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Old 23rd January 2009, 06:12 PM   #11
Bigun is offline Bigun  Canada
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Hi,

I like the idea of doing some experiments but of course in reality my HT set up does allow me to accept a much taller box (e.g. floorstander) with a larger volume than the mFonken.

I'm not that confident that my ears are very expert - actually I was thinking it would be handy to have a microphone and spectrum analyzer software for my iMac so I do something more scientific, like watching what happens if I make adjustments. But I'm getting ahead of myself with all this armchair DIY - first step is buy some wood (perhaps start with something that won't be the final box) and get something in place to listen to

The modeling really doesn't do it justice I would agree.

You mention good bracing and padding - I had a question about shallow enclosures (if I go floorstander or shallower) and the risk I read somewhere about sound reflecting off the back of box where it's so near to the cone. Do you think a shallow box requires some special considerations regarding the bracing behind the speaker and if so is it as simple as ensuring the back of the box has some kind of surface that is angled to the front of the box to direct reflections away from the cone (see attached) ?
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Old 23rd January 2009, 06:55 PM   #12
chrisb is offline chrisb  Canada
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Gareth:

Maybe someday I'll take a lesson on how to archive links to previous posts or photos for posting, but for now I'll need to rely on others.

FYI, there is a small CSA floorstanding member of the Fonken family that would well be worth considering for a video system. It definitely has more extension into the lower midbass area than the "milli", and with the support of powered woofer(s), I'd expect quite satisfactory results for most musical and modest HT systems, particularly with carefully selected bass management control in the latter.


http://homepage.mac.com/tlinespeaker...127-FS-Mk2.pdf

http://www.planet10-hifi.com/fonken.html

Hopefully it won't take long for Dave to respond by posting a couple of ( or links to ) pictures of this design.



Regarding the bracing, note on most of the drawings on the P10 website, including the in first of above links, that the bracing generally runs vertically in the longer dimension of the enclosure, and they usually include a number of holes.

In fact the 2 smallest 2 of this group are the only ones in which the bracing is not extended to contact at least 3 of the enclosure panels (in the case of the Prime, the vertical brace is full height, and couples 4 of the surfaces), with a U-shaped driver cut-out.

An idea for wide/ shallow cabinets that's been percolating in the back of my mind for several years, and I've just never got around to, is to create a "stepped cone" by stacking a series of circular plywood cutouts, with the smallest approx the diameter of the magnet, and in contact with it. It would certainly serve as a driver brace, as well as possibly help with radial dispersion of the rear wave energy to the damped side and top/bottom panels. This may have been done before, or be similar to what you envision, but I don't recall seeing any reports of such.
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Old 23rd January 2009, 09:09 PM   #13
Bigun is offline Bigun  Canada
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forgive my ignorance, but what is 'CSA' ?

my plan is for typical 5.1 set up where each satellite is a single driver and a sub rather than a woofer, meaning I want a single separate sub which operates at low enough freq. as to not be directional. The HT rear surrounds have to mount on an a ceiling bracket due to the configuration of my basement - the viewing area doesn't neatly end at a rear wall and so I'll probably hang them horizontal to avoid creating lumps on my forehead

So perhaps all the speakers will be the same design, the rears and centre mounted horizontally, the left/right mounted vertically. All 3 front speakers will be mounted on the wall, or just off it via suitable brackets.

Hence the speakers should have an LF roll-off that will work well with a sub. I haven't researched this yet but I gather that this means the cross-over frequency between the sub and the other speakers will be somewhere around 100Hz (i.e. both down at -3dB) and the sub designed so that it's flat from 80Hz down as far as can be reasonably achieved (subject to the room effects) ??

If this is right (?) and the calculated freq. response I posted above for the mFonken is also correct (?) then they are actually good for the job. But I think I can afford to go larger (taller for vertical orientation) and I believe something around 8Lites would be close to ideal. What I hope to have time for this weekend is to shamelessly take a p10 design and stretch/squeeze it to suit my size constraints, run a calculation to determine the port size and ... go buy a router!

I will employ bracing as per p10 suggestions, my little diagram was just to look at the idea of something specially shaped near the back of the driver.
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Old 23rd January 2009, 09:13 PM   #14
chrisb is offline chrisb  Canada
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in this context, CSA = Cross Sectional Area

There's certainly no shame in borrowing some of your design inspirations, we all do it from time to time, but unless you want to build your learning curve into this project (and the attendant multiple iterations of actual enclosure builds), you might want to check with Dave off-line regarding revised dimensions for vent tuning.

He's got numerous more plans already mapped out that aren't posted on the site, and might already have one that would work for your application.

FWIW, some rough calcs on net enclosure volumes are approx:

Fonken Prime / GR Fonken & Floorstander- approx 13 litres

mFonken ("milli") 4.5 litres


so the 127 can definitely work in a range of volumes with appropriate tuning.


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