divide the speed of sound by 2 meters
340/2=170
170Hz
give or take
depending on air pressure and temperature
more or less
340/2=170
170Hz
give or take
depending on air pressure and temperature
more or less
Hmm, 'sound is round', so assuming a round baffle to keep it simple and SoS = 344.424m/sec, then as a rough approximation: 344.424/pi/2 = ~54.82Hz/F3, but there's a terminus end correction of radius*0.613 that needs to be accounted for: 344.424/pi/(2+(2/2*0.613) = ~41.96Hz.
If F6 is what you're looking for, then it is 1/2 octave away, or 41.96*0.707 = ~29.66Hz. Or just use Linkwitz's formula for F6: (0.17*344.424)/2 = ~29.28Hz. I assume the inaudible discrepency is due to him rounding the numbers off a bit in his lumped sum value.
GM
If F6 is what you're looking for, then it is 1/2 octave away, or 41.96*0.707 = ~29.66Hz. Or just use Linkwitz's formula for F6: (0.17*344.424)/2 = ~29.28Hz. I assume the inaudible discrepency is due to him rounding the numbers off a bit in his lumped sum value.
GM
So...so far we got 144Mhz, 170Hz, and 42Hz. Anyone else????
😀
You know how this scientific stuff is
"Industry, science, and technology! Big men putting screwdrivers into things! Turning them! And adjusting them!"
😀
You know how this scientific stuff is
"Industry, science, and technology! Big men putting screwdrivers into things! Turning them! And adjusting them!"
F3 of 42Hz and fully into 2pi at 170Hz is pretty close. However, this is all theory. With these kinds of frequencies in a room, you will probably get completely different results due to roomgain and standing waves.
Hybrid fourdoor said:
Depending on how you define "fully" all answers are correct. Unless you really mean fully (ie nothing gets around to the back side), then the answer is "infinite".
rcavictim
Your comments are inappropriate for this forum, and not required here, so I have removed them to Texas. Please behave from now on or further action will be taken.
pinkmouse said:
rcavictim
Your comments are inappropriate for this forum, and not required here, so I have removed them to Texas. Please behave from now on or further action will be taken.
Well 'ya see officer......here I was in the proper lane doing the speed limit when someone says "2 meters". Just so happens that triggers a nerve because I do care and am most concerned with the direction where amateur radio is going. I apologize for posting clearly off topic.
Hmm, obviously I was not thinking in terms of F0 WRT 2pi space radiation, but it would be 1/2 octave above F3, or 1.414*~41.96 = ~59.33Hz, so I don't see how ~170Hz or any other frequency 'up' to 'infinite' can be correct, especially since 'infinite' as I understand the term = DC.
GM
I'm not sure where the 1/2 octave is based upon. According to the bafflestep model in LspCad, the range between F0 and F6 is round about 4 octaves, hence F0 of 42*2*2 ~ 170Hz.GM said:
>I'm not sure where the 1/2 octave is based upon. According to the bafflestep model in LspCad, the range between F0 and F6 is round about 4 octaves, hence F0 of 42*2*2 ~ 170Hz.
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OK, we are back to what he means by 'full'. To me it means the lowest frequency the baffle will support before it starts 'falling away' in time. This is its -3dB point, and since sound rolls off at 6dB octave, F0 or F6 is either 1/2 octave higher or lower from this frequency.
If by 'full' he means F0, then the ~59.33Hz/0dB point answers his question, at least in theory for a thin, round baffle suspended in free space. At 2m wide, in a real app it will probably not be even close for a variety of reasons.
Baffle step covers a wider BW because it is a gradual change in directivity of which the F0/F6 of the baffle size is just a slice out of the core of the larger spherical BW of the signal.
GM
====
OK, we are back to what he means by 'full'. To me it means the lowest frequency the baffle will support before it starts 'falling away' in time. This is its -3dB point, and since sound rolls off at 6dB octave, F0 or F6 is either 1/2 octave higher or lower from this frequency.
