Dual Mid-Ranges in a 3-way Design

[wigginjs]

I'm currently designing a 3-way speaker that will use a 1" dome tweeter, 5 1/2" midrange, and 10" woofer actively crossed. The mid-range in question is rated for 35W continous power (nominal impedance of 8ohm). The power ratings of the tweeter and woofer are significantly higher and the amp I plan to use to power the midrange has a max output of about 60W@8ohm. I'm considering wiring two of these woofers in parallel to increase the power handling capability of the midrange section of this speaker. A few questions:

1) In my cabinet design I've made sure to keep the midrange and tweeter very close, but the addition of a second midrange driver obviously creates a much larger area from which midrange frequencies will be produced (from about 200Hz - 3000Hz). The two midrange drivers will be arranged so that one is right above the other on the front baffle. I'm not sure if this larger radiating area will have a positive or negative effect on the overall sound and imaging of the speaker. Any comments on this?

2) Does wiring the midranges in this way create any problems with respect to interference between drivers? This is to say, if I use two as opposed to one will the create a problem when crossing over from one set of drivers to another.

3) Is this the correct way to go about increasing the power handling capabilities of the mid-range section? I listen to music at relatively low volume levels (never any louder than about 100dB), the midrange driver in question has an SPL of about 87, should I even be worrying about the added power handling?

Thanks very much for your time.

[Bill Fitzpatrick]

Use 2 mids in parallel, one above and one below the tweeter. At 87db each, they should match nicely to a 91 or 92db tweeter.

[wigginjs]

Justify your answer =)

[Bill Fitzpatrick]

I don't really need to as scores of very good MTM designs will attest.

On the other hand, as you pointed out, you may have concerns where none need be. Your mid, with the need for reproducing low frequencies removed, is likely up to the task at hand.

[Kittle]

And is it safe to assume one can get the same SPL and wattage adjustments by using 2 woofers in the same configuration?

Where woofer SPL = 88 and midrange/tweeter SPL = 91-93.

[wigginjs]

I don't really need to as scores of very good MTM designs will attest.

I didn't mean it that way. I just wanted a more elaborate explaination of your reasoning for a MTM arrangement instead of a TMM or TM arrangement.

[Salas]

An MTM needs lowering the cross frequency bcs lobing occurs with 2 mid sources separated by the tweeter as the L/2 frequency they reproduce exceeds their centre to centre distance.
Also if the phase difference is anything other than 90 deg where the mids cross to the tweeter you get no symmetry and tilts on the vertical polar response.
One common deviation of neutriality that such an arrangement has is that it exagerates the horizontal dispersion around cross to T. Resulting in a hump of room power response and perceived forwardness. A neat trick to keep the benefits of sensitivity and power handling (see lower distortion) is to keep down the forward response around cross about a dB or so. It takes careful voicing and a calibrated mic.

[planet10]

Originally posted by m0tion
I didn't mean it that way. I just wanted a more elaborate explaination of your reasoning for a MTM arrangement instead of a TMM or TM arrangement.

1st off, power handling for home hifi speakers is given alot more attention than it deserves -- there is no reason to consider a 2nd mid just because of the power handling ratings.

As for TM vrs TMM vrs MTM, i like TM better, but if you are going to add a 2nd mid to the front the MTM gets the tweeter closer to both mids so should be able to support a higher XO.

This is a fairly common arrangement (especially when you consider all the MTMs used with subs)

dave