Matched/Identical Center vs. 'Traditional' Horizontal Center - Issues & Preferences? - AVS Forum
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post #1 of 46 Old 07-07-2012, 12:09 PM - Thread Starter
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I'm at a point where I'm looking to re-do a number of items in my home theater - my 8 year old RP HDTV finally developed a major problem, so I'm now looking to rethink a lot of things (getting rid of the "entertainment center", upgrading my 10 year old AVR, etc.).

Part of this process is considering how all of this will work in my living room - I currently have a set of 5 Infinity SL-20s in a 5.0 setup, but they've never been well placed in the front. (Well, the back is kind of screwy too, but that's another post.) At one point, I had a dedicated Infinity horizontal center channel, but I was never happy with the sound (which is why I went out to eBay to complete my SL-20 set).

I'm not unhappy with the Infinitys, and I might keep them - but I'm also looking at the option to move to something else, possibly floorstanding/tower speakers as L/R. This brings me back to where I originally started with my old center channel - have they improved in terms of consistency between the main speakers, as well as off-center quality?

I'm also trying to consider how I'm going to make a new TV work - I'm leaning away from wall-mounting, so I haven't seen any built-in mounts on any furniture that lifts a 55" to 65" TV high enough to put a 15" inch tall speaker (my current SL-20s) under it without blocking it. I can get small floor stands, but then I can't really use part of the storage in the TV stand (since the speaker would be in front of the doors).

I guess I'm torn between what I know (fully matched speakers) and what would seem to fit best (horizontal center channel) in a new setup. I'd appreciate feedback from folks who've looked at this, and have thoughts on sound and configuration. Thanks.

You stole a TV from me! I saw it on TV!
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post #2 of 46 Old 07-07-2012, 03:27 PM
 
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Without writing a chapter from an acoustics text:
If you want accuracy of reproduction, you will use a matched (identical) speaker.
If you want aesthetics, use whatever fits or that "looks nice".

And anticipating the followup:
Yes, there IS a difference. Only you can decide, all things considered, if it is significant enough for you.
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post #3 of 46 Old 07-08-2012, 05:41 AM
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Quote:
Originally Posted by dragonfyr View Post

Without writing a chapter from an acoustics text:
If you want accuracy of reproduction, you will use a matched (identical) speaker.

Perhaps a pedantic point: I think you should use the best speaker for the application that is similar enough to the rest of the system as to not cause problems with matching. This leaves latitude for varying the speakers to consider where they are likely to be used.

There is a basic rule, which is that the acoustics of a speaker's location has a powerful effect on the speaker's sound. The speaker whose location is most likely to be most physically different from the rest iseems to be the center channel. (of course leaving out the subwoofer for obvious reasons).

It the center channel speaker's acoustical context is very similar to the rest, then your rule would seem to be a reasonable one.
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post #4 of 46 Old 07-08-2012, 06:42 AM
 
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Not sure what debate is really possible here.

Per the various surround standards guides, placement relationships of the front center, left and right speakers are well defined.

So are the optimal 'composition' of ALL 3 front speakers as quoted from The Recording Academy's Producers & Engineers Wing Recommendations For
Surround Sound Production
:

All main speakers should be identical, of the same brand and model. Only full range direct radiator speakers should be used; satellite and dipole speakers have no place in the professional mixing environment (see section 3-2). Mid-field monitoring is usually preferred for surround mixing. (Unlike nearfield monitors, mid-field monitors are designed to be used free-standing and not placed on top of a console meter bridge.) In the interest of uniform frequency response, all main speakers should be placed on speaker stands; the front speakers should not be placed on top of the console meter bridge. The use of movable speaker stands can be helpful if the rear speakers are to be shifted or angled differently from project to project because of genre-specific considerations (see section 3.3.1).

Now what others CHOOSE to do is up to them.
The main concern if one addressing such common application as 2 L&R speakers combined with a horizontal D'Appolito/MTM configured speaker featuring polar loving that exists in the form of vertical bands running from floor to ceiling as a result of the crossover region. Vertically oriented speakers at least have this polar lobing existent on a horizontal plan that is designed to be out of the listening axis window above or below head height.

Unfortunately, vertical polar lobing nulls running from floor to ceiling don't care about one's height and as such, impinge on a very real region of the 15-30 degree off center axis listening region. ()Folks might do well to remember just what the MTM configuration was intended to correct when Joseph D'Appolito introduced it - it was intended to correct for an upward ~15 degree polar lobing tilt, for which the additional "M" was introduced in an effort to counteract and balance this.

In any case, such a speaker combined with am "MT" configured vertically oriented L&R speaker will NOT exhibit similar polar dispersion nor timbral similarity.

