You are Thinking About Sound the Wrong Way
Вставка
- Опубліковано 23 тра 2023
- Most people tend to think of sound from a speaker as air moving. This leads to the idea that something that will block wind (like thin plastic) will also block sound. The air is moving, but there is no "flow". Instead, think of that movement as shivering - it's vibrating very slightly but not going anywhere.
As with all solids, some sound will reflect off of the thin plastic, but almost all of it will pass right through unobstructed. Think of light hitting a pool of water - some reflects and some goes through so you can see the bottom of the pool.
So a damping material like rockwool performs essentially the same as it would in its raw state, if it is sealed inside a plastic bag.
Sound is energy that travel through and acts upon mediums. Mediums are any solid, liquid or gas (like air) and they vibrate when sound passes through them.
They can also reflect the energy. If the sound is travelling through a medium (like air) and if it meets another medium of different thickness, density and mass some of it will reflect. The new medium (like a wall) will reflect some of the energy and let some pass through.
For example a thick, solid concrete wall will reflect almost all of the energy that hits it, while a thin wall made from lighter, less dense material will only reflect the higher frequencies and let most of the bass frequencies pass through. You can hear this effect easily with your stereo playing in another room.
Damping absorbs energy and converts it to heat. When sound passes through a damping material, some of it is converted to heat and used up in that way. That's how the piece of rockwool I put inside the speaker stopped the standing wave - it absorbed the excess energy from that standing wave and converted it to a very small amount of heat.
Sound is not simple. Most think of it in 2D terms, when it is fully a 4D process. It moves through 3D space with a beginning and end time. It usually starts at a single point, but then expands out in all directions from that point until all of the energy has been converted to heat. This expanding is called propagation and the sound energy is spread thinner and thinner as it happens.
Think of a balloon being inflated and how the rubber gets thinner as the balloon gets bigger. There's still the same amount of rubber there was when the balloon was not blown up, but it's now spread over a much larger area.
For sound to dissipate quickly, something has to speed up the conversion of that sound energy to heat. That's the function of damping, like that rockwool I used.
You can help support the work I do in making these videos:
Project plans for sale: ibuildit.ca/plans/
Join the ibuildit community on Loacals: ibuildit.locals.com
Support this channel on Patreon:
www.patreon.com/user?u=865843...
#diyspeakers
#johnheisz
#audio
My "Scrap bin" channel:
/ ibuilditscrapbin
My main channel:
/ jpheisz
Website: ibuildit.ca/
Facebook: / i-build-it-25804801424...
Instagram: / i_build_it.ca - Навчання та стиль
Most people tend to think of sound from a speaker as air moving. This leads to the idea that something that will block wind (like thin plastic) will also block sound. The air is moving, but there is no "flow". Instead, think of that movement as shivering - it's vibrating very slightly but not going anywhere.
As with all solids, some sound will reflect off of the thin plastic, but almost all of it will pass right through unobstructed. Think of light hitting a pool of water - some reflects and some goes through so you can see the bottom of the pool.
So a damping material like rockwool performs essentially the same as it would in its raw state, if it is sealed inside a plastic bag.
Sound is energy that travel through and acts upon mediums. Mediums are any solid, liquid or gas (like air) and they vibrate when sound passes through them.
They can also reflect the energy. If the sound is travelling through a medium (like air) and if it meets another medium of different thickness, density and mass some of it will reflect. The new medium (like a wall) will reflect some of the energy and let some pass through.
For example a thick, solid concrete wall will reflect almost all of the energy that hits it, while a thin wall made from lighter, less dense material will only reflect the higher frequencies and let most of the bass frequencies pass through. You can hear this effect easily with your stereo playing in another room.
Damping absorbs energy and converts it to heat. When sound passes through a damping material, some of it is converted to heat and used up in that way. That's how the piece of rockwool I put inside the speaker stopped the standing wave - it absorbed the excess energy from that standing wave and converted it to a very small amount of heat.
Sound is not simple. Most think of it in 2D terms, when it is fully a 4D process. It moves through 3D space with a beginning and end time. It usually starts at a single point, but then expands out in all directions from that point until all of the energy has been converted to heat. This expanding is called propagation and the sound energy is spread thinner and thinner as it happens.
Think of a balloon being inflated and how the rubber gets thinner as the balloon gets bigger. There's still the same amount of rubber there was when the balloon was not blown up, but it's now spread over a much larger area.
For sound to dissipate quickly, something has to speed up the conversion of that sound energy to heat. That's the function of damping, like that rockwool I used.
