Using Two Heresy's as Center Speaker

[DrWho]

Better. (obviously, or I would have changed it!). It produces a fuller sound, probably because of two woofers.

DRBILL

Do you have any way to measure the frequency sound levels of one vs. two? I'm interested in whether you are experiencing any frequency cancellation with the two speakers side-by-side. Some say that it is not a good idea to use two of a speaker model for the center channel. Just wondering.

I've always heard this also, but, if you go to the Lucasfilm THX website, it is recommended that the rear channels be placed side by side directly in the center rear, firing forward for movies and turned 90 degrees away from each other for "gaming".

Yea but what does this "Lucas" guy really know?

The "Lucas" guy really knows that the rear channels are reproducing identical source material, which is going to dictate a certain coverage pattern that is optimized by having the rears closepacked and spread in that manner.

[DrWho]

I would challenge you to hear the comb-filtering or any other anomolies

for that matter just by ear, because you will not. It Could it be

measured with sophisticated measuring equipment - perhaps.

Just curious what specific experiences you've had trying to hear and

measure comb-filtering??? Like what specific tools did you use? Or what

kind of envioronment were you in?

I only ask because I would argue that it is extremely easy to hear and

even easier to measure. So perhaps your methods were flawed? Or maybe

we're trying to measure different things?

I would actually argue that if you are unable to hear it, then you are

listening in a room that is introducing so many acoustical problems

that the notion of "high-fidelity" isn't even plausible...even with the

best equipment. I know them's some bold claims, but consider the

ramifications...

Apart from the comb-filtering, you also have to deal with the new power

response of the system. Side by side you're going to narrow the

horizontal polars of the bass region which is going to conflict with

the horizontal polars of the squawkers being wider. This is going to

cause a sudden imbalance which will indeed be audible (since we hear

both direct and reflected sound in a home environment). You also get

more coupling in regions where the polars are less controlled, and less

coupling where the sound is beaming...which is going to happen in 3

regions for every case (beaming happens at the top-end of each driver's

response and the widening happens at the bottom end). This is

especially problematic with exponential style horns. Ultimately, the

conclusion is a very jagged frequency response, even if comb-filtering is avoided altogether.

So in light of all these compromises, what are the gains? At best, a

little bit more output. The crazy thing is we could achieve this extra

output without the compromises by just turning up the amplifier driving

the single speaker.

Since we're still operating in a linear region of performance, the

distortion differences aren't going to be huge...certainly not at a

level worthy of introducing all sorts of other negative side-effects.

If you were dead set on using two Heresy speakers inbetween a pair of

Cornwalls, then I would disconnect the squawker/tweeter in one of the

cabinets and then wire the two cabinets in parallel. This will give you

a 6dB rise over the woofer passband, which will get you more in line

with the bass heaviness present in the Cornwall (helping to better

match the timber). Ideally I would have the cabinets such that the

woofers were on top of each other with the high frequency section

centered. This will help to get the polar response of the woofer

section to more closely match that of the squawker section. If your

head level isn't going to be directly centered between the two woofers,

then you might consider moving one of them further away so that your

head is equidistant from each woofer. This will ensure that you're in a

region of maximum coupling.

I think that's enough info for now. If anyone would like to learn more

about the process of using two speakers to cover the same passband,

then let me encourage you to google "speaker array" and learn about all

the great achievements the proaudio world has made since the 70's. It's

actually interesting to note that in many cases, you can end up with

less output by not arraying correctly! And in fact, many of the

comb-filtering problems we realize in the home can be described as

exactly that...

Now I'm sure someone will chime in and say that "hey, it works for me"

to which I would like to respond "hey, there's a higher fidelity that

you're missing out on", but that never comes across well...especially

from a youngen like me. So allow me to tuck behind the other experts

out there and mention that there are hundreds, probably thousands that

would back me up on this and I would be more than willing to point you

in their direction.

[sfogg]

What he said.....

Shawn

[sfogg]

"I've always heard this also, but, if you go to the Lucasfilm THX website, it is recommended that the rear channels be placed side by side directly in the center rear, firing forward for movies and turned 90 degrees away from each other for "gaming"."

THX processing adds a sort of 'spatializer' effect between the two rear speakers, they are not simply reproducing the same identical material in the two speakers.

THX processing has never simply fed a mono signal to two surround speakers. For example in their early days processing Dolby Surround material they sort of shifted the mono surround channel over two speakers with their 'decorrelation' processing (time/frequency shifting) and they have expanded on that since then with their ASA stuff they do now.

