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PM 2.1: rattling noise from subwooofer


TwoCables

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I noticed during parts in movies where there's a sound effect going (and sustaining) that's pretty much all low-end and no mids or highs that my subwoofer rattles a little (meaning, it probably rattles for almost any low-end but I can't hear it when it's drowned out by mids and highs coming out of my satellites). The first time I heard it, I spent several minutes pinpointing the source and finally pinpointed it as coming right out of the port on the front. I verified this over and over and over just to be 100% certain of it.

 

So, I took the amplifier off the back with plans to unplug the subwoofer from it so that I could look at it very easily. However, I saw no way to unplug it. In addition to that, i was suddenly extremely afraid of being electrocuted by one of the capacitors due to suddenly remembering that it's quite possible. So, the best that I could do was hold the amp by the panel, shake it and then proceed to check the plastic tube that makes the port on the front. To check the tube, I tapped it using the fleshy part of my fingers (rather than allowing my fingernails to make contact with it). I also verified that the tube isn't loose - it's still firmly glued in place.

 

When I shook the amplifier, I heard no ratttling (nothing is loose that I could tell). When I checked the port tube, it seemed rattle-free, so I don't know where to go from here. Can you help? Or, is this the way all of the PM 2.1 subwoofers are?

Edited by TwoCables
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It's called "port chuffing" which is mainly due to reaching the limits of your sub. Port chuffing is due to air-pressure change in the sub enclosure. It might be really rattling on the floor as well. Is it placed on hardwood floor?

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It's called "port chuffing" which is mainly due to reaching the limits of your sub. Port chuffing is due to air-pressure change in the sub enclosure. It might be really rattling on the floor as well. Is it placed on hardwood floor?

 

No, it's definitely coming out of the port. The sound is loudest at the port (but it's a quiet rattling sound). With my ear physically touching the mouth of the port and then moving away in any direction, it becomes very clear that the sound is coming out of the port.

 

So, are you saying that port chuffing has a rattling type of sound to it?

Edited by TwoCables
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Chuffing has a chuffing sound. Is the port loose? Sometimes the actual port tube or tube flare comes loose.

 

Don't worry about getting shocked. Just use the one hand rule. Put your other one behind your back. The only shock would be local to that hand, and there would be no way it could travel through your heart.

 

Most modern electronics have bleed down resistors on high voltage cap circuits. In about a minute after removing power a modern electronic device should be safe to handle. It is best to be safe with the 1 hand rule, however.

Edited by mustang guy
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Chuffing has a chuffing sound. Is the port loose? Sometimes the actual port tube or tube flare comes loose.

 

Don't worry about getting shocked. Just use the one hand rule. Put your other one behind your back. The only shock would be local to that hand, and there would be no way it could travel through your heart.

 

Most modern electronics have bleed down resistors on high voltage cap circuits. In about a minute after removing power a modern electronic device should be safe to handle. It is best to be safe with the 1 hand rule, however.

 

The port is still firmly glued in place. I forgot to mention that in my original post, so I added it just now. So, I thank you for asking.

 

Regarding the risk of being electrocuted, would the capacitors in the PM 2.1's amplifier be drained if I put the switch back to the On position for a moment and then followed that by toggling between off and on for good measure (ending in the Off position when I finish, of course)?

 

Also, if I did get electrocuted using the one-hand method, then what would it be like? Painful and scary? Or no big deal at all?

Edited by TwoCables
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You do not need to find out. If you are checking it out, beware the capacitors as the method you described, unless discharged can give you more volts by a factor of 6 or more.

Was hoping you had sorted out the rattle then. Glad you are still at it. Sub it seems tends to rule here with the folk.

Good fortune

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You do not need to find out. If you are checking it out, beware the capacitors as the method you described, unless discharged can give you more volts by a factor of 6 or more.

Was hoping you had sorted out the rattle then. Glad you are still at it. Sub it seems tends to rule here with the folk.

Good fortune

 

Damn, you have a good memory. :) Thank you!

 

You're right that I don't want to find out what that would feel like. I most certainly wouldn't be smiling and saying, "that was shocking". It sounds like I'd probably be injured and seeking medical assistance right away. Maybe?

