I will do some more measurements tomorrow just to make sure that the left speaker is firing on all eight cylinders like the right one is, then it's off to the races. they both sound good, but just to make sure
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I will be working on getting the mids down in frequency as low as possible to take full advantage of what I've done with the Mid/tweet cabinet. How low I can go without any deleterious subjective effects is anyone's guess. 300hz to 3khz? Maybe.
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Did a floor bounce cancelation calculation for the mid at the listening seat. Almost 200hz exactly. That would go a long way toward explaining my "subjective" judgements early on about the seeming lack of energy at the 200 hz crossover point. The devil's in the details.
The 4" mid has an xmax of +/- 3.5mm, so it's bulletproof down to at least 300hz
The 4" mid has an xmax of +/- 3.5mm, so it's bulletproof down to at least 300hz
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Yes, that would work, but by raising the crossover up to 300hz, I can avoid doing that entirely, so it looks like 300 will be the minimum.
so ultimately, anywhere between 300 to 600hz.
so ultimately, anywhere between 300 to 600hz.
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Floor bounce isn't the simple issue of a single cancelation though, It's actually comb filtering. A 200hz valley will be followed by a 400hz peak followed by a 600hz valley, etc, etc.. Every untreated reflective surface does this, and it's just part of existing in an acoustic reality and why anechoic chambers sound so horrid to us. Anyway, trying to avoid the really big peaks and dips by the use of judicious crossover points relative to room dimensions, speaker placement(Also driver placement within that speaker) and ear placement is the best place to start, followed by absorptive and reflective acoustic treatments.
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I love thinking in terms of both time and space and how they're inexorably related to the loudspeaker/room/listener interface.
I'm sure this has been posted before on this site, but it's highly recommended reading. Get his book on psychoacoustics if you want to delve into it further
http://mlacoustics.com/PDF/FTarticle.pdf
http://mlacoustics.com/PDF/FTarticle.pdf
Another issue I'm trying to think through, is that even though I can take the midrange down lower on the top unit, should I. Upper midrange purity has always been my primary goal, and adding lower midrange content to that will have some benefits(Cohesion) and some costs(like increased IMD and THD. My icepower amps only do 25 watts into 8ohm too, and the mid driver is pretty inefficient). If I do go with a higher midrange cutoff, I will obviously have to do some similar modifications to the cabinet directly beneath it so they can cohesively match better.
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Crossing higher will reduce intermodulation distortion and Doppler distortion caused by cone movement. But I think you will be safe from 3-400 Hz and up. Chances are that the other cabinets are fine, as long as they don't resonate in their operating range. Can you do outside measurements to verify that?
4ohm driver I may consider in the future. Cutout is perfect, but I'd have to drill new holes. The relatively high third harmonic in the mids would be non existent with an 8th order roll off at 2khz
SB Acoustics SB12CACS25-4 | HiFiCompass
SB Acoustics SB12CACS25-4 | HiFiCompass
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It would take a ton of work to do outside measurements(And the neighbors would get pissed🙂) . A technique that John Atkinson has used is to place the speakers in question face to face, as close together as possible and out of phase with each other. The only noise left will(should) be cabinet noise, as long as the speakers are closely matched. Do you think that technique would work with correlated pink noise?
The lower I take the mids, the less worried I am about general cohesiveness
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I haven't heard of that technique before, sounds interesting. I might try that myself. I find it difficult to analyse waterfall or wavelet graphs at such low frequencies, especially indoors. But if you measure your bass and mid modules in the exact same location, and that the exact same levels, you should be able to do a direct comparison between the graphs to see if your bass modules are inferior at those frequencies.
To be fair, I will not be listening to tracks recommended to me until things get sorted out. Hold tight, I haven't forgotten🙂
I will be pulling my speakers out into the exact middle of the room for some nearfield measurements with adjacent sidewalls and floor damped which should help a little bit anyway. The room is 24ft long, which should help a little too.
Each individual measurement will be exactly 12" directly in front of each module, with the other units obviously turned off. The sweep length will kept as short as possible. I'll try some longer sweep lengths too, just to see If I can get away with it.
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The thing about IMD that measurements don't show, is that with music, there's a literal infinity of possible combinations. The wider the bandwidth the driver operates with, the more potential for chaos. Whether this is audible or not is another matter.
damn! the parametric eq was on. I couldn't figure why some of the individual responses were lumpy.🙂
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there seems to be a problem with the tweeter mounted directly on the sorbothane. Oscillations occurring starting at 2khz and up. No wonder why it sounds bad at a 2khz crossover point, it's not the tweeter, it's the sorbothane. in retrospect it makes sense in that if you take the frequency high enough, sorbothane will start to oscillate. Taking the rubber grommets off the back and tightening the bolts further will be the next step. Both tweeters are behaving identically, so I at least get a high mark for consistency🙂
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