A new Center Channel Design study...

[JonMarsh]

well, I'm pretty charmed the more I listen to the CC equivalent with just one channel... I don't want to wax too poetic, and I know that for the CC speaker the ATS panel dealing with the floor bounce is a key element. But the drivers work together well in this Duelund configuration, and I don't see any reason to not expect similar synergy with the RSS210HF, albeit at lower sensitivity levels- but much more extended bottom end.

[JonMarsh]

OK, for those following along with the sausage grinding, here's the "Official" V1.0 release crossover schematic- it's what I'm listening to, and parts that are available from PE have PE part numbers.

Note that the shunt LCR network down by the tweeter section has nothing to do with the tweeter operation, it is just an impedance flattening network so that the overall input impedance and current phase is more linear.

Schematic is prepared with Eagle PCB 6.6 on a Mac.

[JonMarsh]

Oops, just caught a typo, L11 should be 12 ohms. Will update this soon.

[JonMarsh]

Here we go... the "big update" for the shunt impedance flattening network!

And maybe a few general comments, too. Hey, it's a Sunday morning, should be a relaxed agenda (but isn't).




OK, a few comments on how this is put together and component choices- ones I made, once you might make to lower the cost. Don't forget this build is based on a Duelund three way concept, with a center frequency of about 800Hz, so the midrange is wired out of phase, but in principle the drivers are all operating in the same relative phase at any level above -15 dB (my arbitrary design target; improving on that is difficult, and pays few benefits.)

• L13 is a largish value due both the 8 ohm nominal load of the woofers, and the relatively low "crossover" point of the Duelund with a center frequency of 800Hz and an aleph of 2.75. See graph above. Terming the crossover point is somewhat arbitrary, as the LF function is a variable slope filter. L13 was selected carefully to optimize the DCR and checked for distortion- the Jantzen C-Core series performs very well, if you understand the pluses and minuses of the core material, and it's frequency limitations. The distortion plots show that.
• Because L13 value of 7.5 mH is not available off the shelf, even going to HiFi Collective in UK, who orders everything custom build from Jantzen, I used an 8.0 mH inductor and unwound it to 7.5mH, then "sealed" it with J-B Weld. Because of the high frequency loss characteristics of the C-Core material, one must use a low measurement frequency to get an accurate inductance reading- 100Hz is preferred, and what I used with my BK-Precision meter. Do not use a meter that has just a single test frequency, it will usually be to high, like 10kHz, in order to handle small value inductors with some accuracy.
• Where recommended components are available from Parts Express, I included the distributor part number as an attribute of the schematic component- for example 268-832 for the Jantzen 8.0 mH C-Core inductor. Capacitors were selected considering both cost and performance. Yes, C5 and C1 are connected in series with the woofer, this is the same technique used in the experimental Modula Xtreme many years ago, for providing a linear tapered LF response.

• The midrange crossover started off pretty simple, got simplified further, then made more complex adding the series notch filter. I have a preference for Clarity CSA caps for high quality midrange applications, but of course you may have different favorites. It's a question of performance versus cost, and for the midrange, upgrading to something like Jantzen Superior Z drives the cost way up, but with a limited return in performance in most cases. The LCR Fb shunt network could be lowered dramatically in cost by using NP electrolytic, but don't forget the 5% dissipation factor, and relatively poor aging characteristics. I felt more comfortable with MF PP, and had some Solen on hand. The Fb network has to be tuned lower than for a typical midrange, because TangBand considers this to be a functional two way driver all on it's own, though the Xmax is limited. OTOH, that Xmax is in an underhung motor, so as shown previously, within that 4mm of travel, it's more linear than most woofers rated at 8mm.
• For the midrange crossover, given the power handling requirements, Dayton 20W parts were chosen, some used in parallel. The original first pass POC design did not have the series notch EQ, but it was deemed necessary after a variety of measurements, though it really did sound pretty fair with the midrange bump in response. So, you "could" consider that part optional, but I wouldn't.
• Note, the W6-2313 bamboo cone part is pretty well behaved- to the extent that their full range reference design has NO crossover on it, and uses natural roll off on the upper end- the only circuit near the LF on their schematics is a shunt impedance network to stabilize input impedance. Also, the LF characteristics are kind of unusual, I'd say, "engineered", because in a typical "normal" size enclosure, it exhibits no baffle step- not quite as accurate as the AS series Accuton, but pretty similar. This network won't remotely work with other coax's I've tested, such as Seas and SB-Acoustics.
• The TangBand coax is in fairly good stock at PE, in case anyone else wants to play with it.

• The tweeter portion of this TangBand coax is another intriguing element- sharing an inverted dome design reminiscent of Focal and other TangBand parts like the titanium 25-1983, a relatively rare bird these days, but seems to share a very well controlled HF behavior with minimal ultrasonic breakup, and an easy to work with profile. HD3 is quite low at nominal level, and a nominal crossover target at 2500Hz seems reasonable, considering the extended response. See below.
• The crossover is basically a second order high pass, with some attentuation and a modifiable shunt impedance for 2dB level variation in what I consider to be the presence range- depending on personal taste and program material, a setting adjustment may be preferred. For music program material, I preferred the lower setting.
• A wide range of choices can be considered for the input capacitor C11; I used a combination of a Solen Silver cap at 5.6uF + a Jantzen Superior Z, partly because I had them on hand- my normal choice and recommendation for best performance is the Jantzen Alumen 6.8uF. Not inexpensive, though... less golden ears might be happy with substantially more reasonably priced parts!
• Resistors are Mills non-inductive 12 watt, paralleled for power handling when needed. They truly are non-inductive, that is, no more than a piece of wire of the same length. Good LCR meters don't lie. A silver contact Cole Hersee 5582 switch is used, available on Amazon.

For all of these, keep in mind, I would call them POC development layouts- final build layouts can undoubtedly be improved on. (cue: Steve Manning...)











Now, a little more listening, then putting these away for when I can "install" and setup in the AV system in what is currently a computer room.


Next up: SMJ-40/Saint-Saëns! And only fitting that Sven reminded me about the Seiji Ozawa recording of the Symphony No. 3, the only one of the top three recordings of that symphony I don't have, so I remedied that this morning and then some, also buying, at Sven's suggestion, the Warner Ozawa boxed set collection. over 25 CD's. That will keep my out of the bars for a while, ripping those with XLD!

[JonMarsh]

And for further reference, the measured system impedance plot:






And for additional reference, my happy dance at having this stuff done!




(The GIF is an oblique references to comments made by a nephew who says the FOO believes I have alien DNA, as a way to explain how different I am from the rest... )