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Multi-Way Conventional loudspeakers with crossovers

MCM 55-2960 Thiele & Small
MCM 55-2960 Thiele & Small
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Old 18th May 2018, 11:59 AM   #1
Michael Chua is offline Michael Chua  United States
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Default MCM 55-2960 Thiele & Small

I recently ordered some MCM woofers for testing. I was left sorely disappointed. Their T/S is way off.

MCM 55-2960 Qts=0.569
DATS 55-2960 Qts=1.188

That is close to double the published specs. Incredible.
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File Type: gif MCM-55-2960-MCM_TS.gif (58.1 KB, 88 views)
File Type: gif MCM_55_2960_TS.gif (38.3 KB, 86 views)
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Last edited by Michael Chua; 18th May 2018 at 12:03 PM.
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Old 18th May 2018, 02:40 PM   #2
John Busch is offline John Busch  United States
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I bought some a couple of years ago on sale just to see what I would get.

It is funny.... same issues you have..... but they are well built, nice appearance - materials of construction & pretty flat in their frequency response. What gets me is that it is just as easy do build it per spec as it is not to. The high Q indicates either very poor magnet material or an undercharged magnet... maybe both? Sad.... so close yet so far!
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Old 18th May 2018, 02:52 PM   #3
TMM is offline TMM  Australia
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What i've found is that a lot of woofer T/S specs measure very differently with small signals compared to 2.83V which is what some of the manufacturers use. Usually Fs and Q measure higher and Vas lower on small signals compared to 2.83V.

I'm not sure what voltage the DATS uses but you can measure Fs and Q with just an amp, a resistor, multimeter and some test tones. Readjust the volume every time you change the test tone frequency so the voltage across the speaker driver is always 2.83V and see what you get. Not saying that the MCM woofer isn't way off spec, but perhaps the DATS makes it look worse than it is.

Last edited by TMM; 18th May 2018 at 02:56 PM.
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Old 18th May 2018, 08:52 PM   #4
drewmc is offline drewmc  United States
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To me, the change of T/S parameters with level is another sign of a poor driver. This is a type of nonlinearity.
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Old 18th May 2018, 10:29 PM   #5
ScottG is offline ScottG  United States
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Quote:
Originally Posted by TMM View Post
What i've found is that a lot of woofer T/S specs measure very differently with small signals compared to 2.83V which is what some of the manufacturers use. Usually Fs and Q measure higher and Vas lower on small signals compared to 2.83V.

I'm not sure what voltage the DATS uses..

You can go as high as 2 volts.

http://www.daytonaudio.com/media/res...hite-paper.pdf



gornir's comparison with Smith and Larson's version vs. Dayton DATS (..actually WT3, similar to DATS but with fewer functions):

www.audioexcite.com >> Blog Archive >> Measurement Tools!

Smith and Larson's Woofertester Pro allows you to measure at up to 200 watts for T/S.
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Last edited by ScottG; 18th May 2018 at 10:38 PM.
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Old 19th May 2018, 12:11 AM   #6
Michael Chua is offline Michael Chua  United States
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Quote:
Originally Posted by John Busch View Post
I bought some a couple of years ago on sale just to see what I would get.

It is funny.... same issues you have..... but they are well built, nice appearance - materials of construction & pretty flat in their frequency response. What gets me is that it is just as easy do build it per spec as it is not to. The high Q indicates either very poor magnet material or an undercharged magnet... maybe both? Sad.... so close yet so far!
I feel exactly the same way. Assembling a woofer is not complicated.

My guess is they used the wrong magnet. QC is a serious problem for parts OEM in China. I have power amplifiers from China with wrong XLR wiring.

I have yet to do a frequency sweep with this driver. Hopefully, it is fairly flat like in their datasheet. I'll then need to figure out how best to use this woofer.
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Old 19th May 2018, 12:23 AM   #7
freddi is offline freddi  United States
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MCM 55-2960 Thiele & Small
maybe the mud magnets really contain mud


one MCM branded speaker which met spec was the 12" DVC woofer used by Marshall Leach in a sub - sat project.

Last edited by freddi; 19th May 2018 at 12:26 AM.
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Old 19th May 2018, 12:42 AM   #8
Michael Chua is offline Michael Chua  United States
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The only 12" DVC is the 55-1465. is that the model you're referring to?

Apart from the 8" 55-2960, I also purchased the 10" 55-2981.

Same issues. Qts is doubled. As is Qes.

However, with this 10", I may be able to get away by using it in a Closed box of 100 liters.

The box simulations can be found HERE.
Attached Images
File Type: gif MCM-55_2981_MCM_TS.gif (58.6 KB, 49 views)
File Type: gif MCM-55_2981_TS.gif (38.4 KB, 49 views)
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Old 19th May 2018, 01:31 AM   #9
freddi is offline freddi  United States
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MCM 55-2960 Thiele & Small
that's it - here's how mine looked pretty much out of the box for qts

Click the image to open in full size.
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Old 19th May 2018, 12:36 PM   #10
Michael Chua is offline Michael Chua  United States
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Thanks fred.

The T/S are almost the same as the specs. Looks like the MCM are a bit of a hit and miss.

Here's my TS for the MCM-2982. Again, the same issues. Qes and Qts almost double.

Fortunately, I can still use a 150 liters sealed box.
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File Type: gif MCM-55_2982_MCM-SPECS.gif (68.1 KB, 6 views)
File Type: gif MCM-55_2982_TS.gif (38.7 KB, 5 views)
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