Scope theater redesign - please help with two key decisions - Page 2

Mark, I start with "A".
Center channel not withstanding, the sound stage can collapse when the speakers are too far apart. The depth and width of the sound stage is very much affected by the design of the specific speaker and the acoustic treatments used (as well as the geometry of the seating in relation to the speakers). Sucking out the side wall reflections can kill a sound stage.

A point to remember is (in residential sized rooms) as the speakers move further apart, they get closer to the side walls. The impact of wall proximity can be very significant and a contributor to sound stage failings.

If the speakers are on stands behind the screen you have the advantage of pushing, pulling and twisting the speakers after construction. If you're using a true baffle wall, you've got to start with full polar radiation plots of the speakers ... this is a real engineering problem because those speakers ain't moving once installed.

Lobing may or may not be a problem depending on the speakers being used. Elevating the speakers above the ears, above the ears and aiming downward, may or may not place one or more rows (seats) in a problem area. (An advantage with raising the speakers and aiming downward into the seating area is it will reduce the SPL delta between rows.) Elevating speakers above ear level (whose ears, which rows) will not inherently exacerbate lobing issues ... it is speaker dependent. On the other hand, lobing effects are generally not realized by casual listeners who are seated ... moving around the room can make lobing artifacts very apparent. Excellent speaker designs are making lobing less and less an issue ... in many cases, much less an issue than the difference in the high frequencies between the first, second, third, etc. rows of seats ... particularly in small residential rooms ... not a problem in two channel since two channel is so focused on one and only one seat.

The two channel boys have it easy. They can get by with horrid speaker designs (from ma lobing perspective) due to two inherent factors in 2-channel "audiophilia" rooms: (1) the sound has to be good in one, and only one spot approximately the size of a 10" cube which is a bunch easier to do than good sound in 16 seats; and, (2) 2-channel is so full of it's own inherent distortions from reality ... (well, I won't go there again).

Masking panels - The impact of the masking panels when closed to 1.78:1 will vary from non-audible to a higher roll off in the high frequency range. The non-impact could be a result of really good masking panels or the fact the roll off is in a frequency range we adults tend to have lower sensitivity. The audibility issue would largely stem from a timbre mismatch between the center and L/R speakers. This, however, can be easily compensated for by an EQ device which allow for multiple profiles to be saved and recalled.

A very detailed and awesome response. Thank you

I agree. Thank you Dennis for that great explanation. Nothing like having a real expert put in his two cents worth. It has motivated me to play around a bit with my speaker placement, which are presently located in the front left and right corners of the room, just outside the 2.35 screen width. My question for Dennis - is that a bad location?

Speakers in corners ... never a good idea. If you cross overs are at 80 hz, they have to be further than 3.5 feet from any wall ... in the absence of specific treatments to resolve the SBIR issue.

Our mains are just outside of a 2.35 retractable AT screen and are toed in about 30 degrees. The drivers are just over 1' from the side walls and 3' from the front wall. They are Definitive Tech BP7000's. The center speaker is a DT CLR 3000 that's about 2/3 up from the bottom of the screen and angled down slightly straight at the seating areas. It works fine for our set up. Due to the entertainment towers and DLP rear projection set up behind the retractable, this is the best we can do. It may not be optimum, however the results are 100% satisfactory to us.

I do wonder if possible future adoption of "wides" could impact this discussion on the proper placement of front soundstage speakers. I could easily imagine an argument being made for main L/R at +/- 22.5 deg and then "wides" being placed at +/- 30-40 deg, instead of the equilateral +/- 30 deg spacing that admittedly arose from more music driven heritage (and my own preference stems from primarily music listening in large enough rooms to avoid boundary issues) and audyssey style +/- 60 deg wides?

Would we ever see a processor allow enough flexibility to use 45 deg spaced speakers for HT with the wider ones being wides, and 60 deg spaced speakers for multichannel music with the three inner ones (center and 45 deg spaced) being used for extracted center/panned center sounds?

