Whats the best way to protect speakers?

[Subthumper]

Hi all, I've been doing a lot of repair work for a local studio and they've asked me to put some sort of protection system on all thier PA speakers. This is mainly due to idiots putting bass's, synths and kick drums through what should be only for the vocals and accoutsic's etc. ie the usual array of 300-400w peaveys and carlsbros.....and compact 12 and 15 cabs. Most of their cabs have got protection on the tweeters but what is the best way to protect the bass drivers? Is a fuse sufficient? Or is there a way other than using an amp with a self limiting system?
Any help here is most appreciated.
Cheers Just

[Protium]

PA speakers should be fine with everything. What about a notice telling them not to do it

[King Tut]

Blimey - I always put Kick through my wharfedale titan 12's and they're still going. I can feel some self flagellation coming on.....!

[Bill Fitzmaurice]

[quote name='Subthumper' post='309583' date='Oct 18 2008, 06:48 PM']Is a fuse sufficient? Or is there a way other than using an amp with a self limiting system?[/quote]
Fuses don't work. A brickwall limiter set so that the amp cannot deliver too much power no matter what is the only foolproof protection.

[tempo]

Would a hi-pass filter not help?

[Bill Fitzmaurice]

[quote name='tempo' post='309688' date='Oct 19 2008, 05:21 AM']Would a hi-pass filter not help?[/quote]
Yes, it would, and for that reason it should be standard equipment. But it won't prevent overpowering of the drivers.

[Thunderhead]

Up-rate the bass drivers so they can take anything the amp can throw at them, even distorted. Yes, I know you're not supposed to distort a PA, and NORMALLY (assuming an intelligent sound engineer) it's actually safer to use less speaker capability than the amp can deliver so the amp doesn't get driven into distortion... but that relies on the sound engineer actually listening for the distortion and not doing it! If musicians are in control, you need to assume the worst .

Pick bass drivers which can handle more than double the RMS power of the amp (per channel) - preferably even more - and if possible use one impedance step above the amp's minimum load too, so it cannot deliver as much power - ie use 8-ohm speakers if the amp can drive 4 ohms per channel, or two 16s if it's a mono amp with a 4-ohm minimum load... these are harder to find in PA type speakers though.

Yes, this does reduce the efficiency of the system and you won't get as much volume as you think it should be capable of... that's the idea! If it matters, I've also done a lot of repair work for rehearsal studios over the years and this is the only guaranteed way to prevent damage, both for instrument amps as well as PA cabs. If you deliberately under-load the amp, you'll also help prevent power stage damage too. (Don't do this with valve guitar amps though, they don't like to be underloaded.)

If this is not what they want to do (high-powered drivers are more expensive), you may need to modify the amps so there is a signal level pad (fitted internally) between the preamp and the power amp - this will stop the amp reaching full power if you arrange it so the preamp goes into distortion earlier than the power amp. This is a simple kind of brick-wall limiter, really.

With all these methods you may still need to increase the protection on the tweeters too, since reducing the volume of the amp and making it distort sooner will still have the usual effect. Increasing the value and power handling of the crossover resistor will help - it will also reduce the HF response of the cabs which is probably an advantage in helping with feedback in confined spaces.

As you can guess we are not talking ideal solutions for great performance and sound quality here . Just over-engineering to the point it's difficult to break things .

Edited October 19, 2008 by Thunderhead

[Bill Fitzmaurice]

[quote name='Thunderhead' post='309962' date='Oct 19 2008, 01:26 PM']Up-rate the bass drivers so they can take anything the amp can throw at them, even distorted. Yes, I know you're not supposed to distort a PA, and NORMALLY (assuming an intelligent sound engineer) it's actually safer to use less speaker capability than the amp can deliver so the amp doesn't get driven into distortion... but that relies on the sound engineer actually listening for the distortion and not doing it! If musicians are in control, you need to assume the worst .

Pick bass drivers which can handle more than double the RMS power of the amp (per channel) - preferably even more - and if possible use one impedance step above the amp's minimum load too, so it cannot deliver as much power - ie use 8-ohm speakers if the amp can drive 4 ohms per channel, or two 16s if it's a mono amp with a 4-ohm minimum load... these are harder to find in PA type speakers though.

Yes, this does reduce the efficiency of the system and you won't get as much volume as you think it should be capable of... that's the idea! If it matters, I've also done a lot of repair work for rehearsal studios over the years and this is the only guaranteed way to prevent damage, both for instrument amps as well as PA cabs. If you deliberately under-load the amp, you'll also help prevent power stage damage too. (Don't do this with valve guitar amps though, they don't like to be underloaded.)

If this is not what they want to do (high-powered drivers are more expensive), you may need to modify the amps so there is a signal level pad (fitted internally) between the preamp and the power amp - this will stop the amp reaching full power if you arrange it so the preamp goes into distortion earlier than the power amp. This is a simple kind of brick-wall limiter, really.

With all these methods you may still need to increase the protection on the tweeters too, since reducing the volume of the amp and making it distort sooner will still have the usual effect. Increasing the value and power handling of the crossover resistor will help - it will also reduce the HF response of the cabs which is probably an advantage in helping with feedback in confined spaces.

As you can guess we are not talking ideal solutions for great performance and sound quality here . Just over-engineering to the point it's difficult to break things .[/quote]
That seems an awful lot to go through when a $100 limiter is all that's required. As far as using lower powered amps goes, that invites overdriving them to clipping, and clipping has the nasty habit of taking out tweeters, even when they're supposedly protected.
Another tried and true remedy is a hefty damage deposit. Abuse is far less likely to occur when there's a penalty for doing damage.

[Thunderhead]

[quote name='Bill Fitzmaurice' post='309976' date='Oct 19 2008, 06:57 PM']That seems an awful lot to go through when a $100 limiter is all that's required.[/quote]That may be true for PA amps. Even so you will have to connect it in some way that prevents it being disconnected or bypassed by the users, which they may well do even if told not to. And you can't do it for the guitar and bass amps.

[quote]As far as using lower powered amps goes, that invites overdriving them to clipping, and clipping has the nasty habit of taking out tweeters, even when they're supposedly protected.[/quote]Not if you up-rate the protection as well . (Increase the values and power rating of the crossover resistors to restrict the power reaching the tweeter.) You have to basically [i]intend[/i] the amps to be driven into clipping (since they will be whether you do or not) and then rate the speakers high enough to withstand it.

[quote]Another tried and true remedy is a hefty damage deposit. Abuse is far less likely to occur when there's a penalty for doing damage.[/quote]That's a good way to lose business at your studio - musicians don't like having to pay extra even if they think they're going to get it back - and definitely not if they think they might not - and the sensible ones don't like the idea of being blamed (by implication) for damaging equipment when they don't. It's not always deliberate abuse either - many musicians just don't have a clue and don't realise that what they do may damage the gear.

Trust me, I've worked for several rehearsal studios and over-rating the speakers by at least a factor of two or better (especially in conjunction with raising the impedance) works, doesn't offer any opportunity for getting around it, and doesn't put off the customers.

Edited October 20, 2008 by Thunderhead

[rodl2005]

[quote name='Bill Fitzmaurice' post='309976' date='Oct 19 2008, 05:57 PM']Another tried and true remedy is a hefty damage deposit. Abuse is far less likely to occur when there's a penalty for doing damage.[/quote]



I good one this. I ALWAYS was VERY careful when I used to hire gear & had to pay a hefty deposit for damage- or leave a credit card to cover any damage I did. Not that I did any b4 THIS, but it DID make me be EXTRA careful!!!