Sliding HP filter with DRPA, a-la Bag End INFRA processor

tonyman108

Hi folks. I've had a DRPA for a couple of years, and love it. I mostly build my own speakers, have long been a multi-amping afficionado, and the DRPA makes that whole process a lot easier on the back, wallet, and most importantly, the ears.

I'm pretty good at twiddling with active crossovers, including the DRPA. But here's a twist on the usual requirement:

I've been looking at Bag End subs lately, which are small-ish (relative to the PA norm for their driver size) sealed-cabinet subs that only work well through the use of a rather expensive dedicated outboard processor (they call it the 'INFRA' Integrator) that does two things, AFAIK...

- It creates a 6 DB/octave bass boost with a knee at the cabinet's (higher than normal) box resonance.

- This big bass boost would quickly cause excessive cone excursion (and amp power requirements) when confronted with loud LF content, so the processor implements a sliding high-pass filter. In other words, rather than just gain-limiting the bass, it slides a bass-cut filter up in frequency when a threshold is exceeded. I assume this threshold is calculated with a response that is weighted to model the driver/cabinet combo's excursion limits.

As much as I admire the engineering concepts, it pains me to think of paying $600 for a glorified EQ box. Can anyone think of a way to approximate this behavior with the DRPA, or any of its big brothers, for that matter?

Thanks,

Tony

kpippen

Hello Tony,

Thank you for posting this!... I never heard of Bag End speakers so I did some research and read some reviews...

I noticed their market leans more towards theater and home audiophile but...they also have several pro-audio products... I found the reviews to be quite interesting and favorable... I read in one review:...the timing alignment between their subs and mains is seamless and very impressive... I also noticed they have been around for quite some time (30-40 years I think),...and that their products have been used at Disney...

Lots of calculations are made when designing conventional speakers...ie cabinet shape, volume, compression, porting, etc... Cabs are specifically tuned to the driver (based on Theil Small parameters) and sometimes vise versa... The INFRA processor actively tunes the driver to the cabinent... A bag end speaker on a conventional system without it's processor would probably sound like crap...:shock:

Anyways,...to answer your question: No...the DriveRack cannot be utilized to emulate the INFRA Processor... To gain any benefit from the Bag End speaker the technology must be supported by it's processor...:(

Cheers,

Kevin

PS. Thank you for my Sunday morning reading!... I learned a lot about a product I didn't know existed...:D

Gadget

I think the 260 would be a better choice but the same tools used for the job are available in the processor I believe. The problem comes in figuring out the necessary processor settings. When dealing with subs that can go very low we need to remember that if the 3db down point is say 35 hz that we either need to increase that 35 hz level or decrease the frequencies above it that are louder and mask he 35 hz, or both. Same goes for frequencies like 8 hz that my Sunfire sub is capable of. Bag end has been around for a long time and I have had some experience with them but remember this, a small sub will still be small in a big room...You need to move some serious air in pro audio and while little is nice on the back it doesn't always translate into usable for pro audio. The bar I'm house sound in had a band that would come in with a pair of bag end subs and a pair of small 10 inch 2 ways bag end tops and he nearly blew them up every time trying to get sufficient sound to get up over the band. Same with a Bose system with that silly little sub and speakers on a stick...woefully inadequate... I have been a speaker builder for years and on a pursuit of the little but deadly system... I have some tops that work great in smaller to medium rooms but when long throw and pattern control are necessary horn loaded cabs become necessary, and they are heavy... even the small line arrays are really heavy... Hell, bag end speakers are HEAVY... We all want speakers that are invisible, loud as hell and perfect with balance... that has proven to be an elusive commodity. For gig sound in big rooms you need multiple cabinets the greater the coverage the more speakers or those with wider coverage patterns are needed. Remember also that overlapping coverage patterns cause interactions that cause lobing, nulls and modes that distort the sound and cause coverage problems and intelligibility issues.

Gadget

tonyman108

Gadget,

I'm a physicist, and have been designing loudspeakers and PA's for a while now. 30 years, actually. I understand your points about there being no free lunch. I don't doubt your experiences with the Bag End and especially the Bose stuff running out of grunt in some situations.

