|Description: Single Driver speaker system. Driver: Fostex 6N-FE103 (4" full-range).
Enclosure: vented type (rear port).
Dimensions: 164mm(W) x 630mm(H) x 216mm(D). Weight: 6.6kg.
Frequency range: 80Hz-20kHz.
Sensitivity: 90dB/W (@1m).
Cost: approx. 15,000 yen (excld. drivers).
History: Made in 2006. Now used in the 2nd system for the study room.
This speaker system is planned to be installed in the second system in
my study room and used for enjoying music in a lighthearted mood. Unlike
the main system, Gaudi, the system's goal is replaying easy-listening music
in good sound quality at relatively low volume.
The period during which I designed and built SS-312 overlapped my long sick leave. I supposed it as sort of rehabilitation. So I didn't try to build a complicated and difficult-to-build speaker system but simple one.
My plan was building a pair of compact speakers with a single full-range driver for each.
I just had two units of Fostex 6N-FE103, which I had bought for the midrange driver of SS-307. I tried it out but stopped using it soon because of its poor sound quality.
I expected that it was a good full-range driver even though it was not satisfactory as a midrange driver.
It was rather troublesome to build stands for the speakers separately. I planned to combine the enclosure and the stand.
As mentioned above, the drivers are a pair of Fostex 6N-FE103 I bought
This is a limited-production model. The table below shows its specifications:
|Lowest resonance frequency (ｆ0)||90Hz|
|Reproduction frequency response||f0-20kHz|
|Sound pressure level||90dB/W(@1m)|
|Effective diaphragm radius (a)||4cm|
|Recommended enclosure type||Bass reflex|
|Recommended enclosure internal volume||6l|
|Baffle hole diameter||93mm|
I decided to use Mogami NEGLEX 2497 for the cables, which was left over when I built SS-309.
For the material of the enclosure, I chose 15mm thick lauan plywood, because it is easy to cut and finish.
To achieve enough volume of bass sounds with a small enclosure, I chose
bass reflex type enclosure.
The goal was that the bass band should be extended down to at least 90Hz at full level. I'm sure you won't feel lack of bass sounds if bass is extended to the 90Hz band, as long as you're listening to background music.
The dimension of the enclosure is almost the same as the one recommended by Fostex. The only exception is the dimension of the bass-reflex port (vent) and its position. It is placed in the rear baffle (backboard) like SS-309.
The joints are not processed in particular. The boards are simply glued by wood bond. Though wood screws are also used, they are only a supplementary means. The purpose of them is to keep holding the joints till the bond dries.
One of the side boards is not glued, and fixed with wood screws only. For most speaker enclosures, the backboard is detachable, though, the side board is detachable for SS-312.
This construction is just the same as SS-309 so that I can assemble the enclosures in the familiar process.
I made use of a PVC tube for water pipe as the bass-reflex port by cutting it into the desirable length.
The front baffle is made of two boards one on top of another so that it can hold the driver firmly.
The bass-reflex port is designed so that the port resonance frequency (fb) becomes the same as the recommended enclosure.
First, I calculated fb of the recommended enclosure and it was 87Hz. The dimension of its port was 50mm(D) x 88mm(L). The PVC tube's internal diameter (D) was 56mm. Then, I calculated the length (L) that made fb=87Hz, and it was 115mm.
The enclosure is so small that I omitted bracing.
All the parts for the enclosures except the ports are cut out from one standard 15x1820x910mm lauan plywood board.
[Dimensional drawing and cutting plan]
As sound absorbing material, I used Nihon Muki Micron Wool again as in the SS-309 project. The quantity was small.
The building procedure is the same as SS-309. I intended to maximize assembly accuracy by employing the familiar process:
(1) Put one side board (hereinafter referred to as the fixed side board) on a level workbench. (2) Assemble the parts except the other side board (hereinafter referred to as the detachable side board) on it using wood bond. (3) Slide each part to make the baffle side flush. Since the parts are not mortised, they can be slid a bit while the bond is wet. (4) Make flush the top board side. (5) Screw all the parts with each other.
The kerfs that joint the detachable side board are made flush with a sander, and insulating tape is affixed to retain the box air-tight.
As for the finish, I chose the way that doesn't take much labor and time.
The lauan plywood had beautiful grain. I decided to spray it with colored varnish after sanding the surface of the enclosure lightly.
The grille was a genuine part of Fostex (I've forgotten the model number).
It was fixed together with the driver.
The cable was soldered directly to the terminal of the driver. If the cable should be replaced afterwards, it would take much labor. But it was not so possible for SS-312. And, by omitting terminals, the cost can be reduced. So I chose this type.
I bought the plywood board and had it cut at the do-it-yourself store nearby
where I did the same thing in the SS-309 project.
