Adventures in Room Equalization Part II (2 Viewers)

[Greg Monfort]

>Here's what I'm curious about. For purposes of discussion suppose we are in a home theater with a really bad echo that even I can hear . (You know like in a large bathroom.) Apparently our hearing is smart enough to differeniate between the direct and indirect sound in this case. So in this extreme case if I didn't like what it sounded like obviously I would change the room treatment to kill the echo not try to change the frequency response of the speakers to fix the sound.
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Correct, though I've known 'pros' that try EQ anyway.....
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>In rooms with less extreme reflections (echos) aren't we doing basically what I described above, unnecessarily changing the speaker's response, when we attempt room equalization above bass frequencies?
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Yep, see my previous two responses. In our efficient hearing BW we should be using acoustic solutions for acoustic problems IMO. The same holds true when trying to correct the speaker's acoustic response in this BW. IOW, XO time alignment or phase coherent designs, damping material or horn baffle to control dispersion, etc..
GM

 

[Larry Chanin]

So... would you like to buy that Ultra-Curve Pro from me that you suggested that I buy?
Just kidding!! I couldn't resist.
Thanks again for your input.

 

[Greg Monfort]

>So... would you like to buy that Ultra-Curve Pro from me that you suggested that I buy? Just kidding!! I couldn't resist. Thanks again for your input.
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Yeah, well, not realizing what type speakers you had, and your unwillingness to revamp the room, what other suggestions for a cure to your problems did I have?

If it did real time on the fly corrections.... I didn't know that it didn't when I recommended it. The subject had come up previously on another list and someone said it did. Sorry about that. The info on the net is worth what you pay for it sometimes.

You're welcome, I think.

GM

 

[Larry Chanin]

Greg:
No, I really was kidding. I'm sincerely glad I took your advice. At only $200 it was a great value and learning tool. I'm having a great time learning about "the good, the bad, and the ugly" of equalization with a hands on approach instead of just theorizing. I think this knowledge is going to pay off big time in my next home theater. At the minimum beyond learning I'll be able to use it to adjust the bass.
But, I had you going didn't I?
Maybe we're talking about different things, but the Ultra-Curve does do auto corrections on the fly just as you said. You just turn on the auto correct feature and it cranks up the test signals and sets all 31 frequencies of the graphic equalizer on both channels untouched by human hands. However, its only an inexpensive gadget and so it may add up to 16 dB boosts if you let it. I prefer to manually adjust everything with the help of the ETF5 computer program.
I know that you recommended not equalizing my main speakers, but I was wondering if you see any value in attempting to tweak the mid-range speaker equalization by performing close in microphone measurements?
Thanks.

 

[Greg Monfort]

>Maybe we're talking about different things,
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We are. I'm talking about its inability to adjust equalization while in the RTA mode.
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>I know that you recommended not equalizing my main speakers, but I was wondering if you see any value in attempting to tweak the mid-range speaker equalization by performing close in microphone measurements?
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Not if I understand Polk's scheme. By using L-R phase cancellation to firm up imaging, shifting them could really make a mess of it. Of course you can always play with them to see if it helps in-room. Like you said, any info to add to your knowledge base will help if/when you do a much less compromised room, though these speakers really aren't well suited for HT if a CC is used.

GM

 

[Larry Chanin]

Greg:
Thanks. You never fail to have insights to stuff that I've been oblivious to, but now that you bring it up I clearly see your point.
Prompted by your comment I sent an email to Polk Audio asking for their take on the issue of using SDA speakers for home theater and multichannel music.
As you probably know the SDAs, as the name Stereo Dimensional Array suggests, were originally designed in the '80s for stereo applications. They were eventually discontinued, but there is a small group of very loyal SDA enthusiasts who love them. I think its fair to say that while a few of us use them for home theater, most of these guys are using these vintage speakers mainly for music.
However, more recently in the '90s Polk Audio briefly resurrected the SDA design in a high-end home theater application, the Signature Reference Theater System (SRT). You may recall that in Part I of this thread I mentioned these frightening speakers with ear-bleeding SPLs. Here’s a link to, believe it or not, the smaller version that Cinepro was marketing
Link Removed. Notice the two center channel arrays designed to work with the huge SDA type mains.
While I'm waiting for Polk Audio's response I'll try experimenting with the center channel turned off for movies and music. From previous brief experiments with music I'm pretty sure that sitting in the sweet spot with the center channel turned off yields better sound, but I can't recall specifically hearing an improvement in imaging. For movies with dialog being so important and the likelihood of having guests sitting off-center, turning off the center channel will probably produce bigger problems than the degradation of stereo imaging. Well, I guess we can add yet an other issue in my sonically compromised room.
Thanks again.
Larry