How many then could we imagine across the front? Seven? Probably not for many many years if ever.

All the L R positioning aside. The AT screen with the center behind the screen as opposed to center below or above the screen goes a LONG LONG way. One of the single best upgrades to grace my theater.

zamboniman,

I am convinced that AT Screen with Center behind the screen is what I will do.
Did you use the same speaker for L,R and Center?

Thanks

At first no but eventually yes.. when I changed to AT I just moved my "traditional" horizontal center channel. At the time I had a Klipsch RB75 for LR and RC7 for C. I eventually upgraded to Seaton Sound Catalysts for all 3 being the same.

Interesting. Thinking back to my very first system, the LCR array was 3 identical JBLs bookshelves. So I've never had an "add on" centre speaker. And I got the idea from a BOSE brochure of all places. They were promoting a 3 cube version of their infamous AM5 system. That, combined with a look behind the screen of a real cinema cemented the idea of 3 identical LCRs for me as the only way to do this. I am now onto my 7th set with my latest being 2 way actives.

Why are all the speaker manufacturers still making center channel?
Are they needed because most folks don't use AT screens or even projectors and center channels are optimized to do a decent job below or above the screen/TV?

I wouldn't say they are necessarily "optimized" to work above or below a TV or fixed projection screen, but simply that they "fit" above or below.

There are obviously examples of good designs where every attempt was made to minimize problems with the horizontal layout, usualy by using vertical HF orientation with low xo, and some going as far as exotic curved line arrays or curved planars. And there are many many examples of commercial offerings that simply put some drivers in a horizontally oriented enclosure using the same components and xo as their L/R model and call it a day. In fact, even from rather "reputable" companies you will find speakers that are meant to be used either vertical for L/R or horizontal for center, usually with some marketing blurb about the benefits of "identical" L/C/R. What a travesty.

Yes a Centre channel speaker is needed because the Centre speaker plays up to 90% of a film's soundtrack, making it the most important speaker.
Manufactures make dedicated Centre speakers and they also make "add ons". It typically the 'add on' units that don't match in as well or don't sound as good. Regardless if you have an AT screen, you still need a matching centre speaker.

Many manufacturers will make a center channel with a horizontal orientation ... to fit above or below a solid object (like a TV). The problem is no horizontal speaker can ever be timbre matched to it's "partner" L/R speakers in a vertical cabinet. There's a few laws of Physics standing in the way of that success.

Regardless of what a processor may be able to do with ambiance extraction, the sound stage creation is far more a function of the room's interaction to the speakers than the speaker angles.

High, wide, high and wide, and on and on has been with us for a long, long, long time in various forms. We've had the ability to do height since the 1970's. I've had a Yamaha DSP-1 since 1985. Yet today, we're just on the cusp of getting producers to mix to 7.1 (as opposed to re-mix).

I wouldn't advise holding your breath until something more than 7.1 is available as something more than a gimmick (or a reasonably serious attempt at it).

As Dennis says, the ONLY speaker that can create sound equal to a phantom is another identical speaker. I'm sure I read the difference between the phantom created by a pair of speakers Vs the sound from an identical "real speaker" is less than 2dB at about 2K.

Back to the placement discussion, I found these images of my first CIH system.

Not the positions of the L and R speakers. At the time (2006) it seemed a like a good thing as I was getting right into 2CH about then and would agree wider is certainly better for that. It was with video that I realized I had made the wrong choice for speaker placement.

So a redesign was in quick order.


I also played with lowering the screen and tilting the speakers up.

After that came the AT screen and rest is history as I now have what I believe to be the best of both being site lines to the screen and height of the speaker to deliver sound to the ears.

To be precise, that is not what Dennis said. Matching a phantom C with a real C speaker is not possible at all due to the combing in the phantom. Physics are at play there, too.


It has been my experience that three identical speakers can sound identical (as identical as a human could want, anyway), but I have also found cases where they do not sound identical due to environmental issues that differ between the speakers. So physics plays a role even when we start with identical speakers.

