How Bass Goes Through Walls like Magic

[@IBuildIt]

READ ME!!!! My explanation can sound like a distinction without a difference, but it's the impedance match loss that's the key to understanding it. If the wall is acting like a big speaker cone, like your speaker that's creating the sound, you will have large losses from the impedance mismatch. Speakers are massively inefficient at transferring mechanical energy to the air due to the impedance mismatch between the cone and the air. Now I should say that some of that IS taking place - it's unavoidable - but the main mechanism is as I describe it in this video. This is even better illustrated by a thinner material, like a sheet of plastic hung to seal off a doorway between two rooms. Virtually all of the sound passes right through from one room to the other. BUT, if the transfer method was the one commonly described, you would have huge impedance losses from the sound energy trying to make the plastic move, and then with the plastic trying to move the air on the other side. Instead the plastic sheet is just moving WITH the sound energy, like it has become part of the air itself. In other words, it's along for the ride. The sound, in effect, pushes through the plastic as if it doesn't exist at all. Much like my finger presses the button on the control panel on my stove as if the plastic isn't there. My finger presents an overwhelming force to the barrier the plastic provides. Same with a wall, but the wall (being thicker, stiffer and heavier) is more of a barrier and reflects back more of the sound energy that's acting on it. Only the longer wavelength lower frequencies make it through, and that's why you hear mostly the bass on the other side of the wall. Barriers do three things with sound: reflect it, absorb it and let it pass through. It depends on the mass, density and stiffness of the barrier how much it does each of these three things. Thick, heavy, dense walls will let very little sound through and reflect most of it back. Thin, light barriers let most of the sound through. That's the basis for effective soundproofing. Acoustic treatment tries to absorb sound. Absorbing the sound converts the mechanical energy to heat to dissipate it faster than it normally would. The goal with acoustic treatment is NOT to soundproof a room, but to reduce the reverb time in the room and cut down on reflections. Acoustic treatment improves the sound quality you'll get in a room, but doesn't do much to stop it from getting out of the room.

[@alminshaar232]

Hello John! Really great to see you. I just came across your video after a really long time. I used to watch all your videos and I learnt a lot. You are a gentleman. Stay Blessed !

[@rickrudd]

My fav band.

[@paulhirst3548]

I really enjoy your explanations John. Nice choice of music. I never was a big Steely Dan fan but I do like Donald Fagan's solo work. Memories of the 80's.

[@MrAnimal1971]

This makes so much sense! I visited a home made studio that no sound was coming from inside. The had cinderblock walls with sand in the cavities. The inside was normal construction with insulation in the walls, I believe. The point is that the density of the walls made an impressive studio. BTW I listen to Steely Dan in my shop too!!

[@gregmatula9749]

I love that Larry Carlton guitar work on Don't take me alive.

[@imqqmi]

I think number one is air gaps, most rooms have them like windows, doors, vents, gaps between ceiling and walls even though plugged with silicone kit or hidden behind wallpaper or wood trim, then as you suggest moving along the pressure waves just like closed speaker cabinets and lastly when the frequency hits the resonance frequency of the wall or building it transfers into contact sound as well. This can travel through a whole block of buildings. Since it travels a lot faster in a solid it's difficult to locate where the sound is coming from and due to the low frequency of course.

[@scoobtoober2975]

Just clicked on youtube steely dan. End of this video. I mean i just pause it and come back in an hour. Very good. Thanks for the recommendation. So much music is compressed/made for radio stuff. Cheers

[@kennethnielsen3864]

Thanks for sharing.

[@allenrogers9320]

0:32 yes john love your explanation.top notch. Im following now. Dig it. I knew i liked u. But when you said Steely Dan it was a shoe in. Thank you.

[@scoobtoober2975]

John, Love this talk. My comment is based on a few rooms at RMAF. Were most of the rooms are a similar shape and size. And when there you do the door test. Stand at the door and decide in 2 seconds to go in or not. Treatment, angles, speaker size etc. all played into it. It was ELAC room (Andrew jones in person) doing the demos. Those rooms always sounded good. Natural, pleasant, airy and calm. Vs Raidho blasting your ears off with muddy mid/lower tones. One year they were good, the room was bigger, very plesant, the next few years they were in a small normal room and sounded muffled/muddy . Small normal elacs in a small room are great. But was it the treatment, speaker size, volume the bass/mids were trying to move. Or Andrew Jones starring at you and smiling back as you are smiling in enjoyment. Then telling you they are only 500$ a pair. You are on to something with the impedance of the speaker interacting with the room. Not the electrical impedance.

[@rebbel67]

On the off chance that you don't know it, John, may I suggest also Royal Scam, another album of theirs? Especially "Kid Charlemagne", and the guitar solo in it, is wonderful, in my book.

[@IBuildIt]

Kid Charlemagne is on the best of dick I have, great song :)

[@rebbel67]

@@IBuildIt Ah, nice. That hadn't cross my mind, that best-of cd.... 😁

[@rubenvh9792]

Good video

[@scoobtoober2975]

For the plastic bag trick. I think a diagram or napkin drawing of the pressure wave of mid/lower frequencies. How they will impact a flat surface. They are huge compared to fibers/fabric openings/cracks. Door closed vs open while playing that tone. dB meter in the hall. 100hz wavelength is 10 feet. It will radiate from the source is a sphere then bounce and add/substract to the other waves.

