Using PVC Pipe For A Back Loaded Horn


2007-03-18 9:22 am
theres a transmission line or TQWT site that has a few PVC pipe enclosures. I can't remember the name of it. I think Mr Linkwitz also did something in PVC.

Back-loaded horn as opposed to transmission line needs to get larger toward the mouth. the cost of so many reducing elbows (which aren't made in big numbers) would be more expensive than wood.

You could use a larger pipe and make the taper by putting a partition inside at an angle a bit like the tapped horns or a folded voight pipe. If i did that I'd probably use sonotube instead, PVC gets expensive over 6 inches. I expect the expansion rate will mess up once you start using more than half of the cross sectional area of the tube.

Edit: here's the site I was thinking of, check out the seraphim, a TL but it will give you some ideas for working with PVC
Jim -

I've done a bunch of them.

OzMikes comments pretty much sum up conclusion and fit in with all the maths.

Think sheet metal dryer vent tubing , duct tape and paper mache. Cheaper to get proper flow of angles but too much work.

Easier and likely closer to correct maths simply cutting angles in whatever material you use.

I built an ABS horn once.

Hi I'm Rob Sampson the guy looking like a Taliban on his way to an audio DIY fest above. The horn, as I implemented it was pretty much a failure.
I used a base that featured an inverted U of 4in ABS with a length .5M. Onto that I placed, at the front, variously, straight or expanding taper ABS pipe sections of about 1M. On top of that I had an ABS Tee section with a driver mounting baffle at one end and a removable plug at the other. The removable plug facilitated changing the volume of the chamber behind the driver. The back end of the inverted U sported various configurations of 45 degree Tees. I started with one for a 1-2 expansion, then two more for a 1-4 expansion, four more for a 1-8 expansion. I stopped at a 1-8 expansion as the gaggle of 45 degree Tees was getting out of control.
I tried FR 125, FE127 and FE108 drivers. In all cases the response was lumpy in the extreme. The FE 108 was the worst; with an expanding taper and a 1-8 flare and a total length of about 2.2M there was no mid bass then a sudden excitation of the horn at around 70 hz. then quickly dropping off again. Very disappointing. The other drivers sounded better with no flare, in a straight taper T-Line configuration. The FR 125 was the best with a very smooth response down to just below FS of the driver.
I have stayed with TL configurations in this format since then.
Perhaps the constraints of the 4 in. pipe with regard to total volume of the system are dooming an ABS horn solution. I really don't know enough about horn theory to speculate.
Re: I built an ABS horn once.

Audio-Lego said:
Hi I'm Rob Sampson the guy looking like a Taliban


Thanks for the account of your experience with 4" PVC pipe. I am new to this hobby and I have a billion ideas rushing thru my head. Since I have yet to build my first real project I'm sure all of them are stupid.

The guidance of veterans like you is a huge help in sifting thru the BS and focusing on a solid project.
Re: I built an ABS horn once.

Audio-Lego said:
Hi I'm Rob Sampson the guy looking like a Taliban on his way to an audio DIY fest above.

I suppose that might look like a rocket launcher to someone who doesn't know better!

Actually Bob, I think you look like a fellow from the Avalanch Control Service out on duty caught in the headlights. :D

There is a story about how someone had their Bose Wave Bass Cannons confiscated at Israeli Customs because they were thought to be some sort of military ordnance.
The Japanese are still real big on this PVC thing.

Can't remember where but there's an American web site that wants big bucks for 'decorative' ones and likely selling a few monthly.

I messed a bunch with it til I realized there must really be something to this 'math thing'. Even pvc gets expensive. Rob - you were an inspiration to me way back when! I've cut so much pvc I now own the Worlds largest collection of small pieces .

Copy other peoples work and then paint flames, cars or women on them, it's your best bet!

I have done a few 'original' things that to even my surprise sounded pretty decent - pure luck! I'd never be able to explain to anyone why it actually worked.

My thought has always been conical.

As in, get a PVC tube the diameter of the driver, mount a long tapered cone to the magnet, following the expansion profile up until where it reaches the diameter of the tube (where the cone ends). Probably desirable to rig some sort of armature to hold the cone steady in the tube. Then, you couple this into a secondary flare, which comes forward and surrounds the driver, a pseudo coax arrangement like Pass' KleinHorn
found the nautilus pvc

loninappleton said:
There's that Nautilus one of pvc as well but I no longer have the
picture. Less cute than the Seraphim, but yes pvc up in the diameters needed to get a full throat is not cheap. As sculpture though, they are really impressive. Imagine a shofar or similar large mouth horn shape
in a spiral configuration.

Found it: PVChorn.html

There's the PVC "Periscope" at Full range diver forum hosted by James Melhuish as well.

Also the spiral horn which is a Japanese treatment:

One note on my own experience with PVC. I made a number of experiments with 4" pvc and my RS1197's.

I configured a TL length in pvc various ways-- even stretched out straight to 81 inches. This put the terminus up by the ceiling. Testing samples of pipe organ music is best for this sort of thing.

Then I gave the pipe and elbows to the recycle facility in Appleton.

Practically however, the BIB is a good solution. I think one motivation for the PVC experiments was lack of tools and ways to get wood cut (without going to a custom wood shop.) With PVC all you need is a hacksaw, some elbows and maybe a hole cutting set
with a 4" and 5" to make the baffle.

I'm still undecided about the Harvey style dual throat builds.
Rethm's Saadhana (and previously the "Second" and "Third") make extensive use of PVC pipe, cut and tapered for some portions of the BLH.

Rather a lot of painstaking work to maintain the consistency required for even a limited production product.

The powered bass portion of this current system uses more conventional wood materials.

I had the opportunity to hear a pair of the Seconds 5 years ago, (VSAC2003) and the memory of impression is still quite vivid - the almost electrostatic speed and transparency that they delivered in the midrange had, I'm sure, as much to do with the choice of driver and exquisite detail taken to mitigate its misdeeds with careful modifications, as did the particular materials used in the fabrication of the complex cabinet. At the same show ( and the prior in 2001 )there were several other Lowther based systems, including a small BLH demonstrated by the manufacture's American distributor. To my ear the Rethm is still the only Lowther system I could contemplate living with, but since my lottery numbers seem as jinxed as Hugo Reyes, (except for the winning part ) I'll have to be happy with DIY FE127 in bamboo / birch plywood cabinets.
Re: Re: found the nautilus pvc

wixy said:

I quite like the look of that, would be interesting to try!

Is there any science though to getting it 'right'?

Could I replicate something like that and expect a good result?

Maybe GM can chime in here. His recent tutorial remarks said that the
critical dimension is the horn mouth expansion in a Back Loaded Horn (BLH.)

The guy who made that Nautilus shows step by step how to do it
but he will also make one for you IIRC.

For total visual impact that one that Greg showed from the club in Japan (which also included a few construction shots) is the nuts.