Formidable Fostex Front Horn

[cervelorider]

3/4" Canadian Maple Ply Conical front horns utilizing the Fostex 126e. Combined with Eminence Alpha 15A's in H Frames and each powered by a 100watt sub plate amp. Horns are rolled off with a cap just above 200hz.
126e's powered by a 2.5watt 6CL6 spud amp.

[Josephjcole]

Interesting horns... can't say I've ever seen anything like them. Certainly no compression. How did you go about designing them? I would be interested in hearing your thinking behind them, and your listening impressions.
thanks
Joe

BTW if I had more money I would be a cervelorider too, as it is I'm just a cheap Hong Kong knock off carbon fiber rider...

[CLS]

Wow, how interesting! I bet it'd sound great

And reminds me of this: waveguided open baffle

and another B200 in dipole waveguide which I can't find now....

[nebojsa]

So how does it sound? What are the dimensions and how did you come up with the design? Looks very interesting. I just looked at your username, Cervelo? Nice. Great bikes.

[cervelorider]

I'm ashamed to say that I now ride a Postal Edition Trek 5200, but rode a Cervelo Soloist back when I created my screen name.

I built a large conical front horn a couple of years ago that was designed by my friend in Switzerland. He is a member here too and builds some incredible tube amps and open baffles. His design had different dimensions and I also made some novice woodworking errors during that build. Despite my goofs, it gave me a taste of the sound that could be achieved with a full range Fostex driver and large front horn. It kept my interest in pursuing one with a few modifications to the dimensions.
I’ve built numerous single driver back loaded horns, including various Nagaoka designs and three of the frugal horn designs. Four of which I still have in my room for comparison.
I’m also intrigued by some of the very large LeCleach horns, large Oris horns and the Klipsch Jublilee among other giant horns. I was also inspired by Bill Woods and some of his large, wood, conical horns. Like most of us audio diy’ers, I’ve poured through countless articles, threads and opinions on the web.
In the end, I based my design mostly around the three articles by J. Dinsdale and statements he made in his three part series.
I wanted to build it as big as I could for a low cut off, use a rapid flare, and still have it fit through the shop doors. I chose the 126e as it is one of my favorites of the half a dozen Fostex I’ve heard and its specifications lend itself to horn loading. (Planet 10 enabled 126en is sublime)
Tractrix, LeCleach & round conical horns were eliminated due to the complexity combined with my novice woodworking skills. Conical has its fans and detractors, but there is no arguing that it easy to build and that was a very important factor for me.
At present, I’m using a Bottlehead Quickie tube preamp with two outputs. One to the 6CL6 tube amp powering the Fostex Horns and the other to each of the two plate amps. I have a .0047 KimberKap as a high pass on the interconnects going from my source to my spud tube amp. The 100watt plate amps have their own low pass crossover, phase reversal switches and gain settings which has allowed a lot of flexibility in integration once placed in the room. Of course there would be other ways of crossing over, but this is the way I’ve chosen to do it for the time being out of personal preference, cost and “tweak ability“ in gain/roll off as placement of any horn I‘ve owned seems to be “fussy“ when it comes to room interaction and placement.
I would compare the sound of these horns with the 126e in an open baffle, but with more efficiency, dynamics and micro detail. In addition, the soundstage presentation is very, very big as one would expect with such a large horn. My ears don’t detect any honk or cupping sound. I’m not sure how much efficiency I’ve gained, but it is substantial.
There is a fairly large peak at 157hz, below the horn cutoff, without a filter, when they are run full range. With the high pass, the 150hz region is down 9db and is not an issue. The dipole H frames are exactly what one would expect if one has heard an Eminence Alpha 15a or other large open baffle suitable 15” on an open baffle. I’ve also heard the Hawthorne Audio Augie in my room when a friend brought them over. They are great sounding too, but I had two Alpha’s on hand from a previous open baffle build. No box sounds like no box. It is the most natural, uncolored bass I’ve had in my room so far and they integrate well with the horns.
My brain & ears really like this combination with all the music I‘ve played through them so far. Five other sets of ears, who have all heard my other speakers, have expressed positive impressions for what that is worth.

[Glowbug]

Now that's something I'd like to build

Do you have a bigger picture of dimensions?

[ScottG]

Treble response will be fairly depressed in level relative to the midrange with this horn.

As a potential parts swap, consider the Altec Lansing 204 (instead of the fostex):

http://www.altecpro.com/pdfs/CF204_SS.PDF

(..the CF-204 8A version, without the transformer.)

[planet10]

Derek, a fun project.

I'm glad the Dinsdale was useful. The one out on the net is a pdf i made (but didn't openly distribute because of potential copyright issues). It was a great help to me when i started playing with horns (my original copy was supplied by KEF in the documentation they supplied in the late 70s for dealers selling the KEF raw drivers)

dave

[tinitus]

Good to hear it works

[cervelorider]

Dave, thanks for posting the Dinsdale articles. I printed them quite a while back and forgot where I got them, but many thanks for making them available. I owe you and Scott at least a nice dinner and an entire evening's worth of drinks by now. How I wouldn't enjoy personally meeting both of you and making good on that payment.

Dimensions of the mouth are a 2:1 ratio, 24"x48". The side panels are 24" deep. The mouth is 5.5" tall by 6.5" wide. Center to center of the top and bottom panel is 29.75 inches. The dimensions lend themselves to good use of a 4x8 sheet of plywood. I cut the side panels first, laid them in a jig with a center post the size of the mouth opening. If one looks at Bruce Edgar's midrange horn article, there are photos of his jig. Mine was just a whole lot bigger, but the time it takes to build the jig is necessary IMO. It keeps everything aligned. I leaned the side panels against the post and then used an angle finder to figure the bevels on the top and bottom pieces, as well as the bevels on the mouth end of each section. I'm sure there is a better way to calculate the bevel angles, but let's just say I have a brain that does better with art than math. I could probably measure them now with a protractor if someone wants to duplicate this build.
I rounded all the mouth edges, but I'm not certain how much of a part this plays in the sonics on a horn like this. Looks nicer though.
The stands were designed & built to bring the driver to a height of 32" at the center.

Regarding the highs, I'm measuring highs into 16,500hz before they start to roll off signficantly in comparison to the mids. Cymbals sound very natural too. The 126en has always been one of my favorites when it comes to the highs. My pet peeve is splashy, unatural sounding highs and Planet 10's 126en doesn't have that quality!

BTW, these are off the charts in negative WAF points.