The attenuation from resistance. Ok I have overstated the "freely" part, its not free. But it's not reflected either. If low frequencies reflected off hard surfaces, then low frequency bass traps wouldn't work.
However, the main point was this. The common reason why people claim curved enclosures are better is that they don't allow the accumulation of standing waves. I said that this isn't true at low frequencies, and that is because the wavelengths are too long. That is true.
However, the main point was this. The common reason why people claim curved enclosures are better is that they don't allow the accumulation of standing waves. I said that this isn't true at low frequencies, and that is because the wavelengths are too long. That is true.
pjpoes said:
Low frequencies are indeed reflected off hard surfaces. How do you think basshorns work? Or room/cabin gain? The boundaries MUST act as reflectors, rather than largely passing through, or else basshorns wouldn't work and room gain wouldn't exist.
Low frequency bass traps wouldn't work? Why not? They're not hard surfaces, they are soft and absorptive.
no broadband absorbers are soft. True bass absorbers typically have a solid hard surface. But hey, I'm no expert here, so I could be wrong. I don't believe that low frequencies can reflect off a surface with a distance shorter than the wavelength, but I might be off on that. I've asked two different experts to clarify this for us.
However, when I looked up standing waves, what I found was that a standing wave can not be created in a tube shorter than it's wavelength. That absorption can reduce or eliminate standing waves, but are not effective at low frequencies. Why is that then?
However, when I looked up standing waves, what I found was that a standing wave can not be created in a tube shorter than it's wavelength. That absorption can reduce or eliminate standing waves, but are not effective at low frequencies. Why is that then?
Still waiting on a response from my "experts", but in the mean time, my quick search for reflection came up with this. This is from are often quoted and mostly loved Wikipedia. It's consistent with other things I found, but was most easily cut and pasted.
"Sound reflection
When a longitudinal sound wave strikes a flat surface, sound is reflected in a coherent manner provided that the dimension of the reflective surface is large compared to the wavelength of the sound. Note that audible sound has a very wide frequency range (from 20 to about 17000 Hz), and thus a very wide range of wavelengths (from about 20 mm to 17 m). As a result, the overall nature of the reflection varies according to the texture and structure of the surface. For example, porous materials will absorb some energy, and rough materials (where rough is relative to the wavelength) tend to reflect in many directions — to scatter the energy, rather than to reflect it coherently. This leads into the field of architectural acoustics, because the nature of these reflections is critical to the auditory feel of a space. In the theory of exterior noise mitigation, reflective surface size mildly detracts from the concept of a noise barrier by reflecting some of the sound into the opposite direction."
The key words I saw were that sound waves were reflected off a surface as long as the surface was large as compared to the frequency. Low frequencies are very large, 20hz is 17.2 meters long, there is no enclosure large enough to reflect internally the 20hz wavelength. 100hz is 3.44 meters, again, few if any enclosure has a length over 9 feet. 300hz is the first point when you see a wavelength approach a meter or less, and so I would say that standing waves can not be created below 300hz in most enclosures because sound can not be reflected at those frequencies within the enclosure, since the surface is not physically large as compared with the wavelength. A room is different, it is physically large. However, I would argue that you don't get 20hz standing waves in normal rooms since I can't see how any dimension of a normal room is going to be equal to or greater than 17.2 meters.
I don't know what the specific mechanism is behind how a horn works, but I don't believe it's reflection of the sound wave, since that would require a very long horn. Note that, Hemholtz resonation makes no comment of reflection.
"Sound reflection
When a longitudinal sound wave strikes a flat surface, sound is reflected in a coherent manner provided that the dimension of the reflective surface is large compared to the wavelength of the sound. Note that audible sound has a very wide frequency range (from 20 to about 17000 Hz), and thus a very wide range of wavelengths (from about 20 mm to 17 m). As a result, the overall nature of the reflection varies according to the texture and structure of the surface. For example, porous materials will absorb some energy, and rough materials (where rough is relative to the wavelength) tend to reflect in many directions — to scatter the energy, rather than to reflect it coherently. This leads into the field of architectural acoustics, because the nature of these reflections is critical to the auditory feel of a space. In the theory of exterior noise mitigation, reflective surface size mildly detracts from the concept of a noise barrier by reflecting some of the sound into the opposite direction."
