Something stirs in the Undergrowth

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Ray P
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Re: Something stirs in the Undergrowth

Post by Ray P » Mon Jan 13, 2020 6:57 am

IslandPink wrote:
Sun Jan 12, 2020 10:20 pm
More to the above - what the cap change suggests is that there's different phase behaviour in the two cables.
Please tell us that the cables are different other than the colour of the sheathing?

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IslandPink
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Re: Something stirs in the Undergrowth

Post by IslandPink » Mon Jan 13, 2020 8:02 am

Yes !
PM me if you want to know.
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Re: Something stirs in the Undergrowth

Post by Ray P » Mon Jan 13, 2020 8:29 am

IslandPink wrote:
Mon Jan 13, 2020 8:02 am
Yes !
Phew, that's a relief!

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Re: Something stirs in the Undergrowth

Post by nicoch » Mon Jan 13, 2020 10:17 am

on black there is a carbon , on white titanium oxide

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Re: Something stirs in the Undergrowth

Post by IslandPink » Sun May 10, 2020 7:06 pm

Hmm.. secret ...but very useful improvements :
http://www.troelsgravesen.dk/Edge-coating.htm
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Re: Something stirs in the Undergrowth

Post by chris661 » Mon May 11, 2020 9:11 am

Yep, looks pretty interesting.

Looks like a primary cone resonance is damped out nicely, and with phase-plugged drivers the benefits apply higher up, too. Understandably so - the surround can "catch" any higher resonances.
Drivers with dustcaps don't get all the benefit, by the looks of it, since there are some resonances that the surround can't directly dampen. I wonder if he'll try a similar treatment at the dustcap/cone junction.

Thinking in Thiele-Small for a moment, it looks like this will lower Qms, so Rms will rise. I remember Rms being something you considered important, Mark, but I can't remember if you wanted it to be high or low.

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Re: Something stirs in the Undergrowth

Post by Scottmoose » Mon May 11, 2020 4:07 pm

Damping the edge-resonance of the cone can certainly help as Troels notes; if you want suggestions on materials, I suggest you ask Dave, he's been applying differential damping to cones for decades.

I'm slightly puzzled by Troels's reference to phase shift being more problematic than the deviation in the frequency response, since loudspeaker drivers are basically minimum phase devices, so the phase follows the FR. I suspect what he means in terms of the cause is that with non-rigid cones, the periphery often resonates and if insufficiently damped, goes briefly out of phase, hence the notch in the response (usually between about 900Hz - 1.4KHz in a 6in - 7in midbass). You can tell it's a cone issue in many cases by comparing to an alloy cone model from the same range & in the same size. Usually no sign of it in a quality design.
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Re: Something stirs in the Undergrowth

Post by IslandPink » Mon May 11, 2020 6:36 pm

I don't see a problem with what he said. Yes, if you reduce the amplitude dip then you reduce the phase shifts. I agree with him that the phase shift ( which peaks on the max downslope and again the other way, on the max upslope of the amplitude) is the bit that does the damage, because it disengages the harmonics from the fundamentals - and in the upper midrange that's the worst place for it.
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Re: Something stirs in the Undergrowth

Post by Scottmoose » Tue May 12, 2020 8:05 am

I wasn't offering thoughts on mechanisms of audibility, just noting that the text currently gives, or can give, the impression that FR and phase are independent, which may cause confusion amongst people who aren't aware that drive units are minimum phase devices and the phase simply follows the FR. No doubt that isn't the intention, but it could have been made a little clearer (while fully acknowledging I only know enough English to scrape by on, let alone speak any other language, and have massive admiration for those who can). It looks like he's revised some of the earlier text so I suspect in the next round of copy-editing he'll make some adjustments.
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Re: Something stirs in the Undergrowth

Post by chris661 » Tue May 12, 2020 10:10 am

Scottmoose wrote:
Mon May 11, 2020 4:07 pm
I'm slightly puzzled by Troels's reference to phase shift being more problematic than the deviation in the frequency response, since loudspeaker drivers are basically minimum phase devices, so the phase follows the FR.
I suppose the phase shift has direct implications on how well a HF driver might integrate if the dip is at/near the crossover point. If the phase remained unchanged but the frequency response dipped, the HF driver might fill that in okay, but if the phase moves so that the drivers cancel over a narrow bandwidth, then the dip will be worse than the midbass driver alone might suggest.