Having said that rears directly behind a listener is psycho acoustically a bad idea due to the human hearings propensity for rear to front localization reversals.

Shawn

[Erik Mandaville]

It might be an idea to try both (single and dual Heresy/ies). Choose what you prefer. I once contemplated doubling up our Heresies for a center channel, but I think the single one we are using would be hard to improve upon. What I would do over adding a second speaker with the idea of obtainging larger or 'bigger sound,' would be to move up to a single La Scala or Belle. We had a La Scala center channel for awhile, and I liked that.

What sounds best to you is what matters, and I know of those who prefer two speakers in the center, despite what they know about the technical ramifications. Test and measurement are important tools, but what you like in your home for how you listen is ultimately more important -- IMO.

Erik

[Erik Mandaville]

Not knowing very much about 'pro' (as opposed to the domestic version -- which I don't know very much about, either!), I've always wondered what large, public theaters use for a center channel. Is it just a single channel and dedicated single loudspeaker?

Erik

[sfogg]

"I've always wondered what large, public theaters use for a center
channel. Is it just a single channel and dedicated single loudspeaker?"

Sometimes, though obviously a very potent single loudspeaker. For smaller theaters (under 525 people) John Allen's HPS-4000 system used basically a LaScala as the front speakers along with subwoofers.

There is also a sound format (SDDS) which can have 5 channels of sound up front.

Shawn

[Erik Mandaville]

Hello, Shawn:

"Sometimes, though obviously a very potent single loudspeaker."

I might be wrong in my interpretation, but does this imply that some non-SDDS theaters may also use more than just a single, dedicated speaker for dialogue and other center channel information? If so, do they all receive the same (center) input signal? Granted we are talking about much larger spaces, but it seems to me that, given the subsequently also much more powerful amplifiers and larger loudspeakers, which compensate for that larger area, that the same acoustic parameters/priorities would apply.

"John Allen's HPS-4000 system used basically a LaScala as the front speakers along with subwoofers." In what sense? Do you mean more than just one La Scala for the center channel, or a single La Scala each for L and R and a third for the center?

I haven't tried two Heresies for a center channel. Maybe I'm missing out on something....

Erik

[sfogg]

Erik,

"I might be wrong in my interpretation, but does this imply that some non-SDDS theaters may also use more than just a single, dedicated speaker for dialogue and other center channel information?"

Probably in some situations. But traditionally the center speaker has been one speaker. Do a search on Altec Voice of the Theatre for example to see what was used for decades in theaters. They offered very different sized speakers for different sized acoustic spaces so that a single speaker could handle the job.

SDDS is no different by the way. It is just that it has 5 independant channels of information up front (as compared to 3) so as such has 5 speakers reproducing it.

"Granted we are talking about much larger spaces, but it seems to me that, given the subsequently also much more powerful amplifiers and larger loudspeakers, which compensate for that larger area, that the same acoustic parameters/priorities would apply."

The do apply. If there would be a need to go to additional speakers in a huge acoustic space it would be because a single speaker wouldn't have the output ability or coverage ability to handle that space. If multiple speakers were to be used it would not simply be plopped next to the first one and run. Each would cover a section of the theater as defined by its dispersion pattern/directivity... in effect cutting up the theater such that each speaker was covering a smaller space. In effect if you were in its coverage area you would be hearing mostly that one speaker (excluding bass which conviently also couples better between multiple speakers due to the wavelengths involved)... not multiples.

In the home a single horn speaker can easily handle the output requirements for theater and for up front duty more often then not would have the dispersion required as well.

"I haven't tried two Heresies for a center channel. Maybe I'm missing out on something...."

You are... comb filtering.

Shawn

[Erik Mandaville]

Shawn:

"Each would cover a section of the theater as defined by its dispersion pattern/directivity... in effect cutting up the theater such that each speaker was covering a smaller space. In effect if you were in its coverage area you would be hearing mostly that one speaker (excluding bass which conviently also couples better between multiple speakers due to the wavelengths involved)... not multiples"

Sure, that makes sense. I haven't been in an actual theater in literally years (home is much nicer!), and just never paid much attention back then. So, each section is sort of treated individually -- or as individually as possible, at any rate."

"I haven't tried two Heresies for a center channel. Maybe I'm missing out on something...."

You are... comb filtering.

