CanThe AR-9 Replicate The MGC-1 ?

[ar_pro]

I've been reading some test reports on the MGC-1 speaker, and I'm wondering if I can somehow utilize my extra pair of AR-9 speakers to replicate the MGC-1's ambience effect. If the second pair of speakers was placed directly behind the main pair, and turned out at 90 degrees (mirror-imaged), what would be the result? From what I've read, the MGC-1 processed the signal to its secondary ambience-drivers through a 20 millisecond delay, and rolled off the signal below 450Hz, and above 5 kHz...there was also some attenuation from the effects of a foam baffle. If the second pair of 9s was operated without its tweeter (the woofers would also be disconnected), and fed the signal through a modern digital delay (with independent volume adjustments) and amplifier, would we have something worth listening to? I'd appreciate any comments here...I'm really open to suggestions.

[kkantor]

This kind of ambience re-creation is a subject that remains near and dear to my heart. I'd love to share thoughts here, and assist how I can. I'm very curious about how an arrangement such as you propose will sound.

My first thought is that you will need to find some means of radiation pattern control. If the two speakers overlap too much in the direct field, the comb-filtering will be severe. Given that the AR-9 is a moderately wide dispersion speaker, some kind of off-axis absorption might be called for, particularly on the front-firing system.

In terms of the side-firing tweeter, I would leave it on. The lack of HF ambience output on the original MGC-1 was mostly a design tradeoff, related to the quality of the delay lines available at the time. But the side-firing speaker should remain restricted to frequencies above a few hundred Hz.

Please do keep me posted, and let me know if I can assist.

-k

[Guest]

Hay guys,

What is a MGC-1?

Ed

[ar_pro]

Thanks, Ken for your reply...it's a pleasure to have the opportunity to hear your opinion on the idea. I've been thinking about this for awhile, and coincidentally came across an old copy of "High Fidelity" that had a short review of the MGC-1 - they ranked it "among the world's great loudspeakers". That said, it's unlikely that I'll ever own the MGC-1 (my wife is agreeable to two pairs of AR-9s, but she's not nuts!), and I'm very pleased with my rebuilt & restored 9, so the notion of combining the strengths of the Model 9 with some of the attributes of the MGC-1 is really tempting. You're absolutely right about the dispersion characteristics of the 9...the "sweet spot" in my listening room is pretty wide, and I would think that there could definitely be some interference with the side drivers. Would it be possible to adapt something like Sonex foam to act as a buffer for the front drivers? And how critical to the overall effect is the flared foam construction around those side drivers (boy, do they look like horns!)? Am I tring to kill an ant with a sledgehammer, here? Would it be as effective to just use AR9 upper-range drivers mounted on a flat panel, rather than a complete AR9 system for the effects channel? If this was the case, the panel could be more easily located relative to the front-firing AR9, and attaching an absorbtive material would be pretty simple. The delayed signal could feed a separate amplifier (maybe with a remote control for volume) that would allow the listener to easily adjust the output of the "effects" drivers. Could an equalizer serve the purpose of attenuating the response above and below the desired range? Apologies for all of the questions!

Anyone interested in seeing the MGC-1 review, just send an email to: ar_pro@techie.com

[kkantor]

The MGC-1 was a speaker developed by AR in the mid-80's that used electronics processing and an unusual configurtion to try and overcome some of the psycho-acoustic (human perceptual) limitations of traditional speaker designs.

http://www.aural.org/resume_01_files/articles/aud-magic/

There are also publications to be found at www.aes.org if you search under my name.

-k

[kkantor]

Questions are good.

1- The panel alone would work fine, and certainly outperform the original MGC-1's side unit.

2- The original shape and material was critical, and took a long time to develop, but we were shooting for very constant directivity. Sonex will work, at least to first approximation, that is to restrict the front signal and reduce comb filtering. If you decide you need to control the POWER response of front system, the Sonex may prove inadequate, unless you layer it into a pseudo-horn.

3- EQ is a good thing on the side speakers. It lets you adjust the long-term power response without messing up the tonality, as well as restricting the bandwidth.

4- See if you can get you hands on a cheap Behringer "Edison" EX-1. This will allow you to extract and control the L-R and L+R signals sent to the side speakers, much as in the original.

More questions!

[ar_pro]

Well, after thinking this thing through, it would be a waste to attempt using my 2nd pair of AR-9s as the effects speakers in this set-up. After disconnecting the woofers and attenuating the upper & lower response of the remaining drivers, there's not much left of an AR-9, is there? Adjusting the 2nd pair of floor-standing speakers to the correct angle would also be a big challenge. It seems that the better approach would be to use dedicated drivers on a panel, with the appropriate isolating foam structure added. Ken, could you please explain the rationale for using effects-channel drivers that were different than those used as the primary drivers? And I'd really like to know why the woofer system of the 9 (or the single woofer of the 3a/LST) wasn't used in the MGC-1...was this a cost consideration? Thanks for the info on the Behringer EX-1...I had intended to use an ambience-extraction device that Old Colony offered a long time ago...it's an op-amp based version of the Hafler design that functions at line-level, but the Behringer would be considerably more flexible.