[@BikeBoatandTravel]

Back when I bought my first CD player in 1986 I think that The Nightfly was probably the second piece of vinyl I replaced.... after Crime of the Century... LOL

[@NackDSP]

Steely Dan, vibrations so good they can move anything. : )

[@Ro-ni7nm]

John, you have cracked the code when it comes to cultivating comments!!I haha Personally i think walls just like drivers can be described using t/S parameters... such as sensitivity, cone area and fs, compliance etc.

[@Audio_Simon]

Also helps to remeber the wall has a huge surface area that enables it to transmit sound quite effectively, even though it doesnt physically vibrate a lot compared to a speaker cone.

[@IBuildIt]

You are still thinking in terms of the relay race, where the wall is the speaker for the sound on the other side. If that was the mechanism, you'd get very little sound through a sheet of thin plastic because the impedance match losses would be too great.

[@scoobtoober2975]

If you are trying to reduce/block sounds going throughout your house. Just buy another house down the road. Or shed man/tv room separate. A practical way is to follow the STC rating system. Punch line is double wall style with no air vents touching main house. Get a separate room heat/cool. like mini a mini split. It'll dehumidify pretty good. Jeff renovision did this to some extent. Adding mass to the walls too, mass loaded vinyl. Seal the outlets, seal the door (solid one). All sorts of things. Very expensive and time consuming. Just turn the bass off at night. Tons of rockwool. Or concrete. Yes the low low goes forever.

[@ivansbacon]

Everything on Gaucho is good. Love New Frontiers, '"yes we're gonna have a wing ding"

[@gregmize01]

Ethan Winer would be proud!

[@peternewman9713]

You're a Teacher's Teacher, John. By the way Steely Dan is great!

[@vmoutsop]

I’d you own physical media you are required to hate it 😂

[@Peter_Tissot]

for fuck sake, 1 million ads

[@chrisf7249]

It’s kinda both. This guy has some great ways of explaining things, but this is not his best.

[@IBuildIt]

Here's your opportunity to point out how it can be improved - you have my ear. But I should say that you need to read my pinned comment to get all of the facts for the presentation. I almost always add more thoughts to go along with what I say in the video.

[@chrisf7249]

@@IBuildIt I will read the pin in a bit but my first thought is to compare a weighted passive radiator to the wall. It’s not just the surface that surface that tunes the box, but the mass/density of the radiator affects your your impedance losses. Same as a wall. The wall has to move to transfer the energy to the air in the adjacent room. I will read your pin later today and think about a better way to explain my understanding of this subject. FYI another good source on this subject is courses on sound proofing walls and floors. Been through a few..

[@IBuildIt]

A passive radiator is a special case and you've actually given me an idea for a new video explaining how it works. But I'll give a quick one here: The PR stands in for the port in a bass reflex system, so they operate in roughly the same way. The port in a vented box is tuned to let the sound of the resonating air mass inside the box out, so that it helps extend the low end. The PR does basically the same - it's being driven at the tuning frequency by that resonating air mass inside the box and acts as a low frequency driver to extend the low end response. So, in effect, the "voice coil" of the PR driver is the resonating air mass inside the box. In other words, it's behaving like a sub woofer and will have the same type of impedance matching losses as any other cone driver.

[@chrisf7249]

@@IBuildIt just finished reading your pined explanation. I disagree with how you describe the lower frequencies just flow through walls. I think we can all agree sound / noise is vibrations of the air. With no air there’s no sound. The room with the source of the noise, has the sound vibrations flowing through the air, then that vibrations in the air hits the wall it can do the three things you mentioned. Reflect, absorb, or transfer through the wall. Like you said, absorption is converting the vibrations into heat. Reflecting is self explanatory, but to transfer through the wall the wall has to vibrate from the sound, and then the other side of the wall has to make the air vibrate on the other side of the wall. If the surface of the wall doesn’t vibrate, the sound doesn’t make it through. This can be reduced in standard wood framed walls a number of ways. One of the best is to use 2x6 base and top plates and 2x4 studs. You then alternate what side of the plates each stud line’s up with and fill the wall with mineral wool insulation. The sound hits the first surface of dry wall, it vibrates the wood studs it’s attached to but not the dry wall on the other side due to it not being attached to it. Then the vibrating insulation worms up the air trapped within itself and then there’s nothing left to vibrate the drywall on the other side. You can also just poor a foot thick concrete wall and obtain better sound proofing. Concrete vibrates less the thicker/stronger it is. I think you keep referring to impedance losses to explain why you understand it a different way. Can you please explain what exactly you are referring to as impedance losses? There’s transfer coefficient and adjustments made due to surface types. But I’m not sure what you are referring to as a impedance loss.

[@IBuildIt]

The wall system you describe is effective for reducing the amount of sound that goes through the wall, but it mainly does that by absorbing the sound energy on one side, and not chiefly by breaking the transfer of vibration. It's similar to a CLD panel (constrained layer damping) used in speaker boxes, where the inner layer absorbs the vibration and reduces how much energy is transferred to the outer layer. But neither of these methods are particularly effective for blocking really low frequencies, like anything below 100Hz. And then nothing in what you said explains the impedance match losses you would get, and that's the key point. @chrisf7249