Discussion arising from Geddes loudspeaker - Page 26 - diyAudio
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Multi-Way Conventional loudspeakers with crossovers

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Old 25th April 2008, 09:48 PM   #251
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Quote:
Originally posted by chrisb


I'm not sure if your question (i.e. which for which driver/s was this designed ) has yet received a reply - the answer is specifically, Fostex FE127E and CSSFR125.


...but you may have missed the discussions of how we arrived there. Several years ago, we did in fact built 2 pairs of the same enclosure design from MDF and BB plywood.



While I recall volumes of bandwidth expended by all on the MDF vs BB debate, throughout all the polemics and technical buzz-speak with which I quickly tire, I can't recall if you mentioned ever actually repeating this exercise?

Thanks Chris,
The drivers are fairly cheap, so I may build a pair and see what I have been missing. I have a number of projects happening right now that will need to be finished first.
Also, as i sit here now, there are 3 pairs of speakers staring back at me, two more pairs down in my basement, a pair in my "lab" and a pair in my shop. There is a general consensus that I already have enough speakers.
Oh, I didn't mention the ones on the back deck.

Lately, since it has been brought to my attention, I have been turning the idea around in my head about a pair of Summa type speakers, with B&C drivers. I've been wanting to try the B&C's for a while, and the prospect of turning a tractrix waveguide mold is luring me.

The listening test for MDF was talked about last year, in the other thread. Don't take this the wrong way but you can't expect me to take that as conclusive proof of an audible difference. Too many variables.
My challenge would be for Dave to consistently single out which speaker (built be me, with the drivers measured and matched) is made with MDF. This is the only way I'd accept it.

Yes, there have been volumes said, but there are volumes said about other irrelevant subjects here also. I, for one, try to make my posts concise and to-the-point, without a lot of technical doublespeak designed to veil the absence of substance.
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Old 25th April 2008, 10:08 PM   #252
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John, is that avatar new?

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Old 25th April 2008, 10:10 PM   #253
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Quote:
Originally posted by ShinOBIWAN
John, is that avatar new?


Just say YES to MDF!

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Old 25th April 2008, 10:14 PM   #254
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Quote:
Originally posted by chrisb
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Beautiful work there Chris.
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Old 26th April 2008, 02:38 AM   #255
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Default Re: and???

Quote:
Originally posted by auplater
Okay... now what? Are you gonna actually DO some calculations and show that this statement has any actual relevance to your position?

They have already been done. And experimental data to. The 1972 AES paper mentioned earlier is a good start.

dave
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Old 26th April 2008, 02:53 AM   #256
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Quote:
Originally posted by MJL21193
Dave, the inversely proportional thing sounds impressive. Can you please explain it to us who are not math majors?
A graph help? This graph is in units of pressure. It takes energy to excite a panel resonance. If the energy is not at the frequency of the panel rersonance it won't excite that resonance.

The excercises in this thread have reminded me that the 4 AES Loudspeaker Anthologies should be in an serious speaker builders libraries.

dave
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Old 26th April 2008, 02:58 AM   #257
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Default Re: Re: and???

Quote:
Originally posted by planet10



They have already been done. And experimental data to. The 1972 AES paper mentioned earlier is a good start.

dave
That's nothing more than the pressure in the box for constant radiated power for given box volumes. I don't see how that's relevant to your statement here:

"An analysis of the braced comparison -- remember the energy available to excite a resonance is inversly proportional to the SQUARE of the frequency".

That doesn't help the situation directly. As for being inversely proportional, it also indicates that it takes less box pressure to attain the same radiated power, so the fact that the box pressure for a given radiated power drops as frequency rises simply means that it will take less box pressure, hence less panel vibrational movement to attain the same output from a resonating panel. The only important point is that if the resonant frequencies are raised, they may be more easily damped, since most damping materials are more effective at higher frequencies.

If you have some other point of which we're unaware, I don't see it. Raising resonances above the passband of the driver/XO used isn't new, IIRC that was one of the points Gedlee (or someone in the thread) made early on.

Dave
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Old 26th April 2008, 03:34 AM   #258
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Default patronizing c^&%

Quote:
Originally posted by planet10


A graph help? This graph is in units of pressure. It takes energy to excite a panel resonance. If the energy is not at the frequency of the panel rersonance it won't excite that resonance.

The excercises in this thread have reminded me that the 4 AES Loudspeaker Anthologies should be in an serious speaker builders libraries.

dave

Ah, I see.. talking down to the unwashed masses... because they don't worship the almighty full range ethos...

maybe a refresher course in physics 101 would also help, eh?

John L.

not to mention
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Old 26th April 2008, 03:56 AM   #259
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Quote:
Originally posted by planet10


A graph help? This graph is in units of pressure. It takes energy to excite a panel resonance. If the energy is not at the frequency of the panel rersonance it won't excite that resonance.

The excercises in this thread have reminded me that the 4 AES Loudspeaker Anthologies should be in an serious speaker builders libraries.

dave

That's fine. It's what you have been saying all along. Crystal clear to me now and I have to say I was a little dense about it before. I gave you endless argument, when I did not properly see what it was you were saying. I will re-program myself to this approach, as it's clearly a better way of building to control resonance.
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Old 26th April 2008, 04:37 PM   #260
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Quote:
Originally posted by auplater
Ah, I see.. talking down to the unwashed masses... because they don't worship the almighty full range ethos...
If you think so.

More a definition TMM -- something to define a frame of reference for all those lurking and trying to learn something.

This basic stuff is applicable to any box. For a woofer you can target just getting the panel resonances out of band. ie if you are XOing a woofer @ 200 Hz, the XO is removing available excitation energy.

dave
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