"Budget" JBL Pro Build and System / Component Modeling & Simulation

[miscrms]

Greetings!

After lurking for quite a while I wanted to start a thread here to introduce myself and see if folks have any thoughts / feedback on my project. I'm afraid I've gotten bit by the audio bug bad after quite a few years of hiatus. As a teen I thought I was going to be an audio designer when I grew up. It seemed like the perfect blend of my loves of music and engineering. I was building speakers based on the equations in my Radio Shack speaker design book, and scraping together pennies to buy equipment. In engineering school I had the lucky chance to work with some really top notch sound gear doing sound support for various local and visiting artists, and to hear some great concerts at one of the best acoustical halls in the world, Troy Savings Bank Music Hall, where Dorian Records did some great recordings at the time bringing in some really great artists. In school it soon became apparent that my opportunities were going to be pretty limited in audio, but I also found a love for RF / microwave electronics. Sort of audio on steroids Then life / kids etc happened and while I always continued to dabble in audio and home theater, it was always pretty tame.

I hadn't really planned to get back into things on such an ambitious scale, but when the opportunity arose to purchase the speakers out of the local University's 1960s vintage concert hall I somewhat inadvertently got sucked back in It's not exactly ideal timing as with a young family my resources are somewhat limited, but I've been fortunate to have some space, time, spousal support and money to work with. For better or worse I also don't think I have a very developed / critical ear, but as a closet musician I do appreciate musicality and impact and have quite diverse tastes. As as an engineer I am appreciative of the technology under the hood, and vintage ingenuity and quality. If you're interested you can read a little about my adventure so far here:
http://audiokarma.org/forums/index.p...budget.677257/



I suppose there are really two topics here:
1) planning the next phase of my basement system, and
2) Seeing how much of my day job skills (high speed digital / microwave IC design / layout / test) I can leverage to better understand audio systems and their components.

On the first topic, I currently have a very enjoyable setup (5ch w/ 2 way bi-amped RLC) cobbled together downstairs for dual listening and home theater purposes. I've slowly been accumulating and repairing more bits and pieces in the mean time, and am coming to the point where a major reshuffle is coming. In general I am focused on exploring using older pro gear as a means to maximize performance per $. And I just like it for some reason Here's what I have to work with at the moment:

Amps:
2x Altec 1608A (replaced marginal electrolytics, replaced burned output stage / driver resistors on one, debugged flaky driver card instability)
2x Altec 9440A (replaced marginal electrolytics, experimenting with upgrading coupling cap to film, ceramics to film / silver mica)
3x JBL 6260 (repaired flaky relay on one)
1x JBL 6290
1x Yamaha P-2200 (needs repair on intermittent meter, maybe electrolytics)
1x McIntosh MA-230 (replaced failed/marginal electrolytics, diodes, thermistor, modified for pre-out and post-in, still needs some cleanup)
1x HK AVR7000 (failed input card, modified for 5ch power amp, needs PS cap replacement)

Speakers:
2x JBL 4648A w/2226H
4x JBL 2446H w/ 2365A CC biradial horns, 2x 2506B brackets
2x JBL 2404H
2x JBL 8330
1x JBL 4660 w/2346 "everest" defined coverage horn
1x JBL 4646A
1x JBL 2446H w/2380A FF horn
1x Intersonics ServoDrive Contrabass (made belt set, replaced bad motor, reglued separated cone/surround)

Sources / Control / Other:
1x Sherbourn PT-7030 - Pre/pro, hdmi switching, bass management, parametric EQ
2x JBL 5235 active crossover, cards 3x 500 CCBREQ, 1x 800 FFBREQ, 1x 80Hz, 1x blank
4x UREI 539 Room EQ
1x UREI 535 Stereo EQ
HDMI sources (Mac Mini (Plex/Itunes), PS3, PS4, WiiU)
Other sources (Denon DCD 3520 (needs belt), ELAC 50H (needs work), ELAC 750 (needs work) - these may be going in a modest vintage listening setup upstairs
Panasonic P54G10 54" plasma (probably reusing for different room)
Panasonic P65VT50 65" plasma (probably replacing 54" plasma and projector)
Sony VW40 projector, tab tensioned 4:3 draper accessV screen (probably going away)

Test Equipment / Misc:
HP 4192A Impedance Analyzer
HP 35665A Dynamic Signal Analyzer
AudioTools iOS w/UMIK-1
GTC CM100 mA scale AC/DC clamp current meter
Misc. Cheap DVMs
Dale 5.8Ohm 200W resistor load
Collection of various vintage/nos caps (rel, wonder, sprague, Siemens, motor start/runs, silver mica, etc), coils, resistors, magnet wire, diodes, etc
temp controlled solder station (vintage Hexacon)
Various simulators (Cadence Spectre, ADS, Spice, etc)

I'm intrigued by the idea of using the 4192A to characterize and model speakers as Z11 blocks, and the 35665A to create 2 port networks of various active / passive components and then simulate the whole thing and play with different options particularly for crossovers. I'm also anxious to just get the system rebuilt and enjoy it lol.

