Collaborative Open Source Coaxial Speaker(COSCS): 10” coaxial design [COSCS-10]
This project is the result of the free sharing of engineering talent and the open-source culture of AVSforum (http://www.avsforum.com/forum/155-diy-speakers-subs/) and diyAudio (http://www.diyaudio.com/forums/multi-way/). The general idea was (1) to create arelatively inexpensive surround speaker that could keep up with my high efficiency mains (4 Pi's) and (2) have a final design that could be sourced from multiple vendors for world-wide availability. If community participants use the design as a launching point for modification please distribute them back into the community.
Eminence Drivers: Solid performance characteristics, goodsupply chain, and reasonable cost --- Beta-10CX: Widely used for HT and home audio, even insome stupid expensive commercial products --- PSD2013-8: Fairly new compression driver, improved response curve and power handling
Enclosure Design: Target is solid response to 80 Hz, as one surround speaker will be stand-mounted approximately 50" from the floor away from any walls (nearly 4 Pi acoustic space, radiation into free space, that is in the open with no walls, floor or surfaces nearby) I wanted to go ported. As they are surround speakers I wanted the enclosures as small as possible.
Enclosure Calculator:
winISD: Models that when using a BW (2nd order) HPF @ 80 Hz the Beta10CX reaches cone excursion limits with 175 W, producing 12.58 m/s peak air velocity, and SPL over 115 dB from 90 Hz and up. Obviously this is best case scenario and does not predict actual performance with 1005 accuracy.
According to Matt, this design has (1) a more complex crossover that helps maintain a flatter response shape then the original Volt-10 that makes thetop end more refined; (2) a lower and steeper crossover that helps to bury the woofer'sbreakup a bit better and (3) the midrange pulled up slightly to give it a morebalanced sound.
XO Parts List:
XO Schematic:
XSim Freq Response:
Matt's Measurements:
(1) Measurements, On axis with drivers:
(2) 0-90 degrees off axis (10 degree increments):
(3) Average from 0-30 degrees:
(4) Response and phase at 20 degrees. (On axis REW has a phase tracking issue and adds 360 degrees of rotation at 6k, hence the 20 degree off axis measurement.):
Enclosures will be made from 3/4" birch plywood. The plywood was CNC'd by Gorilla83 (big thank you bro!). Once I am recovered from a recent medical event will get busy putting them together. Finish will be Duratex to match my L/C/R and sub builds.
How much audible difference (and what kinds) do you gents think there would be compared to the standard Volt-10? I haven't even moved mine into surround duty yet, I've been using them for mains since around April, but I'm just curious.
That is a good question. I have not heard the Volt-10's (or these either) but it appears this design will have a little more top end bite due to the Ti diaphragm. Matt, the designer of both, indicated this design has a bit more balanced sound than tbe Volt-10's. I have no idea if any of the differences are significant.
My main objective was for a design that would always be available for the DIY crowd. The parts are all off the shelf and available multiple vendors. I was planning on getting the Volt-10's, but they were not available when I was ready to buy so this project was born.
The only thing that concerns me is the 0.5" tall slot port. Due to skin effect, I don't think that is going to flow as much air as you think. With a 10" driver, 0.75" or 1" would be better. I know that changes things a little bit, but it would be worth it. I guess the saving grace is that it's only 4" deep. But you do have enough length in your cabinet to go 8" deep and 1" high. Could even put some "spacers" on the side.
IOW, your port is 12.5" x 0.5" x 4" long. The air velocity calculations are assuming a round port, which minimizes the skin effect, whereas a thin slot port maximizes it.
Changing it to an 8.33 x 0.75" x 4" long port would be better, or even 10" x 1" x 6.5"
@djkest, those are valid points. I modeled the slotted port with winISD (0.5" x 12.5" x 4.0") and it shows a maximum air velocity of 14.928 at 65.75 Hz. I did not factor in skin effect and it does make sense that a thin port would maximize its effect. As the boxes are already cut there is not really much I can do at this point, I guess at worst case the F3 of the speaker will be higher than the computer model suggests and Audyssey XT32 will set the XO higher than 80 Hz.
Yes it does, I would think it is less of an issue in surrounds than jn mains or subs. We will see, when built I will bust out the measurement microphone and REW (and pretend I know what the he// I am doing with them ).
I'd say Matt knows how the 3 compare, assuming he has first hand experience with all 3. That said, they all seem really close to the same thing and I wonder if it's worth the extra headache for DIYSG to carry/stock all 3. Even as mains, would the differences be realized?
Now the black vs blue cone...that's a different story. Gotta have priorities.
For surrounds I don't think either 3 will be different enough to matter. My understanding is that the Eminence CD with the titanium diaphragm gives the model in this thread a bit of bite while the phenolic diaphragm in the Volt-10XL is a bit smoother but that both sound very nice.
For the price it's not a bad bit of kit. It is not a shop grade tool by any measure but for light use it's quite good. If you get one PM me and I'll tell you about the mods I did to it to make it a bit tougher.
@NWCgrad & @mtg90, I am assuming we could use this design/crossover for a dual PR setup as we discussed in the coax thread here, correct? All things being considered, it should yeild very similar results to the V10's, correct?
Steve, would you happen to know the mounting depth of the Beta-10CX/PSD2013-8 combo? I have to do everything I can to make these as shallow as possible.
@NWCgrad & @mtg90, I am assuming we could use this design/crossover for a dual PR setup as we discussed in the coax thread here, correct? All things being considered, it should yeild very similar results to the V10's, correct?
Steve, would you happen to know the mounting depth of the Beta-10CX/PSD2013-8 combo? I have to do everything I can to make these as shallow as possible.
Wow, can't wait to hear your impressions once you get them in. Even a Ti phragm can be tamed. It was done well with the XO schematic I used with the selenium d220ti and I am sure Matt did a fantastic job as always with this bad boy. Makes me want to order a few Volt 10's right now!!!!! Kidding, kidding..... Thanks for the shout-out, I just started the 10-cx love affair, I like that other people are finishing it/ taking it further. Once the newer high-end 10" design is completed, I will likely get a pair of these CD's and XO's to see how they all do collectively.
I have the data in winISD and calculate if you have an idea of port opening size you would like, and whether you like round or rectangular (round can be easier).
My XO's and the PSD2013-8 that I sent to Matt arrived in the mail today. Matt packed them like they were vials full of Ebola, carefully and with lots of padding.
I am still out of commission so will be a few days before I can start building the enclosure.
Here is a schematic layout of the basement theater with speaker positions:
NOTE: The red dot is the position of my head in primary listening position.
My XO's and the PSD2013-8 that I sent to Matt arrived in the mail today. Matt packed them like they were vials full of Ebola, carefully and with lots of padding.
Steve, can you or Matt (@mtg90) tell me where you got the actual xover board? Or was that something costom made on the fly?
Also had another general xover question for the class.
I've seen schematics floating around identifying problem areas that may arise if placing certain xover components too close together. Would there be any detriment to the design if one had much more room to space out the individual xover components?
I would be very interested in a sealed variant for use as surrounds and ceiling use with my Elusive 1099's. I'd be happy with the Volts, but they may not be in stock when my HT build is done in a few months. A more readily available option like this is welcomed.
They should work fine as sealed, I will try to get up and running once I finish building the cabinets and measure as ported and sealed (if my POS laptop is up to the task).
The intent was to have a viable option for times when the Volt is unavailable. Erich can only maintain so much inventory as it's a huge financial liability that most would not be willing to take on.
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