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Old 27th May 2007, 05:36 PM   #1
garymtb is offline garymtb  Australia
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Default centre speaker

Evening all, i'm new to the game , looking to make a slim line centre speaker. hoping for something that is about 900mm wide, 180 tall and 350 deep, handle music and a/v. Planning to make a unit that looks and hopefully sounds good too, solid timber-which might be a challenge!

Ok so aethetics might be dominating practicality but it has to fit into the decor and be able handle a weighty lcd tv on top of it.
All units i see for retail, are about 400-500 wide.
Also that when building speakers you need to start with the drivers specs, so i might have the cart before the horse?
Can anyone suggest a plan for this sort of build?
cheers
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Old 27th May 2007, 11:02 PM   #2
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Horizontally aligned speakers are a total PITA. How do you get wide, uniform dispersion without lobing or colourations from a speaker that is only good at vertical dispersion?

If you sit slightly off-axis, it's like watching an old LCD with a narrow viewing angle, where the image that you see with one eye is darker than what you see with the other eye and it screws with your mind.

180mm is not much room for a tweeter to be positioned above or below a midwoofer, so I'd either:

1) change the design and make room,
2) use an array of closely spaced 1" ~ 3" wide-range drivers on a curved baffle to improve dispersion.

Edit: at the moment, I'm liking the idea #2 for a curved horizontal array using e.g.: Aurasound or HiVi drivers. If the speakers are small enough, you could probably have separate arrays of say, 19mm tweeters and 3" ~ 4" midranges. I'm not sure how it would sound though.
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Old 28th May 2007, 03:14 PM   #3
garymtb is offline garymtb  Australia
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thanks for the thoughts lech
ok so how far above the woofers would the tweeters need to be,? entirely? vertically aligned? why exactly do the drivers need to be on axis- i dont quite get the physics of this? and why are there so many designs using horizontally aligned drivers in mtm configurations? there are some designs that appear to have 'critical acclaim' —or at least have been designed by some guys who from their rep and resume should know how to get a decent sound? George at North Creek and the 'vision centre' is one example. Time heading Acoustic Research etc sounds like fair experience. Of course this is assuming AR has some credibility??... They're using some hi end components at least...

perhaps this query and home theatre in general is too far an excursion from the motivation of this forum...

ht is a compromise in some ways i guess
still i'm hoping to find a design that can marry form and function fairly well and that may include increasing the height of my planned enclosure,

anyone else care to tender a plan that might fit these specs?
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Old 28th May 2007, 06:17 PM   #4
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I'd stick with the time proven MTM personally. There is little reason to attempt to reinvent this particular wheel IMO.

The MTM laid on its side is used because it is the only pratical method of getting several drivers positioned near the center of the TV. Theoretically we would like the speakers mounted dead center of TV screen. You can do MTTM or WMTMW or other variations.

One of the most over looked parts of the center channel is matching the sonic qualities of the center to the main speakers, especially if you will be using your HT as a means of playing SCAD & DVDA.

Another option, one that is dear to me at the moment, is to use a couple of full range speakers. It certainly simplifies the job. I'm doing exactly that in a FR-T-FR config with a simple 1st order electrical x-over. I'm basing it on the wicked little 4.5" CSS 125's.
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Old 29th May 2007, 04:03 AM   #5
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Quote:
Originally posted by garymtb
thanks for the thoughts lech
ok so how far above the woofers would the tweeters need to be,? entirely? vertically aligned? why exactly do the drivers need to be on axis- i dont quite get the physics of this? and why are there so many designs using horizontally aligned drivers in mtm configurations?

At the crossover frequency the midwoofer/s and tweeter will play the same tone at the same amplitude, but the phase will vary depending on the listening angle. Depending on the angle there can be either constructive or destructive interference.

Because people's ears are usually at about the same height, they tend to be more sensitive to horizontal phase effects rather than vertical ones.

