Acousta-stuf in Chorus-II

[leok]

There was a post here a few weeks ago suggesting placing some Acousta-stuf inside a speaker cabinet (I think it was RF-7). My Chorus-IIs have always sounded a bit boomy in upper bass. I always figured it was the room.

So, after reading the post I purchased some of the material, expanded it, pulled out the mid horns, and inserted a pound in each cabinet. Big difference. Bass is much more distinct. Worth a try.

I'll try the RF-7s next since they were the subject of the post. I've never had a problem with the RF-7 bass, but who knows.

Leo

[capo72]

I've been away from the board for a few weeks, so I missed the earlier thread. I'm interested to hear your results. Please share when you get time.

Jeremy

[DrWho]

Yikes! The Chorus II's are anything but boomy - it is definetly your room.

The implementation of "acousta-stuf" is going to vastly change the behavior of the passive and result in a further decrease in efficiency...basically meaning you very likely have no more bass coming out of the speaker []

I suppose if it sounds better in your room that's all that matters, but I don't think I'd recommend this mod for everyone.

[leok]

Jeremy,

The damping pretty much just cleaned up the frequencies covered by the 15" woofer: 40Hz - 600Hz. Highs are unchanged. Bass goes just as low, and with the same power as before, but notes and timbres are much more distinct, making them sound more powerful, or at least more musically meaningful. Low end of big grand pianos is more impressive and realistic. Bass imaging is much more in line with the excellent job done by the horns. Rock is more dynamic.

I suspect a lot of cabinet echo and standing wave noise was being created and escaping via the woofer and passive radiator. The material damps those echoes. I had been aware of a rather muddy low end to the system, but, like I said, had always attributed it to the room. The room's still a problem, but no at all as bad as thought.

DrWho,

The nice things about this treatment is it's cheap, easy, fast, and easily reversed. As far as reducing efficiency of the passive, I'm not so sure. Doesn't the pasive simply add a half octave or so at the very low end, with anything higher being directly radiated by the woofer? In any event, I wouldn't say any appreciable amount of useful bass has been lost, just some mud and boxy coloration, making the bass more effective. I think it's worth a try.

Leo

[DrWho]

The reason damping material works is it converts acoustical engergy into heat. That means less energy left to move the passive radiator. One way you can think about it is the damping material makes the cabinet seem larger than it really is - which will also lower the tuning of the PR (an additional drop in efficiency comes with the extra bandwidth).The chorus II is already an overdamped system so you didn't really improve the time-response (ringing and group delay), but rather you pretty much just implemented an EQ (reduction of the lower frequencies).

But if your room has issues in the 40-60Hz region I can see how this might lessen the percieved effects of the room. The rate of decay (the room ringing at whatever frequency is plaguing you) isn't going to change, but the overall magnitude will be less and thus less noticeable. A sort of band-aid fix.

I was just trying to point out that there was nothing wrong with the Chorus II's in the first place. Maybe I was a bit too defensive of the people that think "ah, no damping - this speaker must be crap." But I'd still argue that fixing the issue with the room would sound more natural than modding the speakers to compensate for the room. But if room treatment isn't an option then by all means mod the speakers to taste.

[leok]

DrWho,

I completely agree. If the problem is the room, fixing it in the speaker is a band-aid and fixing the room would certainly be a better approach.

Maybe someone with a more suitable listening room can give this a try and report on the results.

I'm not convinced the Acousta-stuf is absorbing that much energy in the 40 - 60 Hz region where the radiator is intended to add radiating surface, However it seems to remove some box resonances that were coloring the sound and scrambling the image.

You're probably pretty busy, but since you have a good ear, and understand the physics, possibly you could give it a try and let us know what you hear. The material is not objectionable to work with.

Leo

[leok]

I added some additional damping to the RF-7s (1/2 lb each). There is a fair amount of damping already in the RF-7s (different from the Chorus-II in that the RF-7 uses ports and Chorus-II uses a passive radiator which may add its own damping). In any event, there was no significant change in the RF-7 sound.