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Discussion Starter #1
I'm not sure if this is the right subsection to post in, feel free to move it.

Recently was given an RCA 5.1 system (RT2781H, i know, not the greatest) that I'm now using for my computer audio. Today I had the pleasure of watching smoke come out the subwoofer port, and then smelling the wretched burning for the rest of the day. Bye, bye, driver! Now comes the fun of replacing this speaker given the very limited specifications I could obtain. I was told that the speaker was, "85 watts max at 10%THD," and the only other specification I could find was an impedance, 3 ohms...

I'm considering many options, but I certainly don't want to buy something out of the responsive range. I did find a "Tang Band W6-1139SIF 6-1/2" Paper Cone Subwoofer Speaker" that looks decent, with a 50w RMS/100w peak and 4 ohm impedance, but I feel this might be out of range for the amplifier.

Anyone with any suggestions to replace in this box?


Oh, and :wave: hi! Glad to be here! (First post...)
 

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Are you sure the smoke wasn't coming from the amp? It may not be the driver that bit the dust. Either way...

Powered subwoofers are designed holistically, so each part is relying upon the other to act in a very specific manner. You can't simply replace any one component with something generic that doesn't have the same characteristics as the original. Doing so will generally result in a less than satisfactory outcome. Given the original cost of that system it might be time to consider something new instead. I suspect trying to 'fix' your current subwoofer would be throwing good money after bad.
 

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I'm positive it was the driver that was smoking, yes. I've already disassembled the box and pulled the still smoking driver out once this happened. At this point, I'm just looking for a subwoofer driver that would hold up to the original "SL03024208" driver that was inside. Unfortunately, I can't seem to find any data on this particular number driver to help guide me to a close replacement speaker, hence the request for some help. In all honesty, I just don't have the money to buy another full system, which is why I'm still attempting to repair just the driver. I'm sure there must be something close that I can get.

I can tell you, though, that this is just two speaker wires that are soldered directly to the driver that are then hooked into the rear of the receiver. There is no internal amplifier in the speaker box itself. The signal from the unit is the only power it receives. I was under the impression that powered subwoofers had some sort of integral amplifier inside of the box, separate from the receiver/head unit, and was assuming this is a simple unpowered subwoofer. I could be wrong, though. I certainly don't claim to be an expert by any means in audio.

Honestly, just was wondering what driver I could possibly use to replace this driver to get near the original quality and volume of sound.
 

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Safer to go higher ohm than lower ohm. So if the replacement driver is really cheap you could try it for fun.

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As long as you're sure it was the driver and not the amp, the Tang Band W6-1139SIF is probably a much nicer driver than what came in there already and would be good as a drop in replacement without worrying about performance.
 

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Discussion Starter #6
I'm positive it was the driver. The receiver does the amplification, and sends it to that unpowered subwoofer box. As the smoke and burning came from the subwoofer box, and the only thing in it besides the port is the driver, I'm sure it wasn't the receiver sending the smoke through the wires to the subwoofer box, lololol.

All joking aside, I'm really wondering if there's a speaker that could do just as good of a job without costing $50+. After all, the entire 5.1 setup and receiver came in at $200 retail. I'm assuming the original component was dirt cheap, although I certainly buy a of a lot less speakers than RCA.
 

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The amp could have went dc and could have fried the voice coil. If you have a piece of junk speaker connect it to amp if speaker smokes then dead amp

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Discussion Starter #9
So if the amp goes dc, wouldn't that just hold the speaker in or out until the winding overheats? Wouldn't that mean that the speaker wouldn't actually play, since the signal isn't oscillating? I know it was playing, and I certainly don't have a speaker that could handle the amp, really, besides some old 15w speaker from an old Pontiac Vibe that I wouldn't mind sacrificing, but at that point how do I know if it fries from DC or from overpower? Can I just use a multimeter and a test frequency to directly test the channel?
 

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So if the amp goes dc, wouldn't that just hold the speaker in or out until the winding overheats? Wouldn't that mean that the speaker wouldn't actually play, since the signal isn't oscillating? I know it was playing, and I certainly don't have a speaker that could handle the amp, really, besides some old 15w speaker from an old Pontiac Vibe that I wouldn't mind sacrificing, but at that point how do I know if it fries from DC or from overpower? Can I just use a multimeter and a test frequency to directly test the channel?
You wouldn't have to turn the volume high I believe with a speaker connected if the amp is dc it would fry the speaker just turning it on was the speaker playing when it smoked

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I suppose if you put a volt meter on the amp output if it in dc you would get a reading with no input signal

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I suppose if you put a volt meter on the amp output if it in dc you would get a reading with no input signal

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If it was playing when it smoked then it may have been overloaded or maybe it just was the end of its time.I would connect a Ginny pig speaker and play it just to be sure and if it continues to work then replace the speaker with a speaker you choose

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If you were saturating the output of the amplifier and putting 10%THD through the driver, it's highly possible to burn out the coil without experiencing any damage to the amplifier... which could unfortunately mean that the TB driver may suffer the same fate. This is why under-powered amps are at least as dangerous as over-powered amps, if not way more dangerous.

