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Member
Join Date: Jan 2004
Local Time: 07:43 PM
Local Date: 10-12-2008
Posts: 15
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The short answer: search in this forum for sa-wm40 and read about filling the enclosure with $2.00 of polyfill and coat the woofer with ModPodge, both from WalMart.
Long answer:
The Sony SA-WM40, and its successor the SA-WM500, are the most talked about subs on this forum in the budget range, it seems like. I think they get so much attention because its particular characteristics seemed to make it fairly improveable with some simple modifications. People like that sort of thing. I know it gave me a good feeling to in a sense, "Beat the System" in achieving the equivalent of a $500 - $600 sub (people say) for $150 or so.
I really just wanted an okay sub to replace a really crappy one, so I got mine at Sears without researching. Not too smart, but apparently I lucked out.
You can easily do a search here for sa-wm40 and you'll see a lot of posts about the modification.
But since it's still too early for me to actually do work at my desk, I'll post what I know here too. =)
Our subs are known to have pretty good output, but as they're $250 list subs and not $600 list subs, there are some compromises. The cone is not an exotic material like Kevlar, but rather treated (hopefully) paper. The case isn't the most rigid and resonance-free. The amp probably isn't terribly highi-end and is probably more prone to distortion. There could be more bracing in the case.
Those above items contribute to make the sub more "loose" and "boomy" than one would like. Some people are into that, though. They just want loud bass, not caring if it's accurate bass (a G-flat is a G-flat, an E is and E, instead of all the bass sounding "one-notey"). If you're one of those people, then you should stop reading, because these modifications will not contribute more volume to the bass. Rather, it'll make the bass more accurate, tighter, less boomy. For audiophiles and videophiles into music and home theater, this is a good thing. Read on!
Another compromise with the design of the sub is the volume of its enclosure. I don't know a lot about speaker design, but I read that a bigger enclosure makes it easier to reach lower down (although more expensive, exotic methods can achieve the same thing, like in $1,000+ subs). A bigger enclosure would have made for more materials, more bracing, more weight, and would be more obvious in a family room (at this price level, the owners probably don't own a dedicated theater room).
One way to increase the apparent volume of the enclosure is to stuff it with a fluffy material like poly fill. This is often used for making dolls, stuffing pillows and couches, etc. Thus, you'll find this in the fabric & crafts section of Wal Mart. Some people use sheets of batting stapled to the inside of enclosure. Others use loose stuffing, which is what I did. The additional material slows down the sound waves, "tricking" the sub into thinking it's a larger box.
The other modification is to stiffen the paper cone. Presumably, the paper was treated somehow? (I've read that that's one of the many shortcuts that Bose speakers take, is that they use super cheap, untreated cones. For the $$ they charge and the research they claim, you'd think they used metalescent polypropylene or some such!) Still, people have gained great results by coating the cone woofer with a material to strengthen and stiffen the cone. We do this in order to gain less distortion and cone breakup.
We're trying to achieve a more accurate bass at the lowest levels (25-35 Hz), and anything below 35 Hz is getting more difficult to achieve, placing the most stress on the magnets, cone, amp, etc.
It is suggested you use a sponge applicator to spread two thin coats on the back side of the woofer, and three coats on the front side. I'm guessing that three thin coats are better than one thick one, because each coat as irregularities in the coating. The liquid will be thicker in some areas than others. Our brush strokes will be uneven. Having multiple coats allows the thicknesses to be averaged out more randomly.
Now, for the specific instructions, in case you're still reading and haven't looked at the other posts....
Remove the grill cover.
Remove the eight screws holding the woofer in place. Four are phillips. Four are hex.
This is the hard part, which is why I asked about it online. Remove the driver. The suggestion to stick a flathead screwdriver in the seam and pry was a good one...it worked. Be careful, though! The gray ring around the outside, with indentations for where the screws go...it's some kind of laminated paper layer material. It tears, it breaks, if you're too rough on it. Watch it closely as you work. Also, don't lift the driver out too far.
When there's a crack to peek inside, as you get your fingers under the driver, see the wires leading to the amp from the back of the driver. Mine were taped down, and pulling the driver out was putting a strain on the wires.
You may be able to unplug the wires from the driver. I didn't pull hard enough to find out.
I just propped the driver up at an angle in the hole so I could work on different sides of the back of the cone.
A 3/4" brush works better, as you have nooks and crannies to get in amongst.
While the modmodge is drying, fill the inside walls with the polyfill. I bought a 20 ounce bag and used about half. I left ample room for the driver. And you cannot block access to the port leading out the back of the sub.
Replace driver, re-screw (i tested before resealing to make sure the sub still worked and a wire didn't become disconnected).
You'll spend $10 and twenty minutes double the value of the sub.
I have yet to test this, as the evening didn't work out for me last night...but so many people verify this mod i trust it.
Good luck!
David Hoffman
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