 

Anyway, I'm thinking that I will try to find a way to change the way the air goes into the tube. Maybe I'll use a rubber band (wrapped around the tube) to enable me to stretch a rubber band or two across the top of the tube. I mean damn, with the way the low-end sounds during this rattle, it seems to me that it's nowhere near its limit! It just sounds to me like the tube is too small or that they should have built in some crossbars inside the tube to diffuse the air a little bit as it moves through it. Mine doesn't appear to have the simple plug-in design; I think it's soldered to the circuit board.

 

When I said that I will need to find a way to do this, I meant that not being able to simply unplug the subwoofer from the amp is going ot make it a bit of a challenge. However, I feel that it will be more than worth it - even if this takes me a ridiculously long time.

Edited by TwoCables
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Might have to consider a sealed sub if this chuffing thing keeps getting up. If it still rattles then, an x-ray may be in order.

Some rattle, if intended can be some mighty fine bass.

 

This is the PM 2.1's subwoofer. I can't just replace it. Besides, I don't have that kind of money. I need to modify this thing so that the chuffing stops (if that's what this sound is).

 

I don't know what you mean by, "Some rattle, if intended can be some mighty fine bass". Any rattling noise is unwanted because it's distracting. It needs to be clean.

Edited by TwoCables
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I'm having trouble figuring out how to get a rubber band or two stretched across the opening of the tube (on the inside of the subwoofer, of course). I mean, I had envisioned a rubber band wrapped around the tube holding a rubber band or two stretched across the opening, but that's proving to be quite difficult. I'm afraid of breaking the tube off of the inside.

 

So, what if I were able to find some kind of a flexible screen or maybe a piece of old pantyhose and modify it so that more air could pass through but still get diffused so as to get rid of this air turbulence? Would this be a bad idea for any reason, including any potential harm to my sound?

Edited by TwoCables
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Let's start simple.

 

Go to this website and find a frequency which makes the resonance the worst. http://plasticity.szynalski.com/tone-generator.htm Turning up the volume at that frequency should make the noise worse, so it should be easier to find.

 

How would knowing the frequency help? I'm not going to reduce frequencies that I enjoy hearing/feeling just to eliminate the chuffing. I've read that chuffing is caused by air turbulence in the tube, and so I'm trying to break up the air as it enters the tube so that the turbulence is reduced.

Edited by TwoCables
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ugh...

 

You want to make the noise LOUD so you can figure out what is rattling. Sending a sine wave will keep the satellites from getting signal. A chuff is NOT a rattle.

 

good luck...

 

I did that on day 1 of discovering this issue, but I could not reproduce it no matter what low frequency I tried - even at volumes louder than when the sound occurs in these movie scenes I've heard it in.

Edited by TwoCables
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I'm getting somewhere! I made it worse. I put 4 thin strips of tape across the top of the tube parallel to each other spaced fairly evenly apart, each about 3-4mm wide. So, now I know for sure that it's the air turbulence. All I have to do now is figure out how to get it to stop. I might try loosely stuffing a some kind of a thin cloth in from the outside. I'm betting that it's due to the bend in the tube.

 

Edit: Just to learn, I stuffed my cotton cloth in the port that is like a very thin dish rag and while I had some success, I also ended up with less low-end. This is getting interesting, but also disappionting because it seems that I might not be able to do anything about it. In other words, I'm learning that this subwoofer is not capable of producing what I want for low-end! ha :)

 

At least it's better than my Altec Lansing VS4121 speaker system!

Edited by TwoCables
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I'm getting somewhere! I made it worse. I put 4 thin strips of tape across the top of the tube parallel to each other spaced fairly evenly apart, each about 3-4mm wide. So, now I know for sure that it's the air turbulence. All I have to do now is figure out how to get it to stop. I might try loosely stuffing a some kind of a thin cloth in from the outside. I'm betting that it's due to the bend in the tube.

 

Edit: Just to learn, I stuffed my cotton cloth in the port that is like a very thin dish rag and while I had some success, I also ended up with less low-end. This is getting interesting, but also disappionting because it seems that I might not be able to do anything about it. In other words, I'm learning that this subwoofer is not capable of producing what I want for low-end! ha :)

 

At least it's better than my Altec Lansing VS4121 speaker system!

I'm not sure how low the 2.1 goes. I have one at the office, but I have never tested it. My 5.1 does nothing much below 25Hz.

 

Have you tried putting the sub in a corner? If that is possible, you will get a ton of gain and you might even get that low end.

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