dipole baffle size in relation to frequency, rolloff point

[thadman 10+ year member]

Does the size of the (open) baffle matter when the driver is forced to play frequencies where the frequency is MUCH larger than the baffle itself?

300hz = 45"

150hz = 90"

The wave is going to get around the baffle regardless, would I gain anything by increasing baffle size to 24/30" vs 15"?

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[Beat_Dominator 5,000+ posts]

Yes, the width and height will pretty much determine your tuning frequency.

 

[thadman 10+ year member]

on a 15" baffle 1/3 of the wavelength would reach me @ 300hz, so -18dB (15=900hz) / 17% of the wavelength would be left, 6x the displacement -36dB @ 150hz

on a 24" baffle ~1/2 of the wavelength would reach me @ 300hz, so -12 (24"=565hz) 26.67% of the wavelength would be left, 3.75 x the displacment -22.5dB @ 150hz

I guess I answered my own question, thx

 

[thadman 10+ year member]

How do I combine width and height to determine roll-off frequency?

do I add both values and divide by 2? or is there a more complicated formula?

 

[thadman 10+ year member]

Could I extend baffles perpendicular to the front baffle down the back? say 6-12" from the sides and not get any bad effects?

 

[Beat_Dominator 5,000+ posts]

That's a good question, I had looked for some formulas a while back and the best I could find was an excel spreadsheet somewhere. I lost it though //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

You might try searching "open baffle speaker design" and see what you come up with.

 

[thadman 10+ year member]

Could I extend baffles perpendicular to the front baffle down the back? say 6-12" from the sides and not get any bad effects?

-or-

How do I combine width and height to determine roll-off frequency?
do I add both values and divide by 2? or is there a more complicated formula?

??

What question are you responding to

 

[Beat_Dominator 5,000+ posts]

Could I extend baffles perpendicular to the front baffle down the back? say 6-12" from the sides and not get any bad effects?

I'm not totally sure. In a review of some SoundLab speakers a guy tried to add these side "wings" and he said it screwed up the upper bass really bad. I'd try to stick with a flat baffle if possible, unless you find something that says it'll work the other way.

 

[Beat_Dominator 5,000+ posts]

How do I combine width and height to determine roll-off frequency?
do I add both values and divide by 2? or is there a more complicated formula?

^ That one //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

 

[thadman 10+ year member]

//content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[Beat_Dominator 5,000+ posts]

open baffle designs are tricky //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

 

[thadman 10+ year member]

Is this right?

lets say 75hz (180.8"), 15/180.8 = 8.3% (12x needed, or -72dB @ 75hz)

24/180.8 = 13.3% (7.5x needed or -45dB @ 75hz)

37.5hz (361.6") 15/361.6= 4.15% (24x needed or -144dB @ 37.5hz)

24/361.6 = 6.6% (15x needed or -90dB @ 37.5hz)

so is it baffle width in relation to wavelength size -or- is it logarithmic in relation to the difference?

1(565hz=original baffle width of 24")- (6+ needed) -2x(282.5hz)- (6+ more, 12) -4x(141.25hz)- (6+ more, 18) -8x(70.625hz)- (5.25 more, 23.25dB) -15x(37.5hz)

-23.25 @ 37.5hz on 24" baffle

 

[Beat_Dominator 5,000+ posts]

I believe it's more like a log. relationship...... but I'm not 100% on that.

 

[thadman 10+ year member]

Yeah its logarithmic because the logarithmic equation corresponds to the 6dB/octave roll-off

 

[thadman 10+ year member]

75hz

15" baffle, 12x needed, -21dB

24" baffle, 7.5x needed, - 17.25dB

3.75dB gain from switching to 24" baffle

37.5hz

15" baffle, 24x needed, -27dB

24" baffle, 15x needed, -23.25dB

3.75dB gain from switching to a 24" baffle