Soundproofing and room size

dboomer said:
When I used to teach classes I would play a 40 Hz tone and then a 50 Hz tone (sine wave) and ask the members of the class whether the sound got louder of quieter. About half the class would say yes, louder and half softer. But the level of both frequencies was exactly the same. The reason this happens is because the dimensions of the peaks and dips changes with frequency.
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“The dimensions of the peaks and dips changes with frequency” is false. Amplitude can change independent of frequency, and changing frequency has no effect on wave amplitude. 50 Hz would be perceived as slightly louder by human ears because of the equal loudness contour, but that is an effect of perception, not a change in the wave itself.

Amplitude is a function of power and how that power is transferred or dispersed. Not wavelength.

I’m confused what point you were trying to make anyway since you said half the students thought 50 Hz was louder and half thought it was quieter. What effect is that?
 
With pressure (density) the wave length becomes shorter and the wave speed decreases. The Frequency Remains the same.
 
dboomer said:
With pressure (density) the wave length becomes shorter and the wave speed decreases. The Frequency Remains the same.
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The formula you’re talking about is for the velocity of the sound in a medium. Frequency and wavelength are inversely proportional, and you can calculate velocity if one of them is a fixed value. But variable velocity in different mediums is totally irrelevant to room size. Even if we consider the different pressures in a large or small room, that formula only says whether the sound will reach us faster or slower, and in this case we’re talking microseconds.
 
bongoman said:
“The dimensions of the peaks and dips changes with frequency” is false. Amplitude can change independent of frequency, and changing frequency has no effect on wave amplitude. 50 Hz would be perceived as slightly louder by human ears because of the equal loudness contour, but that is an effect of perception, not a change in the wave itself.

Amplitude is a function of power and how that power is transferred or dispersed. Not wavelength.

I’m confused what point you were trying to make anyway since you said half the students thought 50 Hz was louder and half thought it was quieter. What effect is that?
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I'm talking about the differences in wavelength. Look at a simple sine wave. If you stand at the distance where the wave crosses over from positive to negative (half wave length) there is zero energy (silence). Now inside a room with walls a ceiling and a floor this becomes much more complicated. You have to consider the interactions because you have bounces coming from many different directions (eigentones) but the principle hold just fine.

The difference between 40Hz wavelength and a 50Hz wavelength is roughly 4 feet. So if you were standing at a peak at one frequency if you moved over about 1 foot you would move into a null (roughly)
 
bongoman said:
The formula you’re talking about is for the velocity of the sound in a medium. Frequency and wavelength are inversely proportional, and you can calculate velocity if one of them is a fixed value. But variable velocity in different mediums is totally irrelevant to room size. Even if we consider the different pressures in a large or small room, that formula only says whether the sound will reach us faster or slower, and in this case we’re talking microseconds.
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Different pressures in a room are almost zero. I’m talking about the differences between an open room and closed headphones where there is a big difference in pressure. So let me restate …

The lowest frequency wavelength you can create are directly related to roomsize. My point was that the OP was talking about a room the size of his drums. Unless he’s talking about Terry Bozzio’s kit, I’m assuming he’s talking about a small space.

Ok, Terry‘s kit size wouldn’t really allow for that. Btw … I designed and built all the electronics in Terry’s kit.
 
dboomer said:
Look at a simple sine wave. If you stand at the distance where the wave crosses over from positive to negative (half wave length) there is zero energy (silence).
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With the example you give, a 40 Hz sine will have “zero energy” 80 times per second. Outside of those micro instants each 80th of a second, the wave does have energy. Our ears and brains collect the information over time and assemble a sense of what it means, what we hear. So we receive *any small portion* of the wave above and below the center line, and we hear the entire wave. The idea that standing exactly a certain distance from the speaker would mean standing in the one spot where a wave has “zero energy” is false from a neuroscience standpoint, illogical considering the short time frame, and it ignores the question of where in the cycle the wave began. If the wave left the speaker starting at a high point, it would reach you then at a completely different point in the cycle than if it started at the midpoint. Also, these waves are not lines on an oscilloscope, they are changes in air pressure. Consequently we perceive them as pressure fluctuations, not as points on a curve. On top of all that, acoustic instruments produce a wide range of frequencies simultaneously, so that even if you stood at the theoretical half wave point for 40 Hz, you would not be standing at the half wave point for all the other frequencies that make up the instrument sound.
 
