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Car Forum / Driving, Maintenance, Tuning / Car Audio / December 2003My take on the Eddie-Tom debate
Admittedly, I haven't gone through all the posts here about this. But I've yet to be introduced with any evidence that there is indeed a "low" frequency enhancement strictly due to orientation (yes, I realize the use of the term "low" is a bit arbitrary). As Scott pointed out in a previous thread, Eddie's tests fail to isolate the orientation component because of the translational shift in cone location. So what possible mechanisms exist to cause the phenomenon that Eddie describes? He insists that it's cancellation. But how does this cancellation occur if the cone is in the same location? Isn't the wave propagation outside the box isotropic at low frequencies? I'd expect two things to prevent isotropy: occlusion and cone shape. We know occlusion isn't the cause because the wavelengths in question are much larger than the box size. And I can't think of a reason why cone shape would have a significant effect either. Someone help me out if I'm overlooking something. However, we do know that there's usually a difference. Turn your box around and there's often an effect plain as day. But what IS the effect? Does it really consist of "low" frequency response changes based solely on orientation? I see no evidence in support of that. So I conclude that there are two mechanisms responsible for the change: 1) Change in cone location can have a dramatic impact on "upper" bass (eg. 100-120Hz). 2) Higher frequencies, in the form of harmonics and high frequency content of certain "low" sounds, have a significant effect on the perception of low frequency sounds. I suspect that you may be underestimating the psychophysical aspect of the issue. Mark read the posts you are out of whack in your take on it! the woofer postion in the car IS the difference NOT the direction the woofer points.... if you had read my web page http://www.installer.com/tech/aiming.html you would have save yourself a buncha wasted typing. Eddie > Admittedly, I haven't gone through all the posts here about this. But > I've yet to be introduced with any evidence that there is indeed a [quoted text clipped - 27 lines] > perception of low frequency sounds. I suspect that you may be > underestimating the psychophysical aspect of the issue. > Mark read the posts you are out of whack in your take on it! > [quoted text clipped - 38 lines] > > perception of low frequency sounds. I suspect that you may be > > underestimating the psychophysical aspect of the issue. What is the psychophysical effect to the microphone and test equipment? I thought psycho had to do with people. I'm a retired electronics tech with 30+ years experience but not in audio, I supervised a calibration laboratory that calibrated some of the same model gear Eddie used during some of those years. I too have been reading the posts because I used to compete in IASCA (was at 1995 World Finals in Dallas), and was hoping for an explanation regarding an effect in my Ford Probe at bass frequencies. So I do have a question regarding bass and my understanding/mis- understanding of this thread. Here goes: If at 100hz and below bass is simply a pressurization of the cabin shouldn't it sound the same everywhere/anywhere inside? It pressurizes all of the air, or am I missing something here? I.E. there would be no directionality to the bass. That being true, why does the bass sound like it comes from the rear if that's where your bass box is? Why then did people go to great lengths and expense to mount subs under their front floors or in the firewall? Why did an IASCA SQ judge complain about my car (not at world finals) and deduct points because he was an installer and everyone knows if the subs are in the back the sound should come from the back ( I have speaker time align capability with my Pioneer ODR gear)? I guess he thought the bass came from the back at live concerts, which was what our reference/ideal sound was supposed to be. Am I not understanding Nousaine's explanation and it's effects on vehicle sound i.e. cabin pressureization and sounding the same throughout based on this explanation? I also have a nasty 20db spike at about 86hz IIRC, but that's probably because the box it too small. Sorry if this is OT. I. Care > > Mark read the posts you are out of whack in your take on it! > > [quoted text clipped - 40 lines] > > > What is the psychophysical effect to the microphone and test equipment? I was referring to the cause of the change that we perceieve when we listen to it. > I > thought psycho had to do with people. I'm a retired electronics tech with [quoted text clipped - 14 lines] > directionality to the bass. That being true, why does the bass sound like > it comes from the rear if that's where your bass box is? It's the higher frequency content that provides much of the directionality. We tend to forget that subwoofers do in fact reproduce frequencies greater than 100Hz, even when the xover is set low. > Why then did > people go to great lengths and expense to mount subs under their front > floors or in the firewall? Why did an IASCA SQ judge complain about my car > (not at world finals) and deduct points because he was an installer and > everyone knows if the subs are in the back the sound should come from the > back ( I have speaker time align capability with my Pioneer ODR gear)? I > guess he thought the bass came from the back at live concerts, which was > what our reference/ideal sound was supposed to be. I'm not sure why people go to the trouble. I think it has to do more with scoring points than achieving good sound. >I'm not sure why people go to the trouble. I think it has to do more with >scoring points than achieving good sound. EXACTLY. Its all about the points and a clearly better sounding system, to the majority of people, can lose because the other guy could get more of those little points. > Mark read the posts you are out of whack in your take on it! > [quoted text clipped - 4 lines] > http://www.installer.com/tech/aiming.html > you would have save yourself a buncha wasted typing. Position - orientation ... doesn't matter. Your own graphs show very little difference under most circumstances between front-firing and rear-firing at LOW frequencies. On the order of about 1-2 dB it appears. That's hardly a significant effect. It borders on the threshold of audibility. The effect is much more pronounced greater than 100Hz. Therein lies the difference that we all note when we do the experiment with our ears as the measurement device. So how are these findings any different from Tom's? > So how are these findings any different from Tom's? Tom says NO difference at all. Some folks say they can hear it, Tom says it cant happen and is a figment of thier imagination. Tom also claims my graphs are FAKES! > > So how are these findings any different from Tom's? > > Tom says NO difference at all. That's not what he told me. In his corvette, he said that there's a difference above 100Hz. > Some folks say they can hear it, Tom says it cant happen > and is a figment of thier imagination. If that is what Tom says, then his own data shows he's wrong. > Tom also claims my graphs are FAKES! Not sure why he would. They look the same to me. Very small differences below 100 Hz, larger differences above 100Hz. |
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