However, I'm doing sound for a particular type of music; a-capella with vocal percussion. In the venues I'm concerned with, this music (and the occasional acoustic music festivals that I do) has need for quite a bit of headroom (and sound quality, if I'm going to be associated with it) from 150Hz up, but does not need huge max levels of bass when compared ot a rock gig at a bar. Because of the VP, though, it is nice to have some deep bass if you can get it.

I'm trying to refine a scaleable PA system that is tailored to this rather specific use. I have the midbass and HF sections covered nicely, but the bass is a headache. In a big show, I can and will bring some big bass bins. But for smaller shows, I need a quicker load-in, and I'm trying to design a rig that will still sound good.

As you point out, you can't have small, loud, and efficient all at the same time. As for weight, you can do some things there, if you are willing and able to employ exotic materials in the drivers and cabinet construction. That's what I'm contemplating right now... not buying Bag End cabs, but using their design philosophy (and maybe their drivers, which I see on EBay from time to time).

Yes, the bass extension / output / efficiency / cabinet size tradeoff is a matter of physics. Amp output, woofer power handling, and woofer excursion limits are a matter of engineering, and that engineering has improved dramatically over the last few years. Same goes with cabinet materials.

I think that, given the large & light amplification out there, and high-power, long-stroke woofers that exist nowadays, that I can, for medium-sized venues, safely sacrifice efficiency and maximum output in exchange for a smaller cabinet volume.

As the ELF/Infra system illustrates, you don't have to make your tradeoffs static. That was the point of my question.

The Infra processor implements something (exactly?) like a Linkwitz transform, plus a sliding-shelf bass cut filter. The sliding shelf filter is a neat idea, and I think it might sound better than a limiter in a lot of situations.

It lets you push the size / bass-extension tradeoff in a new direction... you implement a giant bass boost that pretty much guarantees you will run out of driver excursion or amplifier power, but then you cut back on that boost when things get louder than the driver can handle. But if things are not out of the driver's performance envelope, you get great bass.

I know that trick won't let you fill an arena with bass from a single 18\" driver in an 8 cubic foot box. But I don't do arenas, I think it's neat, and I want to try it. I was just hoping that someone could think of a trick that would let me experiment with the concept using the DRPA, which I happen to own.

Gadget

All right .. thanks Tony.

I have a suggestion that may just help you in this quest and even simply things a bit perhaps... Some time ago my son built the Bill Fitzmaurice \"Table Tuba\"... Not a tiny box, but still quite small and movable, that has such a long horn path that it is so driver friendly that it can use drivers from 8-10 inch from whatever manufacturer... I had him use the HL 10A from Eminence.. a long throw little brother of the Lab12. This cabinet goes DEEP.. and with a little EQ can go well into the sub 30hz range... the use of the HL10 requires a beefier speaker mounting plate than specified in the original design, but the cab can be built in a very short time with readily available materials. I had my son build \"mirror image\" pairs so the open woofer chambers could be set side by side and still be open. I have done full fledged rock and country shows with just a pair of these and my proprietary tops. This was done in fairly large venues, and with acceptable results... even considering the music for the rock show was \" Smashing Pumpkins\" \"eske\"...I drive the pair with a 2400 (ala kevins mighty rack of Behringer 2400 watt amps.. in bridged mono) watt bridged amp and am quite pleased with the results... the material outlay was minimal also..(under $300 for a pair) I would think that in an acoustic enviorn that these would really shine...especially when corner loaded.( they were designed as a home theater woofer) Now the problem here is that to properly time align a system you need some delay capability.. that the DRPA does NOT have...BUT if you could get the tops within a few feet of the subs you could have quite a setup.

I have a problem with front loaded subs...They have unacceptable distortion figures... In horn loaded designs the longer the horn path the lower the distortion, the greater the bass output and the lower the register available. You even get free power from the horn design...I built the Labsubs and they spoiled the HELL out of me... Imagine bass that you can FEEL outdoors 1/2 mile away with only 6 cabs...and 5000 watts...I'm afraid I will never be able to listen to a front loaded design with the same zeal as I had when I built my first dual 18\" subs.. right on through the turbo manifold 18's...YUCK, they make me sick now.

Well thats all for now..Tell me what you think.
G