MTM or TMM, with 2 10" woofers and a CD/waveguide

[penngray]

I have two 10" woofers and a waveguide.

I have a certain look I want and that means I can not do a MTM.

How bad is a TMM design? The reason for the MM is because I would like to double up the two 10" woofers to increase the sensitivity closer to the CD.

Maybe increasing the sensitivity is not important enough? Instead I could just do a 2.5 Design. with the 2nd 10" woofer helping with the BSC stuff.

Some guidance on my foolish thoughts is always appreciated

[Jed]

Generally speaking, a TMM is done in 2.5way configuration to avoid lobing issues that you would get when 2 midbasses are placed below the tweeter and share the same frequencies. As you know, in a 2.5way, the lower "M" is rolled off before the upper one to solve much of that issue, if done correctly. However, in your case, by using dual 10" woofers, you'll have to cross fairly low to avoid lobing issues even in a 2.5way configuration, because the lower woofer will be at quite a great distance away from a waveguide loaded tweeter.

Jed

[penngray]

I figured as much. Maybe I will insert a 6.5" above the 2 10" woofers.

[Paul W]

I agree with Jed's reasoning for not trying a 2-way TMM.

For the 3-way proposal, the 6.5" mid will determine the lower limit for the high end polar pattern (in other words, "directivity" will not extend very low). Match directivity of the 6.5 and WG at XO with a WG the same size or a bit larger than the mid and you should be "good to go".

[penngray]

Thanks paul, I figured the 6.5" would need a smaller waveguide.

Argg....there is always something. I have 10" round QSC waveguides ready for this project so I was thinking 10" mid range to match the size.

I guess I can go with one 10" for the mid and then figure out my bass requirements.

[Paul W]

I have a couple of (very low distortion) 18Sound 10NDA520's I'm not using. :W

[penngray]

I just picked up Beyma 10BR60s but Im definitely interested.

What is the XO point for those with a 10" QSC waveguide?

I might have a hard time getting that waveguide down to far below 2KHz.

I will PM you. Thanks!

[Paul W]

I'd definitely keep it under 2k.

[kevinp.]

for what its worth, Klipsh has been doing 2 ways TMMs and TMMMs even for years. Never owned one, but I never heard anything objectionable in store auditions.
Penn you certainly have enough equipment to at least try it actively, no?

[penngray]

Yes, I can do active so I can minimize problems, changing the delay per driver.

I have always been curious about TMM that exist. I know the theory is bad but in practice does it always matter?

This build isnt going to be my main set either so ultimate SQ isnt overly important, Im already using low cost CDs. Its just another build that Im not sure will go anywhere

Of course, I do not want to be a complete moron with it

[Dennis H]

You could do an active-passive 2.5-way hybrid and save an amp channel. Put an inductor (coil) in series with the lower woofer. Run both woofers from the same amp and measure them together.

[penngray]

I found this site with some great PA builds

http://www.jobst-audio.de/index2.html

You have to translate it from German, Google is awesome with that.

Click on the PA link in the left corner and there are some cool waveguide builds, measurements/XOs too.

The LMT-210 is the build Im interested in. It does a waveguide and two 10" woofers...the same layout as the one Im talking about here.

So the only question, how bad is the lob?