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2017/04/27 updated

SS-307: Three-way Loudspeaker System

SS-307Description: Three-way loudspeaker system. LS units: Fostex T925 (horn-loaded tweeter), Fostex 6N-FE88ES (3.5" full-range), Fostex FW305 (12" woofer). Enclosures: vented (midrange), vented (woofer).
Dimensions: Midrange box: 400mm(W) x 185mm(H) x 270mm(D). Weight: ?kg. Woofer box: 400mm(W) x 710mm(H) x 290mm(D). Weight: ?kg.
Cost: approx. 120,000 yen.
History: Made in 1982. Improved in 1984 (Rev.A), 1993 (Rev.B) and 2000 (Rev.C). Discarded in 2001.

Photo: SS-307C in 2000.


Three-way loudspeaker system that meets the requirements specified in the Gaudi system design.
Multi-enclosure scheme is employed to make future upgrades easy.


Selection of key parts

I used used loudspeaker units (LS unit), because I didn't have a deep pocket. So the range of the selection was limited.
As for the woofer, I had decided to use a 30cm (12 in.) woofer in the system design. I looked for used ones in a good condition. I happened to find a pair of Pioneer PW-A31 in a classified ad of an audio magazine (MJ). The ad said the pair was nearly new. The seller was an audiophile living in the same prefecture. I contacted him without hesitation and he agreed to sell them to me. I don't remember the price exactly, though, it may have been the half of the original price.
For the midrange, I chose Fostex FE106 Sigma (4 in. full-range) I had bought for another loudspeaker. Because I couldn't afford horn units at that time, though they were cheaper than today.
I employed dome tweeters instead of horn type, since dome type was a lot cheaper. It was a Technics. I forgot the model number. It looked like an expensive one. I bought them at a junk shop in Akihabara. I forgot the price too, though, it must be cheap. The specification was unknown, but I decided to use them, since tweeters with lower sensitivity than the woofer can be used in multi-amplifier systems.

All the LS units were replaced afterward for upgrading. I replaced the tweeters with long-sought horn tweeters. But I couldn't afford midrange horn units until I got ones for next loudspeakers (SS-309).
The final configuration was as follows:

I selected lauan plywood board for the enclosure material, because it was available at a nearby lumber shop and easy to cut. I didn't consider other materials.

Design of the woofer box

I designed a slit vent bass reflex scheme for the enclosure of the woofer (woofer box). The slit vent has high air resistance and damps resonate of the vent. I expected tight bass sound.

I designed the slit vent according to my "textbook", written by Japanese audio experts and edited by Dr. Takeo Yamamoto of Pioneer Corp.
Though dimensional error affects the characteristics of the slit vent more than those of ordinary pipe vents, I didn't care much about it.

The tweeters were mounted in the woofer box. The Technics dome tweeter was designed to be mounted on the baffle from behind. Without counterboring, it would be deeply sunk from baffle surface. So I made sub-baffles of aluminum board, and mounted the tweeters on the sub-baffles. I mounted the assembly on the main baffles.

Not to take trouble, I didn't paint the woofer box.

Design of the midrange box

I didn't take account of bass response since it was the midrange module though the LS unit was full-range type. This enclosure was a sealed-box and relatively large for FE106 Sigma. A filling was stuffed to prevent standing waves.

The midrange box wasn't painted either.


I cut the plywood boards with a power circular saw I borrowed from my friend. I made the cutouts for the LS units with a padsaw.

My Own Review

完成直後のSS-307(1982年)I was unable to check the operation of the bass reflex vent, because I didn't have measurement skill at that time. But I was impressed by its extended and powerful lows. I thought it was a good decision I chose the large woofer.
Thanks to the deep bass, Hard rock music became one of my favorite kinds, though I hadn't liked it until then. Especially, I was charmed by The Knack's My Sharona (FM air check).
There was one catch. The bass sound was dull. I think it was caused by poor sound quality (SQ) of PW-A31 around the cross point. The guy who sold it to me also said he wanted to sell it because he didn't like its dull sound.

I installed SS-307 in the living room after I got married. My wife complained a lot about its shabby looks and told me not to place junks like this in the living room.
I was determined that I would build better looking loudspeakers.

(Photo: newly built SS-307 in 1982)


Rev. A: Upgrade of the tweeter (1984)

The dome tweeter was replaced with Fostex T925 (horn tweeter).
T925 was designed to be placed on the top of the enclosure. I did so.
I left the dome tweeter on the woofer box as a blanking plate. I removed the wire for the tweeter only.
SQ was significantly improved. Gaudi became a hi-res system just like a multi-amplifier system.

Rev. B: Upgrade of the woofer (1993)

I replaced the woofer when one of Pioneer PW-A31 was broken.
At that time, only Fostex and Technics produced 12" woofers among Japanese audio manufacturers. I chose the most inexpensive one: Fostex FW305.
The frame diameter of FW305 was smaller than the diameter of the cutout for PW-A31. So I made sub-baffles for FW305, and attached them on the baffles of the woofer boxes. The sub-baffle covered the slit vent. I fixed a pipe vent at the position where the dome tweeter was mounted.
SQ was improved by a notch. Bass was no longer dull.

Rev. C: Upgrade of the midrange units (2000)

I wanted to improve SQ more. I replaced the midrange units.
I had two pairs of full-range units that I happened to spot at an audio shop at Akihabara District and bought when I went there to purchase audio parts. They were Fostex 6N-FE103 and 6N-FE83ES. They were both limited-production.
First, I tried 6N-FE103, of which dimension is exactly equal to that of FE106 Sigma. But I felt SQ was worse.
So I decided to use 6N-FE88ES. Because its frame size was smaller than the cutout for FE106, I made a sub-baffle and attached it on the baffle of the midrange box.
I took this opportunity to add a vent to the midrange box. Now the midrange module could be used as a full-range module too.
SQ was apparently improved. 6N-FE88ES had high SQ in high band as if it could be used as a tweeter. This fact may improve total SQ.
In return for the good SQ, the looks of SS-307 turned to be worse and worse. The multiple upgrades made it so patchy.

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