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Post by fbczar on Oct 29, 2024 9:27:26 GMT -5
I wanted to see how the subs perform aimed straight into the long length of the room perpendicular to the side walls, vs 30 degrees toed in. I was hoping to see a positive change in how much they engage the length resonance mode, potentially reducing the decay time. What I found was at 30 degrees there is a rise in level of about 3db from 60-100Hz. That would be nice, though it doesn’t buy me much because Dirac flattens that range just fine. But, I also found that the decay time of the resonances at 40Hz and slightly below were extended on the waterfall and decay plots … like 60ms longer. That’s not good … I was actually hoping for the opposite. So I put them back to aiming straight down the length. Acoustic centers around 3ft from the side walls and 7 1/2ft from the front wall. View AttachmentView Attachment What happens when you move the OB subs closer to the front wall relative to decay time and frequency response? |
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Post by marcl on Oct 29, 2024 9:40:16 GMT -5
I wanted to see how the subs perform aimed straight into the long length of the room perpendicular to the side walls, vs 30 degrees toed in. I was hoping to see a positive change in how much they engage the length resonance mode, potentially reducing the decay time. What I found was at 30 degrees there is a rise in level of about 3db from 60-100Hz. That would be nice, though it doesn’t buy me much because Dirac flattens that range just fine. But, I also found that the decay time of the resonances at 40Hz and slightly below were extended on the waterfall and decay plots … like 60ms longer. That’s not good … I was actually hoping for the opposite. So I put them back to aiming straight down the length. Acoustic centers around 3ft from the side walls and 7 1/2ft from the front wall. View AttachmentView Attachment What happens when you move the OB subs closer to the front wall relative to decay time and frequency response? I actually have not moved them much because they weigh about 180lbs each and there isn't much space between the TV and the 3.7 with the attached baffle. I know that the current position allows the baffle on the 3.7 to add to the baffle length of the sub. Also, best placement should still be at the 25% point from front and side walls. I'm currently somewhat farther out than 25% from the front wall but that is so the sub isn't in the way of the TV. So in practical terms the only variable I could try was toe in. That's also because I decided not to put them laying across the floor, because that would give up the stereo separation that I determined that I could hear. |
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Post by marcl on Oct 30, 2024 15:10:32 GMT -5
A bit more tweaking today. What I observe is that when I have the subs playing stereo - left channel panned to the left sub, and right channel panned to the right sub - I see in the waterfall plot some resonance at 40Hz where my big modal peak is situated ... so even though the amplitude is flat, the decay is longer at 40Hz. This is with both channels each driven separately. But interestingly, when I play LFE which goes to both subs, that decay seems to be canceled and it drops off more quickly at 40Hz.   So an experiment ... I just panned the left and right channels inward a small amount and measured ... essentially mixing a small amount of left bass to the right channel and vice versa. What I found was that I could get a bit better decay at 40Hz and also 20Hz where there is also the fundamental of the room's length axial mode. The result ... a little less "stereo bass", but better decay at the resonant frequencies, and a little more gain for each channel's bass which is useful to flatten and extend the response. It actually measures pretty flat with the Dirac filters from two weeks ago, but I'll do a new full calibration tomorrow. |
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Post by marcl on Nov 4, 2024 17:29:13 GMT -5
Yesterday's Philadelphia Area Audio Group meeting was at the home of a young engineer who's developing a speaker design and hoping to market it. The drivers in the speaker are Purifi 6" with a beryllium dome tweeter in a transmission line MDF cabinet. The subs are built with 15" Rythmik servo drivers - two each - in a 200lb 8 cubic foot cabinet, powered by Rythmic servo amps. Sounded really good in his very well-treated loft over the garage shop. Of course there was pizza, sandwiches, beer, wine and soda downstairs ... and Hanna's home-baked cookies! I love audio! We come for the music and stay for the cookies!    These subs are sealed, but I immediately identified with the sound ... very similar to mine, given the servo design. |
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