kfr01 wrote:
haemphyst,
While you might not be able to say, "you have 2 12"s and 2 10"s," won't the sound be slightly muddied without the help of some time delay, variable phase, eq, or some combination?
Now, maybe I'm totally off-base - physics was more than a handful of years ago for me and I've just recently become highly interested in audio. But here are my concerns with different drivers in different places in the car anyway... Please feel free to knock my thoughts down at will, I am honestly curious::::
I don't think the fact that the actual cones are larger gives me pause, rather, I am concerned with the different motors, different enclosures Q?, and locations. |
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As I said in a post just a moment ago, thanks for bringing up these issues. It DID make me consider and reconsider some of the statement I came up with earlier.
kfr01 wrote:
1) Delay caused by different motor inductance numbers
1) Different motors, with different inductance numbers (thanks Steven), will have different transient response characteristics. In other words, woofer 1 will be firing slightly ahead of or behind woofer 2. Even if located in similar positions in the vehicle, wouldn't this cause a slightly muddied sound? Won't one woofer be settling slightly behind the other? Won't this lead to slightly looser sound as the beginning and ends of signals will be playing supported by a single woofer rather than two? |
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True, the motors will likely be a bit differnt, and everything Steven says regarding inductance and transient responseis correct. I was (for all intents and purposes) assuming that the driver were all to be run in a similar bandwidth, let's just say 80Hz and down, OK. The wavelength of an 80Hz note (or tone) is 14 feet (give or take). How much additional inductance would be required to cause one driver to be THAT much slower than the other, so as to cause a smearing of a 14 foot long tone? Twice as much, FOUR times as much? Even at those numbers, (and I have not set down with JBL, made up a driver, and tried it with different inductance values to see where the frequency response starts to have problems, with impedance peaks and the like) I doubt very much that there is going to be a significant problem as far as transient response is concerned. How much truly transient information is there REALLY at 80Hz and below?
kfr01 wrote:
2) Delay caused by different locations
2) Our friend AJRXtreme talks about placing his low frequency woofers in two completely different locations. One set located very close to him, another located relatively far away. Won't this difference cause some noticable time / phase / cancellation problems? Now, I realize the lengths of the waves are very long. But won't the close set arrive at our friend's ears significantly prior to the far set? Won't this cause the same sort of muddiness or bloat that I have a hunch would happen above? |
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Again, read the above statement. At 14 feet long (minimum length - sound waves get LONGER as the frequency goes down) if one pair of woofers is 8 inches further away (straight line) that is not very much of a phase shift, and the phase shift actually gets BETTER as the frequency goes down due to the lengthening of the wavelength. Also, any phase shift he MAY experience is not going to dramatically affect his "loudness", which is, after all what he is really after - he said so. This is NOT by any means, an audiophile system, which would choose ONE high quality woofer, put it in a PROPER sealed enclosure, and run with it.
kfr01 wrote:
3) Different enclosure Q's
3) Different enclosure Q's. Different motors have different T/S parameters. Unless care is taken to match the enclosure Q's (or at least get close), won't this also cause differing transient response behavior? One speaker might be rather tight, another boomy? One having greater extension, the other more peak? Cabin gain exists because the bass notes stay in the car, even though the waves are very long, won't SOME cancellation related addition and subtraction occur? |
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In a small cabin such as a truck, It would be VERY difficult to determine the differences in Q as well. HOPEFULLY, he will build the enclosures to a decent Q (depending on the mfr, they may recommend a different Q than another would - I expect close to a 1.1 for maximum power capabilities - this means reliability). Sealed enclosures are also very forgiving as far as internal volume is concerned - plus/minus 15% is not going to affect Q very much, and that's a pretty significant difference in volume.
kfr01 wrote:
Playing pink noise or a sweep, you're right .. these considerations probably wouldn't have much effect on frequency response. None of these considerations will probably matter to most people, especially those just interested in SPL. However, one thing I'm slowly learning as I research speaker building more is that overall sound quality goes beyond just the frequency response graph. |
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Actually, I think that it would be more noticeable with steady state information than it would be with dynamic information like music. It would be ESPECIALLY noticable to the microphone. You would be able to move the mic around and detect the peaks and nulls in the system. Granted, it would be very small movements, but it would find them.
kfr01 wrote:
Also, some of these things can be corrected for with some of the features on DSPs and some analog signal processors. Others can be taken care of by switching the phase 180 degrees or taking care to obtain similar box Q's. When someone comes here asking though, shouldn't we warn them that different sized woofer in different locations playing the same frequencies is probably not ideal for sound quality? I mean, we can still tell him/her to go for it, but shouldn't they know that it isn't the recommended path for sound quality?
Again.. please comment, I'm in a learning process here and wouldn't be surprised if most of these were wrong or don't matter.
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You are correct. There ARE devices that might help alleviate some of the issues discussed here, but because the drivers are going to be different distances from the listening position, no amount of phase delay will ever help all of the issues for every seat. TD's only MOVE the null or peak from one place in space to another, when you have a setup like this. I think that, being all he is interested in is an SPL system, and given that the drivers are ALREADY going to be all over the truck, using different drivers in different enclosures is not going to do anything to the detriment of his goal. I do agree with you in reference to someone building an SQ system, yes he should be warned that this will NOT give optimal sound quality. You and I both seem to agree that one would NEVER build an SQ system like this, and if someone were to ask, I would steer tham away from it.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."