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Sony SA-WX900 Push-Pull Subwoofer (Pictures, Measurements & Mods)

kiwifi

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I like push-pull subs, but I was unaware that Sony had made any, until I noticed one for sale on a local auction site.
P1090998.jpegP1100001.jpegP1100002.jpegP1100003.jpeg

In fact Sony has made two models that I know of. A dual 10" 250W sub (SA-WX700) and the one that I found, which is a dual 12" sub with a 1000W B&O IcePower 1000A amplifier inside! It appears that Sony produced these subs for a few years in the early 2000's, and although they were basically ignored by the hifi press, the user reviews that I found were largely positive. The only problem that I read about, was that the smaller SA-WX700 had a tendency to fry its power supply after a year or so.

Unusually, the lower (inverted) driver is pushed up inside the cabinet using a cast housing. This eats up a lot of the internal volume.
P1100005.jpegP1100006.jpegP1100007.jpegP1100014.jpegP1100018.jpegP1100024.jpeg

What amazed me was the components that make up the SA-WX900.
The Nichicon made power supply has a 12A line input fuse which at 240VAC implies 2880W of capacity
P1100009.jpegP1100011.jpegP1100012.jpegP1100013.jpeg

The regulated SMPS feeds 120V to an IcePower 1000A module rated at 1000W RMS @ 4 ohms 0.04% THD+N
P1100010.jpeg

All of which make me wonder why Sony chose to label the power consumption at 220W. Did they leave off a zero?
P1100004.jpeg

The two drivers have cast aluminium baskets and huge magnets, weighing in at 21lbs (9.54kg) each. The cones are made of Rohacell
P1100019.jpegP1100020.jpegP1100021.jpegP1100022.jpegP1100023.jpegP1100016.jpeg

Here are the measured TS parameters for the Sony drivers (Part # 1-825-374-11)
TS-SonyB-2.PNGTS-SonyF-2.PNG

As you can see, their measurements are very close to each other
TS-SonyF.PNG

Where Sony appears to have dropped the ball is in the construction of the cabinet. Apart from the MDF front baffle and the lower board that connects the four feet, the cabinet is made of 25mm chipboard without any internal bracing or sound deadening material. The only concession are the small pieces of rubber, stapled and glued to the middle of three of the sides.
P1100017.jpegP1100015.jpegP1100025.jpeg
 

ppataki

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I can see some Hungarian and Polish text on the back of the cabinet - I wonder if this particular unit was originally sold in one of those countries
(I am from Hungary so was really funny to see that; totally did not expect it :))
 
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kiwifi

kiwifi

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I can see some Hungarian and Polish text on the back of the cabinet - I wonder if this particular unit was originally sold in one of those countries
(I am from Hungary so was really funny to see that; totally did not expect it :))
The previous owner bought it new. I assumed that was in NZ, but who knows...
 
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kiwifi

kiwifi

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Here is how the various filter settings affect the frequency response. The cutoff frequency control is set to 200Hz (max).
There are two modes - "Music" and "Movie" and three levels of "Boost" (0, 1, 2)

For some reason the Music mode adds a shelf at around 20Hz.
Movie_MusicNB.jpg

Music Mode with boost levels
MusicBoosts.jpg

Movie mode with boost levels
MovieBoosts.jpg

All together
Movie_MusicBoosts.jpg

In my room I found that Movie mode plus Boost level 2 sounded best. The Music mode just seemed to make the bass muddy. YMMV.
If you want all the filters off, then it looks like the setting to choose is Movie with Boost set to zero. None of this is explained in the user manual!

One of the mods that I am considering, is to add a switched balanced input directly into the IcePower module. This would bypass the filter board completely and allow DSP filtering in its place.
 

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kiwifi

kiwifi

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Mod #1: Install 4 x 5cm castors wheels. Total cost 14NZD
P1100026.jpeg

The SA-WX900 weighs 48kg and takes two people to lift safely. Adding wheels makes it so much easier for one person to move it around.

I find it hard to believe that Sony supplied spikes with this sub!
 

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kiwifi

kiwifi

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In my room I found that Movie mode plus Boost level 2 sounded best. The Music mode just seemed to make the bass muddy. YMMV.
If you want all the filters off, then it looks like the setting to choose is Movie with Boost set to zero.
I watched a movie and had to reduce the boost setting to zero in Movie mode! 75dB at the MLP only requires the volume setting on the amp to be at 25%.

I haven't done the full MSO calibration on this sub yet. It is simply connected to the second sub output of my AVP with Audyssey XT32 handling the calibration, but I am really impressed with what I have heard so far. It is holding its own in a room with four MSO integrated subs. It just needs some upgrades to the cabinet to really shine...
 
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kiwifi

kiwifi

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Here are the planned modifications to the cabinet to increase stiffness and the dimensional volume. From the TS parameters the ideal sealed cabinet (Qt = 0.707) for two of these drivers should be about 107L. The current volume is probably half that, so the plan is to move the electronics to a separate enclosure, seal/extend the back and mount the drivers from the outside, eliminating the casting that pushes the bottom driver up into the cabinet. This will also allow the cabinet to be stuffed with sound absorbing fill.

