strange thumping sound...

[fenderguy]

hey all. I have a DSM 1515 sub, and i've been noticing a problem. Shortly after i turn on my stereo (within a couple minutes), shortly after i turn off my stereo (within a couple minutes), and sometimes just at random (stereo on or off) my sub will just start thumping. Not even a deep thump either (although it is rather loud)... it sounds like someone is knocking on the wall in the room next door or something. It thumps 6 or 7 times, and then stops. I'm assuming it's picking up some sort of signal from something? i don't know. My cerwin vega LW12 is about 7 feet away, and it doesn't do this. However it seems to me that when i had my cerwin where the DSM is now, it did the same thing. Is there anything i can do to make it stop? I've just turned the DSM off for the past few weeks because it's annoying, and i don't want to damage it. Any help would be appreciated.... thanks guys!

[Sonnie]

That is very strange indeed. I've never heard of anything like that before. You sure there's not a rat in the wall behind the sub?

Have you tried using a long extension cord and plugging the sub into another outlet far away? I'd try and get on another circuit... or the same circuit you have the CV plugged in... then try another further away.

[Danny]

ok heres my two cents.
First try unplugging the sub from the rest of the gear and running it on its own, if the problem isn't happening it's not the sub if it is then you have a problem with the sub.
Then unplug individual items and run the rest of the system without it. (one piece of equipment at a time) if you have a problem then you've eliminated the gear not connected at the time if no problem then its a fault with the gear that you disconnected.
If you do all this and still have a problem look at other factors (eg unbalanced/unshielded cabling), interference from other devices etc.

Hope this helps

D.

[fenderguy]

thanks for the responses guys. To clarify... the Cerwin and the DSM are both plugged into the same outlet (along with a 27" TV, and my entire stereo/surround) which all draws a lot of juice. I know that this isn't probably best, however i have NO choice. I live in a "single" dorm room, and there is only one outlet point. As i mentioned before, the cerwin vega used to do something very similar when it was in the exact spot the DSM is in now, execpt it made a loud POP!! every now and again. My room (as you can imagine) is very tiny, about 12' x 7' maybe (probably kinda small for the massive amount of stereo equipment in it but... meh) and so there is no other place i can go with the DSM. And if i have to choose between the 12" cerwin, and the 15" DSM... my choice is easy.... CERWIN BABY!

so I'm pretty sure i'm picking up some sort of interference over where the DSM is. If this is the case, how can i go about shielding the sub better?

It should be mentioned that at the moment i'm sorta daisy chaining the subs. Sub out of the receiver, into the Cerwin... then out of the cerwin, into the DSM.

Thanks again guys!!

[Otto]

Hi Nick,

Kinda like Dan suggests above, we need to narrow in on the cause of the problem. The first thing I would do would be to disconnect whatever signal cable runs from the CW to the DSM. Leave it in its original location, but just break the connection at the CW end. Then turn the DSM on/off and see if the problem still occurs. Try to keep all else equal during the test. Then post what happens, and I or someone else can help with a next step.

BTW, what kind of signal are you using from the CW to the DSM? Speaker-level or line-level?

Good luck!

[fenderguy]

ok.. i'm running line level inputs. i disconnected the line-out (and thus the line-in to the DSM) from the cerwin and i get a constant hum from the DSM no matter what i do. If i disconnect the line at the DSM the sub makes no noise. Is this just what happens when you have a line disconnected or is this bad? The line isn't the best... but it's not bad. It's from Radio Shack, and is pretty heavy gauge for RCA cable. I'm thinking it is just the fact that the RCA itself is exposed on the Cerwin side then is causing the hum... i don't know.

Thanks again for your help guys!!

[brucek]

It should be mentioned that at the moment i'm sorta daisy chaining the subs. Sub out of the receiver, into the Cerwin... then out of the cerwin, into the DSM.

Why ?

Is this just what happens when you have a line disconnected or is this bad?

A long unterminated coax cable is an antenna.

brucek

[fenderguy]

[quote=brucek;12876] Why ?

You have a better idea? I'm running two subs... and there's only one sub output from my reciever. I'm thinkin that's why subwoofers have line level inputs AND outputs no? I'm not being sarcastic... just sayin.

