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Re: [Phys-l] speakers


On 2011, Apr 26, , at 07:30, Anthony Lapinski wrote:

I have an old Fisher speaker system. Remove the grill and it shows a
woofer, midrange, and a tweeter. Red/black connectors in back. Works well
with a Radio Shack amp.


Not mentioned (by previous posters) is the damping (factor) of the amplifier. That system is likely designed for a VT amp. Hence the 8 ohms -- the output impedance of op-amp amps is usually somewhat lower. This will affect the damping. Whether it's a good idea to obtain a better match w/ the addition of a power resistor I don't remember. Curiously reducing the damping by adding resistance in series may improve the sound, tho it means even a worse mismatch in E transfer.



One may characterize speakers w/ a sig. gen. driving the amp. Insert a series resistor to decouple the damping by the amp. Measure the EMF after the resistor and you will find the resonances of the speakers and the enclosure. You'll hear them also and a sound level meter will be better. R/S sold them. Using a dual trace scope will also be revealing. (EMF across a resistor for the i and the other channel the EMF across the speaker.)


Still do:

http://www.google.com/search?client=safari&rls=en&q=sound+level+meter+radio+shack&ie=UTF-8&oe=UTF-8#q=sound+level+meter+radio+shack&hl=en&client=safari&rls=en&prmd=ivns&source=univ&tbm=shop&tbo=u&sa=X&ei=NPW2TcSFJrDciALk57Qi&ved=0CGsQrQQ&bav=on.2,or.r_gc.r_pw.&fp=e7a3bcc05b1d8fbd&biw=1000&bih=737


To measure the output Z of the Amp. load it w/ a variable resistor and measure the R when the EMF is half; that's the Z.


Your library may have old copies of speaker builder and the audio amateur. Old colony I think was associated w/ them. They made kits and upgrades for VT amps. I still have an old colony mic. preamp.

They appear to be succeeded by audio xpress -- there's glass audio also.


http://www.audioxpress.com/


bc still has several KT66 -5881 amps. and the original Willi Studer recorder. (A36)** (VT's) plus an A77



**As late as the '80s pro audio engineers said it sounded better than the the latest digital recorders. I used (still have) the Sony 501es PCM digitizer -- It has an interesting drop out resistance by using a massive (at the time) memory so the info is interleaved. If a drop out occurs only part of a note is lost and it interpolates. It has a lamp that lights whenever it interpolates. I last used it in 2000 when my hearing failed.