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Old 7th January 2006, 09:31 PM   #1
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Default Help me to design the ultimate Center-Speaker

...for a room of a size 6m*7m in a 7.1-system and a large screen with 4.1m*1.75m (161" wide and 69" high) with a listening/viewing distance of 5 m.

I have build and designed many speakers and I will choose chassis from Etonwhich are used by high-end-players like Avalon and others. As tweeters I like clearly ribbons better than normal tweeters, so I am thinking about using Fountek-Ribbons (plus I have some of these speaker left from other projects).

My impressions playing around with some commercial speaker like Caton Ergo 500 (two 7"-aluminium-chassis, metall-dome-tweeter, bassreflex), have tought me the following regardins requirements:

- a big screen needs big sound. Sounds trivial, but the Cantons are not small speakers. Nevertheless three of them (L/R/Center) still sound small when you look at the screen (screen: . My brain simply tells me: Something is wrong with the sound, it sounds smaller than what you see infront of you.

- A vibrant, contrast-rich-picture needs transparent sound. I have build point-sources and line-source with domes, ribbons, listened to electrostatic speakers as well as to magnetostaic panel speakers. Again, my brain tells me when I see on a large screen crystal-clear what happens, and the sound is not natural, with highest transparency, that this is simply wrong. To my surprise a hoe-cinma want at least as much resultion in sound /holografic capabilities than a classic stereo-setup.

- Dynamic sound is important- Fine-dynamics as well as big dynamics, so it is like comparing how two enigines one needs to drive at 6000 rpm all the time or one only needs 2000 rpm to achieve the same power level. So, we not only want power-reserves like a JBL-K2 might reproduce, but we want as well a senisitive speaker which sounds from top to bottom right when the movie is quieter or you simply want to listen more quietly, but which seemlessly can do the big, authoritive sound.

- Full-range is important. I would use the subwoofer only for the lowest levels. The speakers need to go down at least to 80 Hz, better 50hz (-3db), as otherwise male voices can't be reproduced in a naturla sounding way.

Anything on requirements I am missing ?

Let's move on to design-principles. I have some open questions where I am very interested to learn from you folks.

- One Center or two ? Impact on the overall design ?
I read some articles where it was suggested to have not only one center, but two: Ideally one below the screen and one above the screen. Both are getting the same signal, so that the illusion should be that the speaker is in the middle of the screen. The obvisouly would have as well the advantage that you split the work between the two speakers, so that four the same volume level you would have less distortion and more resouerves. Is anyone using the setup ?

- Number of and Positioning of speakers in the baffle ?
Here I have really difficulties to understand the rules of the surround-game. With normal Stereo-speakers, you have the classical philosophies like D'appolitto, point-sources, line-sources etc etc., but I wonder what are the laws for a center speaker ? When I look at the design of this mighty center from Teufel(which uses as well the ETon-speakers): http://www.teufel.de/de/THXsysteme/s_517.cfm I see that they tried to combine a vertical (!!!) d'appollitto-system for super-tweeter, tweeters and midrangers, with a horizontal for the bass-chassis. Well, we could say that the bundling of bass-frequencies are anyhow not that relevant, so we could look at this as a vertical-classical d'appolito-system build for highest volume-levels for much bigger rooms that the one I have. Why than not only using a normal speaker as a center would be my question ? An why are many others presenting their speakers as horizontal centers ? Only for convenience reasing to fit it easier in a rack ? It should make a difference in how a speaker radiate whether or not you let it plat vertical or horizontally positioned.

- Chassis-selection / X-over-Design
Has anyone a center with a ribbon and can comment ? A weakness of ribbon can be that they have a smaller sweet spot than domes have. Any experience in this application ?

Ideally I would try to build a two+half-way-speaker with a 12db-x-over. For surround that means: We need enough woofers to have the reserves which as well can go high enough without any errors, so that the tweeter can be cut-off high enough without being destroyed at high-levels. Two and half means that we use the same woofers, but some of them will only play in the lower frequencies as we face the fact that a bundling will hapen at the higher frequencies and we want to have at the high frequencies only one or two woofers working (point-source or d'appolitto).

I am looking forward to learn more from your experiences / projects, before I start with mine.

