2-MH, Various, woofer problem

Read more on the Acoustat 2-MH in our home audio section

Paul Johnston2004-02-23 22:21

A local fellow wants to sell a pair w/ a bass module (MK131??) w/ a 10 inch woofer init, but the surrounds are rotten -- can you give me some info on this units\' specs so I can try to find a replacement?? Most helpful is the Ref SPL as I can match a woofer to the box if I have that...

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Andy Szabo2004-02-23 22:21

Sorry, but I do not have any specifications on the MH woofer. I doubt that Acoustat could have supplied the Thiele-Small parameters even when the company was still active. Using TS parameters for woofer design was not as common then (1980\'s), and I am pretty certain that Acoustat did not do any such analysis.

In my opinion, all of the pre-Spectra woofer systems produced by Acoustat were rather weak. Unlike Acoustat\'s approach to the ESL design (which was very thorough), I think the woofer systems were thrown together without much regard to selecting the optimum woofer for the given enclosure, or particularly to designing optimized crossovers. One of my first projects when I joined Acoustat was to redesign the woofer crossover in the Model One. With some minor changes, I was able to significantly tighten the bass, and produce a much smoother transition to the ESL. I do not think Jim Strickland was much involved with designing the woofer systems, and it shows.

It was not until the Spectra series, when Acoustat was able to work closely with Rockford\'s loudspeaker division, that TS parameters were used to optimize woofer system design. This applies to the models SPW-1, Spectra 11, and Spectra 1100.

But I digress. I suggest you obtain the best 10-inch woofer that you can find. You\'ll want to choose one that is designed for use in a sealed enclosure of about the same volume as the MH woofer cabinet. Try it with the existing crossover. Be aware that at least several ohms of resistance are built into the crossover coil: this is done to reduce the level of the woofer, to match the ESL. If the replacement woofer is more efficient than the original, you may need to add series resistance to reduce the woofer level.

David2004-04-20 15:42

Had the same problem with the subs in my 2MH\'s. Bought them in 1984 - woofers surround had rotted by 1995. I shelved the woofers until recently and had been using Vifas (the sound was not even close). One of my local electronic stores carries replacement rubber surrounds for speakers. The original surrounds were made made from a poly foam (doesn\'t like UV light or hyrocarbon based sprays). I purchased a set of rubber surrounds for A$28 and set about recovering my woofers. By the way, I had priced replacement woofer units while they had been available. A$200 each plus freight. The hardest part in refurbishing these woofers, is removing the old foam. The surround foam was removed from basket with a sharp blade. Thats the easy bit. The foam on the cone can be made softer with the spouces/girl friends nail polish remover (acetone based) and wiped off. The cone is made of polyproplene, very robust. Try not to move the cone to much thought. The last steps involve bonding the rubber surround to the cone and then the basket with the special cement that is supplied with the rubber surronds. The idea is to let the spider do the work of centralising when lining up the cone and the basket. My refurbished woofers have been running for over a year and are as good as when they were first run in.

Ken Fisher2005-03-29 10:01

Hi. I had a similar problem with the woofer surrounds on my model 2-MHs. I bought them in 1983 and by 1997 the woofer surrounds had disintegrated. After a lot of digging, I became convinced that the woofers were very similar to 10 inch Peerless woofers of the early \'80s, which also had poly cones. You can actually buy an entire 10 inch Peerless driver for ~$100 in LA which has an impedance curve that looks appropriate for the MH enclosure. I can report very good success sending the woofers to a firm in California, which is still performing this service. In 2003, I sent the woofers to be \'re-edged\' to: Orange County Speaker 12141 Mariners Way Garden Grove, CA 92843 800 897 8373 also on the web.....www.speakerrepair.com/OCSAuth.html They are using a different foam for the surrounds, and the units sound much cleaner in the 50 to 80 Hz range. Cost was $75 plus shipping, and the repairs are still solid two years later. If your cones are trashed, they can replace those as well. I suggest that you send the drivers to them and let them center your voice coils. Ken

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