So.....generically speaking, when the wavelength produced by the speaker is the size of the cabinet, it reflects off the cabinet, giving you approx. 6 dB more SPL....that I understand.
For the longest time I could not understand why it is a "loss" of bass and not a gain in "midrange/treble".
I think I know why, please confirm.
When a speaker is rated at say 87 dB, that is as measured on a large baffle, which means with the +6 db baffle step. So when that 87 dB speaker is used on a narrow cabinet (narrower then the test baffle), you get a ~6 dB loss in SPL, correct????
For the longest time I could not understand why it is a "loss" of bass and not a gain in "midrange/treble".
I think I know why, please confirm.
When a speaker is rated at say 87 dB, that is as measured on a large baffle, which means with the +6 db baffle step. So when that 87 dB speaker is used on a narrow cabinet (narrower then the test baffle), you get a ~6 dB loss in SPL, correct????
It is in fact a gain in midrange and treble, but since everyone uses speakers mounted on some kind of baffle or another (the driver itself acts as a baffle to frequencies that ‘small’ relative to it), it is taken into account in the efficiency rating, yes. So relatively speaking you get a bass drop.
Also, baffle step is not generally considered to be when the wavelength is bigger or smaller than the baffle, but usually done by the half wavelength. So if the half wavelength is bigger than the baffle you get the drop in bass.
At least I hope that is right
Also, baffle step is not generally considered to be when the wavelength is bigger or smaller than the baffle, but usually done by the half wavelength. So if the half wavelength is bigger than the baffle you get the drop in bass.
At least I hope that is right
No kidding!An externally hosted image should be here but it was not working when we last tested it.
This is just a semantic problem. There are two ways of looking at it.
1. If the driver is thought of as playing in full space at low frequencies, there will be a gain of 6 dB at high frequencies compared to the level at low frequencies due to the baffle step.
2. If the driver first is mounted in an infinitely large baffle, there will be a 6 dB gain over the entire frequency range. If the baffle then is narrowed to the size of an ordinary loudspeaker, there is a loss of 6 dB at low frequencies.
Once both points are understood, it becomes unimportant which explanation model you choose, since they are equivalent (sort of).
1. If the driver is thought of as playing in full space at low frequencies, there will be a gain of 6 dB at high frequencies compared to the level at low frequencies due to the baffle step.
2. If the driver first is mounted in an infinitely large baffle, there will be a 6 dB gain over the entire frequency range. If the baffle then is narrowed to the size of an ordinary loudspeaker, there is a loss of 6 dB at low frequencies.
Once both points are understood, it becomes unimportant which explanation model you choose, since they are equivalent (sort of).
An externally hosted image should be here but it was not working when we last tested it.
Thanks everyone. I have read the different diffraction websites but was still missing something....I was missing the connection that the spec'd sensitivity of speaker already has the approx. +6 dB factored in.
So, part II of my question. How wide is the standard baffle speaker mfg. determine the sensitivity with? The reason why I ask, does the sensitivity of larger woofers, like a 12" or 15" woofers have the "baffle step" factored in? Or since they are measured at such a low freq. they are measured with "2pi" loading?
Curt's explanation is a good and that is the one site I haven’t read about baffle diffraction on!
http://www.geocities.com/cc00541/bafflestep.html
http://www.geocities.com/cc00541/bafflestep.html
That's a nice page. Well explained.
In a related question - What is the transition wavelength for an Open Baffle? The point at which the rear wave meets front wave and causes the 6dB drop.
I know I've read the calculation before, but can't seem to find it anywhere now. Searched all over. Just the quick and dirty. You know - baffle is this wide so bass starts roll off at this frequency.
Strange that I can't find it. Is it hiding in plain sight?
In a related question - What is the transition wavelength for an Open Baffle? The point at which the rear wave meets front wave and causes the 6dB drop.
I know I've read the calculation before, but can't seem to find it anywhere now. Searched all over. Just the quick and dirty. You know - baffle is this wide so bass starts roll off at this frequency.
Strange that I can't find it. Is it hiding in plain sight?
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