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RWB 5th October 2012 04:04 PM

Bi amped FAST design, active crossover
Hi all,

I enjoy hifi but I'm a bit new to it all, so go easy on the technical jargon.

I am just about to order a set of CHP-70 (1st gen) to build a set of frugal horns. However, this is just a short term project while I get some designs sorted for this project. These will be good for the acoustic music in my collection but totally inadequate for loud and/or fast bass heavy music e.g dub and reggae, drum and bass, house, heavy metal etc Even some of the blues and rock has thunderous bass so I want something that can handle it.

The plan is to build two enclosures with two separate enclosures built within the each unit. They'll end up big and fairly imposing but I want them to be statement pieces of furniture in themselves*, while throwing out serious sounds! What I'm really looking for is recommended speakers and plans for for bass of sub enclosures. There are plenty of plans for full range enclosures, not so many (that i can't find) our there for bass and subs, FAST style enclosures.

There are several enclosure calculators on the web but seeing as I'm only just getting into the DIY side of hifi and beginning to learn the science behind it, I'm left a little bemused by them. Are these good and reliable or are they guidelines for dimensions, port size etc?

I guess having an active crossover, bi amped and EQ gives me a lot of flexibility with enclosure choice. Being 22 means that I wont be settling into one location for a while so having a tunable rig makes sense to me. Please feel free to correct me if my thinking is wrong and chip in with alternatives.

Willing to spend about 160 ish bass/sub drivers and hoping to reuse the CHP70s from the frugal horns for the full range drivers and use an enclosure plan from the Mark Audio website. I maybe persuaded to buy more speakers if I really like the FH's but already looking at spending quite a bit with a second amp and the crossover anyway!

*I'm a third year furniture student with a full workshop, including a CNC machine at my disposal. So they don't just have to be square boxes.

RockLeeEV 5th October 2012 04:37 PM

For box design I recommend Martin J King's transmission line worksheets. They will ensure you don't mess up driver or port placement - two critical factors in uncolored reproduction. For sealed box use the closed TL worksheet, for vented use the ML-TL worksheet, and for tapered TL/QWT use the tapered TL or TL sections worksheet. Stuff like winisd is good for getting rough estimates - then do the more in depth stuff in the MJK mathcad sheet.

While active crossovers do simplify things, I can't stress enough the importance of having measurement gear. Electric crossovers do not always translate into the desired acoustic behaviour. You may only need (x-2) order electrical slope at (f + 400hz) to get an x order acoustical slope at "f" hz. Only measurements will make this clear.

As far as FASTs go, do have fun. But don't let yourself become so attached to any one idea that any one group prefers.

planet10 5th October 2012 06:52 PM

Why not just add helper woofers to the FH3 to achieve the same goal?


Vix 5th October 2012 07:29 PM

The idea of FAST is very appealing. There are so many combinations. I mean, fullrange of choice on top, and then, bass can be..anything (If I just had the means to try all of those combinations that come to my mind).
In your case, as Dave said, it is best to keep FH's, use them as standalone for easy listening, but also have a pair of stereo woofers that could "transform" them into beasts, when needed. A simple square box for a woofer is boring enough, so why not be creative? ML-TL can sound pretty good (see my el-cheapo FAST). But there are many other options as well. I was thinking about building a BIB with 8" midbass driver. It would serve as bass support up to some 500 Hz. Just a first order crossover. FH would be hi-passed at that frequency as well, so less risk of over-excursion. (play louder). Or, one could also try a tapped horn as a woofer, but I am not sure if it will be useful high enough.Or, one could try Open baffle woofer (18" hi qts speaker in H-frame). Many options really, some tried, some not, but a heck of fun! :D

RWB 6th October 2012 03:46 PM

Ok, so If I ad a couple of woofer into the mix I'll have covered. Do I still go bi amped? Do I use an active sub woofer? Were can I get plans?

RWB 6th October 2012 05:05 PM

These look like they fit the bill nicely. Peerless XLS10 10" Subwoofer (830452) and Passive Radiator (830481)

For the passive speaker, can I just use any old (same diameter) driver with the guts torn out?

Kjeldsen 10th October 2012 01:22 PM

what does FAST stand for?

boris81 10th October 2012 04:14 PM


Originally Posted by Kjeldsen (
what does FAST stand for?

Fullrange And Subwoofer Technology.

sreten 10th October 2012 10:26 PM


FAST = Full range ASisTed.

rgds, sreten.

planet10 10th October 2012 10:46 PM

I like sretens's acronym expansion -- it more accuratly descibes what is trying to be accomplished, but boris' is more widely used.


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