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Old 21st October 2012, 06:14 PM   #1
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Default Help with big monitor design

I have been asked to help build a pair of monitors that will be mostly for amplified acoustic guitars in rooms approximately 40' x 80-100' deep. The owner wants to use two TAD 1603 drivers, two Audax PR170MO mids, and a Morel horn tweeter (model number escapes me now, I remember its rated 220watts) for each side. He wants the 1603's in separate sealed compartments, one going down to 80Hz and the other starting out around 200 Hz and both sloping off first order at 600Hz, and the Audax mids to cross at 3K Hz. I am having some difficulty determining the best size for sealed enclosures for the 1603's and how to model the two combining in the 250-600Hz range, and the same issue with the two Audax mids combining. I want to put the two TADs in one cabinet with two compartments, and the mids and tweeter in a separate box that will sit on top. Thats about as far as I have gotton with this design...I thought I would ask for some ideas here before I went too far as this is a bit out of my depth.
Thanks for any suggestions, observations.
Canefire
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Old 21st October 2012, 06:34 PM   #2
tinitus is offline tinitus  Europe
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wow, that must be real big acoustic guitars
sorry, couldn't resist it

you say rooms, so I guess its supposed to be portable PA ?
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Old 21st October 2012, 10:10 PM   #3
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Yes they will be moved often. In the past we have rented the large three way ATC speakers and used Hafler amps.... 600 watt I think. My memory isnt what it used to be...
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Old 21st October 2012, 10:16 PM   #4
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re:'He wants the 1603's in separate sealed compartments, one going down to 80Hz and the other starting out around 200 Hz and both sloping off first order at 600Hz" - ???? why?
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Old 21st October 2012, 10:26 PM   #5
Pano is offline Pano  United States
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In a ~30L box (1 cubic foot) the TAD 1603 should have an F3 of about 72 Hz, or so says Unibox. It will be a little peaky around 125Hz, but that might sound nice.

Don't know why you'd want to low pass them 1st order, 2nd ought to be better and keep you out of dirt up top. Unless you want that for effect.
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Old 21st October 2012, 10:58 PM   #6
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Yeah... my bassbox calcs are looking far better with a third order on the 1603. I cant understand why he asked for the 80 and 200 crossover points on the woofers either...I don't think thats the way to go and he may have been guessing. I pretty much need to come up with something that will work using his existing drivers though. How would you guys use two 1603's, two PR170M0 and a Morel CAT 378 in a system?
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Old 21st October 2012, 11:11 PM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Canefire View Post
How would you guys use two 1603's, two PR170M0 and a Morel CAT 378 in a system?
I wouldn't choose any of those drivers at all
but if it has to be, I might use one of those woofer designs where the woofers are placed opposite each other in a V
and I would definately build a plywood horn for mids and tweeter
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Old 21st October 2012, 11:21 PM   #8
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I'd be more concerned about two things:

- polar response, most importantly how it "illuminates" the audience
- the ability of the "tweeter" to handle the energy that is required, the signal being unlimited and uncompressed.

The system needs to be fairly low distortion at the SPL that it will play at.

Fwiw, Pano, a 1 cuft box for a 1603 is rather small...

Personally I'd opt for putting both of the 1603 in parallel and getting the extra power and SPL that a pair will afford. Also the polar response is slightly better in the horizontal plane for two stacked, but maybe not enough to notice. It doesn't matter if they are in separate boxes or not.

The other option is that there are some interesting horn loaded arrangements that if not too big or heavy will afford substantially more output.

A digital (class D, etc...) amp might be a best bet for the low end of the system. Scads of power, and no weight.

I am very skeptical of the Morel product really handling 200 watts, perhaps... best be certain of what it can do before committing, imo.

I'd go for an array of the right sort of horns for the top end,
or even an old Altec type multicell, guaranteeing good horizontal dispersion... something like a 1003 will cover down to 300Hz, and if you run it from say 600 or higher, then you will find it has close to ideal frequency response (being rolled in above the cutoff of the horn sections, and even though the individual horns will beam a bit at higher frequencies, that will be one heck of a lot better than any single tweeter (even with a horn loading, since that only extends the LF end of the response and leaves the higher freqs mostly untouched). All you would need is to use a pretty good compression driver. You'd get ~109db/1w SPL from the horn + compression driver vs. far less from the morel.

If you do the math, the compression driver, even rated at 40 watts will undoubtedly run rings around the morel. At the very least it will produce far more dB SPL than the Morel, and I'll bet it starts out at probably more than 10dB louder, perhaps even more (haven't read the spec).

The pair of 1603 run in parallel and with the mutual coupling plus the extra power from halving the impedance may will provide 6dB higher SPL for the same input level, now you have 106dB/1w/1m not 100dB/1w/1m from the same pair of drivers. That's the equivalent of going from a 100 watt amp to a 400 watt amp, assuming the speakers could handle the extra power (heat) and not be up against the excursion limited output.

In the case of the compression driver + horn, the difference between the 100dB (assumed) Morel driver and them is equal to going from a 100watt amp to a 800 watt amp, which the Morel surely will not handle, fwiw.

Some things to consider...

_-_-bear

PS. the system as described is more akin to a studio monitor for a small to medium sized control room than a PA/SR design, imo
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Last edited by bear; 21st October 2012 at 11:23 PM.
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Old 21st October 2012, 11:30 PM   #9
tinitus is offline tinitus  Europe
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got it

all woofers in each their Altec A7 style designs with front horn/waveguide
just much less high, and stackable
now that would look cool
all stacked
and on each side a line array of.... some smaller widerange drivers
a wall of sound, and one BIG guitar
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Old 21st October 2012, 11:31 PM   #10
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Quote:
Originally Posted by tinitus View Post
I wouldn't choose any of those drivers at all
but if it has to be, I might use one of those woofer designs where the woofers are placed opposite each other in a V
and I would definately build a plywood horn for mids and tweeter
These designs which have become very common are usually set up to mate with some sort of tweeter arrangement, where the tweeter is somewhat horn loaded and the dispersion is controlled by the box shape, and the "V" in terms of the horizontal dispersion at the bottom of the tweeter's range. Then the woofers are some what horn loaded and "time aligned" by being ahead of the tweeter physically. This solving a problem or two.
But typically these boxes are lower mid and up boxes, not intended to go particularly low. They seem to run a pile of LF subs below the stage level, and fly these V speakers in a vertical array...

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