I wonder if you could increase the effectiveness of polyfill by putting it in a sealed bag and squeezing out most of the air?
At 40 Hz the wavelength is more than 8 meters. Your bag is very small in comparison and therefore invisible to the sound. I am actually surprised you got -3 dB attenuation from it. I would put that to mass damping effect more than any kind of absorption.
The minus 3db was the rockwool damping in the bag. The bag by itself was .3db reduction.
If sound is the movement of energy, then why is it attenuated by the temperature of air?
:
@@Thomas..Anderson Soundwaves are longitudinal. The energy of soundwaves moves particles back and forth between source and destination.
When a neighbor notices the noise coming from your listening space.
When you hear the family shouting in the other room.
Yep, sound is an energy that travels through solid stuff👍🏼👍🏼
Recently a car audio engineer showed me a car speaker design. He told me that it will be sort of revolution in car audio. He said its a ring mode driver. It is a extremely flat full range driver starting around 150Hz and reaching up to 20kHz. I mention this, because it can be seamless integrated in any surface and fully covered with a lot of materials without the need of a grill or opening. The covers almost have almost no effect on the function of the driver. In fact they become part of the driver.
Very well explained. Thank you very much 😊👍
Great video. You my man are a wealth of knowledge. I learn something new from you most of the time. Just when I thought I understood sound, you educate me on something I had wrong.
More AB comparisons please. These videos have the potential to be timeless.
I'm about to start another build, a big one, and with a Qtc of 0.5 it's already somewhat wide and quite deep but over five times as high as it is deep.
I initially could not tell a difference between the tall and the short box, but I wasn't looking at the screen at the time, and (if it was mentioned) I wasn't aware of how the comparison was being shown.
I now know that even though I can tell a difference, I do not care for that improvement as much as I want/need to be so tall.
Maybe even a SoundCloud or some other lossless way of sharing the comparisons for the quite discerning could be another source of ad revenue?
This is like mythbusters for DIY loudspeaker design.
Most tell tale comparison would be: Stuff the cabinet with absorbing material and run a full audio band impedance sweep. Then bag the same material and put it back inside at the same places. Run an impedance sweep again. Compare.
I think many of us had the wrong idea because of people saying things like, " boy, that subwoofer moves a lot of air" or "bigger speakers move more air".
Of course! The best analogy that confirms the argument is seismology, that allowed us to characterise earth layers (size, location, material) with changes of medium (density), by measuring residual energy from the initial energy released by earthquakes and deduce transfer functions.
The way that helps me to more intuitively understand this concept is imagining it being over my ears. I wouldn't expect a plastic bag to have much if any effect on my hearing, while in a more abstract situation I wouldn't be so certain, despite it being the same concept.
If anything, the bag's pliability will help add to the polyfill's affect on slowing down the speed of sound even more. I.E making the apparent enclosure volume even larger. In the upper kHz frequencies however the plastic films do attenuate/reflect significantly.
I cannot believe that you went to the trouble to do this. For your safety you really should have a haz mat suit on when handling that stuff. Plastic bags are nasty. 🙃
John, for completeness. Did you try a plastic bag filled with air?
I'm curious if you have you tried denim insulation. I'll say it's surprisingly difficult to cut. I ended up using a track saw with the blade mounted backwards. But now I have enough to stuff boxes for the rest of my life.
I would have like the same tests with a frequency of 10 or 15 KHz to see how thin plastic reacts in the upper range.
What type of amp are you planing? I bet they are AB class. Same power output for all channels?
Sounds like you tested this around 40 Hz. The length of a 40 Hz wave is about 28 ft (8.6 m). The wave pressure the bag "sees" is essentially isobaric with respect to it's surface. The wavelength is too long for a phase offset to cause any practical motion. I like how you dive into the physics of your tests, like you are challenging monther nature to give up her secrets!
Wad up a ported sub box with rockwell or fiber glass and put a good light and camera in front, give it 40Hz, and then say there is no risk.
Is there no kazoo effect? Can regions of the crinkled plastic resonate unpredictably?
My father used unspun sheep’s fleece in his speakers, works well because it’s denser than fibreglass insulation and safe to handle.
My understanding is that the energy created by the sound is what moves the air as well as the movement of the objects (hands). The bag and rock wool will absorb the energy.
But the plastic bag is having the opposite problem most people were concerned about, which you show. The intent of insulation is to absorb reflected sound that would normally bounce off the internal walls of the cabinet, correct? You did show in your video that the plastic bag actually reflected certain frequencies….frequencies that would normally be absorbed by the insulation.
