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Multi-Way Conventional loudspeakers with crossovers

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Old 13th July 2013, 09:47 PM   #9101
ra7 is offline ra7  United States
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For wavelengths equal to and below the largest dimension of the cabinet, air inside the cabinet acts as a spring, i.e., it gets compressed as a whole. I assume there are no waves and nothing to reflect or bounce around inside the cabinet to come back out.

I'm not able to express the full physics behind it. I guess I need to think through it fully.
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Old 13th July 2013, 10:01 PM   #9102
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Quote:
Originally Posted by gedlee View Post
I'd like to see some measurements that validate this effect. I tried and was unable to do so.

I attempted to measure this effect by using a back on a cabinet and then piping the back wave away to "infinity". I was unable to measure a difference that could not be accounted for by just a lumped volume box stiffening the cone which happens with an opaque cone not a transparent one. If it were acoustically transparent then there would be no stiffening from the box at all.

To be sure there is some leakage, but 80-90% as was claimed is simply not reasonable. Based on my tests I'd guess it at less than 10% or some 10 dB down. I would have to have been that low or the results would have been obvious.
I realize there are several other things going on, but does this measurement not indicate at least some of the effect? It is a 1cm nearfield of a woofer (measured out on the cone, not in the center) in a large cabinet, with absorptive material being added.
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Last edited by dumptruck; 13th July 2013 at 10:05 PM.
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Old 13th July 2013, 11:32 PM   #9103
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Originally Posted by Pano View Post
What would be a practical way to measure this?
Unpowered driver in an infinite baffle (eg. closed door between rooms). Various noise sources one side (from known transducer).
Microphone otherside of baffle

Fun part comes when you start to electrically damp the speaker - from open circuit to short circuit. Oh, add some reactive (cross over) components too.

Ps - remember to repair the door before your other half gets home!
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Old 14th July 2013, 01:49 AM   #9104
gedlee is offline gedlee  United States
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Originally Posted by dumptruck View Post
I realize there are several other things going on, but does this measurement not indicate at least some of the effect? It is a 1cm nearfield of a woofer (measured out on the cone, not in the center) in a large cabinet, with absorptive material being added.
Its a rough indication, but there are several things going on. And the issue isn't "is there?" of course there is, the issue is "how much?" and is it a significant audible effect.

Ra7 has it right. For the most part the internal reflection is just a stiffening pressure inside the cabinet. Of course it could only do this if in fact the cone is highly opaque to sound (not transparent as was initially claimed.) By the time the wavelength become sufficiently short that it could actually travel through the cone as say a bending wave or something like that, some interior absorption does the job very well.

I hear this claim all the time as a reason not to have a box and I just don't buy it.
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Old 14th July 2013, 02:00 AM   #9105
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I would say that the effects of not having a box are much greater than anything the box itself could create. Allowing the rear radiation to do what it wants is a magnitude or more greater than any reflective internal wave could ever do compared to what the interaction of front and back waves are going to do. I'm with Earl on this front.
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Old 14th July 2013, 09:55 AM   #9106
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I'm a little surprised that asserting that speaker cones are fairly acoustically transparent would be controversial. I've been mounting small to large speakers on IEC-or-larger baffles for twenty years now, and it's pretty obvious that sound goes through a passive (undriven) speaker cone. Just put your head next to the disconnected speaker and listen.

Can you hear ambient sounds coming through the hole where the speaker is mounted? I do. Compared to the open hole with no speaker mounted, yes, there's some attenuation, but it's not like 3/4" solid birch ply, which is pretty opaque acoustically.

As a side note, I grew up in Japan, where the paper shoji dividers (between rooms in a traditional village inn) are notoriously acoustically transparent ... the original "paper-thin walls" that apartment dwellers in big cities like to complain about. No, I didn't live in a village inn, but I've been a guest more than once. Rooms with shoji dividers aren't very warm, either, which is why each room will have a small heater in the center to keep guests warm during the winter.

Taking the argument to a logical extreme, if paper cones are acoustically opaque, why go to all the trouble of making enclosures out of heavy, expensive, hard-to-machine MDF or birch ply? Why not just use paper conveniently formed into cones? It would weigh a lot less and you could make an acoustically opaque enclosure with nothing more than scissors and tape.

Last edited by Lynn Olson; 14th July 2013 at 10:23 AM.
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Old 14th July 2013, 02:27 PM   #9107
gedlee is offline gedlee  United States
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Originally Posted by Lynn Olson View Post
I'm a little surprised that asserting that speaker cones are fairly acoustically transparent would be controversial. I've been mounting small to large speakers on IEC-or-larger baffles for twenty years now, and it's pretty obvious that sound goes through a passive (undriven) speaker cone. Just put your head next to the disconnected speaker and listen.
For this test to be a valid test, the cone would have to be glued so that it cannot move as designed.
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Old 14th July 2013, 02:55 PM   #9108
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Earl,
Are you arguing that speaker cones are not acoustically transparent? I don't think Lynn presented his findings as a scientific test, just an observation...
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Old 14th July 2013, 03:26 PM   #9109
pos is offline pos  Europe
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Originally Posted by gedlee View Post
For this test to be a valid test, the cone would have to be glued so that it cannot move as designed.
Just putting a piece of wire between the two terminals to simulate an infinite damping factor, or plugin it to an actual amplifier, would be more representative of what is really going on inside the speaker: the cone is not glued in place, and its movement can possibly influenced by the "back wave" (or whatever is should be called)
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Old 14th July 2013, 03:54 PM   #9110
limono is offline limono  United States
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....Just putting a piece of wire between the two terminals...
Off Topic , but it's a good practice while shipping big fragile speaker drivers , especially vintage .
On Topic
Lynn you mentioned an option with two woofers and were considering one 416 and one 515 . Would it be 2.5 kind a system ? I have that option and I'm thinking how it could be done.
Rgrds, L
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