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Chorus II on Steroid


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Just thought I'd share some pics of a recent mod performed to my
Chorus II's courtesy of Mike Hurd for loaning some stuff to play with...

Driver is a BMS 4594ND:


Horn is an 18 Sound XT1464:


then y'all know what a Chorus II is. I had to do some surgery to
disconnect the MF/HF and the internal xover so that I could connect the
amplifier directly to the woofer.

Processing and amplification is
being done in a pair of Crown XTi 1000 amplifiers. The BMS 4594ND is a
dual diaphragm driver, so there is an extra passive crossover for
dealing with the MF to HF transition.

Source material is lossless audio from my laptop going through a Tascam US-144:


And then here is a picture of the setup, which clearly shows that this is still a bachelor pad [;)]


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And then here's a closeup of the passive xover between the MF and HF, and a shot of the expensive mounting techniques being employed:

They really made the cables on their passive xover way too short and way too cumbersome for connecting in a sane manner, but that doesn't really affect functionality.


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And how about a shot of the raw frequency response measured at the mouth of the horn and gated to remove all reflections:

Note that this is 3dB/division on the vertical scale, and 20 to 20k logarithmic on the horizontal scale. The raw response is within about an 8dB window right off the bat. Some of that is related to how they implemented the passive xover.


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Here is after EQ:

Again note the scale...EQ'd response is easily within a 3dB window. The craziness in the HF is more than likely related to my microphone than the actual speaker, but no need to go into all those details. The response is with a 600Hz high pass filter which is why it's rolling off the way it is. I don't have good plots of the woofer behavior because the frequencies are too low for good gating.


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So how does it sound? Pretty fricken sweet....definitely a huge step
up from the stock Chorus II. The polar response is real tight on these
horns (60x50) so it's almost like listening to huge headphones. It's
hard to get the polars to line up well with a single 15" woofer, so
there's some weirdness and tweaking that is needed to balance out the
power response against the on-axis response. If I sit low on the couch
so that the couch blocks out all the indirect sound, then it sounds
just fine.

I gotta say that this combo turned out to be way
smoother than I expected. I was worried about the interaction between
the squawker and tweeter driver, but it doesn't seem to be too much of
a problem. I've gone through a lot of heavy metal recordings and other
genres and it's so amazing just how real all the cymbals and vocals
sound. There is no grating sound going on here, even with super heavy
guitar distortion....just smooth smooth smooth. There's a few moments
from the Tool - Lateralus album that get a bit grating, but I think
it's cuz they are way overdriving their compressors in the mastering
studio (as that's what it sounds like).

There's also a crispness
to percussion sounds that I've not noticed before on any other speakers
that I've played my demo source material on. Loreena McKennit - The
Mummer's Dance from the Book of Secrets album is one of my test tracks
because it's got many many layers of different instrumentation. You can
very distinctly make out the striking instrument on the various types
of percussion....totally eery as I wasn't listening for it and there it
was, super natural, but so easy to hear.

Does it top a K402? I
don't think so, but I'd like to hear one again just to make
sure...maybe even side by side. I definitely think it keeps up with a
K510. If you don't mind the super tight polars, then I'd say it easily
betters the K510. I dunno how much of that is this fancy driver though.

Well I gotta get back to listening....got a few more albums I want to get through.

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I am sure glad you have a pair of Chorus II's and take care of all the experimentation. That set up blows my mind.

I was expecting to see you set up the the Chorus II's for biwiring. Then working over the xover to pad the mid. Then throw in a set of Crites titanium tweets. Next a crown(K2) on the woofers and some tubes or class A SS on the mids and tweets. Did I say all that out loud?

Very nice Doc. Get those Chorus II's to perfection and you got another customer.[Y]

Oh by the way I am huge Tool fan. You got to get them sounding their best on the set up!

Let me add after critically listening for awhile:

The warmth and control of the marantz pre I'm using sure sounds fine.

The power and neutrality of the Crown K2 is unbelieveable. Such attack of the notes and control of the 15inch woofer.

Tried a few of the old Cd players I have laying around and I tell ya the little Oppo is a superstar.

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Feel free to swing on by sometime if you wanna give them a listen...won't be here forever as I'm just holding them for Mr. Hurd until he can come and get them.

I actually don't know how much this upgrade would cost...I think the horns are cheap, but those drivers have gotta be expensive....and then throw in an extra amplifier and an active crossover. A passive could probably be designed, but that's a lot more work.

There's a few changes I'd like to try to the EQ...I'm always trying out new approaches to the EQ process (trying to make it as few steps as possible). I also started the whole process while the passive xover was still hooked up inside the Chorus II, which is why I went for the lower xover point. Now that I can run the 15" full range, I can get better time-alignment and should be able to get a smoother passband. I did most of it by ear because my measurement microphone has been beat to snot over the years and so I'm not as quick to trust what it tells me anymore. I need to go into work and have it calibrated sometime....maybe buy a new one too since they're so cheap.

We'll have to see what the future holds for my audio career. Speakers are definitely my passion, but I've been having a lot of fun working at Shure. Speakers are a nice change of pace after doing circuits all day.

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Cool: for reference, the horns are pretty inexpensive as it goes, but the drivers are over $ 600 USD each... so there's about $ 1400 USD sitting there...

That's only some of the parts for my active main LCR speaker project, in parts alone ( horns / compression drivers and woofers ) there is $ 4G in parts, not counting the lift of 24 mm thick BB plywood, or the power amps / active crossovers.

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looks pretty wicked Mike! So that little passive comes with the BMS driver, and you're actively crossing over with the Crowns- schweet.

So are you gonna cut the holes and make the modification?

Seems that this might be a good PA solution to some of those less-stout drivers- I like the dispersion pattern.

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  • 2 weeks later...

I have the Forte II's, is my crossover similar to the one mounted behind the new horn?

Similar in what way? I believe the xover in the Forte II is mounted to the rear of the input terminal, but it is a passive xover like this one....it should have more parts actually because the one in the picture is only a 2-way passive xover. I'm taking care of the woofer to top-end crossover inside the XTi's.

And no, I'm not gonna cut holes in my Chorus II cabinets. It would make more sense to just build a new cabinet if I was gonna go that route.

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The Chorus II / BMS combo isn't super optimum, the 15" woofer most likely doesn't have enough bandwidth to match up with the horn's intended low cut off point. It would work better if you can get the frame of the woofer touching the horn on the baffle, as well as using a woofer with a wider bandwidth, something like the Acoustic Elegance TD15M / X / S.

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