Hi everyone .
when you enclose a speaker in an enclosure the rear surface radiates the waves inside the cabinet and after bouncing, a certain part of them come back and hit the speaker membrane.
a fibrous mass or a pyramidal sound-absorbing panel is usually used to solve the problem of standing waves but is it an optimal solution to also solve the problem described above? or are there other methods and tricks? .
bye thank you .
when you enclose a speaker in an enclosure the rear surface radiates the waves inside the cabinet and after bouncing, a certain part of them come back and hit the speaker membrane.
a fibrous mass or a pyramidal sound-absorbing panel is usually used to solve the problem of standing waves but is it an optimal solution to also solve the problem described above? or are there other methods and tricks? .
bye thank you .
Hi,
Roughly simplified: sound inside the box could be a problem only on high frequencies, whose wavelength is less than two times longest dimension of the box. On longer wavelengths it's just uniform pressure inside the box varying with movement of the cone and not causing any extra sound in a way, this is why you'd have a box in the first place.
But, when wavelength is short enough to fit inside standing waves happen, now pressure varies in different parts inside the box, which might hear through as unwanted sound. Damping material inside the box should dampen the standing waves, the modes.
In general, typical damping material like the pyramid foam, is more effective on high frequencies than lows so more effective on the higher order modes, and least effective on the lowest mode. Thus, you might want to design the system so that the lowest modes are not an issue, perhaps use low pass filter so that modes happen above pass band, and use sufficiently effective damping. You could also position the source(s) so that lowest mode doesn't get excited by putting acoustic center middle of the longest dimension. Perhaps do them all.
Don't forget the walls could resonate / balloon so add bracing. Also the outside dimensions and shape is important, sound whose wavelength is similar to the box dimensions strongly interacts with the box, baffle step being easiest to identify.
Have fun!🙂
Roughly simplified: sound inside the box could be a problem only on high frequencies, whose wavelength is less than two times longest dimension of the box. On longer wavelengths it's just uniform pressure inside the box varying with movement of the cone and not causing any extra sound in a way, this is why you'd have a box in the first place.
But, when wavelength is short enough to fit inside standing waves happen, now pressure varies in different parts inside the box, which might hear through as unwanted sound. Damping material inside the box should dampen the standing waves, the modes.
In general, typical damping material like the pyramid foam, is more effective on high frequencies than lows so more effective on the higher order modes, and least effective on the lowest mode. Thus, you might want to design the system so that the lowest modes are not an issue, perhaps use low pass filter so that modes happen above pass band, and use sufficiently effective damping. You could also position the source(s) so that lowest mode doesn't get excited by putting acoustic center middle of the longest dimension. Perhaps do them all.
Don't forget the walls could resonate / balloon so add bracing. Also the outside dimensions and shape is important, sound whose wavelength is similar to the box dimensions strongly interacts with the box, baffle step being easiest to identify.
Have fun!🙂
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What shape does the lobe generated by the posterior membrane have? Is it similar to a cone?.
for example, I am experimenting with a Karlson 12 (which is a bandpass) with a heavy modification to the front chamber, this is completely different from the original one. If the measurements I have made are correct, I have obtained a good gain in the area of frequency ranging from 25 to 600 Hz.
being able to direct all the internal reflected waves towards the two reflex ports would be an excellent thing, but even if it were possible, a small part of the waves that are reflected more than once will still be there.
for example, I am experimenting with a Karlson 12 (which is a bandpass) with a heavy modification to the front chamber, this is completely different from the original one. If the measurements I have made are correct, I have obtained a good gain in the area of frequency ranging from 25 to 600 Hz.
being able to direct all the internal reflected waves towards the two reflex ports would be an excellent thing, but even if it were possible, a small part of the waves that are reflected more than once will still be there.
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I think you shouldn't use terms like 'reflection' inside an enclosure. Internal dimensions are far too small to make a raytrace model valid.
You could try to model such speaker in hornresp, or with BEM software like AKABAK. It gets quite complex fast and not possible to simplify like in my previous post. You definitely can utilize the rear sound, but that too is wavelength dependent as you've found out.
Simple thought experiment: If you have a path for back wave to exit, the length is more or less static. Lets assume we have one meter long tube from back of the driver and exit next to the driver. If you play sound whose wavelength is two meters long, the sound from back would travel half wavelength longer than that of the front and be in phase with the front sound and make constructive interference with it. Now, imagine playing 1 meter long sound, it would have full wavelength delay and be opposite phase as the front sound and would make destructive interference. Opposite effect, due to different wavelength.
In addition, there would be resonance(s) with the tube, which you could also utilize. You could have multiple tubes, resonators, attenuation with damping, and so on, but still the same fundamental issue would remain: wavelength changes with frequency, dramatically, while your construct stays more or less static in size. This means the construct has different effects on different wavelengths.
