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Multi-Way Conventional loudspeakers with crossovers

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Old 4th December 2012, 02:09 PM   #321
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Quote:
Originally Posted by Beau View Post
Nice, but you are going to have lobing issues with such a large mtm. Id suggest ditching one of the mids.
Hmm, depending on the room, that may be the wrong advice. In fact, in most situations, I would say Silent may be better off using the MTM.

When using a single mid, the main lobing pattern will be vertically assymetrical with most types of crossover and create more floor-bounce issues. On top of this the angles of the lobes are such that what hits the floor is radically different than what hits the ceiling, and the difference in spectral balance can be bothersome to the hearing system. Translation: you may hear much more of the room. The MTM version is likely to create LESS of a lobing issue not more, because it keeps vertical symmetry and the floor/ceiling bounce are more spectrally coherent with each other.


If it's comb filtering you're worried about, the MTM may also be better than the single mid - even though there is potential for more comb filtering, the peaks and nulls as long as the arrival times are close to exactly the same. Meaning: the mids must be very closely aligned so they are at the same distance to the ears.

That being said, there are exceptions to the rule! I've built both types, and in some rooms, I have seen specific instances where a single mid subjectively performs better.

But as a general principle, the MTM (also called D' Appolito array) will interface better with most rooms due to the symmetrical lobing patterns. It's no accident that most of the best HT designs use MTM rather than single mids.
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Old 4th December 2012, 02:27 PM   #322
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Thank you Jack for your very imformed opinion. Shouldn't be overly hard to put the second mid back in, and worst case scenario if it sounds worse I can always just unplug in and leave the driver in place.
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Old 4th December 2012, 02:31 PM   #323
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Originally Posted by Silent Screamer View Post
Did a bit of tweaking...
A further refinement would be to shape the profile of the supporting structure behind the tweeters to look like propeller edges. This would minimize the reflection issue to the point where the distance from the tweeter is almost not an issue. BTW, the previous MTM version that you have drawn, even with the flat and reflective edges, is not going to present much of a problem anyway. But if you want to push the envelope, taper that piece front and back so that the sound flows around it. It's fairly easy to do this, and it has the potential to look much nicer, so I would vote in favor of this option for sure!

A good experiment to visualize the effect of this is to put a knife under running water. If you turn it so the flat is perpendicular to the flow you get lots of splashing. Turn it so the edge "cuts" into the water and the flow is so unobstructed it makes almost no difference at all if the knife is there or not. And it doesn't much matter if the knife is fat or skinny, does it?

So you could make your supporting beams fairly thick, and so long as they taper down to a thin profile at the edge, the flow will be very good and reflections will be minimal. With a knife edge the distance issue is very much minimized and you can design for the best looks.

Suggestion: By knife edge, I mean something closer to what you see on a propeller blade. It doesn't have to be dangerously sharp, and accidents can and do happen, so round off the edges to look like a propeller blade.
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Old 4th December 2012, 02:55 PM   #324
puppet is offline puppet  United States
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There was a paper posted here recently about the mtm subject. (posted by member "line source") While that configuration can sum flat on axis .. the off axis response can be the headache. There were some good guidelines to follow within the paper. Perhaps it's worth a read?

Here it is: http://www.birotechnology.com/articles/VSTWLA.html
Some other worthwhile reading here too: http://www.excelsior-audio.com/Publications.html

Last edited by puppet; 4th December 2012 at 03:01 PM.
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Old 4th December 2012, 06:28 PM   #325
zmyrna is offline zmyrna  United Kingdom
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Silent S
I am worried that you are going through the exact route that Stig has taken:
no baffle, two many drivers, too many crossover points.
Stig has since moved to a two way system with planar B&G radia drivers
MTM is difficult, WMTMW is a no-go. That is not my opinion; Lynn Olson says so.
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Old 4th December 2012, 11:37 PM   #326
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Thank you all for the varied responses. Jack we did a similar thing many years ago with the crankshafts in our cars, called knife edging, to a help the crank cut the through the oil in the sump, so I am familiar with the concept.
I was planning to radius the leading edge with a round over anyway, but I might use a straight chamfer instead to give a sharper leading edge.

Whether I do Mw-Mw-M-T-M-Mw-Mw or M-M-T-Mw-Mw-Mw-Mw really doesn’t cause any real issues from a design stand point as long as I settle on one or the other before I start cutting wood.
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Old 5th December 2012, 10:11 PM   #327
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Originally Posted by Silent Screamer View Post
Whether I do Mw-Mw-M-T-M-Mw-Mw or M-M-T-Mw-Mw-Mw-Mw really doesn’t cause any real issues from a design stand point as long as I settle on one or the other before I start cutting wood.
Better yet make some crude prototypes of each and compare, then later refine the edges, etc. My opinions and those of others can be helpful, but it's best to experiment and find what you like best.

I think the WMTMW approach may well be the best, especially if you can use steep slope "constant group delay" filters like DEQX offers.
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Old 6th December 2012, 01:58 AM   #328
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The DCN28 has plenty of crossover options up to 96 dB Link/Riley. I want to mount each of the drivers so they have a small amount of vertical swivel, so I could do the mounts properly now, and just play with the different layout in MDF first.
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Old 7th December 2012, 08:53 AM   #329
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I just showed this to my partner and she said the same thing as I was thinking, we have come full circle back to the ugly man again. Is there no escaping the ugly man? interesting designs?
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Old 7th December 2012, 12:34 PM   #330
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And something along the same lines but a litttle different.
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