Restore NS-70t Midrange [Archive] - Audio & Video Forums


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01-15-2008, 11:34 PM
Hi to the group. I'm looking for some advice on correcting a minor problem with one of the tianium midrange drivers in my beloved vintage Yamaha NS-70t monitors. For those unfamiliar, these are dometic Yamahas modeled after the famous NS-500 and NS-1000 studio monitors. The driver metals are not as esoteric as their big brothers', but these are capable speakers with fabulous midrange and high end transparency.

The problem is during a move about four years ago the movers managed to damage the dome of one of the mids. I was delighted to find out you can disassemble the driver, and was able to (gently) push the dome back without cracking or holes. The surround likewise appears intact. The only change from new condition is not all the compressed insulation material that was in the back throat and chamber of the driver survived.

Audibly the driver works fine, except that I notice that there is a resonant frequency that will create a buzz or higher order distortion. It appears to be limited to a single frequency, around 400-500hz. I'm assuming this might be a backwave or standing wave issue within the now poorly dampened rear chamber of the driver.

The questions are:
- does this sound like a reasonable guess?
- what type of material should I replace the missing damping material with?
- can anyone think of another possible causation for this distortion?

Thanks in advance, I look forward to the group's input!