I can tell you from direct experience with that exact driver that it is definitely good. I had a pair in vented boxes in a car not too long ago and they were almost too much for the rest of the system, even at 50wpc. If it looks like it will fit, it should be good. Just watch it with the volume control. At $50/ea you don't want to be replacing them very often.

I can also tell you from direct experience with MANY low-end systems like that RCA that as the low-quality amps age, they tend to produce more distortion at lower volumes largely as a result of being operated too close to their limits for extended periods of time... several hours per duty cycle, day in and day out for weeks or months. They sound worse and worse over time, and then the drivers get eaten alive. I'm guessing also that the way this RCA system is laid out that you can't replace the subwoofer unit entirely because it is also providing signal processing and power for the rest of the system... so you might be best served (biggest improvement for smallest investment) by throwing the whole thing in the trash, saving the cash on the TB driver, and get a better quality system to do the job.
 

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Discussion Starter #15
I'm pretty sure there's no signal processing in the subwoofer. This is a system with a receiver. The subwoofer is unpowered, and only has signal wires running into the box and directly to the driver. There is zero involvement of the subwoofer in this unit besides to produce bass. It could be replaced with any simple subwoofer, I'm sure. I've ran other speakers in the subs place before with no qualms. And as this system has aged, it has done so mainly in a corner with no use. This system was basically brand new at time of using it. I bet there were less than 50 hours of use when this happened. I'm pretty sure that the cheap driver used just fried.

Ok, now learning time. What do you mean by saturating the signal? And wouldn't the volume need to be rather high to get to 10%THD? How can this increase in distortion over time cause drivers to begin frying at low volume, what is the actual mode of failure here?
 

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"Saturation" in this context means that you're attempting to pass a signal through some stage of your system that is larger than the threshold of that stage. This is most likely to occur at an input (e.g. plugging an portable media player into an auxiliary input, and running the volume up to max on the player), but in less than perfectly designed systems it is possible for the preamplifier outputs to saturate the amplifier inputs... essentially, turning the volume knob up past a certain point (usually around 65-70%) will drive the amplifier circuitry past their input threshold. That's why you'll see a power rating coupled to a THD %. In your case, having that power rating coupled to 10% THD means the designers were willing to allow that circuit to be significantly overdriven for the purpose of quoting a higher power output.

The problem with this approach is that allowing the distortion to exist and subsequently be amplified tends to cause undue heat buildup in individual circuit components. Every time this happens, you tend to do two things: 1) you shorten the lifespan of individual components (resistors, capacitors, diodes, transistors, etc) and 2) as those components creep towards the end of their unnaturally short lives they will begin to under-perform. As you might imagine, a damaged component struggling to do its job in a circuit will have detrimental effects on the performance of the circuit as a whole. This often manifests as an increase in distortion at the final output, or slightly less often in reduced output. The reduction in output is actually worse, because then the user will almost always respond by turning the volume up more (because "this thing used to be louder!") and accelerating the damage. The mode of failure varies between the unit's complete inability to produce undistorted sound at any volume, or simply failing to produce sound at all... in the latter case it could be either a dead speaker driver, or a dead amplifier.

I'm speaking from experience having to replace ~$100 boomboxes every year when I taught high school colorguard because students and instructors expected a $100 boombox to produce enough sound to fill a large cafeteria. 6 months later, when it sounded like marbles in a steel trashcan, they always wondered why these things died so quickly.

Your case sounds different though... the explanation above was to answer your question about saturation and distortion. I'm siding with you on thinking it's the driver, and that replacing it with the TB might be your best bet. Since it's a completely passive subwoofer and they didn't outsource processing/amplification to the subwoofer box, (which is a not-uncommon approach) you should be fine. If the factory-installed driver was 3-ohm, the TB will be giving the amplifier 33% more impedance, which is less work for the amp.
 

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I'm positive it was the driver that was smoking, yes. I've already disassembled the box and pulled the still smoking driver out once this happened. At this point, I'm just looking for a subwoofer driver that would hold up to the original "SL03024208" driver that was inside. Unfortunately, I can't seem to find any data on this particular number driver to help guide me to a close replacement speaker, hence the request for some help. In all honesty, I just don't have the money to buy another full system, which is why I'm still attempting to repair just the driver. I'm sure there must be something close that I can get.

I can tell you, though, that this is just two speaker wires that are soldered directly to the driver that are then hooked into the rear of the receiver. There is no internal amplifier in the speaker box itself. The signal from the unit is the only power it receives. I was under the impression that powered subwoofers had some sort of integral amplifier inside of the box, separate from the receiver/head unit, and was assuming this is a simple unpowered subwoofer. I could be wrong, though. I certainly don't claim to be an expert by any means in audio.

Honestly, just was wondering liteblue what driver I could possibly use to replace this driver to get near the original quality and volume of sound.
Its really helpful. Thank you very much.
 
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