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Old 7th September 2012, 02:30 PM   #7991
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I recently re-coned some old PM2A Lowthers of mine with the new style cones, mounted them on 200Hz Le Cleac'h horns with no cross over, and was surprised at how relaxed and enjoyable things became. I have been listening and trying stuff with 420Hz horns and compression drivers (JA661B) these last four years, and enjoyed the music, but suspect probably I never got it right regards the cross over. Positioning is easy - fully agree on the apex should be just in front of the listening position. You get to know the right angle just by looking at the horns. I have had Vitavox 15" K15/40 bass drivers mounted in 1.5m 50Hz horns during all this period. It is not too hard to get a reasonable flat response to about 70 or 80Hz. The image and precision is all there, not holographic, but special. But as I type, the Lowthers are making music, rich and seamless. (playing Patsy Cline). I know it is a case of making everything sound good regardless, with somewhat overblown lower mids, (I just let the bass horn go on up to 400hz or so with a 12dB LP). But it plays vinyl just oh so well. http://www.lencoheaven.net/forum/index.php?topic=9746.0

I guess it was all under better control with a digital cross over (dbx driverack) and multi amps but but I just like the raw sound of CL 12dB cross overs and a single amp better. So hoping for some help here on how to make a nice passive cross over with all the incomprehensible stuff taken care of in good cook book tradition. Somehow I know this is not going to happen :-). I am married to my bass horns but designing cross overs to suit them rgds phase I suppose is asking a lot. The upper end response roll off is a confusing thing.

I took care of level matching for the compression drivers by winding speaker level transformers on Nickel cores, and that goes a long way. Things got better. I hope to keep cap sizes down by doing it upstream of the above.

I also have project coming along for 160hz horns on LM555W drivers, with the idea to get the rich Lowther low cross over sound combined with compression driver precision.

Great to have this thread underway again, zeroing in on holographic sound for all.

martin
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Old 7th September 2012, 02:51 PM   #7992
Jmmlc is offline Jmmlc  France
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Hello Martin,

If you could send me both :

in pir format :
- impulse response obtained using Arta of the bass horn
- impulse response obtained using Arta of horn loading the Lowther

in lim format:
- impedance curve file of the bass-horn loaded loudspeaker
- impedance curve file for the horn loading the Lowther

Better to have the microphone in fixed common position when measuring the IR of the bass loudspeaker and the lowther.

Then using my own Matlab code I'll be able to calculate and simulate for you a crossover with equalization of impedance of the loudspeaker.

As an example here a crossover I designed for a friend :


Best regards from Paris, France

Jean-Michel Le Cléac'h


Quote:
Originally Posted by Truetone View Post
So hoping for some help here on how to make a nice passive cross over with all the incomprehensible stuff taken care of in good cook book tradition. Somehow I know this is not going to happen :-). I am married to my bass horns but designing cross overs to suit them rgds phase I suppose is asking a lot. The upper end response roll off is a confusing thing.
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Old 7th September 2012, 03:07 PM   #7993
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Hi Jean-Michel, That is very kind of you, thank you. Was not expecting such a positive response, and so fast. I have just begun my 3 month Long Service leave (no nice of the government here in Australia) so if my wife permits, I will work on this and come back with the required data.

very best regards from Perth, with Spring just beginning and flowers coming out,

martin
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Old 7th September 2012, 06:46 PM   #7994
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An odd problem:
My big Altec horns had been driving me nutty. It was a phase/polarity problem.
Even tho I knew that electrically they were in same polarity, they didn't sound like it. It sounded like one was flipped to opposite polarity, out of phase. Change the polarity on one side, and they sounded right. Impulse response would now show them to be 180 degs out of phase, but the vocals where stronger and better placed. Put them back "right" and vocals would drop out. It just didn't make sense. (The woofers didn't do that at all.) I went 'round and 'round with this, getting more and more frustrated.

Then I remembered that I had aimed the speakers very precisely (with a laser) to cross at a point about 2 feet behind my head. Sitting right in the middle would cause the center image (mostly vocals) to drop way down. Moving a little to the left or right would pop the vocals right back in. WTF?

So I toed in the speakers more. Voila! Center image was back and sweet spot much larger, the space much better defined.

The only thing I can figure is that the horns must have been so perfectly aligned to left-ear/right-ear that whatever was in phase between them just canceled out at my head. Weird. Crossing them further forward fixed it. All good now.
This doesn't make sense and would drive me nuts until I tracked down the cause! I find the quickest way to get to the bottom of situations like this is to send a true mono signal (ideally from the same channel of the amp if the amp can tolerate the parallel impedance) to the pair of drivers in question and listen for a solid central phantom image. If that seemed normal, I would go upstream from the amp. Is it possible there is a polarity inversion on one channel of any of the interconnect pairs between source and speaker? Is the cartridge wired correctly, if you are using vinyl?

