The Rat Pipe – An Internet Bred, Super-Low Budget, Full-Range Rodent that Delivers the Goods
by Dave Taylor, Lafayette, Colo
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Some Colorado Audio Society members, just like me, have no doubt wanted to experiment with and get a taste for full-range drivers, but may not be quite ready to take the plunge into purchasing those Lowthers just yet. Here’s a way to sample the full-range menu, learn about speaker design, and have some rewarding fun. Cost will be about $50, along with eight hours or so of your time. I think you will be surprised at the ROI.

I must confess to being a DIY Internet junkie for speakers and tube amps. I spend a good hour a day on DIY forums checking out the latest banter and designs. Talk in the Full Range Driver Forum and elsewhere on the merits of the Radio Shack (Rat Shack) 40-1354a driver intrigued me. I have built traditional 2-ways and subwoofers, as well as push pull EL34 based amplifiers, but the SET renaissance and heightened interest in full-range speakers began to pique my interest. And, after all, is there a better way to spend a weekend than breathing the MDF dust flying off the old Craftsman radial saw and router?

After reading reports from NY Blast, an annual single-end tubefest, and then reading Herbert Jeschke TQWP (tuned quarter wave pipe) article on the Full-Range Speaker web site, I figured how could I go wrong at a price of $13 for the Radio Shack 1354a drivers.

(Okay, now that you have picked yourself up from the floor and stopped guffawing about the fact we are actually conversing about a $13 Rat Shack driver, read on.) As further assurance of this “el cheapo” driver’s sound quality, a group of audiophile listeners had actually voted Herb’s speaker best sounding at NY Blast. We’re talking Rat Shack consensus! So something must be right in this driver, I concluded.

Some further Internet snooping scored an excel program by John Rutter that calculates design parameters for folded TQWPs. Essentially, in the folded design, one just takes a full-length pipe like Herb’s and bends it over onto itself. After a quick download, I plugged in the parameters of the 40-1354a and had my design. Internal dimensions are:

Height:
37.3” (I rounded to 37)

Width:
5.25”

Depth:
9.12 inches (I rounded to 9)

Port Height:
5.25”

Port Width:
3”

Volume:
1628 cubic inches or 26.7 liters

Pipe length:
67.7”

Driver position:

29.3" (I rounded to 29.25) from the top of the port, or 33” from the bottom of the speaker.

I was next off to Home Depot for some ¾” MDF to add to the scraps I already had in the garage. One 4’ x 8’ sheet will do the job for two speakers (yes I know one side is an extra inch longer).

For a pair of speakers, I cut the following pieces:

(4) 6.75” x 37” for baffle and back
(4) 9” x 37” for sides
(4) 6.75” x 10.50” for tops and bottoms
(2) 5.25” x 29.5” for the inner panels
(2) .75” x 5.25” for throat piece

External volume of the speaker comes out to 38.5” high, 6.75” wide and 10.5” deep. This makes for a very attractive sized floor stander. At 33 inches from the floor (when not using spikes on the speaker bottom), the center of the driver is positioned near optimum listening height.

I joined all the MDF panels with standard wood glue and drywall screws. I wanted to build this baby in one day so I did not bother with clamps. I ran the screws into pre- drilled holes and counter sunk them. About one screw every three inches. While all looked air tight, I ran a quick bead of some Elmers squeeze caulk along all the internal corners to make sure.

I did not glue the top or bottom plates, as I wanted access to fill the line if necessary. To keep things airtight, I put some gasket material between the top and bottom panels and side walls and front. When screwed on, they were airtight.

I routed a flush mount for the driver on the front baffle. On the back of the speaker, about 2/3 the way up (makes no real difference other than how much hookup wire you want to use), I stayed with the Radio Shack theme and mounted a pair of RS binding posts. I had to route out a recess to flush mount them, as their posts are not long enough for ¾” MDF . My only variance from the Rat Shack theme was to use some inexpensive Monster speaker cable I had lying around for my hookup wire. It was soldered on with RS solder though, and a very cheap soldering iron to maintain the no frills, no pedigree, el cheapo approach.

I took Herb Jeschke’s advice and damped the pipe areas behind the driver. But instead of his recommended carpet, I used 1/8” thick foam from my local hardware store for about 12 inches on the front pipe’s back wall, and for about 12 inches down the back pipe’s rear wall. Below that for the remaining length of the back of the front pipe I glued felt. I also applied felt to the back of the rear pipe below the foam for another foot or so. No science was involved here, just what looked good. Total cost for foam was $2, and felt was about $2.50. 3M spray adhesive stuck it on nicely.

I stuffed the rear pipe section with some old fiberglass insulation I had in the garage. Stuffing was light to moderate. No science, just what kind of looked good.

After soldering the hookup wire to the drivers and mounting them with small drywall screws, I was ready to rock and roll. I used cheap, adhesive-backed weather stripping as an airtight seal behind the drivers,

I hooked them up to my home-brew EL34 push pull amp that runs through a Dyna PAS 3 preamp and Pioneer DVD player (el cheapo 24/96).

At first, the sound was a little thin. But as driver break in quickly occurred, these babies really came to life. I suggest a minimum of 4-6 hours of listening for break in. So what are their sound qualities? Quick, tight bass. It doesn’t go to the lowest octave, but what is there isn’t bad.. Very nice mids, and the highs are there also. I see no reason (make that hear no reason) to add a tweeter. Very nice pace and rhythm. Good detail. Nice layering of textures. A very lively sound. Virtually no fatigue. They really make some nice music. For a total of about $50 invested, these are speakers that deliver. And that is a fairly ridiculous – if not preposterous -- statement given the cost of the Rat Pipes.

To verify my ear’s findings, I invited over my audiophile neighbor who is also a musician. He has a tube system worth about 20K – C-J amp and pre, Meridian CD and Project turntable, B&W Matrix and Theil speakers. He was pretty impressed. But he flipped when I showed him the box that revealed it was a Rat Shack $13 driver. “It’s a trick! It’s a trick!” he exclaimed.

No trick.

I did not tweak the drivers in any way. At least not yet. But some treat them with a layer or two of Damar varnish. Nor have I listened to them on solid state, an amplification medium not suited to my genetics.

I’d have to say if you want total bang for the buck, as well as a chance to make a go at DIY speakers and TQWP design, give the Rat Pipes a try. What have you got to loose? In all candor, I have heard $1,000 speaker that cannot come close to these little babies. Will they sound like Ron Welborne’s Oris Horns or replace your current main system speakers? No! Nyet! Of course not!!! But for some rock bottom el cheapo experimental fun, you can’t beat the Rat Pipe.

Praise and thanks to Messers Jeschke and Rutter, as they are the true design impetus and gray matter behind the Rat Pipe. I will try and get some photos posted in the weeks ahead.

So, fellow Colorado audiophiles, throw some caution to the wind, plunk down your hard earned $50, break out the circular saw, and crank out some Rat Pipes