Something stirs in the Undergrowth

Dedicated to those large boxes at one end of the room
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IslandPink
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#2161 Sad end to a ....

Post by IslandPink »

Sad end to a once proud Horn :
Ex-horn.JPG
Need to make some space ...
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#2162 Re: Something stirs in the Undergrowth

Post by IslandPink »

Just ordered two custom acrylic pieces to make the upper panels for the OBs. Better late than never. Had a guy at work draw up the requirement as a DXF ( and PDF ) file. £155 for the two pieces including postage - bit steep but I guess the Perspex has gone up since I last ordered. I will still need to take the parts to a local machinist to put a 15 degree edge chamfer on the lower edge where it butts to the main front panels.
MJ_PERSPEX_COVER.jpg
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IslandPink
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#2163 Re: Something stirs in the Undergrowth

Post by IslandPink »

SimonC - might be of interest - I'm having difficulty contacting you on email, so if you read this, here's something useful on the coupling-chamber volume for the FE208Ez.
http://www.diyaudio.com/forums/full-ran ... ost5387703
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#2164 Re: Something stirs in the Undergrowth

Post by IslandPink »

Working with the FE208Ez again on ( proto - rough ) Perspex baffle. I'm refining the 'Pinkzilla' notch filter..
http://www.audio-talk.co.uk/phpBB3/view ... la#p121175
..values with careful listening on tracks by John Fahey, The Fall and Colin Walcott. Trying to get least harshness or 'squawk' on things like vocals, trumpets etc without messing up tone or dynamics. I really rate the 208 driver, it has loads of tone, dynamics and low-level presence but it has a few faults. It's also a mega-suitable horn driver. The 3.5kHz peak is the area I'm targeting.
Current adjustments from the above are around 5.4uF cap instead of 3.9 - reducing frequency of notch dip to ~3.4kHz , and 3.3R instead of 4.7R , which reduces the notch to more like 3.5dB than 4.5dB.
The aim is again to use the Aurum ribbon tweet blending in 1st-order from say 5kHz.
This is for the back-burner project of the Dallas II horn. If the mids and bass work to my liking then it could be a seriously good non-extreme speaker requiring at most 2 amps. OK you could add a tapped horn for 80Hz and below to beef-up.
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SimonC
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#2165 Re: Something stirs in the Undergrowth

Post by SimonC »

IslandPink wrote: Wed Mar 28, 2018 9:59 pm SimonC - might be of interest - I'm having difficulty contacting you on email, so if you read this, here's something useful on the coupling-chamber volume for the FE208Ez.
http://www.diyaudio.com/forums/full-ran ... ost5387703
Thanks :)
I'm here and lurking. Sorry about being so quiet, I am chipping away at the Dallas in between other work...

Cheers
Simon C
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#2166 Re: Something stirs in the Undergrowth

Post by simon »

I'd completely forgotten you played around with the notch filter Mark! Now my Quasars are fully built I should have a play too. You're using a parallel crossover though?

I do wonder though. At modest levels I don't hear the notch (not saying it's not there), and I wonder if the effects of the cruddy mdf baffle and close proximity of the rear wall might swamp the effects.
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#2167 Re: Something stirs in the Undergrowth

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SimonC wrote: Tue Apr 03, 2018 12:35 pm Thanks :)
I'm here and lurking. Sorry about being so quiet, I am chipping away at the Dallas in between other work...
Cheers
Simon C
Chipping-away is always good to hear in the context of speakers !
Loose end ( didn't get a reply ) - can you confirm which email you want to use for Dropbox to review simulations, Simon ?
no need to give the full address on here - just a bit will do.
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#2168 Re: Something stirs in the Undergrowth

Post by IslandPink »

simon wrote: Tue Apr 03, 2018 12:43 pm I'd completely forgotten you played around with the notch filter Mark! Now my Quasars are fully built I should have a play too. You're using a parallel crossover though?
I do wonder though. At modest levels I don't hear the notch (not saying it's not there), and I wonder if the effects of the cruddy mdf baffle and close proximity of the rear wall might swamp the effects.
This a different scenario to the Quasar , Simon. I have grappled with how to use a low-pass or a notch filter for a FE208Ez-based Quasar - with the existing series crossover - and gave up, more or less. You might be able to use the passive series crossover as normal, but put a small notch filter in between stages of the amp you are using. In this case the three ( L,C,R ) components would probably be in the feed from driver to output valve - and probably the value of the grid-leak resistor of the output valve would be the 'load' the notch filter sees. I have no idea what the values would be, without making up a Spice simulation - at present I haven't got it set up again on this new machine ( another job to do - urgent ) .