The guaranteed maximum error was 1mm, but I didn't find any error (maybe 0.1mm or so).
I bored the cutouts for the drivers and the ports by myself.
I also cut the PVC tube for the port by myself.
I assembled the enclosures in the procedure I had planned.
Before assembling the enclosures, I fixed the bass-reflex port with bond. The port stuck out a little so that the length of the port could be adjusted later by cutting or extending the pipe.
The fixed side board was put horizontally, the baffle, backboard, and top and bottom boards were put vertically on it, and the parts were glued each other with wood bond. Bond was applied plenty so that, in case that a slit occurs at a joint, the bond will fill it. The bond I used was a commonly-used type, not a quick-drying type.
While the bond was still wet, each part was adjusted in position to make the front and top surfaces flush.
After the positions of all parts were fixed, screw holes were drilled in the kerfs by inserting the bit of a power drill into the prepared holes that had been drilled beforehand. This work needed an extra care not to move the parts.
Each wood screw was not tightened individually. First, all the screws were screwed halfway. Then, in order to keep the joints from sliding, one screw was tightened a little with a screwdriver (not a power screwdriver), then another was tightened in the same way, and so on, till all the joints were secured. Finally, all the screws were tightened firmly with a power screwdriver.
The above process must be done quickly before the bond dries. When the work was done, a lot of bond leaked out of the joints. It was left till the finish process.
When the bond became adhesive, I turned over the boxes with care not to slide the fixed side boards. Then I screwed them on the boxes. Now the boxes were rigid.
At this point of time, the cables were placed through the holes, and sound deadeners were fixed in the boxes. I decided the amount of the sound deadeners by intuition.
The adhesive tape was affixed on the kerfs and small holes were cut out at the positions of the screw holes. Then, the detachable side boards were screwed, and the boxes had all six walls at last.
Before painting, I sanded the enclosures a little with an circular abrasive
paper attached to a power drill.
As for painting, I sprayed clear varnish on the surfaces of the enclosures. I did it without any particular techniques. I did it in my yard when the weather was fine.
I affixed instant letterings on the backboards to read my brand 'NOBODY' and the model number 'SS-312'.
After the varnish was completely dry, the drivers (LS units) were fixed.
Before fixing the drivers, I soldered the cables to them. The cables were so thick that the drivers couldn't be fit to the cutout of the baffle if they were soldered directly to the driver. I extended the cable with thinner wires.
The wood screws used for fixing the drivers were the accessary of the driver. The drivers were fixed with the genuine grilles.
|Soldered cable||6N-FE103 fitted to baffle||Screwed w/ grille||Completed|
SS-312 was installed in my second system in my study room as planned. Though my friend's amplifier
was used in this photo, it was a temporary configuration and MA-205 is used normally. (I was checking the amplifier upon request of the friend)
And, a small laptop PC was used as a DVD player in this photo, but a portable
CD player (Kenwood DPC-X517) and an IC recorder (TASCAM DR-1) were used
as music source regularly (DPC-X517 was discarded October 2011).
After the installation, I didn't do anything about measurement and tuning.
I played music for many hours every day to break in the new loudspeakers since the installation. The sound quality was getting improved day by day, and reached the satisfactory level. SS-312 offered better bass weight than I had expected, and its sound was heard well-balanced.
I judged that tuning was not necessary and declared its completion. In fact, I was already tired and didn't feel like doing any more.
No tuning and no improvement was against the design policy of NOBODY. I wondered if I should give NOBODY-brand to SS-312, but I did so because of the special situation that I built it in my long sick leave.
I skipped wood filling and sprayed varnish soon. I was disappointed that
beautiful grain woody texture didn't appear.
I haven't learned painting techniques properly. I am going to learn it before next chance.
The accuracy of SS-312 enclosure was improved than SS-309 thanks to the
same construction and assembly method. They were familiar with me, and
I built the enclosures with ease.
The worker of the DIY shop who cut the plywood board was the same man who did it for SS-309.
As the left photo shows, the enclosure was assembled so exactly that even a hair cannot go in between the boards.
As the right photo shows, the enclosures stood to a level when they were installed.
As described above, deep bass doesn't come from SS-312, though, its sound
is well-balanced and comfortable. It's suitable for background music in
the study room.
The combination of SS-312 and MA-205, which offers mild, soft tone, is best fit for healing music.
SS-312 is compact and floor-standing type. It's easy to install it. I think
the book-shelf type is rather difficult to install.
SS-312's lower body serves both as a stand and a CD/DVD rack. It is more convenient than I expected.
I think SS-312 is a user-friendly speaker.
I think I've got the intended results. SS-312 is a good speaker system
to enjoy background music at my leisure time.
Its construction is simple, and no special technique is needed to build it. It's recommendable for easy-going DIY audio.
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