Newbie's latest project

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Hi all,

Just joined today, and put my first post in the introductions forum. Cal Weldon asked me to post up some pics of my current project so here goes:



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Panels for second speaker
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Front view
The sections in between the middle four braces have still to be routed out and there's a 25mm outer panel to go on.
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Rear View
As with the front, the inner rear panel will be routed out between the middle four braces and there'll be an additional 25 mm rear panel.

Top, bottom and sides are all 25 mm, bracing and inner front and rear panels are 18 mm.

The braces still have to be routed out. The cabinets have been partly dry-assembled to cement the port into the base.

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This bad boy is the 2.2mH Intertechnik air cored inductor for the bass driver.

Drive units are Scan-Speak 18W/8531G00 and D2905/930000.

Internal panels will be lined with 2mm bitumen with 10mm foam atttached. There will also be some Monacor MDM-3 behind the bass driver. The cabinets will sit on a 30mm thick plinth on 50 mm spikes to give the port room to breathe.

I was initially going to build a ProAc 2.5 clone, but after reading Troels Gravesen's extensive paper on the 2.5 clone I opted to go with the 9300 tweeter as the 8513 doesn't work well with the newer 18W/8535. After some further thought I decided to go with the 18W/8531G00 Revelator instead of the 8535. I wanted to bottom port the cabinet to make placement less fussy, and use a big port to minimise noise. It just so happened I had a length of 102mm ID soil stack pipe lying around as well. For a 33 litre cabinet at 33 Hz, the port comes out at about 400 mm.

I'm using Troels Gravesen's SP98 series crossover as a starting point. Depending on how my drivers measure, I may have to tweak a little.

Thanks are also due to Finn Dahle for the cabinet construction idea from his 2.95 Clome. Unfortunately I don't have access to CNC routing, so all of my recesses and cut-outs had to be hand routed.

Incidentally, I read a post earlier today regarding difficulty in finding 25 mm MDF in the UK. I got mine at my local Travis Perkins, about £25 for an 8' x 4'. The guys in the wood yard were also kind enough to cut it into 4 sheets of 4' x 2' on their table saw for free.

Veneer will be bubinga, although I haven't decided how I'm going to stick it on or finish it yet.

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Some more progress -

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Bracing cut outs finished, T-nuts for plinth in place.

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Dry fit of panels, T-nuts for rear panel in place.

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Bitumen/foam damping added, panels ready for assembly.
 
Latest progress report:

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Assembled skeleton

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Front 25mm panels and small rear panels added. Nail holes filled, ready for sanding. Grill frames cut.

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Removable rear panels and plinths with first coat of primer sprayed.
 
The port is 102 mm ID (4") and 400 mm long (15 3/4"). If I've got my sums right, it should be tuned to about 33Hz. I didn't want to use a smaller diameter port. Because the port flare is only 80mm from the floor, I was concerned that using a smaller port might cause chuffing. Once I take delivery of the woofers, I'll fit the drivers and do some impedance measurements to see exactly where the tuning frequency has turned out. If it's too low, I can trim the port back a bit.
 
Thanks Cal. They're getting there slowly. I'd forgotten how long it takes to build a pair of speakers.

It'll be a few weeks before I get round to the veneering. Since I'm using raw veneer, I'll need to let it flatten for at least a week before I can use it. It's my first veneering project, so I'm straight in at the deep end, but Bill Martinelli was kind enough to give me some advice. The man is a god when it comes to veneering. If you look down his home page a bit, the curved veneer cabinets are simply stunning!
 
gfinlayson said:
Progress is getting slower now. The plinths have had 4 coats of MDF primer and 3 coats of gloss black. One more coat of black then a few clear coats and some rubbing out should see it.

In between spraying coats of paint, I've made up the nameplates for the back panels:

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how did you make the nameplates?
 
Progress update:

Plinths are finished, crossovers assembled, tweeters fitted to the cabinets. The 18W/8531G00s arrived yesterday, and are now fitted. I couldn't get Speaker Workshop to play, so I haven't been able to check the port tuning frequency, or do any measurements yet, so that's a job for the weekend.

I'm suitably impressed with what I've heard so far. The 8531 produces BASS in SPADES. Big, deep and tight. How Scan-Speak get this much bass from a 7" driver I just don't know. Midrange is smooth and detailed, with no harshness. The D2905/930000 is very detailed, without a hint of sibilance even when put through the wringer with a track like Eva Cassidy's 'Autumn Leaves'. The soundstage is impressive too, wide and deep, with good placement of instruments and performers. I think I'm going to like these - a lot.

The veneer is flattening as I write this, so I'll be starting to that next week.

More pictures to follow.
 
OK, I finally got Speaker Workshop to play ball with my desktop PC, so here's the measurements:

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Frequency response 400 Hz to 22 kHz, 1/3 octave smoothing. There's still a little bit of room interaction below 500 Hz, but otherwise, not bad.

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Impedance in red, minimum phase in blue. The port tuning landed at 32 Hz against a target of 33 Hz, so I'm not losing any sleep over it ;)

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Step response, 3ms time window

All in all not too bad. Just got the veneering to finish, and I'll post some pictures of the finished article.

Graeme
 
I've just re-run some tests on my soundcard using RMAA 5.3. The soundcard response is severely compromised below 10 Hz, so I expect the odd behaviour in phase and impedance is due to measuring anonmalies below 10 Hz.

Maybe I should re-jig the impedance graph to show only from 10 Hz upwards.
 
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