Here is the original box (upside down with the feet removed)
Screen Shot 2023-01-21 at 8.46.46 PM.png

Here is what will be added around and inside the original box. Each baffle is tied to its opposing panel using stays and all the panels are stiffened using ribs.
Screen Shot 2023-01-21 at 8.43.24 PM.pngScreen Shot 2023-01-21 at 8.44.21 PM.png

The complete assembly without back and bottom panels.
Screen Shot 2023-01-21 at 8.48.19 PM.pngScreen Shot 2023-01-21 at 8.49.37 PM.png

Materials are a mixture of 18mm and 12mm MDF, plus solid wood for the ribs and stays. Everything screwed and glued. The final step will be to wrap everything in a layer of 6mm MDF, to hide the screws and joins to the old cabinet, then paint.
 

restorer-john

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And that's how you make an SMPS supply. Nichicon Japan. Compare it to those garbage Hypex supplies with cheap components, poor heatsinking and dubious construction. Even a replaceable ceramic fuse.

index.php



Impressive subwoofer. Sony again hiding their light under a bushel.
 

restorer-john

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That SMPS looks also to be fully regulated if I'm not wrong.
 
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kiwifi

kiwifi

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That SMPS looks also to be fully regulated if I'm not wrong.
No idea, but I wouldn't be surprised. I couldn't find any information on this PSU online. In the SA-WX900 service manual it is referenced as a "black box" in the circuit diagrams.
 
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kiwifi

kiwifi

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So this is what has occupied my spare time for the last three weeks. Construction of the upgraded SA-WX900 cabinet...

Staring point, with the plate amp removed. The bottom driver is pushed up into the small, chipboard cabinet that has no bracing or stuffing.
P1100030.jpeg

Add ribs to the existing cabinet
P1100031.jpeg

Make a new bottom baffle and box to hold the bottom speaker
P1100032.jpegP1100034.jpegP1100033.jpeg

Construct a back box to cover the hole left by the plate amp and increase the internal volume
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The original cabinet plus extensions
P1100038.jpeg

Before the extensions can be permanently fixed, the internal stays are added. These run from the baffles back to the opposite face. They are also tied (screwed) to each other and the ribs.
P1100039.jpegP1100040.jpegP1100041.jpegP1100042.jpeg

A screen to stop acoustic fiber fill falling into the cone of the lower driver is made from the part that originally pushed it up into the cabinet
P1100043.jpegP1100044.jpeg

Final assembly and wrapping with MDF. The slightly oversized sheets are glued in place and then trimmed to size with a hand held router.
P1100045.jpegP1100046.jpegP1100047.jpegP1100048.jpegP1100049.jpeg

Making the amplifier box
P1100052.jpegP1100050.jpeg

Final prep and paint. The original bottom panel (seen in the foreground of the third image) will be reused with castors attached, to act as a dolly.
P1100051.jpegP1100053.jpegP1100054.jpegP1100055.jpeg
 
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kiwifi

kiwifi

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RenSong

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This is so cool, I can't wait to see the finished product
 
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kiwifi

kiwifi

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Done! The plate amp is mounted on the side for purely aesthetic reasons...I didn't want to be able to see it from where I sit.
P1100056.jpegP1100058.jpegP1100059.jpegP1100061.jpeg

Here's a size comparison...
P1100060.jpeg

In the center is a (standard) SVS PB-1000 subwoofer.
On the left is the passive M&K MX-5100 that I built and detailed here.
On the right is the upgraded SA-WX900, which now has external dimensions of 45cm (W) x 69cm (H) x 70cm (D) (originally 44cm x 55cm x 53cm)
 

restorer-john

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Done! The plate amp is mounted on the side for purely aesthetic reasons...I didn't want to be able to see it from where I sit.
View attachment 264187View attachment 264188View attachment 264189View attachment 264191

Here's a size comparison...
View attachment 264190

In the center is a (standard) SVS PB-1000 subwoofer.
On the left is the passive M&K MX-5100 that I built and detailed here.
On the right is the upgraded SA-WX900, which now has external dimensions of 45cm (W) x 69cm (H) x 70cm (D) (originally 44cm x 55cm x 53cm)

It's a beast. Will be interested how it compares to the others.

I'm glad I don't live next door. ;)
 
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kiwifi

kiwifi

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Here is the impedance sweep for the drivers in their new cabinet.

At first, I ran out of stuffing, so the cabinet was only lined. The resulting value of Qt was disappointing at 0.82 (Fs 45.5Hz) compared to my target of 0.707
EnhancedSony_Lined.PNG

When 750g of polyester stuffing was added, the Qt improved considerably to 0.75 and Fs lowered slightly to 44.6Hz. Subjectively, the sub sounds much better now that the stuffing is in place.
EnhancedSony_Stuffed.PNG
There is more than enough gain available, so I also took the opportunity to wire the drivers in series, rather than the parallel connection that they were originally. So now the gain knob on the Sony amp is at 12 o'clock rather than 10 o'clock. The increased load resistance (13.7ohm vs 3.5ohm) across the amp should result in lower distortion and cooler running.
 
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