Waveguide ZA-SR71 ??

[peace brainerd]

Zaph's waveguide TMM uses the SEAS 27TDFC. His SR-71 uses the same tweeter. So mounting it in a waveguide has been done, and is well documented.

I've been waiting (not ready yet to do my own design) for a well documented, affordable, waveguide two way (the TMM is just too large for me) to pop up somewhere ever since Zaphaudio posted the TMM.

All of a sudden Jon Marsh over at htguide has begun a waveguide two way build using the same woofer as the SR-71 but with a much more expensive tweeter and crossover. Probably looking at close to 500 dollars. The 309 dollar SR-71 parts kit at Madisound is right at the upper end of my budget.

What is the likelihood of coming up with a workable crossover modeled from information available on Zaph's site for mounting the SR-71 tweeter in the MCM waveguide? Any likelihood at all of being able to use the major components in the kit and modifying them? Or would this certainly require a whole new set of crossover parts?

Zaph|Audio - ZA-SR71
Zaph|Audio

So close, and just out of reach.

[DcibeL]

I think you will enjoy this. Small waveguide Seas DXT tweeter, but the final design achieves the same goal, very very smooth power response.

[peace brainerd]

Your're right, I do love that. Except for the following...

Quote:
Originally Posted by DIFORCE
On the side note ,Mark you kinda miscalculated the total cost on your site ,the woofers and tweeters are 259.40 $ while at the total cost they are 159.40 $ so total cost without cabs is less then 500$ not 400$

"Ooops! I did chisel off $100. Oh well, it's worth it"



It's a fantastic design and, as was noted in that thread elsewhere, may even be a clear step up from the SR-71. But with such a nice design to be available already, with a crossover from a very reputable builder and using the same woofer with a very very competent tweeter for 309 dollars, Madisound's kit is really a very good deal. That's why I'm so interested in the possiblity of ordering the kit and getting some help in modifying the crossover.

[Jay_WJ]

This will be really easy (and accurate) modeling because we already have an in-box measurement of the waveguided 27TDFC on Zaph's WGTMM page. In fact, I already did a similar thing. Take a look:

Matching surrounds for Zaph Waveguide TMM - Techtalk at Parts-Express.com

I also have ER18RNX data so it will be real easy for me to medel up a crossover for you. Let me know if you're interested.

jAy

[Jay_WJ]

One more thing to consider. Note that by using a waveguide on the tweeter, the crossover design should be changed from LR 4th order to LR 2nd order. LR 4th order may also be possible, but why not take advantage of a smoother power response of a LR 2nd order design, which is achieved thanks to the waveguide? This means you have to cannibalize the kit crossovers and the only things you can save are the inductors by unwinding them and small 3.3 uF caps. Perhaps, still a bit less costly than Mark K's design, but I'd give a careful thought before making a decision.

jAy

[Jay_WJ]

Okay, it turns out that additional parts cost only $20 if you can unwind the 3.3 mH steel laminate core to get 2.7 mH. Or, if you don't want to bother to do the unwinding yourself, simply add $28.40 for a pair of 2.7 mH steel laminate cores at Madisound. Below is the modeling result. In case you wonder about the accuracy of my usual modeling work, you may want to ask a question about me at Parts Express Tech Talk forum.

Jay

[peace brainerd]

Jay_WJ,

Thank you very much for that. Is that schematic you posted for the second order crossover using the ER18RNX? So the addit parts cost for the second order crossover should be only about 20 dollars? There is a discount included in the assembled parts in that kit for 309 so I'm still probably better off modifying that crossover than backing up and reordering the whole thing piecemeal.

Approx 20 added to the kit order and approx 25 (that's with s&h) for the waveguides from MCM puts me in the range of 260 to 270 dollars. That's still pretty nice since I'm concerned that Jon's version is going to exceed 500 dollars for parts costs.

I don't own an LCR meter. Is it possible to calculate the number of turns that would be necessary to get 2.7mH?

Thank you so much for your interest in this.

[peace brainerd]

Oops, I did the same thing there. I shaved off 100 dollars.
360 to 370 dollars.

So we're talking a savings of anywhere from 130 to 150 dollars on this compared to Jon Marsh's or Mark K's. Marsh's will probably exceed that by a bit. But I'm also facing possibilty of a generating a few unknowns perhaps in the design?

[DIFORCE]

Please note that jhon from zaph have also heard about marks design. He stated that as far his concerned , marks design is a step up. He couldn't bieleve you could cross the tweeter that low and achive those exellent results. All that from the measurments posted by mark without hearing it ! Well ... Zaph knows that proper measurments can tell the entire story , and the people that did hear marks design at some diy meeting choose it as "best in show". Zaph's approval , and that unofficial title made me decide to choose marks design over the sr-71.

[peace brainerd]

447.92 is the total according to mark k's website. Shipping will bring that to 460 or so.

Damn. Every time I start to get excited about a project, including non audio stuff, I always suffer price creep. You keep convincing yourself that just one more step up from your cost/performance ideal is not going to matter. A few steps later you end up suprised at where you finally land.

No doubt about it this design is worth every cent and then some. In fact, as is often pointed out, a speaker pair of this caliber would cost up to ten times this from a boutique source. And given that boutique speakers are usually 'voiced' to give immediate gratification in the showroom (over salted, sugared, and spiced), a design this good is probably unavailable outside of diy.

But five hundred dollars is, well, five hundred dollars! Just takes some of the diy thrill out of this for me. 190 dollars for crossover parts. Excessive perfection?