Factory T/S specs or DIY measurements? Help! - diyAudio
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Old 13th May 2012, 03:58 PM   #1
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Default Factory T/S specs or DIY measurements? Help!

Well, you guys have made me totally confused. Again. The most frustrating aspect of DIY speaker design for me is the fact that the more I learn, the more I realize how ignorant I am of the subject matter. I have done a boatload of research and still feel as though I am groping in the dark toward my goal. I console myself with the knowledge that although I am an amateur in the sense that my knowledge and experience are limited, I am also an amateur in the sense that I love working and playing with audio electronics.

I read with interest the thread on the full-range forum about the accuracy of Audio Nirvana published T/S specifications. Some of the posts stated that some manufacturers test their loudspeakers at levels that may differ from other references and with differing measurement equipment and measuring conditions than those that may be economically available to the average DIYer. Some posters stated that though they obtained DIY measurements different from the factory specifications, when they built enclosures based on the factory specs they obtained the desired results. Some said that their DIY measurements were largely identical to the factory specs. In addition, I know from my own research that not all manufacturers test their drivers on baffles identical to those used by other makers.

All these variables are adding to my confusion. What must I do to obtain accurate T/S values to design the proper enclosure for a specific driver? I had thought that I could "break in" my selected drivers with continual playing for a period of time and then use an economical tester such as Dayton Audio's DATS (the newest version of WT3). Now I am unsure if that method will obtain reliable data. Thus, I am seeking help from those who are more knowledgeable and experienced than I by asking these questions:

Is it possible to get accurate T/S values with common DIY methods? By accurate, I mean values that when used to design and build an enclosure will give the desired results. If so, what are the best DIY methods and equipment available at reasonable cost to the average working-stiff hobbyist? Please share your personal experiences.

Is it possible to design and build enclosures based on the factory specifications and get the results predicted by the enclosure design software? Please give specific examples of speakers you have built based on factory specs and the results you obtained.

Are some manufacturer's test data more reliable than others? Please name those makers whose data you have found to be most reliable.

Any supplemental information or links to helpful articles will be most appreciated. Thanks to all.

Last edited by majerjack; 14th May 2012 at 12:39 PM.
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Old 14th May 2012, 11:55 AM   #2
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Can anyone offer any assistance?
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Old 14th May 2012, 12:17 PM   #3
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Accuracy of T/S measurements can be a real problem. The usual approaches of a hobbyist and a pro would be the same: current drive to measure resonance and -3points, then added mass or added stiffness (test box). You should probably be happy if you get within 20% of someone elses numbers.

Compliance variation can give a lot of numerical error without much difference in the end result. Everything shifts with woofer resonance but the final vented box performance will hardly change at all. A lot of the parameters vary with drive level so this will throw in some more uncertainty.

Published results might be off, depending on how reputable the manufacturer is. T/S numbers are seldom guaranteed and typically come from an ideal preproduction prototype.

Take your own measurements with care and judge the results with a grain of salt. You will probably get numbers that are close enough. The end result (final system measurement) will be hard to measure with total accuracy but don't lose sleep over it.

David S
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Old 14th May 2012, 12:25 PM   #4
tvrgeek is offline tvrgeek  United States
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Manufactures specs are only to give you a general ideal if a driver that may be suitable for your design. I find my measurements are not too far off from Seas. I also find the cheaper the driver, the more optimistic the specs. With, some measurements , like Le, methods vary widely. For design, you should measure yourself.

I highly recommend Joe DeAppolito's book on measurement. Zaph and Linkwitz webs. Looks through the OEM's pages any you may find comments on how they measure their drivers.
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Old 14th May 2012, 12:48 PM   #5
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Thanks, gentlemen. Does anyone have any experience with the Dayton Audio DATS/WT3 test system? Does it give reliable numbers?
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Old 14th May 2012, 12:54 PM   #6
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Yes, it works well and gives consistent results. Accurate? I don't know for sure, but it seems to give the same numbers as doing it by hand the old, tedious way.

Measuring VAS is always the tricky part.

As Tvrgeek points out, the cheaper the driver the less reliable the published T/S parameters.
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Old 14th May 2012, 01:50 PM   #7
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ive always found taking measures of impedance plots the 'slow' way to be accurate enough, or at least the figures ive obtained over the years were within 10% of published and contiguous between drivers to a closer tolerance. So i have confidence in them. Drive level is the main bugbear. I usually take measurenent with a 1k resistor, and a 50 ohm for higher drive. Ive yet to try the higher drive, but id expect ts to be different, as others have found. Whether the change is +ve or -ve is beyond me at present.
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Old 14th May 2012, 08:16 PM   #8
tvrgeek is offline tvrgeek  United States
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I have been using the Woofer Tester II for years. Excellent unit. You should sttill pick up Joe's book.
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Old 14th May 2012, 08:17 PM   #9
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Oh, I measure VAS both sealed box and mass displacement. When I do it enough times they are within 10%, I figure I got it correct.
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Old 14th May 2012, 09:05 PM   #10
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Can you tell us a little more about how you measure VAS? I use the added mass method, but have heard that the sealed box may be more accurate. Do you find they differ often?
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