Crossover point at 400 hz. on an Altec 288-16K driver - Damaging?

[Cut-Throat]

I had mentioned to a speaker designer at the RMAF in Denver about 2 weeks ago that I was using an Altec 288-16K driver and had a single order crossover that had Crossover points of 400hz and 6K hz. -- He said that low a crossover point could damage the 288 Driver. He got distracted and did not finish the explanation of this to me.

My questions are.

1.) was he correct on this?
2.) If so, could someone explain why this would be?
3.) And also if so, How could I be using this for 5 years with no damage so far.

I mentioned to the speaker designer that I was using low powered SET amps with these drivers and he thought the risk of damage would be even greater because of the clipping levels would be so low.

So, I am a bit confused and looking for some clarification. thanks

[bowtie427ss]

Since your experience has already proven him incorrect, i'd erase most of what this "speaker designer" said from my mind.

Beyond external physical forces, the only things i know of that will damage your 288's are over excursion of the diaphragm, and over temperature of the voice coil.

I'm pretty sure that Altec made horns that provided acoustic load for these drivers down to 300hz(203, 311-60, 311-90, 803, 1003, 1803). I'm not aware of networks that had a crossover point below 500hz, however i'm pretty sure that a lot of these were actually driven full range for PA/paging use, maybe with the addition of a hi pass filter somewhere upstream to protect them from the lowest octaves.

I'll leave it to those members far more knowledgeable than i to expand on how wrong he is.

[GM]

Right, a typical compression horn driver has a very wide usable BW if its loaded with a large enough horn as witnessed by the various 1" exit WE horn systems. While a 500 Hz horn is considerably larger than the minimum required, it's to keep the driver from over excursing at rated power through the XO's BW, so a lower power rating can be traded for a lower XO point with the caveat that the slope order ideally needs to be increased to ensure that the driver can't bottom out down where the horn unloads.

I haven't worked through it, but I imagine that with a so-called 'brick wall' filter, a 1005 could probably be XO'd all the way down to where it unloads around 140 Hz IIRC, though its power handling would be very low, maybe not even a watt.

GM

[Cut-Throat]

Right, a typical compression horn driver has a very wide usable BW if its loaded with a large enough horn as witnessed by the various 1" exit WE horn systems. While a 500 Hz horn is considerably larger than the minimum required, it's to keep the driver from over excursing at rated power through the XO's BW, so a lower power rating can be traded for a lower XO point with the caveat that the slope order ideally needs to be increased to ensure that the driver can't bottom out down where the horn unloads.

I haven't worked through it, but I imagine that with a so-called 'brick wall' filter, a 1005 could probably be XO'd all the way down to where it unloads around 140 Hz IIRC, though its power handling would be very low, maybe not even a watt.

GM

Sorry, but I did not follow you here at all.

Are you saying the 288 Driver could be damaged by what I'm doing or it's OK?

[bowtie427ss]

Are you saying the 288 Driver could be damaged by what I'm doing or it's OK?

As the frequency drops diaphragm excursion increases for a given spl. The limiting factor becomes the diaphragm physically contacting the phase plug. As per GM's post, this can happen at a substantially lower input level than what the drivers standard power rating might be.

I'm sure what you're doing is fine so long as you respect that your power handling is reduced a bit.

FWIW, if you go to the 2nd page of threads here you'll find an interesting thread where a fella is running a small format 802-8G down to 200hz.

[Cut-Throat]

I'm sure what you're doing is fine so long as you respect that your power handling is reduced a bit.

Can you elaborate on this? - I not sure how I am supposed to 'respect' this.

[bfish]

As the frequency drops diaphragm excursion increases...

Yeah, 4x per octave for a given input power. Say, 1W at 500Hz causes 'x' excursion, that same watt at 250Hz moves the 'fram FOUR TIMES as much.

So, the lower the power input, the lower the potential frequency (ignoring the horn).

[Ronald Lee]

According to my Altec AL1712-3 6/75 brochure, only the 290 driver with the phenolic diaphragm is recommended for use at 300HZ xover, with only the appropriate Altec horns, ie Altec 203B, 311-60 & -90, 803B, 1003B, and 31A.

[Old Guy]

According to my Altec AL1712-3 6/75 brochure, only the 290 driver with the phenolic diaphragm is recommended for use at 300HZ xover, with only the appropriate Altec horns, ie Altec 203B, 311-60 & -90, 803B, 1003B, and 31A.

True...with a couple of caveats...

That paper is about 20 years older than the driver in question. The K has a lot of mass added to it.

The K is a much newer design...but above and beyond that, Altec was referencing Pro applications, not Home Stereo. Home stereo apps generally operate at lower power. And drivers will often tolerate lower crossover points at reduced power.

[Panomaniac]

Yes - and that's the crux of the matter! =)

Opinions. Ah....
I remember when I used to mix front of house. There was always at least one idiot in the crowd to tell you how to do it better. So the saying was: "Everyone has two jobs - their own, and audio."