Pro woofer protection?

[jhollander]

I’m working on a prosound woofer/ bass bin for a friend and I’d like to add a high pass so he doesn’t blow this up on day one. Is a simple 250V cap all that is needed? Maybe a cap and a poly switching resistor?

[Paul O]

Re: Pro woofer protection?

Is a simple 250V cap all that is needed?

No the filter needs to be a lot steeper than that so it's usually done actively before or inside the amp. What amp is being used?

[billfitzmaurice]

Re: Pro woofer protection?

I’m working on a prosound woofer/ bass bin for a friend and I’d like to add a high pass so he doesn’t blow this up on day one. Is a simple 250V cap all that is needed? Maybe a cap and a poly switching resistor?

He's far more likely to hurt it via over-powering than too low frequency content. A limiter correctly set to prevent exceeding xmax is the only sure cure. If you do high pass a 3rd order slope is the minimum that's useful, taking passive out of consideration. Poly switches won't hand the current that woofers draw.

[Sydney]

Re: Pro woofer protection?

... add a high pass so he doesn’t blow this up on day one. ...

As it is common to have either an Octave or One-third octave band Graphic EQ in a pro sound system - the old practice is to pull down the bottom octave slider(s) and engage any infrasonic filters.

[jhollander]

Re: Pro woofer protection?

I'll see what mixer amp he has in the morning. I was hoping to bullet proof something. If the advice is to run open, I'll just need to warn him to set up his rig right.

[Sydney]

Re: Pro woofer protection?

Back in the early 70's we used to have parties, and the host(s) would often overdrive and as a result blow drivers.
As a safeguard I installed speaker fuses.
Contrary to opinion of some; used correctly they ( fuses ) provide protection; as voltage is increased - current increases proportionally. ( Double the voltage and the current is doubled ).
Fuses prevented damage from transients ( or short term overload ) on HF drivers and longer term overload on woofers; My observation is it is the primary cause of most woofer failure.

The gain structure of the sound system can be measured to gain insight to power levels produced.

[jhollander]

Re: Pro woofer protection?

Well, he's got a Peavey analog mixer amp with about 300 wpc. After recommending a separate amp for the subwoofer and determining he has zero desire to help build something, he's moved on to a used powered prosub.

This project is dead. Which is kind of disappointing as I was hoping to find a home for my Eminence Kappa 15 LFA.

[wg_ski]

Re: Pro woofer protection?

It may be possible to run without a separate amplifier, if you can run the bass bin off one channel and the mains off the other. You'd still need a crossover (active) and the mixer box needs insert jacks between preamp/poweramp. Some do, some don't. And of course, the mix is mono but that's not a show stopper.

300 watts wouldn't be enough to hurt a 15LFA in a cab tuned to 40 Hz. Maybe 25 Hz sustained sine waves, but you're just not going to get that from a band mix. An occasional trip past x-max from a dropped mic won't hurt anything either at that power level. With more wattage feeding it, it would be another story.

An entry-level powered sub isn't likley to have a better driver than the 15LFA or more than 300 watts. If you spend real money, yeah, you can get better.

[jhollander]

Re: Pro woofer protection?

Agreed he could run off the mixer amp, but this is getting really marginal as he's running 2, 12 inch PA tops with this. Certainly nothing we'd recommend for a 4 piece band.

[flyboyd]

Re: Pro woofer protection?

A correctly set up limiter will be your best bet.

The limiter needs to have a very fast attack time, very slow release time (a few seconds or more) and infinity to 1 (brickwall) ratio charactoristics, and a threshold set to prevent both over excursion & long term thermal limits (whichever occurs first).

I'm using the brickwall limiter in the DCX2496, with the release set to the maximum 4 seconds available (short releases act like a compressor and increase the signal density, increasing the chance of thermal damage).

If you're using modelling software to design your box, it should give you an idea of the voltage that will reach xmax. The driver specs should give you an RMS power handling (which is the thermal limit, and probably on the ambitious side of safe). use this to calculate the thermal voltage limit, with a calculator like this http://www.sengpielaudio.com/calculator-ohm.htm Use the lowest of the two voltages.

With the speaker disconected, amp turned fully up, and an A/C multimeter on the amps speaker terminals, play a sinewave in the usable bass range (say 70hz) throught the mixer > limiter > amp, and adjust the limiter threshlod till the voltage limit cannot be exceeded, no matter how high the mixer volume is turned up.

If available, set a high pass filter too.