# 3-way active speaker - midrange choices with an AMT tweeter



## Wemyss (Jul 10, 2012)

Hi,

I’m planning to build an active 3-way speaker system and would be grateful for your views on choices of a good midrange speaker unit. I know there are really good units by Seas, Scanspeak and of course the famous ATC SM75-150, etc.

However, I’ve come across a fairly new midrange unit from Morel: TSCM 634 which seems to have the best overall properties, i.e. high sensitivity, high power handling (has a 3” voice coil) and able to easily cross-over at 300Hz. It has no real directivity issues until well after 2kHz where I hope to cross-over to an AMT (air motion transformer) HF unit. Recommended cross-over for this unit is 2kHz)

So, two questions really:

1) Has anyone used this Morel midrange unit and what do they think of it?

2) Am I likely to come across any problems crossing over from a cone to an AMT?

I know that Adam and Legacy and others have successfully integrated cone mid drivers with AMTs.


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## ajinfla (May 10, 2009)

Wemyss said:


> However, I’ve come across a fairly new midrange unit from Morel: TSCM 634 which seems to have the best overall properties, i.e. high sensitivity, high power handling (has a 3” voice coil) and able to easily cross-over at 300Hz. It has no real directivity issues until well after 2kHz where I hope to cross-over to an AMT (air motion transformer) HF unit. Recommended cross-over for this unit is 2kHz)


Hi Wemyss,

That driver appears to have a voltage sensitivity of 89db, or around 86db/watt. That's fairly average, not high. The 3" VC will yield high power handling above mechanical (xmax) and thermal limits. Also, any 6" driver will become directional > 900hz or so, this one included. The manufacturers data only goes out to 45 deg. The impedance shows a resonance right around 2k.
Bottom line without a 15+ page explanation, I would not cross above 2k. If the AMT can handle it for your desired max volume, around 1.8k or so should be ok.
The nice thing about active is you should be able to experiment.

cheers


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## Wemyss (Jul 10, 2012)

Hi,

Many thanks for your advice. As the Morel midrange is a 4 ohm unit (rather than 8 ohms), I should have realized the 86dB/watt makes it average for sensitivity. To be honest I hadn’t noticed the bump in the impedance plot around 2kHz, so it would make sense to crossover at 1800Hz – I think the AMT tweeter will be OK with this, but perhaps I should use Linkwitz-Riley 4th order filters between the mid and hf units? I’m thinking of using a MiniDSP for all this.

Thanks again for your help.


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## ajinfla (May 10, 2009)

Wemyss said:


> To be honest I hadn’t noticed the bump in the impedance plot around 2kHz, so it would make sense to crossover at 1800Hz – I think the AMT tweeter will be OK with this, but perhaps I should use Linkwitz-Riley 4th order filters between the mid and hf units? I’m thinking of using a MiniDSP for all this.


The nice thing about DSP like the mini is that you can experiment with different filters, eq, time delays, etc.
Keep in mind the important response is the target electro-acoustic one, the combo of your electrical (like 4th order LR) _and_ the native response of the driver in cabinet. That may require different electrical filters for each driver and/or some response shaping (PEQ) to get the desired filter slope in the driver passband. Once you get good summation on axis, be sure to reverse the phase of one driver to check for a nice deep null at XO. Then check to make sure your off axis is smooth as well. Finally, drive them hard and listen for any distress. That should tell you whether you crossed the tweeter too low.

cheers


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## Wemyss (Jul 10, 2012)

Hi,

Once again, many thanks for your advice re electro-acoustic response around the crossover region. Once I obtain the units, amp and MiniDSP, I’ll get going on the measurements and see how it all turns out!

Thanks again.


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