[kkantor]

>Well, after thinking this thing through, it would be a waste

>to attempt using my 2nd pair of AR-9s as the effects

>speakers in this set-up. After disconnecting the woofers and

>attenuating the upper & lower response of the remaining

>drivers, there's not much left of an AR-9, is there?

True, but no need to attenuate the upper driver.

>Adjusting the 2nd pair of floor-standing speakers to the

>correct angle would also be a big challenge. It seems that

>the better approach would be to use dedicated drivers on a

>panel, with the appropriate isolating foam structure added.

Certainly, that does seem more reasonable.

>Ken, could you please explain the rationale for using

>effects-channel drivers that were different than those used

>as the primary drivers?

They worked pretty well, and we needed all the space we could get in the enclosure. All that mattered from the side was good power response over the required frequency band, and in this regard they matched the front drivers very closely. No need for good impulse response, etc. Besides, they were typically equalized.

>And I'd really like to know why the

>woofer system of the 9 (or the single woofer of the 3a/LST)

>wasn't used in the MGC-1...was this a cost consideration?

No way to answer this one honestly without getting into the petty politics at work at the company during that period. The "Engineering Department" had been assigned to do the woofers, while the "R&D Department" did the research, crossover, electronics, voicing, all that stuff. Of course, the natural resentments and pressures arose, and some people didn't want a "research" speaker to outperform the top of the conventional line in bass performance. I argued, I lost. Oh well, I got over the resentment after a few decades, but I still feel the bass is a weakness of the product. Subwoofer, anyone?

>Thanks for the info on the Behringer EX-1...I had intended

>to use an ambience-extraction device that Old Colony offered

>a long time ago...it's an op-amp based version of the Hafler

>design that functions at line-level, but the Behringer would

>be considerably more flexible.

Yeah, the EX-1's are fun and instructive to play around with, even in a good, plain vanilla stereo system. On the right recording, you can do surprising things with the stereo image.

-'night!

Ken Kantor

Insomniac Audio Systems, Inc.

[ar_pro]

Thanks for the details regarding the side speakers, Ken...since the mounting panel would be independent of the AR-9 cabinet, there'd be more than enough room for mounting matching AR-9 drivers. I understand that impulse response wouldn't be a consideration, and the normally-wide dispersion has to be restricted, but matching the power response of the front drivers would be a big plus with this arrangement, no?

Was the foam used in the MGC-1 subject to the same kind of deterioration that plagued driver surrounds? I don't think Sonex presents a problem, but I'm still looking at other types of foam - maybe something that could be shaped or cut into the proper configuration.

Regarding the woofer design on the MGC-1, I've always wondered about the reasoning behind those twin 8" drivers...actually, they would probably give the MGC-1 more of an "acceptability factor" among that certain group of audiophiles who disregard big woofers out of hand!

[kkantor]

I still have a pair of MGC-1's in storage, and access to another pair. I haven't seen any signs of foam decay. That problem that plagued older foam surrounds was pretty much solved by the time these were built. And it had to do with the flexibility, heat compression, etc. I think Sonex, and related products, are pretty good these days. I'm assuming you aren't in the tropics... or leaving the speakers outdoors under an ozone hole...

Maybe the best way to experiment would be to get some thick, >open cell< foam from a local foam shop. Something they haven't cut with a hot wire, which will close the surface cells and impair sound absorption. It sure would be cheaper than acoustically spec'd stuff, and will probably work well enough to start. Once you got a shape you liked, you could invest in some Scott Foam or Sonex, etc.

-k

[Guest]

Mr. Kantor,

I just have a curiosity question regarding the camaraderie or competition between speaker designers of the 70s. Forgive my failing memory, but where the AR MGC-1 and Symdex Sigma speakers contemporaries, or were you first?

If they were available at the same time, did you and Kevin Voecks ever compare notes (wasn't he down the street in Worcester at the time?) on psychoacoustics and the like? Or would that have been a major no-no?

Unfortunately, the only time I've ever seen a pair of MGC-1s was in a Norwood office when I stopped by to pick-up some replacement drivers and I'm not even certain that was an AR office (could have been whatever AB Tech was then). They were certainly gorgeous but I didn't get to hear them.

I really liked the Symdex Sigmas (paired with AR3a woofers), but was far less impressed with anything I ever heard from Snell. The Mirage line he worked on were, well, disappointing at best to my ear.

I guess the next question would be do you pay attention to the work of other designers or just avoid "too much information noise?"

Bret