Originally Posted by Mfusick
Ok take a look at this:
School me up on how I should be thinking. Couple specific things I'd like to know is:
What controls the tuning ? How do I adjust the low corner up and down?
What controls the height of the peaks and valleys ? How do I smooth things out ?
Is there some kind of "auto calculate" way I could find the optimal result for a specific driver at a specific tuning ?
First of all, go back to the design tutorial, but instead of 'CON', make the segments 'PAR'. I wrote the tutorial 5 years ago, and HornResp is a much nicer program now. PAR will more accurately model what you build (2 parallel sides, flaring in one dimension). Also, Make the Horn an 'OD' horn, by double-clicking 'Nd' until it reads 'OD'.
From the 'Input Prameters' page, go to the 'Loudspeaker Wizard'. You can then use sliders to control each variable.
Tuning (low corner) is a function of horn length and flare rate (how fast it gets bigger).
The peaks and valleys are controlled by controlling each parameter. It is a series of tradeoffs. To get one thing, you often have to give up another. Use the sliders and see what I mean. Start with the 'S1=S2=S3' throat like in the tutorial, and only play with L23 and L34 and S4. Make S1=S2=S3 slightly bigger than 1/3rd the Sd of the driver (this sets the compression ratio), make Vrc 100L, and play with L23, L34 and S4. You can see that by changing the length and flare rate (by changing the mouth area), you can change the tuning, and you adjust the ripple amount. making the throat longer and shorter changes the ripple amount.
Then, you can change the compression ratio. You will find that smaller compression ratios give you better looking responses, but it comes at a cost. More distortion, and when you build, you will not get what you modeled at higher SPL, too much 'friction' in the horn to put it plainly... I use a compression ratio less than 3 for 15" drivers, and less than 2.5 for 18" drivers. For 12" and smaller, you can increase the comp ratio to a certain extent. This is where trial and error rule supreme. I always err on the side of a larger comp ratio. That means a larger box. But to play low, you need enormous, VERY well braced boxes. If you can feel a panel vibrate on a horn, that is lost SPL out of the mouth.
You have lots of fooling around to do with hornresp. You will soon graduate to varying the size of S3 and adding another segment to further control the horn once you know what you are doing with the simple horn.
Although the hornresp-included tutorial/help is cumbersome, read it and look up the terms you do not understand.
I like OD horns because they are easy to design and fold, but they have to be much bigger or used in multiples for the same SPL at the same low corner as a TH, and highpassing for excursion control is optional if you will not flood them with power. I do not like THs as much because they are harder to fold, and expose one side of the driver to the 'air', increasing directly radiated distortion components that are lowpassed in the OD horn by the horn itself...and highpassing for excursion control is usually not optional. That said, THs are one of the most efficient ways to get mammoth SPL at a certain low corner in the least cuft without having to use multiples, and with little power. Because they have no rear chamber, you essentially use that space for more horn. There are also time domain issues, but these are all the tradeoffs inherent in designing a subwoofer.
Get some measured T/S specs and get to crackin' and moving those sliders around. You can do much better than the model you posted.
As you can already tell, you will find a model you like. It will change about eleventy billion times, then you will finally translate that model into sketchup and fold it, and build it, and measure it. You will learn lessons, and repeat the exercise until you find something that will work well and fits your needs, then build 8 of them and collapse your house.