Speaker Protection help

[diydidi]

Steve and Ted you're both right on the money. It is definitely a case where the staff on duty are handing out equipment that are not matched and i know that even with "training" they still may get it wrong. I've already started changing out blown drivers for higher rated generic ones, that is really the answer although we right back to the begging if someone brings in a power amp and mini desk.....yes apparently this has happened.
I've had a play at a relay driven protection system that cbarrow7625 had suggested, link to follow.
I have my reservations in actually building it into any of these cabs, if i did, the line in would have to be dumped into a 50 or 100w resistor when tripped, just in case a valve amp was being used, that would at least cause the user to stop playing and investigate. Any way have a look it's not very exciting but knowledge gained should be knowledge shared... well IMHO.

https://www.youtube.com/watch?v=aU6GstGROu0

Hi.
Is you're relay circuit fast enough to respond to transients?

[malukaluis]

Not sure diydidi, i wrong in thinking that transients are short lived therefore not present at the coil for long enough to cause any serious damage?

[Enzo]

You are wrong. Speakers can die from a variety of causes.

Overexcursion is one. Send too large a pulse, and the voice coil can hop all the way out of the magnet gap. If it then does not center exactly back into the gap, your speaker is ruined.

Transients are indeed short lived - by definition. But a strong transient can cause a voice coil to arc somewhere and burn it, or even cause it to burn out like a fuse.

Excess power also damages speakers. Not so much running 100 watts into a 25 watt speaker for a moment. But extended periods of say 35 watts into 25 watt speakers will cause them to overheat and warp or melt the voice coil.

I have to admit I am more worried about simple too much power all afternoon, rather than the occasional sky-high transient. I never thought about it, but in addition to whatever you come up with, perhaps a simple MOV of appropriate rating across the cab would limit transients.

And that leads me to think that "speaker damage" is like other problems such as "hum" in that the damage can come from a variety of unrelated sources. And each source would have its own cure. The protection against impulse damage (transients) would be something different from protection against long term over-power. Your master protection system may have to be a collection of several things.

[rjb]

...operate on cash. If you've got ten rooms, taking £100 deposit on each - when the local crackheads get wind of this you'll be robbed in about 5 seconds.

Presumably, the room rent would also be paid in cash. Why would taking deposits be any more dangerous?

[Steve Conner]

The guys running the rehearsal studio probably ARE the local crackheads anyway.

The way I see it, the size of transient that a tube amp can produce is limited by saturation in the output transformer. It can't produce a massive thump that would blow the voice coil out of the gap.

I was once working on a solid-state power amp while it was hooked up to a speaker. I was half expecting disaster, so I used a cheap speaker borrowed from a boom box. My scope probe slipped causing 55V DC to appear on the output. There was a very loud CRACK! and the speaker didn't work any more.

Also, once I was playing bass in a rehearsal room, and the grill on the bass cabinet was loose and rattling, so I removed it and sat it to one side. One of the studio people came in and freaked out: You wrecked our f****in speakers! I hadn't noticed, but someone else had poked in all the dust caps on the woofers, and he thought it was me!

[drewl]

It's a fine line to walk, but usually if a band breaks a piece of equipment they are liable for it.

I repair equipment for a rehearsal studio, and man the abuse that stuff gets!
I got to be friends with the owner, alot of times people would rip the jacks out of the speaker cabs by grabbing their head and forgetting it was still attatched!

I fix at least a couple amps a week, broken jacks, pots, blown amps.

Mainly my friend uses big ass PA cabs for bass and loaded the 4x12's with high powered speakers so they rarely got blown.

[J M Fahey]

someone else had poked in all the dust caps on the woofers, and he thought it was me!

Ok, now, just between you and me, no one's listening ..... it was you who poked all those dust caps in, wasn't you?
Was it FUN????

[Enzo]

Yeah, you have to back the microphone away just a LITTLE bit...

[bob p]

I see a different problem here. I see people with no stake in the game abusing the gear. They have no incentive to care for the gear. Give them one. Take a security deposit before renting the room. Make them responsible for blown gear.

Enzo is right -- these people have no skin in the game, so they don't care about the outcome. Because they aren't being held responsible for their actions, they encur no risk by acting irresponsibly. The best way to make them care about the outcome is to make them encur risk by forcing them to become responsible for their actions. When they become financially responsible for the losses that they cause, then they'll have plenty of incentive to stop being carless.

Collecting a security deposit is a great idea.

Another approach would be to shift the failure point so that their head blows up instead of your cabinet. Now I've got all sorts of nefarious ideas popping into my head...

[J M Fahey]

Well, simply fusing the speakers will achieve that, both by protecting them *and* leaving output transformers unloaded at full power.
Talk about an unexpected lightshow

Now seriously, those 4x12" should be stuffed with 100 to 150W RMS (each) PA type speakers
No 4 or 6 6L6/EL34 guitar head should be able to blow it.

[gbono]

Presumably, the room rent would also be paid in cash. Why would taking deposits be any more dangerous?

Oh dear you must live in a very safe place ;-) People are robbing banks in very "safe" areas here - if you increase the income of a rental studio, by the adding a deposit fee, the sharks will come.

[Enzo]

I think his point was that the sharks would already be there for the rental cash.



I know I have told this before, but...
We used to be a Klipsch dealer, and their large PA cabs came with fuses. We pulled the fuses to find they were 20 amp fuses. Called the company to find out why. They told us that fuses really do a poor job at best of protecting speakers in any way. But SO MANY people had asked for fuses, they added fuse holders to the speaker jack plate. The factory installed 20A fuses, which would never become a nuisance blow problem if left alone. Their instruction was that anyone dead set on fuse protection could determine the best value fuse on their own and install them in the holders.

[bob p]

the sharks would already be there for the rental cash.

Sharks? When I lived in Indianapolis, I was told by a police officer that 2 of 3 adults had concealed carry permits. I was surprised by that. The next time I walked down the street I kept asking myself who those 2 out of 3 people might be. I think the number in the UK is a lot lower.

They told us that fuses really do a poor job at best of protecting speakers in any way.

Fuses may do a poor job of protecting the speakers, but like JMF said, they can do a great job of destroying a tube amp when they open. I don't think fuses are the answer unless your intent is to train the renters to limit their volume level by damaging their equipment or by causing frequent nuisance trips. When nuisance trips become too frequent they'll just rely on the old trick of wrapping the dead fuse in foil, and then your protection scheme doesn't work any more. Maybe a circuit breaker would be a better idea because there's no removable part for them to tamper with.

[bob p]

This thread reminded me of the old tweeter protection circuit that EV used to use in their crossovers for the ST350 tweeter -- a light bulb. When there got to be too much power, the tweeter didn't get any louder but the light bulb did get brighter.

I guess you could put two zeners cathode to cathode across the speaker terminals to build a bipolar transient voltage suppressor.

[Enzo]

Or just buy transient suppressor diodes to start with.