Spectra 1100, Woofer and grille

Read more on the Acoustat Spectra 1100 in our home audio section

Chris Behrens2004-02-23 22:21

Andy, I just acquired a pair of Acoustat Spectra 1100s in pretty good condition. The seller was not the original owner, so he couldn\'t tell me much, so let me ask you some questions:

What kind of woofer is the original 8” woofer? Are there any identifying marks on the magnet or unique cone/dust cap/surround materials used that will help me to know if it\'s original? I know that the inductor on the woofer cross-over board is dead! What is the value of this inductor? Where can I get a replacement part? Can I get one at Radio Shack or Digikey, etc?I also noticed that the input cup had been fooled with, so I took it off and I noticed that the inductor looked like it had been heated up and the insulation material inside had some of the red glue melted on it (sounds like what happened in your experinces, but not as messy). I don\'t have an LRC meter, but I do have an audio oscillator to test if the low-pass filter works, but what is the intended cut-off frequency for the 8” drivers?

When I tried to take off the trim pieces to take the grill cloth off, it seemed like they had never been removed or not removed very recently as I can hear ”crud” rolling around in one of the panels. How often do they need to be cleaned? I just fear that after so many cleanings, the trim panels won\'t stay stapled to the frame anymore.

Also, my velcro on the speaker grills does not adhere anymore. I replaced the pieces on the grill itself with industrial strength velcro, but it does not adhere to the speaker cabinet. What type of velcro is that and where can I get replacement pieces for it (they look quite ugly without the bottom grills on)?

One final question, and this one is not related to Acoustats. I am an undergraduate finishing my Electrical and Computer Engineering degrees at University of Missouri-Rolla, and I\'m interested in Graduate School and possibly a career in acoustats such as yourself. I have never had a class on anything related to acoustats or acoustic electronics, nor do they offer any. What type of universities would I look into for this? How did you get into this field? Thanks,Chris


Andy Szabo2004-02-23 22:21

The Spectra 1100 woofer was custom designed and manufactured by Rockford\'s division Carbonneau (now called RAD, or Rockford Acoustic Design). I don\'t have a record of the part number, or any particular way to identify if you have the original woofer. I know that the part number started with ”AA”, but I don\'t remember if it was stamped on the woofer. Be advised that two slightly different woofers were used during the 1100\'s production, so comparing your speaker to another 1100 may not be valid. The change was forced by a component that was no longer available. Despite slight differences in appearance, Acoustat considered the two woofers to be sonically identical.

A schematic is available on this website for the Spectra 1100. The crossover coil is 2.3 mH, 1.8 ohms. Don\'t bother to look for such a part at Radio Shack or DigiKey. You might try contacting one of the mail-order outfits that specialize in do-it-yourself speaker components. It may be necessary to use an external resistor in series with the coil to bring it up to the desired resistance. That resistance value is important to match the woofer\'s level to the ESL.

The woofer crossover begins to roll-off at 6 dB per octave around 150 Hz, and then steepens to 12 dB per octave above 200 or 250 Hz.

In regards to cleaning the grille cloth, there is additional information posted in the Technical Bulletins section. The frequency of cleaning is a matter of condition and personal choice. With the difficulty in removing the trim strips, it\'s not something you want to do unless necessary. My grille cloths are black (which helps) and, except for vacuuming in place, I\'ve never cleaned them in over ten years. As to the ”crud” you hear rattling around inside, don\'t worry about it unless it causes a performance problem.

In regards to cleaning the ESL panels themselves, I described how to do this in Q & A section 8.1, Membrane Cleaning. This process is rarely if ever required, and should be done only as a last resort if sonic performance has degraded due to dirty panels.

I don\'t remember the original vendor for the Velcro dots used to attach the lower grille. It\'s just as well, because the originals did not stick very well, either. I think the oil finish used on the wood prevents the self-adhesive Velcro from sticking properly. I used contact cement to re-attach my bits of Velcro, and they haven\'t fallen off since.

The answer to your last question is ”dumb luck”. I attended Drexel University in Philadelphia, class of \'82, majoring in EE. Since I already had an interest in audio, I tried to take as many analog circuits and acoustics courses as I could. At the undergraduate level, not much was available. I suspect that, today, the situation is no better, and perhaps even worse, due to the increase of things digital. (Back then, we were still feeding punch cards into a mainframe!)

Perhaps the one thing that really helped me was Drexel\'s Cooperative Education program. In this program, an undergraduate degree takes five years, with the student alternating six months of academic work with six months of hands-on industry experience. I was fortunate that the David Hafler Company was located only a few miles from home, and somehow I convinced them to hire me as an intern (most students took jobs assigned by the university). Upon graduation, I was hired permanently by Hafler, who later acquired Acoustat, and the rest is history.

It\'s a tough industry to get into, but one with many rewards. How many jobs are there, that allow creating the best of something that makes people very happy, and you can take one home for yourself to enjoy? Being such a small and highly specialized field, I doubt there are many college courses, even at the graduate level, that would help to prepare you. Find a company that you admire, convince them of your passion for audio, and hope they are hiring!

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