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Old 9th September 2002, 03:57 AM   #1
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Default The Square Wave Project

So here it is.

This thread will deal with the design of a full range speaker system that will, as nearly as possible, reproduce a square wave.

<font color="#ff0000">First, I would like to say that this thread will be totally intolerant of off -the-subject issues. I will report to a moderator anyone who goes of into never, never land. I started this thread and I'll be damned if I'll let anyone screw it up.</font>

The criteria, as I see it, are as follows:

1. Must be done with off the shelf dynamic drivers. NO horns may be involved.
2. Must be done with analog only techniques. NO digital filters.
3. Must be practical for DIY.
4. May be bi or tri-amped.
5. Should reproduce a 30Hz square wave.
6. Assumed is a 20Khz 2nd or 4th order roll-off.
7. First arrival times are the issue. No consideration should be given to room interactions. That is to say, we are looking at an anechoic response of a single system.
8. Recognized attributes of a speaker system must be maintained. That is to say, low distortion, decent power handling, etc.

I make the following suggestions as per my own ideas and some previous input from the other square wave thread. Remember, this is only a starting point.

1. The system is a 3 way.
2. The mid range speakers should be 6 or 8 Tangband W4-654S in a vertical curved array with the focal point at the listening distance.<a href="http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=8184019&St=9404&St2=-44059799&St3=61944947&DS_ID=3&Product_ID=117926&DI D=7"> Link to speaker specs. </a> I challenge anyone to find a mid-range driver more suitable than this. I believe that 2 midrange drivers used in a MTM configuration might be preferable but I don't think that drivers with sufficient power handling AND the requisite high frequency response are available. <u>Suggestions welcome.</u>
3. The woofer should be sealed with a Qts of .7 and have an F3 of about 30Hz.
4. The selected tweeter should have the lowest resonant frequency possible and be a ferrofluid 1" dome. <u>Suggestions needed.</u>
5. This first part of the challenge should be the mid/tweet crossover and the success can be shown with a 500Hz square wave. I favor the subtractive or difference type crossover.
6. It is preferable that the system is physically time aligned to allow the potential use of passive crossovers rather than use active all pass networks.

Time for some input. And, again, if you can't stay on topic, please don't post.
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Old 9th September 2002, 05:03 AM   #2
navin is offline navin  India
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tweeter the lowest Fs I kow is of the SS 9900 at 500Hz. but you want a tweeter with ferrofluid why?
otherwise I can recomend the Morel MDT33. it can handle power (and since 1990 the coils are replaceable from the face plate).
woofer
10" SS 8565 in 2 cu. ft.
Focal 10" (there are many).

regards
navin
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Old 9th September 2002, 05:33 AM   #3
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Hi Bill,

Very nice. Here are some initial thoughts/suggestions/questions.

The Tangbangs look great. 8 drivers will allow series/parallel hookup for an 8Ohm nominal load. More drivers will also help to minimize IM with the wide bandwidth.

Maybe a Quasi-MTM configuration with 4 TB's up and 4 TB's down.

Crossover to the tweeter above 5kHz to maximize the mid-range bandwidth, isolate the fundamentals in the mid-range, and minimize time delays of the crossover (90 degrees at 6kHz is a smaller time delay then 90 degrees at 3kHz).

Maybe a ribbon tweeter for its resistive loading (just a thought)

Why the low resonance in the tweeter?

Still Think'in.
Rodd Yamas***a
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Old 9th September 2002, 06:23 AM   #4
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Default Re: The Square Wave Project

Quote:
Originally posted by Bill Fitzpatrick
5. Should reproduce a 30Hz square wave.
Perhaps as per the previous thread this should say a 30Hz square wave passed thru a 30-20kHz bandpass filter.

Quote:
2. The mid range speakers should be 6 or 8 Tangband W4-654S in a vertical curved array
This is pretty head-in-a-vise restrictive (and realistically totally impractical). A single mid/full-range in the middle would make it a lot more sense and make the goal of a square wave easier. Something like a Jordan JX92 would be a good choice.

