Can You Trap Bass? What is a Bass Trap, Anyway? Room Acoustics
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- Опубліковано 23 січ 2021
- Like I said, I'm not an expert, but I've learned a lot over the past few years between dealing with audio issues in my workshop and getting ready to do this room. The short answer is bass traps work to reduce sound energy in a room in the bass region. There are basically two types: velocity and pressure.
Velocity is that rockwool or fiberglass or foam and it slows the speed of the sound as it passes through it. Think of waving your hand through water as opposed to waving it through air. It takes more effort and therefore uses up some of the energy the wave has.
A pressure trap works by reacting to a low frequency wave in the same way you can feel the floor or walls vibrating when a subwoofer is pumping out dance music. That vibration also uses some of the energy from the sound wave, reducing it.
Biggest problem with pressure traps is they are limited to a very narrow band, while velocity traps are more broad-band, covering more frequencies.
In an upcoming video I'll measure the frequency the wall panels I made vibrate and get a better idea if they are actually doing anything.
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The short answer is bass traps work to reduce sound energy in a room in the bass region. There are basically two types: velocity and pressure.
Velocity is that rockwool or fiberglass or foam and it slows the speed of the sound as it passes through it. Think of waving your hand through water as opposed to waving it through air. It takes more effort and therefore uses up some of the energy the wave has.
A pressure trap works by reacting to a low frequency wave in the same way you can feel the floor or walls vibrating when a subwoofer is pumping out dance music. That vibration also uses some of the energy from the sound wave, reducing it.
Biggest problem with pressure traps is they are limited to a very narrow band, while velocity traps are more broad-band, covering more frequencies.
In an upcoming video I'll measure the frequency the wall panels I made vibrate and get a better idea if they are actually doing anything.
I am building a recording/live streaming studio in my basement...and this is some awesome info. Thank you, Mr Heisz.
Those 'holy' panels remind me of a QR code.....
WOW! Just scanned one and it directed me to woodgears.ca!!!
How about destructive interference. Could you build a "bass-cancelling" system? Hard to only cancel the bass waves that have been in existance for some amount of time though. Hmmm. Great channels (woodworking too!)
I used a combination of both pressure and velocity methods on my dust collector. Worked great, as the pressure was targeted at the main tone, while the absorbers cleaned up the rest. 21 dB reduction!
@@ericsimonson3128
Very astute question.
Yes, destructive interference or cancelation designs work very effectively.
There's different types;
Years ago Nelson Pass designed the Phantom Acoustics Shadow...
a mic/amp/woofer system whereby in a 7' tall column, with woofers at each end, would "eat up" and null the excessive bass energy... via an inverted polarity approach.
If I remember correctly, I believe Stereophile covered in a review.
Easier and something any enthusiast can assemble is a DBA, Double Bass Array, somewhat of a pitch and catch system.
Ideally it's comprised of four subs on the front wall, four subs on the rear wall. Again ideally the drivers are spread out... one driver in each corner of the front wall (bottom left, bottom right, top left, top right) and a mirror image on the rear wall.
Via adjusting the delay/polarity of the rear wall sub drivers, acoustically you can theoretically null all resonant behavior occurring front to back.
Pitch and catch.
This can dramatically increase clarity and resolution within the bass range.
Very well done, John. Semi-retired recording engineer here. Ethan Winer would approve, even though your approach is divergent from his. Good stuff!
Came here to drop his name. If anyone reading this is interested in learning more about treating a room, start with Ethan Winer!
Ethan is the man!
Hey John, this was super interesting! Just watched the diffuser build video and I'm glad you put a link to this channel at the end! Cheers!
After watching maybe 100 videos, this is the one that best seems to capture every aspect of acoustic treatment and "sound proofing" in a coherent and easy to understand way. I love the professionalism of Acousitc Fields, but between the sales pitches and abrupt end of each video, I had to watch dozens to get this much information. Great job, and to anyone else poking around, this is a great place to start and get a solid understanding of how sound works in a space.
Great work... super valuable that you went thru and measured at each juncture... you know audio folks love to disagree or pontificate about method (I’m not saying it isn’t important) but the results are what matters... and you have certainly improved the response of the room!
so glad i discovered you and your channel. its inspiring in so many ways.. thanks
Very nice step by step and great results. There are times when I want to rip everything out and just start all over again but there are just too many other projects on the go at the moment.
