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Yet another praise to Sony sa-wm40 mods


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6 replies to this topic

#1 of 7 Cagri

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Posted April 08 2003 - 07:19 AM

I finished my modifications last nite and since then watched several bass heavy scenes from different movies and listened to my favourite CDs. The difference is night and day, even to a person who isn't an audiophile, i.e., me. I stuffed the sub with about 15oz. of polyfil taken from a pillow, and added four spikes. Ended up with lower SPL with pre-mod settings, adjusted the gain to read same SPL as b4 and there we go; the sub hits much tighter and I am definitely sure that it plays lower notes now. Stuffing the polyfil is very straightforward and has been covered in many previous posts, but one thing I have to add, if you use loose polyfil like me without glue or staples, when you work on the left side wall of the sub try not to leave the cables going to the driver between the polyfil and the wall. I did that way, leaving the cables, and was lazy to pull all the stuffing back and do it once again and I think I'll have to open it later on to check if the cables pulled the polyfil when I replaced the driver.

One thing about adding spikes; on the front left corner inside the sub, behind the on/off swithch, there is a small unit. If you intend to screw the spike from the point where the plastic foot is, use a short screw. I used a 16mm one for that corner, 20mm for other three. Pull the plastic feet off as they don't let the screws go in properly unless you screw them with a drill. If you place the spikes to a point inside the feet, that's fine as well but I felt the balance would be better when spiked closer to the corners. Use strong spikes as the sub is heavy.

Finished in 45 minutes and it has been a big upgrade, just do it if you haven't done already!
Too much debt...

#2 of 7 Richard Moya

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Posted April 08 2003 - 08:38 AM

I have a question for all the Sony mod people and subwoofer DIY'ers out there.

Does stuffing the actually change the "physics" of the box? IT would seem to me that when modding, what we are doing is decreasing the area for the bass to resonate. I know most subs casings are calculated based on the speaker used. Does this mod affect it for the better or worse?

Also, I had read one post on here that suggested internal "bracing" on the corners of the sub casing in order to stiffen the wall thus making the box resonate less and achieving a cleaner tighter bass. Doesnt this also decrease the space inside and alter your bass?

One more. Ive seen the polyfil method but was wondering if the same polyfil "batting" about 3/4in thick would do just fine. For some reason the loose filling doesnt seem right to me. I would think batting attached to the sides and spray glued would be a more secure mod.

Thanks everyone for your responses............

#3 of 7 Cagri

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Posted April 08 2003 - 09:46 AM

Richard, as far as I know stuffing the box with loose material such as polyfil obviously physically decreases the free space inside the box but the affect of doing so is just the opposite, i.e. the driver 'thinks' it is in a bigger space as the air it generates when moving is absorbed by this loose material, thus for some reason produces tighter bass. Maybe someone else will chime in and explain the technical side of this effect.

Some prefer stuffing the sa-wm 40 with sheet type polyfil. I was also feeling that sheet type would be more secure, but loose stuff is safe enough. It just holds itself inside the box firmly and I guess it serves better for the purpose as it is looser than the sheet type.
Too much debt...

#4 of 7 Charles J P

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Posted April 08 2003 - 10:20 AM

Cagri is right. How big of a box a sub "thinks" its in is based on how long it takes the sound waves generated by the back of the driver inside the box to get back to the driver. By stuffing the box you are doing two main things.
1) Reducing resonance inside the box, hence the tighter sounding bass.
2) The stuffing slows down the sound waves so they take longer to get back to the driver so it feels like its in a bigger box. A bigger box (all else being equal, and up to the design limitations of the driver) will make a sub play lower. Like how a tuba plays lower than a flute because its resonation sytem is bigger.

#5 of 7 Cagri

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Posted April 09 2003 - 12:40 AM

By the way, reading the other post about the blown sa-wm40 I wonder; in my fairly large listening room I had to turn the gain up more than 2/3 on the sony and the receiver's setting is -2. Is it asking too much a work from wm40's amp?
Too much debt...

#6 of 7 BobAZ

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Posted April 09 2003 - 08:09 AM

Cagri and others that have spiked their WM40
What spikes did you use and where did you get them? I'm looking at the 3/8" or 1/2" sets from PartsExpress:
SPEAKER CABINET TOE SPIKES 4PC SET 3/8" Part Number 240-725
SPEAKER SUPER TOE SPIKE 4 PC SET 1/2" Part Number 240-730

Thx
a.k.a digitalmanAZ on other DVD/HT sites
Onkyo TX-SR600, JBL S-CenterII, JBL S36IIPM, JBL N24, SVS PC12-NSD

#7 of 7 Cagri

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Posted April 09 2003 - 09:14 AM

BobAZ, here's what I have used (retailer is in the UK though)

http://www.richersou....l.php&p=101010

The inserts of the spike sets you've mentioned seem a bit large, but they should be fine, be careful to insert them away from the on/off switch unit. I recommend part# 240-715 though, or something alike ( I am sure you can find a cheaper set) with thinner screws as it would be easier.
Too much debt...