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Old 27th March 2010, 04:38 AM   #431
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Nice Soong, nice.

Dan
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Old 27th March 2010, 05:10 AM   #432
soongsc is online now soongsc  Taiwan
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Thanks. There seems much to be learned.
In the Newell and Holland book on loudspeakers, it mentions smooth acoustic impedance is an important factor. In my experience, stored enegy plays an important factor in how clean the sound reproduction will be. Now looking at these sims, it seems acoustic impedance is more related with efficiency of the system, and probably has less to do with any honk or HOMs than I originally thought.
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Old 28th March 2010, 04:17 PM   #433
Elias is offline Elias  Finland
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Hi,

It took a while but here's some wavelets of the JBL2431H in RCA MI9594 horn.

Here's a multiresolution wavelet from 500Hz-20kHz up to 20ms. The right hand side is normalised to 0dB at every frequency.
Click the image to open in full size.

And here's 'conventional' wavelet:
Click the image to open in full size.


And here's the same but from 1kHz-20kHz up to 10ms:
Click the image to open in full size.

Click the image to open in full size.


There is two long resonances, at about 7.5kHz and 15kHz.

Before 2ms there is two strong reflections. Interesting would be to know if the reflection at 3ms is from the horn or the room?


Where is the honk in this horn?

In this big horn throat-mouth-throat distance is about 1.5m and thus it takes about 4.3ms for a mouth reflection. But there is nothing much seen at 4.3ms??

It might be needed to measure this horn outside without room reflections to separate the honk from the room? Have the snow melted yet?


- Elias


Quote:
Originally Posted by EarlK View Post
...
  • The horn is a huge old RCA 60 degree radial / similar to the Altec 311-60 ( minus the mouth vanes ) .
  • Rough dimensions of the horn are ;
    • Mouth ; 13H x 24.5W ( 33cm x @ 62.23 cm )
    • Depth ( to driver ) @ 29" ( 73.66 cm )
    • Depth ( to diaphragm ) @ 30" ( 76.2 cm )


...

ps ; heres the ARTA file zipped .
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Old 28th March 2010, 04:26 PM   #434
thend is offline thend  France
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Quote:
Originally Posted by Elias View Post
It might be needed to measure this horn outside without room reflections to separate the honk from the room?
Or use the impedance curve.
Simple and effective.
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Old 28th March 2010, 04:32 PM   #435
Elias is offline Elias  Finland
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Quote:
Originally Posted by thend View Post
Or use the impedance curve.
Simple and effective.
Does a room reflection show up in the impedance in your tube method?


- Elias
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Old 28th March 2010, 04:47 PM   #436
thend is offline thend  France
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Quote:
Originally Posted by Elias View Post
Does a room reflection show up in the impedance in your tube method?


- Elias
Probably, but very lesser than horn reflection.

I was talking about impedance even without tube, for wavelet.
The tube has other advantages
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Old 28th March 2010, 04:58 PM   #437
mige0 is offline mige0  Austria
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Location: Austria, at a beautiful place right in the heart of the Alps.
could we possibly do a wavelet correlation between the two methods ?
We would need from the same horn both, the acoustic and the impedance measurement.

Also - I was thinking about doing some measurements right at the throat for comparison.
This should have further benefit in diminishing room interaction. With all the wavelet software checking and also some basic coding I haven't had time to do myself - but its definitely on my list...

Michael

Last edited by mige0; 28th March 2010 at 05:00 PM.
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Old 28th March 2010, 07:29 PM   #438
Pano is offline Pano  United States
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Well I don't know, but what I see in those wavelet graphs is mostly junk between 1-3KHz.
That's where it is the messiest. And in the freq. range, it should be very easy to hear.
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Old 28th March 2010, 08:13 PM   #439
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Quote:
Originally Posted by Elias View Post
Where is the honk in this horn?

In this big horn throat-mouth-throat distance is about 1.5m and thus it takes about 4.3ms for a mouth reflection. But there is nothing much seen at 4.3ms??
If "honk" is down near cutoff, there is certainly trouble just below 4ms.

The stuff up top is something other than honk, by this view.
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Old 28th March 2010, 08:44 PM   #440
ScottG is offline ScottG  United States
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Originally Posted by ZilchLab View Post
If "honk" is down near cutoff, there is certainly trouble just below 4ms.

The stuff up top is something other than honk, by this view.

Not entirely.

You can see periodic resonances that travel up from the primary "mouth" resonance.

What you can't see is how the entire output is modulated by the mouth resonance - i.e. freq. response "ripple" at the average. (.."average" meaning full-output.) In this respect (and generally), I prefer a well-scaled series of CSD plots at varying axis's.
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