The key words I saw were that sound waves were reflected off a surface as long as the surface was large as compared to the frequency. Low frequencies are very large, 20hz is 17.2 meters long, there is no enclosure large enough to reflect internally the 20hz wavelength. 100hz is 3.44 meters, again, few if any enclosure has a length over 9 feet. 300hz is the first point when you see a wavelength approach a meter or less, and so I would say that standing waves can not be created below 300hz in most enclosures because sound can not be reflected at those frequencies within the enclosure, since the surface is not physically large as compared with the wavelength. A room is different, it is physically large. However, I would argue that you don't get 20hz standing waves in normal rooms since I can't see how any dimension of a normal room is going to be equal to or greater than 17.2 meters.
I don't know what the specific mechanism is behind how a horn works, but I don't believe it's reflection of the sound wave, since that would require a very long horn. Note that, Hemholtz resonation makes no comment of reflection.
Well, a horn specifically DOES work by reflecting the sound wave into a controlled dispersion window. By moving from direct radiation to a much smaller beamwidth, they're able to get increased on-axis sensitivity.
Without reflection of the lowest frequencies a basshorn doesn't work. And with transmission of low frequencies freely through box walls, any enclosure would have bass cancellation.
You don't need a large surface to reflect a wave, only to do so coherently. There's lots of misunderstanding around bass action. Many believe that you need a room big enough to allow 1 wavelength to reproduce a frequency. This supposition is totally disproven by the fact that headphones can reproduce bass.
Does the sound need a 17m enclosure to have something 17M long inside it? If the wave is able to hit one wall, reflect, and strike another and another, it's eventually 17M long, there's no reason this wave needs to hit the enclosure walls at the zero crossing, it can encounter a boundary at any point within it's waveform. It just takes a lot of reflections and some loss to get to the full length.
Without reflection of the lowest frequencies a basshorn doesn't work. And with transmission of low frequencies freely through box walls, any enclosure would have bass cancellation.
You don't need a large surface to reflect a wave, only to do so coherently. There's lots of misunderstanding around bass action. Many believe that you need a room big enough to allow 1 wavelength to reproduce a frequency. This supposition is totally disproven by the fact that headphones can reproduce bass.
Does the sound need a 17m enclosure to have something 17M long inside it? If the wave is able to hit one wall, reflect, and strike another and another, it's eventually 17M long, there's no reason this wave needs to hit the enclosure walls at the zero crossing, it can encounter a boundary at any point within it's waveform. It just takes a lot of reflections and some loss to get to the full length.
I'm sorry badman, but that is incorrect. Horn's do not work by reflection. To quote Dr. Geddes on the subject, "when wavelengths are long, they move along the horn length like a lump." It's just a mass of air, it's not reflecting around the horn. Shorter wavelength reflection in the horn he called HOMs, it's an undesirably effect. The actual increase in efficiency happens from diffraction, not reflection, no? I think you are confusing the two concepts.
The formulas for reflection require that the wavelength be smaller than the surface. Wavelengths of sound see surfaces as large or small depending on the relationship between that wavelength and the relative size of the surface. Yes, a 17m wavelength needs a distance physically as long or longer to cause a reflection.
I did mistate somethings earlier as I was so fixated on the issue of internal reflections and internal standing waves. What I was told from both Dr. Geddes and another PhD from the University of Indiana, also an acoustics expert, is that an enclosure acts as a pressure vessel. Enclosures thus do enclose something, I was incorrect when I said that low frequencies don't "see" the enclosure at all. They do, but the waves don't bounce around inside, that is an incorrect view.
Look up the terms diffraction and reflection and tell me that we aren't arguing over a misunderstanding of the definition of terms? I even found a multitude of articles discussing how diffraction is often used interchangeably with reflection.
