Flogging a dead (Aerogel) horse?

[ap]

I am about to bite the bullet & replace my mids with Vifa XG18s, but before I do is the Audax Aerogel any good? I am using the PR170zo & although I can get it to sound quite good it occasionally on some tracks it just sounds wrong (Im guessing its cone breakup) & fatiguing -I'm at a point where I redo the xover for the 25th time or just replace them with something else - is it worth perservering with them?

[billschu]

I have the HM170Z0 from waaay back when. The mids are nice but they really suffer from reflections inside the cabinet. They are supposed to be ported but I actually use mine sealed in a large 2.5 way speaker and have a fair amount of fiberglass stuffing behind it. It's the only way it sounds real good to me. The insulation behind it absorbs enough of the back wave to make it sound clean. This was one of the early ones so my only other experience with the Aerogel is the HM100Z2.
The HM100Z2 has a fair amount of distortion to it on its own. Maybe the HM170Z0 does too but at the time, no tools were available to me. Think late 80's.
The HM100Z2 is interesting in that it sounds quite good even with its higher than average distortion rating. The weird thing is that around 2Khz the off axis response is a tad higher than the on axis response. I got lucky and the speaker that uses this and the Morel MDT30 has a very similar on and off axis response.
The HM100Z2 won't win any SPL contests. It's small and can be used ported for a very small bedroom/computer speaker or for background music or as a nice midrange. I shied away from it when I noticed the distortion but then kept trudging on. Maybe I will bring these to the next DIY? Folks may be curious. I made one small ported set and then used the same drivers in a sealed config in a small 2.5 way with a 6.5" woofer. I was trying for a very small floorstander with high WAF. It didn't pass the WAF however and they are in the basement.

Bill

> I am about to bite the bullet & replace
> my mids with Vifa XG18s, but before I do is
> the Audax Aerogel any good? I am using the
> PR170zo & although I can get it to sound
> quite good it occasionally on some tracks it
> just sounds wrong (Im guessing its cone
> breakup) & fatiguing -I'm at a point
> where I redo the xover for the 25th time or
> just replace them with something else - is
> it worth perservering with them?

[damkor]

I am using the
> PR170zo & although I can get it to sound
> quite good it occasionally on some tracks it
> just sounds wrong (Im guessing its cone
> breakup) & fatiguing

What filter do you have on it? And with what tweeter? Up to 2kHz? 3kHz? All these pro mids are very efficient and they will "burn" your ears out in the upper midrange unless they are properly equalized. Or you can try it in a front loaded horn. Please post the xover and a measured or published response/impedance curve. And what width cabinet. It could be you are being too conservative with the filter/Xover.

[damkor]

...in a typical box, placed out in the room, the mid's response will rise about 11dB between the low and high cutoff frequencies, so you have to take account of that. (5dB inherent in the response, 6dB BSC) At least on the order of 8dB. And I would cut it off 2nd order at no lower than 500-600Hz, and cross to a pair of high sensitivity 10" woofers. You're aiming for around 93dB overall sensitivity.

Without taking account of the rising mid response, it will end up terribly bright, even if...especially if...you blend the tweeter for a relatively smooth transition.

[ap]

> ...in a typical box, placed out in the room,
> the mid's response will rise about 11dB
> between the low and high cutoff frequencies,
> so you have to take account of that. (5dB
> inherent in the response, 6dB BSC) At least
> on the order of 8dB. And I would cut it off
> 2nd order at no lower than 500-600Hz, and
> cross to a pair of high sensitivity 10"
> woofers. You're aiming for around 93dB
> overall sensitivity.

> Without taking account of the rising mid
> response, it will end up terribly bright,
> even if...especially if...you blend the
> tweeter for a relatively smooth transition.

You are exactly right & I have attenuatedthe mids by a lot, my target is 86db, being used with two 6.5" woofers. I am knocking up a quick website about them so will post the link soon.
Ultimately I think I will change them for something else.

[damkor]

I have
> attenuated the mids by a lot, my target is
> 86db, being used with two 6.5" woofers.

Okay. Usually when people have a problem with the sound of a system, it's the crossover not the drivers, but it sounds like you know what you are doing. If you've kept the region from 500 to 2kHz flat, and level with the woofers' below that, then you've done all you can.

I'd also be attentive to the sound of that mid at the upper end. It will beam and you will get cone break-up. I don't think it sounds as smooth as the paper version, but that's only what I've heard from others.

[ap]

> I'd also be attentive to the sound of that
> mid at the upper end. It will beam and you
> will get cone break-up. I don't think it
> sounds as smooth as the paper version, but
> that's only what I've heard from others.

I think thats exactly what Im hearing, cone breakup above 2k, I hadnt really experienced it before as I have always used either paer or poly cones.