When you held the plastic bag close to your face, the timbre of the recording changed. Moreover, when you covered the mic with the empty bag, you commented that the mic picked up more sound, which would seem to indicate some sound was being reflected around inside the bag, causing a boundary reinforcement.
Am I missing something here? Are you saying the frequencies being reflected by the plastic are not crucial frequencies for the insulation to absorb? Are you saying the overall reflected sound is so low that it’s negligible? Both? Or something else?
The fibers transduce the vibrating air into heat. By encapsulating the fiber material, you have prevented the air particles from interacting with the fibers.
Is there not also air inside the plastic bag interacting with the fibers? The bag is not a vacuum.
Peter Walker (designer of Quad ESL speakers) did a live demo where he would hold a sheet of diaphragm material (thin plastic) in front of his face and ask the audence if they could hear any difference when he spoke. The answer was of course no. said what you are hearing is my voice vibrating the plastic on his side and the plastic then moves the air on your side and you hear it. What if, instead of my voice vibrating the plastic sheet we do it with an electrostatic charge? That's a Quad ESL.
That's a relay race kind of way of looking at it, where sound before the plastic hands off to sound on the other side of the plastic. A better way is to view it as a marathon over different terrain. Flat and level, then a shallow river to cross and flat and level again until you come to a mountain you can't climb so you need to go back.
Can you expand on the differences of low frequency vs high frequency in relation to deflection, reflection, absorption and pass through
I mentioned this on his last video. If you imagine a totally immovable object, it would reflect most of the energy and absorb some as sound.
But reflection has a lot to do with mass and frequency. I'm sure there some tables out there.
Absorption is weird, you kind of need a material which is flexible enough to dampen the energy, but bounce back. Hence why rubber is a great vibration insulator.
The absorption has a direct correlation to the thickness vs wavelength at x frequency. Lower freq has a longer wavelength and as such needs more material to dampen it. this is exactly why you will usually hear bass from your neighbours cars ect rather than the rest of the audio when all the windows are closed. The thin walls and windows can block the higher freq, but the lower freq can still penetrate due to the wavelength.
I was just going to ask about foam. When i was younger I made a car subwoofer and lined it with foam ("egg-crate" foam to be exact). Then later moved it to my home theater system. It was actually a 12" home theater woofer to begin with. It sounded great... that's all I remembered. So I did the same to my floor standing 3-way speakers and thought it improved the sound as well. Probably not... maybe. But, in any case, look forward to that next. Always learn something new . In fact, I am realizing how little I knew to begin with. :)
Egg crate foam really isn’t the best material to use. It’s been show that it’s just far too thin and porous to really do much to the sound waves, at least nothing like a proper fill like fiberglass.
@@danhorton6182 Yeah... that was what I was thinking (now that I know a little more). But, honestly, the rockwool in a plastic bag just completely blows my mind. It's hard to wrap my head around it. But, I'm still learning. :)
@@TheVTRainMan lol, I get it. I’d you’re worried about itchiness or health hazards of fiberglass you should try denim insulation. I love it, I use it and rockwool.
All you would have to do to disprove the naysayers is to take a speaker and cover it with a blue plastic tarp then crank it up. It will neither rattle/crackle the blue plastic tarp or really block much of the sound. You'll lose some of the high end, but not all of it.
Naysayers are generally not interesting in empirical scientific proof. They exist in a self made, and therefor a self supporting, belief paradigm.
Its taking away air space. So the box cubes will be less.
If I am not mistaken it doesn't really go through the plastic bag, but is "reproduced" on the other side.
It's like a transducer only in this case you are using sound to produce sound.
While that explanation might be more intuitive, it doesn't actually work that way.
Replace the plastic with a thin sheet of lead and there will be a significant reduction in sound transmission due to the much higher density of the lead. It reflects back much more of the sound, but is still acted upon in the same way as the plastic sheet.
If it was just purely a reactionary effect, then any material of any density at the same thickness would transmit the sound equally.
@@IBuildIt There will be less "transmission" because there is more reflection like the plastic bag will reflect less but "transmit" more.
But the mechanism of the transfer you describe relies on the the sheet moving when acted upon by sound energy, which happens whether it reflects or not. The sound still hits it regardless of how much is reflected back. Think about it.
@@IBuildIt Of course it will still hit (can't reflect without being hit).
Soundwaves are mechanical waves. If more is reflected less is passed to the next medium -> conservation of energy.
Good point.
So where are the impedance mismatch losses? A speaker driving air isn't anywhere near 100% efficient, but you expect a less than 1db loss (what I measured) from this system.
A few observations.
