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Old 13th May 2007, 07:57 PM   #21
azrix is offline azrix  United States
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Well, I would never tell anyone not to try something that's not dangerous. I find what you've written about the QSC prototype you heard very interesting.

I personally feel your issues are more with finding or building a good horn and then finding a woofer that sounds good to you. It sounds like you have the rest of it covered.

I would think you'd want something like Gedlee's Summas , but those are expensive and no longer being made. He crosses a 15" woofer over to a 1" compression driver at 1khz. I would think a 2" compression driver would work fine in a similar configuration for PA use.

The imaging issue is partly related to diffraction, which most pa speakers make no attempt to reduce. A baffle inset into the rest of the cabinet is a bad thing, though it may make the boxes stronger (I don't know, I assume that's why they do it).

You might also look at Stage Accompany. They have a ribbon tweeter that is designed for PA use. The little I've heard about them is good.
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Old 13th May 2007, 09:30 PM   #22
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I think it wasn´t mentioned before:

www.pa-forum.de

is a german pro-sound forum. Most people are able to understand and write in english there, so you might give it a try.
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Old 13th May 2007, 09:58 PM   #23
gtphill is offline gtphill  United States
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Quote:
Originally posted by Zero Cool

WOW, you have made a lot of assumptions here.

While i dont have funds to just run out and buy a set of boxes at 1k each+ today. I do have the funds to build these in stages. coulple hundred here, couple hundred there. and i am willing to spend whatever to build these. the budget has never been the issue.
Budget and time are issues, however, if you are looking for someone else to help design crossovers, etc. All that work has to be performed in the as-built cabinets with the drivers installed. Ultimately you, or someone volunteering to help, has to perform some hard core acoustics measurements on the completed project.

I am sure that there are others here who have the time flexibility to work in stages on a project, unfortunately I am not one of them-right now. Possibly in a year.

Quote:
Secondly. I have access to a full blown woodshop and i have built many many many boxes, cabinets, road cases, subs, etc and have studied the construction of many PA cabs. Some 20 plus years ago i built a very large set of PA cabs (copies from a then local sound co's cabs) that are still in use today(by someone else).
I did make an assumption here, and I apologize. You made no mention of your building experience, so I assumed incorrectly. I am sorry!

Quote:
I am interested in doing this for the excersize of if. the learning process.

Thank you to everyone that put forth positive information here. But i see this isnt going to go anwhere here. there is just too much no you cant do this, and not enough, yeah lets try this and give it a shot. that is very frustrating. not at all what i would have expected from DIY'ers.
To really learn the process, start by spending $300 for SoundEasy. Then buy, and digest, John Kreskovsky's speaker design tutorial. Then get a suitable soundcard and omni measurement microphone, and build the T/S parameter measurement jigs for the program. Learn how to do free field and groundplane measurements, build impedance conjugate filters, etch crossover boards, etc.

At the end of that time you will have the tools you need to build any speaker you want, professional or otherwise. You already have the wordworking chops! That latter part puts you well ahead of me...

Since I never gave some driver thoughts, I suggest these to start your journey.

Mid:
http://www.eighteensound.com/index.a...roduct&pid=241

CD and Horn:
http://www.eighteensound.com/index.a...roduct&pid=189
http://www.eighteensound.com/index.a...roduct&pid=178

Low:
http://www.eighteensound.com/index.a...roduct&pid=259

A passive crossover for these three sets of drivers would be quite involved, but a three way triamped system with a DSP would be fairly straightforward to set up.

Let me apologize again for making an assumption earlier. I am really not trying to be negative. I probably should have left the thread alone, given that my chances for involvement turned out to be small. I apologize for that. There are probably plenty of folks out here in the DIY world who would be willing/capable of tackling a crossover for a design that you built.

My apologies!
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Old 14th May 2007, 07:19 PM   #24
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I think the biggest single issue you will run into building a passive two way PA cabinet is the impedance behavior of the compression driver. As Phil mentioned, the mechanical resonance of the driver is going to cause some very large peaks in the impedance curve. These will be damped to some degree by the horn loading. If you build a passive crossover, you will need to build parallel notch filters to flatten the impedance curve of the driver.

If you use a passive xover without flattening the impedance curve of the driver, the ringing in the time domain is going to be awful. In my experience this is the single biggest mistake that PA manufacturers make in passive cabinets.

I strongly encourage you to make the system active. You will then get the best possible transient response out of the compression driver. It won't be good, just less bad. Even if you build a three way system, with one passive and one passive section, I would use the active xover in the mid/high range. Remember hearing is much more sensitive to problems from 1-4kHz, than 100-400Hz.

