Learning about folded horns

[lowerFE]

Hi, 

 

I'd like to learn about folded horns in detail to design a folded horn sub to go behind my couch. I'm thinking of using the Eminence LAB 12 driver in a 10 cu ft (or smaller, if possible) enclosure with a low frequency knee of 20Hz, and extension to at least 120Hz (150Hz preferred, so no tapped horns). If possible, I'd like to it to be as slim as possible, no more than 11-12'', preferably 10'' deep. 

Where can I learn more about how horns work and how to design a horn subwoofer?

 

Thanks

[LTD02]

grab a copy of hornresp if you haven't already.  plop in some values and starting playing around.  if the horn gets too long/thin, it may not load the driver properly, but I'm not sure precisely how to define for you.  a compression ratio of 3:1 should be fine and with a robust driver, a little higher may be ok. here is a quickie to help get you started, but it is larger than 10 c.f. (which is small for a 20hz front loaded horn).

 

[lowerFE]

grab a copy of hornresp if you haven't already.  plop in some values and starting playing around.  if the horn gets too long/thin, it may not load the driver properly, but I'm not sure precisely how to define for you.  a compression ratio of 3:1 should be fine and with a robust driver, a little higher may be ok. here is a quickie to help get you started, but it is larger than 10 c.f. (which is small for a 20hz front loaded horn).

 

 

I did get hornresp, but it doesn't help me much when I don't know how horns work. That's why I want some reading material so I understand how horns work before jumping into hornresp. 

 

On a side note, 10 cu ft is too small for a single 12'' 20Hz horn? The DTS-10 is only 9 cu ft per 12'' driver and it is a 14Hz horn. I know it is a tapped horn, but tapped horns can't be 50% smaller than a folded horn for the same tuning, are they? If they are that's incredible. 

[maxmercy]

Man, you have a lot of reading/learning to do.  Go to AVS and search the archives.  Terrific conversations and data.  Look for posts/threads from lilmike, maxmercy, soho54, billfitzmaurice, and especially TomDanley.  You have many hours of learning ahead of you.  Also search for folded/folding/horn/tapped/tutorial for other threads.  

 

If you are very detail oriented, have a science/math  background, and have lots of time and wood on your hands, you can become a competent horn designer/builder.  But make no mistake:  Your first horn WILL be your worst horn.  You will learn lessons, re-design, rebuild, and get better as you go.  If you think you can crank out a DTS-10 or F20 on your first try designing a horn, then you need to find another hobby.

 

If your time is more valuable to you than that, just hit the easy button and build a proven DIY design (limike has several, Ricci does as well), or buy a plan from Bill Fitzmaurice.  If your budget is large enough, forsake the horn and build a sealed system for greater bandwidth, or a vented system sacrificing bandwidth for SPL.  

 

If that last sentence did not make sense, then you have a lot of reading/learning/simulating/building to do. 

 

JSS

[lowerFE]

I'm well aware I can (and have the budget to) do build something better with other alignments of the same size. But since I found a way to hide the sub away by putting it behind my sofa, I no longer have to pour money into very expensive small subwoofers that I planned to build and my curiosity of getting max bass for the dollar is getting to me and I want to try this out. This is purely a (very fun) hobby.

 

Are there any books or papers where I can learn from the basics to the advanced?

[maxmercy]

Man, I wish.  There are papers here and there that are very mathematically rich, but don't give a lot to go by.  More practical papers are by Bruce Edgar, and Paul Klipsch.  No book I am aware of.  This is where lilmike could chime in.

 

I will tell you now, that you will likely lose money on the deal.  unless you build something that has already gone through several optimization iterations, you will be doing those iterations yourself.  It can be very fulfilling, but also frustrating as you realize you have just created a 20 cuft box of firewood, and likely toxic if burned (and you inhale the smoke) if it is plywood or MDF.

 

That being said, I have designed, laid out and built a horn from scratch; it was very fun to do, and I still use it.

 

JSS

[lilmike]

Not a lot to add to what has been said here, the salient points have all been mentioned.

 

Books, papers, and endless forum reading will only get you started, in my experience, there is simply no substitute for actually doing something. While you could just jump into the deep end, I'd recommend walking before you try to run. I started with small horns for a lot of reasons, but the biggest two were time and cost. A number of 1-day, 1-sheet builds have taught me a lot about what worked and what didn't.

 

One fundamental: Building a horn (or for that matter, any multi-resonant cabinet) without owning and knowing how to use measuring gear is a fool's errand.

 

Learn to accurately measure impedance, Thiele-Small parameters and SPL, in that order.

 

The gear doesn't have to be expensive, it just has to be functional and accurate. I've used my DIY mics and impedance rigs with free software and a $20 sound card and achieved results that were perfectly adequate for DIY work as well as entirely repeatable. Not nearly as dead-nuts as my $$$ gear, but 90% is an "A", and I was well above that point. 

 

Horn design for me is a trial and error approach. In my case, there have been plenty of errors along the road, I don't talk about those much, but they kept the shop warm for a while. Arauco makes for some expensive firewood.

 

Measure the driver you're working with.

Model the driver you're using.

Draw, then build the horn that you modeled.

Measure the results.

 

If the results match the simulations, great. If not, join the club. Then it is time to put on your thinking cap and figure out why.

 

Like any other enclosure out there, sub horns have their own set of weaknesses. They're not a full-bandwidth solution by design, and the laws of physics can be cruel in that regard. Stored energy can be a challenge. EQ can be a challenge. 

 

I design speakers for fun, I have for a long time. I've played with a LOT of different cabinet alignments over the years. Currently, I choose to play with tapped horns. We'll see what tomorrow holds when it gets here.