So, to cut to the chase, not only does this industry sourced doc define this, but myriad other design industry guides do as well, as well as quotes from far too may prominent designers - the most prominent that I can cite being Russ Berger who is likewise very plain in his recommendation that the front speakers be identical - (with EVERY source recommending proper placement):

"The surround sound setup design is not all that different from a left/right setup. Considerations to keep in mind are: left to right symmetry, monitor placement, and mix position. I would suggest starting with identical monitors at ear level with minimal reflective surfaces between you and the speakers."
(from Room Tuning With Russ Berger by Rich Tozzoli, EQ, June 2006)

If desired, I'll let you guys debate Russ. biggrin.gif
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post #5 of 46 Old 07-08-2012, 06:52 AM
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Quote:
Originally Posted by rosenkavalier View Post

I'm at a point where I'm looking to re-do a number of items in my home theater - my 8 year old RP HDTV finally developed a major problem, so I'm now looking to rethink a lot of things (getting rid of the "entertainment center", upgrading my 10 year old AVR, etc.).
Part of this process is considering how all of this will work in my living room - I currently have a set of 5 Infinity SL-20s in a 5.0 setup, but they've never been well placed in the front. (Well, the back is kind of screwy too, but that's another post.) At one point, I had a dedicated Infinity horizontal center channel, but I was never happy with the sound (which is why I went out to eBay to complete my SL-20 set).
I'm not unhappy with the Infinitys, and I might keep them - but I'm also looking at the option to move to something else, possibly floorstanding/tower speakers as L/R. This brings me back to where I originally started with my old center channel - have they improved in terms of consistency between the main speakers, as well as off-center quality?
I'm also trying to consider how I'm going to make a new TV work - I'm leaning away from wall-mounting, so I haven't seen any built-in mounts on any furniture that lifts a 55" to 65" TV high enough to put a 15" inch tall speaker (my current SL-20s) under it without blocking it. I can get small floor stands, but then I can't really use part of the storage in the TV stand (since the speaker would be in front of the doors).
I guess I'm torn between what I know (fully matched speakers) and what would seem to fit best (horizontal center channel) in a new setup. I'd appreciate feedback from folks who've looked at this, and have thoughts on sound and configuration. Thanks.

Soffet-mounting is a strategy that generally provides all of the speakers with a consistent acoustical environment, and seems to work well with any reasonable number of identical speakers. In these days of obsession with ear-level mounting of everything, this is heresy but it can work amazingly well and solves a number of other problems. BTW if speakers aren't floor-standing, whether they are on their sides or standing up can have manageable sonic importance.

No matter what you do, some location-dependent spectral tailoring will probably be required to optimize things. Modern AVRs generally provide the means to do this. These days, even entry-level AVRs such as the Yamaha RXV 371 have 3 independent multiband equalizers for mains, center, and surrounds.
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post #6 of 46 Old 07-08-2012, 07:03 AM
 
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I will see you and raise you regarding your point!!!!biggrin.gif

Properly performed soffit ('flush/in wall'...) mounting (assuming proper stable mounting and mechanical decoupling procedures are followed, etc.) is the SINGLE BIGGEST improvement that can be made with regard to speaker-room interaction PERIOD. (And any spatial LF increase due to spatial loading is easily compensated...)

We have absolutely NO disagreement there.

I am absolutely amazed that with folks building dedicated rooms and given the opportunity to do this properly that this is not the number one first improvement they make!

Just be sure to do it properly, as I am just as amazed to see SO many who DO try this bastardize the attempt so badly, and that is simply heartbreaking! Its not difficult, but you DO have to follow best practices. An excellent place to start is to refer to the tutorial/learning center resources at the Genelec website.


Oh! And let me add one important addendum and disclaimer!!!
"In wall" speakers are NOT, either generally or necessarily: the same thing as properly designed and mounted 'soffit mounted' speakers!!!!!! In fact, if I were to make a generalization, they unfortunately SELDOM correlate to properly designed and mounted 'soffit mounted' speakers.
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post #7 of 46 Old 07-11-2012, 11:52 PM - Thread Starter
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Thank you for all of the responses - I have more to think about as I plan my upgrades.

You stole a TV from me! I saw it on TV!
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post #8 of 46 Old 07-16-2012, 04:20 AM
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I'm in the middle of upgrading also and have been listening to many systems (roughly 60% in homes, 40% in showrooms) for the last 5 weeks. I'd never heard of or considered this idea of three identical speakers for L/R/C when I started so I wasn't looking for it. (It doesn't get much air time in the forums.) After listening to these systems I now think it's something worth striving for - assuming of course your space/setup will allow for it acoustically ... bowing to the expertise of others in this forum/thread.

I first began to notice a trend of HT setups with projectors/screens often sounding better. Then I noticed that it was, more specifically, identical vertical front 3 speaker sets that was catching my attention. I also saw two set-ups with HDTV's (one wall mounted, one on a fairly elegant "stand") that had the same aural qualities, and that I'm now considering for my HT upgrade. In both cases the bottom of the TV was only around 33" from the ground. One setup had bookshelf speakers (Ascend Sierra 1's) on short wood stands, angled up just slightly. The other used a short-ish, 31" tower (Gallo Classico CL-3's) as the front three.

Guess I'm posting because both left such an impression - they sounded exceptional (even when compared against systems costing several times more) and, they looked great. Well ... at least to me ; )

Good luck!
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post #9 of 46 Old 07-16-2012, 08:17 AM
 
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Quote:
Originally Posted by rosenkavalier View Post

I guess I'm torn between what I know (fully matched speakers) and what would seem to fit best (horizontal center channel) in a new setup. I'd appreciate feedback from folks who've looked at this, and have thoughts on sound and configuration. Thanks.
Whatever you do, make sure you don't do this: http://i148.photobucket.com/albums/s23/darqueknight88/AudioSystems/HTelectronics.jpg
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post #10 of 46 Old 07-17-2012, 10:58 AM
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Quote:
Originally Posted by sdg4vfx View Post

