SDA 1B impedance tests

jimbo1421

Hello,

I decided that before I started rearranging the living room I would test all the drivers on these recently acquired speakers. As I mentioned in my other thread on these speakers (http://www.polkaudio.com/forums/showthread.php?t=85190&page=2), I had been having trouble getting a good center response, vocals seem recessed down a long hallway compared to the left and right. It is not a subtle effect, but it could be a room effect. If I unplug the interconnect cable the center regains its relative volume. The room is currently arranged as shown on Page 1 of the attachment.

I tested the impedance of each speaker, then pulled each driver, checked the connections for +/- phase. (Black/blue=positive, white/green=negative, right?) I disconnected each driver, tested the impedance and listened to it on a separate amp. All the drivers put out a roughly equal level of sound. Impedance varied 7% between the lowest and highest tweeter values, 9% between the lowest and highest stereo speaker values and 15% between the lowest and highest SDA speaker values. The values reported below could vary as much as +/- 0.3 ohms (3-4%) as I was holding the probes on the terminals; I tried to pick the middle value. (Perhaps I should have made up spade connectors on the multimeter leads to get a more precise value.)

Here are the results:

Speaker/ Ohms

Right (overall)/ 3.7
Top tweeter/ 6.7
Bottom tweeter/ 7.2

Top Stereo/ 8.7
Bottom Stereo/ 9.5

Top SDA/ 8.5
Bottom SDA/ 8.2

Left (overall)/ 3.4
Top tweeter/ 6.9
Bottom tweeter/ 6.8

Top stereo/ 9.4
Bottom stereo/ 8.7

Top SDA/ 9.4
Bottom SDA/ 8.4

Can anyone comment on these readings? Are they acceptable? Would they account for the center problem I am hearing?

Thanks so much for your time.

Jim

nooshinjohn

I think I would try shuffling the drivers around to ballance the ohm readings between cabinets, and locations. For example, you indicate that you have Top Stereo/ 8.7
Bottom Stereo/ 9.5 in the right and Top stereo/ 9.4
Bottom stereo/ 8.7 in the left... flip the two drivers in the right cabinet so that the 9.5 is in the top slot and the 8.7 is in the bottom. Do this with all of the drivers and see if yoy cannot get equal readings in both speakers.

John

jimbo1421

Thanks, John. What you say makes sense. Before I try that I am going to make up some spade connectors for the multimeter probes and do another set of measurements. That +/-0.3 ohm variation while measuring bothers me more after thinking about it.

Jim

Jim

jimbo1421

Hello again,

Here are the new impedance measurements, on page 1 of the attachment. Pretty close to the old ones but with tighter error factors. I got some alligator clips for my multimeter. Page 2 shows the proposed new arrangement, if I read you right, John.

Are these ohm measurements anything like what they should be?

I wonder if I am even making these measurements in the right way. Each driver was disconnected, removed from the cabinet and tested. Should the speakers have a signal running through them while testing? I could get test signal software for my laptop and run it through my amp to each driver and test it then.

Jim

nooshinjohn

I would try it that way and see what you get.... maybe someone else can weigh in as well.

TECHNOKID

Consumer grade electronics may have tolerance between 10 - 20%, this is normal. Reading soemwhere between 7 9 ohms is good for cosumer grade electronics (not like military tolerance which would be in the 2 - 5% tolerance for example). Never try to feed a signal through while doing impedence measurement, you will more likely blow the fuse. When you do the impedence measurement, you are actually feeding the meter battery voltage through thus giving you the reading (voltage through meter selected resistance) worse condition you could also blow this variable resistance. Don't forget that multimeters can also be uncalibrated and also affecting your reading (same here, consumers don't invest money to get their multimeter calibrated while again using the same example, the military would). Your mani concern, do see a reading or not? Are they the same model number driver for ech sections? Coil impedence do not change value that I know of, they either are open or shorted and none of this is the problem. You must also make sure a minimum of 1 lead to the driver is totally disconnected from any other circuitry as otherwise they could affect your reading(s) IE: a resistor in either parallell or series would change your actual coil reading and so would another coil. In the case of a capacitor, the reading would fluctuate since the capacitor would tend to charge/discharge up to the value of the meter internal battery. That is what your cross overs cct are mainly made of: resistors, coils and capacitors!

Cheers!
TK

jimbo1421

Thanks John & TK,

I tested the resistance of all eight MW 309 out of the cabinet and completely disconnected. I also did a listening test: laid them all out on a table, connected each one in turn to my AVR right B channel and listened to the same 30 second Chopin prelude in quick succession. I could detect no difference in volume or sound quality between them. I did the same with the tweeters. So I think I can rule out a bad driver as the cause of my missing center, right?

All the speakers appeared to be wired in phase - black/blue to positive (red dot), white/green to negative.

While I still have the SDAs apart, what else should I check for? Keep in mind that as an electronics technician, I am a pretty good carpenter.

Thanks,

Jim

Schurkey

jimbo1421 wrote: »

I tested the impedance of each speaker,

jimbo1421 wrote: »

Here are the new impedance measurements,

Maybe I'm missing something--I don't claim to be an expert.

HOW are you testing for "impedance"???

Seems to me you're testing for DC resistance; and that's not the same as impedance at all.

jimbo1421 wrote: »

I had been having trouble getting a good center response, vocals seem recessed down a long hallway compared to the left and right.

When you figure out the problem, LET ME KNOW!!!! I've disconnected the SDA cable on my 1Bs because they sound very odd with the cable connected; and I finally got sick of it after close to twenty years. I too have verified phase of the drivers--and did not find a problem there.

I don't doubt there's "something wrong" with my 1Bs; but I don't know where else to look, and they sound pretty good with the SDA cable gone.

jimbo1421

Schurkey wrote: »

Maybe I'm missing something--I don't claim to be an expert.

HOW are you testing for "impedance"???

Seems to me you're testing for DC resistance; and that's not the same as impedance at all.


When you figure out the problem, LET ME KNOW!!!! I've disconnected the SDA cable on my 1Bs because they sound very odd with the cable connected; and I finally got sick of it after close to twenty years. I too have verified phase of the drivers--and did not find a problem there.

I don't doubt there's "something wrong" with my 1Bs; but I don't know where else to look, and they sound pretty good with the SDA cable gone.

OK, DC resistance. Like I said, when it comes to electronics, I am a pretty good carpenter. I would be glad to learn the difference.

I am beginning to think that whether SDA sounds "right" or "odd" depends on the recording engineers who probably weren't listening on SDA speakers as they made their mix. Maybe it is just chance that it sounds right on the SDAs. I have mentioned center vocals sounding very recessed. Vocals that are shaded to the right or left sound a lot more forward. Another example: a recently acquired LP of Boccherini guitar quintets. Listening with SDA, I had to double check the liner notes to make sure there were not two guitarists playing. Nope, just one, and in regular stereo that is all I heard.

I have started to listen again to the recommended albums from the SDA Playlist Sticky to see if I can tell what makes for a good SDA sound. Age doesn't seem to matter. My ancient copy of Dave Brubeck's Take Five sounds very good. There isn't much in the center on that album, just piano on the right, sax and drums on the left.

I will continue to experiment with them just to see if I can hear what everyone else here is so enthusiastic about.

Regards,
Jim