miniFAST Boombox Build

My friend and I have been thinking about this idea for a while and the other day we made some test builds. The idea is small active 2.1 boombox using two fullrange drivers and a (sub)woofer. The objective for this project is a small box with as much low extension as possible. After trying different drivers we settled on the Fostex FF85WK as fullrangers and a TangBand W6-1139SIF for bass duty. Crossover is in the 250-300Hz area. For amp we use the Hifimediy DDX320v2 2.1 Digital Amplifier with a Connexelectronic SMPS300R 38V.

Here are some pictures of the test build using some leftover 15mm BB ply. The fullrangers are each in their ~1.5 liter sealed chamber, 75% stuffed. The woofer is in a 11.5 liter BR enclosure with a 50mm port tuned to 35Hz.

The DDX320v2 has an adjustable electronic crossover, which can be set between 80-360Hz, we settled on 280Hz. It uses a 2nd order low pass and 1st order high pass

So how does it sound? Okay I would say, but not amazing! We made a comparison with some budget 2-way bookshelves, the Dali Concept 1, placed very close together to be fair :) Our boombox surely wins on the low frequency extension, but it isn't as "clear", "open" and "crisp" as the Dalis.

This is of course only a test build. We haven't measured it yet, and no EQ or time alignment has been applied so far. Filter options are very limited with the DDX320v2, but we also have a miniDSP and various amps so we can experiment.

Thoughts and ideas are greatly appreciated!
 

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IG81

Member
2008-02-22 1:21 pm
So how does it sound? Okay I would say, but not amazing! We made a comparison with some budget 2-way bookshelves, the Dali Concept 1, placed very close together to be fair :) Our boombox surely wins on the low frequency extension, but it isn't as "clear", "open" and "crisp" as the Dalis.

Very cool project!

Maybe you need to give the FF85WK some time to break-in, not that I noticed that huge a difference on my pair. OTOH, maybe the FF85WK is just bringing to light what are actually flaws in the Dali speaker. The little Fostex is a very good little driver and relieving it of bass duty as you did is probably the best thing you can do to it. This could be a pretty hi-fi lil' box!

Maybe that 6" sub is kinda "slow" and does not convey tuneful mid and upper bass? Not to mention that it is trying to reproduce the lower voice registry. The Peerless NWR1643308 6" midwoofer could work in this volume with a much larger and shorter vent for increased vent efficiency. It would not go as deep, but give f3~50Hz with probably much better quality upper-bass and lower midrange. You'd have more play room on your active crossover to experiment as well.

IG
 
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Very cool project!
Thank you! :)

Maybe you need to give the FF85WK some time to break-in, not that I noticed that huge a difference on my pair. OTOH, maybe the FF85WK is just bringing to light what are actually flaws in the Dali speaker. The little Fostex is a very good little driver and relieving it of bass duty as you did is probably the best thing you can do to it. This could be a pretty hi-fi lil' box!
The Fostex have had some break-in. I bought them months ago and have been using them for other projects. And I agree, they do sound very good compared to other full-rangers I've heard in similar size. However, it doesn't appear to me that the Fostex are "bringing to light what are actually flaws in the Dali speaker" as you say. It rather feels like the sound "opens up" when I switch from the boombox to the Dalis.
I've had this idea of making a tapered TL style chamber for each of the Fostex, inspired by Planet 10's Tysen. Do you think this will affect the sound much compared to our current 1.4 litre sealed enclosure with stuffing?

Maybe that 6" sub is kinda "slow" and does not convey tuneful mid and upper bass? Not to mention that it is trying to reproduce the lower voice registry. The Peerless NWR1643308 6" midwoofer could work in this volume with a much larger and shorter vent for increased vent efficiency. It would not go as deep, but give f3~50Hz with probably much better quality upper-bass and lower midrange. You'd have more play room on your active crossover to experiment as well.
Maybe this yes, but it just sort of defeats our objective to have deep bass from a small enclosure. I could of course also just use two sets of small 5" midwoofer + tweeter and and have a more traditional 2-way stereo boombox (another project actually :D). It could probably be even smaller, though it wouldn't go as deep, but sure as loud as the our current miniFAST.
I didn't think the W6-1139 had problems if kept under 300Hz. Maybe I should try cutting lower and with a steeper XO. I also wonder how much phase and time-alignment matters as this has not been looked at yet.
By the way, which Peerless are you referring to? Couldn't find that model number you wrote.
 
So when you say "yes" I assume you mean for the better? :) Could it be that the FF85WK simply don't behave very well in a sealed enclosure?

Yes, performs better. "not open" typically is reflection coming back thru the cone. THe uFonkenSET for instance is more open than the slightly smaller uFonken, the TLs are larger volume and lower back pressure.

dave
 
The official part # might be 830875 then. :) I used the number listed over a Solen.

IG
Could be worth a try. Only problem is it's 8 ohm. The woofer should ideally be 4 ohm in a 2.1 like this. Makes it easier to find a digital amplifier (4 single-ended: 1 for each full-range driver and 2 bridged together for the woofer). Thanks for the suggestion though.
 
Yes, performs better. "not open" typically is reflection coming back thru the cone. THe uFonkenSET for instance is more open than the slightly smaller uFonken, the TLs are larger volume and lower back pressure.

dave
Interesting. So, if I made TLs a la Tysen for the Fostex in this application, could they then have similar sized enclosures (1-1.5L) and a length of only 15-17cm?
 
That woofer will stand ~700Hz cleanly, if its anything like its Neodymium sister. I wouldn't call it "slow" by any stretch.

If you're using some signal processing (or if you can plug a laptop in), apply a little treble boost and see what you think.
FWIW, I wasn't impressed with the budget Dali speakers I've heard. Call the Fostexes correct, and say the Dalis are too bright ;)

Chris
 

IG81

Member
2008-02-22 1:21 pm
That woofer will stand ~700Hz cleanly, if its anything like its Neodymium sister. I wouldn't call it "slow" by any stretch.

I never heard the driver, it was a mere theory. Good new for the OP then! :)

FWIW, I wasn't impressed with the budget Dali speakers I've heard. Call the Fostexes correct, and say the Dalis are too bright ;)

Chris

+1 ;) Afterall, how could a commercial (yuck - dirty word) product rival anything DIY? :D

IG
 
Could be worth a try. Only problem is it's 8 ohm. The woofer should ideally be 4 ohm in a 2.1 like this. Makes it easier to find a digital amplifier (4 single-ended: 1 for each full-range driver and 2 bridged together for the woofer). Thanks for the suggestion though.

In a boombox this woofer is probably not a good choice due to the volume it requires. When i was working on my latest MTM (with FF85wk) 2 of the Peerless would have needed 30 litres, the 2 SilverFlute W14 i ended up using needed 10litres -- the SF are available in both 4 & 8 ohms. The W14 are cheaper IIRC too.

dave
 
Interesting. So, if I made TLs a la Tysen for the Fostex in this application, could they then have similar sized enclosures (1-1.5L) and a length of only 15-17cm?

The sub enclosures & TL in my last ate up 3 litres and were ~26 cm long. The TL is not very critical in dimension but erring on the large size and longer line is probably better... it is dominated by the damping, but larger gives more room for damping.

dave