As an electrical engineer I find this very interesting and refreshingly free of nonsense and voodoo. Since I haven't really studied acoustics, most of this is new to me (but it fits in well with what I know about wave propagation).
The lack of nonsense and voodoo (and believing in measurements and not just my golden ears) means I wouldn't make it in the high end audio business :)
Actually, scratch some of that - there are a few that don't that I highly respect.
@@IBuildIt
Check out *Erin's Audio Corner* on UA-cam and his website if you haven't already.
One of the best videos I ever seen thank you for all the information you are showing us and enjoy your room.
I can't wait. I am so interested in how you finish this room and what speaker design etc. Great Channel!
Such a difficult task! Cool to see your tests and the results.
This is by far the best build video. The waterfall graph is the only thing that matters with these treatments and acoustic panel manufactures never include it in their testimonies. John has a completely square room and made it work with proof. Outstanding!
Your room is sounding pretty good John, good work. Like what I'm working with right now is targeting specific frequencies, more to learn about that for sure. It gets problematic for sure the deeper down the absorbent rabbit hole you go :)
I really dig your content.
The mis-understanding of what you're doing and explaining is staggering... and you explained it quite well.
Two important characteristics of sound in small room acoustics... that many people are entirely oblivious to is wavelength size, and why that matters, and secondly... behavior in the time domain.
Perusing these comments so many that took the time to comment ... just haven't got to the point in their audio journey of being exposed to and understanding the time domain and what you're pursuing here.
The muddying effects of latent energy in the bass octaves is one of the biggest issues in HiFi.
A room subjectively sounds better when it's reverberation is relatively uniform top to bottom.
Most all rooms possess excessive reverberant energy in the bass octaves compared to mids/highs.
With the mids/highs, if it's not direct/early reflections, then ideally you want to retain that.
So, it's prudent to attack that excessive energy without overly affecting the mids/highs ... otherwise you're not evening out the ratio.
Damp the bass as effectively as possible, while working to retain adequate liveliness in the mids/highs.
Merely wanted to drop a note in appreciation of your content. Didn't intend to add all this, I know you've got this.
All the best
I have to say your efforts paid off quite well. People may not understand by simply looking at the graphs, but the changes are fairly dramatic for what you can expect.
So, John is basically building a walk-in headphones. Nice!
Interesting to see the process, Thanks
Wow it shows how the decay times is decreeing in your measurements. Well done 👍
Great video… easy to understand and explained in layman’s terms !!!
Thanks for the information and good advice.
We will listen to a beautiful voice and not disturb the neighbors either.
Looking forward to your next video! I'm especially interested in how you'll treat the back of the room.
Very interesting ! Great Insights.
Thanks, Your explanation is easy to follow.
Great video, very insparing. 👍
Damn good video, you explained your methods, and showed the results at each stage. Very informative and 'real world'.
Wish I lived near this guy so I could pick his brain. Amazing work.
you have probably build better acoustic treatment in your room than you’ll find in majority of professional recording studios around the world . well done!
I use the sofa. Looks amazing John.
Would love to see a tour of your house with all the before and after photos. That would make an amazing video!
Audio guy, Musician here. Well done and we'll explained. 😸👍🎶
very interesting stuff. didn't know about any of this.
What a champion effort.
Really thanks. Very usefull your explication. Thanks
This is so interesting.
My first thought when I saw the video title was " Why is John making a video about fishing?" . Then I noticed it mentioned acoustics. Interesting topic, thanks for the video. :)
The train analogy was a good one.
Fascinating
I have 4 bass traps and several panels that I built for my main listening room. I have the bas traps from floor to ceiling in the corners, triangle-shaped and free standing one on top of another. You seem to have gotten good results however. I wanted something quick and easy so I just dampened the hell out of my room :) Edit: some panels are on the sides and I hung two from the ceiling over my listening position.
Very Cool John... Makes Perfect Sence! lol
Great video!
In short you can say you don't want the bass to "echo". Like with an empty room you hear the highs echo.
Listening to your explanation it seems as if this is like speed bumps for low frequencies. This is how I understood your explanation as a layman.
