No graph here, but the math is quite simple to get you in the ballpark. The speed of sound is about 13,500 inches/second. Elevation in relation to sea level and atmospheric conditions can change that but it's close enough. A conical horn (os approaches conical near the mouth) will have a usable -6dB point that defines the coverage angle down roughly to the wavelength of the mouth diameter. Let's use a 15" round conical horn as an example. 13500"/15"=900hz - meaning that 15" is about the wavelength of 900hz and is a reasonable assumption for the lowest the horn will hold the pattern if it's designed correctly.
You can use this as a rough guideline for a direct radiator in a box as well. The wl corresponding to the piston diameter will give you an idea of the -6dB point where the driver will have a 90° pattern. We'll use a 12" woofer for this example. 13500"/12"=1125hz. This is about where a 12 will be at 90°. Being a direct radiator the beam is progressively narrowing so it's not going to stay at 90.
These are, of course, rough (notice how many times I've used that word!) guidelines but they are useful when considering if something is worth trying or not. Do the math, and you can see that an 18" wg is not a good match for an 8" woofer if directivity matching is important to you. Exact details of the actual device in question can change things a bit as well.
You can use this as a rough guideline for a direct radiator in a box as well. The wl corresponding to the piston diameter will give you an idea of the -6dB point where the driver will have a 90° pattern. We'll use a 12" woofer for this example. 13500"/12"=1125hz. This is about where a 12 will be at 90°. Being a direct radiator the beam is progressively narrowing so it's not going to stay at 90.
These are, of course, rough (notice how many times I've used that word!) guidelines but they are useful when considering if something is worth trying or not. Do the math, and you can see that an 18" wg is not a good match for an 8" woofer if directivity matching is important to you. Exact details of the actual device in question can change things a bit as well.
These are my 300Hz conical horns I built. They need some tweaking to get them sounding good.
The horns acoustic cut-off is 300Hz, the driver can play down to 500Hz, and the diameter is about 15". Using your math
13500"/15"=900hz - Is this the ideal XO point
The current woofer is a 10" driver
13500"/10"=1350hz, Would you cross over at 900hz and avoid it beaming at higher frequency?
I guess the ideal size driver for a 15" horn @ 900Hz is 15" woofer?
If I wanted to go lower with the conical horns, because the the horn and the driver are capable, is it best to match the xo to the woofers?
An externally hosted image should be here but it was not working when we last tested it.
The horns acoustic cut-off is 300Hz, the driver can play down to 500Hz, and the diameter is about 15". Using your math
13500"/15"=900hz - Is this the ideal XO point
The current woofer is a 10" driver
13500"/10"=1350hz, Would you cross over at 900hz and avoid it beaming at higher frequency?
I guess the ideal size driver for a 15" horn @ 900Hz is 15" woofer?
If I wanted to go lower with the conical horns, because the the horn and the driver are capable, is it best to match the xo to the woofers?
Does great sound count?
These drivers (Radian 850pb 1.5" modified) sound really good low, accidentally flicked them onto full range and at quite volume they sounded pretty good.
My main target was to go as low as practical. I figured with an acoustic cut-off of 300hz, they should be crossed over about 500-600Hz.
How best to mate a 1.5" exit driver on a 15" conical horn to woofer for as best constant directivity.
These drivers (Radian 850pb 1.5" modified) sound really good low, accidentally flicked them onto full range and at quite volume they sounded pretty good.
My main target was to go as low as practical. I figured with an acoustic cut-off of 300hz, they should be crossed over about 500-600Hz.
How best to mate a 1.5" exit driver on a 15" conical horn to woofer for as best constant directivity.
I have found that directivity has to be measured. Rules-of-thumb are fine for estimates, but if you are looking to do the best job possible then you must be dealing with reality and accurate data. Conical drivers are seldom the directivity that one would expect from the simple flat piston model and waveguides near there lower operating range are never very predictable. An "acoustic cutoff" of 300 Hz says nothing about the directivity at 300 Hz or any other frequency. The two things are completely unrelated.
So unless you have actual measurements, the higher resolution the better, "constant directivity" design is a wild guess.
So unless you have actual measurements, the higher resolution the better, "constant directivity" design is a wild guess.
True, forgot that detail about directivity. I guess if one want same or higher directivity in a smaller size one has to go cardioid or dipole.
Soon, when my dipole is assembled I'll have to do some measurements and send them so they can be thrown into polarmap. Would be interesting to see if there are any major problems left to solve.
To me the sole remaining problem is how to make an NA12 cheaper. It doesn't have many flaws otherwise.
I seem to stick to the usual, cross a 15" at 750-800hz, 12" at 1.2khz, 8" at 2khz, all at 24db/octave.
But when I want to crank my double 15's as loud as they will go, I spin the crossover up to 1khz (to save my 1.4" compression driver).
Then again, if I had a larger mid/tweet horn (say a 2352) then I might cross to the 15's lower (maybe 500hz-650hz).
Norman
But when I want to crank my double 15's as loud as they will go, I spin the crossover up to 1khz (to save my 1.4" compression driver).
Then again, if I had a larger mid/tweet horn (say a 2352) then I might cross to the 15's lower (maybe 500hz-650hz).
Norman
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