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Old 21st May 2007, 04:31 AM   #801
Variac is offline Variac  United States
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Did I see an oblique reference to this previously on this thread?

http://aa.peavey.com/downloads/pdf/qwp1.pdf

I think someone said it isn't good enough for our purposes so I haven't mentioned it before. It sure would be easier to make for Diy'ers, but of course that isn't the main goal here. The author acknowleges the problem of diffraction at the mouth in most horns. Possibly instead of the foam (or felt ) at the edge of the mouth, there could be a 4" radius fold back at the edge. That is quite easy to do with molding when you have a square section!
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Old 21st May 2007, 10:14 AM   #802
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It looks pretty reasonable to me, and a simple and effective edge termination. It even reminds of some of JohninCR's posts using expanding foam to create a smooth termination for the waveguide.

Going through all (OK, many) of the OB posts in the many different forums over the last several years has been interesting reading. Our friend Thorsten has had a lot of good things to say, and I appreciated this Open Baffle Study as well.
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Old 21st May 2007, 08:12 PM   #803
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Hi MBK,

Point accepted in relation to transients.

I still think however, that electrical compensation for baffle induced peaks will make music reproduction sound less natural because the pre and post transduction compensations will work in different time frames; ie. not coherent.
Only the steady sine response measured in time isolation will become flattened.

Thus the 'Q' of edge induced peaks should be minimized by mounting the driver at one edge of a baffle, with it some way down from the top in relation to the frequency range required.

Cheers ........ Graham.
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Old 21st May 2007, 08:32 PM   #804
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I'd like to quote Rudolf from another discussion:

"Ferekidis has shown that a baffle, which does not exceed 2.2 times the effective driver diameter, works best with regard to minimised edge diffraction. The complete derivation is only available in German:"

http://www.randteam.de/papers_lf/daga_2001-lf.pdf

Rudolf Finke's Dipole-Analysis site is at:

http://www.dipolplus.de/

Wish I could read German! This is interesting stuff. The graphs alone are quite informative.
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Old 21st May 2007, 09:08 PM   #805
mige0 is offline mige0  Austria
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Default subjective compromises

Hi

Quote:
Thus the 'Q' of edge induced peaks should be minimised by mounting the driver at one edge of a baffle, with it some way down from the top in relation to the frequency range required.
Sadly there simply is NO ideal speaker position on an OB. And to my belief, no such thing like an IDEAL OB shape as well..
Try yourself with EDGE and also vary the listening angle horizontally and vertically and also the size of the speaker in relation to the baffle size you will see immediately.
(Lynn, could you please post the "rudder shape" you found to have good response anything I tried in this direction had really inferior FR. Didn't quite understand your description I'm afraid.)

What CAN be done is :
1.) to optimise for a relative low impact of different listening angels at an estimated listening distance.
2.) to optimise for easy equalisation not necessarily maximal flat FR
This was my aim for the test baffle above with the given speaker.



Quote:
I still think however, that electrical compensation for baffle induced peaks will make music reproduction sound less natural because the pre and post transduction compensations will work in different time frames; ie. not coherent.
Also here we HAVE to live with a compromise. As you see in the CSD the FR is quite different from what is the decay which simply means you have to balance to something that is an SUBJECTIVE optimum in listening perception.
Listening to the test baffle, it indeed sounds slightly more "natural" when the compensation of the notch at 544 Hz is reduced from the 6 dB shown in the measurements to about 4 dB. For XO I use a simple 6 dB at aroud 2 kHz .

The Dynaudio speakers also have to break in some longer, as they didn't play for more than a decade now.

Greetings
Michael
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Old 21st May 2007, 09:44 PM   #806
mige0 is offline mige0  Austria
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Hi

Quote:
Ferekidis has shown that a baffle, which does not exceed 2.2 times the effective driver diameter, works best with regard to minimised edge diffraction


Greetings
Michael
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Old 21st May 2007, 10:01 PM   #807
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Default Re: subjective compromises

Quote:
Originally posted by mige0

Lynn, could you please post the "rudder shape" you found to have good response anything I tried in this direction had really inferior FR. Didn't quite understand your description I'm afraid.

Greetings
Michael
Sorry about the slow posting of the Edge simulations. This partly due to my awkward personal situation: I have a Mac TiBook downstairs, where I am typing now, as well as a Mac G5 and an AMD X2 PC upstairs, where I do the simulation work. It's easier to keep the leg elevated with the laptop - well, perched on my lap - than it is sitting down at the desk, where I have to take frequent rests and raise my leg on the desk. If I get too involved, I tend to forget to attend to my physical needs (raising the leg and massaging it).

