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Old 9th January 2015, 02:23 PM   #1
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Default MTM Drivers wired in series

Have made a bit of an error with my project. All of my drivers are 8ohm impedance. However, if I use the woofers in parallel, correct me if I'm wrong, that will be a drop to 4ohms. would I loose any efficiecny if I were to wire the woofers in series?
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Old 9th January 2015, 03:54 PM   #2
TBTL is offline TBTL  Germany
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Your calculation is correct, you will get an impedance of 4 ohms if the woofers are connected in parallel. This is not a problem for most amplifiers.

For series connection, the efficiency remains the same. However, the sensitivity (sound output for given input voltage) decreases due to the higher impedance of 16 ohms. Furthermore, if both woofers are not approximately equal, strange things could happen around the resonance frequency, because the impedance peaks of both woofers will not be at the same frequency.

Last edited by TBTL; 9th January 2015 at 03:56 PM.
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Old 9th January 2015, 04:00 PM   #3
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Thanks for your response. How do I account for the tweeter which is also 8ohm?
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Old 9th January 2015, 05:23 PM   #4
system7 is offline system7  United Kingdom
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That's pretty easy. Just find a simple two way design with your woofers and tweeters. Works best with a Butterworth 3 design, as it goes.

Then double inductance and resistance on the bass filter, and halve capacitance and wire the woofers in series. And you have an MTM that works well in a common bass enclosure.

What are the drivers? People always leave out the precise detail that matters.
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Old 9th January 2015, 05:39 PM   #5
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Quote:
Originally Posted by system7 View Post
That's pretty easy. Just find a simple two way design with your woofers and tweeters. Works best with a Butterworth 3 design, as it goes.

Then double inductance and resistance on the bass filter, and halve capacitance and wire the woofers in series. And you have an MTM that works well in a common bass enclosure.

What are the drivers? People always leave out the precise detail that matters.
Thanks for that Steve. I'm using four Volt BM 220.8's and two scanspeak D2905/9700 tweeters.
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Old 9th January 2015, 06:41 PM   #6
system7 is offline system7  United Kingdom
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Not cheap rubbish you are deploying there! I can tell you are a money is no object kind of person.

I really don't know if Wilmslow are on the money here, but my advice on MTM stands for their MT design:

SM108 Near Field HOME STUDIO MONITOR

You will need to double the enclosure volume. The rest is as I stated it.
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Old 9th January 2015, 06:53 PM   #7
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Thanks again Steve. I'm a maechanical design engineer so the cabs and baffle I've got sorted. The beauty about buying Volt is you can get good feed back from David who's designed it. Hand made in England, I wouldn't want anything else. It's just a pitty that no one here makes an oem tweeter as far as I know and I've looked endlessly.
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Old 10th January 2015, 12:51 PM   #8
system7 is offline system7  United Kingdom
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Volt BM220.8 :
Volt Loudspeakers | BM220.8 (8″)

Looks like a polycone that won't need much filtering. You might get away with just a series coil, and capacitor and resistor shunt.

I say this more theoretically than anything, but BW3 filter is the correct solution for D'Appolito MTM. I'd think an LR2 or LR4 will beam too much at crossover. Very much in the old KEF tradition.
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Old 10th January 2015, 04:10 PM   #9
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I agree with the BW3 after reading previous arguments. I now have questions as to how a poly cone makes a difference?-sorry. I have come across this and I would be interested in your or anyones opinion on the builders assertion that ports should be located either side of the tweeter for better mid sonics. They're a clone of the Wilson Cub.

SpeakerBuilding.com - The Proteus - To D' Appolito or not to D' Appolito, that is the question, Page 1
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Old 10th January 2015, 04:48 PM   #10
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Those are some very nice drivers, I haven't heard them but am very keen - have heard lots of good things. New or 2nd owner if you don't mind my asking?

Also, not D' Appolito was my vote, FWIW, can't remember what lead me to that conclusion in the end though....
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