A few years ago I built the three front channels of the Audax HT designs by Joe D'Appolito. They are very impressive. I did not build the rear channels as I already have decent dipole/bipole polk fx300i's.

Recently I have acquired a nice 7.1 channel receiver, and would like to add a rear surround speaker. I have extra audax drivers laying around that I could build one of their rear surrounds, which utilizes one midwoofer and a tweeter, but I would really like to build a dipole surround with one woofer and two tweeters, kind of like the athena AS-R1.2. (http://www.athenaspeakers.com/model-AS-R1-2.htm)

So, is it possible to modify the xover for the original design of one of these surrounds to include the extra tweeter? I know nothing of electronics, except for how to read a schematic to build speaker xovers. And second question, will someone do this for me? :) :) :)

Thanks in advance.

Sorry, I was at work and didn't even think to attach a schematic of the original xover when I posted earlier. So here it is.

Thanks,

Duane

Two ways to do this. The simple 'no-brainer' method or the normal method.

Simple;
The bottom crossover shown in the picture is for the tweeter. C2, L2, and the
two resistors. Just duplicate that circuit for the second tweeter and connect the
input, plus and minus to the same speaker terminals as the other drivers.

Normal;
Try to reverse engineer the circuit and recalculate the component values for
two parallel tweeters, ie 1/2 the impedance. Use a crossover calculator found
in cyber.

/guessing

Is that a 4 ohm tweeter? if so, those component values imply 2nd order
butterworth, ~ 3.5khz crossover plus the two resistors are attenuators.
If it is a 4 ohm tweeter, then proceed. Use C2 = 16uF capacitor, L2 = 0.13 mH
inductor. You can leave the resistor network the same because the tweeters are
dipole surround, essentiall aimed almost opposite each other. If it isn't a 4 ohm
tweeter, then use the simple method to be safe or report back. lol

Here's the link to that project:
http://www.madisound.com/Audax%20Kits/doit/us_ht04.shtml
http://www.madisound.com/Audax%20Kits/doit/us_ht08.shtml

And the tweeter: http://www.audax.fr/

8 ohm; Fs 1090 Hz; sens 92 db 2.83V/1m

Here's the link to that project:
http://www.madisound.com/Audax%20Kits/doit/us_ht04.shtml
http://www.madisound.com/Audax%20Kits/doit/us_ht08.shtml

And the tweeter: http://www.audax.fr/

8 ohm; Fs 1090 Hz; sens 92 db 2.83V/1m

If 8 ohm driver, then I don't know what type of filter that is. Without knowing
it will be hard to recalculate new crossover part values unless you were to
simulate this in software {I don't have}. The 8 ohm variable doesn't
seem to compute using the common filters used in crossover design. You can
use the simple method to make the project work. I'm just using internet crossover
calculators to see if it's a generic design. Maybe someone else can verify the math.

This was taken from the audax plans; it describes the xover for the surrounds.

The woofer crossover network is 2nd-order electrical, but it combines
with the natural roll off of the woofer to produce and overall 4th-order
acoustic response. The tweeter also achieves a 4th-order characteristic
with a 2nd-order electrical filter. Crossover component values are given in Table 3. All coils are air-core.

I don't know if this helps or not... this stuff is all greek to me.

If I hook up the second tweeter using the "simple" method, would that reduce the overall resistance rating of the speaker? I think the speaker is rated at 8 ohms. I would not want to drop below 4 ohms nominal... or so I think. I really don't know that much about all this. thanks for the help!

Duane

Doing the simple method isn't a big deal. You only need one capacitor and coil plus
two resistors per extra tweeter, this is low cost unlike if the crossover was a higher order
network with tons of components. The extra tweeter won't taxi your power plant, the power
consumption by tweeters is very small. Build it, should be cool.

Thank you so very much! Maybe I'll add 2 more tweeters if it's that easy. That's good to know that it won't be too taxing on the amp. Indeed I will build this... and I'll have a blast doing it. I have two kids now, so it will probably take a while to complete this, but I will be sure to post back as progress moves forward.

Thanks again!

Duane

If you're going to take awhile with it anyway, download free Speaker Workshop and you'll be able to work up a good crossover. That's what I use for crossover design.

http://www.pvconsultants.com/audio/frdgroup.htm
http://home.twcny.rr.com/cnydga/FRDtools.html

stevdart,

Those software programs look fun, and I would love to be able to learn them, but I don't see myself having the time in the forseable future to learn how to use them properly. Between new software at work and a 3 year old daughter and an 8 week old daughter and an old house that needs finished remodeled and a rear speaker that needs built and a garage that needs cleaned out.... well, you get the point. My busy schedule is one of the reasons I depend on this forum for quick info on my AV hobbies. Granted, I take more than I give, but that's just how it is.

By the way, here's a quick scale model I drew up of what the new speaker will look like. It's 7.5"x7.5"x21" with 25 degree panels for the tweeters. I realize at first glance that the angles look like they should probably be a little steeper, but the way I have it gets the volume just right while maintaining identical size faces to mount the drivers... all the while getting high marks in spousal approval. I think the shallower angle is better anyways, since the speaker will be located about 9' behind the listening area in a 30' long room. I can mess around too with wiring this thing up as a dipole or a bipole... might make some difference.

I can't believe how psyched I get about this kind of stuff. I just absolutely love it. If I could make a living at it I would.

thanks again guys!

Duane