I'm in the middle of upgrading also and have been listening to many systems (roughly 60% in homes, 40% in showrooms) for the last 5 weeks. I'd never heard of or considered this idea of three identical speakers for L/R/C when I started so I wasn't looking for it. (It doesn't get much air time in the forums.) After listening to these systems I now think it's something worth striving for - assuming of course your space/setup will allow for it acoustically ... bowing to the expertise of others in this forum/thread.
I first began to notice a trend of HT setups with projectors/screens often sounding better. Then I noticed that it was, more specifically, identical vertical front 3 speaker sets that was catching my attention. I also saw two set-ups with HDTV's (one wall mounted, one on a fairly elegant "stand") that had the same aural qualities, and that I'm now considering for my HT upgrade. In both cases the bottom of the TV was only around 33" from the ground. One setup had bookshelf speakers (Ascend Sierra 1's) on short wood stands, angled up just slightly. The other used a short-ish, 31" tower (Gallo Classico CL-3's) as the front three.
Guess I'm posting because both left such an impression - they sounded exceptional (even when compared against systems costing several times more) and, they looked great. Well ... at least to me ; )
Good luck!

My old home theatre equipment has been collecting dust since I moved a few years back but am just about 3/4 of they way to finishing my new basement theatre. All these years I have been waiting for the day I could resurrect my system with front L-C-R floor standing 3 way speakers. I have these Canadian made Post Audio DM16 speakers I bought way back in '92 for like $600. Some may scoff (and I know its not high end by any means) but these speakers pound. They are your real, old school 3 way speakers. Two 12's, a big mid and a tweeter. All these years I kept an eye out for another pair and about a year or two ago I found some locally and I scooped them up. When the new theatre fires up I'll have these DM16's powering my L-C-R and I plan to have the center standing upright just like the L & R. I plan to wall mount the 60" panel directly above the center. Screen height will be a little bit higher than ideal but I'll be sitting 15' back plus I'll try to look for a high couch. The extra speaker I'll keep for spare parts in case something goes. I still have a good 15" PSB subwoofer but with those 3 towers of power I probably won't even need it. If you can get away with identical LCR's go for it! In some programming there is so much action loaded into the center channel. Subwoofers are nice but I've always admired the sound of a full range 3-way speaker and when I say "3-way" I mean your old school woofer, mid, and tweet setup, not these 3 way floor standing speakers with a tweeter and 5" mid and 2 or 3 6" "woofers".
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post #11 of 46 Old 08-26-2012, 02:48 PM
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Quote:
Originally Posted by diomania View Post

Whatever you do, make sure you don't do this: http://i148.photobucket.com/albums/s23/darqueknight88/AudioSystems/HTelectronics.jpg

What, specifically, is wrong with the setup you linked to?
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post #12 of 46 Old 08-28-2012, 03:09 PM
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Quote:
Originally Posted by DarqueKnight View Post

What, specifically, is wrong with the setup you linked to?

Not the original poster but it looks like there may be a sound bar on top of the cabinet and 2 center speakers inside it. No way for 2 or more physically offset speakers to avoid having frequency response cancellations and reinformements that change with minor changes in the listener's position (if you do it just right you might be able to get the Doobies' Listen to the Music type phasing). The open doors will reflect sound and generally wreak havoc with frequency response (depending on what they're made of. Slotted/mesh screens might have less deleterious effect. The dueling centers inside the cab are themselves designed to maximize frequency response anomalies when one moves one's head . So each has FR problems and when you add them together the FR rpoblems mulitply.
That's all I see quickly..
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post #13 of 46 Old 08-28-2012, 07:31 PM
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Quote:
Originally Posted by arnyk View Post


Perhaps a pedantic point: I think you should use the best speaker for the application that is similar enough to the rest of the system as to not cause problems with matching. This leaves latitude for varying the speakers to consider where they are likely to be used.
There is a basic rule, which is that the acoustics of a speaker's location has a powerful effect on the speaker's sound. The speaker whose location is most likely to be most physically different from the rest iseems to be the center channel. (of course leaving out the subwoofer for obvious reasons).
It the center channel speaker's acoustical context is very similar to the rest, then your rule would seem to be a reasonable one.

Aren't these different variables for the same choice?  The acoustics of the speaker's location is different for every speaker although the center is more likely to be mid-wall than any of the others.  But how does that change the basic goal that all should sound identical?  It is more likely that an identical speaker should sound more similar to the others than a different speaker will, regardless of position.


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post #14 of 46 Old 08-29-2012, 06:37 AM
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Quote:
Originally Posted by dragonfyr View Post

Not sure what debate is really possible here.
Per the various surround standards guides, placement relationships of the front center, left and right speakers are well defined.
So are the optimal 'composition' of ALL 3 front speakers as quoted from The Recording Academy's Producers & Engineers Wing Recommendations For
Surround Sound Production
:
All main speakers should be identical, of the same brand and model. Only full range direct radiator speakers should be used; satellite and dipole speakers have no place in the professional mixing environment (see section 3-2). Mid-field monitoring is usually preferred for surround mixing. (Unlike nearfield monitors, mid-field monitors are designed to be used free-standing and not placed on top of a console meter bridge.) In the interest of uniform frequency response, all main speakers should be placed on speaker stands; the front speakers should not be placed on top of the console meter bridge. The use of movable speaker stands can be helpful if the rear speakers are to be shifted or angled differently from project to project because of genre-specific considerations (see section 3.3.1).
Now what others CHOOSE to do is up to them.

