Jim Turner
New Member
I just picked up a set of Fisher XP-55B's from Facebook for $30. Cosmetically they are in great condition. The Box seemed a little smaller than I was expecting. The first thing I did was hook them up to my 12watt per channel amplifier and listen to music. First thing I noticed the high frequencies seemed lacking. I remember reading others post about a resistor in series with the tweeter so I opened mine up. The crossover (assembled on the back of the woofer) had a a 9.2 ohm resister and an 8uf capacitor in series with the tweeter and the woofer ran at full range.
First I replaced the capacitor with a fresh one and reassembled the speaker and the higher frequencies was better. I suspect the capacitor had developed some high ESR because of its age. Though the higher frequencies was better I could tell that resistor was attenuating more than it should have, at least to my ear. So I temporarily removed it and retested the speaker. Now it had to much on the high end. I then used my calibrated microphone and noticed a huge lull right at 1100 Hz. So I removed the tweeter and checked its polarity and it was wired with the negative and positive terminals reversed. I know it was like this from the factory because it had a manila envelop with speaker screws stuck to the back of the tweeter magnet lol. So someone had dropped that package of screws in there and it has been like that for over 50 years lol.
The Tweeter has an Re of 9.7. Woofer Re of 5.9 combined the tweeter with the 9.2ohm resister, the 8uf capacitor using a first order crossover calculator I come up with a factory crossover right at 1000Hz. Before I took this apart I had assumed it was 1.5kHz. Lightly pushing in on the tweeter cone it does move quite a lot. I have tweeters made for 3k crossovers and they don't visibly move at all.
The acoustic suspension speaker has a low end of about 72 to 75Hz 3db down... I found an old add online that suggest this speaker goes down to 37Hz... lol only at 24db down. The internal volume of this speaker is only 0.56 cubic feet. Even the best 8" woofers from parts express that can work in a volume that small does not really go down farther than what this does. The woofer really does not perform past 1kHz either.
After testing I ended up using a 5ohm resistor and 10.2uf capacitor in series with the tweeter and it has leveled out pretty good, But I am not done fine tuning it. I but the woofer really does need a second order network as it is causing a spike with the tweeter at around 3k.
What I would like to do is convert the cabinet to a base reflex with a 1 3/4" port 4" long on the back. Then replace the woofer with a Dayton Audio DSA215-8 and change the crossover closer to 1400 to 1600Hz and use a second order on both the woofer and tweeter. This will put less stress on the extended range tweeter and lower the base from 72Hz to 51Hz. I should be able to get higher power from this as well. I find if my speakers can go as low at 50 to 60Hz it makes such a huge difference on enjoying the music without the need for a subwoofer.
I feel these speakers are so plentiful there is no reason to keep these untouched and original if such a huge improvement can me made. I would not listen to these on a regular basis with such a crappy base response. They would either just go in storage or I would have to re-sell them. Going to install some 10-32 hurricane nuts for the woofers too. One screw is already stripped out.
First I replaced the capacitor with a fresh one and reassembled the speaker and the higher frequencies was better. I suspect the capacitor had developed some high ESR because of its age. Though the higher frequencies was better I could tell that resistor was attenuating more than it should have, at least to my ear. So I temporarily removed it and retested the speaker. Now it had to much on the high end. I then used my calibrated microphone and noticed a huge lull right at 1100 Hz. So I removed the tweeter and checked its polarity and it was wired with the negative and positive terminals reversed. I know it was like this from the factory because it had a manila envelop with speaker screws stuck to the back of the tweeter magnet lol. So someone had dropped that package of screws in there and it has been like that for over 50 years lol.
The Tweeter has an Re of 9.7. Woofer Re of 5.9 combined the tweeter with the 9.2ohm resister, the 8uf capacitor using a first order crossover calculator I come up with a factory crossover right at 1000Hz. Before I took this apart I had assumed it was 1.5kHz. Lightly pushing in on the tweeter cone it does move quite a lot. I have tweeters made for 3k crossovers and they don't visibly move at all.
The acoustic suspension speaker has a low end of about 72 to 75Hz 3db down... I found an old add online that suggest this speaker goes down to 37Hz... lol only at 24db down. The internal volume of this speaker is only 0.56 cubic feet. Even the best 8" woofers from parts express that can work in a volume that small does not really go down farther than what this does. The woofer really does not perform past 1kHz either.
After testing I ended up using a 5ohm resistor and 10.2uf capacitor in series with the tweeter and it has leveled out pretty good, But I am not done fine tuning it. I but the woofer really does need a second order network as it is causing a spike with the tweeter at around 3k.
What I would like to do is convert the cabinet to a base reflex with a 1 3/4" port 4" long on the back. Then replace the woofer with a Dayton Audio DSA215-8 and change the crossover closer to 1400 to 1600Hz and use a second order on both the woofer and tweeter. This will put less stress on the extended range tweeter and lower the base from 72Hz to 51Hz. I should be able to get higher power from this as well. I find if my speakers can go as low at 50 to 60Hz it makes such a huge difference on enjoying the music without the need for a subwoofer.
I feel these speakers are so plentiful there is no reason to keep these untouched and original if such a huge improvement can me made. I would not listen to these on a regular basis with such a crappy base response. They would either just go in storage or I would have to re-sell them. Going to install some 10-32 hurricane nuts for the woofers too. One screw is already stripped out.