Quote:
3. The woofer should be sealed with a Qts of .7 and have an F3 of about 30Hz.
Butterworth is maximally flat amplitude, wouldn't it be better to have a maximally flat time alignment? Bessel (Q=0.578) gives the flattest phase.

Quote:
4. The selected tweeter should have the lowest resonant frequency possible and be a ferrofluid 1" dome.
practical, but restrictive. They aren't often considered, but there are some pretty good cone tweeters (Jordan JX53). Ferrofluid means flatter impedance response at the resonance making a simplier XO possible.

Quote:
5. This first part of the challenge should be the mid/tweet crossover and the success can be shown with a 500Hz square wave. I favor the subtractive or difference type crossover.
That only works if it is active. Requires that the acoustic centres line up -- ideally vertically & horizontally

dave
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Old 9th September 2002, 06:31 AM   #5
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Quote:
Originally posted by navin
tweeter the lowest Fs I kow is of the SS 9900 at 500Hz. but you want a tweeter with ferrofluid why?
The lowest Fs in a T that i know about is the PEARL PR-2 tweeter with an Fs of 150 Hz -- unobtainum thou.

The low resonance and ferrofluid are both preferrable due to the (likely) 1st order XOs required to maintain time coherency (the active subtractive XO would give a 2nd order on one half -- 3rd order is also doable but the bump on the bottom of the derived half starts getting kinda big). phase_accurate's stacked concept or the subtractive XO with time delay would be required for steeper XO, but that eliminates any passive XO.

dave
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Old 9th September 2002, 06:36 AM   #6
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Another criteria for the tweeter is that it should have a very small mounting profile, so that interdriver distance can be minimized and if a step gets involved for physical alignment we have maximum versatility (ie a pod like on the B&W nautilus).

Another thing that should be thrown into the pot, is that if the T is behind the mid acoustically (ie a co-axially mounted tweeter), this can, in some cases, be time compensated by a high order bessel -- passive or active.

dave
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Old 9th September 2002, 07:52 AM   #7
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it all depends on what SPL the 30Hz square wave will be at.

one way to get a tweeter with a small front is to take an existinng tweeter with NDfeB magent and remove the face plate or take a car tweeter (Vifa D26NC can be used).

I have see a ss 9900 modfied with to fit too but that is a lot of work.

WMTMW with a D26NC and 2 Tangaband Mids and 2 6/8/10" woofers should do.
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Old 9th September 2002, 11:35 AM   #8
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Hi Bill

Maybe you should also specify how much "tilt" you would allow on the top and bottom of the 30 Hz square-wave sice this is definitely depandant on the lower cutoff frequency and vice-versa.
Even for a very relaxed spec a lower cutoff frequency of less than 20 Hz would be necessary.
I would by no means want to say that such a low cutoff frequency would be a bad thing to have, far from that !!!
But it wouldn't be easy to achieve !

Another thing that has to be specified is how much tolerance regarding the amplitude response you would allow.

I will post some more info that could be useful for the "wideband-midrange people" within the active subtractive thread.

Regards

Charles
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Old 27th September 2002, 10:19 PM   #9
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I was wondering how you were going to actually verify that you got a square wave output? You cant use a scope or a mic can you?
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Old 28th September 2002, 12:46 AM   #10
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If someone has a better idea than a scope and a mic, I'm ready to listen.

As I see it this will be a out of doors test either, maybe both, buried face up in the ground and/or a high platform. And, obviously, the mic must be at the focal point not some arbitrary 1 meter. Where did that come from anyway?

-3db at 20Hz should be no problem. I'm thinking +/-3db on the amplitude response.

"Head in the vise restrictive". A good point to bring up with a vertical array. Horizontally there is no problem of course. Vertically, well . . . we all do our critical listening sitting down and the focal point can be selected by the individual builder to suit his listening height and distance. With the proper choice or mid/tweet crossover frequency I don't see any more of a problem than with a MTM. And, in terms of room power response it will be fine also. So if you're standing in the kitchen fixin' one of those delicious burnt weenie sandwiches, you may not be able to experience square wave nirvana but everything will still be excellent.
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