- The mic/empty bag test; ... perhaps the surface area grabbed more wave energy, coupling that air mass more ideally.
- For decades concert PAs have had to fire through covers, banners, huge signage.
Certainly not ideal from a FOH perspective. Encountered often on budget festival type events with a title sponsor.
- Its generally accepted that covering bass trapping in 6mil sheeting for example, performs like a low pass filter.
It varies, but it returns energy above a midpoint ... it's often employed to retain liveliness, when adding proper effective LF control via many bass traps.
Most rooms need all the LF absorption possible, yet doing so without preserving vital liveliness may not be as pleasant.
- NSYNC came thru our venue, RCA Dome, in the early 2000's. This was the biggest tour production in the world.
No expense spared touring.
But for "cool" visuals ... the PA fired thru an external grill!
I couldn't believe it.
Pop Odyssey Tour
Big point source PA, each cabinet faced with an exterior shiny metal grill ... for aesthetics ... a tour that big.
That should never happen!
fwiw, everyone got their hands on that tour ... "bill to band", "bill to band", "bill to band" ... I saw it.
Every element of that tour was as over the top as you can imagine. Circus like.
The "steel" arrives a week earlier. Cranes handle and build the stage structure, from a constant flow of flatbeds negotiating our King-Kong door airlock.
Over a few days, they build every trick feature a concert could have.
As an opening misdirection, they appear on an elevated platform midfield (unknown to concertgoers, the act was rolled into position via road cases, right thru the center of the crowd!).
In addition to cabling to fly five wide across the length of the stadium ... trick hidden features everywhere. Conveyor belt thrust catwalks out into the crowd. Five futuristic mechanical bulls appear ... with every lighting, pyrotechnics effect possible, platforms rising and falling.
Every effect ... smoke, fire, light, platform, pyro, laser, the main video display dropped down into an example!
Akin to a Vegas permanent residence show ... that level of complexity.
We parked 20 to 30 motor coaches, INDOORS for that show. A car hauler of exotic cars, sport bikes for toys while they're in town. Additional haulers with 60 golf carts ... 60, one band, one night ... two hours!
Excess, layers of it.
Like I said, EVERYONE had their hooks in while the getting was good.
Someone had the bright idea to fire the finest PA cabinets in the world thru a set piece, an ornamental grill.
John, your video reminded me of those times.
One thing I failed to notice while doing the mic in the bag recording was that it was a lot closer to the speaker. So that probably accounted for the higher volume.
Good point ... the smallest differences are magnified greatly due to relative proximity.
Not in anyway in critique of your thought proking content, John.
But, variations like that illustrate why subwoofer testing is best performed outdoors, ground plane at 2m.
The extra meter facilitates all the energy (driver, vent, etc), has coalesced into summed wave energy.
Also, the doubling to 2m elicits greater consistency across the data.
If I had a subwoofer design business, then definetely I'd use an accurate method to measure their output.
But for everything I do the in room response is enough to get an idea of how they are performing. I'm only using my stuff in my rooms, so if it works there, it's good enough.
@@IBuildIt
fwiw;
Due to extraordinary dBspl, pro audio mfr Danley, measure their offerings at 10m, and 28.3v, rather than 1m, 2.83v.
Their products are extreme, ... subs w/109dB sensitivity at 1w, capable of 150dB.
Full range, point source with 160dB capability!
Extraordinary numbers.
With the microphone inside the bag, there was only one layer of plastic between the driver and the mic. In your other tests, there were 2 layers of plastic between.
The comments about the bag crackling reminded me of a silly experiment I did many years ago. The idea was to dump a bunch of styrofoam peanuts into a couple speaker boxes. I actually did this as a gag, because I thought it would have comedic effect (i.e. the noise styrofoam peanuts make). To my surprise, it did not have the desired effect. It didn't make any "styrofoam peanut noise." But I also don't think it did anything to dampen the boxes.
Hey John love the video. Any chance you’d be willing to add a material to the dampening challenge? I’ve used Ultratouch denim insulation as a materiel before and felt that it did incredible. Obviously it doesn’t have to be Ultratouch. If you can’t easily get it I would be happy to send you some. I insulated the walls of the 16x20 foot room and the silence was deafening. I’ve never been in a room that absorbed sound like that. After that i started using it as a filler in speakers and subwoofers. Anyways, thought it would make for an interesting product comparison, especially for those who don’t want to breath fiberglass or have itchy arms.
I can't see it being more effective than fiberglass or rockwool, but almost certainly better than polyfil. For me the itchy factor isn't an issue, so I'll always go with the one that's the most available at a reasonable cost.