I'm still at the stage where the leg is prone to edema, and I try to avoid keeping it down for too long. The lack of progress on the X-rays from February 20th to March 20th was due to edema, as far as I can tell, and the progress since then is the result of good blood flow in the leg, which is why I try to avoid sitting in positions where it is lowered and not being active.

It's occurred to me that it might be a while until I can fly again, and maybe not ever in the cheap seats in tourist class - that would be risking Deep Vein Thrombosis, which is a risk for air travelers in trapped in too-small seats for long international flights. I'm 6 foot 2 inches, not a small guy, so sitting in tiny seats for a long time is especially uncomfortable - and now, dangerous.

Putting that physical grossness aside and pending the PC -> Mac file transfer, here's a verbal description: imagine the rudder of a Swissair 747 - although kind of smaller, maybe 1.2 meters high. The top of the rudder is 600 mm across, and the bottom is 850 mm. The top overhangs the bottom by 150 to 200 mm.

Visualize the front of the aircraft facing to the right. Now forget the airplane, just think of its rudder, with the leading edge on the right, and the trailing edge and overhanging portion to the lower left. Remember I am also simulating the floor reflection, so there is a virtual rudder underneath the real one - it now looks like the swept wings of an aircraft, pointing towards the right.

The widerange driver is on the upper right, close to the top surface and right (leading) edge of the baffle. The midbass and bass drivers are mounted more or less in a vertical line below the widerange driver, although I run the Edge simulation looking at the WR driver by itself (1 driver) and also with all 6 drivers running at once. When I look at the single WR driver by itself, I'm not interested in the floor reflection, but am interested in all of the baffle diffraction, including the mirror-image baffle beneath the floor.

Since there's a reasonable chance I'm going to tip the baffle backwards by a few degrees, in order to time-align the bass and WR drivers, I move the virtual microphone between 1 meter high and the middle of the baffle height, as well as looking at 3, 12, and 100 meter distances.
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Old 22nd May 2007, 12:13 AM   #808
jamikl is offline jamikl  Australia
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Lynn, have you tried Google translate. Translates German fairly well although parts are ambiguous, especially for me with my limited knowledge, but you may have better understanding of the ambiguities.
jamikl
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Old 22nd May 2007, 03:03 AM   #809
GregOH1 is offline GregOH1  United States
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Lynn, I may have made a mistake . I have the 12nda 520,s the Delta Pro 15A's and the Radian 745pb are being shipped from Cal. I was told ( USSpeaker) that I should go with the 16 ohm Radian because it would need less padding. I intended to use a digital crossover for at least the Delta to the wide/HF. I also have no problem with tri amping if that would be best , I have no doubt this will not be my last project. That said , I thought a digital crossover /Eq ( DCX, Dbx Rane ?) would provide a Nooby such as myself the ability to get this OB off the ground with out the analog crossover expertise of yourself and others. I"m having the screws and plate removed from my foot in the morning so I'll have some down time to decide on how to power this OB. I'll return to my thread and post better photos soon, I hope.
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Old 22nd May 2007, 06:58 AM   #810
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Quote:
Originally posted by GregOH1
Lynn, I may have made a mistake . I have the 12nda 520,s the Delta Pro 15A's and the Radian 745pb are being shipped from Cal. I was told ( USSpeaker) that I should go with the 16 ohm Radian because it would need less padding. I intended to use a digital crossover for at least the Delta to the wide/HF. I also have no problem with tri amping if that would be best , I have no doubt this will not be my last project. That said , I thought a digital crossover /Eq ( DCX, Dbx Rane ?) would provide a Nooby such as myself the ability to get this OB off the ground with out the analog crossover expertise of yourself and others. I"m having the screws and plate removed from my foot in the morning so I'll have some down time to decide on how to power this OB. I'll return to my thread and post better photos soon, I hope.
I think you're headed in the right direction. The biggest problem with the Behringer DCX is that the op-amps and electrolytic coupling caps are the cheapest possible, basically the same parts quality as used in a Chinese-made Wal-Mart boom box. But fortunately all the analog circuitry of the DCX is on a separate circuit board connected with ribbon wire, and there are aftermarket kits to replace the DCX analog electronics at a modest cost. I'd expect DBX and Rane to sound good right out of the box - both are quality pro brands.

You will still want to protect the Radian with a medium-value high-quality solid-foil polypropylene series capacitor - the slightest turn-on pop or DC offset will kill the compression driver dead, and the coupling cap will block the bad stuff from getting in.
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