speaker protection/ newbie?

[djgout]

Hello all, I'm new to this board but recognize some of you from TapeOp.

I'm kinda the default tech at a studio because I used to work for an installation company and can solder like a trained monkey who's really good at soldering.

I've got a few questions about fusing speakers. We're planning to fuse up about 6 pairs of monitors this week. I know you take the maximum handling power and divide by the impedence and then take the square root of that number to find the proper size fuse to hold constant at the maximum power, but how much of a pad should I allow to be sure the fuse will blow before the speaker? How have any of you gone about actually attatching the fuse holders to the speaker?

Also, are there any good techs in Boston, aside from sending stuff to Mercenary or Sonic Circus or Alactronics? We've got some V72s and PQ14Ss that have been acting up and really can't afford to have them reracked, we just wanna get them checked out.

thanks
justin

 

[Test Point]

I can't tell you how many speakers I've replaced that were blown and the "fuse" was still intact....when an amp hits the rails because of an internal defect and there's no built-in DC protection inside the amp, it's usually less than a millisecond (I may be exaggerating a bit) and the voice coil is toast...but the fuse ain't....If your speakers are under powered for the amp(s) you are running, you're just begging for problems...my rule of thumb is to make sure that the speakers can handle at least double what your amp will deliver and use good amps that have good DC and over current protection circuits built into them...
Good Luck
TP

 

[mcs]

[quote author="Test Point"]If your speakers are under powered for the amp(s) you are running, you're just begging for problems...[/quote]
On the other hand, if the amp is overpowered, it is less likely to clip or put out DC and blow the speakers.

I would say an underpowered amp is the best way to destroy speakers...

Best regards,

Mikkel C. Simonsen

 

[Test Point]

[quote author="mcs"][quote author="Test Point"]If your speakers are under powered for the amp(s) you are running, you're just begging for problems...[/quote]
On the other hand, if the amp is overpowered, it is less likely to clip or put out DC and blow the speakers.

I would say an underpowered amp is the best way to destroy speakers...

Best regards,

Mikkel C. Simonsen[/quote]

MCS,

Yes, I guess that's what I was saying but probably not clear enough....it's really a balancing act and setting levels correctly all the way down the signal chain, from the mic inputs all the way through to the speaker outputs. in short, my experience is that speaker fuses just don't react fast enough to an amp hitting one of the rails (usually means that 55-100 or more volts DC hits the voice coil and instantly destroys it).

TP

 

[PRR]

> fuse up about 6 pairs of monitors this week.

Waste of time. If someone hits them with high power in the tweeter range, the tweeter will melt at power MUCH less than the full-range power of the speaker. If you get very low tones, speaker cones will slap and rip with very little actual power.

The only way to go for monitoring is to get speakers (and amplifier) MUCH louder than any client will ever need.

In PA, it sometimes works to set-up a limiter very carefully (probably after the crossover, which means active bi-amping); but this will foil critical monitoring by adding compression.

 

[thermionic]

On the other hand, if the amp is overpowered, it is less likely to clip or put out DC and blow the speakers.

Couldn't agree more :guinness:

If you want to get into the realm of rolling your own protection, Randy Sloane's book "High power audio amplifier construction manual" is essential IMHO, ISBN: 0-07-134119-6 Book outlines numerous circuits for DC/short protection.

You can also buy self-powered o/load protector kits such as the one made by Velleman: http://www.velleman.be/ (Scroll to "kits" then "audio", then scroll down to DC-protection module). Be warned that the Velleman only comes on at a few hundred milliamps DC which is too much for some people's taste.

A basic method that could offer some protection (not DC) would be to put an ammeter in series with one of the power rails, and work out what a comfortable current limit (via a dummy load) will be for a particular monitor. This is not an exact science, but will enable you to calculate a margin for a rail fuse that will hopefully blow before your main-driver's voice-coils in an ac situation (but won't do a lot for the tweeter if you're on passive x-overs as PRR has asserted).

Cheers,
Justin

 

[hitchhiker]

Rod Elliott has a speaker protection project. #33

heres the link;

http://sound.westhost.com/project33.htm

 

[djgout]

thanks everyone.

yeah i've always believed that having an amp capable of overpowering the speakers was the way to go.

the reason we want to fuse them is that working with some clients they just want it insanely loud and we've had some problems blowing speakers because of the client just reaching over and cranking it up. so we're trying to keep from having to keep replacing speakers.

we understand that power surges and DC pops are fast enough to kill the speaker without killing the fuse. but won't fusing the speakers keep the client from killing the speaker?

 

[Test Point]

I have used a DBX compressor with a "peak-stop" in the signal path for years and never had a speaker blow out since I started using one....the one I use is an old DBX-166, NOT recommended for studio work as it is kinda noisey, but it fills the bill for keeping everything throttled back and saves my high priced speakers....just a thought.....you can pick up a DBX like this for about $100 on ebay.....BUT it won't protect your speakers if the amp decides to flip your speakers the bird by throwing 75 vdc their way.

Test Point