Baby TL build

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Bill poster

Bill poster

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Joined 2008
#1
Not quite finished yet, one up and running.

I used a pair of Alpair 7M grey, the tapered line length is approx 84 cm (slightly under optimal). Hope factoring in air coupling will add effectively 5% more length
Overall dimensions are roughly 25 X 23 X 16 cm

Listening impressions at a relatively low volume are .. the A7 is a truly great driver. Detailed midrange, just the right amount of treble, no problematic sibilance..
Jazz sounds great. Snare drums etc

Some bass present but not sure the foam I used is right. Too dense? I can hear a lot of upper frequencies escaping the exit of the line.

Will finish cab 2 tomorrow and tweak..
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#3
Hi Bill, nice looking build - I used Genuine Herdwick Sheeps Wool that I bought from qta systems. May be better than a closed cell foam, will struggle technically as to the reason why but I suspect the wool is more absorbent than closed cell foam, so absorbing unwanted resonance. Best of luck with your build.....I'm looking at a black wood stain that will buff up like piano black. ( 7 - 10 coats ) then polished. God help me !! All the best, Steve. By the way I'm nothing to do with qta systems !!...Nice chap there friendly comms.
 
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#5
Foam is not all that effective. Line the walls near the driver with ~12mm wool or cotton felt. The rest of the line can be lined (like the Woden Labyrinths) or use quality teased poly stuff (ie acoustic-stuff) Well teased sheep's wool works to but tends to sag a bit and, if untreated, is moth food.

dave
 
#6
Cheers guys.. I only had that foam to hand. Bit of a mistake. Will rip it out tomorrow and replace with wool or poly, whatever I can get locally from the fabric shops in Brick Lane.
Not sure I can reach some parts inside but pretty sure my thai wife can get her hands in there!
 
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#9
If the fabric shops serve the automotive upholstery market, they will have wool or cotton felt available. It is a matter of personal preference, I like wool felt over polyfill, though sometimes I use both in a project. Not an expert by any means, but many use denim or recicled denim insulation; not sure of the advantages, if any.
 
#10
PMC uses foam to line their transmission lines. Seems to work well for them. It depends on what level of damping you need. I like to dampen the twin impedance peaks until they squash and almost become one peak with two small cusps. This gives a smooth extended bass and very low group delay similar to a sealed alignment but with deeper extension. I use polyfill and sometimes fiberglass. I line the area behind a driver with BASF phenolic sound absorption foam (same as Mr Clean Magic Eraser).

Desired impedance peak signature when damping is ideally placed (from simulation):
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http://www.diyaudio.com/forums/multi-way/281778-low-cost-pmc-inspired-tl-monitor-dc130a-dc28f.html
 
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#14
MDM3 now all gone apparently....

According to Monacor's site there's an MDM4 involving cotton felt but I've not seen it advertised for sale yet.

Alternatively "35mm Dacron for camper van lagging" is £28 for "lots" delivered to your door from eBay. Also ordered recycled wool carpet felt ATM.... Hopefully arriving next week.
 
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