bongoman said:
With the example you give, a 40 Hz sine will have “zero energy” 80 times per second. Outside of those micro instants each 80th of a second, the wave does have energy. Our ears and brains collect the information over time and assemble a sense of what it means, what we hear. So we receive *any small portion* of the wave above and below the center line, and we hear the entire wave. The idea that standing exactly a certain distance from the speaker would mean standing in the one spot where a wave has “zero energy” is false from a neuroscience standpoint, illogical considering the short time frame, and it ignores the question of where in the cycle the wave began. If the wave left the speaker starting at a high point, it would reach you then at a completely different point in the cycle than if it started at the midpoint. Also, these waves are not lines on an oscilloscope, they are changes in air pressure. Consequently we perceive them as pressure fluctuations, not as points on a curve. On top of all that, acoustic instruments produce a wide range of frequencies simultaneously, so that even if you stood at the theoretical half wave point for 40 Hz, you would not be standing at the half wave point for all the other frequencies that make up the instrument sound.
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Take a look at what you are saying. It is nonsense.

First, when indoors (and the topic here is a room) The dead spot isn't an 80th of a second, it is a standing wave that essentially is constant and non moving. (Standing waves essentially don’t happen outdoors because there are very few reflections compared to indoors)

Second, assuming almost all harmonics are even multiples of a fundamental, they are also zero in the same spot as a fundamental. But there are even more additional null spots. So whatever frequency is null every 4’ then the second harmonic is null at 4’ and at 2’, the third null at 4’, 2’ and 1’ and so on. But in the normal course of things the harmonics get halved in amplitude. Now that might make you think there would be hundreds of completely silent standing wave points. Again, the reason that isn’t so is due to the eigentones. Acoustics in practice get pretty hairy in a big hurry because of comb filtering. In general, Mother Nature overwhelmingly shapes all tones by subtraction.

Third, whatever point you are trying to make about speaker positioning, the speaker is constantly moving and assuming the speaker is moving you have to look at the total (speaker) system which most likely included some porting.

Please, if you want to keep doubling down on “facts” that just aren’t true then cite the math that supports your claim (as you asked me to do, and I did!) As always in science, the math has the answer. If you can’t do the math (and no shame if we all can’t) than you have to rely on someone’s interpretation of what the math means. That’s where things become troublesome.
 
I've been reading two (non-exclusive) arguments.
First, it's all about having multiple layers of different materials.
Second, it's all about that mass, mass, mass, with a bit of damping.

I'm inclined to think that mass is the argument for appeasing the neighbours, but multiple layers (and a teeny kick drum) makes more sense for appeasing the person in the next room.

Any thoughts on that?
 
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dboomer said:
The reason you can hear long wavelengths in headphones is because they create pressure. In normal atmosphere you need length.

Anyone that has mixed down a recording in their bedroom and then played it in the living room knows the low end gets louder. In your bedroom you keep adding low end EQ but it doesn’t really do anything if the dimensions of your room are too small. They when you play it back in a big room all the low end you added comes to life
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Especially with maple shells that generate the fat lows and mids. These require more space to develop standing waves. Birch shells tend to work in smaller rooms. This has been my personal experience in over 4 decades of playing numerous venues. But nothing scientific to reference, personal experience only.

Also - the best way to handle room noise that I have found is to place your instruments in basement below ground, and treat the ceilings and walls with acoustic panels over the sheet rock. Obviously have a plumber check all water connections and pipes that run along the basement ceiling to avoid floods (this happened to me when a 6$ dishwasher hose that connected to the hot water pipe popped and flooded the basement). Build yourself a drum riser out of 2x4's and floor boards just in case.
 
Syncopated_1 said:
Especially with maple shells that generate the fat lows and mids. These require more space to develop standing waves. Birch shells tend to work in smaller rooms. This has been my personal experience in over 4 decades of playing numerous venues. But nothing scientific to reference, personal experience only.
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I’m not sure where you are going with this. Inside a room the standing waves are a product of dimension and frequency and it doesn’t matter how you generate that frequency. There are also standing waves inside drum shells and those will depend on dimension and wood density. The potential standing wave is fixed by the height of the drum shell. But remember at whatever frequency the standing wave is in your shell, if you don’t tune to that frequency then it doesn’t generate and therefore will have no effect on the sound.

It’s probably a very small part of a drum’s overall sound. But whatever value one gives to the character of sound from a given wood, the size of the drum and the tuning matter. The character of the sound contributed by the wood not linear and is different at different tunings. So to say “walnut always sounds like this” isn’t exactly true as it will depend on the size and the tuning.

