Can you blow out a passive crossover?

drphoto · « **on:** 15 Dec 2007, 11:47 pm »

Well, I got a little carried away last night and blew out the tweeters in my Merlin TSM-Ms. No biggie, as it's fairly easy to replace the driver diaphrams, in fact I had a spare set on hand. Well replacing them did not solve the problem. I put a volt meter on the leads to the woof, and got a reading, but not on the tweeter leads. Could I have damaged the crossover? Seems like the tweeter would have blown first.

mgalusha · « **Reply #1 on:** 15 Dec 2007, 11:54 pm »

It's possible a resistor opened up or a capacitor failed. I have seen torched resistors in crossovers. You might check to see if there is a fuse somewhere but my guess would be a fried resistor.

Davey · « **Reply #2 on:** 16 Dec 2007, 12:28 am »

Did you check the tweeters before replacing the VC's?

Your voltmeter being your ohmmeter? You should get a reading directly on the tweeter leads, but you won't if probing the tweeter input to the crossover since a series capacitor will block DC......even when good. A simple process of elimination should find the faulty component. Your ohmmeter should be all your need.

The question is why did you burn out the tweeters....if you did. The MDT-30 is a pretty rugged driver. Too low a power amp?

Dave.

brj · « **Reply #3 on:** 16 Dec 2007, 12:44 am »

Yes.

When I was first breaking in my speakers I had one of my external crossovers let go after the associated tweeter had its ribbon let go. Looking inside the crossover enclosure, it appeared that some resistors overheated and cooked the originally gloss-white finish of my Sonicaps (to which the resistors were glued) to a nice brown color. There was a bit of "splatter" inside as well, but I couldn't determine if that was from the overheated caps "venting", or possibly from some glue that liquefied. I had the system running during for an extended period of time to break-in the woofer surrounds, but the Arcam receiver wasn't hot, so I don't believe that it was clipping - which is one definite method of stressing a speaker. We never really nailed down the exact cause with any certainty, but all was well after replacing a few of the caps and resistors, and installing a new ribbon in the tweeter.

In my case, the overheated resistors were either on the tweeter or mid-range portion of the network. Without checking my notes, I'd guess the tweeter network, because I know the tweeter needs to be padded down quite a bit to match the sensitivity of the woofer. I don't know the sensitivities of the Merlin drivers off-hand, but tweeters are usually more sensitive, so I'd check that network first.

Good luck!

drphoto · « **Reply #4 on:** 16 Dec 2007, 06:04 pm »

Amps used are Stratos Monos w/ cap upgrade. The Merlins are high passed using ACI 85hz passive filters. It was loud, but not distorting.

I measured voltage at the leads w/ the meter set to AC. Just to check, I desoldered the leads to the woof and touched them to the tweeter terminals (w/ volume very low!) and the tweeter appeared to work, so it must be the xover. I'll try to pull some of the stuffing out of the way and see if I can spot a fuse. Doubt if there is one in there on a speaker of this level.

Could I test for a blown resistor by putting an ohmmeter across it? Seems like if it was blown it would be like an open circuit.

Oh well, I wanted to send them back for the 'magic mod' anyway, but just not right after Xmas expenses.

Thanks for the replies.

jqp · « **Reply #5 on:** 18 Dec 2007, 01:14 am »

1. Connect ground to lightning rod...

doodlebug · « **Reply #6 on:** 18 Dec 2007, 03:55 am »

IF you were cranking it when they tweet went, you may have taken a crossover cap with it. When you get inside the cabinet, look for a cap that may have cracked or otherwise, broken open. This would have happened from heating. There is a voltage limit on these caps that _may_ have been violated. What's the size of your amp(s) driving these beasts?

Cheers,

David

slbender · « **Reply #7 on:** 18 Dec 2007, 06:29 am »

Can you blow out a passive crossover?

First of all, burning in speakers is like military intelligence, a true contradiction in terms, its more likely its the USER is the one who burns in, or becomes changed, not the speaker, so blowing your drivers to burn them in is a waste of time, money, and electricity.