Exactly. As a practical matter not that many audiophiles come within a country mile of following these instructions. The presence of special models of center channel speakers which is the market is stuffed with exactly breaks this rule.

Furthermore, anybody who uses 3 identical speakers stretched across the front is very likely to have a center channel that sounds significantly different from the rest because of the differences in its acoustical environment from that of the mains.

Unless the home user duplicates the exact makes and models of speakers and the physical location of the speakers used by the mixers, he is pretty much on his own. Since professional mixing environments tend to be individual and different, trying to do so is mission impossible.


I also find the requirement of direct radiator speakers full-range speakers to be curious and biased to the point of being obsessive. To be relevant a speaker needs to have pretty flat response down to 30 Hz at the least, and 20 Hz to be accurate. Few professional monitor speakers actually in use do this. While fully-horn loaded speakers are currently somewhat uncommon in the realm of professional monitors, direct radiator tweeters mounted in wave guides are common enough and violate the spirit of the directive.



Note that the above picture clearly shows a waveguide-loaded tweeter. It is a picture of one of the most widely used and highly respected studio monitors (Mackie HR824) around, and one that shows up in pictures of the systems of some highly-respected and quality-conscious AVS contributors.

And are they full range? Extant independent measurements show that they are pretty clean down to 50 Hz, but have rapidly rising distortion below that. So clean response down to 32 Hz, let alone much below 50 Hz is mission impossible. BTW I'm not unhappy with HR 824s at all - I'd love to be able to afford a pair or 5 or 7 or 9 or 11. I'm just using them to make a point because they are widely used and well-documented. Furthermore they strongly resemble widely-used and respected European products, and there is a high quality Chinese clone of them as well.

So, do we do what they say, or do we do what they do? ;-)
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post #15 of 46 Old 08-29-2012, 07:02 AM
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Quote:
Originally Posted by DarqueKnight View Post

What, specifically, is wrong with the setup you linked to?

Is that or is that not one or more center channel speaker(s) that varies considerably from the mains, to say the very least?
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post #16 of 46 Old 08-29-2012, 09:10 AM
 
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Quote:
Originally Posted by DarqueKnight View Post

What, specifically, is wrong with the setup you linked to?
Acoustic lobing. The setup I linked to is your own setup in which case, you should've asked, "What specifically is wrong with my setup?".
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post #17 of 46 Old 08-30-2012, 11:34 AM
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Quote:
Originally Posted by DarqueKnight View Post

What, specifically, is wrong with the setup you linked to?
Quote:
Originally Posted by diomania View Post

Acoustic lobing. The setup I linked to is your own setup in which case, you should've asked, "What specifically is wrong with my setup?".

I did recognize my own HT equipment. I also think that other readers would have seen my screen name in the link and surmised that the picture was my setup. It actually would have been more correct to ask you "What specifically do you think is wrong with my setup?".

Rather than saying "don't do this or that", a fairly detailed answer citing potential performance deficiencies would have been more helpful to the OP and other readers. Something similar to JHAz's comments was what I had in mind:
Quote:
Originally Posted by JHAz View Post

Not the original poster but it looks like there may be a sound bar on top of the cabinet and 2 center speakers inside it. No way for 2 or more physically offset speakers to avoid having frequency response cancellations and reinformements that change with minor changes in the listener's position (if you do it just right you might be able to get the Doobies' Listen to the Music type phasing). The open doors will reflect sound and generally wreak havoc with frequency response (depending on what they're made of. Slotted/mesh screens might have less deleterious effect. The dueling centers inside the cab are themselves designed to maximize frequency response anomalies when one moves one's head . So each has FR problems and when you add them together the FR rpoblems mulitply.
That's all I see quickly..

Thanks for your insights. That is not a sound bar on top of the cabinet. It is the base of the plasma television. The doors are metal mesh and are closed in normal operation. They were open for photographing the gear. I am attaching a better picture of the system in operation.

The dual MTM centers are Polk Audio LSi9 bookshelf speakers laid on their sides and angled up 5 degrees. They are a fairly close timbre match for the Polk Audio SDA SRS front speakers. A single center channel speaker was not a close enough match in sonic weight to the large front speakers. Power amplification is provided by a trio of Adcom GFA-5500's, one each for the dual centers, front speakers and surround speakers.


Quote:
Originally Posted by arnyk View Post

Is that or is that not one or more center channel speaker(s) that varies considerably from the mains, to say the very least?

Yes. See my response to JHAz above for details. I once tried three identical speakers in the front stage. That provided a less cohesive front stage than the arrangement I am currently using. Your comment quoted below seems to indicate that you understand that three identical speakers across the front might not be optimal for every environment and personal listening preference.
Quote:
Originally Posted by arnyk View Post

Furthermore, anybody who uses 3 identical speakers stretched across the front is very likely to have a center channel that sounds significantly different from the rest because of the differences in its acoustical environment from that of the mains.
Quote:
Originally Posted by diomania View Post

Acoustic lobing.

Please elaborate on the sonic detriments you think occur in my HT system when listening to the following scenes from the Blu-ray edition of "Terminator 2: Judgment Day":

1. Linda Hamilton's opening monologue where she discusses the aftermath of the nuclear strike by Skynet. I perceive her voice as crystal clear with excellent articulation and sonic weight.

2. Chapter 6: The scene begins with a police car entering at the right and moving to the left. The car engine and front tire sounds begin at the right speaker, move to the center and end at the left speaker. The solid "thump" as the police officer closes the car door, the clear "klop-klop" sounds as he walks to the front door and the clear dialog are very engaging.