The formulas for reflection require that the wavelength be smaller than the surface. Wavelengths of sound see surfaces as large or small depending on the relationship between that wavelength and the relative size of the surface. Yes, a 17m wavelength needs a distance physically as long or longer to cause a reflection.
I did mistate somethings earlier as I was so fixated on the issue of internal reflections and internal standing waves. What I was told from both Dr. Geddes and another PhD from the University of Indiana, also an acoustics expert, is that an enclosure acts as a pressure vessel. Enclosures thus do enclose something, I was incorrect when I said that low frequencies don't "see" the enclosure at all. They do, but the waves don't bounce around inside, that is an incorrect view.
Look up the terms diffraction and reflection and tell me that we aren't arguing over a misunderstanding of the definition of terms? I even found a multitude of articles discussing how diffraction is often used interchangeably with reflection.
There surely is confusion and a misunderstanding here, but it's not badman. Best not tell him or anyone else he's incorrect unless you know what you're writing about.
What happens to a wave that's produced by the backward motion of a driver inside an enclosure? Does it change into neutrinos and pass through the cabinet walls? How does a transmission line enclosure or bass reflex enclosure work if it doesn't reflect rearward energy? Are there little people inside, furiously playing bass instruments to mimic what is coming out the front of the driver?
And how does diffraction increase efficiency of horns, or anything else?
"Enclosures thus do enclose something." I can hardly believe that! Are you certain?
So you've read a wikipedia article and now you're an expert? I think you better read a few more articles more carefully. Despite having consulted with the authorities, your view of acoustics and wave motion appears to lack clarity.
Tom E
What happens to a wave that's produced by the backward motion of a driver inside an enclosure? Does it change into neutrinos and pass through the cabinet walls? How does a transmission line enclosure or bass reflex enclosure work if it doesn't reflect rearward energy? Are there little people inside, furiously playing bass instruments to mimic what is coming out the front of the driver?
And how does diffraction increase efficiency of horns, or anything else?
"Enclosures thus do enclose something." I can hardly believe that! Are you certain?
So you've read a wikipedia article and now you're an expert? I think you better read a few more articles more carefully. Despite having consulted with the authorities, your view of acoustics and wave motion appears to lack clarity.
Tom E
the soundwave doesn't reflect back, it's the mass of air moving around. I am not confused, I do not believe I am incorrect. I have asked PhD professionals about this, and the answer I got was, NO They Don't Reflect Inside the Enclosure, The Wavelength is TOOO Long. When I looked up the physics, I found the terms, physically large comapred to the wavelength. Yet people keep telling me I"m wrong. It's not reflection of the wave, that is the wrong term to use, at its physically impossible.
No I never said that the sound turns into neutrino's, but sound isn't particles either, it requires some other form of matter, with mass, to transmit in the first place.
I already said I was incorrect saying that the rearwave escapes, well the way I put it was wrong, what I was getting at was correct, wavelengths larger than surface are not "seen" by the wave as a hard surface and reflected, thus no standing waves.
A horn is an impedance matching device in-which the mass of air projected from the high density speaker is matched to the comparitively low density air, with the change from low displacement to large. It doesn't happen from reflection. The soundwave doesn't reflect along the track of the horn tube, it follows down it straight, as a mass of air, again, because the wavelength is far too long to actually bounce around.
No I never said that the sound turns into neutrino's, but sound isn't particles either, it requires some other form of matter, with mass, to transmit in the first place.
I already said I was incorrect saying that the rearwave escapes, well the way I put it was wrong, what I was getting at was correct, wavelengths larger than surface are not "seen" by the wave as a hard surface and reflected, thus no standing waves.
A horn is an impedance matching device in-which the mass of air projected from the high density speaker is matched to the comparitively low density air, with the change from low displacement to large. It doesn't happen from reflection. The soundwave doesn't reflect along the track of the horn tube, it follows down it straight, as a mass of air, again, because the wavelength is far too long to actually bounce around.
If the concern is enclosure resonance, has anyone considered attempting to get a very lossy, low resonance enclosure? ie get the resonance below the bottom octave.