Best Regards

Frank
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Old 7th January 2006, 10:58 PM   #2
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First off, your post is so long, I already forgot the beginning.

On to your center channel, First off I thought I was crazy the other day when I put my little Bose satellites on top of some old 3-way towers and they sounded much larger and more dynamic than ever before, glad to here it was not just me.(Leave me alone the Bose are the reason Im here, well the comparison to my sennheiser headphones anyway!)

Of course this is just psychoacoustics. the center channel should have the same drivers, crossover and the box tuning should match as closely as possible to the mains. I read this in dickason's loudspeaker design cookbook 7th ed., and had to try it. Using 2 alternate center channels I noticed the imaging went away, and it sounded like sound was coming from 3 different speakers as opposed to a "proper soundstage"

Horizontal woofer array, From what I read comb filtering starts at the frequency whose wavelength is equal to the center to center distance between the woofers(drivers). BTW this concerns my next project, so if anyone knows about any details/errors on that definition please speak up. For a three way center with two woofers (horizontal) and a vertical mid tweet array there should not be a problem, depending on crossover frequency. Personally, Im going to be trying a B&G planar and cross it(~700hz) to two dayton reference series 8" woofers, my mains will be identical.

As for 2.5 way, FWIW, Dickason tried both 2 way horizontal MTM and 2.5 way with the same drivers and noticed a slightly enhanced off-axis response with the 2.5 way but with what he described as an unnatural sound. You might have to build both to know for sure.

One center or two, I was thinking the same thing!!! I plan on building a DIY projector within the next few months, and I will have to deal with this same issue. Im curious what others have noticed on this in terms of imaging.
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Old 8th January 2006, 12:43 AM   #3
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Forget the center channel. It will be localized too low or too high depending whether you place it above or below your screen.

The only way to match such a large video image with your audio image is with line arrays. No point source speaker can do it. Replace your current mains with a large line array on each side of your screen.

As a cheap experiment, buy a sheet of plywood and rip it in half lengthwise for a couple of OB line arrays. Buy 32 of the 49cent pioneer full rangers (16 for each side), 2 high efficiency bullet tweeters (about $20 ea.), and a pair of Lpads to adjust the tweeter volume. About $100 and some elbow grease will prove that this will give you the sonic image you are looking for and then you can develop your plans for a high quality array pair.
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Old 8th January 2006, 01:49 AM   #4
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Quote:
- One Center or two ? Impact on the overall design ?
You can go crazy with this stuff if you want - I'd point out that many have cited the opinion that the centre channel is mainly about dialogue; we're talking about our most sensitive spot here. I wouldn't go the line source route although I like the OB point - very transparent - & I'd avoid crossovers like the plague. If you get four decent FR drivers (above, below & either side) the image will come from the centre, & if you put them together in 2 parallelled series configuration, you'll get an extra 6dB. If you want to go mad, think about using lowther horn designs - I've heard they give the most natural sounding vocals around, and you'll have more than enough dB's to frighten the neighbours next time "Arnie" pays a visit
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Old 8th January 2006, 03:02 AM   #5
mrsteve is offline mrsteve  United States
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Can you audition a few systems in a high-end audio salon?
It's best to listen to something than to speculate on something.

I'll just add my two cents here.
-Ahem-

A big screen needs a big sound.
What do actual commercial movie screening rooms use for sound reproduction, hmm?
Horn loaded transducers seem most popular at the movies.

I don't have room for a proper horn-loaded system, so, the next-best thing, for me, were line-source speakers.
Big sound, efficient too. Almost as good as a horn loaded system...and almost as good dispertion control as a horn.

Nope, not strictly Hi-Fi, but pretty decent theater.

Do yourself a favour, and don't over-think this: listen to a few systems before committing to an expensive design.
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Old 8th January 2006, 09:41 AM   #6
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OK, guys what I have not written: For the Frontspeakers (L/R), I have already a line-array build and ready for usage. It consists of 18 4" Eton-drivers per side and 12 Fountek Ribbon 2 (the big ones). These speaker were intended to be used for stereo, not surround, but after the latest learnings I think I will use them for Surround as well. As they are not yet in my house and I am still in the process of building my home-cinma-room, I was not able to hear them in my house for a cinema-application yet. Cleary, Line-sources can be a wonderful thing. The dynamic is unbelieveable, while I get the transparency and sweetness of true high-end-drivers (compared to horns, or FR, which never can copete with an excellent ribbon).