@@IBuildIt I get that, I don’t mind the itchiness at all. I have two unopened packs of Rockwool Safe n’ Sound in the garage as well as two of the ultra touch. I wasn’t necessarily thinking for you, I know you don’t mind fiberglass, more for your viewers. I’ve been in a room lined with fiberglass and this was definitely different. I just thought it would be cool to see a comparison using your testing methods. I know you say you can’t see it being more effective, I’m sure people would like to see test results proving that. I’m not an audiophool, but I can definitely hear a difference when stuffing a cabinet with it vs rockwool or fiberglass, maybe that comes down to density, I don’t know. Just an idea.
The absorption coefficient changes for different frequencies from product to product, usually based on density. So it may be more or less effective at a certain frequency range than rockwool or fiberglass. That can change how it sounds, but you'd really need a very controlled comparison for that kind of subjective test.
@@IBuildIt yeah that definitely makes sense. Just thought it would make for a good video discussing alternatives for stuffing and acoustic panel material for those who want an alternative. You’ve already proven that polyfil sucks in comparison and that is likely the most widely used material. They use polyfil because they don’t want to deal with fiberglass, at least many people I know do. Those that I have shown the denim fiber have switched from using polyfil. Many don’t know about it as a material
Thanks for the great video, I wouldn’t use plastic bags for fear of the sound waves not penetrating the plastic, but duh, they’ll just transfer their energy like they do with drywall.
But what happens when you put your head in the bag, can you still hear the sound? 😀
Seal it in a silk or high threat count cotton bag?
I just layer polyfill on top of the rockwool and glue together in panels, acts as a filter.
dont know if it my headphone or ur bass speaker , but i hear a slight rubbing sound on the voicecoil (headphone HD650)
I don't think people need to put insulating in plastic bags. Any fabric with a tight enough knit (like a bed sheet) will keep the nasty tiny fibers of insulation from getting pushed out the port from air movement. I don't get all geared up in a hazmat suit when building acoustic panels, but it is very irritating to my eyes, throat and lungs. If the air pressure going out the port of my speaker is enough to blow out my (rather snug) foam port plugs when I turn it up, then even at moderate volume there is enough air flow to push those tiny glass/rock fibers out into my living room. It's not that difficult to keep it contained and it isn't smart to allow it blow around your house freely. That sh!te dices up tender lungs and scratches eyeballs. Those two organs are kinda important to keep in good shape.
I must confess, this topic both fascinates as well as frustrates me. I still don't fully understand why sound absorption panels, then, are made with fabrics. So if it's energy, why is that the case? I'd love to see a test between a 2'x4' sound panel. One with insulation only, one with fabric covered insulation, one with insulation covered with plastic (maybe a trash bag) and one with a trash bag only. Then see what differences there are. I love this topic, but damn am I an idiot on the subject... groovy video
Can you test No Rez? from g r research
You need to get some no-rez from Danny at gr research and see if it's really that much better than rockwool or fiberglass.
Doubt it is as good as rockwool and fiberglass, let alone better.
So why cant sound travel in a vacuum?
No medium.
Wind is DC air, sound is AC air. plastic is almost like a DC filter that passes most AC.
I thought it interesting that the bag was being sucked towards the speaker at 4:53.
Interesting
Convention wisdom for as long as I remember (70's) insist it's merely an illusion ... examining a cone at full stroke, and seeing one direction appear more prominent.
However with all the drivers being Klippel'd, many drivers exhibit significant deviation of in vs out, vis-à-vis travel.
@@FOH3663 No illusion. If look at 4:50 and compare it to 4:55 you can clearly see it. Just use your keyboard's left and right keys while the video is paused. I think maybe the sound/air is wrapping around behind the speaker, maybe there is port back there.
@@Take-the-Ticket
Yes, agreed.
I see it ... that's what I'm saying.
I'm not.
i must old and deaf. i could no hear the tone. nice video though.
Maybe your speakers just don't reproduce 40hz?
@@Take-the-Ticket maybe.. after your video I took 2 online tests. not good results so maybe specsavers here I come.
@@trickydicky165 Again.... if your equipment is unable to produce a frequency at an appropriate level... That is an equipment issue not a hearing issue.... 40hz is not typical for early hearing loss.
I couldn't hear the tone on my TV, but could hear it easily with headphones. Because the TV speakers are weaksauce.
@@ShainAndrews hi yea thanks for that. I tested my daughter (16) on a 1-100 hz test on computer. She heard from 2 hz. I heard from 50. So it’s my ears.
I hope this helps as well. nasa.gov/specials/Quesst/science-of-sound.html