Like binarywhisper said: practicality is the issue, and people often forget to match the centre speakers with the Left and Right ones.
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Old 29th May 2007, 01:15 PM   #6
garymtb is offline garymtb  Australia
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interesting, seem to recall some of that phase and interference theory from high school physics.

reviews on the css 125s do sound very complimentary.
even to the point that the tweeter might not be required, i guess hearing the things is the best solution.

nice looking units too. they talk about the things being tested in a 200litre enclosure... how would a larger enclosure affect the preformance of the speaker—i was under the impression there was an optimum volume which produced the best results, and a smaller or larger box would be less satisfactory.
the box i propose would be around 37 litres the css cones and maybe a tweet would make for a good looking unit...

what are the characteristics you would try to match between centre and mains, loudness can be adjusted, so is it more a question of tone, and if so how best to match?
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Old 29th May 2007, 01:30 PM   #7
rabbitz is offline rabbitz  Australia
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Default Re: centre speaker

Quote:
Originally posted by garymtb
Also that when building speakers you need to start with the drivers specs, so i might have the cart before the horse?
Can anyone suggest a plan for this sort of build?
cheers
For a start, get the Loudspeaker Design Cookbook by Vance Dickason as it goes into details on centre speakers as well as all other aspects of loudspeaker design. It also includes a complete HT design which you can use as a reference.

Pick some drivers from Peerless, Vifa, SEAS (Scan-Speak too expensive for this exercise) which are readily available in Australia then start doing some searching. There's always a debate on TM vs a sideways MTM but they are not as bad a made out and as long as you are not too far off axis it's not a problem (just grab the best seat). The key is to get the tweeter as high as possible and the woofer as low as possible while maintaining centre distances to suit the crossover.

I personally used to use a vertical TM for a centre speaker but recently had to compromise with a angled TM that's shown in the pic. The key feature is the vertical height distances between the drivers with a short distance between the tweeter and woofer. This one uses a Peerless mid-woofer and Vifa tweeter chosen for it's sound and small faceplate.

If you are going down the path of music using 5.1 (wise?), then all speakers need to be the same where HT can have compromises. I do use the same mid-woofer on all my 6.0 speakers but have 3 different tweeters.
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Old 29th May 2007, 04:44 PM   #8
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Default Re: Re: centre speaker

Quote:
Originally posted by rabbitz I personally used to use a vertical TM for a centre speaker but recently had to compromise with a angled TM that's shown in the pic. The key feature is the vertical height distances between the drivers with a short distance between the tweeter and woofer.
Nice job on the speaker. You definitely wedged the drivers in there as tight as was humanly possible
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Old 29th May 2007, 05:04 PM   #9
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Quote:
Originally posted by garymtb
what are the characteristics you would try to match between centre and mains, loudness can be adjusted, so is it more a question of tone, and if so how best to match? [/B]
well the best way to match tone is to use the same drivers for all of the speakers in the system but it goes further. The same cabinet design and materials as well cross over design and components.

That is where the MTM design really shines. A single design can fill all 5 positions in the 5.1 setup giving a near perfect tonal match.

You don't have to make the enclosure for the center channel larger just because it physically needs a bigger box to support the TV. You can make the same required enclosure inside of a larger box.

If you have an excellent ear and the time to experiment you can build something that will be a match for existing speakers but it requires experience and time.

The reasons for the emphasis on matching your center to the rest of the speakers can to "some degree" be explained by using two different brands of speakers for your front 2 channels. Just on the surface the idea makes no sense at all. We go though a great deal of trouble to either build or acquire a pair of speakers that image well and present a decent sound stage. That cannot be done if we are using a variety of different components and designs for each individual speaker in our system and to a lessor degree the same can be said when you use differing sets in our home theater.

As mentioned I am using the CSS 125's for my main channel but I didn't mention that I am building a complete 5.1 system using the same drivers. Its a great first DIY project as all the materials, including plywood and x-over components, for the entire project is under $1000 taxes in. If I don't like it or wish to move up the food chain of DIY I doubt I will have much trouble selling them to one of my friends that are always complaining about their 1 box systems.
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Old 30th May 2007, 12:41 PM   #10
garymtb is offline garymtb  Australia
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hey guys thanks very much for your input, its beginning to make sense. I still need to get my head around the various specs of individual drivers and the resulting acoustic properties, as well as the requisite electronic components that go inside the box, crossovers etc i'm a a little vague on some of this so I have been thinking of the cookbook and will probably get one.
Yes nice work on the speaker rabbitz, i hope mine turn out so well.
Binary whisper I checked out the cssfr125s and they get a pretty good rap! You say you'll go with a tweeter as well but the specs say they're good for 20,000hz? they'll make a good looking setup.
how many of the 125s are you getting for under a grand?
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