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Subwoofer repair or replacement?

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TheGiantHogweed View Drop Down
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    Posted: 14 April 2021 at 5:53pm
I am rather stuck with what to do with my setup at the moment. I am aware I am very restricted in space as my room is only 3x2m and only have a small amount of space for a desk.

I have a pair of JBL control 1 speakers which I am very happy with. The fact that they have very little bass is ideal as i have them on tall narrow shelves. The issue I had with other speakers was that they just vibrated and sounded too boomy. These don't suffer at all in tight spaces.

I currently have my Wharfedale SW150 on the floor behind where i sit. It won't sound ideal, but it is central and as bass isn't very directional, it isn't too bad a set up I'd say.

One issue I've always had with this subwoofer is transformer hum. I doubt this is anything I can change myself. I've taken the rear panel off and it literally is the transformer humming and being in a box that amplifies it; like a driver! It isn't that loud, but is annoying at night as this is my bedroom. There is an auto-standby option, but it is useless and i will get onto why later as it isn't relevant yet.

The main issue is something that has steadily been getting worse. There seems to be an annoying buzz below 60 - 50hz that comes from the driver. I have taken it out and it still is clearly audible when not in the enclosure. It is tolerable - in fact not noticeable a lot of the time with music with a lot happening in it, but music with more bass and not as much other frequencies can sound a mess at times.

Here is an example i recorded with my microphone: http://www.wetherby.me/wiki/pub/Sandbox/RandomImages/subwoofer_test.mp3

Just with an online tone generator. The frequencies below 50hz or so just sound like they are broken or something. I'm sure there never used to be roll off or buzzing as bad as this.
Seems odd though if it claims to go down to 35hz both on the crossover dial and the manufacturer's claimed frequency response.

Until more recently, i'd been pretty pleased with the sound, but had one main issue which I just accepted. The JBLs roll off around 100hz, and as the SW150 has a crossover maximum at 85, there is a little hole in the middle effect with just that region of bass just a bit lacking. But now both that and anything much below 60 isn't great.

What really surprises me is that I got a couple of dirt cheap subs from richer sounds that were passive pioneer ones from discontinued surround sound systems. Even with a cheap ebay 2.1 amplifier board (just for the subwoofer output), the sound from this with my JBL control 1s isn't a night and day difference when i compare it to the SW150. Really makes me think subwoofers beyond at a certain price point are a little pointless really. The main difference is that the SW150s bass is just slightly tighter and more under control, but it doesn't justify the price difference.


The standby feature isn't really relevant to this question, but it is another problem with the subwoofer. As it seems to go to sleep within 30 seconds of playing music quietly rather than detecting when nothing is on. And it saves 2 watts of power and 20% of the total consumption when it is on. Just pointless!


I just don't know if I'm better off looking for a way to sort out the driver problem on mine, or may be better off getting some cheap subwoofer. The hard thing for me is getting the crossover to be suitable to pair with my JBLs.



It may also be to much hassle or too expensive to do anything, so I will have to think about some options.

Would appreciate some advice.


Thanks.
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Tinnitus Rex View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tinnitus Rex Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2021 at 6:22pm
 Just a thought, have you tried gently poking the speakers "tinsel" lead offs with a match stick (or something) while you have a low sine wave going through the driver? Sometimes ,where they solder the lead offs, it can fatigue fracture the fillaments of the wire so it just  forms an  inconsistant connection that appears as micro distortion. If the sound changes as you flex the lead off this might be the case.
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ceharden View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2021 at 9:50pm
Power the SW150 driver from the ebay 2.1 amplifier to get rid of the transformer hum issue?

Regarding the driver, it might be there's an issue with the glue joint between the cone and the voice coil or maybe even the coil itself.  You can sometimes detect it by applying some pressure to the cone while playing a signal.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 6:58am
Originally posted by ceharden ceharden wrote:

Power the SW150 driver from the ebay 2.1 amplifier to get rid of the transformer hum issue?

Regarding the driver, it might be there's an issue with the glue joint between the cone and the voice coil or maybe even the coil itself.  You can sometimes detect it by applying some pressure to the cone while playing a signal.


Yes - or "tapping" the cone lightly at various points and see if there any sort of buzz (without signal). That would show any sort of problem like the glue coming off the coil, etc.


