Finally Beyma has made a rather good looking 220x220mm waveguide fore their 100db AMT ribbon 
I plan to use it with double Eminence BETA-8...the new model with a cone design similar to the very popular Alpha-6
It seems not only to be the best suited, but also the cheapest
Wonder whether there will be honkydonky homming issues, or if its different with the ribbon loading
I plan to use it with double Eminence BETA-8...the new model with a cone design similar to the very popular Alpha-6
It seems not only to be the best suited, but also the cheapest
Wonder whether there will be honkydonky homming issues, or if its different with the ribbon loading
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pjpoes said:
A lot of "ifs", but no the vast majority of the sound will not pass through the cone. Of coarse thickness, mass, etc. are all factors, but I have tested this myself and I was unable to measure ANY sound coming through the cone. There obviuosly is going to be some, but it low enough that only a very elaborate and precise measurement would be able to detect it. Hence, I write this off as one of those audio nonissues that are so common in our business.
Own tries
Hello,
thank you all for the interesting stuff, written here.
After lots of drafts this seems to be an satisfactory approach to a "waveguided" line.
The very rough measurement (the speaker driver was not equalised) shows the function in principle. Although the response is not smooth, the directivity is present down to below 1kHz. The WG is about 350mm wide and 140mm deep.
The strong narrowing above 9kHz is a matter of the too large throat, presently beeing 32mm wide, which will be narrowed to approximately 15mm later.
Does this small simulation, trying to express the wavguide, show the stated HOMs?
I want to use a "WG-formula" for round waveguides, giving the walls shape for this line type. As I read here(?), this may be not the right way.
Hints for improvements would be helpful.
Thank you in advance!
Regards, Timo
Hello,
thank you all for the interesting stuff, written here.
After lots of drafts this seems to be an satisfactory approach to a "waveguided" line.
The very rough measurement (the speaker driver was not equalised) shows the function in principle. Although the response is not smooth, the directivity is present down to below 1kHz. The WG is about 350mm wide and 140mm deep.
The strong narrowing above 9kHz is a matter of the too large throat, presently beeing 32mm wide, which will be narrowed to approximately 15mm later.
Does this small simulation, trying to express the wavguide, show the stated HOMs?
I want to use a "WG-formula" for round waveguides, giving the walls shape for this line type. As I read here(?), this may be not the right way.
Hints for improvements would be helpful.
Thank you in advance!
Regards, Timo
Re: Own tries
Thats an interesting approach and it may be that those are HOM, they are clearly not smooth wavefront in an angular sense so they have to have some angular dependance and as such would have to be HOM. But the details of the sim are not clear to me so I can't be sure if this is correct or not.
Timotiki said:
Thats an interesting approach and it may be that those are HOM, they are clearly not smooth wavefront in an angular sense so they have to have some angular dependance and as such would have to be HOM. But the details of the sim are not clear to me so I can't be sure if this is correct or not.
Well thats exactly what the "box stiffness" is, right? Its the refections inside of the box acting back on the cone. They don't have to go through the cone to do that, its simply a force balance thing.
There can be effects where the cone, mostly the suround, is more effected by the force that the cone and this can cause the surround to move out (from the internal pressure) while the cone moves back, and all surrounds do this to an extent. But speaker manufacturers have mostly gotten this kind of thing under control.
There can be effects where the cone, mostly the suround, is more effected by the force that the cone and this can cause the surround to move out (from the internal pressure) while the cone moves back, and all surrounds do this to an extent. But speaker manufacturers have mostly gotten this kind of thing under control.
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Joined 2003
How about hi-resolution measurement comparison of driver(s) on an "infinite" open baffle vs the same baffle with box of choice attached to the rear of the baffle?
Sky-hooks are not very practical, but ground plane measurements are. If the reflections are significant, they should produce visible disturbance in the measurements.
Sky-hooks are not very practical, but ground plane measurements are. If the reflections are significant, they should produce visible disturbance in the measurements.
Re: Refractive gradients
Hello John,
You are right, the refraction index as we can define as the ratio of the speed of sound in air and the speed of sound in the material is not the most adapted parameter to describe what we are looking for on the topic.
