response. Then placing them back and measuring again. And then comparing the empirical data. You can also see this by empirical absortion data like this: http://www.bobgolds.com/AbsorptionCoefficients.htm

Notice that the coefficients of absorption are never 0. Even right against the wall they take a little bit of the low end. Lets go full circle though and say that despite this, most peoples home made traps are probably too thin, too light and too close to the wall. And thus are taking out less LF than they may have thought.

All this being said, one should not just place treatment in their rooms randomly. One should buy a measurement microphone and maybe measurement software (unless you want to do it by hand) and actually measure their room response. Then from that make decisions about what treatments are needed. Then try them in places and remeasure. Without measuring your room you really have no idea what they are doing to the room’s sound in various positions. You can’t just go by eye.

That’s my 2c.

ManAbyss – 11-23-2011, 06:37 AM Edit Reply
When you refer to “Gik Monotraps” which excactly do you mean? Because there are no traps by that name in Gik. I’m asking because I’m really interested in buying some acoustic treatment from that company since all I hear are good comments about them.

Desolation – 11-23-2011, 09:43 AM Edit Reply
Originally Posted by Robert200
I saw that interview last week… He really contradicts a lot of the generally held beliefs… I love Pensados Place but I do wish they would take a media lesson on when to shut up… a lot of times the guest will be talking and right when they get to the money line… the other two will pipe up with something and make the key sentence indistinguishable …. Regarding sound absorption and proofing… this stuff is supposed to soundproof a room… is you do the whole room and fill the cracks and air spaces… etc… Mass Loaded Vinyl, MLV for Soundproofing Your Walls and Ceilings I’m just wondering .. what would happen if you sandwiched a sheet of this stuff between 2 pieces of the 703 or the rock wool… maybe you wouldn’t need the 2nd piece… maybe you wouldn’t need any… just tack up a piece of this vinyl in a 2′ x 4′ frame…. … it gets back to absorption versus soundproofing… if this is for sound proofing… not sure how it would work in a bass trap scenario….
I’m not an acoustics expert but as an architect I have used MLV for reducing sound transmission. It really works best in that application when it can felx slightly, i.e. with an air space behind it. The normal installation is directly behind gyp. bd. in the walls or ceiling so if it is placed over furring strips that provide an air space between the MLV and the cavity wall or ceiling insulation the STC will be greater. In theory it will work as a membrane for a bass trap but I haven’t seen any definitive performance data. There is one company that produces a curved base trap with a MLV membrane, see http://www.acousticgeometry.com/pdf/…rve_System.pdf

dudermn – 11-23-2011, 12:22 PM Edit Reply
Ya, he does look a bit like Jesus too.

Robert200 – 11-23-2011, 04:40 PM Edit Reply
Acoustical Diffusion, Recording Studio Acoustics, Professional Studio Sound – Garage-Size Recording Studio Combination Guide – The Curve System Here is Acoustic Geometrys take on using membrane to diffuse and absorb….

Cailyn – 11-23-2011, 08:25 PM Edit Reply
I think people should understand the limitations of recording in the home environment and act accordingly. I get that my acoustical treatments aren’t perfect. I understand that my bass traps probably aren’t doing an adequate job. So what! Working in a home studio has limitations, always has and always will. I don’t have the space, the money, or the technical know-how to create a ‘perfect space’. I do know what sounds good. If the project I’m working on sounds good in my studio AND on six other systems I use to cross-reference my imperfect home studio, it’s probably okay. Odds are, no one besides another audio engineer will know the difference. I prefer to spend more time making music and less time stressing over the inadequacies of my bass traps. Just my not-so-humble point of view.

mbejackson – 11-24-2011, 01:06 AM Edit Reply
Originally Posted by retrogradeorbit
As a graduate physicist …

That’s my 2c.
Very well stated Retro. A DIY’er suddenly jumping on the Helmholtz or Membrane bandwagon can actually create more problems than he solves as these types of traps are ‘tuned’ to a comparatively narrow band v. a superchunk or 4″ of 703 across a corner. And IMO, store bought, after some proper analysis would definitely be the way to go. I’ve often wanted to hang some LMV in front of my superchunks just to see what happens. : )