Kind of and I can see where you get that from my train comparison. The treatment is used to pull some of the energy out of the low frequencies, like putting a pillow over someone's face that's screaming at you :)
Thanks John
the panels with the holes look great
Great content thanks
Good luck with getting rid of standing notes with in a 8 foot tall sailing But you do give some really good tips an you do have a really good understanding of how acoustic works
John really interesting stuf. And although you are not an expert its so worthy for us to see how experiments can work out. Subd!
John, I’m wanting to learn more about acoustics like you did.
What literature and resources can you recommend? Thank you.
Could you try a Helmholtz resonator at 40hz to try to fight those modes? I have seen some built that sit in the corner and look like a small trash can.
Thank you for not just making us rely on you habilities to form complex phrases full of subjective interpretation and add some proper measures.
I am personally designing / building my "Dream" wood workshop. I have been down the rabbit hole of sound in an effort to to reduce the sound that is inherent to a shop and also for music. I can listen to this video and without question "hear" that the room is "treated" ( it sounds good, and I am sure will only get better ) and looking back at your shop videos its now amusing to watch one of your videos from say 2015 vs your more recent ones. Could you maybe do a video showing / explaining the treatments you have in place in the shop? GREAT VIDEO!!
Great video thanks. I see perforated panels on the front, they act both like basd trap and diffuser.... on side wall I.dont't understand the approcch. Is diaphragmatic panel.?
Спасибо тебе большое мужик. Очень полезное видео, все понятно. Удачи с работой!!!
Nice channel 👍
Spacing of the panel off the wall is basically allowing you to get almost the same absorption as if the entire area depth was treated. There is a big misunderstanding going on where many people are claiming that an air gap is better than full depth absorption, when in fact it is the opposite. However, using an air gap can reduce the cost considerably (if you build several panels) while attaining almost the same performance.
Live sound engineer. Current times mean outdoor venues with power issues meaning portable generators on a budget. Noisy!! Been struggling with building sound enclosures. Reading as much literature as possible and watching UA-cam videos. Glad that I was a drywall metal stud carpenter in my younger days. In some of the literature, I've seen where 25 gauge metal studs are better than wood for sound reduction even with the sound transfer of metal. After hearing you talk about the plywood giving a little (in and out like a speaker cone), maybe that's where a high gauge metal stud would be better than a wood stud, in that it has more give. Just a thought. Carl
P.S. I like how you are working through a problem with no perfect solution. I feel your pain!! LOL
I always like it when you really sink your teeth into something, like with the clamps. You talk about little else for a while.
If you don't want to drill all those holes, I hear you can also put up panels with slits between them. Like slim vertical boards with space between them.
i saw in music studio wooden frames and on them diferent materials on one it was thin plywood they just hang them there when they need them and i think they focus it right way i dont know if this is same as u are doing mybe it help :D
For the ultimate in room treatment, cover the walls with rough sawn lumber, cover the ceiling with cork.
I am not sure if you are using the same equipment you do for the shop videos but the sound from this is very clean, easy to tell that the room is well treated. Hope everything lives up to expectations.
Favorite song: We Rock wool! 😜
I know next to nothing about this subject but now I know a bit more. 😀
What’s the thickness of the plywood you used for the diaphragmatic absorber, and what would you suppose would be the affect of using a thicker plywood? Thinner?
How about a Helmholz Resonator as absorber tuned to 37 Hz? This could help with your Room modes
Wow. That’s amazing. Are you Canadian ?
- Nick from Toronto
Hey John, Great video! I find your woodworking videos fantastic because I used to be a carpenter and now I'm a sound designer working in film and TV. I used my construction 'skills' (Not so great anymore haha) to build studios and currently on my 5th and last one. I am no physicist but I am in love with acoustics and I do know the fundamentals fairly well, though, like you said it's an extremely complex topic. You mentioned that your room is too small for the waves to bounce around but that isn't true. A 80Hz wave is roughly 14 feet, which explains your RTA readings as well as the harmonics. You can also prove this in your shower, just make a high end to low end sweep with your voice and you'll hear the tub mode pop as you get really low (Mostly a harmonic of a higher frequency but its a fun test).
The trick to stopping modes or standing waves is to cut the frequency off 1/4 into the wave, so a trap that's 3.25ish feet would stop that pesky 80Hz mode, practical? NOPE so to get around this is you find material that soak up the frequencies that are being an issue, Rockwool is great because it is relatively good at soaking up lower end frequencies, at least in its coefficient tests. Though the thicker you make a rockwool panel the more low end it will reduce (but like you said take away the high end). The resonant absorbers that you've made are a great way to save space.
