Additional Chapters by lilmike:
Tapped horn tutorial:http://www.avsforum.com/avs-vb/showt...4#post17835074
OK folks, as promised, a simple HornResp Tutorial for how to design an offset driver, conical, front loaded horn.
Here are the basics:
The Left purple and blue areas are the horn 'throat', the Rightmost area is the horn 'mouth'. The S1, S2, S3, Vrc and Lrc are parameters we will change in hornresp to design a horn....
OK, here's the hornresp input box:
The driver I chose is the 12" Dayton DVC, so go ahead and fill in its parameters in your hornresp program....and double click the 'Nd' until you get an 'OD' like you see circled....
Now, lets get the OD letters to turn black, to say everything is OK with the inputs. Input the following values for Ang, Eg, S1, S2, S3, S4, L12, L23, L34 and Vrc and Lrc (see pic below):
What we're inputting is that the horn is standing in a field with no boundaries nearby (Ang), and that we are feeding the driver 2 Volts. We are also saying that the horn has a straight throat chamber (areas S1=S2=S3) where the driver will mount, and there will be 20cm in front of the center of the driver cone, and 20cm behind the center of the driver cone. I chose 20cm to give a little room past the driver flanges. The horn flares from 100sqcm (S3) to 1000sqcm (S4) over 400cm of length. S1 to S2 is the blue part in the above diagram, S2 to S3 is the purple part, and S3 to S4 is the yellow part. Vrc is the volume of the rear chamber, and Lrc is the height of the rear chamber.
MAKE SURE YOU DOUBLE CLICK on the L12, L23 and L34 boxes so that they say CON, so you can enter a length.
Here's what you should have so far:
Now click 'CALCULATE' and say 'YES' to the suppression of rear chamber resonances....and you get an spl graph.
You can see the response is far from ideal, but this is a tutorial on what you can adjust, and what it does....
So, lets adjust one factor at a time.
To adjust throat volume, make S1=S2=S3, and make them all the same value. In this case, I am doubling them:
And the change in response (original response in grey).
You can see that the low end of the response smoothed out some! By making the throat smaller than original, it will make the response peaks bigger.
So, what happens if we change the mouth area (S4)?
S4 has been doubled.
Here's what we get (original again in grey):
You can see that adding mouth size increases sensitivity and the height of the peaks and valleys, and decreases extension...
Now, what about length (L34)?
Horn length (L34) has been doubled, here's what we get (original in grey):
Response is just about as ragged, but you gained extension to lower frequencies....
Now, here's what happens when you change the size of the driver chamber (Vrc):
We have made the chamber 1/2 as small as before. Here's what we get (original in grey):
By making the driver chamber smaller, we get a 'boost' in response at the 'low corner' of the horn, before response drops off the cliff. To tame that boost, simply increase rear chamber size.
So, let's say you want a horn that will play well to 30Hz (for recorded, bass-heavy music, but no movies). We play with ONLY 4 THINGS: Throat chamber size, Mouth Area, Length, and Rear Chamber size. A bit of fooling around, and I get this (took 3 min):
Which gives this for response:
The box is 262 liters. Compared to a DVC in a 100 liter box:
Compared to two DVCs in 100 liter boxes (with 2V into each):
Compared to three DVCs in 100 liter boxes (with 2V into each):
So it takes 3x the drivers with 3x the power in sealed boxes to get close to the same sensitivity as the horn.
But what about max output/excursion?
Xmax limited output for the horn (around 22V in):
Now, the three sealed boxes output at Xmax (18V into EACH BOX):
Now you're raising your BULLSH*T FLAG....."The excursion max is at 10Hz, way below the 30Hz you need, you dumb*ss!!!"
Yup, you are right. But look at the excursions for both the three sealed and the horn at 30Hz..... they are just over a milimeter or so of each other.....So I consider it a decently fair comparison, hypothetical though it may be.....and, for the record, I didn't optimize the sealed box for the DVC. 100 liters seemed like a nice round number.....
But you get the point. With a horn, you get more ragged response, a larger box, but more output in a passband with less power.
But how often will you play your sub in an open field? Chances are, not very....so you can change the 'ANG' parameter in hornresp to show you how the sub will play when next to a wall (1.0 x Pi), or in a corner (0.5 x Pi). Here's the same 30Hz DVC 12" horn inside in a corner, with only 2V in, compared to it in an open field (open field in grey):
You can see that the difference is HUGE. You not only get more output, but the response is smoother, and you get more extension! To get the same performance in an open field, you'd need 4 of the horns stacked together....boundaries are good for bass with standard speakers, but GREAT for bass with horns...
Hope this helps folks.....