Why are tweeters offset in MTM speakers?

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#5
It's a good thing to calculate this as part of the MTM design process. It is dependent on your crossover frequency and your baffle placement (supply these if you want assistance). You could calculate the cancellation angle yourself or Vituixcad could do it..
 
#7
Aside from the already mentioned baffle step (avoiding 1 big step at one frequency and instead have 2 frequencies with a smaller step) and distance between the woofers, there's also a a difference in dispersion. You can further modify it by the shape of the edge.
 
#8
The woofer spacing is about dispersion in one form or another (no other property of their spacing is likely to be as significant a design consideration). Presumably you're referring to the contribution of the baffle in the regular sense, ie directivity that culminates in the baffle step.
 
#9
AllenB said:
The woofer spacing is about dispersion in one form or another (no other property of their spacing is likely to be as significant a design consideration). Presumably you're referring to the contribution of the baffle in the regular sense, ie directivity that culminates in the baffle step.
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I am very aware about the behaviour in dispersion of the woofers, vertically and I think you know I am. So, yes, I am talking about the horizontal dispersion of the tweeter. If the tweeter comes much closer to the inner edge it disperses towards the middle (listening position) like having a much smaller baffle. Combined with a big chamfer or rounded edge, you can practically model the dispersion to your liking. It's really worth to simulate that before, there are tools for that (forgot which ones though, I usually use WGs and horns since quite a while).
 
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#10
I didn't mean to imply anything about you personally. I try to consider matters of the language barrier, translation or other kinds of misunderstanding, just as I try to remember that there may be others reading my posts.
 
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#12
djn said:
I’m building small speakers for my daughter’s desk.
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Then don’t build an MTM for near field…..too close a listening distance and the drivers don‘t sum……my experience has shown me that 10x the center to center spacing of the midwoofers is the minimum listening distance for this alignment and the point where the drivers sum.

You can get around this though by building it as a 2.5 way instead adding the .5 coil to one of the two midwoofers.
 
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#13
I just happen to have the guts from a sound bar which is four 3" mids, two 1/2" tweets, and two crossovers. I also have two cinder blocks and some exotic woods. So, If I only use one mid but the crossover is for two mids, can I or should I but one mid in front and one in back?

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#14
Well, the design choices in these speakers were mainly visual (you can remove the divider in the middle 😉 ) and non-practical (you probably don't know it yet but questionable practical decisions (having a 1/4" jack sticking out on the side with a plug in cinder blocks and the port on the front)), which is definitely not a catastrophy but surely gives room for improvement. 😉 They absolutely got their own charm and I actually like that. The drivers seem to be a good match too (both Monacor I'd say if I had to guess).

For your question: For a starter project, heavily modifying/rebuilding such a sound bar is quite ambitious. No, you should not put the 2nd mid on the back and you can't use the same crossover either. Developing a speaker is 99% work on the crossover and changing the baffle dimensions that drastically got great acoustical benefits but makes it a lot more work to modify create a new one.

You need to start measuring. It's not that expensive but without knowing what you actually have (no, model and brand do not help there), it's just just as random as the lottery numbers next month. Here in the forum are guides on how to start and you will get ample of good advice and help here too but it's too much to explain everything here in this thread. You started to ask the right questions so I'm quite sure you are on the right path
 
#15
We offset the midTweeter to get the 3 drivers into as close a physical distance as posiblle. These are abit unusuakl in that the XO is below the quarterwave frequency of that difference — XO at 250 Hz. All drivers close enuff to act as one. You all get a bit more room tunign options with the midTweeters either on the inside or the outside.

A12pw-MTM-comp.jpg


dave
 
#16
Dave, that's not nearly as critical as the tweeters are also relatively low xo'd FR, so you get all their benfits without much of the downsides. A round over of the edge would likely be a benefit but there's another improvement you really should do: The port is extremely wide but very narrow in height. No round over. TQWT? Anyway, That increases the turbulences, losses even at moderate levels. Increase the height of the port and reduce the width, that will work wonders in precision and control at medium and higher levels.

Very nice design of the speakers and the mounting rings though, that's very nice. Ofc haven't heard them but I know these have great potential.
 
#20
Ah, I see. That driver just came to my mind because it's easy to handle, it's very reasonable priced and measures very well (except for the lone 7k resonance) and sounds great. However, it looks a lot different and I can see why that might be a no-go.
 
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