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TheGiantHogweed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheGiantHogweed Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 9:07am
Thank you all for your suggestions. Powering the driver with a cheap amplifier is something I hadn't thought of. It does involve cutting the wires inside, but shouldn't be hard to put back after testing with a connector block or solder and heat shrink.

The subwoofer as a whole weighs around 20kg and isn't easy to move around.\ will try taking the driver out and doing the tests on it suggested.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 9:38am
20kg? Hahaha.

I've got this one for sale at the moment, if you want:--










Only 50kg. Yours cheap if you want to pop down & pick up!!   LOL





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TheGiantHogweed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheGiantHogweed Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 11:05am
Well, compared to many other comparable sizes at the moment that are around the same price as mine, they seem to be under half the weight.

Anyhow, after tests, i found there is nothing wrong with the driver at all. It is the amplifier that sends these messed up frequencies to the driver. 50-70 hz seems perfect. Anything above or below that has a noticeable buzz.

However, if i use my cheap amp as pictured, it sounds far cleaner:


Just covered the bolt holes with tape to avoid air noise while testing.

So then, with the things that annoy me being the transformer hum and the amplifier issues, it suggests that the board on the back isn't very good or just isn't to my liking at all. The advantages to this cheap amplifier are that there isn't this hole in the middle effect, but the issue is that it only gradually rolls off right into the mid bass. would be ok if i had a better listening position, but it is certainly more obvious now that my subwoofer is behind me.

Now i know the issue is with the board in the back of this, I could almost do with replacing it, but boards like that seem  very expensive for what my budget would allow. Given how good a £10 board from china sounds and the only real issue is the crossover and a bit of background hiss, there must be a reasonable option somewhere.

The main other disadvantage is with the way i currently have things set up. I have the speaker cables split going to the input on my subwoofer, then to my speakers. My cheap ebay amp doesn't have speaker inputs, so i have to use the headphone socket of my amplifier (pioneer A-209r) to allow me to control the volume along with my speakers. Don't like to use the headphone socket though as when I switch between a and b speakers, it still sends the audio to my subwoofer and my other speakers really don't need it!

I'm very impressed with what this cheap amp is capable of, but i could do with something better, but certainly doesn't need to be a big step up. Could do with something that has an input and output for speaker cable (so not line level), a low pass filter and a crossover that has an option to go up to or over 100hz to match my speakers better.

At least i know now that I can re use the driver and enclosure. It isn't even that bad as it is all the time, it can just sound a bit odd when hitting certain bass frequencies when there isn't much else happening in the music.


Edited by TheGiantHogweed - 15 April 2021 at 11:12am
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TheGiantHogweed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheGiantHogweed Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 3:42pm
I think I have worked out with the sort of thing I want.

This is the board on the back of the subwoofer:


When I take this out, it does look like it is in a sealed enclosure, so I should be able to replace this with another one and it shouldn't matter if it doesn't fit perfectly - so long as it isn't larger. The problem is, I can hardly find any that have high level speaker inputs which is the only thing I could use unless I use the headphone socket on my amplifier which isn't really ideal.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 5:20pm
That has stereo speaker level inputs? A bit odd. How do they mix that into a single driver? 


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markie View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote markie Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 5:24pm
Dual voice coil????
If it's got wheels or tits it's gonna cost a fortune
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Post Options Post Options   Thanks (0) Thanks(0)   Quote APW Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 6:00pm
Originally posted by Earplug Earplug wrote:

That has stereo speaker level inputs? A bit odd. How do they mix that into a single driver? 


You start by treating each speaker input as a high-level balanced signal that’s padded down to level that an op-amp differential amplifier can handle…. then it’s just a case of mixing the two signals together to create a single signal for the sub’s amp.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 15 April 2021 at 6:48pm
Originally posted by APW APW wrote:

Originally posted by Earplug Earplug wrote:

That has stereo speaker level inputs? A bit odd. How do they mix that into a single driver? 


You start by treating each speaker input as a high-level balanced signal that’s padded down to level that an op-amp differential amplifier can handle…. then it’s just a case of mixing the two signals together to create a single signal for the sub’s amp.


Yes - but the idea of those inputs is to use external amp with it's processing - like on most 5.1, etc.

Those would normally just have a single sub out.


"Dual voice coil????"

Yes - that might be it. Can't find anything in the manual/brochure I found.



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