[Otto]

Hi there,

I kind of expected the hum. Does it do the thumping thing, though?

[fenderguy]

i didn't leave it on that long... when the receiver it was hooked up to was off the subwoofer thumping was very rare (only a few times a day) It was more common (i think) when the receiver was either on, or just previously turned off. Now that it is no longer hooked up to it... i don't know. I'll unhook the RCA completely and leave it in the ON position... and see what happens.

[Otto]

Sorry, I may have misread the OP. I though it was when you turned the sub on. My mistake. In this case, I would try taking the CW out of the loop and connecting the DSW directly to your receiver. You may also try a Y cable to connect two subs directly to the receiver, rather than going through the CW.

[brucek]

fenderguy says:

You have a better idea?

Otto correctly answers:

You may also try a Y cable to connect two subs directly to the receiver, rather than going through the CW.

brucek

[fenderguy]

brucek wrote:

fenderguy says:


Otto correctly answers:


brucek

I wasn't disagreeing with anyone, you act as though i was . But thanks for the tip otto. I had my sub off for about 2 weeks, and since i turned it on yesterday i haven't heard the thumping. I even hooked it up and was using it last night... i forgot how much i loved that big ol girl. It will most likely start again, when it does i'll get a Y and avoid daisy chaining. i'm still not exactly clear as to what the benefit would be though. Isn't the line level input output on the cerwin nothing more than a Y basically? Plus this way i don't have to have a 16' RCA cable to get to the sub. I just use two 8' cords (one to the cerwin, then one to the DSM)... seems to work easier.

Thanks guys!

[Otto]

Hi Nick,

I think brucek was just pokin' back at your "you got a better idea?" comment. I'm sure it's fine...

As to the CW performing as a Y connect, I'm not sure. There could be some other circuitry in there doing who knows what... Yeah, see what happens when you take the CW out of the loop. If the problem is gone, great! If not, let us know...

Best luck.

[Jerm357]

Are you sure the thumping sound is not one of your dorm room neighbors banging on the walls so you turn it down

[kickingrass]

Gents,

I have the same thumping problem with my two Paradigm Servo 15's. Sounds like someone banging on the ceiling to get me to turn down my system( that never happens :-)
I have tried new power cables, powering them through a Belkin filter, disconnecting the line level inputs and yet they still do it. I have caught the cones moving and the front panel light flickering when it happens. The only way I can recreate the symptom is to use my cell phone near the sub. I also live in an apartment type house with downstairs neighbours who have teens who use their cell phones alot. The subs go really crazy when a cab shows up out side. I think his mobile radio is stronger than a cell phone. Happens every time there is a cab outside waiting for the teens downstairs. I feel it is some type of shielding flaw in the design. My Paradigm PW2200 never had this problem. I spoke to Paradigm directly and they had me do the usual checks that I mentioned above. Then I bought a second sub and now have the same problem on both. Not a deal breaker but a pain in the a%# nonetheless.

Carl

[brucek]

I have caught the cones moving and the front panel light flickering when it happens.

The front panel light is connected to the power supply, so for it to be flickering, you must be drawing a lot of current. I know when I play a really low sine wave signal through my servo-15 at high levels the front panel light will dim a bit. This just shows me that I am drawing a lot of current from the supply and it is sagging a bit from the load. For your light to flicker, it seems quite strange....

Is the signal coming in the line-input cable? Since you have two units, you can leave one hooked up and one not hooked up (but both turned on) and see if it is coming in on the interconnect.

brucek

[kickingrass]

I actually unplugged the line input right at the sub amp( when I only had one sub) and the sub still thumped. ( I had to wait a day or two for it to happen)

Carl

[brucek]

I actually unplugged the line input right at the sub amp( when I only had one sub) and the sub still thumped

Amazing... I have the same sub with no trouble.

brucek

[kickingrass]

Strange for sure. I sent an e-mail off to Paradigm again to see if they can come up with anything beyond
the usual suggestions that I have already tried.
Carl

[kickingrass]

here is the reply I received from Paradigm.


Hi Carl

Your email has been sent to the designers and R&D.

I will let you know if there is anything that can be done as soon as they
respond.

Sincerely,
Gary Takeda
Paradigm Technical Support


Now I sit and wait.

Carl