# 2 way LCR... waveguide design.



## hydrovac (Nov 9, 2009)

I've been on the search for some time now, for a set of behind the screen LCR main speakers for my home theater. I'm trying to build DIY speakers based on designs suggested by members here.

Since this is a HT application, I want to get good off-axis response… BTW, in the name of sound quality and taking advantage of not needing sub-80Hz response… I want to go sealed.
I'm pretty confident I can dial in a nice active Xover. The concept is a 2-way speaker with a 12” mid bass and a 1" tweeter with a waveguide.

I'm soliciting your help by asking you guys what you think are the best design options with these drivers? I will start by building just one to see if it really works...
http://www.ahujaradios.com/speakers/professional-pa-speakers/l12-mb200.html
http://www.ahujaradios.co.in/speakers/pa-compression-horn-drivers/cdh-800.html
http://www.ahujaradios.co.in/speakers/pa-compression-horn-drivers/cdh-200.html
So just throw something out there to get the ball rolling.


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## ajinfla (May 10, 2009)

Hi Krishna,

I could not find any measurement data in your links. Am I missing them?

cheers


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## hydrovac (Nov 9, 2009)

Thanks for the reply AJ...

There is no measurement data. The manufacturer has provided T/S parameters only.
Is it possible to model a design?


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## ajinfla (May 10, 2009)

If the T/S parameters are accurate, at best you could model the free space bass alignment for different size boxes with something like WinISD, etc.

cheers,


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## GPM (Jan 14, 2007)

hydrovac said:


> So just throw something out there to get the ball rolling.


Hmm, you say 2-way, but list a mid-horn also. Regardless, the woofer’s 90 deg -6 point is around 1 WL of its effective piston dia. = ~1.356 kHz whereas the mid horn is presumably this somewhere around 2.5 kHz and the tweeter around 4 kHz, so there’s no normally acceptable match-up at all among this group.

GM


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## hydrovac (Nov 9, 2009)

GPM said:


> Hmm, you say 2-way, but list a mid-horn also. Regardless, the woofer’s 90 deg -6 point is around 1 WL of its effective piston dia. = ~1.356 kHz whereas the mid horn is presumably this somewhere around 2.5 kHz and the tweeter around 4 kHz, so there’s no normally acceptable match-up at all among this group.
> 
> GM


GM,

By two way, i meant woofer and any one of the waveguides!

Upon request for assistance regarding enclosure design, this is the proposal i got from the manufacturer. Can I attempt to build the enclosures? Your opinions please...

_"Dear sir

The cabinet design i have sent to you is what we recommend for FOH indoor "live" with 15 OR 18 inc sub augmentation...
The cabinet dim are ID,
PORT Length is 2 inches,
(-3db)FR 55 -18000 HZ when bi-amped, spl 1khz/1m/1w is 100db,
Recommended CX point is 2khz ,
recommended i/p power for low freq drive is 200 to 300watts RMS,

If your amp output is 130watts [email protected] 4 or 6 ohms or less , i will not recommend above set up .
Hope above is useful to you.

Best Regards"_


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## GPM (Jan 14, 2007)

Greets!

OK, just checking. With these components, they are designed to be used as a 3-way system.

Ok, you want sealed since you have a sub system, but they say use a vented alignment anyway with 200-300 W even though it only has 2.5 mm Xmax and a 200 W rating...........

A 12” driver’s polar response has collapsed to around 70 deg/2 kHz, so is a very poor match to either horn once you move much off axis. I really wonder about these folk’s business practices.

Anyway, inputted the specs in WinISD Pro V 0.7.0.900 and when I use BL, Mms, Vas it calculates a much lower 36.52 Hz Fs and when I calculate Vas, Qts using the published 45 Hz, it calculates a much lower 88.93 L Vas, 0.508 Qts, which for a T/S max flat alignment:

36.52 Hz = 5.549 ft^3/34.48 Hz vented
36.52 Hz = 2.693 ft^3/63.48 Hz sealed

45 Hz = 7.474 ft^3/35.37 Hz vented
45 Hz = 3.464 ft^3/64.20 Hz sealed

With the manuf. cab data, a ~1.8 ft^3 net is required for a ~55 Hz tuning using dual 2.6” dia. x 2” long vents is a typical prosound alignment with a ~4 dB mid-bass peak, which with 200 W = a too high ~9% vent mach, though it can’t handle this much power without exceeding its 2.5 mm Xmax. 
Since you’re using a sub system, a LR 100 Hz 4th order high pass solves the high vent mach and mostly flattens out its mid-bass hump.

The sealed alignments are maximally flat and with an 80 Hz/4th order LR high pass yields the same driver protection roll off slope as the vented’s 100 Hz, so with superior overall performance I recommend the 3.464 ft^3/64.20 Hz sealed alignment and hope the specs are no further off than they already are.

GM


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