How necessary is a HPF in a speaker cab?

[superbassman2000]

I have an unloaded 210 that I'd like to load with BP102s. I was just wondering if I should throw in something like a 80hz HPF to keep from damaging the speakers? I mean, I will be plugging a 350w amp (with a limiter) into what should be a cab that can handle 400w, and my logic states that the amp isn't going to be throwing anything at the speakers that it can't handle, but I'm also an idiot. Is this a recipe for disaster, or will it be just fine?

[T-Bird]

Hi.

A passive low frequency HPF is prohibitively expensive, complex and relatively heavy. You probably don't want that?

No passive low frequency bass cab that I know of has a HPF, people tend to use their ears .

Regards
Sam

[BassmanPaul]

Originally Posted by superbassman2000

I have an unloaded 210 that I'd like to load with BP102s.

Please read the FAQ on page one. You have to match the drivers to the cabinet for a successful outcome. Just shovelling an arbitrary driver into a box is a crapshoot at best.

[Arjank]

Originally Posted by superbassman2000

I have an unloaded 210 that I'd like to load with BP102s. I was just wondering if I should throw in something like a 80hz HPF to keep from damaging the speakers? I mean, I will be plugging a 350w amp (with a limiter) into what should be a cab that can handle 400w, and my logic states that the amp isn't going to be throwing anything at the speakers that it can't handle, but I'm also an idiot. Is this a recipe for disaster, or will it be just fine?

If you want to use a hpf you should use for example a Pro-EQ Platinum Bass Preamp/EQ/D.I. - Fishman Transducers, Inc.
This thingy has a build in low cut filter too get rid of that low rumble.

[dhomer]

A couple things come to mind... I've had BP102's in both sealed and vented boxes. If your box is vented, those drivers need about 5 cubic feet of internal volume to work right. Box tuning would be in the high 30's, and it might not be a bad idea to run some sort of HPF, maybe in the 35-40Hz range. They will work in a sealed cab of considerably smaller size. However the low-frequency response heads downhill 6dB/octave about 120 Hz, depending on box volume.. HPF's wouldn't be needed or recommended..

[Alexander Eddy]

Originally Posted by T-Bird

Hi.

A passive low frequency HPF is prohibitively expensive, complex and relatively heavy. You probably don't want that?

No passive low frequency bass cab that I know of has a HPF, people tend to use their ears .

Regards
Sam

A large capacitor will give you 6db/octave will it not? They're hardly expensive, complex or heavy

[Arjank]

Originally Posted by Alexander Eddy

A large capacitor will give you 6db/octave will it not? They're hardly expensive, complex or heavy

In theory yes.
In this case no.
Why?
The inductor only works like a 6dB/oct filter if it "sees" a constant resistive load throughout it's working range. In this case the impedance should be linear from the lowbass to the lowmids. But, the woofer is in a closed cabinet(which will create one impedance peak at the Fb) or in a ported cabinet which creates two impedance peaks.
You can smoothout the impedance peak of the closed cabinet with an lcr network , this could work. But you can not smooth out both peaks of a ported cabinet. This will just not work.

The large capacitor also needs to handle lots of power, this is going to be expensive.

[superbassman2000]

Originally Posted by BassmanPaul

Please read the FAQ on page one. You have to match the drivers to the cabinet for a successful outcome. Just shovelling an arbitrary driver into a box is a crapshoot at best.

Thank you. I am well aware of what I am trying to do. You'll also notice that wasn't my question.

Originally Posted by dhomer

A couple things come to mind... I've had BP102's in both sealed and vented boxes. If your box is vented, those drivers need about 5 cubic feet of internal volume to work right. Box tuning would be in the high 30's, and it might not be a bad idea to run some sort of HPF, maybe in the 35-40Hz range. They will work in a sealed cab of considerably smaller size. However the low-frequency response heads downhill 6dB/octave about 120 Hz, depending on box volume.. HPF's wouldn't be needed or recommended..

This is what I was looking for--Thanks!

[billfitzmaurice]

Originally Posted by Alexander Eddy

A large capacitor will give you 6db/octave will it not? They're hardly expensive, complex or heavy

6dB filtering is of no value at all.

The large capacitor also needs to handle lots of power, this is going to be expensive.

Capacitors don't have power ratings. They're voltage limited, and even in the size required here aren't that expensive. But as I said a 6dB filter is the equivalent of bull tits. The minimum required is 18dB, which needs two capacitors and an inductor, and in this case the inductor would run you at least $50.

[Arjank]

Originally Posted by billfitzmaurice

They're voltage limited, and even in the size required here aren't that expensive.

I know they're voltage limited, I just wanted to keep it simple to read.

Not expensive? Yes if you use an electrolytic capacitor
I would not use a regular electrolytic capacitor in such a setup. Or, at least run 4 of them in series parallel wiring.
Use an MKT foil capacitor or better and then it gets expensive. Here's a capacitor voltage calculator http://lautsprechershop.de/tools/ind...ndensor_en.htm