I know that would be the result, and we actually talked about this when I was using that sort of 3-in-1 center channel arrangement with the Lowthers on either side of the Synergy. I've gotten very good results with a single Heresy, but regardless of what I *knew* about possible comb filtering effects when using the Synergy/Lowther combo for improved (as in louder) output in our pretty big room, I didn't detect any sense of discontinuity or anything. They were all balanced to exactly the same SPL, and it really seemed pretty seamless. How that setup would have actually measured might have told an entirely different story on paper, but I guess what I'm suggesting is that the paper story may not always relate on a 1:1 basis to the real life experience; and that given the choice between the two, I would prefer to continue with what sounded best based on perceived (not tested) performance, alone.

Never heard of SDDS before, thanks.

In addition to comb filtering, I also have a bunch of copper wire to wind into tight circles.

Erik

[sfogg]

Erik,

"but regardless of what I *knew* about possible comb filtering effects when using the Synergy/Lowther combo for improved (as in louder) output in our pretty big room, I didn't detect any sense of discontinuity or anything. "

Just for the record comb filtering isn't just 'possible,' it is occurring. Wether or not the increase in it is worth the tradeoff compared to the other possible benefits in that setup only you can say. The Synergy was fairly mismatched with your K'horns so adding the Lowthers could have been enough of an improvement to override the comb filtering problems. Tradeoffs as always. It could be argued that the Synergy couldn't keep up with the K'Horns so the additional benefit of extra speakers was an improvement there even with the increase in comb filtering. If you had an identical K'Horn in the center would multiple K'Horns in the center be an improvement?

"How that setup would have actually measured might have told an entirely different story on paper, but I guess what I'm suggesting is that the paper story may not always relate on a 1:1 basis to the real life experience; and that given the choice between the two, I would prefer to continue with what sounded best based on perceived (not tested) performance, alone."

Understood, but understand my preference for avoiding comb filtering is based on listening as well.

I don't like the sound of comb filtering. It does not sound natural, esp. on vocals. Everyone speaks from one point in space, not multiples. I have done much to reduce comb filtering in my system. Such as the very sharp crossovers (reduces comb filtering within the speaker itself) and having vocals steered to a center channel (ala Lexicon like you do) because I find that just simply sound more solid/full/real and gets rid of that phasey, sort of hollow sound that you get with mono vocals over L/R that most don't even notice until it is gone. That is due in part to the reduction of comb filtering. Doing that then slapping another speaker in the center to comb with is a step backwards IMO.

But I fully realize some people just either don't recognize what comb filtering sounds like or simply aren't as bothered about it as I am. It has *always* been there for L/R listeners so I think some simply expect it to be there and the reduction of it either might not be immediately apparent or they may even want it to be there as they are so accustomed to it. But compared against the real world it isn't natural.

FWIW, I think the reduction in inter-speaker comb filtering (along with an off axis response that doesn't get to hinky... just narrows with frequency) is what some single driver fans really like about their speakers. They just might not recognize it as such.

Shawn

[Erik Mandaville]

Shawn:

I meant possible 'effects' in terms of whether I could detect them or not. But I understand your point, that it's there regardless, and things can be done to minimize the influence on what's heard.

More than one K-horn for a center channel? Let me take the safe way out and say, "I don't know, I've never tried it." Obviously it's not something that would lend itself very well here. But your point is whether I thought it would be an improvement to have more than one, and my answer is that I think most likely not. The single Heresy has been working very well, but the other isn't too far away! Never hurts to try.

Erik

[Roc Rinaldi]

......along with an off axis response that doesn't get to hinky... Shawn

Hinky?

[sfogg]

".....along with an off axis response that doesn't get to hinky... "

OK... how about...

.....along with an off axis response that doesn't get to wacky? Sorry about the technical terms here

What you hear at your listening position in your room is the composite of the on axis and off axis response of your speaker(s).

Basically a single driver speakers dispersion will be wide down low and then as the wavelength of sound gets smaller and smaller (frequency goes up) its dispersion will get progrssively narrower and narrower as the driver beams.

That would likely be audibly less objectionable to say a two way with very poorly matched dispersion at the crossover point. Where you could all of a sudden jump from a beamy woofer to a wide dispersion tweeter which subjectively in some rooms could end up sounding like a recessed midrange even if on axis in a non-reflective environment the speaker measured flat.

Or something like a pair of drivers working together with too much space between them for the bandwidth they are asked to cover and they end up combing which will cause a 'hinky' off axis response.... ragged.... which you will hear at the listening position.

Shawn

[Erik Mandaville]

" a 'hinky' off axis response.... ragged.... which you will hear at the listening position."

"Hinky" registered here just fine.

Erik

[Roc Rinaldi]

I am now in the "Hinky" camp.