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WWMTM vs WMT

Digital_Thor

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So.... I touched upon breakup in woofers and smaller midragnes in 3 way designs, and got a lot of great advice and interesting food for thought :)

Now my thoughts are going to wander a bit around the subject of bass.

Cardioid seems like an awesome idea, but a bit to tricky for me to fiddle with at the moment - even though I find it cool in both the D & D 8C and Kii3.

But what about the bass arrangement? What is the compromise of using either one or two woofers and/or midranges?

Usually I hear that it's an issue of sensitivity and spl of the complete system - makes sense. But is there any true benefit to have an MTM for better horizontal dispersion, or will it simply make it all more complicated?
Also with woofers. Would a single WO24 from SB, be easier to integrate with the midrange, than a couple of 7-8" woofers. My guess would be that I have to cross around 300hz to avoid trouble by having two drivers playing the same frequencies and also blend with the midrange. But how much of an issue is this, when using fourth order LR?

I still play with my fully active setup with two 8" woofers, 5" midrange and 1" tweeter + 4 subs. It plays really well and has been judged by quite a few, to be really good. But why not dig deeper and become wiser :D
 

AnalogSteph

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An MTM for better dispersion? Usually you have to be careful not to make things worse, as it can be quite hard to cross over low enough for M-M midpoint distance not to exceed half the wavelength and cause lobing. This is why MTM centers don't really work all too well and 3-ways are substantially preferred in this application.

Likewise, the WO24 has an Sd only about 20% higher than a single typical 8" at best, so unless Xlin turns out to be substantially greater as well (>1.6 times) I wouldn't count on it being an upgrade vs. what you have, quite the contrary (that's going off displacement, e.g. Sd * Xlin). You may have to go with more like 12" (or 2x 10" or even 2x 12"). Know your TSPs and do the math.

Compared to the PA guys who are at times running a 15" as high as ~1 kHz, you have it downright easy with the W/M crossover. What are you running now, like 600 Hz? I imagine a decent 5" should have little difficulty playing down to 300 Hz if need be. That may only be necessary once you go 15" or something anyway.... I'd look at 2x 12" and maybe 400 Hz first. Two woofers side by side would obviously make spacing less critical than if stacked WWMT, though WTMW may be an option as well. Depends on how unwieldy a baffle you can tolerate and the minimum distance you'd like to keep between W and T.
 

Plcamp

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I suppose MTM would allow you to use two one-size-smaller mid units and possibly widen dispersion vs a single larger mid driver, plus lessen the dispersion angle difference at tweeter cross?
 

bigjacko

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In my understanding MTM should not change horizontal dispersion. If there is vertical up or down tilt lobing MTM can solve that.
 
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Digital_Thor

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Sorry guys - I made an error :facepalm:

It was the vertical dispersion that I thought about, when referring to an MTM.

At the moment, I use a Seas DXT, Dayton RS125(8 ohm) and two SB23NRX + 4 x 12" Peerless XXLS.
I could raise sensitivity a bit by choosing a Dayton RS150 in 4 ohm and maybe gain a bit cleaner bass by shifting to a set of Dayton RS225, which seems to be able to play in a smaller volume - hereby making the speaker easier to look elegant.

An alternative could be to build a bigger waveguide with an SB26ADC or Bliesma, bigger midrange like the SB17CAC or MW16TX and then a 12".
But this would be expensive and gains would maybe be too small to notice in total - maybe just confusing and difficult to compare, since it's a different construction all together.

Therefore, I considered to simply add another RS125 in a MTM - since I'm actually quite happy with its performance and really can't find anything that performs as precise, especially when price and off-axis FR is taken into account.
 
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Digital_Thor

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Maybe I have found 4 pieces of used Seas W22EX001 - for a good price . Could they be a worthy or even be considered as an upgrade in comparison to either SB23NRX or Dayton RS225? I aiming for a close boxed to play from around 4-500hz down to around 70-80hz where my subwoofers starts to be fully blended into the total response.
 

Adam_M

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The W22's are excellent drivers, especially when used in the frequency range you describe. I'm listening to a set of them now and I'm pushing them a bit up than I think is optimal (1650 LR4), but still quite enjoy them. The ABSOLUTELY need a notch to crush the resonant peak. I ended up needing a tank cap on the big inductor + LCR trap to tame it.

...But don't take my word for it. Here's SL:
https://www.linkwitzlab.com/mid_dist.htm
" Since these tests were done Seas introduced the W22EX001. Like the W18EX001 it has very low distortion, but with 1.75 times the cone area it can move more air. This driver is my first choice for any new open baffle speaker design. The large resonance peak at 5 kHz requires a notch circuit. The PHOENIX pcb provides three optional room equalization notch filters. One of them could be allocated to this task and be patched into the midrange channel. The harmonic distortion of the W22EX001 has a broad peak between 1.3 kHz and 3.5 kHz. The reason for this is that distortion products generated at these frequencies are amplified by the raised frequency response around 5 kHz. The notch filter will not help this situation and the driver should ideally only be used below 1 kHz. The distortion peak at 4.8 kHz in the Seas data sheet is a measurement artifact. There is no increase in distortion. "
 
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Digital_Thor

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Last edited:

Adam_M

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Yeah, it still matters. I'd run it through a box calculator (I like WinISD or Unibox) with measured T/S parameters and make sure the rolloff shape doesn't get peaky, reaches deep enough, and the power handling is OK for your forecast input power. If the box gets too small you are going to induce a peak somewhere in the midbass.
 
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