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In Reply to: RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics posted by josh358 on March 02, 2017 at 10:39:49
I didn't give up on the barrier just that I did not get to that stage of experimentation yet after having moved to the short wall for wall loading positioning schemes and Limage type setups along with moving to time aligned 3rd order LP crossovers in the reverse split setup. I guess I can just put up the boards and see what happens though nothing is really completely optimized .
On the long wall placements I settled down with 1st order equidistant and used a pair of barriers like yours but flush to the front of the MT panel. That is where the observation came from about the opposing sidewall.
Follow Ups:
Well I tried the RFZ barrier again last night with the boards somewhat further back and the results were at least as spectacular. I'm beginning to think that more is going on here than the M-T first reflection, I think it's blocking the higher frequencies from the woofers (lower will just go through and around) so that essentially I'm hearing only their first reflections. But whatever happens and it will be a few days before I finish rebuilding my computer and can look at the impulse response it's basically large room performance in a small one with the kind of lateral and z-axis localization I'm after.
Before that, I'd tried the ambio barrier again, this time from MGBert's recommended listening distance, but again with only partial effect. I'm not sure how much of that has to do with diffraction but some of it is just that I didn't have time to change the baseline after I moved closer so I was getting a hole in the middle at that distance.
I ended up listening to the sample files on the ambiophonics site with the barriers still in the RFZ position. As I said to stchelvam, the effect was rough because the speakers were at the wrong angle but I was nevertheless impressed -- there was an awesome immediacy to the sound that reminded me of a binaural recording, or the front part of one anyway.
This stuff -- nulling room acoustics and crosstalk cancellation -- really takes things to a different level.
From Josh358: "This stuff -- nulling room acoustics and crosstalk cancellation -- really takes things to a different level."
And that, sir, was the drum I was beating when I was posting about this a few years back. It really dwarfs the improvements you get from fancy cables or amps. In fact, it's worth just getting long lengths of plain zip cord to use as speaker cable until you get placement nailed.
And yes, the MMGs are probably better candidates since, according to Floyd Toole's book "Sound Reproduction: Loudspeakers and Rooms" which has an entire section (9.1.3) which he calls "An Important One Toothed Comb - A Fundamental Flaw in Stereo" which relates to the crosstalk phenomenon, the critical frequency is about 1,300 Hz. So the MMG tweeter is definitely in play there. The link to the Toole book I posted earlier seems to no longer include that section; pity.
Of course, it also has zero WAF. ;-)
MG-bert
Fortunately I have Toole's book so I'd already read the chapter. I'd recommend that anyone curious or even not curious get a copy, it's well worth it.
I tried more ambiophonics experiments this morning, this time with the recommended 20 degree angle, but couldn't get it to work very well -- the same experience I had with the MMG's. Perhaps the side-by-side arrangement of the midrange and tweeter interferes with the timing of the crosstalk cancellation? I could hear decent spread beyond the speakers but it was no wider and probably narrower than the usual image with the speakers at 60 degrees. It just didn't match the true ambio barrier. That was just plain right, and if I could get my speakers to do that without pink styrofoam touching my nose my life would be complete.
I take it you're still using your original setup at home?
Josh358: "I take it you're still using your original setup at home?"
Short answer is yes, unfortunately I don't get to listen to it as often as I'd like.
Longer answer: I have tried to do the setup shown by st.chelvam, and got pretty good results. I used my 2 FRT panels as the barrier, stiffeners touching so the total barrier was about 4" wide, and using those foam pipe insulators on the forward edge as a headrest. I had my Gunned MMGs touching the FRT panels, about 4 feet away from my ears. So the angle between the tweeters was between 10-20 degrees, which should be ideal. I was thinking, though, that the fact that the FRTs are wooden panels did the configuration a disservice, since the high frequencies bouncing off the hard surface might have had a smearing effect. So I have a plan to glue some insulation to that reflective surface (thinking the textured foam used as mattress cushions) to reduce those reflections. These reflections don't seem to be a problem with the separated configuration I wrote about initially, btw. Haven't had the opportunity to do that yet.
