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Old 7th May 2008, 03:59 AM   #1
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Default Precision Devices PD.158 Xmax?

Anybody having this information?

I've tried the company, but they have not been very helpful in this matter, which make me not so very keen on having them make my future drivers. Anyway, I would like to know, I would like to know Le as well.
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Old 7th May 2008, 05:09 AM   #2
Wizard of Kelts
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From the pages of BK electronics, which sells them:

http://www.bkelec.com/Pro/Drive_Units/pd/pd158.htm

The linear displacement is plus or minus 4 mm. That is because the voice coil winding depth is 19 mm, the voice coil gap height is 11 mm, and (voice coil winding depth - voice coil gap height) / 2 = linear excursion.

Therefore, the stated maximum displacement of 13 mm is the mechanically limited displacment, (always greater than the linear displacement), before damage may occur. The specs do not state if that is plus or minus 13 mm, or just 13 mm from front-to-back. My guess is that a typical 15 inch PA driver would be plus or minus 13 mm-that is about normal.

It apparently is a single coil driver, yet it gives specs of L1 = 1.26 mH and L2 = 2.81 mH. I do not know what this means. Full specs are available as a pdf which is linked on that page. I don't have Acrobat on this computer yet, (just did a full reformat on the hard drive), so I can't access that pdf file yet. You can, if you wish.
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Old 7th May 2008, 02:54 PM   #3
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Ussually Le is measured at 1 KHz, but some companies also measure at 10 KHz or other frequencies, IIRC you need L1.

Quote:
The linear displacement is plus or minus 4 mm. That is because the voice coil winding depth is 19 mm, the voice coil gap height is 11 mm, and (voice coil winding depth - voice coil gap height) / 2 = linear excursion.
At the moment it's common to calculate Xmax as stated above but adding 1/4 of the gap depth, which would give 6.75 mm.

The majority of PA manufacturers uses the latter, for some speakers it holds ground, for some it doesn't. Best is to always calculate Xmax yourself (and sensitivity for that matter) for correct comparison between different speakers.

Johan.
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Old 7th May 2008, 06:54 PM   #4
Wizard of Kelts
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There are a couple of things I did not know, about commonly including an extra 25% for the linear excursion and about L1 and L2.

This is good to know. Thanks for the updates, Johan.
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Old 10th May 2008, 03:21 AM   #5
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That PDF file, is the one at the companys home page, and does not state linear travel, but thanks to you, I can now calculate it by my self, sweet.
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Old 10th May 2008, 08:19 AM   #6
kstrain is offline kstrain  Scotland
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in case it helps:

I chose PD1550 over 158 because it allowed a lower response (I wanted to get close to 20Hz with no droop in the middle of the response), has a little bigger xmax and claimed low distortion.

Also, and this can be important where PD is concerned, it was readlily available a few months ago.

I checked bluearan.com (probably best UK price), but they are out of stock of both 158 and 1550.

Ken
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Old 20th May 2008, 07:55 AM   #7
DIAR is offline DIAR  Finland
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I have PD1550 but I have not yet built the enclosure. Check out http://www.thomann.de
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