So, it's a balancing act, a good system minimizes various audible issues without introducing new ones. So, closed box is not necessarily a problem, like is not naked driver, nor karlsonator. All of them would have some bandwidth where they work nice, but beyond that the performance drops. Usually crossover is utilized to change to a physically different size source/construct to carry the performance over wider bandwidth.
Simple thought experiment: If you have a path for back wave to exit, the length is more or less static. Lets assume we have one meter long tube from back of the driver and exit next to the driver. If you play sound whose wavelength is two meters long, the sound from back would travel half wavelength longer than that of the front and be in phase with the front sound and make constructive interference with it. Now, imagine playing 1 meter long sound, it would have full wavelength delay and be opposite phase as the front sound and would make destructive interference. Opposite effect, due to different wavelength.
In addition, there would be resonance(s) with the tube, which you could also utilize. You could have multiple tubes, resonators, attenuation with damping, and so on, but still the same fundamental issue would remain: wavelength changes with frequency, dramatically, while your construct stays more or less static in size. This means the construct has different effects on different wavelengths.
So, it's a balancing act, a good system minimizes various audible issues without introducing new ones. So, closed box is not necessarily a problem, like is not naked driver, nor karlsonator. All of them would have some bandwidth where they work nice, but beyond that the performance drops. Usually crossover is utilized to change to a physically different size source/construct to carry the performance over wider bandwidth.
There is simple math to it, standing waves relate to wavelength and physical dimensions of box, or a room, or pipe whose ends are open, one or both closed.
20Hz is 17m long, while 20kHz is 1.7cm long, all speaker boxes as well as most domestic rooms fall between these and have modes, and standing waves if there was sound.
Take a small bookshelf speaker, say 20cm internal dimension. First mode is half wavelength, so at 40cm which is about 850Hz, well within pass band of a small two way speaker woofer bandwidth. Even if longest internal dimensions was only 10cm the first mode would be on passband of typical two way speaker with dome tweeter: 20cm, which is about 1700Hz.
Take a tower speaker, 80cm tall two way. It would have modes through the whole midrange from 1.6m long wavelength, ~200Hz, up all the way to crossover. But, thats why you'd use the damping material, to reduce the standing waves, make them non issue.
Ever thought about it: if modes were much above pass band you wouldn't need the damping material in the first place. Damping inside the box introducess loss (damping) which would just reduce efficiency at drivers main resonance, and you'd need more power to get same acoustic output at the resonance than without damping. Idea of the box is solely to get more acoustic output on low frequencies, and damping reduces it, so why use box at all?
How audible any of this is? depends on many things like crossover and the room, and how much other audible things there is that grab your attention. Making loudspeaker system peeling worst offender at a time and eventually you'd be wrestling with "box sound", beat it and go for next issue, no big deal. Or never mind any of it, what ever feels fun and worth your time and attention.
Have fun! 🙂
20Hz is 17m long, while 20kHz is 1.7cm long, all speaker boxes as well as most domestic rooms fall between these and have modes, and standing waves if there was sound.
Take a small bookshelf speaker, say 20cm internal dimension. First mode is half wavelength, so at 40cm which is about 850Hz, well within pass band of a small two way speaker woofer bandwidth. Even if longest internal dimensions was only 10cm the first mode would be on passband of typical two way speaker with dome tweeter: 20cm, which is about 1700Hz.
Take a tower speaker, 80cm tall two way. It would have modes through the whole midrange from 1.6m long wavelength, ~200Hz, up all the way to crossover. But, thats why you'd use the damping material, to reduce the standing waves, make them non issue.
Ever thought about it: if modes were much above pass band you wouldn't need the damping material in the first place. Damping inside the box introducess loss (damping) which would just reduce efficiency at drivers main resonance, and you'd need more power to get same acoustic output at the resonance than without damping. Idea of the box is solely to get more acoustic output on low frequencies, and damping reduces it, so why use box at all?
How audible any of this is? depends on many things like crossover and the room, and how much other audible things there is that grab your attention. Making loudspeaker system peeling worst offender at a time and eventually you'd be wrestling with "box sound", beat it and go for next issue, no big deal. Or never mind any of it, what ever feels fun and worth your time and attention.
Have fun! 🙂
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Depends on its size relative to its intended passband, which peters out at its upper mass corner (Fhm = 2x Fs/Qts'), so damp to 'taste' if used above this point. 😉
(Qts'): (Qts) + any added series resistance (Rs): http://www.mh-audio.nl/Calculators/newqts.html
(Qts'): (Qts) + any added series resistance (Rs): http://www.mh-audio.nl/Calculators/newqts.html
Hi, think this: if a woofer box looks like an acoustic double bass, smells like one, and sounds like one you can be sure you'd hear standing waves, resonance. If it's a speakerbox it probably shouldn't sound like that, make sound of it's own. Standing waves, resonances, can be beutiful though, thats the music, right? various fundamentals with their harmonics, all standing waves 🙂
Currently listening on Cannonball Adderley version of Autumn leaves, very beautiful even on headphones 🙂
Currently listening on Cannonball Adderley version of Autumn leaves, very beautiful even on headphones 🙂
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Can you explain why there are no standing waves please? I’ve used a Dayton DATS on my speaker build and this seems to indicate resonances at frequencies relative to the internal dimensions. Am I wrong to assume that the “blips” on the impedance curve indicates enclosure resonance?
