Hi All
With my recent frustration with drivers that weren't really suitable for what I wanted I realized that my lack of experience was hampering my ability to make good decisions. So, I've decided to tackle a smaller project first which has completely different parameters. Specifically, I'm building a system to take out in the desert at the end of the summer. This system must be cheap to the point that I can't lose any sleep if none of the drivers survive the trip. I plan to build the cabinets fairly sturdy, there' s not much that the desert can do to cabinets. But the drivers and the amp, that's a different story. To that end, I've chosen a handful of the cheapest MCM drivers. They may not sound great, but, they will make noise. For this particular audience, that's sufficient.
One of the issues with these drivers is that people complain that the measured T/S params are very different from the published specs. So, keeping in mind that I'm very new to this and probably doing something wrong, here's my frst attempt at measuring T/S parameters of the 55-2982 12" woofer.
I'm using LIMP and a diy jig with a 7.65 ohm reference resistor and an NI Audio Kontrol 1 interface and no external amplifier. For these first measurements, the drivers have not been broken in. Also, the diameter is my best guess from measuring and yields an Sd value that compares to another measurement of the same driver in some other thread that is either here or on the parts express forum.
These are the MCM published specs.
Resonance Frequency Fs: 36.23 Hz
DC Resistance Re: 6.3 ohm
Mechanical Q Factor Qms: 2.823
Electrical Q Factor Qes: 0.476
Total Q Factor Qts: 0.407
Equivalent Cas air load Vas: 121.67 liters
Efficiency Bandwidth Product EBP 89.017
Voice Coil Over Hang X-max 7 mm
MCM Audio Select 12'' Die Cast Professional Woofer - 350W RMS | 55-2982 (552982) | MCM Audio Select
These are my measured specs. FS is slightly higher than MCM reports, that this might be expected as the drivers haven't been broken in.
Fs = 42.70 Hz
Re = 6.30 ohms[dc]
Le = 383.02 uH
L2 = 3894.50 uH
R2 = 25.63 ohms
Qt = 0.29
Qes = 0.34
Qms = 2.15
Mms = 77.70 grams
Rms = 9.716533 kg/s
Cms = 0.000179 m/N
Vas = 76.38 liters
Sd= 551.55 cm^2
Bl = 19.739441 Tm
ETA = 1.70 %
Lp(2.83V/1m) = 95.44 dB
Added Mass Method:
Added mass = 34.02 grams
Diameter= 26.50 cm
These seem to model nicely in a narrowed THAM-15. Using the specs as given, they seemed to need more volume and worked better in the full size THAM-15. The mass of the cone is some 20+ percent ligher than a 12PS100, but, a bit heavier than the Dayton 12. I won't be building horns to take to the desert, most likely that will be some sort of bandpass design so that the amp can be very simple and the crossovers less critical. But, I plan to experiment with the second pair and I don't really care if I let the smoke out in the process.
If you buy four, these can be had for about $30. So they're cheap enough to learn some lessons the hard way with. I'll measure the other three tomorrow and probably whip up a better frame for measurement. Right now they are being suspended from the center of my camera tripod.
One of the reasons that I just built a jig to measure with is that I have some odd 12" drivers lying around. I had no idea that it was so easy to get basic measurements. I also realized quite quickly that very slight variations in the physical environment can cause significant variance in the measured params. In other words, my measurements might be total crap, I'll repeat this tomorrow with a better mount.
I'll post more measurements and pictures as I go. Comments, questions, and suggestions are welcome.
best,
gs
With my recent frustration with drivers that weren't really suitable for what I wanted I realized that my lack of experience was hampering my ability to make good decisions. So, I've decided to tackle a smaller project first which has completely different parameters. Specifically, I'm building a system to take out in the desert at the end of the summer. This system must be cheap to the point that I can't lose any sleep if none of the drivers survive the trip. I plan to build the cabinets fairly sturdy, there' s not much that the desert can do to cabinets. But the drivers and the amp, that's a different story. To that end, I've chosen a handful of the cheapest MCM drivers. They may not sound great, but, they will make noise. For this particular audience, that's sufficient.
One of the issues with these drivers is that people complain that the measured T/S params are very different from the published specs. So, keeping in mind that I'm very new to this and probably doing something wrong, here's my frst attempt at measuring T/S parameters of the 55-2982 12" woofer.
I'm using LIMP and a diy jig with a 7.65 ohm reference resistor and an NI Audio Kontrol 1 interface and no external amplifier. For these first measurements, the drivers have not been broken in. Also, the diameter is my best guess from measuring and yields an Sd value that compares to another measurement of the same driver in some other thread that is either here or on the parts express forum.
These are the MCM published specs.
Resonance Frequency Fs: 36.23 Hz
DC Resistance Re: 6.3 ohm
Mechanical Q Factor Qms: 2.823
Electrical Q Factor Qes: 0.476
Total Q Factor Qts: 0.407
Equivalent Cas air load Vas: 121.67 liters
Efficiency Bandwidth Product EBP 89.017
Voice Coil Over Hang X-max 7 mm
MCM Audio Select 12'' Die Cast Professional Woofer - 350W RMS | 55-2982 (552982) | MCM Audio Select
These are my measured specs. FS is slightly higher than MCM reports, that this might be expected as the drivers haven't been broken in.
Fs = 42.70 Hz
Re = 6.30 ohms[dc]
Le = 383.02 uH
L2 = 3894.50 uH
R2 = 25.63 ohms
Qt = 0.29
Qes = 0.34
Qms = 2.15
Mms = 77.70 grams
Rms = 9.716533 kg/s
Cms = 0.000179 m/N
Vas = 76.38 liters
Sd= 551.55 cm^2
Bl = 19.739441 Tm
ETA = 1.70 %
Lp(2.83V/1m) = 95.44 dB
Added Mass Method:
Added mass = 34.02 grams
Diameter= 26.50 cm
These seem to model nicely in a narrowed THAM-15. Using the specs as given, they seemed to need more volume and worked better in the full size THAM-15. The mass of the cone is some 20+ percent ligher than a 12PS100, but, a bit heavier than the Dayton 12. I won't be building horns to take to the desert, most likely that will be some sort of bandpass design so that the amp can be very simple and the crossovers less critical. But, I plan to experiment with the second pair and I don't really care if I let the smoke out in the process.
If you buy four, these can be had for about $30. So they're cheap enough to learn some lessons the hard way with. I'll measure the other three tomorrow and probably whip up a better frame for measurement. Right now they are being suspended from the center of my camera tripod.
One of the reasons that I just built a jig to measure with is that I have some odd 12" drivers lying around. I had no idea that it was so easy to get basic measurements. I also realized quite quickly that very slight variations in the physical environment can cause significant variance in the measured params. In other words, my measurements might be total crap, I'll repeat this tomorrow with a better mount.
I'll post more measurements and pictures as I go. Comments, questions, and suggestions are welcome.
best,
gs