OTOH, I see no reason why a center speaker cannot sound "as identical as a human could want" to the L/R even if it has different physical arrangement of drivers. One of the things I like about my Aerials is that I can achieve that seamless matching of timbre across L/C/R. It requires EQ to get there, to be sure.

I'm putting up a non AT screen. Speakers will be below. I will have a center channel speaker (Paradigm CC-690). I will move the mains side to side until I find the best spots for both movies and stereo music. I will then locate them where I determine the best compromise position is for listening to both. I expect Audyssey XT32 on my AVR will deal with some placement issues. Does anyone have a problem with that?

I've yet to hear an identical LCR speaker setup that didn't have timber changes while panning across the speakers. Usually due to acoustic interactions with the room. i.e. closer to the walls for the LR.. They can be brought closer sounding still with EQ. That said I still firmly believe that identical LCR is much better than something different for a lot of reasons. My main point is that if you think the speakers will sound identical even having them all the same you're not being realistic.

And "timber" matched center channels and surrounds for that matter (even ones having the same drivers) are one of the biggest marketing farces out there by speaker companies.

Ha! If the "human" can hear the difference between $1 per foot cable and $1000 per foot cable, the difference green ink on the edge of a DVD/CD, you can certainly hear the difference in timbre. OTOH, having seen so many mismatched centers in rooms with lots of magic stuff (like cable lifters, etc.), maybe they can't.

I wouldn't exactly say it's a farce. Note that in my previous comments I did condemn many manufacturers for throwing drivers in a horizontal box and calling it a day. Others at least try to minimize dispersion and lobing issues.

That being said, many people do have to live with one horizontal design or another and if "timbre" matching at least provides for the same high frequency drivers and general crossover design to be used, that in itself is of some value and will at least be far superior to completely mismatched designs.

Maybe these folks are not listening through speakers, but through wallets. One could say it's all in their head.

However, let's assume some folks have high acuity of hearing. Put them in a perfect room with identical L/C/R speakers. Play the L, then play the C. They may well report they sound different, but only because it's true. HRTF makes it so. Now we can really say it's all in their head. In other words, just because someone says they hear a timbre mismatch in the speaker outputs does not mean it is so.

If centre is 0 degrees, at what angle does the effects of head related transfer function become apparent?

To whom? The person who can hear the effects of the green pen?

According to Fig 14/15 of this paper, there are visible response differences every 10 degrees away from 0 (straight ahead). This paper suggests that is about the minimum detectable.

Where can I get me one of these green pens? Does a red one work as well?

Obviously, there are many things which will affect the perceived timbre of L/C/R's. Among them is the simple fact they are placed differently with respect to the room's geometry as well as differences in height above the floor.

I disagree.. or maybe it's the definition of timbre matching... to me that means they should sound approximately the same.. however I've yet to stumble on any that do.. some "visually" do and that goes a long way.. Maybe there are some but I haven't heard them. In reality I've yet to see even 2 identical speakers placed within inches of each other have the same "timbre". A good exercise to try. Get a couple book shelves that are the same put them a couple feet apart and run some audio level setting pink noise through them toggling back and forth. This should also be easy to do with most modern surround sound receivers. It's an eye opening experience for many.

Can you hear green ink too?

NO..

I'm not treading in the snake oil noise here.. They usually sound obviously different. which is another reminder of just how important the room is on the sound you hear. A major part of the overall sonic experience is the room. It just kills me that people will throw hundred if not thousands of dollars and thing like new cables.. .or that shiny new AVR.. All while ignoring one of the most important items. Heck take the same single speaker if you want. Move it around the room just a foot or so at a time. The sound heard at the listening position will change dramatically.

Yes, the room will have in impact on the sound at listening position. I certainly agree. Some rooms will obviously be much worse than others. Dramatic changes only an inch or two apart? I think there are serious room issues.