Standing waves cut in above a certain frequency. This is related to the size of the box vs the wavelength. This is why damping material that fits in the box is able to be effective.
That’s my understanding too.
However, I was curious about why picowallspeaker repeated his statement that standing waves do not occur within a loudspeaker because the internal dimensions are too small. I know of a HiFi manufacturer who has also said something similar and consequently built loudspeakers without any damping material. I’m particularly interested in knowing if picowallspeaker has any evidence to support his statement.
However, I was curious about why picowallspeaker repeated his statement that standing waves do not occur within a loudspeaker because the internal dimensions are too small. I know of a HiFi manufacturer who has also said something similar and consequently built loudspeakers without any damping material. I’m particularly interested in knowing if picowallspeaker has any evidence to support his statement.
Well, I read It every day, SW in a box, and sometimes, once a year, I exclamate: "there are no SW in a speaker box"
Then I return to sleepy mode.
Then I return to sleepy mode.
🤣
There are none because you can't see them. Besides. they're in a box.
But really, cognitive dissonance happens to us all. One believes there are no standing waves in rooms, another is convinced there are none in a box. And even if one accepts the existence, one is inclined to think they contribute to sound reproduction quality.
There are none because you can't see them. Besides. they're in a box.
But really, cognitive dissonance happens to us all. One believes there are no standing waves in rooms, another is convinced there are none in a box. And even if one accepts the existence, one is inclined to think they contribute to sound reproduction quality.
Yeah there is no problem until one perceives there is. "box sound" can be quite noticeable, but still kind of hard to say what is it that makes it. Panels resonating or something inside the box, something outside the box, and it is likely combination of multiple things. Then one would start to poke around trying to do something about it and one reasonable cause could be modes inside the box. Luckily they are easy to mitigate with damping material so one can test if it has any audible effects.
Now, the question is did the sound change with added stuffing, did "box sound" disappear? Be sure to have unstuffed box to A/B test, but do any listening tests outside! If you are comparing two separate physical objects, they cannot be at same physical location, so in room they would have different interaction with room and sound would change due to that alone, at least in small rooms. Perhaps swap positions and listen if the sound changed, or record with mic in room, or come up with any other way to eliminate factors that might affect. Point is to get a sense how important it is for perceived sound quality compared to some other things you are familiar with.
Does any of it matter, well, possibly not if one is not interested in such details, or hear such details, or think it's nonsense without trying. It (any issue) stops being nonsense the minute one hears something is not right and figures out what it was. Just be realistic about it, box sound does not disappear changing cables for example. If it did, it wasn't box sound but something else, possibly interesting in itself, another issue to wonder about.
Differences between better and worse sounding systems is due to multiple things: better system is better not because of some secret sauce but because the designer was able to determine and implement most things that contribute to good sound, and eliminate most things that contribute to poor sound. If you cannot determine, then you cannot implement, and it's just mixed bag of good and poor 😉
Now, the question is did the sound change with added stuffing, did "box sound" disappear? Be sure to have unstuffed box to A/B test, but do any listening tests outside! If you are comparing two separate physical objects, they cannot be at same physical location, so in room they would have different interaction with room and sound would change due to that alone, at least in small rooms. Perhaps swap positions and listen if the sound changed, or record with mic in room, or come up with any other way to eliminate factors that might affect. Point is to get a sense how important it is for perceived sound quality compared to some other things you are familiar with.
Does any of it matter, well, possibly not if one is not interested in such details, or hear such details, or think it's nonsense without trying. It (any issue) stops being nonsense the minute one hears something is not right and figures out what it was. Just be realistic about it, box sound does not disappear changing cables for example. If it did, it wasn't box sound but something else, possibly interesting in itself, another issue to wonder about.
Differences between better and worse sounding systems is due to multiple things: better system is better not because of some secret sauce but because the designer was able to determine and implement most things that contribute to good sound, and eliminate most things that contribute to poor sound. If you cannot determine, then you cannot implement, and it's just mixed bag of good and poor 😉
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@markbakk
........and many do! I was surprised at how many of the truly large MLTLs (60-72 " H x 30-40" W x 24-30" D) I've done for Altec, etc., where even the minimal damping I've suggested that Altec used in their much smaller studio/consumer models ( top, one side, back around the driver, was removed at least partially and some removed it all! Even with optimal driver, vent locations there's significant eigenmodes.
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You are not wrong, and they can often be seen more clearly in the acoustical power and group delay responses.
For example - a driver in a relatively small 10 litre sealed enclosure:
You’re not helping me to understand your statement picowallspeaker. This is forum made up of amateur enthusiasts, many of whom are willing to share their experience. Your last posts are very troll-like.