The sound of my HT system is accurate enough that I, and others, have been deceived into perceiving the soundtrack effects of doorbells, distant door knocks and off-camera telephone rings as the real thing actually occurring in my home.

I like what I am hearing now, but I realize there is always room for improvement. What suggestions can you offer for improving sound performance in my HT setup. I expect that such suggestions would be generally applicable to the issues discussed by the OP.
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post #18 of 46 Old 08-30-2012, 12:19 PM
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Quote:
Originally Posted by arnyk View Post

Perhaps a pedantic point: I think you should use the best speaker for the application that is similar enough to the rest of the system as to not cause problems with matching. ...It the center channel speaker's acoustical context is very similar to the rest, then your rule would seem to be a reasonable one.

And if it's not... like when watching a movie?

I tried same L/C/R, and the center location was an obvious issue due to use of full BSC in my L/R design. This was my first DIY project and I was astounded how obvious this problem was, even with the speaker pulled out and vertical.
>> identical L/C/R require identical positioning within room or large variances will be heard.

My center is an MTM, sideways in it's permanent location, and I listen on-axis. Initially, it was a vertical design used sideway.(I have never heard lobing in my room, but that doesn't mean you might not.) Now it's a true horizontal design, voiced as a CC. I'm still on-axis, but I found dialog clarity greatly improved by the different voicing.
>> identical L/C/R require a common program, such as multichannel music, for best performance. In dialog-centric applications, a uniquely voiced CC is far superior for dialog clarity. Of course, Jom Marsh is one heck of a designer!

I'm with arnyk, my ears tell me conventional wisdom is missing something here.

HAve fun,
Frank

Links to referenced systems
L/R: http://www.htguide.com/forum/showthread.php4?t=13969
and
ON-wall CC: http://htguide.com/forum/showpost.php4?p=146516&postcount=30
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post #19 of 46 Old 08-30-2012, 11:19 PM
 
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Originally Posted by DarqueKnight View Post

Rather than saying "don't do this or that", a fairly detailed answer citing potential performance deficiencies would have been more helpful to the OP and other readers. Something similar to JHAz's comments was what I had in mind:
Not as helpful is what the OP and other readers told you?
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Please elaborate on the sonic detriments you think occur in my HT system when listening to the following scenes from the Blu-ray edition of "Terminator 2: Judgment Day":

1. Linda Hamilton's opening monologue where she discusses the aftermath of the nuclear strike by Skynet. I perceive her voice as crystal clear with excellent articulation and sonic weight.

2. Chapter 6: The scene begins with a police car entering at the right and moving to the left. The car engine and front tire sounds begin at the right speaker, move to the center and end at the left speaker. The solid "thump" as the police officer closes the car door, the clear "klop-klop" sounds as he walks to the front door and the clear dialog are very engaging.
No, lets not. It's got to be The Lord of the Rings: The Fellowship of the Ring, opening monologue by Cate Blanchett and the end just before the credit rolls when Elijah Wood saying what's to come. And perhaps one or two scenes in the middle. That T2 is too old of a movie to use for such thing even if it's BR release.
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The sound of my HT system is accurate enough
Accurate to what? And what method do you use to determine that?
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post #20 of 46 Old 08-31-2012, 12:21 AM
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Originally Posted by diomania View Post

Not as helpful is what the OP and other readers told you?

I must admit that you lost me here. The OP (original poster, i.e. thread author) has not told me anything. He has only made two comments in this thread, both of which were made before my first comment.
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Originally Posted by diomania View Post

No, lets not. It's got to be The Lord of the Rings: The Fellowship of the Ring, opening monologue by Cate Blanchett and the end just before the credit rolls when Elijah Wood saying what's to come. And perhaps one or two scenes in the middle. That T2 is too old of a movie to use for such thing even if it's BR release.

Oh...ok. I thought you had some expertise in evaluating audio system performance by looking at pictures of the components.
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Originally Posted by diomania View Post

Accurate to what?

Your question does not make sense. I plainly said that I, and others, have heard movie sound effects and mistook them for actual sounds in my home. If the sound effect can fool people into mistaking it for the real thing, it must have some accuracy with respect to the actual sound.
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And what method do you use to determine that?

I understand. Thanks for giving it a try.
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post #21 of 46 Old 08-31-2012, 03:42 AM
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Originally Posted by DarqueKnight View Post


Rather than saying "don't do this or that", a fairly detailed answer citing potential performance deficiencies would have been more helpful to the OP and other readers.

Please see the rest of this thread and others like it for that kind of information
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The dual MTM centers are Polk Audio LSi9 bookshelf speakers laid on their sides and angled up 5 degrees. They are a fairly close timbre match for the Polk Audio SDA SRS front speakers. A single center channel speaker was not a close enough match in sonic weight to the large front speakers. Power amplification is provided by a trio of Adcom GFA-5500's, one each for the dual centers, front speakers and surround speakers.

The symmetry between these amplifiers and these speakers with the mains appears to be very poor.
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I once tried three identical speakers in the front stage. That provided a less cohesive front stage than the arrangement I am currently using. Your comment quoted below seems to indicate that you understand that three identical speakers across the front might not be optimal for every environment and personal listening preference.

That's the nice thing about basing everything on personal preference. You can always claim that it does the best job of meeting your preferences and nobody can reasonably say otherwise.