The issue with modes is that only the lower end ones are a problem because they are the ones that fit in smaller rooms and they are the most noticeable, there are so many higher frequency modes in your room but they all are un noticeable as they are too numerous. So the theory that I build into my studios is, use as much rockwool as possible to soak up the low end, then treat the high end with quadradic diffusers. A reason I don't like resonant absorbers is that they are tuned to a specific frequency and any change in the room, like a couch will change what happens and the math gets out of hand.
I'm a really big fan and I hope you take this information well! Great video again John!
I didn't say they won't bounce, I said they don't fit - a 20Hz wave is 56' long. 56' is bigger than 14'.
Not sure why so many people choose to misinterpret what I say.
The room modes are 37hz, 40hz and 70hz - length (slightly more than 14.5'), width (14') and height (8'). You calculate that by doubling the dimension and dividing that into 1130. The first harmonics are 74, 80 and 140.
@@IBuildIt hey John, well what you said is that the frequencies involved don’t fit in the room but they do. Anything over 80Hz fit in that room and would cause problems.
This is really interesting, although I don't understand a lot of it.
I am curious about how well your plywood wall membrane will work for low frequency capture and /or diffusion. Whisper wall uses a similar approach, but the material they use is much lighter than wood. To capture anything below 800Hz, I would suggest leaving gaps in the wall panels along the rear wall, that are covered with acoustically transparent cloth. If possible I would have these openings run from floor to ceiling and be at least 2' wide. This should work as a bass trap down to about 80Hz, and diffuse a portion of the the frequencies below that.
*Edit- My apologies, It would have helped if I had finished the video before writing my comment. You pretty much did what I was suggesting, but you placed two on the front wall and have a semi-reflective surface on the front of the trap. I like how you approached it though.
Theater is looking good. I don't know anything about bass traps, but have used dynamat for car stereo installations in the past, of course the purpose is different. My Denon AV receiver has a multipoint EQ that is set up with a microphone, would adding bass dampening via panels improve the curve then, or what if the room already has drywall. Interesting stuff.
Adding panels to reduce the reverb time will always help - you really can't add too many in the typical room.
Nice video and measurements. You should try to put sack with sand in corners -they are good and not expensive bass traps.
"Hole-y Diffuser" is my favorite Dio album.
"Hole-y Diffuser, Batman" !
Thanks for the video and great work you have done.
How do you address the first reflection points? (Yes this video were about bass.)
But do you going to create a "reflection free zone" when you are done?
Broadband absorbers (at least starting from the room's cut-off frequency) at first - and second if necessary - reflection points so that they are at least 10 dB lower than the direct sound at the listening position.
Does the TV panel add any bad reflective noise? And would a projector screen be acoustically transparent like cloth? Very interesting video I love the new channel addition to your lineup.
Being behind and between the speakers is about the best place for it, since it's not getting a lot of direct sound. Probably won't be a problem big enough to solve.
Have you done any work on reducing shop noise?
Did you have those panels mounted with caulk? Pretty much made them fully isolated.
What diagram you used to get the circles for cut out you got
And how did you deal with fiber glass and rockwool dust in the air?
The one thing that this video gets across well is just how large you really need to go to get significant taming of modes as low as 40hz. Most videos have no measurments and make exagerated claims as to how big a difference a couple of panels will make to the bass response
For some reason, I'm envisioning you recreating the old Maxell "Blown Away" commercial, the one with the guy in the chair getting "blown away" by the amazing hi fidelity of the cassette tape (amazing that was in 1979, damn I'm old).
Cassettes were great, I think I still have a few of the ones I had back in high school (early 80's) here somewhere. Nowadays everything is on my computer - everything else is too much work and that's especially true for vinyl.
@@IBuildIt My Father-in-law collects LP's so we have about 10K of them in our garage, he has ~50K 55's and 78's at his house.
That was Pete Murphy from Bauhaus.
All measurements and techno details aside are you pleased with how it is working/sounding to the naked ear? It looks great by the way...
I can hear the improvements, but I'm a long way from finished.
