Loading caps and 902 sonics questions

[Russellc]

Recently on another forum A member inquired of me about removal of loading caps on 902 8T drivers. It seems there was some confusion about the term, he thought I was refering to a capacitor. With a little explaining and a very clear contribution from wunhanglo, it was made clear for the gentleman. Another poster felt there was no improvement to removing/leaving the loading cap in sonically. I swear I hear a difference, but sometimes after putting forth the effort, One may hear what one wants, or perhaps its a "difference" rather than an "improvement." Does anyone know what the effects (sonically) are of removing/leaving in the loading caps? I worry I am hearing what "I want to hear" and may have misinformed the original posters inquirey. Would appreciate someone educating me here. Thanks,

Russellc

[Todd W. White]

The loading caps were used on the 808's, 908's and the 902T's. They did several things;

1. They reduced the excursion of the diaphragm, thus increasing it's power handling capacity.

2. They protected (to a degree) the diaphragm, therefore, from damaging transients caused by solid state amplifiers when they went into clipping.

3. They also reduced the HF output, especially above, if memory serves, around 12kHz. This results in NOTICEABLE frequency response problems in the upper registers, mostly, though, in the ability of the driver to reproduce the upper harmonics properly (there's not much REAL audio up there, you know - just harmonics).

I always take them out, replace the screws, and install thick felt in the rear cover. Then, if you are using the aluminum diaphragm, you have a standard 802/902, which always sounds better than the "T" version!

[billfort]

I recently removed the loading caps in my 604G compression drivers and glued a piece of felt in the back covers as Todd mentioned. I didn?t notice any improvement in treble extension (I have the tangerine phase plug version) but did notice a smoother midrange ? less of that 604 mid shout. I?m using low power SET amps in a small room so have no concerns with reducing power handling.

A beneficial mod (with no downside) that improves the 604G in the one area I found them a touch disagreeable at times.

Billfort

[Kenny Brant]

Russellc, I took the caps off the back of my 902's and put some self sticking felt on the inside of the back plate. It smoothed out the sound and I didn't lose any highs. I think it integrates better with my mid woofers. I like the results. I can change it back any time I want to.

Thanks, Kenny

[Stovebolt6]

Does the 909-16a have the loading cap? How does this prevent over excursion? does it cause the driver to roll off higher than without it?

Dan

[GM]

My notes says no, but that doesn't mean someone didn't add them. It prevents overexcursion by increasing the air spring on the rear of the diaphragm (less trapped air). It causes a broadband peak in the horn's response, so EQ is required to raise up the HF response and more midbass efficiency to match it if a ~flat response is desired.

For HIFI use, it's not needed unless you host 'headbanger's balls' like I used to.

GM

[Stovebolt6]

GM,

Great explanation about the air spring concept. This is the first description that actually makes sense to me. I think that my 909s have them. Could someone post a picture so I know what I am looking at?

Thanks again!

Dan

[gdahl]

Originally posted by J Daniel:


Could someone post a picture so I know what I am looking at?

Dan

<font size="2" face="Verdana, Helvetica, sans-serif">Hi Dan,

Have a look at this:

http://cgi.ebay.com/ws/eBayISAPI.dll...&category=3276

With the rear cover off, this is all you see on the back of the driver. If you don't have loading caps, you will see the diaphragm itself.

Gary Dahl

[Stovebolt6]

Thanks Gary,

Yup, I have 'em. Thanks all.

Dan

[gdahl]

Hi Ron,

Nice to hear from you!

I've been getting back into Altec/horns again, after about five years away from them. Now that Lynn Olson lives here (and has taken an interest in horns), I stand a much better chance of dealing with some of those niggling crossover and integration problems. Lynn's great with crossovers, and he still has his MLSSA system.

Good move, fixing up your 904's. I'll bet they sound great now. What is the rest of your speaker system like?

If you would like to see what we've been up to (but no horn stuff), check out our site:

http://www.nutshellhifi.com

Gary Dahl