Mark, the phase wiggles here are orders of magnitude smaller than those created by a typical crossover network. I suspect that some people are more sensitive to time domain problems (ie, phase shifts) than others, and I'm happy to accept that you might be much more sensitive than most.

IIRC, you liked the system I brought to Eggborough a while ago, which was a pair of FE126eNs in some compact folded Voigt pipes, driven by a breadboard 6EM7 SET. Looking at that system for a moment, there was no crossover. I think I'd installed a notch to take out the 6.6kHz peak on those drivers, and that's about it. In terms of phase shifts, that's about as good as it gets. There'll be a load of shift at the bottom end where the cabinet starts rolling off, but the rest of the range ought to have been pretty linear. Now, that system did some things really well, but power handling and "oomph" weren't on that list.
In order to maintain that flat-phase-response clarity while adding the dynamics and "grunt" of a good multi-way speaker (what I assume to be your goals - correct me if I'm wrong), there are two possible ways of doing it that I can see:
- Line source of full-range speakers, which presents its own issues
- FIR processing of a multi-way speaker

Given where you are at the moment with your cabinets etc, I'd love to bring the Powersoft amps over (10x channels of FIR, variable output impedance <400Hz and power) and see how good we can make it. Once the lockdown is over, let's see if we can arrange something.

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Re: Something stirs in the Undergrowth

Post by Scottmoose » Tue May 12, 2020 4:45 pm

chris661 wrote:
Tue May 12, 2020 10:10 am
I suppose the phase shift has direct implications on how well a HF driver might integrate if the dip is at/near the crossover point. If the phase remained unchanged but the frequency response dipped, the HF driver might fill that in okay, but if the phase moves so that the drivers cancel over a narrow bandwidth, then the dip will be worse than the midbass driver alone might suggest.
Right. Since it's usually lurking in the approx. 900Hz - 1.4KHz region for most 6in - 7in midbass units (and alarmingly close to that in a few smaller ones too), usually not a major issue for XOs, though certainly something to be aware of in the rare cases. The Edingdale SR & GT are / were one of that breed; we were OK as the 6in Satori midbass edge-resonance wasn't severe enough to cause any problems. I can certainly think of a few where there's a possibility of it causing some headaches though.
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Re: Something stirs in the Undergrowth

Post by IslandPink » Tue May 12, 2020 10:13 pm

..comment tomorrow... need to catch up on sleep..
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Re: Something stirs in the Undergrowth

Post by Nick » Thu May 14, 2020 9:34 am

Ian posted this on FB, though it might be of interest.

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Re: Something stirs in the Undergrowth

Post by ed » Thu May 14, 2020 12:08 pm

here's the page for the horn itself if anybody is interested:

https://josephcrowe.com/products/es-600 ... d-cad-file

I was intrigued by the equation to cnc direct connection. He seems to place importance on this aspect so I'm wondering if it's a departure from the usual method of cutting using cad files.
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Re: Something stirs in the Undergrowth

Post by SimonC » Thu May 14, 2020 1:02 pm

ed wrote:
Thu May 14, 2020 12:08 pm
I was intrigued by the equation to cnc direct connection. He seems to place importance on this aspect so I'm wondering if it's a departure from the usual method of cutting using cad files.
Not really, its an elegant solution to a problem that doesn't really cause any issues. Provided you are getting enough points out of excel to define the surface adequately the surfacing tools in any modern 3D cad package will take care of the interpolation between the points to give you the same end result.

What it does let you do is edit the design very quickly though. Generating a cloud of points in excel, importing them into cad and then surfacing them is a painfully slow and boring process. That equation driven style of cad works well for shapes that follow a straight central axis (straight horns), as soon as you curve this axis (folded horns) then the equations get very tricky to set up and old school excel points usually win again.

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