Rules of thumb when designing a TMM 2.5 way

Dave Bullet · 15th March 2007, 11:22 PM

Are there any rules of thumb - especially around the 0.5 woofer when designing a TMM 2.5 way?

For example:
- Use the same model driver for both 1.0 and 0.5 woofers
- Placement on baffle (or even rear of cabinet?)
- Design so that the high pass rolloff begins at the bafflestep frequency
- physical proximity to 1.0 woofer (if on front baffle) - ie. should it be right below or can it be closer to the floor to even out midbass dips etc...

... the one I am really interested in...
- any rule of thumb about the 0.5 woofer should be X dB down at frequency Y so as to not interfere with a) crossover phase tracking / midrange clarity?

The reason I am looking toward a TMM design is:
a) simpler to design a crossover (?) than a full 3 way design with 3 different driver
b) more cone area to drive bass for a larger room (I find I overdrive TMs in my living room)
c) Avoid vertical lobing issues with an MTM

Thanks,
David.

rabbitz · 16th March 2007, 03:54 PM

Some quick answers.

Use the same woofer for the 0.5.

On the rear works extremely well but you need a lot of space to the back wall (>1m).

On the front also works well and within 1 wavelength of the xo frequency but for the low xo, never a prob. I tend to put the 0.5 just above or below the box centre.

I've found from the ones I've done, the best xo for the 0.5 is about a third of the BS frequency... so BS at 600Hz would have 0.5 xo at 200Hz. This tends to have minimal effect on the mids and only supplies what goes missing with BS. I found higher xo frequencies alter the tonal balance too much for my tastes.

Hope this helps.

Dave Bullet · 16th March 2007, 08:31 PM

Thanks rabbitz.

I am most concerned about the 0.5 top end rolloff being too shallow or too high up in Hz to then muddy the midrange. (My current design seems to put the 0.5 at least 60 degrees out of phase with the 1.0 woofer). I'll try lowering the 0.5 rolloff to around 1/3rd BS freq as you suggest.

Of course - that might mean the mid/woofers I intend on using aren't any good for a TMM... might have to keep looking.

Cheers,
David.

15th March 2007, 11:22 PM	#1
Dave Bullet diyAudio Member Join Date: Jan 2002 Location: Wellington, New Zealand	Rules of thumb when designing a TMM 2.5 way Are there any rules of thumb - especially around the 0.5 woofer when designing a TMM 2.5 way? For example: - Use the same model driver for both 1.0 and 0.5 woofers - Placement on baffle (or even rear of cabinet?) - Design so that the high pass rolloff begins at the bafflestep frequency - physical proximity to 1.0 woofer (if on front baffle) - ie. should it be right below or can it be closer to the floor to even out midbass dips etc... ... the one I am really interested in... - any rule of thumb about the 0.5 woofer should be X dB down at frequency Y so as to not interfere with a) crossover phase tracking / midrange clarity? The reason I am looking toward a TMM design is: a) simpler to design a crossover (?) than a full 3 way design with 3 different driver b) more cone area to drive bass for a larger room (I find I overdrive TMs in my living room) c) Avoid vertical lobing issues with an MTM Thanks, David.

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16th March 2007, 03:54 PM	#2
rabbitz diyAudio Member Join Date: Jul 2003 Location: Newcastle, Australia	Some quick answers. Use the same woofer for the 0.5. On the rear works extremely well but you need a lot of space to the back wall (>1m). On the front also works well and within 1 wavelength of the xo frequency but for the low xo, never a prob. I tend to put the 0.5 just above or below the box centre. I've found from the ones I've done, the best xo for the 0.5 is about a third of the BS frequency... so BS at 600Hz would have 0.5 xo at 200Hz. This tends to have minimal effect on the mids and only supplies what goes missing with BS. I found higher xo frequencies alter the tonal balance too much for my tastes. Hope this helps.

16th March 2007, 08:31 PM	#3
Dave Bullet diyAudio Member Join Date: Jan 2002 Location: Wellington, New Zealand	Thanks rabbitz. I am most concerned about the 0.5 top end rolloff being too shallow or too high up in Hz to then muddy the midrange. (My current design seems to put the 0.5 at least 60 degrees out of phase with the 1.0 woofer). I'll try lowering the 0.5 rolloff to around 1/3rd BS freq as you suggest. Of course - that might mean the mid/woofers I intend on using aren't any good for a TMM... might have to keep looking. Cheers, David.

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