LazyE – 11-24-2011, 03:24 PM Edit Reply
this is all very interesting, but having read this and many other articles, in particular the `real traps` and other acoustic web pages i feel that some trapping using 703 or rockwool is far better than non.how otherwise do you explain room analysis results before and after bass trapping?i understand that wave forms require certain resonance to cancel them out and transfer sound energy to heat energy, and therefore yes a `tuned` closed end slotted style bass trap provides the true accurate amount of absorbsion for the given room if all calculations are correct,but for the bedroom recording artist (like myself) the use of owens cornering 703 or rockwool 45etc of ample thickness, mounted properly with breathable fabric and space behind DOES improve the low room resnance in a room. (and also absorbs some mids and highs)the low end is much tighter and ressonance and unwanted reflections are drastically reduced , especially when used properly in the corners.controlling the low end completely is vertually impossible as it depends entirely on the layout of the room, the volume , the possitioning of furnature etc, etc, but we can have a damn good go with a healthy amount of home made bass traps!keep trappin i say!lets face it, any treatment is better than non and there will always be new and improved ways of doing something, but all they do is distract from the actual task of MAKING MUSIC!but thats just my opinion, i am definateley not a sound engineer or acoustics maths man!i just trust my ears and do the best with what i have.peaceE

nulldevice – 11-29-2011, 08:10 AM Edit Reply
Lots also depends on how you define “bass”, too. Very few traps, even pro ones properly fitted, are going to absorb very low frequencies particularly well. There was a discussion on GS a while back about building a trap hat absorbed extremely well between 50-100hz — and it ended up being a cube roughly 2 feet on a side. A requirement for a couple of those? That can get impractical even in a pro studio. In most smaller rooms, anyway, you’re also going to have a lot of noticeable room mode buildup in the higher bass frequencies. Plug some “bedroom studio” numbers into an acoustic calculator and you’ll find a lot of modes between 200-500hz, which is where something like plain-ol’ rockwool will actually do something. Maybe not perfectly, but it’s better than doing nothing by quite a bit. I’ve taken an RTA to my room, and it lines up pretty closely to what the calculator predicts – my most reflective modes are at 150, 210, and 280hz, give or take. Throwing some rockwool superchunks in the corners didn’t fix it entirely – but it helped a lot. There’s a question of the ultimate goal, too. Since most “bedroom” producers are not, per se, in requirement of a mastering-quality environment (and generally sitting a lot closer to their speakers), the ultimate goal is usually not to create an acoustically-flat “perfect” room, it’s just to improve the basic environment to a point where you have to worry less about the dominant frequencies being those coming from the speakers and not the room. Given you also will be worrying about comb off your desk, undiffused reflections, speaker positioning, etc, it’s generally best to just do what you can do to get it “good enough” and not worry terribly much about makign sure you have near-perfect absorption at 78.3hz.

Smurf – 11-29-2011, 10:57 AM Edit Reply
I quit watching Pensado’s Place after 5 shows…I could not stand how he kept interrupting folks in mid sentence with another question before they finished their answer, or like you said, with stupid crap. For all the useful information you could cut out 50min of the show and not miss a thing.. Good thread & subject by the way, another great read!

PRoadarmel – 12-03-2011, 10:13 PM Edit Reply
Brandon, as someone who has kept an eye on your website for a while, and will be getting the KHR set for Christmas this year, do you plan on (is it worth your time) to update the acoustics information in that series to reflect what you’ve learned since you originally wrote the series? Or is that one of the uses of the forums and the community? The idea being the newbies read the KHR stuff and get a handle on this whole recording thing, and then take to the forums to flesh out that knowledge? Just wonderin’

Rgraham4 – 12-08-2011, 08:48 PM Edit Reply
I recently finished a 10 x 18 room, with some guidance from ReadyTraps (they will help with cad design and useful advice for small dollars,nice products too). In a nutshell, I doubled the drywall with “Green Glue” in-between, added about 12 2×4 by 2″, 6 2×4 by 4″ panels of 703, some on the wall, some spaced. Then two wall to ceiling superchunks. Is it acoustically perfect? NO, but it sure is predictable for monitoring, and dry enough to get very clean live tracks that do not have the boxy home studio sound. My room still booms in the sub 100 range, but its not hard to mix around. In my mind, a workable room that can be had for a couple grand, in combination with the great DAW’s available now, is what is bringing recording to the masses. Yeah, we all get to play now!