Perhaps build an enclosure out of thick (like 1-2"), low durometer rubber like they use on gym floors, etc. Or build an enclosure out of an old car tire, they seem fairly dead as far as resonances go.
Perhaps build an enclosure out of thick (like 1-2"), low durometer rubber like they use on gym floors, etc. Or build an enclosure out of an old car tire, they seem fairly dead as far as resonances go.
You need to consider the enclosure as though it's a bicycle pump.
At low frequencies all you are doing is compressing and expanding the air inside. So the enclosure tries to expand and contract like a balloon and, if the panels aren't rigid enough, it will introduce unwanted sound into the room.
However, when it gets to a wavelength where it can set up a standing wave in the enclosure, ~ 300 Hz for a 1m length, then you need to damp this resonance via stuffing and make sure the panels do not have a natural resonance around the same frequency.
At low frequencies all you are doing is compressing and expanding the air inside. So the enclosure tries to expand and contract like a balloon and, if the panels aren't rigid enough, it will introduce unwanted sound into the room.
However, when it gets to a wavelength where it can set up a standing wave in the enclosure, ~ 300 Hz for a 1m length, then you need to damp this resonance via stuffing and make sure the panels do not have a natural resonance around the same frequency.
Some years ago I met one of the guys behind the B&W nautilus 801.
He shoved us wide band measurements of different enclosure shapes with and without stuffing. A sphere had the strongest resonance, a cube was allmost as bad, rectangular box had more resonances but lower in level. The differences between them was alot smaller when the boxes were stuffed.
He also showed measurements of the 801 enclosure, without stuffing it it had more resonances than the sphere, but much lower in level, it wasn`t as good as the stuffed rectangular box but not bad. With stuffing the resonances was lower in level than all the other boxes.
The magnet cover in the 801 is part of the design, to reduce reflected sound coming back out thru the membrane.
He shoved us wide band measurements of different enclosure shapes with and without stuffing. A sphere had the strongest resonance, a cube was allmost as bad, rectangular box had more resonances but lower in level. The differences between them was alot smaller when the boxes were stuffed.
He also showed measurements of the 801 enclosure, without stuffing it it had more resonances than the sphere, but much lower in level, it wasn`t as good as the stuffed rectangular box but not bad. With stuffing the resonances was lower in level than all the other boxes.
The magnet cover in the 801 is part of the design, to reduce reflected sound coming back out thru the membrane.
Here is my ultimate speaker: composite material containing portland cement, curved surfaces, uneven thickness of walls.
http://wavebourn.com/forum/viewtopic.php?p=21995#p21995
Couple of decades ago I made spherical speakers in spherical clay pots. They resonated horribly, even stuffed. Then I made spherical speakers of newspaper pulp with PVA glue, on big plastic balls. They were uneven, end ex-wife called them "Dinosaur's Eggs".
The problem is not only in resonances. All deformations of all materials are non-linear. That causes extra distortions on resonant frequencies.
Now, why best speakers I ever heard are those made of composite material with portland cement mixed with particles of very different shapes and densities?
http://wavebourn.com/forum/viewtopic.php?p=21995#p21995
Couple of decades ago I made spherical speakers in spherical clay pots. They resonated horribly, even stuffed. Then I made spherical speakers of newspaper pulp with PVA glue, on big plastic balls. They were uneven, end ex-wife called them "Dinosaur's Eggs".
The problem is not only in resonances. All deformations of all materials are non-linear. That causes extra distortions on resonant frequencies.
Now, why best speakers I ever heard are those made of composite material with portland cement mixed with particles of very different shapes and densities?
Hi Cirrus 18. In sound-reducing sealed double glazed units, the "air space" is sometimes filled with a gas to help reduce sound transmission. However, the way these units are most effective is by unsing panes of different thicknesses and using laminated glass (a glass/pvb/glass sandwich which sometimes has several layers, different thicknesses, to make best use of the pvb). The air gap itself is only a small part of a complex unit.
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10 year anniversary post??
btw interesting thread! as Im designing a full curved bass bin. Ill mill (CNC) it.] inside and out.
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