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Old 10th January 2005, 12:45 AM   #1
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Default Center channel considerations

Rather than making a center WMTW center channel, would it be possible to use a single woofer next to the midrange and tweeter as shown in the attached pic? or would this not be a very good idea.

Also when measuring the FR should I place the speaker in the actual location it is to be used when designing an XO? (ie: on top or below TV or a simulated equivalent)
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Old 10th January 2005, 12:51 AM   #2
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If you set the woofer crossover low enough it will be just fine to use that configuration. What you need is for the woofer to be acting like a subwoofer and it will cost you more for the crossover parts because lower crossover points require larger values.

However, if you set the crossover below 120 - 130 Hz it should not be a problem. Now with the midrange going lower than before you will need to have a larger chamber of air with it if it is in a seperate enclosure.

Hezz
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Old 10th January 2005, 02:04 AM   #3
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If I would have to cross that low to get good results I would be better off to just go 2 way or all out with a WMTW since I will have separate subs on the LFE channel likely up to near 100hz. I figure the best way to match everything would be for all 5 speakers to have a similar rolloff in the bass area. (my L/R fronts are sealed boxes with an Fsc of about 72 hz and a Q near .71).

(edit:BTW my HT amp isn't very flexible with crossover settings...the lowest setting is 100hz lowpass and the higpass can only be set to 100hz)

I really would prefer a 3-way to get keep the XO out of the vocal range. This of course is probably beyond my abilty to design myself and I am unlikely to find a center channel design to match my specs. So I guess I will have to go 2-way in the end. (all other channels will be 2-way anyway)

By chance, does anybody know of a good WMTW center channel project that would get me what I am looking for?
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Old 10th January 2005, 03:37 AM   #4
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Why bother with a tree way for a center chanel? It doesnt need to go low.. How about an MTM, using the same mids and tweeters as your mains?
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Old 10th January 2005, 10:12 AM   #5
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I would except that most people say that MTM's aren't made to put on their side because they don't sound that great when you are off the vertical axis (or the horizontal axis when it's laying on it's side). So I would think I'd be better off just doing a simple 2-way with a single woofer over an MTM design.
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Old 10th January 2005, 03:53 PM   #6
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Having used the MTM design and originally having it in a horizontal configuration and then switching to a vertical configuration. I would say that unless you have room to put a MTM in the vertical configuration it would be better to go with the standard two way.

If you watch a lot of old films and want to use only the single center channel I would built a three way. But for modern movies a two way is quite sufficient in the center. One thing though is that if you are still using Dolby surround instead of dolby digital there is still a lot of bass information in the center channel and you may want to cover it.

Unless you have test equipment you are better off to buy a kit with crossover already designed or Madisound can design a LEAP crossover for you for about 25 USD. It is well worth it as it will be a better crossover than you can get without spending a lot of time and money with different parts values.

If you are using the center channel with a TV stand you might check out the integrated TV/center channel speaker I built. It works rather well.

I personally feel that the center channel should be designed with vocal reproduction in mind and as long as you cover that well the speaker should be just fine. I also think that silk dome tweeters are better for HT unless you have really high end gear as the metal domes can amplify some of the bad sound of mass market digital playback.

A DIY speaker company name Zalytron used to have a really good WTMW center channel kit. You can search for it. Madisounds MTM VIFA center channel is quite good for the money if you run it in a vertical orientation.


Hezz
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Old 10th January 2005, 05:49 PM   #7
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Right now my DVD player is, dare I say, a Playstation 2 (my real one died) so I only have a stereo signal going to my amp and the amp converts it to the 5 speakers. When watching movies like this does the subwoofer channel get the bass from all the other channels?

When I do get a new DVD player (and I watch in 5.1 dolby digital) what channels get the bass routed to the subwoofer channel then? I'll have all the channels set as large.

My amp has only the most basic of features, its a Technics SA-DX750.
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Old 10th January 2005, 05:56 PM   #8
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One other thing I just thought of when looking through kits. If an MTM were designed as a 2.5 way with 1 woofer just to cover for BSC would it suffer from the same problems when put horzontally?

Also, wouldn't the BSC be different since it will essentially have one wide side if it's on top of the TV and even worse if it's below the TV?

I have too many questions as usual.
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Old 10th January 2005, 07:07 PM   #9
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Merlinx76,

There are some differences in home theater stereos but most of them running in dolby digital send the entire frequency spectrum to all of the speakers when you have large selected. This means full range but is meant to be a simplification.

The subwoofer channel is derived from the others with dolby surround but with dolby digital it is a seperate channel with it's own content. Usually the dolby digital subwoofer channel is a mix from the main speakers so that if you don't have a subwoofer you still get some of the bass effects.

The biggest problem with the MTM is that it gives good wide midrange and midbass energy distribution in the horizontal plane when oriented in a vertical arrangement. When you put it sideways it does the opposite of what you want to happen. Some manufacturers of higer end speaker attempt to compensate for this with a crossover designed slightly different and placing the tweeter high between the two midbass drivers. But more often than not it is an asthetic consideration because most people don't like an asymetrical looking speaker.

Because of the physical requirements of your tv viewing room and space the first thing that you need to determine is where you are going to put the speaker and how big it can possibly be. After you know that you can decide on a design. There is no reason why you could not get very good performance from the three way that you posted at the beginning of the thread.

In my opinion next to having natural timbre sound in the vocal range the most important thing that the center channel can do is have three dimensional imaging. This means that the sound doesn't sound like it's coming from the speaker. For a small speaker this is easier to realize in a two way design.

In my opinion, the best sounding configuration for a center channel speaker would be a two way design build into a narrow pyramidal enclosure and up on a good stand. Like the upper speaker on a Wilson Watt/Puppy. This usually only works on a front projection screen arrangement because most people don't like the looks of this in front of the TV and unless the TV is high enough it won't work. Therefore other compromises have to be made.

It would not be very hard to design a crossover for your original three way with a low crossover point. You can have Madisound do it for your for 25 USD. I designed my main high end watt/puppy clones this way because I wanted the mi-bass speaker to cover all of the fundamental frequencies. I think it has a lower crossover point around 150 Hz. I think that this would work just fine for you. Also, a well made two way would work just fine. The center channel speaker is more forgiving than the others because it generally doesn't have to play full range music.



Hezz
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Old 10th January 2005, 07:16 PM   #10
tiroth is offline tiroth  United States
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You should download Svante's xDir and play around with it. W-TM style can work fine but there will be a lobe off to the left or right. If the lobe is wide enough (read: you are crossing low enough) you may be able to play with the placement such that the main seating area is well covered. This may be significantly better than MTM-on-a-side in terms of lobing.

Because of my design constraints I need to cross relatively high, 300-400Hz range. As a result, I really had no choice but to go W-TM-W to force the lobe to center about the 0 degree axis.

Pretty much everything about a center channel is a compromise if you have to work around a screen/TV so you need to make the best of it. Fortunately there are a lot of potential workarounds.
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