If by 'full' he means F0, then the ~59.33Hz/0dB point answers his question, at least in theory for a thin, round baffle suspended in free space. At 2m wide, in a real app it will probably not be even close for a variety of reasons.
Baffle step covers a wider BW because it is a gradual change in directivity of which the F0/F6 of the baffle size is just a slice out of the core of the larger spherical BW of the signal.
GM
Way too much information.
If you take the question at its most basic, which would be when is a 2 meter wide baffle, with the hieght at least that as well, providing half space radiation, rather than free space, that would be where 2 meters is one wavelength: about 170 Hz. All the conjecture beyond that is dependant on variables that were not offered in the original proposition.
If you take the question at its most basic, which would be when is a 2 meter wide baffle, with the hieght at least that as well, providing half space radiation, rather than free space, that would be where 2 meters is one wavelength: about 170 Hz. All the conjecture beyond that is dependant on variables that were not offered in the original proposition.
~170Hz travels 2m through air in 1 sec, how can this possibly have any bearing on a baffle's radiation impedance BW?
GM
I think full means into completely into 2pi, which is F0 and higher.GM said:
😕
F0 and F6 mean the 0dB and -6dB point. I don't see how these could be 1 octave apart in theory.
You fellas remind me of the group of theologians who sat around the table and wasted an eternity arguing about how many angels could dance on the point of a pin. Why doesn't someone with the test equipment make an actual measurement?!
As an RF antenna designer and still very much a neophite when it comes to acoustical design I must qualify my statement in that I am still trying hard to get a grasp on the nature of the sound field projection as it pertains to this discussion. I think Bill Fitsmaurice is on the right track but I am going to say that only a 1/2 wavelength wide baffle in freespace will be required to support 2 pi radiation so my 'intuitive guess' for a 2 meter wide baffle is half of 170 Hz or 85 Hz!
In practise though edge diffraction is going to screw you up in a sealed box (the sealed box will look like a isotropic radiator radiating into 4 pi steradians) and if an open baffle, no matter what the size less than infinite you are going to see cancellation at the edge or 90 degrees to the main lobe. That cancellation will automatically provide the 2 pi radiation space for the phase from one side of the driver.
My 85 Hz 'guess' stands.
Am I completely out to lunch on this?
As an RF antenna designer and still very much a neophite when it comes to acoustical design I must qualify my statement in that I am still trying hard to get a grasp on the nature of the sound field projection as it pertains to this discussion. I think Bill Fitsmaurice is on the right track but I am going to say that only a 1/2 wavelength wide baffle in freespace will be required to support 2 pi radiation so my 'intuitive guess' for a 2 meter wide baffle is half of 170 Hz or 85 Hz!
In practise though edge diffraction is going to screw you up in a sealed box (the sealed box will look like a isotropic radiator radiating into 4 pi steradians) and if an open baffle, no matter what the size less than infinite you are going to see cancellation at the edge or 90 degrees to the main lobe. That cancellation will automatically provide the 2 pi radiation space for the phase from one side of the driver.
My 85 Hz 'guess' stands.
Am I completely out to lunch on this?
Such measurements have been done many times...rcavictim said:
The info is here, but there are still some inaccuraties as well. Feel free to measure anyway 🙂
Svante's model may help answer this question and one could download and evaluate the answer as well in the Baffle Diffraction Simulator Program at the FRD Consortium Web Site. It seems as though the debate is not so much over the theory but rather what the questioner meant to ask. It makes sense to use the models that exist and appear to have some degree of accuracy, no?
I was going to use the angels/pin thing too but decided to stick to the facts. I can't figure what the fuss is all about either since the answer to this one lies around page 5 or so of every text written on audio since 1922. I test new loudspeaker designs every two months or so and have yet to come across one that doesn't radiate into half-space at 1 wavelength. If you test outdoors and stand behind the box you can hear the shift from full to half space as you raise the frequency of the tone generator, as the output seems to drop drastically when you hit the shift frequency, until you walk around to the front of the speaker and the level almost magically jumps up again.
Oh, and the answer to that other question is 1,262,513. Give or take.
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