Wow, really nice! What about a ceiling like in your shop? Or is the fiberglass also cheaper than those tiles? I guess they worked pretty well in your shop.
There's fiberglass above those tiles in my shop, too. The bass freight train goes right through ceiling tiles like they aren't even there.
John, does the open ceiling affect the results of the tests for frequency response to the tester?
Everything has some affect. Like the room has two door openings that lead into other rooms. Those rooms would be closed off after (the doors are put on and can close) but are open now and act as resonant chambers that are being included in the measurements. And I won't know until after those openings are closed whether they were bad or good.
Can you not use an equaliser, or something similar, to drop that 37-40Hz range?
where do you buy pressure traps?
Thanks for the video. I cringe when I see folks use the cheap studio foam and claim "we are now sound proofed, neighbors can no longer hear us" :( I'd love to know how you are treating isolation though, your thoughts on tube/tuned traps, and if you've tried making waterfall graph (which are my go to personally). Also, have you considered shortening one wall to avoid the perfect square, or angling it slightly.
Isolation isn't an issue for me. It's quiet where I live and my neighbours are far enough away that any noise I make won't bother them.
As for tuned traps, they need to be huge to work at really low frequencies and also need to be in the right place to work well.
Angling the walls does very little, from what I understand. They'd need to be really angled to make an improvement.
The charts I posted are spectrograms and they are just like looking at a waterfall plot from above.
Makes sense....
Bass trap? Obviously a fish catching device.
I know there is technology to counteract loud machines by inverting the sound wave and essentially canceling the noise. I wonder if it could be adapted for home theaters?
Active bass absorbers are a thing but a pretty expensive and they have to be in the right place to work well.
Can fiberglass be replaced by denim insulation?
Disclaimer, I too am not an expert, but as a music teacher and musician I have done a fair bit of study in the acoustics field. You make great points here, bravo. You mentioned the problems associated with a square room, but almost equally important is the reflection of sound waves from parallel walls. If it is not too late in the progression of your construction, I would build out at least one wall at a slight angle from its opposite wall.
Apparently (from my own research on this) the walls need to be angled by a large amount to have a significant impact. Angling the walls also wastes space, unless they were part of the original room layout - moving an existing wall to angle it is well beyond the scope of what I'm doing in this room.
This isn't necessary if the room is acoustically treated. You will still have standing waves with any room shape. All you do is shift the room moods around.
@@IBuildIt Acoustics literature points out that 10 degrees are the minimum to start seeing effects for angeling parallel surfaces.
What if I built a free standing panels, in a roundish cubicle around my desk. No corners. Leave gaps so pressure can escape. A cloud above my desk. With gap. So pressure again can escape. So my room can remain a live room, it’s all wood. But when I mix, I pull the absorbing panels around me, in a circle ⭕️
You should try to move your sitting position a bit forward or backwards from the center. The center of a rectangle room is bad to start with and probably worse in a square room. I tend to move backwards from center in smaller rooms because speakers need room to breath, but I'm sure you know that you can't get too close to the back wall, or it will open up a bunch more problems.
what is wrong with using an equalizer and speaker placement to achieve this? that is what I have done in the past to even the sound to the room.
Hello John, I am in the process of soundproofing ceiling from my neighbors. I hear them walking (stomping) on the floor. Which is bass frequency I presume. I was heading to buy rockwool tomorrow, but now I watched you video and I am not sure if to use fiberglass instead as you said lower density might be better..? Thickness of the wool will be 4 or 5 inches and then 2 layers of drywall. Thanks
First, soundproofing is not what I'm doing in this room. For that, you need mass - a barrier to reflect the sound back. So the two layers of drywall you mentioned are the main mechanism for blocking sound and any fill you add to the space will only damp the vibrations.
Also if the floor above is vibrating from people walking around, that vibration will be very hard to stop without some kind of isolation. Screwing the drywall directly to the ceiling will make it move with the floor above, acting similar to a big speaker. But isolating the drywall from the floor above will get very expensive, so you might want to lower your expectations and settle for a less than perfect result.
Structural born sound is very difficult to sort, airborn is a lot easier. F. Alton Everest is a good read on the subject
Oh, I thought this was about fishing!
When the room is as good as you are going to get it, are you going to utilize electronics to try to get the rest of the way? Starting with maybe an equalizer?
