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25th October 2018, 11:07 PM  #1 
diyAudio Member
Join Date: Oct 2018

Horn Sensitivity calculation
If we take a look at a driver datasheet here: Specification
We can see that it specifies a 114dB sensitivity for a 90×75° CD horn. Does this mean that we can get up to 130dB of sensitivity in a narrow horn, like the 13° maltese horn? The rule of thumb I'm using here is that for every halving of the horn radiation angle, we get a 3dB boost. Because the 13° horn has almost 1/40 the angle, it gets 16dB louder, thus the 130dB sensitivity. Something is not right here! AFAIK no one has reached this SPL at 1 watt! 
26th October 2018, 04:19 AM  #2 
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Join Date: Jun 2003
Location: Chamblee, Ga.

Well, a PWT is 0 deg and the driver is 118 dB/mW, so at 1W it's going to be 1000 times more = 118+30 = 148 dB in theory, so 13 deg will be somewhat less as you noted.
GM
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26th October 2018, 06:03 AM  #3 
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Join Date: Oct 2018

I just can't believe the number!

26th October 2018, 07:28 AM  #4 
diyAudio Member
Join Date: Oct 2013

A 13 degree horn will be huge. If it must hold its pattern down to 1 kHz, it will have a mouth diameter of 2 meters. And then the length..

26th October 2018, 08:27 AM  #5 
diyAudio Member
Join Date: Oct 2018

Nooo... Weltersys' Maltese horn has good specs at a relatively small footprint ( pics below). Also, It's easy to build and doesn't take too much time and stuff... I would love to build something that produces deafening sound levels with just a few milliwatts...

26th October 2018, 09:11 AM  #6 
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Join Date: May 2008


26th October 2018, 09:19 AM  #7 
diyAudio Member
Join Date: Oct 2018

And another thing I looked through other BMS products and noticed they have tested their bigger drivers (4599, as an example) using much more narrower 20×40° horns...
If the 4540 could approach 130dB/w.m so easy why BMS didn't publish the amazing numbers as an advertisement? No I don't think so. This driver gives 114dB through a 90deg horn, 118dB/W is too low for its PWT, IMHO. 
26th October 2018, 10:39 AM  #8 
diyAudio Member
Join Date: May 2008

Compare to the other BMS spec sheets.

26th October 2018, 12:23 PM  #9  
diyAudio Member
Join Date: Oct 2013

Quote:
The dispersion angle can be approximated by: angle [deg] = 25400 [m*Hz*deg] / (horn width [m] * frequency [Hz]) Last edited by TBTL; 26th October 2018 at 12:26 PM. 

26th October 2018, 10:26 PM  #10 
diyAudio Member
Join Date: Oct 2018

Interesting equation! It seems like the iron law for horn directivity but where does the constant number come from? And what about horn length and flare rate? Should I just go simple and assume the radiation angle is the same as horn angle?
And what is this angle exactly? Is it the 3dB angle or the 6dB or... I'm curious because at 2KHz the angle is still under 40° which is pretty impressive. Also, this reminded me of hailing devices. I now looked among some of them and they were claiming strange specs like 30° directivity at 1KHz with a tiny hand held device. What is going on with them? That is soo far from what this formula suggests. The horn size of theirs sets them off orders of magnitude and exponential flare rates and EQ is of little help at this situation. HS10 (Bullhorn / Megaphone Replacement)  HyperSpike(R) 
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