Crossing the axes at 2 feet behind your head should not cause this if you are on the center line, unless there is some sort of weird anomalous (and asymmetrical) phasing characteristic at certain angles off the center line of the horn - even then the anomaly should be duplicated in the other and shouldn't result in compromised imaging. I also wonder why you chose to cross at two feet behind, instead of in front - is the stereo listening zone wider for you this way?
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Old 7th September 2012, 07:15 PM   #7995
Pano is offline Pano  United States
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Hi Russell, long time no see.

It doesn't make a bit of sense to me either - that's what was driving me crazy. Still not sure what was going on, my explanation is all I could come up with - doesn't mean it's right. Good idea on using the same amp channel, had not thought of that. Still, when they measured in phase at the mic they sounded out of phase and vice-versa.

Why cross behind me? Jeez, I dunno. Probably read about it somewhere and gave it a try. Somehow it stuck. Not a great idea, it seems.
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Old 7th September 2012, 11:38 PM   #7996
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Hi Russell, long time no see.

when they measured in phase at the mic they sounded out of phase and vice-versa . . .
Why cross behind me? Jeez, I dunno. Probably read about it somewhere and gave it a try. Somehow it stuck. Not a great idea, it seems.
I've never heard of a directional speaker doing better crossed behind you. The over-toed (cross in front of you) approach can be useful because it gives a bit of time/intensity tradeoff to widen the sweet spot: when you move left (closer to the left speaker), you also move more on-axis to the right channel, and likewise slightly further off-axis of the too-close left speaker & vice-versa. This approach is not particulary effective with low directionality speaks (popular minimonitors), or speakers that change directivity wildly thru the XO region (like a 10" 2-way cone & dome speaker)

Sorry if I missed it, but where are you seated relative to the walls behind/around you?
You may have some bad speaker-listener-room interaction that high-directivity can alternately exacerbate or hide when changing toe-in.
While high directivity can address certain room issues, it can also make other ones more obvious because the density of reflections at your seat is lower & likely less diffuse (than with low directivity source). Think of the effect of sitting in a heavy mist versus being lightly sprayed with water. Same water; different delivery & level of distraction. Even-ness of polar response is more critical / detectible with high directivity. Always a double-edged sword . . .

If room reflections aren't a problem, maybe your speaks' directivity is disproportionately narrow over a just a portion of the frequency spectrum.

-- Mark
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Old 8th September 2012, 12:44 AM   #7997
ScottG is offline ScottG  United States
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Hi Russell, long time no see.

It doesn't make a bit of sense to me either - that's what was driving me crazy. Still not sure what was going on, my explanation is all I could come up with - doesn't mean it's right. Good idea on using the same amp channel, had not thought of that. Still, when they measured in phase at the mic they sounded out of phase and vice-versa.

Why cross behind me? Jeez, I dunno. Probably read about it somewhere and gave it a try. Somehow it stuck. Not a great idea, it seems.

Could you actually *see* the driver (all of the driver's exit) when placed to "cross-behind" you? Or were cell walls in the way?
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Old 8th September 2012, 01:14 AM   #7998
Pano is offline Pano  United States
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Right now the center cells are pointed right at me. Before it was closer to having a cell divider pointed at me. Didn't seem to make much difference to the mic (point) but it did to my ears.
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Old 8th September 2012, 01:17 AM   #7999
Pano is offline Pano  United States
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Originally Posted by Tubamark View Post
Sorry if I missed it, but where are you seated relative to the walls behind/around you?
Interesting thought. Maybe a strong reflection off the wall behind me. There is significant padding there, but just above me head. Need some lower down.
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Old 8th September 2012, 01:32 AM   #8000
ScottG is offline ScottG  United States
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Right now the center cells are pointed right at me. Before it was closer to having a cell divider pointed at me. Didn't seem to make much difference to the mic (point) but it did to my ears.
As I've mentioned on other threads dealing with "room sound" = bad = largely BS.

It's mostly about the speaker's radiation profile.

NOT just dispersion pattern (or resulting power response), but also:

The spl *gradient* - which is a huge localization cue. Disrupt this gradient (or the direct path from driver to listener and how sound becomes lower and lower in pressure from the source), and you'll get a "phasey" sound.

You can hear this effect here (once at about 38 seconds in, and again at 1:14):
JBL 4428 compact 3 way studio monitor - YouTube



..oddly however, (..and depending on the freq.) - it could be argued that the "phasey" sound" is fundamentally more accurate. (..though in both this video and particularly with your even lower freq. horn, the bandwidth extends to low in freq..)
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