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Multi-Way Conventional loudspeakers with crossovers

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Old 23rd October 2008, 12:56 PM   #4591
gedlee is offline gedlee  United States
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Looks perfectly reasonable. I am sure that those driver parameters could be tweaked a bit, but this is a first cut.

The high end drop is no where near as seveer as shown, but that could be a lot of things. Its probably not lumped parameter up that high. And the inductance could be lower - lots of things.
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Old 23rd October 2008, 01:21 PM   #4592
Kolbrek is offline Kolbrek  Norway
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Good. I will use this driver model in the simulations, unless there is anything you want to change.

Bjørn
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Old 24th October 2008, 02:45 PM   #4593
Paul W is offline Paul W  United States
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Bjørn,

As if you haven't received enough requests ...

It would also be interesting to see simulations for the JBL 243X "throatless" style driver Lynn is also considering.

Paul
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Old 24th October 2008, 05:48 PM   #4594
gedlee is offline gedlee  United States
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I would expect a short throat to make a small difference, but nothing dramatic. The biggest factor is going to be the waveguide not the throat.
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Old 24th October 2008, 11:28 PM   #4595
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by gedlee
I would expect a short throat to make a small difference, but nothing dramatic. The biggest factor is going to be the waveguide not the throat.
For this particular case with the JBL 243X or in general?
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Old 25th October 2008, 02:40 PM   #4596
gedlee is offline gedlee  United States
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In general.
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Old 25th October 2008, 02:50 PM   #4597
Paul W is offline Paul W  United States
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Agree the overall waveguide should make a much larger difference than throat length of the driver. I thought a longer driver throat would provide a bit lower extension.

The top end is what I'm really curious about...no real clue how zero/long driver throat lengths would change performance on a short/zero throat WG like the OS or conical.
Paul
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Old 26th October 2008, 10:07 AM   #4598
SunRa is offline SunRa  Romania
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Mr. Olson and everybody,

do you think the placement of woofers in the emerald physics loudspeaker could produce some un-wanted artifacts in the bass region?

Is it something to consider in this project?

Here are some pics, at the end of the thread : http://www.diyaudio.com/forums/showt...17#post1641517
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Old 26th October 2008, 11:44 PM   #4599
mige0 is offline mige0  Austria
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Quote:
Originally posted by gedlee

.....
The volume and size of the rear chamber = just consider this as part of the diaphragm

For a first order effect yes, and maybe good enough for the simu intended – I agree.



Looking slightly under the surface there are interesting things going on with drivers having a non dampened or a only slightly dampened rear chamber.

If we recall what John Kreskovsky brought into our mind about Doppler modulation – and take this a little bit further - we see strange things happening in the time domain.



To put things into perspective, I set up a quick and simplified simulation.

What we will see is that the SPL reflected by the rear chamber wall and transmitting through the diaphragm as a kind of mirror source adds another - pretty unique - sonic pattern to such drivers.

In order to show the effects happening, I set a extraordinary high modulation depth for the Doppeler_IM in this simulation.






Click the image to open in full size.

In the first picture we can see how Doppler-IM varies frequency by comparing the elecrical input signal of the voice coil (GREEN plot) to the SPL output of a speaker membrane (RED plot) – nothing very new.

Here it is assumed that *only* the front of the membrane is radiating – all the SPL radiating from the back side of the membrane is dampened to dead.

We see the already known frequency modulation of Doppler IM.






Click the image to open in full size.

In the second picture we can see what happens if we overlay the SPL radiating from the front with the SPL mirrored at the chamber.
The membrane is considered to be completely transparent in this case - *and* no dampening of the rear chamber at all.
The delay is set to roughly 12mm / half an inch to mimic a rear wall in the distance of 6mm / a quarter inch behind the diaphragm.

The SPL of the front (GREEN plot) and the delayed SPL from the back (GREEN plot) have inverse frequency modulation as can be observed immediately.
The sum of both frequency modulated SPL's (RED plot) result in a *pure* amplitude modulation !
Its easy to see that the summed SPL (RED plot) sine curve is exactly in between of the green ones.

Wow – surprise, surprise– we get *amplitude* modulation from Doppler IM !






Click the image to open in full size.


In the third picture we see demonstrated that in reality we more likely will end up with a mix of amplitude *and* frequency modulation.
Here I attenuated the mirrored SPL – in order to mimic some dampening in a rear chamber and also a transfer loss through the membrane – i.g. the membrane isn't considered to be 100% acoustically transparent

If we compare the SPL overlay plot *without* dampening (GREEN plot) that does *not* have any frequency modulation – as shown in the picture above – with the SPL overlay plot *with* dampening (RED plot) – the variations in frequency become most apparent.

The amplitude modulation is slightly less though – kind of trade in.


Keep in mind:
Doppler IM *can not* be avoided – it always happens with speakers.


Michael


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Old 27th October 2008, 12:01 AM   #4600
gedlee is offline gedlee  United States
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There is no end of the hypothesis that one can make about "problems" in loudspeakers. What one has to do is to "close the loop" by showing their significance in terms of audibility.

Since in blind tests (published AES paper on Distortion in Compression Drivers) no listener could detect nonlinear distortion in any of three different compression drivers, I would have to conclude that any effects like this - assuming that they do actually occur - are not audible.
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