Speaker overload (tweeter) protection using bulbs (repost)

This is a well established technique for preventing voice coils burning out under conditions of 'overdrive'.

There is a stage monitor I'm having problems with that uses this method.

The HF sounds very distorted and almost cuts in and out.

I looked closely inside and found some damaged push-on terminals. Ah, I thought, probably a poor contact causing the probelm, replaced them, checked driver DC resistances etc, reassembled thinking I'd probably fixed it.

But no, the low level HF and distortion continued.

I'd checked the DC resistance of the protection bulb but later it occurred to me that it might have 'very nearly' burnt out and have a weak spot that wouldn't show up on a DVM but passing signal would heat it and cause this trouble. I'll be able to find out soon enough but I wondered if anyone else had ever encountered this ?

In the meantime I brought the HF driver home to check it's not voice coil rub.

Graham

Reply to
Eeyore
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I imagine that there are variations in lamps, given that they are designed to provide 'light', not speaker protection. I suspect you'll find an issue with the driver, though. Swap them around to check and/or do a sweep test.

I just picked up a set of Bose (I know...they were cheap) 201s at a thrift store. The only thing wrong with them--besides being Bose--were the blown out protection lamps in series with the tweeters. Not bad for $7.99, plus the cost of two lamps...altogether less than $10. They'll make decent computer speakers for my 12 year old.

jak

jak

Reply to
jakdedert

A 'swap', or rather replacement, was done earlier with no good effect. Hence I laid the suspicion on the damaged push-ons. I will still test the drivers though. I have 2 drivers that measure ok plus a third blown one and a replacement diaphragm.

Nice steal. For undemanding work they aren't *that* bad.

Graham

Reply to
Eeyore

I think it's unlikely, because any fracture causes a local hotspot, which rapidly leads to failure. I'd look at the socket instead! :) We've probably all seen strange tin-lead phenomena on lightbulb button contacts. The constant thermal cycling, the pressure, the dissimilar metals...

Bob Morein (310) 237-6511

Reply to
Soundhaspriority

Some Machs and RCFs use a 24 volt projector lamp. I`ve seen these become intermittent - they check fine with a meter, but introduce terrible distortion and crackling under pressure - it sounds just like the driver diaphragm breaking up. They also easily break if the cabinet is roughly handled.

Ron

Reply to
Ron Johnson

here is a novel thought DON"T OVERDRIVE THEM simple and effective

it's what I do the easiest way to overdrive a speaker is to use a amp larger than the speakers rateing George George

Reply to
George's Pro Sound Company

I will double check that. Thanks for the tip.

Interesting point.

Graham

Reply to
Eeyore

24V truck lamp here.

That's EXACTLY what I'm getting. Thanks for the effective conformation.

Well it has been but the bulb's nicely cushioned.

Graham

Reply to
Eeyore

The amps aren't but a blast of HF feedback will do it since it will whistle through the HF filter. I am as it happens going to fit an 80W P-Audio driver in the damn second JBL JRX112M that's blown its puny HF driver for the second time, despite improving JBL's original ineffective bulb protection which was

100% ineffective. Jesus that design is CRAP. 1st order crossover !

Bear in mind these are the 15 year old monitors made of MDF and have been very little trouble generally over the years.

Graham

Reply to
Eeyore

Been using some Wharfedale stage gear for a year or so. The mains are all protected by lamps. I've replaced two in a year but not experienced a distorted HF. You'll find problems in the xover or drive I would assume rather than the lamp.

Reply to
Meat Plow

or maybe it's time to upgrade from that MI grade junk your using George

Reply to
George's Pro Sound Company

Who, me?

Reply to
Meat Plow

From what I've heard they're well considered and in the IAG group now.

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The Chang brothers don't believe in messing about AIUI.

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Graham

Reply to
Eeyore

Easily said - but not so easy to do when setting up this sort of equipment. Let alone when that equipment is being used by all sorts.

Strangely that's not always so.

The best solution would be a decent limiter on the amp input - but these cost if it's not going to sound horrid when it operates. A bulb is a very cheap solution to help protect the speakers.

--
*If love is blind, why is lingerie so popular? *

    Dave Plowman        dave@davenoise.co.uk           London SW
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Reply to
Dave Plowman (News)

We've been using the Warfe pro-audio stuff for a year and have had few problems. One 2500 watt power amp we used for our 18" subs got sent back because it was too sensitive and would fault when pushed hard at

4 ohms. The replacement did not exhibit this behavior under the exact conditions. I've replaced a couple lamp protectors elsewhere.

I wouldn't call Wharfedale junk. It's usable, sounds good and reliable and a lot less expensive than other name brands.

Reply to
Meat Plow

No lamps in my meyers. setting up a system that both sounds good and stays within the limits of the equipment used is NOT hard, it simply requires one know what they are doing. a amp equal to the speaker rms rateing will never burn out the speaker unless the amp is clipped hard and long it will never exceed the excursion of the speaker unless someone fires a gun a inch from a mic at foolish gains set your system up properly and you have no need for these foolish lamps. create cheap MI gear that is used improperly and you need to limit the abuse idiots can administer, to save on the warrentte costs I have never heard a speaker with lamps(I've owned plenty) sound as good as a speaker with out lamps

again no lamps in my meyers, I do have alimiter but it is set well above any threshold I pass music at. why buy a 1000 watt amp then limit it to 300 watts, why not just buy a 300 watt amp? George

Reply to
George's Pro Sound Company

I consider W home stereo grade gear, not suitable for Pro Live Sound, below behringer

Reply to
George's Pro Sound Company

These days always having 'someone who knows what they're doing' is rare. And even less likely with a small band starting out. So you need to make equipment as idiot proof as possible.

Either the amp cannot produce enough wally to damage the speakers or it can - so the gunshot thing is rubbish. But no speaker is designed to handle DC for long - which is what you can get from a grossly overloaded amp. To be certain that DC couldn't wreck the speakers would require a

*much* smaller amp than would otherwise make sense. Or, of course, use an amp which can't pass DC.

Correctly designed the lamp should have little effect on the sound as its cold resistance will be very low. Only when it starts to 'protect' will the resistance increase.

Why are you using a limiter at all, then?

--
*Rehab is for quitters.

    Dave Plowman        dave@davenoise.co.uk           London SW
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Reply to
Dave Plowman (News)

And it is. Another new house engineer recently for example.

Well this is where it gets slightly complicated.

But a simple level limiter still won't stop the amp delivering full power say @ 8kHz. Tweeters aren't meant to see that. It would have to be a frequency sensitive limiter matched to the crossover. Which has given me a product idea of course.

Graham

Reply to
Eeyore

Actually, the easiest way to overdrive a speaker is to play it at a level where it produces audible distortion. But as most listeners have no idea what distortion sounds like...

Reply to
William Sommerwerck

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