I think the article would be more aptly named “Why your bass traps don’t work perfectly”.

 

Brandon Drury

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Brandon Drury quit counting at 1,200 recorded songs in his busy home recording studio. He is the creator of RecordingReview.com and is the author of the Killer Home Recording series.
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16 responses to Why Your Bass Traps Don’t Work

  1. I just want to second what retrogradeorbit said.

    The best name for fibre panels is probably “broadband absorbers”, as Ethan calls them.

    One other point I haven’t seen yet is that you can make them much more effective by putting them across the corners of the room. Because:

    1 – Energy builds up in the corners because there are two planes of reflection. So traps in the corner suck more energy out.

    2 – You get more depth of air-gap without taking up too much space

    3 – The depth of gap varies because of the angle, so you get an even broader range of absorption

    4 – Corners are pretty much dead space in a studio anyway

    Bottom line, if you use large panels, 3-4 inches deep, across all four corners of your room, you will hear a noticeable improvement, even down near 100 Hz – even if a tuned trap might be even more effective. And the benefits in the low mid will be *huge*…

    Ian

  2. why upload the video with restrictions on what countries is available to watch? are you win something with that? wtfc??

  3. That video is from Pensado’s Place on Youtube. Apparently, they have country restrictions….which boggles my mind as well. Sorry for the trouble. I think you can get a gist for what the guy is saying from what I’ve written about bass trap spacing being necessary, but it sure is cooler when a hyper expert in acoustics says it. SMILEY

  4. http://www.deamp.com

    Sorry for doing semi-promotional work in a comment field, but:

    We do helmholtz-resonators on a cheaper slit-design solution (still depends on production volume, though).

    I’ve got full ISO354 data on 200mm resonators, but still the bass absorption dives below 100Hz. I stumbled upon this page since I’m discussing with a customer regarding a solution we have for corner mounted panels, but again no reliable data is available when the wavelength is so long an ISO-room is too small to give any indication unless all products are tested on the identical setup to at least show significant differences.

    I’m also unsure if we get enough corners to get the minimum surface area required.

  5. Why Can’t I watch this video : It says: the uploader has not made this video available in you country…

  6. That’s a Youtube video from Pensado’s Place. I’m not sure what they’ve got going on with their permissions. I’ll add this to my to-do list.

    Brandon

  7. i got it , thanks bro

  8. I’m sorry, but I think you calculated the frequency of absorption effectiveness incorrectly. Frequency = speed of sound/wavelength. For speed of sound = 1083 ft/s and wavelength of 32 ft, the frequency of effectiveness is 33.8 Hz. Bass traps do work, especially corner bass traps, but you still need enough of them to absorb the sound effectively. How many bass traps you needs depends upon the size and response of the bare room. I am an acoustic consultant.

  9. Thanks for the correction, Aimee. I’m a bit confused on which calculation you thought was incorrect (although I’m sure there many SMILEY).

  10. For years, I have tried to get commercially available “bass traps” (I hate that term) to work as advertised, but just could not, especially at frequencies below 100 Hz. I had enough and went on an 8 year R+D mission to develop a real low frequency, < 100 cycles, absorber technology. I achieved part of my goal using the diaphragmatic absorption process.

    Diaphragmatic absorption was not mentioned in your article and it really is a viable approach, but not widely mentioned or understood. We have taken the diaphragmatic absorption process and added a dual front wall, rigid cabinet, and activated carbon to the cabinet's inside to achieve rates and levels never before realized in less than 12" of space.

    We have a broadband and frequency specific absorber using diaphragmatic technology. Yes, they are heavy, but are very powerful. You can see just how powerful they are by viewing the Riverbank Labs test data at: http://www.acousticfields.com/what-makes-us-special/ Scroll down to the page bottom for the test data links.

    Regards,
    Dennis

  11. Sounds interesting Dennis. It’s a real bummer that the fiber-based absorbers do very little unless they are in the 1/4 wavelength ballpark. Ideally, they’d be feet from the wall (and not inches), which is a huge problem in the real estate realm. The problem I found with the resonators (at least from a DIY perspective) was it was simple to get a device to resonant at a very, very narrow frequency range, but they were practically useless at any other frequency. A broadband, membrane absorber sounds like a dream come true. I’ll check it out. Thanks!

