Driver Measurement Page

This page is devoted to measurments I have made on various raw speaker drivers. For low frequency units, I will usually just provide my measured T/S parmeters. For other units I will provide frequency response and eventually waterfall plots as well.

Most manufacturers have certain tolerances that they build there drivers to. Therefore, the T/S parameters will vary from unit to unit. I'm including my measured values to give DIYers out there an idea of how much specs can vary. Some manufactureres, like Audax, Focal and Scan-Speak, have a reputation for their drive units comeing out very close to spec. Other's, like Seas and Vifa do not. This does not mean that Seas and Vifa produce bad drivers, this just means that you should definately measure your mids and woofers when you get them. I use LAUD to measure my drivers, it has a built in easy script that makes the measurements quick and painless.

T/S parameters can be measured by hand, and, as soon as I find my text file on this matter, I will put it up on this page.

Frequency/Time Domain Measurement Section.

Frequency Response For the SEAS 27TFFC Tweeter

The Seas 27TFFC tweeter is probably considered the "step down" from the well liked Excell 1" dome tweeter. The specs show the tweeter is fairly flat, has a low (900Hz) resonant frequency and is pretty efficient. (91 dB 2.83V/1m). The impedance plot of one of the samples that I got shows an Fs at 1075Hz, not too far off. Since I was curious about breakin, I ran this test once when the tweeters were right out of the box, and after several hours of running white noise, pink noise and full range music (softly). There was absolutely no change in the resonant frequency of the tweeter. I'll do the same with my HM170Z0s that I should get tomorrow.

The driver was flush mounted on the largest baffle I could afford to waste (It's not much good for anything else anymore). In order to approximate an infinate baffle, I placed the test baffle on the floor pointing up. For the method used, the results I got were very good. The on axis frequency response plot agrees pretty well with the Madisound catalog so I'd say they are valid. I tried the meausrements with the baffle leaning against the wall, freestanding, etc, however those measurements (as J.W. will agree, measurements are dangerous) were interesting to say the least. (Mostly a lot worse.) When I measured it non-flush mounted..there is a 5dB dip at 8 kHz. (Flush mount those tweeters folks!) The off axis response of this tweeter is as good as I had hoped, the results agree well with the printed specs for the 27TFF which is the same except for the rear chamber.

Here is a measurement I made on a Motorola Powerline Horn tweeter, sensitivity is measured at 97dB 2.83V/1M. This tweeter shows all sorts of frequency response abberations. I haven't included it here, as I'm still not 100% sure of my measurement method, but the waterfall plot for this unit looks even worse. Showing long decays at 2.5kHz, 4kHz, 5kHz and 8kHz. Above 8kHz the unit is so bad I can't tell much of anything. (BTW in case your wondering, no I never intended to use this driver in a loudspeaker project. I got it from work where they are used in weather profiling systems.)

Frequency Response for Motorola Tweeter.

Next up is the frequency response of the MCM 55-1170 woofer. This woofer shows lots of cone breakup everywhere. I'm tempted to order the rubber surround version of it to see if a higher loss edge termination makes a difference. Unfortunately, I'm not sure if all else is equal between the two drivers, but it would still be an interesting experiment. I'm also tempted to order one of the smaller (cheaper) aluminum cone drivers and see how bad it is. I'm just not sure if it's worth the $15 to prove that, yes indeed, the driver is quite unusable for anything more than low-fi applications.

Frequency Response for MCM 55-1170, as used in my small car sub.

T/S Measurement Section

Right now the only drive unit information that I can put up are the measurements made for my Seas CA25RE4X/DC woofers. These are high quality, paper cone, rubber surround units. They have a fairly long throw and decent power handling. I purchased mine from Madisound, although I think Solen and Speaker City can also order these units.

All measurments, unless otherwise noted, are for a driver with both coils in parallel. Notice how the moving mass, Mms, stays fairly close to the original value for driver 1 despite the changes in configuration. This is a good sanity check, Mms should be a physical constant, and can be derived from other values. Also notice the change in parameters such as Qts, Qes, Qms, and SPL. If your going to use a DVC sub in any configuration other than the one specified in the data sheets, don't use the T/S parameters given for the unit. Measure your own.

Check out Seas and Madisound at their web sites.