Ask an Audio geek

[Kosh]

I just purchased a pair of 1979 EPI 100Ws for $5.....woot.

Their 8" drivers need to be re-foamed.  I've done this before (Cerwin Vega) but:

Question 1:
How much is this likely to affect their performance?  I understand that their original design depended on the mechanical characteristics of the drivers rather than an L/C crossover to separate the low and high frequencies.  Clearly the foam I can buy on E-bay isn't from the manufacturer.  But is it close enough?

Question 2:
What is a good way to check against the 'as new'?  I've accumulated enough hardware to measure me a Bode plot.  But I have no idea what it should have looked like from the factory.  I have a darkly humorous anecdote about frequency response in modern vs antique test equipment, but I don't want to put it on the internet as it is slightly disrespectful of Nissan engineers.

In regards to question 2.  The frequency response across the crossover point should be fairly flat.  If the driver characteristics changes to a large degree, you'll see either a spike or a valley at the crossover point between the woofer and the tweeter.  A spike represents an increase is frequency extension (both drivers are playing that frequency range), and a valley would be a degrease (neither driver is playing that frequency range).  I'm not sure of a good tool to measure this would be.  I have an Anthem MRX receiver that came with a calibrated microphone and software that can do this.

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I just purchased a pair of 1979 EPI 100Ws for $5.....woot.

Their 8" drivers need to be re-foamed.  I've done this before (Cerwin Vega) but:

Question 1:
How much is this likely to affect their performance?  I understand that their original design depended on the mechanical characteristics of the drivers rather than an L/C crossover to separate the low and high frequencies.  Clearly the foam I can buy on E-bay isn't from the manufacturer.  But is it close enough?

Question 2:
What is a good way to check against the 'as new'?  I've accumulated enough hardware to measure me a Bode plot.  But I have no idea what it should have looked like from the factory.  I have a darkly humorous anecdote about frequency response in modern vs antique test equipment, but I don't want to put it on the internet as it is slightly disrespectful of Nissan engineers.

In regards to question 2.  The frequency response across the crossover point should be fairly flat.  If the driver characteristics changes to a large degree, you'll see either a spike or a valley at the crossover point between the woofer and the tweeter.  A spike represents an increase is frequency extension (both drivers are playing that frequency range), and a valley would be a decrease (neither driver is playing that frequency range).  I'm not sure of a good tool to measure this would be.  I have an Anthem MRX receiver that came with a calibrated microphone and software that can do this.