  12. Hi Brandon,

    What we found with diaphragmatic absorption was that as density and depth of the cabinet increases, so did lower frequency performance. We figured depth to be important but were a little surprised about the density issue.

    We found that we could control the resonant frequency of the absorber through this density/depth ratio and increase the rate of absorption with the internal cabinet fill material which is the activated carbon. Also, using two front walls instead of one, that moved in vibrational sympathy with each other to slow energy down, aided in overall level and rate of absorption performance. This was also a bit of a surprise.

    The carbon internal cabinet fill material is very powerful. There is over 2,000 sq.ft. of surface absorption area in just one gram of carbon, so you can quickly see how powerful 65 lbs. is in each of our ACDA-10 and ACDA-12 units.

    The ACDA-10 is our broadband absorber from 30 Hz. – 200 Hz. and if you add a foam face you can achieve absorption all the way up through 6,500 cycles. The ACDA-12 is our big “sponge” with a more narrow coverage from 30 Hz. – 50 Hz.

    In an 8 year period, we built 116 rooms of different dimensions and the need for 30 Hz. – 50 Hz. was present in every room and a more broadband absorption rate and level from 30 Hz. – 200 Hz. was also needed, thus the reason for the two unit types.

    Thanks for your interest and response.

    Regards,
    Dennis

  13. I wonder if bass traps can work for extremely low frequency noise coming in.

    I say extremely low because I’m hearing a sound nobody around me hears. So I’m guessing it is at least less than 20 Hz. I can hear lower than that.

    When I’m in my room listening to music, I’m basically hearing a very deep monotone bass (noise). I’m not sure at which frequency, or if it’s made up with more frequencies. All I know is, nobody around hears it. It’s also only in the house itself, nothing outside.

    Can a bass trap be designed that can at least absorb some of this ‘noise’s energy?

  14. I’m assuming you are hearing this low frequency energy when music is playing. Does it happen with all music? It’s quite possible this kind of stuff can be construction work happening nearby (among many other things). Also, when you get down under 30Hz, those frequencies generally need to be extremely loud to be heard.

    The biggest question is whether your friends are hopping into your seat to listen to this low frequency business. If they are sitting 2 feet away from you they will be hearing RADIALLY different low end response due to the standing waves of the room itself. They need to be sitting in the exact same place you were sitting.

    You can definitely build/buy bass traps for ultra low frequencies, but you absorber-style bass traps won’t work unless they are 40′ thick. (Yes, 40 feet. I did pull that number out of my ass, but you get the idea. ) You want to use a resonance-based bass trap generally called a “membrane bass trap”. One could probably be built with a thickness less than a 12″, but the thickness is just one of a few factors.

    I’m not sure how many membrane absorbers you’d need for this.

    First, you’d have to identify that probably frequency as membrane absorbers must be tuned to very specific frequencies. (Unlike fiber-based bass traps). One way to do that is my measuring with a cheap test microphone and using the free Room EQ Wizard. Another way, which is my crude, is to us a sine wave generator and sweep through it until you find the frequency that’s annoying you.

  15. Probably best to use what Focal uses: Ready Acoustics
    http://www.readyacoustics.com

    11 Grammy Award winning Producers and Engineers plus Focal using their stuff? Gotta be a good reason…

  16. I agree to the author of the article. Just want to add, I would recommend everyone to check the material’s absorption coefficient of whatever you’re buying to use as a “bass trap.”
    (0 = 0% absorption, 1 = 100% absorbed sound.)

    The frequently found cheap, foam bass traps (from eBay):
    Frequency Absorption coefficient
    125HZ 0.11
    200HZ 0.24
    400HZ 0.64
    800HZ 1.06
    1600HZ 1.03
    Tells you a lot how effective these are at trapping bass frequencies (ahem. Not very effective. These are great for mid-high freq. tho!) You’ll be spending money on stuff that doesn’t really work (for low freq.) If I were you, I would save up, and either buy commercial bass traps or make some your self (and …don’t use foam.. duh).

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