Suitable for a F.A.S.T. project?

[bigjppop]

So after reading everyone's thoughts over on my "Am I dreaming?" thread I think I've settled on a first project and I'd like some input from the crowd on whether or not this might be feasible/worthwhile.

I'm considering the Fostex FF85K, the CSS FR125SR, the CSS EL70, or something similar from Mark Audio. As an aside, are the EL70 and the CHR70 similar/the same? Just curious. All of these drivers seem to live in the 40-50 bucks a piece range which sounds good to me.

For the bottom half I'm looking at this:

DIYCable.com : Intro » Home » Exodus Subwoofers »

The Anarchy from Exodus seems to be a pretty killer deal (only 45 bucks!) and from my very much limited understanding of all the numbers that are listed on the spec sheet, it looks like it would be a really good match for the above, especially something from CSS or Mark Audio.

I'd like to drive the whole thing with a 35 WPC EL34 based push-pull tube amp.

This will be my first DIY project in the speaker world; am I biting off more than I can chew? Thanks in advance for any advice you can offer.

P.S. Is there a reason that in the FAST projects I've seen here the woofer is side firing? Could it be front firing?

[TheSeekerr]

The CSS EL70 and Mark Audio CHR70 are similar drivers - both are manufactured by Mark Audio, but the EL70 uses a paper cone and has a slightly higher efficiency.

If I recall, the canonical FAST (the Tysen) used a FF85K. I'd probably use the CHR70, because it's locally available and I suspect I'd prefer its characteristics to the EL70.

You'll want to use an active crossover for that pairing (regardless of which full range you choose), which means you'll need two channels of amplification per side, so this project probably isn't a good match for your tube amp.

I believe the side firing driver is just to allow for a slim front baffle.

[Nanook]

depends. If I can scab together a reasonable enclosure, anyone can

Perhaps asking a PP 35w/ch amp to do it all may be a bit much, but...

if you can swing a decent plate amp (or two ), I would strongly suggest the Exodus woofers. They are a great deal, and many have used them to good effect. Depending on your room, it may make it all work out. I think the plate amp idea is great because the efficiency of the mid/woof is only 82dB or so, while the CHR70 is 85. using approximately double the power should get you in the ball park and doesn't rely on the design of a crossover...

If you limit the frequencies going to the MA drivers to about 150-200Hz, driver distortion will be reduced, and lots of bass headroom will be available. Well plenty..theoretically 150 dB @125 watts @ 1 metre, but so unlikely...(it'll all be limited by the thermal characteristics and the impedance) and the efficiency of the CHR70 should also increase.

We'll see if all this works when I build a "mini" Spirit of Orion in the near future...

[TheSeekerr]

Actually, that's a great idea I hadn't considered - use your tube amp for the full ranges on each side, where it's characteristics will be heard, and use some cheap solid state power (one of the class D 2*100W Sure Electronics boards comes to mind) for the woofers.

For a suitable active crossover, see Project 125 . There's also a 2 way version available at Linkwitz-Riley Electronic Crossover . Which one you choose depends largely on the enclosure you use for the woofer - if you go sealed, the two way is a good choice, but if you go ported, the 4 way is a good choice, because it's designed so that some unused devices can be configured as a high-pass filter. This will help protect your woofer below the tuning frequency.

[planet10]

Or a PLLXO. Biamp just makes things that much easier.

If you want to do a passive XO, you need to get the woofer sensitivity to match up with the FR. This usually means at least a couple dB more efficient.

And if you start looking at the size of parts needed for a passive XO, a 2nd amp starts looking good.

dave

[Nanook]

there are a few out there that have an active crossover built into them. Something like this M & K 100 Sub-woofer Amp comes to mind.

The crossover is quite good (it's a second order type, active), and gets out of the way of the music. Of course as also suggested, a stand-alone x-over and another stereo amp of suitable power will get the job done too. Perhaps you already own a suitable SS amp. Then all it would take above the purchase of the Exodus mid/bass drivers is the x-over.

As I am no electronics designer, I'd leave that to Dave and others

[bigjppop]

This is starting to look like much more than a newbie project I had to do some googling to know what PLLXO even meant!

I'm assuming that a FAST design (something like the Tysen) is probably great for someone with minimal "real estate" and might already have some amps/crossovers sitting around. For someone like me that is starting from the ground up and would have to come up with amps, cross overs, etc would I be better off simply going with a couple of small subs ( two boxes with standard plate amps, something like the M&K mentioned above) to augment the full range driver? Obviously I would be building 4 boxes instead of two but I would also gain the flexibility of being able to place the subs where they would sound best as opposed to being tied to where the full range drivers best do their thing.

Dave, what pushed you in the direction you went with the Tysen as opposed to just adding some separate subs?

[TheSeekerr]

There's no real difference in complexity - seperate subs still need amps and an active crossover, so all you've really achieved is building another pair of boxes.

I -think- the idea with FAST is to use a driver which is more a "helper woofer" than a true sub - somewhat limited in low frequency extension, but with excellent high frequency extension to allow for an easy crossover. Whereas a true subwoofer tends to be designed to work best < 80hz or so, and is completely useless by 200hz.

[planet10]

Originally Posted by TheSeekerr

I -think- the idea with FAST is to use a driver which is more a "helper woofer" than a true sub - somewhat limited in low frequency extension, but with excellent high frequency extension to allow for an easy crossover. Whereas a true subwoofer tends to be designed to work best < 80hz or so, and is completely useless by 200hz.

This is well worth keeing in mind.

For a good, well documented consider MJK's passive OB. Jim Shearer's trapezodal implentation with FF85K probably defines the current leading edge of this project.

dave

[Poindexter]

What's a F A S T?

De Poinz wants to know.