What we want is a medium by which we can control the reflection of waves . A low density foam will induce very low reflected wave , a high density foam will tend asymptotically toward a plain material and will induce more reflection of the sound waves.
Now the reflection of sound with a high density doesn't perform as with hard matérial, surely reflection is accompanied by diffusion (speckle?). Poroacoustics is not an easy science.
But the idea to have a gradient of foam in order to control dierctivity without any hard waveguide is something intellectually interesting.
Best regards from Paris, France
Jean-Michel Le Cléac'h
Hello John,
You are right, the refraction index as we can define as the ratio of the speed of sound in air and the speed of sound in the material is not the most adapted parameter to describe what we are looking for on the topic.
What we want is a medium by which we can control the reflection of waves . A low density foam will induce very low reflected wave , a high density foam will tend asymptotically toward a plain material and will induce more reflection of the sound waves.
Now the reflection of sound with a high density doesn't perform as with hard matérial, surely reflection is accompanied by diffusion (speckle?). Poroacoustics is not an easy science.
But the idea to have a gradient of foam in order to control dierctivity without any hard waveguide is something intellectually interesting.
Best regards from Paris, France
Jean-Michel Le Cléac'h
auplater said:
gedlee said:
Wow that really disagrees with my intuition but I haven't tested it so I won't call shenanigans just yet. Say I take a small monitor speaker and put the whole thing inside a large floor standing speaker. If I send some music to the small speaker inside I absolutely expect to hear it. We're talking about paper a few mm thick, when did that become a serious obstacle to the transmission of sound? This makes about as much sense as "soundproofing" your room with a layer of paper bags. I will have to try it and report back.
poptart said:
No one said that there isn't ANY sound coming through the cone, there is. But remember that we are talking dB here and if 10% of the sound goes through, which is a lot, then its 20 dB down. All I am saying is that its small compared to the direct radiating sound.
My video screen is MEANT to be acoustically transparent and it has about 3 dB of loss. A poor acoustical screen is about 10 dB of loss, and these have intentional holes in them. A heavy cone could easily be 40 dB loss.
“If this is true, then how do they radiate sound?”
Take a ribbon or planar magnetic speaker. Obviously they can produce sound, but if you cut a hole in a soundproof wall and “seal” it with the Mylar film the diaphragm is made of, how effective at blocking sound is it?
So for that matter are windows, doors, and walls, even concrete ones.
“I have tested this myself and I was unable to measure ANY sound coming through the cone.”
Really? How did you perform this test?
Take a ribbon or planar magnetic speaker. Obviously they can produce sound, but if you cut a hole in a soundproof wall and “seal” it with the Mylar film the diaphragm is made of, how effective at blocking sound is it?
So for that matter are windows, doors, and walls, even concrete ones.
“I have tested this myself and I was unable to measure ANY sound coming through the cone.”
Really? How did you perform this test?
when he responded to my comment he prefaced that it was dependent on the mass and rigidity of the cone. I think he was saying that for something like a compression driver, the cone is of suitable mass and rigidity to ensure that none of the frequencies it produces are going to pass through the cone. I don't think he meant that a Mylar diaphragm would stop a 50hz wave.
The original statement was about cones, which I took to mean bass/mid cones.
I'm reminded of the fellow who in his quest to build quiet boxes built a box over the front of the bass/mid in order to remove the directly radiated sound.
He was appalled at how much of the driver's now internal output came through the walls.
Admittedly it's not clear how much of that sound is due to vibration conducted from the driver directly to the box, or sound pressure flexing the walls (the mechanism of acoustic transparency).
I'd think that above a couple of hundred Hz it's dominated by the latter.
I'm reminded of the fellow who in his quest to build quiet boxes built a box over the front of the bass/mid in order to remove the directly radiated sound.
He was appalled at how much of the driver's now internal output came through the walls.
Admittedly it's not clear how much of that sound is due to vibration conducted from the driver directly to the box, or sound pressure flexing the walls (the mechanism of acoustic transparency).
I'd think that above a couple of hundred Hz it's dominated by the latter.