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satx 17th April 2013 02:28 AM

My odd little FAST with chr-70.3 build
Thought I'd share my strange little fast build with you. I say strange because I know implementing a full range driver in an open tunnel/open baffle and a small woofer in a small volume enclosure, all stuffed into a standmount size speaker isn't really the normal path one would take. Surprisingly, they do sound quite good though! Really as good as I had hoped.

I had had the Chr-70.3 in a 9L BR which I was very pleased with, but I just can't resist the urge to play and as of late I have been becoming more and more intrigued with the FAST concept. Plus I had actually built the small BR for the chp-70.2 and they were sitting around homeless. The extended range of the chr's and the fact that they seemed to lose their composure a bit when pushed started me thinking of trying a fast with them.

I wanted to make it a medium sized standmount, because I already have too many floorstanders kicking around my house. This creates quite a problem because it's a little hard to make much bass from a standmount and even worse with a good chunk of the enclosure is being taken up by a full range driver instead of a small tweeter. My woofer options were limited because not many are going to do well, bass wise, in these conditions, plus I wanted to keep the cost pretty low because I wasn't at all sure that this would work. I finally settled on the sb13pfc25 5" because it modeled pretty well was cheap and had a bit better sensitivity than the MA.

So, to try to make this long story short, I have a sb13pfc25 in 8L and a Chr-70.3 in a open back tunnel mounted above it in a mid size bookshelf speaker. crossover is at 400hz with a damped 2nd order on the woofer and just a cap and l-pad on the full range. Oh, I also used a small inductor in series with the FR to shape the top end. I don't know why, but thing like cymbals were very forward. I really didn't have this problem when using this driver in a BR.


satx 17th April 2013 02:47 AM

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And... here are some pictures

Crap! for some reason I always have problems uploading photos here. So only a couple at a time.

satx 17th April 2013 02:51 AM

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and more

satx 17th April 2013 03:01 AM

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satx 17th April 2013 03:18 AM

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And finally, here is the last of them. They turned out pretty good in my opinion. Being able to paint over any construction flaws makes for a less stressful build than using Ply:D even though the prep work is a pain. They sound very good to me; really I achieved more or less exactly what I was trying to with these. Relieve the Chr from producing bass to clean-up the midrange even further, they are quite nice all by themselves. Also, maintain or improve upon the bass from the Chr in a BR cab, hard to say here, but they have very good bass with more impact/feel and seemingly the same extension. Unibox shows f3 of 52 hz and f10 or 35 hz well damped box tuned to about 49hz. I don't have measurement equipment except for impedance. Minimum impedance 5.6 ohm @ 150hz, otherwise it stays above 8 ohms.

Thanks for looking. Comments or suggestions are very welcome.


planet10 17th April 2013 05:00 AM

Those look nice.


satx 17th April 2013 05:10 AM

Thanks Dave. I have gotten a lot of good information from your post on here


TiMBoZ 17th April 2013 05:36 AM

Nifty! I like it - for me, it's a fun concept of wide range goes rock 'n' pop, without going all serious with subs etc. Good on ya!


damped 2nd order
Can I ask what are you referring to by 'damped'?

satx 17th April 2013 05:47 AM


Originally Posted by TiMBoZ (

Can I ask what are you referring to by 'damped'?

Thank you!

Sorry, something I heard from someone else on here, not sure if it's a technical term

It's a resistor in series with the woofer's parallel cap. I was getting an impedance dip to maybe 3.5 ohms at about 100-200 and a corresponding audible whomp sound in that region. The resistor brought it up more in line with the rest of the frequency.

TiMBoZ 17th April 2013 05:57 AM


resistor in series with the woofer's parallel cap
Oh Ok yep thanx.

It's like an itch, I'd like to do one with an A7 someday. You just made it itchy again.

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