Any thoughts, concerns, encouragement, admonitions, etc welcome.

Rob

[JeffW]

I don't have any advice to offer, but will say you have a nice collection of gear going!

[1audiohack]

Looks like tons of fun!

That is a dizzying amount of gear and possible combinations. I breezed your AK thread. First thought, while no 238X horn will present like a 2360-2365, the 2382 does not sound like it's siblings. If you need a horn that size for center, try a 2382, they sound much better.

It will be fun to see where you go with this.

Your engineering background and education will serve you well in this hobby. You're in for a good ride.

All the best,
Barry.

[miscrms]

Thanks hack, the center channel is definitely the weak link in the current system. Its not terrible, but was just made up of the left overs in its current incarnation. I guess the ideal thing would be another 4648A and 2360 behind an AT screen, but I don't think that's in the cards or very workable in the space. It's actually not bad when its playing together with the fronts, but in HT its often got a fair amount of time when its playing alone and its noticeably thin by comparison. The 2382 does look pretty cool, I'll have to look into that. The directivity of the one I have is certainly not ideal. I suspect the 12" woofer in the small volume 4646A is another issue. This is kind of what I had in mind when I picked up the 4660. It's a bit awkward to work with but the 15" and box volume are a big step up, and the 2346 horn that went on to be used in the Everest DD55000 is pretty intriguing. If anything it may need a beefier 15, or a custom box to be more feasible.
http://www.jblpro.com/pub/obsolete/4660.pdf

I'm also looking at options for how to integrate the 2404s into the front L and R. I'm playing with a simple first order coupling cap currently, but this is probably non-ideal phase wise. I did pick up some Lpads from parts express as there also will probably be an issue with the sensitivity mismatch to the horns.

That leads to one of the conundrums I'm currently pondering. If I mix active crossovers for front LF/HF with passive for HF/UHF it seems like I'm probably going to have phase issues. Regardless of the order (or driver polarity) if there is a high pass on the UHF and nothing on the HF then it seems like it will be out of phase in the crossover vicinity. If you put a LP on the HF I should be able to match the phase in the HF/UHF crossover transition but I'm concerned that screws up the phase on the HF/LF. That's the first thing I want to look at in the simulator as its making my head hurt to try and keep it all straight in the brain simulator

I could use the second 5235 to tri-amp the fronts using custom cards for the UHF, which would solve that particular issue. Running another set of amps just for the UHF seems a little silly somehow, but I could do it. That would mean sticking with a passive crossover for the center if I go with the 4660, which I was thinking about trying to modify for bi-amp with a custom 5235 card. I could of course try to find another 5234/5, but they do seem to be getting harder to find, or looking at another active crossover alternative. Similar issue for the sub if I add it, although I can use the bass management in the Sherbourn either to crossover the fronts or just put the sub on LFE.

[miscrms]

So here are some preliminary sims to explore the UHF crossover question. For simplification I'm not trying to simulate the existing active crossover, just assuming the bi-amped HF and LF are well behaved and in phase, and that the effect of the 500Hz 18dB crossover is negligible out at the HF/UHF crossover frequency. I'm also just assuming the drivers are ideal 8 Ohm loads for now. All this can be modeled more accurately later.

First is the simplest case of just using an AC couple cap to connect the UHF driver in parallel with the HF as a 1st order 10kHz high pass filter.


As expected this results in a 45 degree phase mismatch at the crossover frequency. Phase mismatch is worse below, which may still be significant as the 1st order roll-on is pretty shallow. Also with no low pass on the horn it will have significant overlap before rolling off on its own, and less than 45 degree but still significant phase error in that region.


So to correct that, I looked at a 2nd order L-R HP on the UHF and LP on the HF horn.


Again as expected this puts the HF and UHF 180 degrees out of phase throughout the crossover/overlap region, which can be "corrected" with a polarity reversal on the UHF and then a little parametric EQ if needed for amplitude correction of the in phase combination of the two.


The main thing I was worried about was how much phase error would this induce at the LF/HF crossover frequency of 500Hz. The answer in this ideal case seems to be about 5.5 degrees, which I assume is pretty reasonable. I'm guessing I'll be lucky to do that well in real life anyway. It could of course become more of an issue if the two crossover frequencies get closer together.

So far I'm thinking this seems like a reasonable approach. It may still make more sense to just suck it up and tri-amp with another active crossover for the HF/UHF, but this at least seems like a feasible alternative.

Rob