Well depends if they built that crossover like a proverbial tank, or out of tinfoil (so too speak). Sort of unlikely any 5 Watt or 10 Watt or larger wire wound cement resistors would go south easily, I've seen some 3 Watt enamel wire wound resistors glowing "orange hot" at about 12 Watts without failing. Of course, if they used 2 Watt metal film R's its difficult to get them to hold up under any kind of overload. Most crossover caps are usually rated for 50 Volts if NP electrolytic, or 250 Volts or more if polypropylene, or polyester, and coils are usually pretty sturdy. So I guess it depends on what parts they put in those Merlin TSM-Ms, and I'm not familiar with them. And it also depends how powerful your amp is. Often the tweeter with the thin wire voice coil is the weakest link. So just as some silicon sometimes will blast itself to bits to save the fuse protecting it...

Often the tweeters are the first parts to go..

I remember that the old AR Amplifier and AR Receiver, the ones with the gold front plates made back in the mid-to-late 1960's, when silicon was fragile and no complex protection was built-in, the driver and output transistors were actually in parallel if I remember that circuit correctly, so the driver delivered the first Watt to so. If either the driver or output parts failed, both would die, and if the user had loaded the fuseholders with 5, 6, or 8 Amp AGC fuses in the speaker line, it would put about 50+ Volts DC at 4, 5, or 6 Amps into a speaker, and an AGC 5 Amp fuse could hold at that current for almost an hour. So if the amp was driving 4 ohm AR's 3's, or other 4 ohm speakers as were commonly used with those AR Amps, the voice coils would rapidly overheat and the woofers would sometimes catch fire without the voice coil failing (or maybe just smolder and smell a bit). People whose house had burned down, or who saw flames, would never really quibble about whether the tweeters also went, or if the crossover was damaged, I guess the heat and smoke and stink of smoldering anything was bad enough.

-Steven L. Bender

Quote from: drphoto on 15 Dec 2007, 11:47 pm

Well, I got a little carried away last night and blew out the tweeters in my Merlin TSM-Ms. No biggie, as it's fairly easy to replace the driver diaphrams, in fact I had a spare set on hand. Well replacing them did not solve the problem. I put a volt meter on the leads to the woof, and got a reading, but not on the tweeter leads. Could I have damaged the crossover? Seems like the tweeter would have blown first.

*Scotty* · « **Reply #8 on:** 18 Dec 2007, 05:58 pm »

Here is a link to some testing which substantiates that driver burn in does occur and is measurable.
http://www.gr-research.com/burnin.shtm Internet Explorer must be used to open page.
Scotty

Kevin Haskins · « **Reply #9 on:** 18 Dec 2007, 06:04 pm »

A poorly designed one can be damaged.

For most home audio applications, you just don't run the kind of power through them to damage anything. The driver will be the first to go by a long shot. But... as I said, you a poorly designed network that doesn't look at the power going through a resistor COULD go. Just don't use a poorly designed product and your should be fine.

Kevin Haskins · « **Reply #10 on:** 18 Dec 2007, 06:08 pm »

Quote from: *Scotty* on 18 Dec 2007, 05:58 pm

Here is a link to some testing which substantiates that driver burn in does occur and is measurable.
http://www.gr-research.com/burnin.shtm Internet Explorer must be used to open page.
Scotty

I'm sorry, but mechanical break-in of suspension components is common knowledge. The electrical burn-in is the subject requiring some flights of fancy. In other words, there is not an iota of physical or research evidence to support it at this point.

What is left out of that analysis, is the fact that cms changes usually have very little effect on the final response. The changes occur in a complimentary manner and the output changes little. So... while I can measure the change in Fs and Cms, its effect on the final system is fairly small.

I like Danny, but I think the article is written in a manner to prove his point, not to seriously examine the subject. Its written to PROVE that driver break-in occurs. Which it does (no surprise as everyone already knew that), but it makes a claim that electrical break-in is responsible for most of this change without ANY evidence to support it.

