I have a Shiva sub in a sealed box powered by a Definitive Technology amp. This sub has worked great for 3+ years until last night. During the low frequency portions of a movie soundtrack I notice a sort of bububububub purring sound through the sub. The louder the bass the faster the frequency of bubub's. Sorry I can't be more technical than that. My question is how do I know whether it's the Shiva driver or the amp that's causing this sound? It sounds to me like an electrical as opposed to a mechanical sound. Thanks!
It doesnt sound like the driver is causing the problem. Check your connections, perhaps try hooking a differnt speaker to the amp and see if it does the same thing. You could also hook the sub up to a different amp and see if it does it. There isnt a whole lot in a speaker that can go wrong. Your tinsel leads can get ripped off, your voicecoil can fry, the cone can be ripped torn or broken, the surround can be torn, the spider can be torn, voicecoil can be misaligned, magnet can be come demagnitized, and thats about it. Mostly when subs start distorting from damage it is due to some damage done to the cone surround or spider which may misalign the voicecoil or cause some other sound to occur. I'd say if you look at the speaker and nothing appears to be broken and you can move the cone in and out by hand without it hanging up then the speaker is probably fine(considering that it's still playing) If the speaker seems fine and the amp checks out it could be your signal source.
Are you sure it isn't in the recording? I ocassionally hear some stuff on a recording that makes me think there is something wrong with the system.
I have a feeling you're right that it's not the driver. When I push on it with my hand it seems tight and I can't hear any mechanical noises. Also, if I push on the driver while it's making the noise the noise doesn't change. Unfortunatly I don't have an extra driver to hook up. I do have another sub that I can hook up to my receiver to check the source. It's just incredibly heavy and upstairs. My guess is it's the Def Tech amp distorting for some reason. Guess I'll try pulling the amp off the back of the sub and check out the Shiva while it's open. I can probably come up with another amp to try as well. Thanks for the suggestions...
Bill- I really did think it was the soundtrack at first. I was watching the Bourne Supremacy and I was sure that it was some weird sound effect they were using for the dramatic, bass heavy scenes. When I switched to the news afterwards though, the sound was still there.
Bill- I really did think it was the soundtrack at first. I was watching the Bourne Supremacy and I was sure that it was some weird sound effect they were using for the dramatic, bass heavy scenes. When I switched to the news afterwards though, the sound was still there.
I finaly got around to pulling the plate amp off the back of the sub. I hooked up another driver I came across and it makes the same noise. That pretty much eliminates the SHIVA. I also tried plugging my other sub into the receiver and it worked fine.
So I'm pretty sure it's the Deftech amp.
Ron E: I did a search on motorboating and that may be the problem. Do you think replacing the capacitors will eliminate the problem? There are two big 10,000uf/80V capacitors on the circuit board which are the most obvious. Since I may have to scrap the amp, I'd be open to trying a cap replacement if they aren't too expensive. Are ther other caps I should be concerned with? Any help would be appreciated.
By the way, in case it helps, I notice that when I first flip on the sub amp I don't get the big WUMP sound I use to get before this problem. Just a little bump sound.
Thanks,
Brian
So I'm pretty sure it's the Deftech amp.
Ron E: I did a search on motorboating and that may be the problem. Do you think replacing the capacitors will eliminate the problem? There are two big 10,000uf/80V capacitors on the circuit board which are the most obvious. Since I may have to scrap the amp, I'd be open to trying a cap replacement if they aren't too expensive. Are ther other caps I should be concerned with? Any help would be appreciated.
By the way, in case it helps, I notice that when I first flip on the sub amp I don't get the big WUMP sound I use to get before this problem. Just a little bump sound.
Thanks,
Brian
motorboating
Actually motorboating is usually caused by a poor ground within the amplifier or improper (too high) gain settings causing the amplifier to pick up on some radiated noise from the AC line which happens to be 60Hz. Try turning down the amp gain on the sub and increasing the subwoofer volume on the amplifier.
Actually motorboating is usually caused by a poor ground within the amplifier or improper (too high) gain settings causing the amplifier to pick up on some radiated noise from the AC line which happens to be 60Hz. Try turning down the amp gain on the sub and increasing the subwoofer volume on the amplifier.
If it's not the gain settings you may have a bad output transistor. The capacitors rarely go bad, it is more likely the output transistors or one of the little resistors near the output section. Those guys melt all the time. Look for some black around the internal components and it may give you a clue as to what may have gone wrong. Good Luck and keep us posted.
-newbie chad
-newbie chad
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