What can be said is that it appears to be very substandard engineering. It does not conform to accepted standards. It looks to me like it was thrown together out of whatever pieces were sitting around.
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Please elaborate on the sonic detriments you think occur in my HT system when listening to the following scenes from the Blu-ray edition of "Terminator 2: Judgment Day":
1. Linda Hamilton's opening monologue where she discusses the aftermath of the nuclear strike by Skynet. I perceive her voice as crystal clear with excellent articulation and sonic weight.
2. Chapter 6: The scene begins with a police car entering at the right and moving to the left. The car engine and front tire sounds begin at the right speaker, move to the center and end at the left speaker. The solid "thump" as the police officer closes the car door, the clear "klop-klop" sounds as he walks to the front door and the clear dialog are very engaging.

The above is not a reasonable standard for judging the SQ of a surround system. The history of audio has been full of freak systems that sounded great with exactly one recording of all the thousands of recordings that people want to enjoy. Again, the very suggestion that this is a reasonable approach to audio engineering shows to me an utter disregard for the science and art of audio.
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The sound of my HT system is accurate enough that I, and others, have been deceived into perceiving the soundtrack effects of doorbells, distant door knocks and off-camera telephone rings as the real thing actually occurring in my home.
I like what I am hearing now, but I realize there is always room for improvement. What suggestions can you offer for improving sound performance in my HT setup. I expect that such suggestions would be generally applicable to the issues discussed by the OP.

Nothing the least bit unusual about that. Besides, its all based on just one man's perceptions about a system that runs in the face of most relevant knowlege about assembling a proper surround system.
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post #22 of 46 Old 08-31-2012, 03:48 AM
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Originally Posted by fbov View Post

And if it's not... like when watching a movie?

Then you are touching on the conundrum of center channels.
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I tried same L/C/R, and the center location was an obvious issue due to use of full BSC in my L/R design. This was my first DIY project and I was astounded how obvious this problem was, even with the speaker pulled out and vertical.
>> identical L/C/R require identical positioning within room or large variances will be heard.
My center is an MTM, sideways in it's permanent location, and I listen on-axis. Initially, it was a vertical design used sideway.(I have never heard lobing in my room, but that doesn't mean you might not.) Now it's a true horizontal design, voiced as a CC. I'm still on-axis, but I found dialog clarity greatly improved by the different voicing.
>> identical L/C/R require a common program, such as multichannel music, for best performance. In dialog-centric applications, a uniquely voiced CC is far superior for dialog clarity. Of course, Jom Marsh is one heck of a designer!

Since voices and other sounds (e.g. a car's engine) are panned from left to right and across the center, there is a clear need in my mind for the voicing of the speakers as installed, to remain as consistent as possible.
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I'm with arnyk, my ears tell me conventional wisdom is missing something here.

In my personal system I finesse the center channel voicing problem by not having one, but rather relying on a phantom center. Since the phantom center is based on the combination of the mains, it sounds like the mains. I'm not sure that this is a general solution but right now it works for me.
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Originally Posted by DarqueKnight View Post

I must admit that you lost me here. The OP (original poster, i.e. thread author) has not told me anything. He has only made two comments in this thread, both of which were made before my first comment.
So you don't know if fairly detailed answer similar to JHAz's would have been more helpful to OP and other readers or not. You just assumed that they are not capable of researching the term "acoustic lobing" on their own.

You assume too much. frown.gif
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Oh...ok. I thought you had some expertise in evaluating audio system performance by looking at pictures of the components.
I was giving you the benefit of the doubt to see if you had some expertise in evaluating audio system performance. Your reply with T2 tells otherwise.
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Your question does not make sense.
As I expected. But I did give you the benefit of the doubt instead of just assuming.
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I plainly said that I, and others, have heard movie sound effects and mistook them for actual sounds in my home. If the sound effect can fool people into mistaking it for the real thing, it must have some accuracy with respect to the actual sound.
You would have to know what they (Linda Hamilton, same car engine, same shoes on same floor material, etc.) sounded like in the sound mixing studio of T2 to be able to compare. Otherwise you have no reference to compare to.
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I understand.
Your replies so far tell the opposite.
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post #24 of 46 Old 08-31-2012, 11:51 AM
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Originally Posted by arnyk View Post

... In my personal system I finesse the center channel voicing problem by not having one, but rather relying on a phantom center...

That's where I started; not going back.

I'm sure you're familiar with comb filteirng that results when the same signal is present from two, physically displaced sources. Your preference confirms the benign effect on human perception, as each of your ears is seeing a different comb filter pattern, and you find it works for you. Hearing isn't simple...

Have fun,
Frank
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post #25 of 46 Old 08-31-2012, 12:54 PM
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Originally Posted by DarqueKnight View Post

I
The sound of my HT system is accurate enough that... What suggestions can you offer for improving sound performance.. (that) would be generally applicable to the issues discussed by the OP.
Darque,
Nice place!

You got it right that a CC must keep up with L/R speakers in sensitivity and power handling, but your approach belies a partial understanding HT requirements. Every time a sound is emited by 2 sources, the waves will interfere. This interference will be in the form of peaks and nulls that vary with location in space. Whenever the two sources are an integer number of wavelengths apart, they will add. Whenever a half-integer apart (0.5, 1.5, 2.5, etc.), they will subract. If the signals are of equal intensity, the peaks/nulls can be -60dB deep.

