how do you determine a driver's efficiency?

[bonsai171]

Hi, i have a pair of advent speakers where the tweeters went bad, so all that is left is the 8" woofers (that still sound good). The speakers are from around 1980 or so. The crossover is at 5000Hz. Is there a way to determine the sensitivity of the driver? What other criteria should be considered when picking a new set of tweeters for these speakers?? Thanks!

Dave

[bhg41088]

you need to consider T/S paramerters into this. but most important to just matching up is impedience.

[Ron E]

1) Measure T/S
do a search for 'epanorama impedometer' for instructions how.

sensitivity for 1Watt is 112+log10(9.6e-10*Fs^3*Vas/Qes)
[for Vas in liters]
sensitivity for 2.83 volts is the above + 10*log10(8/Re)
[Re is DC resistance in ohms]

2) You could play pink noise bands through them and compare them to speakers with known sensitivity to get a rough idea.

3) If you just want to match tweeters, get some tweeters that are more sensitive than the woofer and you can always adjust down with an L-pad.

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[BillFitzmaurice]

The Advents are going to be in the vicinity of 85dB/watt, perhaps a bit less, so what you want is a tweeter that is no less than that, which is pretty much anything out there. Choose the one that gives you the best response in the price range you want, also considering the mounting scheme. It's probably wise to upgrade the crossover while you're in there.

www.billfitzmaurice.com

[kelticwizard]

Just for the heck ot it, which model Advents?

[bonsai171]

BillFitzmaurice:

I tried using a set of Dayton silk dome tweeters that are 89dB sensitivity, and they seem to be a bit softer than the woofers, but it's hard to tell whether that's actually the case, or whether it's due to the acoustics of the room. Upgrading the crossovers is probably a good idea. They are 6dB/octave crossovers, and very low grade components (iron core inductor, and an electrolytic capacitor). The crossover point is 5000Hz. A friend rigged up these two speakers in as an active system once, and they seemed to do a much nicer job integrating at 3000Hz. Also, the system is high power, so i'd probably switch it over to 12db/octave crossovers..

Keltic Wizard:

These are the Advent Model 2002, from around 1980.
http://cgim.audiogon.com/cgi-bin/bb....odls&3&4&zz&zz
Any additional would be great if you have some

[kelticwizard]

There is a whole website devoted to classic New England speaker manufacturers, like AR, Advent, KLH, etc.. It has a bunch of old brochures, plus links to repair services that specialize in these speakers, etc. It also has it's own discussion board. At least one of the repair services, Layne audio, has a website which gives extensive info on these speakers for the DIYer.

This might help you even more, not that this thread should be abandoned either.

http://www.arsenal.net/speakers/speakers.htm
http://www.arsenal.net/dc/dcboard.php
http://www.arsenal.net/speakers/repairs.htm

[BillFitzmaurice]

They are 6dB/octave crossovers, and very low grade components (iron core inductor, and an electrolytic capacitor). The crossover point is 5000Hz. A friend rigged up these two speakers in as an active system once, and they seemed to do a much nicer job integrating at 3000Hz. Also, the system is high power, so i'd probably switch it over to 12db/octave crossovers..

The electrolytic cap is killing your high end, especially since at its age it's likely toast anyway.

I'd steer clear of 2nd order crossovers; they suffer from all sorts of phase issues. Also, if you want to drop to a 3kHz crossover you don't have enough protection. Go third order, figure out the component values here:
http://www.lalena.com/audio/calculator/xover/

Going to 3kHz is a good idea, as the woofer is likely getting beamy above that, which explains why it sounded better when you tried it at 3kHz.

www.billfitzmaurice.com

[bonsai171]

The electrolytic cap is killing your high end, especially since at its age it's likely toast anyway.

Definitely! Maybe that's why the system seems so imbalanced.. depending on how much capacitance it has lost, that could make the high pass much much lower (making a strange integration of drivers too). A 3rd order crossover sounds really good, that should really put things in good shape.

Going to 3kHz is a good idea, as the woofer is likely getting beamy above that, which explains why it sounded better when you tried it at 3kHz.

What does beamy mean?? Sorry!

[BillFitzmaurice]

What does beamy mean?? Sorry

You lose dispersion as the driver cone exceeds a wavelength in diameter. An eight incher has a cone diameter of about 6 inches, which is a wavelength at 2260 Hz; above that the dispersion angle severely narrows. By the time you get to 5kHz the dispersion pattern narrows so much that you have little off-axis response, so you're much better off crossing over as close as possible to 2.2kHz as you are able to.

This is one reason why the industry has gone to 5"- 6 1/2" midbass drivers and separate sub-woofers. A five with a four-inch cone is quite comfortable to better than 3kHz.