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Re: Who’s driver specs do you trust?

Posted by John Sheerin (A) on February 24, 2007 at 07:24:07

In Reply to: Who’s driver specs do you trust? posted by Russ57 on February 24, 2007 at 05:18:55:

It isn't necessarily the manufacturer; the individual driver's design (and parts source) can have a lot to do with it. For example, I bought a pair of JBL 2225's on ebay and measured them the other day. Even though they're old, the specs were almost exactly what was in the spec sheet. I also have a JBL W15GTi (big 15" car sub, neo magnet, differential drive motor). It's not particularly close to meeting the published specs (Fs high about 15%, Qe high about 60%, Vas low by 35%). This is because the moving mass is higher than spec by about 13%, compliance is low by 34%, and BL is about 5% low. Net result, however is not too terrible - in a 200L box, the response difference is the actual driver is about 2dB less sensitive above 150hz, has identical response between 30 and 50hz, and is about 1.5dB lower in output at 20hz (for the same power input). The Q of the box goes from 0.6 to 0.8, so there's less excursion at low frequencies. So the performance of the driver is still in the same ballpark as what the published specs indicate, and the specs are still a somewhat valid way to shop for a driver. In this case, I was more interested in the low distortion motor design. If you want to be really precise, you'll still want to measure the drivers you actually get, but even then, the driver's specs will change with cone excursion and power, so I'm not sure how worthwhile it is to be really picky in doing small-signal box design. What I would be more concerned about is variation between units. Most cone drivers tend to be pretty good in this regard (assuming you get parts from the same production run), but typically this is not spelled out in published specs.

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