Something stirs in the Undergrowth

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More round-the-bend madness. In the smallest bend, the height and width are both changing at the same time

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This is hard ....
Been away this weekend so limited progress.

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Yesterday I spent about half an hour looking at the parts, checking squareness & puzzling, trying to fit the new section into the main build. Eventually I worked out that something needed a minor bit of fettling, then it all fitted together ( phew ! ) .
Today something more substantial in terms of progress :

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Phew
The Keystone Ops have been keeping me very busy indeed over the last week . Finally the second section of the line is boxed-in.

Now for a fairly meaningless test of the first 50cm of the expansion ... :

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Sounds OK considering the very rough & compromised response on this short horn. It's only loaded down to around 300Hz here. Main check was to see if the vocal range & above has any content from the upper KHz range of the Fostex that might spoil the tone in the area the Yuichi takes over. No evidence of that , female vocals are quite strong but with a definite 'low-pass' character as there should be.

Today made good progress, cut & trimmed the wood for the side panel ( 83 x 60cm ) which I bought yesterday in Llandudno. Then I did several more pieces for the second bend, including one piece of 30mm chip-board that was hollowed out to a curve using the router and smoothed with 'Mr Snouty' before being coated with wood-filler to consolidate. Should able to do a bit more assembly tomorrow.

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Aaarg I'm going round the bend (2)
Here further progress after getting the two curved 'flanges' in place that define a 12.5cm width around the 2nd bend; now building the outside of the curve up with a mix of 20mm pine pieces and a big chunk of 30mm chipboard that was sculpted to a cylindrical curve on the inside - this (white ) piece will attach to a bigger piece of 25mm MDF that forms one half of the base panel.
With the white bit in place temporarily, I can listen to the horn at about 62cm length . Already I'm getting hints of some good things - more than at 50cm .

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More heavy fettling during last week & the weekend. The second bend was a struggle.

Then I did some (rushed) testing with the back panel clamped-on to make up the next 30 or 40cm of the line. This was somewhat wishful thinking, given I was then listening from the front (mouth) , with a big chunk of the inside of the final bend missing, no real side panel, and no enclosed back volume behind ( in this case above ) the driver. Anyhow, the frequency range is expanding downwards, that's about all I can say. It's OK to listen to but has various flaws which hopefully will be corrected more or less by the remaining steps.

[simon]

In the nicest possible sense Mark, you're completely bonkers! We do, of course, completely approve.

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Praise indeed !
I realised today, that having used some sections of the old 120Hz tractrix horn on this latest work, I am now one of the world's few qualified horn recyclers
I suspect Kevin Scott is also in this exclusive club.

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Last evening I added an additional large piece of (faced) 30mm chipboard in the inside of the final bend. Now there are only small gaps or blending pieces required in a couple of places.
I did another lash-up, with the second side pushed into place against the OB speaker, with the horn unit now the right way up, and have been listening to this the last two evenings. It's starting to sound really interesting , with tight percussion and good tone in vocals , & handling complex music much better. The remaining steps should be quite exciting. There's the closing-off & tuning of the speaker back-volume for instance , which should improve the low-end tone and phase response. Taking a break in the Lakes now for a week, so will get back onto it from 23rd Oct.

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Well here I am still soldiering on, doing DIY stuff - although I could probably buy something better commercially ( https://parttimeaudiophile.com/2014/05/ ... ing-voice/ ).
Been slow going with a week away and then a cold that has lingered for a week or more, but steadily chipping away at the last pieces and finishing.
The inside of the final bend required a nice piece of Beech and a fair amount of work on it, to plug that gap. Some filler and sanding/varnishing, just finished, here in the first shot.

Also there's a base panel been attached to the outer curve of the 2nd bend and the side-panel.

Before this I'd made and fitted a brace between the second and third 'straights' in the line. I like the way a folded horn can be very effectively braced from one section to the next, so unsupported areas ( and resonances ) can be kept to a minimum.

You may also notice ( hope you did ) in these shots that some of the ends of the various pieces of wood have had strips of iron-on veneer added, to try & get all the ends that will butt up against the final side-piece to the same level - to about 1mm anyway.

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Alongside this I have been preparing the back panel ( 25mm birch, reclaimed from the side of the 'Onken' bass cabinet I built about 7 years ago ) for fitting. After cutting to approx size, I had to patch some torn outer ply layers with filler, then varnish the whole inside surface but with 2 layers in the areas open to the sound waves, down the middle. Just drying here :

This afternoon I made another really tedious piece of slanted wedged MDF to add to the outside of the final bend . Again, no 90 deg angles to be seen anywhere, awkward 32 deg cut with a jig saw , then planing faces while I couldn't hold the wood properly . Glad that's over and it appears to have stayed in position while glueing - fingers crossed !

Only one more piece to be made, now ....

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Been busy in last few days with details of the last bend and the back panel.
I did a couple of tests, Tuesday & Wednesday, very different results.
Tuesday - back panel screwed on at least with 4 screws, so should have been better than last time, but sounded crap. The back panel was about 2" too long at the bottom, so the unit was on blocks at the front and the driver enclosure ( back-volume ) was open. Eventually I concluded this must be the main difference. Sound was woolly, slow and toneless.

Wednesday - trimmed rear panel and got the speaker back on the floor . Much better. The volume & sealing of the driver back-volume must be really important. However.... the sound was not quite as good as lashup no.2 about 3 weeks ago, when the third bend was less complete. So it's proving to be as suspected, the last bend is very critical as regards tone and phase. Piano notes were not quite as toned and punchy.

Tomorrow I hope to do another test, the third bend parts will be all present then and I have more blanking pieces in the back-volume to stop it communicating with other bits of the unit, and connectors on the side-panel so the side panel can be on the ground & hence more or less sealed ; albeit at a slightly larger volume than final. Hopefully things will improve again.

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OK here's a blurry pic of the whole thing just prior to another assembly and test .
If you look carefully you can see there are bits of the horn curve attached to the back panel ( top ) and side panel ( bottom ) which fall into place when the thing is assembled. It just seemed like the best way to do it, for rigidity and reliability when closed-up.
I have installed a speaker connector (pair) through the side panel too, if you look carefully.

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Hmm.
Listening this evening suggests it may be another of those Herb Reichert 'Welcome to the next level' moments.
Tone and snap have not come back with finalisation of the third bend. A few things to do yet in terms of tuning the back volume and getting the Yucihi horn on top of the PMVO to do better time-alignment checks, but I'm not hopeful. We shall see...