You've chosen a CC that's not designed to be a CC (per Polk), and then used two of them, side-by-side. I will wager that you gave "size" a very high priority as the only thing I like about your set-up is the looks. Too bad it's not a painting...

The key issues are:
- your LSi9's are a vertical MTM, with wide mid spacing and an assumed high crossover frequency (Polk doesn't say).
- MTMs have an advantage in sound field uniformity and reduce room interaction when used vertically.
- Unless designed otherwise, "reduced room interaction" when vertical becomes "deep nulls a little off axis" horizontally
- this only occurs above a minimum frequency determined by driver spacing, up through the crossover to the tweeter.

But, since you have two toppled MTMs, you get this problem at all frequencies, varying only in the scale on which peaks and nulls occur. To really understand, read this article:
http://www.audioholics.com/education/loudspeaker-basics/center-channel-designs
and follow both of the links to prior articles, showing the actual data. Also note that their "raised tweeter compromise" discussion ignores the critical variable of crossover frequency. This is likely what your CC's individual FR looks like:
Cheap MTM as CC.jpg 74k .jpg file

Hoppefully, this gets your attention. Focus on the deep off-axis nulls around 1KHz (crossover's a 2.4K, so what's above 2.4KHz is the tweeter... a second disaster here.) That's if you only has 1 of these as your CC. Duals won't improve things. Still happy?

Here's the polar response of my sideways MTM CC:
ModulaIV2PLR1SS.jpg 76k .jpg file

Before you comment on the strong, tri-lobe pattern, read the key - it's at 15KHz. Every dome tweeter does this at high frequency. The other blue line is 1KHz, very close to the 1.1KHz crossover frequecy. Combined with a 9" driver spacing, lobing isn't there, just a slight off-axis dip. 90dB sensitivity (I use the in-wall design, as should you) with 120W nominal power handling makes for a very respectable center channel.

Please understand that 5 years ago, I had a little Polk MTM CC like the bad example above, an "upgrade" from using the TV's built-in speakers (yes, 2 speakers, with all those wonderful interference effects intact). Better, but it didn't sound good, and I like making things, so I entered DIY. Next was a toppled MTM, but a big enough one to keep up with a pair of 10's. I learned there that timbre had several dimension, the most obvious being tonal balance - I used a full baffle step conmpensation design intended for freestanding use, and it was boomy. A different crossover fixed that (no-BSC or "in-wall" design), allowing meaningful timbre comparisons.

Fast forward a year and it's now an full LCR of MTMs, center still sideways, and on-axis, I don't notice anything change as object pan across the field, or with pink noise. But it's still harder to understand dialog than I'd like, so (after more years pass) I spring for the proper design-intent sideways MTM, at a significantly greater cost due to use of a very special tweeter that is both a) small enough to permit a C-C spacing of 9" and b) crosses cleanly at 1.1KHz (Fs below 500Hz)

My wife noticed the improvement. It's one of the few positive comments she's ever had about speakers... dialog clarity is immensly better. With common mid drivers, the majority of timbre hasn't changed, and since it's all voiced by the same designer, overall voicing is very compatible with the vertical MTM's.

... and it fits on the shelf. We all have external requirements to sound quality!

HAve fun,
Frank
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post #26 of 46 Old 08-31-2012, 01:53 PM
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Originally Posted by rosenkavalier View Post

I'm at a point where I'm looking to re-do a number of items in my home theater...

I'm also trying to consider how I'm going to make a new TV work - I'm leaning away from wall-mounting, so I haven't seen any built-in mounts on any furniture that lifts a 55" to 65" TV high enough to put a 15" inch tall speaker (my current SL-20s) under it without blocking it. I can get small floor stands, but then I can't really use part of the storage in the TV stand (since the speaker would be in front of the doors).

I guess I'm torn between what I know (fully matched speakers) and what would seem to fit best (horizontal center channel) in a new setup. I'd appreciate feedback from folks who've looked at this, and have thoughts on sound and configuration. Thanks.

RK, I dealt with similar issues when I was setting up my home theater.

Click on the pictures for larger images.

Figure 1. Home theater front stage.


Figure 2. Home theater rear stage and seating area consisting of a 3-seat sofa and 2-seat loveseat.

The surround speakers are Polk Audio LSi15's. I tried formal surround speakers mounted on the wall, but did not like the sound of that.


Figure 3. Home theater front stage speakers with grilles off.

I wanted a large, cohesive sound stage across the front of the television screen. Running a phantom center provided this at the expense of a very small sweet spot. I use a pair of stereo bookshelf speakers (Polk Audio LSi9's) oriented horizontally for center speakers. Stereo speakers have a wide horizontal dispersion and narrower vertical dispersion. Laying the bookshelf speakers on their sides provided a wide vertical dispersion with a narrower horizontal dispersion. Tilting the face of the LSi9's up 5 degrees, along with the the wide vertical dispersion, resulted in the center sound being localized at the front of the television screen and well integrated with the drivers of the tall front speakers (Polk Audio SDA SRS's), along with a wider (three person) sweet spot compared to the phantom center case.

Placing the center speakers on a shelf above the television and tilting them down also worked very well, but I did not like the aesthetics of that with this television. I also tried a pair of Polk Audio LSiC center channel speakers, but the smaller center weight they generated was not a good match for the SDA SRS's. I also tried a pair of LSi15's for front speakers combined with an LSiC center speaker. I did not like the size of the sound stage with smaller speakers across the front. Polk's LSi series speakers are a close timbre match to the legacy SDA series speakers. An exact match would be the SDA CRS+ bookshelf speakers, but they are large (20"W x 12.5"H x 9.5"D) and present some placement issues.

