MCM 55-2982 T/S Params and a Ghetto System - Page 2 - diyAudio
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Old 21st April 2013, 11:26 PM   #11
OscarS is offline OscarS  United States
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which version of WinISD are you using? Mine most certainly does allow you to see cone excursion.

Click the image to open in full size.

Last edited by OscarS; 21st April 2013 at 11:29 PM.
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Old 21st April 2013, 11:56 PM   #12
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[QUOTE=OscarS;3463399]which version of WinISD are you using? Mine most certainly does allow you to see cone excursion.

See previous post, I was using the Beta, I also had alpha installed but for some reason I wasn't using it. Maybe it crashed, maybe something I was interested in wasn't available. At any rate, I'm using the alpha version now and yes, it has that information.

tnx
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Old 26th April 2013, 04:10 AM   #13
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So, finally, I made some sawdust today. I built a test box out of the crappiest materials imaginable. The baffle is MDF left over from an organ that I dismantled, so, 12" hole already cut, woot! The rest of the cabinet is cut up, partially laminated, 1/2 particle board that was a set of closet shelves that we hated and have been sitting outside for a long time.

It was mostly an exercise to get to know my tools and to get a sense of how these drivers might sound. The baffle had a cutout for a midrange, which served as a port hole, which I had every intention of trying to play with, but for the time being, I just sealed it off.

I found the track saw surprisingly relaxing to use as compared to the crappy table saw that I had. I also realized that for me, the small makita router was the right choice. One nice thing about the track saw is that it's really quite easy to correct certain kinds of mistakes that I would have normally used the sander or the jigsaw for.

Took me about three hours to clean up the salvaged materials, throw it together, and then another hour or so for playing too loud in my DJ room. In short, it reproduces 60 to 80 hz much better than my small tops, but, it wont' cut it for me for the long term.

Holy jesus is it heavy though, sizewize it's about 19"x19"x22", so like 4.5 ft^3. The dimensions were dictated in part by the existing pieces. The ghetto system is def not going to be made out of mdf or 3/4 ply.

I now have a measurement mic, so I'll try to take some measurements this weekend after I tighten up the box a bit. It looks a bit silly right now with my clamps on it from front to back to stop the unglued back from rattling.

Last edited by ghettosynth; 26th April 2013 at 04:13 AM.
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Old 26th April 2013, 07:11 PM   #14
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I played with it a bit this morning. I realized that the crossover switch on my mackie was set to 80hz, it sounds a lot better crossed over at 120hz. It seems to take quite a bit of power, but that's just seat of pants based on past experience with my amp and system.

One is stupidly loud in my small house and allows me to really drop the volume on my tops for a much nicer balanced sound. I think that it will take at least a pair to be useful outside. For their intended purpose though, it will work as they're going to be used in a very small area.

I'm pleasantly surprised considering the cost of the driver.

Off the cuff, I'd say that the sensitivity ratings are BS though. How do I measure sensitivity? Also, I still don't know how to safely measure xmax?

tnx
gs
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Old 27th April 2013, 04:41 AM   #15
OscarS is offline OscarS  United States
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Quote:
Originally Posted by ghettosynth View Post
Off the cuff, I'd say that the sensitivity ratings are BS though. How do I measure sensitivity? Also, I still don't know how to safely measure xmax?

tnx
gs
what test equipment do you own?
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Old 27th April 2013, 05:00 PM   #16
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Quote:
Originally Posted by ghettosynth View Post
How do I measure sensitivity? Also, I still don't know how to safely measure xmax?

tnx
gs
Sensitivity can be using a sine wave of 2.83 volts for an 8 ohm driver. Set the voltage at 60 Hz (where it will be most accurate) then use an SPL meter at two meters laying on the ground outdoors, subtract 6 dB for a one meter equivalent.

You can see the peak to peak excursion quite easily with a white or silver dot on the cone, Xmax is a one way measure, the cone has reached Xmax when the excursion is double the Xmax rating.

Since your cone won't reach Xmax until near full power, make sure you do the tests quickly, and leave time between tests at different frequencies.

You can also just run pink noise, set the HP and LP, run the amp up to clip and see if the speaker exceeds Xmax, if it does, lower the peak limiter settings.
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Old 27th April 2013, 06:00 PM   #17
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Quote:
Originally Posted by OscarS View Post
what test equipment do you own?
Run of the mill electronics hobbyist test gear: decent, but not spectacular oscope, DMM, function generator. Radio shack sound level meter. Dayton measurement mic and a suitable interface. Most other test gear that I have is of a similar caliber but made for RF measurement.

I build a simple jig for limp.

I suspect that Art's method will be a good start for sensitivity.
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Old 27th April 2013, 09:25 PM   #18
OscarS is offline OscarS  United States
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Quote:
Originally Posted by weltersys View Post
Subtract 6 dB for a one meter equivalent.
don't you mean add?
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Old 27th April 2013, 11:07 PM   #19
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Quote:
Originally Posted by weltersys View Post
Sensitivity can be using a sine wave of 2.83 volts for an 8 ohm driver. Set the voltage at 60 Hz (where it will be most accurate) then use an SPL meter at two meters laying on the ground outdoors, subtract 6 dB for a one meter equivalent.
I have a dumb question about this. Is this done with the speaker in, or out, of a box? If out, don't you get phase cancellation, if in, doesn't the box affect the measurement?

I'm sure that I'm missing something.

tnx
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Old 28th April 2013, 01:35 AM   #20
OscarS is offline OscarS  United States
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If the box is a maximally flat alignment, then it won't affect measurements, because the response is flat, by definition. Otherwise yes the box has an influence. In free-air you will get cancellation of course.
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