There shouldn't be any need to eq after if the room is done right. Fixing the biggest issues will make a massive difference over an untreated room.
You've mentioned the walls - sides, front and back - and ceiling; but, been quiet about the floor - so is that tile for echo or carpet or futons and pillows tossed about for additional careful sound throttling? Presumably, to be addressed in another episode (I'll be patient).
I'll eventually do wood on the floor, but in the meantime have thin carpet tiles. Floor is generally not treated, especially when you can do the full ceiling.
@@IBuildIt I've attempted a little additional research into acoustic floor treatment this morning too and what I've come up with so far is that that is usually left to dust balls and pet shed hair accumulating naturally - but that's just from sweeping, I vacuum later today.
Me: I put an old patched subwoofer on my television to get something better
J.H.: Bass traps #6, it's a work in progress
Very interesting. What. program and test mic and sound source are you using? I use a homemade dodecahedron speaker and an Earthworks M30 mic. Just FYI your room is too small to develop a true statistical reverberant field. You are dealing with cumulative spectral decay. And yes you have a massive amount of modes in the small room plus flutter echoes. Some of you assertions are not 100% correct but close enough. You might consider a Helmholtz resonator trap in each corner at the fundamental freq of the lowest room modes. You also need add diffusion to the rear wall. You should get tbe book Master Handbook of Acoustics by Alton F. Everest. Keep it up and i enjoyed the vid
I never said I expected a diffuse sound field in a room this size. What I did say was the goal is to get the reverb time as even as possible. "Aiming for" and "expecting to hit" are two different things.
And since I'm not an expert or even pretending to be one, like I said in the video, it's to be expected that my assertions wouldn't be 100% correct.
I'm using a Umik-1 and REW to do the measurements. Speakers are Elac's.
You're on the right track. But if you want a "warm" room sound but block out bass travel to the exterior I've got one
word for you - Acoustiblok. Hang it like drapes around all of your outer walls - then put up the baffles and panel you
have leaving about an inch airspace. Concrete. The floor is going to be a resonance problem.
This is what I did - I have a metal building behind my house. Half is storage, half is my practice room. The walls are
coated with spray rubber undercoating (the whole building) - seals, helps keep vibration down, minimal soundproofing.
Jam room is built room in a room. Outer walls and divider wall are insulated with rockwool then 2 hanging layers of
Acoustiblok from ceiling (8ft) to floor inside a 2 inch airspace. The inside wall is another layer of rockwool. Foam tape on
all studs including frame to floor. 5/8 plywood walls, floor and ceiling. Floor has a layer of Acoustiblok between the
concrete and a layer of plywood. I did this after the fact when I found out that carpet alone wasn't gonna do the job.
Doubled door entry with both doors layered. Building has 12ft side walls and 14ft peak. Ceiling (or attic floor) has
Acoustiblok, rockwool, Acoustiblok between ceiling studs then plywood on top. Used as extra storage space in building.
Interior is cover with sound absorbing foam with foam corner bass traps. I'm a bass player so If I don't rumble no one
else will that comes to jam. I wanted as "dead" a room as possible so it doesn't bother neighbors.
The most vulnerable part is the entry. Testing at the door is 47db with a full band inside at a db level of 147!
20 ft away - nothing. My house 40ft away. Nearest neighbor to building 90ft. Mission accomplished!
Nice room you've got going John. But if you're looking to keep bass travel down you'll definitely need to cover
that concrete and ceiling and some corner traps which a panel across the corner about 12" wide with holes half
the size you have on the others and then an 18" wide panel with the same size may create a catch in the corners for you.
Currently helping my brother build a studio and that's an idea out of many we've had to keep the main room "warm" and "live'
for recording.
Anyone interested in keeping sound travel down should definitely check out Acoustiblok. Good product and very
helpful people there.
PS Putting Acoustiblok and a layer of plywood under the carpet made a 26db difference.
Something you don't mention, and most people don't understand, is that most sound you hear indoors is from reflections. You hear the initial sound from the speakers, and then 100x as much sound being reflected off of surfaces as it bounces at 700-ish mph back and forth, reducing in strength every bounce. Your efforts are redirecting or reducing the energy of those reflections, and therefore the amount of times they continue to come back to your ears at a significant level. What's left over is easier to listen to, and more accurate to the original recording in the case of music.
And good work sir.