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Old 31st July 2012, 12:41 AM   #1
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Default Driver Matching

Hi, this is my first time designing a loudspeaker so I have a few questions about driver matching. I recently purchased a pair of Peerless 830874 6.5" woofers and used PE's DATS system to measure their parameters. However, the parameter differences between the two drivers concerns me, namely the resonant frequency and the Vas.

Woofer 1: fs = 53.16 Hz, Vas = 0.5722 cu. ft.
Woofer 2: fs = 48.45 Hz, Vas = 0.6377 cu. ft.
(edited)

When designing an appropriate crossover and enclosure, which of the parameters do I use? Do I design two separate crossovers using the two resonant frequencies, or do I average them and use the same crossover? What about for the enclosure volumes?

Thanks a lot for your responses

Last edited by saccharum; 1st August 2012 at 05:29 PM. Reason: updated specs
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Old 31st July 2012, 01:45 AM   #2
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I use the factory data. The difference between your drivers is not all that much.

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Old 31st July 2012, 03:34 AM   #3
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But surely I'd be better off averaging my actual measurements than using the manufacturer's data, right? The Fs's are definitely lower than advertised.
However, the Vas's are significantly higher than the manufacturers: 37L to 12.5L. Any ideas why that might be? I used a method of adding a measured mass to the cone of the driver and having DATS calculate it from there.
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Old 31st July 2012, 04:15 AM   #4
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Quote:
Originally Posted by saccharum View Post
But surely I'd be better off averaging my actual measurements than using the manufacturer's data, right?
Not in my experience -- at least for name brand drivers. Your PE kit will likely be measuring the drivers at a different part of the T/S curves.

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Old 1st August 2012, 08:09 AM   #5
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I would just average them and use that value, although id also repeat the tests a few times to check consistency, average those, then average the pairs averages. It should be accurate enough. Or you could just choose the larger box from each driver, and add blocks to reduce the other box to its reqd volume. As is usual here, others will im sure disagree.
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Old 1st August 2012, 08:41 AM   #6
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Note that the suspension compliance may increase (and Vas will also, Fs will decrease) if you drive them to full excursion for an hour or two. Could be useful to do this and measure the parameters again afterwards.

I once used a Visaton W200S as a sub. Shortly after I built it, I used it at a party. Afterwards it had a much softer suspension
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Old 1st August 2012, 09:14 AM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by mondogenerator View Post
and add blocks to reduce the other box to its reqd volume.
As is usual here, others will im sure disagree.
Hi,

too right , about this part. The values are consistent with minor
variations of Vas for a fixed cone mass. In a typical box where
Vbox < Vas they won't make much difference and the same
box should suit both drivers well.

rgds, sreten.

The drivers will probably run in to more similar values.
I'd just use the larger Vas, lower Fs, for design, the
other driver should be very near with a moderate Vbox.

Edit : specs are 48Hz, 16.7L and Qts 0.4, some would
use an average of this and the measured specifications.
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Last edited by sreten; 1st August 2012 at 09:23 AM.
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Old 1st August 2012, 02:28 PM   #8
gedlee is offline gedlee  United States
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Make sure to excersive the drivers for quite awhile before measuring them and then try to use parameters other than VAS as it is the most variant of all the parameters. In a good box design the drivers VAS will pretty much be irrelavent.
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Old 1st August 2012, 03:00 PM   #9
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Originally Posted by gedlee View Post
In a good box design the drivers VAS will pretty much be irrelavent.
Very good point. If Vb is not << Vas, you have either a very large box, or you would be better off picking a different driver which is more suited to your goals. The point here is that in a good design, the compliance of the box dominates the compliance of the driver.

Of course there are limits to this: the volume displacement of the driver should be small compared to Vb to keep distortion low enough (see here).

Last edited by a_tewinkel; 1st August 2012 at 03:03 PM.
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Old 1st August 2012, 04:53 PM   #10
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Quote:
Originally Posted by saccharum View Post
I recently purchased a pair of Peerless 830874 6.5" woofers and used PE's DATS system to measure their parameters. However, the parameter differences between the two drivers concerns me, namely the resonant frequency and the Vas.

Woofer 1: fs = 53.16 Hz, Vas = 0.5722 cu. ft.
Woofer 2: fs = 48.45 Hz, Vas = 0.6377 cu. ft.
Try using a Test Box instead of Adding Mass.
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