Nevertheless it leaves open the question how to build the centers. I could build them as a horizontal line-array (?), with, let's say 8 4" Eton-drivers and on small ribbon. Or I could build two of them and place one below and one above the screen.
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Old 8th January 2006, 10:15 AM   #7
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Default Re: Help me to design the ultimate Center-Speaker

Quote:
Originally posted by Blitz
To my surprise a hoe-cinma want at least as much resultion in sound /holografic capabilities than a classic stereo-setup.


Now that made me laugh. Bit deragatory toward women though but they can own cinema's too

I imagine a hoe's cinema is lilac/cream with absolutely no speakers because they don't match the colour of the curtains
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Old 8th January 2006, 11:30 AM   #8
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Quote:
Originally posted by mrsteve
Can you audition a few systems in a high-end audio salon?
It's best to listen to something than to speculate on something.

I'll just add my two cents here.
-Ahem-

A big screen needs a big sound.
What do actual commercial movie screening rooms use for sound reproduction, hmm?
Horn loaded transducers seem most popular at the movies.

I don't have room for a proper horn-loaded system, so, the next-best thing, for me, were line-source speakers.
Big sound, efficient too. Almost as good as a horn loaded system...and almost as good dispertion control as a horn.

Nope, not strictly Hi-Fi, but pretty decent theater.

Do yourself a favour, and don't over-think this: listen to a few systems before committing to an expensive design.
Horn designs in commercial theaters are popular because of the fact they have to fill a huge volume and its the best way to achieve that. In a regular home environment this is both impractical and unneccessary IMO.

The best way to achieve a large soundstage which belies the dimensions of the room is to use speakers that image well, have a good dynamic range and are supported by an excellent subwoofer. Another tool which can create a great sense of spaciousness and scale is DRC and room treatments. Many of the problems associated with a claustrophobic soundstage are room related colouration/issues and the very best speakers can be choked in such situations.

I think its folly to soley rely on a speaker to make up for the shortcomming of the room to speaker relationship. Get the room right and then look towards higher end designs and drivers, any other such approach is wasted potential.
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Old 8th January 2006, 04:28 PM   #9
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The manufacturers came up with the center channel idea for one reason, TO SELL NEW EQUIPMENT TO EVERYONE.

I'll also mention one more time because I believe it bears repeating, with a large projected image it makes no sense to have a center channel speaker of any type mounted above or below your screen. You can get away with it using a puny TV, but it doesn't work with a projected image unless you use a perforated screen with the speaker behind it, which is visually and sonically inferior. With mounting above or below the screen you will localize the source center channel content too high or too low in relation to the image. Can you imagine going to a cinema that had the front speakers mounted above or below the screen? Ever go to a drive-in? Did the sound seem to come from the characters or the speaker hanging on your window?
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Old 8th January 2006, 04:45 PM   #10
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Quote:
Originally posted by johninCR
The manufacturers came up with the center channel idea for one reason, TO SELL NEW EQUIPMENT TO EVERYONE.

I'll also mention one more time because I believe it bears repeating, with a large projected image it makes no sense to have a center channel speaker of any type mounted above or below your screen. You can get away with it using a puny TV, but it doesn't work with a projected image unless you use a perforated screen with the speaker behind it, which is visually and sonically inferior. With mounting above or below the screen you will localize the source center channel content too high or too low in relation to the image. Can you imagine going to a cinema that had the front speakers mounted above or below the screen? Ever go to a drive-in? Did the sound seem to come from the characters or the speaker hanging on your window?
I can sympathize with your argument, so please don't take this as refutal for your claims but I can also see the argument for center channels.

Imaging in most speakers is relatively poor off axis and to make matters worst, dialogue will then sound disjointed and unrelated to the image on screen. Sit in the stereo sweet spot and this issue is irrelevant. However movie watching is generall a social thing and not every one can sit in your seat So the best way to re-establish the 'dialogue from the picture' lock is to use a center channel.

Its still compromised but not half as much as using stereo speakers when off axis.

Another thing I really hate is the fact that most of the manufacturers use MTM designs horizontally! What a disgusting sin.
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