*Scotty* · « **Reply #11 on:** 18 Dec 2007, 06:56 pm »

Kevin, slbender's post seemed to indicate that he didn't think a speaker changed at all over time and sounded the same from day one.
I would have liked to link to some information on whether a speakers spectral decay changes as a function of suspension compliance changes.
I suspect that the waterfall plots of drivers look cleaner after the suspension loosens up. The harmonic distortion numbers may also improve as well.
This is sort of an academic exercise at best,for my self, I don't judge a driver on how it sounds cold out of the box because they usually sound better after they have set on the floor playing for two or three days loud enough to make the driver use about half its excursion. As far as drphotos
crossover problems are concerned, Merlin had to attenuate the MDT30 by at least 3dB which means that at least half the power the the speaker saw
above 2150 Hz crossover frequency had to be dumped through the Lpad network before it hit the tweeter. My vote goes towards a blown resistor
as the culprit. PartsExpress has some 12watt non-inductive resistors by Mills that would be good candidates to replace the blown resistors in the attenuation network. They could be paralleled if higher power dissipation was required.
Scotty

drphoto · « **Reply #12 on:** 18 Dec 2007, 11:24 pm »

Thanks Scotty. Would putting an ohm meter across the resistor show me the culprit? My electronic knowlege is limited to identifying parts and decent soldering.

*Scotty* · « **Reply #13 on:** 19 Dec 2007, 01:01 am »

Yeh,You betcha.
Scotty

Davey · « **Reply #14 on:** 19 Dec 2007, 03:38 am »

dr,

Depending upon the actual configuration of the tweeter crossover in your TSM's you may have to lift one lead of a particular component to check it properly. (There may be another parallel path that would provide a bogus reading.)

However, if your ohmmeter reads an open (or a considerabley higher value than it should be) across a resistor...even if it's in the circuit...you've got a bad resistor. There's probably one resistor in series and one in shunt in the tweeter network.

Dave.

TomS · « **Reply #15 on:** 19 Dec 2007, 03:39 am »

Just wondering why you don't just call Bobby and ask him? I'm sure he'd help you through those test without too much problem.

Tom

WYRED 4 SOUND · « **Reply #16 on:** 19 Dec 2007, 05:10 am »

Passive crossovers can easily be blown out, especially when the power ratings are exceeded by the amplifier that is powering it. It is the similar effect as a driver burning up.

Sometimes the designers will incorporate fuses to protect such problems, but they tend to leave them out now a days because of the effect it has on how the speakers sound.

The best bet for a crossover is an electrical one such as we have done with our multichannel that filters out the low frequencies, and allows you to bi-amp the speaker. I hope this helps?

EJ
www.wyred4sound.com

drphoto · « **Reply #17 on:** 20 Dec 2007, 05:59 pm »

Hey Tom, I'm sort of afraid I'll get a scolding from Bobby for mistreating his lovely speakers....

But, as I've wanted to send them back for the 'magic mod', I may just let him deal w/ it. Heck, the mod may replace the crossover anyway. Gotta be something big for what it cost.

I just can't believe the VC didn't blow as I've done before. I've got a bad habit of standing on the throttle and blowing drivers. (in various speakers)

TomS · « **Reply #18 on:** 20 Dec 2007, 06:40 pm »

Quote from: drphoto on 20 Dec 2007, 05:59 pm

Hey Tom, I'm sort of afraid I'll get a scolding from Bobby for mistreating his lovely speakers....

But, as I've wanted to send them back for the 'magic mod', I may just let him deal w/ it. Heck, the mod may replace the crossover anyway. Gotta be something big for what it cost.

I just can't believe the VC didn't blow as I've done before. I've got a bad habit of standing on the throttle and blowing drivers. (in various speakers)

Actually, knowing him like I do, I think he'd be MORE upset if you monkeyed around with it without asking him first

If you really get on the throttle that much (I do too occasionally), you might want to consider moving on to the smaller SP Techs that are really built for that sort of thing

Just a thought.

drphoto · « **Reply #19 on:** 20 Dec 2007, 07:13 pm »

Bobby's nice, but he is a bit of a curmudgeon, at least from my experience.