[JoshK]

I have this $100 pair of Omage AV21 bookshelf speakers, which by the way, are damn good for the $$!  They use nice drivers and the cabinets are very well made, especially considering the cost of the speakers.  The crossover looks very simple and inexpensive, which isn't a shock.  

One of the monitors, however, seems to have a problem with its lower highs.   It sounds like static when playing certain music and gets progressively worse, the longer you leave the speakers playing.   If you turn it off, wait a bit and then replay the music it starts over at not so bad till it finally gets really bad.  

At first, I was thinking the tweeter was blown, although I wasn't sure how that happened since I didn't play them very loud or anything.  They don't sound bad as long as the program material doesn't have music in that frequency (guessing it is in or near the xo range).  I was just going to look which tweeter was being used in this speaker and order a replacement, but I am wondering if it isn't the cap that is malfunctioning and not the tweeter.  Any guesses or ideas?

[bubba966]

I'd think it's a problem with something in the crossover if it gets worse as it's used then reverts back to not so bad after it's cooled down.

I don't have enough experience in these things to say if it's a cold solder joint that's come a bit loose. Or if it's a cap or some other component that's gone bad.

Usually when you blow a driver, it's bad all of the time & doesn't change, right?

[JoshK]

That is what I would have thought, but I am no expert in this area.  I haven't blown many speakers except for car audio drivers.  Never blown a tweeter though.

My guess is it is a faulty cap, but that is just a guess.  I was considering reexecuting the XO with somewhat better parts (Madisound xo parts) as that wouldn't be too expensive and these cheap monitors are good enough to deserve a little more.  They will likely end up being my shop speakers if the wife will let me steal them out of the bedroom system.

[bubba966]

Have you looked at the crossover yet?

Or smelled the crossover or tweeter? If the tweeter is toast it'd smell pretty bad. And I'm sure if a cap was bad it'd not smell so great either.

[markC]

Also could be a bad inductor,(if it has one), in the high pass allowing low frequency through.

[JoshK]

yeah it has an inductor....I just didn't know what they do exactly.

[WerTicus]

just buy new parts of the same value and replace!

given that its all junk it will probably cost you all of 10$ to do it and if you wanted to you could make the speakers sound a whole lot better by using better quality parts.

if you dont know what they do - its a good thing you have the interweb and have all the information just waiting for you to read up on!

If your too lazy to do that then just take the parts to your local bits and bobs electronics store and tell em you want some more of 'these' as you pour the pile into the guys hand and he can measure them for ya

[wreilly]

One of the monitors, however, seems to have a problem with its lower highs.   It sounds like static when playing certain music and gets progressively worse, the longer you leave the speakers playing.   If you turn it off, wait  ...

Try swapping speaker positions first. It may not be the speakers.

[JoshK]

Thanks guys!

I have a multimeter and know how to measure values.  I can identify which part is which and can even read them in a circuit schematic but I have no idea what role they actually do in a crossover.  I need to read some more on the subject but my prof exam have been taking all my free time.

I think I will take inventory of the parts, and order up some better parts off madisound or something.  The crossover is real easy to get to in these speakers.  just pull the binding cup out the back and the xo comes with it.

[JoshK]

How do you figure out what value an inductor is?  I figured out the rest of the circuit but unless I am missing something it doesn't look as though you can measure an inductor with a multimeter.

[gary]

Josh

You might try calling Omage. There's a number at the end of this page:
http://www.davecohifi.com/Files/Omage_catalogue.pdf

Have you tweaked your av21s? It makes a substantial improvement, and they're pretty much free.

http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=327946&highlight=omage

Gary

[JoshK]

Thanks Gary for the info.

My speakers are the newer ones with the simple tweaks already done (no resistor in mine nor screen on port) but I will try out the Zobel network.  I just need to fix this problem with one of the speakers.

[WerTicus]

you need a fairly decent multimetre to measure inductance.... actually very few measure it - i made it a requirement for my second multimetre and managed to find one that measures it for less than 100 dollars but it only measures it to .01 mH and no more accurate than that...

if you bought a standalone inductance metre it would measure to .001 mH

but i suppose .01mH is enough.

[JoshK]

thanks werticus, you answered my question.  The inductors aren't labeled and so I have no idea what they are, or if they are working correctly.

[WerTicus]

also chances are the inductors are made with 1mm or thinner wire that isnt very pure copper you can get fantasticly tight base out of 1.5mm wire that is pure copper.

or as my friend said "did you put spikes on the speakers???"

[ginger]

Josh,
Hope you have the problem fixed by now but if not:

Inductors pass low frequencies and block high frequencies.

Capacitors pass high frequencies and block low frequencies.

Thus the simplest XO will be an inductor in series with the bass driver and a capacitor in series with the tweeter.

Most XOs are more sophisticated than this but the basic principals apply.

Inductors VERY RARELY fail - after all they are just a coil of wire.

Capacitors on the otherhand are very easy to damage.

I would suggest you try replacing caps on the offending unit first. Actually I would check ALL the solder joints first and then start replacing caps if that doesn't fix it.

Debugging:
1) Swap the speakers over to confirm its in the speaker and on NOT one channel of the power amp
2) If its easy to do swap the XO between the boxes to confirm its the XO and not the tweeter. Be very carefull not to mixup the +ve and -ve connections to the drivers. Use a pen to label the XO connections BEFORE disconnecting anything.

Once you've confirmed its the XO then start replacing capacitors.

Hoope this of some help.
Cheers,
Ginger