Unbalanced speakers

[snmhanson]

I recently build a pair of Carmody OS MTMs and have noticed that one side (let's call it the left) hasn't been playing as loud as the other side. I replaced the speaker wire, swapped channels on the amp and double checked polarity to narrow it down to the speaker. It isn't a hugely noticeable difference, though I do have to shift my listening position to the left to balance the speakers out. I also just played a bass-heavy song and the left mid drivers seemed to be vibrating quite a bit more than the right. I should also add that the port tubes were friction fit to length and it is possible that they could have adjusted in that speaker. I did wrap the tube with masking tape to mark the proper length as well as provide enough friction to hold it in place until I find the time to permanantly glue them to length. I realize I am going to have to dig into the speaker to determine the problem, but was hoping someone could point me in the right direction. Any ideas of where to start?

Thanks,

Matt

[MarkL]

Can you swap the xovers between the speakers? That's my first guess.

Could also be speaker cables. Did you swap those? Is one raised off the floor with quartz pyramids?

[Sydney]

If possible: do impedance sweeps and frequency sweeps w a SPL meter.

[mike1001]

is the louder speaker near an adjoining wall/corner?
this can create a slight volume boost, there may not be anything wrong.

if that is the case you can use the balance control.

[rpb]

I recently build a pair of Carmody OS MTMs and have noticed that one side (let's call it the left) hasn't been playing as loud as the other side. I replaced the speaker wire, swapped channels on the amp and double checked polarity to narrow it down to the speaker. It isn't a hugely noticeable difference, though I do have to shift my listening position to the left to balance the speakers out. I also just played a bass-heavy song and the left mid drivers seemed to be vibrating quite a bit more than the right. I should also add that the port tubes were friction fit to length and it is possible that they could have adjusted in that speaker. I did wrap the tube with masking tape to mark the proper length as well as provide enough friction to hold it in place until I find the time to permanantly glue them to length. I realize I am going to have to dig into the speaker to determine the problem, but was hoping someone could point me in the right direction. Any ideas of where to start?



Thanks,

Matt

Touch a small battery to the speaker input. Both woofers should move in the same direction. (If they don't, the polarity of one woofer is wrong.)

Stand up at your equal distance listening spot, and see if the louder speaker switches sides. (If it does, the tweeter polarity is probably wrong on one speaker.)

Play the speakers one at a time with some pink noise, or music, and compare the sound from straight on axis, to about 45 degrees above axis. Should be louder on axis. Do a couple knee-bends standing right in front of the speaker, It should sound "correct" on axis, and like something is missing as you stand up higher. (If the opposite is true, the tweeter polarity is probably wrong.)

Play a high frequency hiss, or 10k test tone, and compare the spl of the two speakers. This would be just tweeters playing, so if one is louder, the padding, or x-over may be wired wrong.

[snmhanson]

Thanks for the replies. I did discover a couple of things that certainly could have contributed to my issues. First, the solders to one of mids was loose and came off easily so I redid that. Second, there was a piece of cardboard that got lodged between the inside of one of the woofer cones and a wire.

I thought I had it licked at that point, however, I tried the battery trick and found that the polarity is off between the mids in two of my three speakers. Now, I don't know how that is possible as I wired them exactly according to the schematic, but obviously I missed something. I also just checked and confirmed that the + on the second mid is connected to the + on the other mid, and the - is connected to the - as well. Correct me if I'm wrong but wouldn't the mids have to be wired + to - and - to + for them to have the opposite polarity? As I said, I have to be missing something here. Can anyone give me a heads up on what I might have wrong? Could something in the crossover be causing the wiring issue or is it in how the mids are connected to each other? I don't see how since the second mid is only connected to the first mid, but I'm no electrician.

Thanks,

Matt

[djg]

Well, it's possible that the speakers themselves are mis labeled as to polarity. Swap the wires as needed to make them all the same and see what happens. It won't hurt anything.

[NEO Dan]

Now you need to check that the drivers are internally "wired" correctly, using the battery + to the terminal marked + does the cone move outward/away from the magnet? If not the driver is "wired" incorrectly internally and you need to mark the driver terminals for correct polarity and hook it back up to the crossover correctly.

[Paul Carmody]

A ha! You may be getting warmer! I have heard of a few HiVi B4N having the polarity mis-labeled at the terminals. You can easily test this with a battery connected straight to the terminals.

[mike1001]

< I did discover a couple of things that certainly could have contributed to my issues. First, the solders to one of mids was loose and came off easily so I redid that. >

I just had one of those and i thought i was the only one who couldn't solder

[snmhanson]

And the verdict is...

I got two B4Ns that were wired in reverse. I switched the wiring around in them and they are perfectly balanced now. As frustrating and time consuming as this was, it was a great lesson. I am going to go test the polarity on all of the speakers I have built. Just to make sure, a 9 volt battery is appropriate for testing drivers - or the entire speaker for that matter - right? No chance of blowing a cone when using a 9V battery?

Thanks again for all of the help!

Matt

[rpb]

And the verdict is...

I got two B4Ns that were wired in reverse. I switched the wiring around in them and they are perfectly balanced now. As frustrating and time consuming as this was, it was a great lesson. I am going to go test the polarity on all of the speakers I have built. Just to make sure, a 9 volt battery is appropriate for testing drivers - or the entire speaker for that matter - right? No chance of blowing a cone when using a 9V battery?

Thanks again for all of the help!

Matt

Use 1.5 volt. There's no need for more.

[Paul Carmody]

[snmhanson]

This goes to show how untrained my ear is (or maybe how great the OS MTM design is). I thought they sounded great and didn't realize they were off until listening to them side by side. Now they sounds really, really, really, great.

Matt

[rpb]

This goes to show how untrained my ear is (or maybe how great the OS MTM design is). I thought they sounded great and didn't realize they were off until listening to them side by side. Now they sounds really, really, really, great.

Matt

I've heard really good sound from speakers where one has an issue of some kind. Eventually, I will notice something is off, and track down the problem. I change x-overs, or drivers so often that it's easy to wire something wrong once in a while. Having measuring capability prevents a lot of this though. Many times, I measure only one speaker, and wire the other like it without measuring. I use jumper leads to connect x-over parts on the floor. I think that over the last couple years, I've had two test leads that were no good, and were altering my x-over even though I hooked it up correctly. A simple defect in the circuit, like paralleling a 10 uf cap with a 1.5 uf can be very hard to trace if the jumper on the 1.5 uf is dead.