And besides, the separated configuration allows for a TV screen so I can control the music selection or watch a concert video. Can't do that with the barrier dead center. Although a VR reality set of goggles would make that possible... ;-)
MG-bert
" So the angle between the tweeters was between 10-20 degrees, which should be ideal."
The crosstalk effect only effective for frequencies below 4000Hz. You may get a better result with the midrange separated by 10 to 20 degrees.
STC: "The crosstalk effect only effective for frequencies below 4000Hz. You may get a better result with the midrange separated by 10 to 20 degrees."
The crossover of my MMG speaker is actually at 1,000 Hz, so the tweeter is handling those frequencies. Working out the geometry I used when I had the speakers as close together as the 4 inch wide barrier would allow, the included angle between tweeter quasi-ribbon centers was 16.6 degrees, and between woofer panel centers was 23.5 degrees. Actually a bit less because I had rotated the panels a bit to reduce phase differences between the woofer and tweeter at the listening seat.
I agree; if I sat further away from the speakers (I actually had my forehead up against the panels I used as the ambio barrier) the results may well be better, especially since the high frequency "smearing" should be directed more away from the ears. I will try that later; too much going on now to devote time to reconfiguring the system.
Which angle should govern: if getting the woofers within a 20 degree included angle means the tweeters are closer than 10 degrees included angle, is that worse than the tweeters being right at 10 degrees but the woofers being greater than 20 degrees? I just had a thought of a new barrier configuration to try, with my 2 FRT style panels touching each other in the plane of the MMG speakers and spreading out to 4" to 6" wide closer to the listener. In other words, a wedge-shaped barrier vice a standard rectangular barrier geometry, as seen from above. That SHOULD direct any smearing early reflections from the FRT panel surfaces further still from the listener. Also, that would allow me to bring the MMGs even closer together; hence the angle questions. Thank you for your interest and assistance.
MG-bert
MG-bert wrote "Which angle should govern: if getting the woofers within a 20 degree included angle means the tweeters are closer than 10 degrees included angle, is that worse than the tweeters being right at 10 degrees but the woofers being greater than 20 degrees?"
I see your point. I guess you can only tell which is correct by experimenting.
Thank you for sharing your setup.
Yes, the ambio barrier articles I've seen all mentioned absorption. But since it isn't practical and I was able to hear the effect with just those slabs of pink styrofoam I'm not going to try it.
Need something more practical! I'll give your barrier setup a more careful try, and also try the RACE setup again, although I'm stymied because even if I can get the Maggies to work I have the same problem you have -- I need to put a screen between the speakers. In a perfect world, I'd have a huge room and a motorized acoustically transparent screen, but realistically, the only way I can think of to do this would be to push the speakers together for music listening and use the laptop rather than the projector.
I think you are right about the driver differences in lateral placement f'ing up the crosstalk cancellation from working. When we first talked about it here a decade ago I was thinking of how polk did its SDS processing, which I heard, and figured that if you did that electronically it would not work with laterally splayed drivers covering the critical frequencies. I didn't say anything since I didn't want to work out the physics explicitly, I just didn't expect it to work unless the mids were left to cover the critical frequency range in its entirety. Something you can do with the Neo8.
You could also do it by biamping and using separate parameters for the midrange and tweeter. I believe ambiophonics software usually allows you to split frequency ranges, in fact, I recall reading that the optimal angular location for the woofer and tweeter are different.
Another issue that occurs to me is that the test recording would have been made with an inverse square point source in mind rather than a 1/D line source. Again, the software would allow adjustment.
That said I've had some very interesting results with the speakers in their normal position. I'd be playing more with it now if I hadn't just learned that Amazon has delayed the deliver of my new table . . .
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