speaker sensitivity mystery

[slant-six]

Hello,

I'm a new member here and am posting because I have run into a complete (to me) mystery concerning a Dynaco A-25 speaker. I have two A-25's with Seas drivers in my main system and a single A-25 in my kitchen mono system. I replaced the crossover capacitors in my stereo pair a little while ago and though there was an improvement, it was subtle. I decided to do the same to the kitchen speaker and used a solen 5uf capacitor. While I was inside the speaker I noticed the woofer was not the same as my others and had a flat disk type magnet instead of the canister shaped one on the seas. It does have the same sort of rubber surrounds, but without the Seas name. Also the sides and back of the box are bare wood (no padding) and there were two pieces of fiberglass sitting inside. When I put it back together I forgot the fiberglass. Before fixing this mistake I thought I would see what it sounded like as is. I use a heathkit ua-2 12 watt amplifier with this speaker and it is barely capable of driving it but it's fine in the small space it's in. When I tried the speaker now the amp was at least twice as loud at a given volume as before. If my other A-25's were this sensitive I could us a SET amp with them. What happened ?? Is it just the stuffing? I didn't change the wiring so I don't think it's an impedance issue.

Sorry for the long post. Does anybody have any idea what happened?

Thanks,

alan

[battradio]

The flat magnet is ferrite and the older ones are alnico . The cap in the single unit could have been worse that the other two .Put the fiberglass back in and see what happens .Also bring one of the stereo pair into the kitchen and try it on the small amp and see if it as loud as the one you have in there now .

Mark

[jukingeo]

Hello,

I'm a new member here and am posting because I have run into a complete (to me) mystery concerning a Dynaco A-25 speaker. I have two A-25's with Seas drivers in my main system and a single A-25 in my kitchen mono system. I replaced the crossover capacitors in my stereo pair a little while ago and though there was an improvement, it was subtle. I decided to do the same to the kitchen speaker and used a solen 5uf capacitor. While I was inside the speaker I noticed the woofer was not the same as my others and had a flat disk type magnet instead of the canister shaped one on the seas. It does have the same sort of rubber surrounds, but without the Seas name. Also the sides and back of the box are bare wood (no padding) and there were two pieces of fiberglass sitting inside. When I put it back together I forgot the fiberglass. Before fixing this mistake I thought I would see what it sounded like as is. I use a heathkit ua-2 12 watt amplifier with this speaker and it is barely capable of driving it but it's fine in the small space it's in. When I tried the speaker now the amp was at least twice as loud at a given volume as before. If my other A-25's were this sensitive I could us a SET amp with them. What happened ?? Is it just the stuffing? I didn't change the wiring so I don't think it's an impedance issue.

Sorry for the long post. Does anybody have any idea what happened?

Thanks,

alan

A couple of things...

First

To answer your question, yes, you probably did notice a bit more apparent loudness with the fiberglass stuffing removed because the stuffing acts as a damping material. This will naturally descrease the resonance in the cabinet. It is effectively the same as making the box larger. Now without the stuffing in the box, the resonances are more prominent and the cabinet 'appears' louder. However, what you are also doing is making the speaker's response curve more peaky. Listen long and hard and you probably will find out you will not like the sound for a long period of time and will be tempted to put the stuffing back in the box.

2nd

A kitchen is hardly what I would consider a good test room...too many reflective surfaces. Hence the sound will be more 'live' and have much presence. Again, it will make the speaker sound more efficient, but it will be hard on the ears over time.

3rd

For SET amps, I hardly consider the A-25 a contender. As I recall this speaker is an accoustic suspension speaker (I believe). It was made around the time of the Advents and these speakers need some power. Dynaco did make the speaker to work with the ST-70 and MK-III amps which are powerful enough to drive that speaker. I seriously doubt a 1 to 10 watt SET amp can even move the speaker properly.

Klipsch and some of the mid 80's Infinity speakers have models that approach the 96db to 100db figure and this is what you are looking for in an SET cabinet.

I have heard that you can find some good deals on some older 80's speakers with large 12" or 15" woofers and they can be very efficient. The trouble with going this route is floor space. They do take up considerable living room real estate.

Geo