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chris661
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#121

Post by chris661 »

If they were both contributing, reversing the phase of one of them would give a large (in both amplitude and frequency spread - it is only first order) dip in output.

Playing with the crossover frequency would be better, and what better way than to use a computer to get it somewhere near?

Have I told everyone about Foobar2000 yet? :)
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Mike H
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#122

Post by Mike H »

I believe so! :D

In theory there should be a big dip, not necessarily in practice. Only one way to find out! And it's a quick and simple sperry-mint
 
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andrew Ivimey
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#123

Post by andrew Ivimey »

Am I missing something (no, don't be rude) but

B&C DE35 Compression Driver looks like an answer to a prayer, spec wise.

so am I missing some crucial point?
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IslandPink
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#124

Post by IslandPink »

OK chaps
Well, I intend for completeness to check the effect of a full 2nd-order high pass on the horn driver this evening . However I think any 'shout' that exists is more likely due to the breakup of the diaphragm as it rolls off ; I did try the extra roll-off at 230Hz as I said above. I can move this one ( acheived by using a small cathode by-pass cap on the DHT ) to about 800Hz using 0.47uF .
I'm trying very hard to avoid moving from 1st-order, as my experience and that of Bruce Edgar and Romy the Cat suggests it works best .

As for the out-of-phase test , I did this a couple of weeks ago and spoke to CV about it. Surprise surprise , in theory, with 1st-order crossovers , he says there is NO dip . In practice I found a 'soft' minimum of 1-2dB as I moved the horn around on top of the Onken box trying to find the best time-alignment .

Yes Andrew , the DE35 looks good . When I went around the houses before and bought the G3 ribbons, it seemed there weren't any great tweeters around for less than £400-500 . For some reason I spent about £450 on a pair of G3 ribbons ... must have been listening to Lynn Olson too much !
Since I've been messing about with the two amp sides, and real speakers, listening with/without crossovers and hearing the benefits of not having anything between the amp and speakers, I realise that it makes more sense to stop messing about and get an extra (small) amp on there for the tweeter. In actual fact I don't need to do too much to do this - I was debating about whether to run 2x2A3 to run the autoformer, horn and tweeter crossover ; now with the full 108dB/w I can just run 1x2A3 ; then the extra juice can run a 71A or something for the tweeter . Both can run off the same driver.
Even the output transformers for the 71A might be solved if Dave Slagle can supply me with a different bobbin for the Autoformer cores ( maybe some shim for the SE gap too ) to turn them into output trannies .

Yippee !
Circuit to follow ...
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IslandPink
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#125

Post by IslandPink »

Circuit hopefully :
no, too big , damn damn ...
:?
Maybe in a couple of days if it scans OK at 200x100 dpi then .
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IslandPink
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#126

Post by IslandPink »

Right
In a bad mood now :evil:
I've concluded via a number of experiments in the last two days that no amount of pissing about with low-pass or high-pass crossovers either in the amp or on the drivers is going to get rid of the 'shriek' in these drivers .
If I play test tones from a CD player it's obvious there is a resonance around 2500Hz , bang in the middle of the useful range.
This is true of the one that seemed OK, which stayed here, and in the one that was sent back to GPA for fixing in 2009 because it wasn't right the first time .

I'm considering the options .....

Grrr :evil:

ILPS
Last edited by IslandPink on Thu Jan 20, 2011 6:26 pm, edited 1 time in total.
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chris661
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#127

Post by chris661 »

Hmmm...

By some rough calculations, a 2.5kHz wave has a length of ~4.5" (136mm for those like me that work in a weird combination of millimetres and inches).

Anything corresponding to that number or a multiple thereof (could even be a half wavelength)?

If not, you could play around with notch filters.........
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IslandPink
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#128

Post by IslandPink »

chris661 wrote:If not, you could play around with notch filters.........
I shouldn't need to, Chris.
I've seen other plots of these drivers and some are pretty nice in the 2.5k area, but quite a few are not .
(This posted edited to tone-down a bit 21st Jan !! )
Maybe I should have bought some old 288-C's ....
Last edited by IslandPink on Fri Jan 21, 2011 5:00 pm, edited 1 time in total.
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Mike H
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#129

Post by Mike H »

Ah!!!

That's a pain in the @*#$?~..


 
 
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#130

Post by Andrew »

An expensive pain in the &$%£, in fact.

Andrew
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IslandPink
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#131

Post by IslandPink »

Note : Edited the 'angry' post a little bit to tone it down a bit .
I'd best do some frequency sweeps of this to make damn sure of what I'm saying here .
I also need to check the 'Fletcher Munson' curve to see how much louder the 2500 tone is going to sound compared to the others.
However that 2500 tone sounds a lot louder and harsher than the ones at 1280 and 5000 . It's the worst place as it's the area where many speakers have a dip to reduce harshness and sibilance .

Hmmm...

Does anyone know someone in the North of England or Midlands who has some 288-C's or similar, to listen to ?


MJ
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IslandPink
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#132

Post by IslandPink »

http://en.wikipedia.org/wiki/File:Lindos4.svg

Not enough difference on the 80dB curves to account for the difference I'm hearing ....
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#133

Post by Andrew »

Can you got hold of a microphone and use a sound card to do some relative measurements?

I doubt the room is adding that much gain at that frequency.

Andrew
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IslandPink
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#134

Post by IslandPink »

The funny thing is that I did measurements of that type with Nick's kit in 2009, and all you see is a little dip followed by a peak, around 2500 to 2700Hz , neither of which are all that big , maybe within 2-3dB overall . What I have seen , though, on the data for a couple of Lynn and Gary D's drivers is a big 'smear' down from 2500Hz on the CSD plots that indicates resonance around that area, and I'm assuming that's what's up with my drivers .
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chris661
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#135

Post by chris661 »

If you play a bandwidth-limited impulse (so the LF don't kill it), does it ring?

You might need to play with physically damping the horns...
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