When you say, at moderate levels you don't hear the notch, do you mean the 3.5kHz spike ?
It's not so much in the midrange where the baffle placement/walls might cloud it, it's a sort of sharp sound or hardness that occurs sometimes with vocals or things like certain guitar notes or brass instruments. The 208 is pretty good, so it's not anything gross like that from a FE206e or a 126 , but it's not meant to be there and can be improved. However even the shallow notch I'm using will take away a bit of 'treble' from the 208 if you're not using a tweeter - so maybe not too helpful in your case. My work is really targeted at using the FE208 with a tweeter in applications like a BLH where there's no additional bass/mid crossover.
I have another idea to use a masking ( annular ) collar in front of the 208 driver as a mechanical filter, to block direct receiving of the HF from outer portions of the cone and force it to 'mix' on its way to a smaller 5" output aperture - which I had on the coupling 'collar' & phase plug for use on horns - this might work quite well, without losing midrange or treble output up to about 2kHz, but I'm sure it'll force the use of a tweeter to boost the treble above 4 or 5kHz in that case. Again, not what you want - but a small amp for a separate tweeter would be the option then - or maybe even a bullet tweet with a simple crossover.
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#2169 Re: Something stirs in the Undergrowth

Post by IslandPink »

simon wrote: Tue Apr 03, 2018 12:43 pm I'd completely forgotten you played around with the notch filter Mark!
It occurs to me that anyone who isn't a bit mad would have tried to split the speaker work up into individual threads rather than one big monster 10-year long thread. That would have perhaps avoided random criticism from people eg. in the Bristol area or West Yorkshire about this project going on for ever with no conclusion :roll:
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#2170 Re: Something stirs in the Undergrowth

Post by simon »

Feck em Mark, this is one of the great DIY audio threads!

I'll have a ponder on your thoughts, thanks.
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#2171 Re: Something stirs in the Undergrowth

Post by IslandPink »

:oops: You are very kind, Simon !

Minor updates :
1. Got the Perspex upper pieces for the OB's back a few days ago. Just took them over to the machinist for the 15 degree chamfer to be put on. Wed or Thurs PM is estimate on that.
2. Been fettling the FE208Ez driver with some limited treatments that were good on FE103e and FF105WK. A light coat of 30% solution of Micro-scale gloss coat ( as beloved of BudP ) on the front of the cone. Then some 'ZIG' glue on the rear, just around and inside the join of the cone to the surround. I also feathered this glue inwards a bit with a sort of zig-zag pattern, might just do something to slightly break up HF annular modes near the edge - see below.
ZIG_FE208.JPG
3. Extended the slot on the 'testbed' Perspex OB downwards to get the ribbon as close as possible to the 208.
Ribbon_closer.JPG
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#2172 Re: Something stirs in the Undergrowth

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Shiny shiny ...
Baffle_upper_2.jpg
Still some work to do.
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#2173 Re: Something stirs in the Undergrowth

Post by IslandPink »

Not kidding 'still some work to do' - the cut-out for the tweeter is undersize vs. the drawing by about 0.4mm, so the tweeter won't fit.
MORE work for the machinist guy to do - and more delays. I suppose there's a few things I can do in the meantime...

Actually, I think I can skim off a fraction of a mm quite neatly with a router, if I set it up carefully and protect the surfaces with masking tape :D
There's a nice job for Saturday . Was already intending to try a combination of jig-saw followed by router for the additional cut-out in the top of the lower panel, so it's not a lot more effort. Phew !
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#2174 Re: Something stirs in the Undergrowth

Post by Cressy Snr »

That perspex really looks the biz.
I bet fingermarks are a nightmare :wink:
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#2175 Re: Something stirs in the Undergrowth

Post by simon »

For 0.4mm I think I might be inclined to try a drum sander in a drill. Apply light pressure and keep it moving around the circumference.

But I've never tried sanding acrylic so it might not be a good idea!
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