 

[Greg Monfort]

>Thanks. You never fail to have insights to stuff that I've been oblivious to, but now that you bring it up I clearly see your point.
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My pleasure! That's what wasting too many manhours experimenting taught me because I couldn't do the math that explains it in short order. :frowning: Even then, it wasn't until I got on the net and found folks willing to help me tie portions of it together since some of it is counter-intuitive (at least to me).
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>However, more recently in the '90s Polk Audio briefly resurrected the SDA design in a high-end home theater application, the Signature Reference Theater System (SRT).
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Yeah, I was underwhelmed with it overall. You're right though, it could play loud enough for any HT.
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> You may recall that in Part I of this thread I mentioned these frightening speakers with ear-bleeding SPLs. Here’s a link to, believe it or not, the smaller version that Cinepro was marketing
The Cinepro Forcefield version of the Polk Audio SRT. Notice the two center channel arrays designed to work with the huge SDA type mains.
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Don't recall these, only seen their amp. Just looking at the specs though, I doubt I would like these either.
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>While I'm waiting for Polk Audio's response I'll try experimenting with the center channel turned off for movies and music. From previous brief experiments with music I'm pretty sure that sitting in the sweet spot with the center channel turned off yields better sound, but I can't recall specifically hearing an improvement in imaging. For movies with dialog being so important and the likelihood of having guests sitting off-center, turning off the center channel will probably produce bigger problems than the degradation of stereo imaging. Well, I guess we can add yet an other issue in my sonically compromised room.
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Note that I said in a more acoustically friendly room, i.e. where the speakers can be set well away from boundaries (or the boundaries are highly damped) and toe'd in. In the present room, I'm sure that a CC would be essential, with it time delayed WRT the mains.
GM

 

[Larry Chanin]

Hi Greg:

In response to your comments regarding the SDA speakers weren't well suited to home theater with center channels speakers I said:

While I'm waiting for Polk Audio's response I'll try experimenting with the center channel turned off for movies and music. From previous brief experiments with music I'm pretty sure that sitting in the sweet spot with the center channel turned off yields better sound, but I can't recall specifically hearing an improvement in imaging.

I went back and tried experimenting again with multichannel music. Now that I'm consciously listening for it, I now realize that the main reason it "sounded better" before was due to the more precise imaging.

I’m using the Bucky Pizzarelli Swing Live DVD Audio hybrid disc in a standard DVD video player. This disc has three versions; 2-channel, 4-channel, and 6-channel tracks. My standard DVD player can play the 2 and 4 channel versions, and my surround processor can create 8 channels if I wish.

This is a wonderful disc. The jazz combo is comprised of five instruments. When using 2-channels the instruments can be clearly heard accurately positioned across the full width of the room in their respective positions. Even when playing solo, the instrument is heard coming from its proper position, i.e., vibes far left, clarinet right, etc. When the center channel speaker is on it still sounds great, but the instruments are sort of compressed across a narrower sound stage. On solos it sounds like each instrument is playing from the center instead of its proper position.

Larry

 

[Greg Monfort]

Yep, as it should. The fact that you get good imaging with speakers ~flush mounted in a 'wall' punctuated with cavities, and pointed straight ahead no less, is testament to the success of Polk's phase cancelling scheme. Frankly, I'm a bit surprised they work this well in such an acoustically hostile environment.
Now just imagine what they're capable of in an optimized room/position, with another pair for the surrounds.
In another thread it's being extolled that without a CC to 'anchor' the dialog to the screen only the 'sweet spot' will have this. I read this as an admission that their speakers don't image very well, or at least in the confines of a typical HT layout.
Anyway, humans are very visual and will place a voice with a face if the image is anywhere on the screen unless a conscious effort is made to pinpoint it. Where you run into trouble is with a relatively small screen with drivers acoustically not far enough away to be outside the viewing area or acoustically too far apart for the viewing distance and/or the speaker's polar response. A CC is a must in these situations.
GM

 

[Larry Chanin]