The following frequency response plots were taken with a Dayton Audio OmniMic system with the microphone placed at (my) ear height in the five seating positions. In each position, the microphone was pointed at the center of the television screen using a laser pointer. The Pioneer BPD-09FD Blu-ray player is set to roll off response after 100 Hz.


Figure 4. Frequency response at center seat on sofa (this is the on axis position).



Figure 5. Frequency response from sofa seating positions: black (center-on axis), red (left of center), green (right of center)



Figure 6. Frequency response from all five seating positions (refer to figure 2):

Black line: Sofa center (on axis).
Red line: Sofa left.
Green line: Sofa right.
Blue line: Loveseat left (closest to television).
Purple line: Loveseat right.

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post #27 of 46 Old 08-31-2012, 02:59 PM
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Originally Posted by fbov View Post

Darque,
Nice place!

Thanks Frank. I should mention that the home theater room was supposed to be my two channel stereo room. A smaller home theater system was going into the living room...but I was overruled. I wasn't expecting a woman to have such strong preferences in home theater.
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Originally Posted by fbov View Post

You've chosen a CC that's not designed to be a CC (per Polk), and then used two of them, side-by-side. I will wager that you gave "size" a very high priority as the only thing I like about your set-up is the looks. Too bad it's not a painting...

The sound and picture quality is decent too.smile.gif

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Originally Posted by fbov View Post

You got it right that a CC must keep up with L/R speakers in sensitivity and power handling, but your approach belies a partial understanding HT requirements. Every time a sound is emited by 2 sources, the waves will interfere. This interference will be in the form of peaks and nulls that vary with location in space. Whenever the two sources are an integer number of wavelengths apart, they will add. Whenever a half-integer apart (0.5, 1.5, 2.5, etc.), they will subract. If the signals are of equal intensity, the peaks/nulls can be -60dB deep.

Fortunately, I'm not getting anything that severe.
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Originally Posted by fbov View Post

- your LSi9's are a vertical MTM, with wide mid spacing and an assumed high crossover frequency (Polk doesn't say).

The LSi9 owner's manual states crossover frequencies of 200 Hz and 2.4 kHz. If I had a dedicated theater room, I would use a pair of SDA CRS+'s mounted above the television (or projector screen) or above and below the television (or projector screen) similar to what this guy did:

http://mysite.verizon.net/res8ycu4/index.html

Quote:
Originally Posted by fbov View Post

But, since you have two toppled MTMs, you get this problem at all frequencies, varying only in the scale on which peaks and nulls occur. To really understand, read this article:
http://www.audioholics.com/education/loudspeaker-basics/center-channel-designs
and follow both of the links to prior articles, showing the actual data. Also note that their "raised tweeter compromise" discussion ignores the critical variable of crossover frequency. This is likely what your CC's individual FR looks like:
Cheap MTM as CC.jpg 74k .jpg file

Thanks for the link. I found many good similar articles several years ago when I was setting up the current home theater. Three of them, circa 2005, can be found here:

http://forums.soundandvisionmag.com/showthread.php?199564-COF-Dual-Midrange-Lobing-Primer

http://forums.soundandvisionmag.com/showthread.php?418939-COF-Lobing-Center-Channel-Speakers-Part-II

http://forums.soundandvisionmag.com/showthread.php?433761-COF-Lobing-Center-Channel-Speakers-Part-III-(Acoustics)

I also spent some time conferring with Polk's customer service and engineering department regarding my options (and resulting performance tradeoffs) pertaining to integrating a pair SDA SRS loudspeakers in a modern surround sound system. After that, I spent some time in email correspondence with SVS Subwoofers regarding a properly integrated subwoofer.
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Originally Posted by DarqueKnight View Post

Figure 5. Frequency response from sofa seating positions: black (center-on axis), red (left of center), green (right of center)
How far left and right of center, an inch, two inches, a foot, two feet or more?
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post #29 of 46 Old 08-31-2012, 04:04 PM
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Originally Posted by diomania View Post

How far left and right of center, an inch, two inches, a foot, two feet or more?

On the sofa, left and right measurements were taken 18 inches off axis. The sofa positions are 12'-6" from the front of the center speakers. On the loveseat, left and right measurements were taken 18 inches apart and both were 6'-1" off axis.
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Originally Posted by DarqueKnight View Post

On the sofa, left and right measurements were taken 18 inches off axis. The sofa positions are 12'-6" from the front of the center speakers. On the loveseat, left and right measurements were taken 18 inches apart and both were 6'-1" off axis.
They should have been at least 24 inches to be of practical seating position given the average shoulder width of people.
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Originally Posted by DarqueKnight View Post

I found many good similar articles several years ago when I was setting up the current home theater. Three of them, circa 2005, can be found here:
...
http://forums.soundandvisionmag.com/showthread.php?418939-COF-Lobing-Center-Channel-Speakers-Part-II
Here's a comparison of yours vs his center speaker laid horizontally (which he describes its lobing problem). Your FR image size was modified to match his for easier analysis. Your center speaker arrangement is causing the problem he describes even at 18 inches apart in measured positions. You should try it at 24 - 30 inches apart and see what happens.
dkcofcenterch.jpg
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