Acoustat Spectra 11

Planar Speaker Asylum

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Back in 1990 I saw a pair of Acoustat Spectra 11â€™s in a HIFI shop. The top end was wonderful but I had the idea that the eight inch woofers could use a zobel. I didnâ€™t buy them then because I had just completed building a Siegfried Linkwitz three-way tri-amped satellite system. Just this weekend however I bought a used pair at a good price. Now, I could see if I was right about the woofers needing a zobel. When I got them home and set up, the first thing I noticed was that there was an imbalance, the lift one had lower output. I had read where a guy said that he had an imbalance in his that he traced to a bad capacitor. I pulled the electronics on that channel and had a look. There are two non-polar caps in series with a resistor. These were 100uF and 150uf. I had some Dayton caps of these values on hand, so I put them in (PartsExpess 027-360 and 027-364). Next, since I was there, I replaced two caps in the low voltage circuit that power the IC. These were 4.7uF and 470uF and I replaced them with 100uF/25 and 2200uF/25 respectively. I did these changes to both channels just to keep things even. The imbalance was gone and the sound from the top end was wonderful and served to point out that the woofers sound did not match the top end. It was time to find out if a zobel on the woffers would really work. I pulled the woofers and plotted their impedance response. They look like typical woofers of 7 ohm impedance. I guessed that 6.5 ohm and 10uF (027-428 and 004-6.5) would do it for a zobel. I tacked one on a woofer and measured its effect. I was dead on with the values! After the resonance peak, they measured flat at just over 7 ohms all the way out pasted 10 KHz. I soldered on the zobels then replaced the woofers and had a listen. Now the bass was clean and deep while tight and well defined. There is no seam between the top panels and the woofers and there are miles of depth! I sent hours listen to them and never did they do anything that made me want to change something more. Although, I did have one more thought about them, what if they had a thinner sock? Standing close to the upper panel I could hear much more detail then from my listening seat. So, would a more open sock help, I think it might. As a last word, well, they may never replace my Maggieâ€™s but they are very nice to listen to. If you have a pair of Acoustat Spectra or otherwise, why not try a zobel on the woofer, you have nothing to lose. Good Luck, bobwire

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Topic - Acoustat Spectra 11 - bobwire 08:03:17 12/11/06 (1)

Re: Acoustat Spectra 11 - tubevibb 08:32:21 12/11/06 (0)

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