Hi, hope I'm in the right place.
I came across a powered Sony subwoofer model sa-wmsp1
I connected it and ran some tests on it and noticed it sounded very odd at the lowest frequencies. I ran a slow descending sine sweep and sure enough when it hits 26hz or less the output shoots up but I'm sure this is not due to the woofer/box but something in the Amp. My guess is it has something to boost the lowest notes for watching movies. I want to bypass this for flat output and would like to know where to look. Any advice is appreciated, thanks!
Printed Wiring Board - Sony SA-WMSP1 Service Manual [Page 4] | ManualsLib
I came across a powered Sony subwoofer model sa-wmsp1
I connected it and ran some tests on it and noticed it sounded very odd at the lowest frequencies. I ran a slow descending sine sweep and sure enough when it hits 26hz or less the output shoots up but I'm sure this is not due to the woofer/box but something in the Amp. My guess is it has something to boost the lowest notes for watching movies. I want to bypass this for flat output and would like to know where to look. Any advice is appreciated, thanks!
Printed Wiring Board - Sony SA-WMSP1 Service Manual [Page 4] | ManualsLib
That speaker can not reach below 40Hz. Easily 12dB down by 20Hz. They apply a heavy bump at 20Hz. Note that they only claim 28Hz. It's all Marketing.
IC101(2) is the bass-boost. "Stock".
The easiest way to defeat this is to jump a wire around both capacitors indicated, "Jumped". Flat to DC.
We don't usually want DC in speakers. A proper choice of resistors in the boost will give something *like* a Butterworth (oldskool math guy) filter, really flat to a point. "Butter".
IC101(2) is the bass-boost. "Stock".
The easiest way to defeat this is to jump a wire around both capacitors indicated, "Jumped". Flat to DC.
We don't usually want DC in speakers. A proper choice of resistors in the boost will give something *like* a Butterworth (oldskool math guy) filter, really flat to a point. "Butter".
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I have the same subwoofer.
I modded it for FFR use by removing the caps concerned with the filtering and and bass boost, relatively easy.
Then added an appropriate tweeter coaxially with a bracket and highpass cap.
Sounds quite amazing now with a portable CD player velcro'd to the top, added a handle there too.
Easy to carry to my neighbor's patio to enjoy some rich-sounding tunes over a few beers.
Oh, and I also added a small silent blower inside blowing through the heatsink fins.
That's to insure the health of the LM3886, since they're becoming hard to get/replace these days.
I modded it for FFR use by removing the caps concerned with the filtering and and bass boost, relatively easy.
Then added an appropriate tweeter coaxially with a bracket and highpass cap.
Sounds quite amazing now with a portable CD player velcro'd to the top, added a handle there too.
Easy to carry to my neighbor's patio to enjoy some rich-sounding tunes over a few beers.
Oh, and I also added a small silent blower inside blowing through the heatsink fins.
That's to insure the health of the LM3886, since they're becoming hard to get/replace these days.
Excellent ideas.
Let me add that given the YUUUGE Bass Boost at an impossible to sustain (at mid/high power that is) 20Hz frequency that amp will clip horribly AND give woofer a hard life, most probably smashing voice against the back plate, even if bumped, so it NEEDS a limiter to begin with, even better if frequency selective so as to limit voice coil *excursion* , which of course is perfectly feasible, and done in Pro/PA equipment.
Did they?
Naaahhhh!!!!
It´s *consumer* equipment!!!
So they just added a couple cheesy *clipping* diodes across power amp input, check D301-D302
Since Subwoofer must live in a band limited cabinet or something, clipping harmonics might be not that noticeable, but the box must certainly sound "weird" when pushed.
So excellent ideas on removing FAKE Bass boost and letting it put out whet it realistically can.
When modding the bass booster, Butterworth is better than plain bypassing since it removes undesirable subsonics.
Personally (hey, my preference) , I would also lower C104-C105 to .047 each to rise subsonic cutoff by 1 octave, where anyway Subwoofer will struggle.
You will be able to drive that amp amp/speaker harder, because it will stay in the "Real World" he he.
PS: not much muscle anyway in an 8" woofer and 50W RMS amplifier (at least they were honest on that 🙂 , they could easily have quoted 800W PMPO or something )
Let me add that given the YUUUGE Bass Boost at an impossible to sustain (at mid/high power that is) 20Hz frequency that amp will clip horribly AND give woofer a hard life, most probably smashing voice against the back plate, even if bumped, so it NEEDS a limiter to begin with, even better if frequency selective so as to limit voice coil *excursion* , which of course is perfectly feasible, and done in Pro/PA equipment.
Did they?
Naaahhhh!!!!
It´s *consumer* equipment!!!
So they just added a couple cheesy *clipping* diodes across power amp input, check D301-D302
Since Subwoofer must live in a band limited cabinet or something, clipping harmonics might be not that noticeable, but the box must certainly sound "weird" when pushed.
So excellent ideas on removing FAKE Bass boost and letting it put out whet it realistically can.
When modding the bass booster, Butterworth is better than plain bypassing since it removes undesirable subsonics.
Personally (hey, my preference) , I would also lower C104-C105 to .047 each to rise subsonic cutoff by 1 octave, where anyway Subwoofer will struggle.
You will be able to drive that amp amp/speaker harder, because it will stay in the "Real World" he he.
PS: not much muscle anyway in an 8" woofer and 50W RMS amplifier (at least they were honest on that 🙂 , they could easily have quoted 800W PMPO or something )
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Wow I'm amazed at the quality of replies here, thank you all. Thank you PRR for those images, I know exactly what to do. What program is that to model the output curve?
JMFahey, I agree converting it to have a subsonic, I can't believe they added a boost circuit below the box tuning frequency on a bass reflex. I however am a bit out of my league with modifying these things, I don't have all the components to do it, but eventually I will learn enough to try. For now I'm going to solder in the bypass and live with it much happier than it is in current form.
Thanks again!
JMFahey, I agree converting it to have a subsonic, I can't believe they added a boost circuit below the box tuning frequency on a bass reflex. I however am a bit out of my league with modifying these things, I don't have all the components to do it, but eventually I will learn enough to try. For now I'm going to solder in the bypass and live with it much happier than it is in current form.
Thanks again!