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Old 2nd January 2005, 04:44 PM   #1
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Default Impedance and Box Volume

Hello everyone and HAPPY NEW YEAR!

I'm a newbie to loudspeaker design and this is my very first post, so try to be kind if I sound a bit block-headed!

First off, let me tell you about myself and what I'm trying to do. I've been tinkering with electronics for roughly 30 years now, and just recently I've been stricken with the vintage electronics bug. In the past 6 months, Ive fully restored a Scott 222, Sherwood S-5500 and a Dynaco SCA-35. They all sound great but I know I could better sound with better speakers. I've got a pair of EPI T/E 320's that could use a little TLC themselves!

Anyway, now it's time to learn about speakers! Here's my first question:

The new PartsExpress catalog has a "Speaker Building Guide", and I noticed that the same speaker models with different impedance versions (4 and 8 ohms) require different box volumes. For example, the 12" Goldwood woofer, Model GW-12PC. In a vented volume, the 4 ohm version requires a 2.1 cu. ft. box, while the 8 ohm version requires a 4.55 cu. ft. box. Why is this?

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Old 2nd January 2005, 10:13 PM   #2
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Welcome to the forum Tubehead Johny

Looking at the specs of the two speakers, it looks like the only difference is due to the different impeadance. The 8 ohm version has higher impeadance and voice coil inductance, which results in a higer Qes, since the Qms is the same for both drivers the Qts changes, hence the difference in the volume required.

If that was all over your head then it's time do some reading on thele/small parameters

Note that the PE site says the speakers are designed for small sealed enclosures...... you might want to think twice about doing ported boxes (the Qts of the 8 ohm version is .49 which is over the magic number of .4 which is generally considered the point over which a driver is not suitable for a vented enclosure

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