The baby brother version of the Community M4 midrange driver is the M200. It is excellent. Definitely the best 2" midrange compression driver anywhere near its price. There are two downsides. You must use it with a high frequency driver and you need a large horn to use all of its capabilities.

For a 1" compression driver, the BMS ring radiators, have by far the flattest response, good distortion and can be used low enough in frequency to make a two way system. They are one of only a few compression drivers I have ever found that have enough bandwidth to make a real two way system with them.

If you use compression drivers and horns, resist the urge to run the xover lower than the cutoff frequency of the horn (determined by the dispersion pattern). If you do this, you will never be able to make the system sound good in a reverberant environment.

In my experience there is very little correlation between the cost of a compression driver and its performance. Like most things in the world, good design doesn't equal expensive materials. Good design equals good engineering which adds almost zero cost to the piece part price.
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Old 14th May 2007, 10:34 PM   #25
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Quote:
Originally posted by Jack Hidley
parallel notch filters to flatten the impedance curve of the driver.
Do you mean a series notch?
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Old 14th May 2007, 11:19 PM   #26
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By what you describe to us when you heard the QSC speakers.
This is a PRO HI FI set up.

I would recommend building 2 Altec A-5.

Components Altec (GPA) 515 8GHP Bass Horn speaker 200watts
Altec Mantaray M-94 horn
GPA 390 HF Driver 50 watts 500 to 15khz
828 Altec Cabinet custom Made.

Cross over either Altec A-5 passive or Active Behringer.


.................................................. ................................
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Old 14th May 2007, 11:32 PM   #27
Salas is offline Salas  Greece
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A good approach would be using passive RLC for the driver + horn impedance and then cut and drive actively. Like the good old Nexo PS 15 does...
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Old 15th May 2007, 03:48 AM   #28
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Cal,

I mean that the filter is in parallel with the load. The RLC filter has an impedance shape that has a minimum where the load has a maximum. The net result is a flat impedance curve for the system.
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Old 15th May 2007, 04:16 PM   #29
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Thanks Jack,

My thoughts were to get the horn up higher then normal. most 2-way boxes run the horn down to about 1.5K or so. my thought was to get it up to 3K or more as a true tweeter. and let a mid do the 300-3K range as a true mid.

I have been looking at the Community M200. I did the large community speaker installation in the Cotton bowl that is featured on the Community system components brochure! In fact i was standing just out of view when that pic was taken. We use plenty of M-200's there and they do sound good. even from the other side of the field! I have been talking to Dave Howe at community about that driver.

I have also been looking at the 18sound 6ND430 midrange driver. this looks like an interesting mid driver that has gotten some good reviews.
this has a high power handling, high acoustic output. and the 45 degree off axis response is actually flatter then the on axis response. plus this comes in 16, 8 and 4 ohm versions.

So my thoughts were to base a design around this driver, or something similar. maybe use 2 or more of them together. maybe in a MTM arraignment with a horn/driver chosen to compliment.

What would the disadvantages of a Single box with sub per side WMTMW arraignment be for live sound use?

Here is a quick concept idea i was thinking of. I thought about using 4 of the 18sound mid drivers at 45 degree angles with a center mounted horn. fiberglass would be used around the back of the horn to dampen the sound aimed at and reflected back from the mids. The idea being to use the 45 degree off axis response. front firing 12" woofers would be used to get the response down to at least 50hz before hitting -3db.

I can see many drawback to such a design. but it is an interesting concept. the drawing is not to any such scale other then the drivers/horn is to scale to one another.

The cavity that mids form hopefully will be large enough so that its resonance is well below the mids operating range. it could also be designed so that the sides in that are are open and that the horn is supported in the center or maybe with thin rails from the woofer areas or something.

It is really sounding like i am going to have to go active and i do understand the benefits which are many. but the down side is the extra expense, weight, and complexity which in my case out weight the benefits...maybe.

It might be interesting to first design the system with an active DSP system. then work on a passive X-over design. So for now. lets imagine we have a DSP box like a DBX drive rack or a BSS Soundweb etc that will offer us multiple channels of DSP power.


I am curious what everyones thoughts would be about such a design. remember this is just a design concept for discussion.

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Old 15th May 2007, 06:28 PM   #30
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Quote:
Originally posted by CONVERGENCE
I would recommend building 2 Altec A-5.
828 Altec Cabinet custom Made.
I think the 828 cabinet is the A7. The 825 was the A5.

Quote:
Originally posted by Jack Hidley
I mean that the filter is in parallel with the load.
Confusing isn't it? A series filter does in fact run in parallel with the driver and the parallel runs in series. It's the configuration of the components in the filter that lends it's name, not how they relate to the load.
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