|1st November 2011, 07:31 PM||#13|
Join Date: Mar 2008
Hi, ahd thanks for all the nice feedback, much appreciated!
Chris, I'm driving each subwoofer with a Crescendo Millennium MOSFET stage rated at about 120W in to four ohm's (the woofers are 4 ohm), x-ed over at 65Hz 24 dB/Oct electronically.
According to the simulations I made, that shoudlbe enough to give full linear cone excrursion down to 20 Hz and about 105dB output from each sub.
The foam used was Armaflex, a closed cell foam used for HVAC thermal and vibration insulation: Armacell - AF/Armaflex Europe
It is very "squooshy" and can be a bit tough to cut cleanly without roughing the edges. A stanley knofe with brand new blade and steel ruler guidance is recommended.
A word of warning though, just after I took the pictures, I discovered that the foam had started to tear just at the edge of the woofer chassis, apparently the "stretch" imposed on the foma when bolting the woofer down was a bit too much. To stop this from propagating further, I took the stanley knife arround the edge of the chassis to releave the foam with a clean cut to stop any further uncontrolled tearing. It stil looks OK unless you get close.
I might get some fresh armaflex and redo the job, this time cutting the foam around the chassis as I bolt the woofers back down flush with the foam face.
With regards to stuffing, I used 100% stuffing with glass-wool (Glava) Mineralull Bygg
A fairly "standard" glass-wool type for building insulation etc..
I filled all the "cells" of the bracing matrix with uncompressed glass wool, except for the front "compartment" just behind the woofer, which was lined with axustilux mat to prevent dust contamination of the woofer.
The stuffing strategy was based on various reading around I did that suggested that this degree of filling would give an effective box Q of my chosen box volume of arround 0.7. As mentioned, this woofer seemed to be fairly insensitive to absolute box size giving very modest variations if kept arround +/-20-30 L within theoretical optimum (un-stuffed).
The bracing added significantly to material cost and construction effort, just drilling those 140+ holes with a hole saw (Which kept clogging up with MDF dust) was a major undertaing all by it self, but was well worht the effort. these babies are DEAD! (Hmm.. that came out a bit wrong..)
Finally a picture of one box with stuffing:
Oh, and for goodness sake, do not omit to put the internal wiring in place before adding the stuffing and slamming on the lid!!!
|2nd November 2011, 09:00 PM||#15|
Join Date: Mar 2008
You're welcome! Concidering the huge ammount of help I've gotten from the forum on various projects, I'm just delighted to give something back and answer any questions I can!
I wasn't quite happy with the sound here the other day, it was alla bit murky and "lacking spark", so I used the tone controll of my pre-amp (50Hz shelving) and played around to I gort something I liked. Semmed a 3-4 dB reduction in bass level made a big difference. I then went on and decreased the level of each sub by 3dB.
I then threw up my measurement mick in the listening position and ran a sweep through both channels. The enclosed image shows the result, ungated measurement wiht 1/5th oct. smoothing.
Not to bad I dare say... Seems the dual sub set up goes a long way in smoothing out room modes at low frequencies...just as hoped for!
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