Greg:
I've done some more critical listening and I now realize that I was misinterpreting what was going on. The Polks are performing quite well.
In my previous posting I thought the use of the center channel was hurting the imaging. Unknowingly to me at the time when the DVD starts it defaults to the 2-channel mix. So what I was hearing when I turned on the center channel was my surround processor synthesizing a multichannel mix from two channels.
When I manually selected 5.1 on the DVD (which is really a 4-channel mix, the mains and the surrounds with no center) the imaging was just as defined as the pure 2-channel mix, except now I had additional rear channel crowd noises, etc. This of course didn't prove anything about whether a center channel hurts imaging on an SDA speaker because the studio consciously left the center out of the mix.
So to better answer the question I pulled out my favorite multichannel music, the Roy Orbison Black & White Night DVD. This was a true 5.1 mix with center channel. The best listening location is in the front in the sweet spot. After turning the center on and off many times I was able to conclude that I could hear no perceptible lose of imaging. Dispite the fact that Roy's powerful voice was coming from the center as intended, I could distinctly hear the lead guitar coming from the far left just as well with or without the center. The only difference that I could hear was the slight decrease in sound level as the center was turned off.
I hope you can see that I'm not one of those guys who just has to defend his equipment regardless of the facts, because its obvious in my previous posting I was quite willing to admit compromised imaging when I didn't know what I was listening to.
SO I'm going to take imaging off my list of compromised sonics, this is clearly the SDA's long suit, especially in compromised locations.
Larry

 

[Greg Monfort]

>The Polks are performing quite well.
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If they are capable of ~completely cancelling out the CC's gain as you imply, then this is an understatement by at least an order of magnitude.
I thought I understood the concept, but I guess not since it wouldn't be capable of this. It makes me wonder why it's no longer available as it would be a boon for HT.
Oh, wait, silly me, then they couldn't sell as many speakers.
GM

 

[Larry Chanin]

Greg:

I don't know about completely canceling out the center channel gain, all I can say is my ears can't pickup whatever cancellation that is occurring.

Perhaps just as the human ear can differentiate between echos from direct sounds, and one person's voice in a crowd, it can differentiate between direct sounds coming from speakers widely spaced apart.

With regard to why Polk Audio phased them out (pardon the pun), as you suggested there's more money to be made by selling to the mass market and it costs more to add an extra set of SDA drivers.

Nevertheless, the application of electronic interaural crosstalk cancellation still survives in Carver's Sonic Holography and Lexicon's Panorama effect. Needless to say these processors use center channel speakers.

Larry

 

[Greg Monfort]

If you can't tell when the CC is turned on when its level is properly set, especially when sitting off axis, then they're cancelling all its gain.

Does Carver still make the holographic preamp? I got one early on and it was like B*** 901s, initially really neat, but rapidly became irritating. I swapped it for a C2, which I'm still using. Haven't heard Lexicon's version.

GM

 

[Larry Chanin]

Quote:

My Lexicon MC-1 has the Panorama effect, but I've never used it due to "duelling" interaural crosstalk approaches. I asked both the Lexicon and SDA enthusiasts as to what I should do. Guess what? The Lex folks suggested that I disconnect the speaker interconnect and the SDA folks suggested that I not use the Panorama effect because its "sweet spot" was smaller than the SDAs. Being lazy I chose the later approach. :b
Larry

 

[Larry Chanin]

Quote:

 

[Greg Monfort]

>So could tell whether it was turned on or off, I just couldn't hear any degradation in imaging.
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I guess I didn't scan past the "After turning the center on and off many times I was able to conclude that I could hear no perceptible lose of imaging." :frowning: Anyway, to my way of thinking, if you can tell if it's on or off there's a difference in imaging since some of the center soundstaging has to collapse for an audible change in amplitude to occur. So based on this, IMO a CC helps at least a little.
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>Below is my email to Polk Audio and Matthew Polk's response. Talk about great customer responsiveness! I only sent this Friday before the Labor Day holiday and here's a response from the CEO!!
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Yeah, this is pretty awesome in today's world of automated communications and compartmentalized organization. I'm just glad he didn't make a liar out of me and my assumptions, though I felt I was on solid ground, or at least as solid as a phantom image would allow.
Since I just use stereo speakers with limited off axis response, DVDs with the new DD 2.0 audio give a really good phantom CC and far field surround effects, so I hope they add this to all future DVDs until something better gets developed.
I sure would like to get a wiring diagram of the SDAs. Do you have one or think Polk will send you one, with a dimensioned driver layout? I'd sure like to experiment with the design.
GM

 

[Larry Chanin]

Hi Greg:
Thanks for your interest. I and a small group of SDA enthusiasts would be very interested in your experiments.
Here's a picture of the SRS 1.2, the largest of the original release of SDA type speakers. The schematic is included.
Larry

 

[Larry Chanin]

Hi Greg:
If it helps, I also found a schematic for my Polk Audio SDA-1C. The 1C is the third refinement of the version 1. As you can see the schematic dates back to 1987.
Cheers,
Larry