If you’ve ever done beating tuning (https://en.wikipedia.org/wiki/Beat_(acoustics)) the same thing will happen when tuning a drum. If you manage to exactly hit the standing wave frequency of any drum the sonic character of that drum will change at that single frequency. Tune a bit higher or lower and it goes away. It would be easy to measure but I’m not sure if everyone/anyone could actually pick it out.
 
Wow! @dboomer and @bongoman started me on an acoustics master class! Thanks for that!!

As a metrologist for 38 years, I've had lots of exposure to acoustical calibration (microphones, audio generators, sound level meters, accelerometers, etc.) and radio frequency calibration (signal generators, antennae, waveguides, loads, etc.). Best as I can determine, @dboomer is spot on with the electromagnetic theory; I'm also betting that @bongoman is spot on concerning practical music listening. Almost any sound generated by a speaker (even a single tone) isn't coherent and collimated. And at standard temperature and pressure in dry air media, there are vagaries in real life. Even a full anechoic chamber isn't perfect (I've been in a couple and it is creepy!). So, while the physics of audio transmission are mathematically provable and constant, real life generally isn't.

Everybody knows that an audiophile quality stereo setup has one or more "sweet spots" in a given room. Move those speakers closer to the corner and it's going to move a bit. That doesn't negate physics, it just muddies things up a bit.

Re the OP's concern: it's probably easier to control the sound leakage that would escape a smaller room, but as a few have mentioned, it comes with diminishing returns. For me, I'd try to design my studio around the largest practical room available for my space and let my budget determine the sound levels outside.

Not to derail the thread, but would an almost infinite frequency be DC? :unsure:
 
I wonder if you could create a two layered plexiglass or graphene for strength drum cubicle with a vacuum between sheets-of course it will need support through walls. You can ventilate it and sound proof that part too. Floor is always an issue though so it would need a larger support with shock absorbers and in it's wallsa vacuum underneath you as well.
Learned two "scientific" wisdom today. A rare glimpse of a lunar eclipse with the flat earth at just the right angle and bullseye.451046349_10161758403614474_4308868111633187031_n.jpg
Then I learned why the US is so resistant to the metric system and it turns out it's because an American art form. Well I'll be. IMG_5113.jpeg
 
Sound is kinetic mechanical energy because it's a wave traveling through air created by mechanical compression-but it's a wave and similar to photons the higher frequencies carry more energy. Photons make up all the electromagnetic spectrum -cosmic, uv, light, X-rays, etc it's just the wavelength of it's travel. Photons are weird because they are a particle with no mass all the energy is carried in the wave, but it acts like a particle and wave-dual nature. Because E=mc2 some group was supposedly recently able to cerate matter from photons-well actually it was an electron and positron -the anti-matter of it-so it was annihilated immediately I guess. Doesn't seem you could create the energy to do it-my guess it's a cheat like Captain James T Kirk. They must have had dilithium crystals. LOL
 
dboomer said:
The sound quality will suffer in a small room compared to a big room. You need at least some 16’ dimensions to develop 40Hz in a room

Audition your bass drum in the shower and see what you think ;)
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So unless I have have a room that's 16' across, I can't play drums? ;)
Actually, I have little suitcase drum that I can use for a kick. My experience is that a full sized kick drum creates a huge, vague racket in a small room. Also, if I have less bass in the mix to start with, that might make the noise a little easier to contain.
Bigger is better, so if shrinking a room won't improve sound reduction, I'll go as big as I can.
 
There are two primary considerations when thinking about small rooms … the maximum length that a waveform it can form and the distances from boundaries to the source.

As I recall (but please check my math) a room 16x14x10 can allow a 40Hz wave. In any event it is not possible to generate a wave longer than the max distance in the room. The second consideration is standing waves in 3 dimensions (eigentones). The standing waves create nulls (dead spots) at multiple points in the room.

Have you ever noticed that your bass drum loses low punch up on a 4’ riser as compared to being flat on the deck? An easy experiment anyone can try is to play a bass drum tuned very low on the floor and compare the lows to what it sounds like if you pick it 4’ up in the air. If you do this in a big room you should hear a cancellation in some lows.
 
The entire wave length will propagate regardless of the length of the room. It will just reflect along the way as it goes in a shorter space. More reflections equals more potential null zones. It would be accurate to say you need a certain length of room for the wave to complete a full cycle with no reflections.
 
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