I delivered my son back to my ex-wife last Sunday after having him for the week, and we had a bit of “situation” develop before I left, involving my 16 - soon to be 17- year old daughter who is an aspiring bedroom DJ and some audio equipment I had given her and some she had purloined from my house on the sly.
My daughter loves techno and I gave her a Denon DRA-275R receiver and some inexpensive, but passable Polks. She loves to play them at max volume and she blew out the Polks after few months, but I figured that it was on one time mistake and replaced the woofers, and told her to keep the volume down. She promptly blew them again. I figured the Polks were of inferior power handling ability and replaced them with a somewhat better pair of bookself sized Wharfdale Black Diamonds. I refused to let her have my more expensive Infinitys because they were very nice and I was concerned she would not take care of them.
Before I left my ex’s house she asked me to look at her receiver as it seemed to be dead. I offered to go up to her room to see it, but she said she would get it and brought it down in the twinkling of an eye. The receiver was simply DOA and kept popping one of s pair of 4 Amp 125 V internal fuses whe powered up. I asked what the heck happened, and the waterworks started. Crying, she brought down her blown pair of Black Diamonds, and then started howling louder and brought down the forbidden pair of Infinitys (blown as well) she had snuck out of my house when I gave her the key to do some research using my net broadband connection a few weeks ago.
I now have one dead little Denon receiver
A pair of blown Infinities - The woofers are simply shredded but
the tweeters are fine.
A pair of Blown Black Diamonds also with shredded woofers
I think the problem is that she has this (to me) fairly complex DJ club mixer she bought with her own money, and uses it to control input from her pair of Technics 1200 turntables. I’m not sure she really knows how to use this thing, and I suspect something she did with the mixer output fried the amp, which in turn fried the speakers, once then again. I don’t know where to begin looking in this chain of audio crimes and stupidity for the source of the problem. It looks like the receiver will be trashed as I do have the electrical expertise to fix it, and it’s not expensive enough to warrant a probable 100+ repair of it's innards when I (she) can get a comparable new unit for around 150. - $ 200. or so.
What the hell happened to these poor speakers, and how can I tell her to prevent this from happening in the future, as any future audio eqipment will be on her dime at this point.
First, if she is blowing speakers like that, she is probably doing some serious damage to her hearing. That should be the prime concern.
Second, “clipping” or overdriving the amp is much more likely to damage speakers than simply feeding them too much power. It is much easier to blow speakers with 100 crappy watts than with 1000 good clean ones. Polks, Waferdales, and Infinity speakers are all of decent to good quality, so I suspect that she was over-driving the amp which leads to distortion aka clipping which leads to blown speakers. If she is using some funky mixer like you say to boost the bass way up, that could be the problem. It is odd though that the tweaters are still good. Usually it is the tweeters that burn out first, and the fact that they are still ok means she probably burned out the speakers by over doing the bass.
How to prevent this in the future? Well, she needs to have realistic expectations; you aren’t going to get club level bass out of bookshelf speakers and a receiver, and if you try to do it you will simply blow them, and your ears, out. If she insists on playing at that volume level there is simply no replacement for big speakers. Efficient speakers would help too, like some Klipsh horns or something like that, but now we are talking about $1000+ speakers and a quality amp to drive the whole thing.
Ooh, another thing I just thought of, you say she is using TT for a source, was she using the phono in on the back of the receiver? If not, that could be a huge problem. You can’t run TTs through just any input on the back of the amp, they MUST use the phono input.
No, she knows enough to use the phono input on the mixer and the line level input on the receiver, though if she did accidently forget and plug the mixer into the phono input that might have done it.
Clipping sounds like a reasonable explanation, but I can’t figure what happened to the receiver that it would blow both speakers, but it is definitely fried. The 4 amp/125V fuse flashes and toasts as soon as I power it up.
What about getting speakers rated higher then the receiver can put out? For instance if I Had a 100 watts per channel receiver and hooked up speakers that are able to handle 200 watts, wouldn’t that solve the problem?
I’m not much of a stereo whiz, but it sounds reasonable to me. And I second what Andrew said. She’s old enough to get a part time job. if my daughter did that and then expected me to keep ponying up equipment she’d be out of luck.
My son when he was about 4 or 5 shredded one set of woofers. He did it the traditional way - wind up maximum gain on the amp, then provide the signal. Instantaneous.
No, as Rhum Runner noted, it could make it worse ( depending on the exact equipment pairing - simple wattage ratings don’t tell the whole story ). Underdriving speakers is almost always more of a threat than overdriving them.
You might be better off pointing her towards some entry level pro gear. You can peruse online places likeMusician’s friend and get some ‘starter’ equipment that will hold up to the abuse.
As herman_and_bill said, the problem with the receiver is probably that the output transistors are blown. They probably took other components with them, so replacing the whole unit is the best way to go.
I’m not familiar with the Denon DRA-275R, but it’s almost certainly a “home stereo” unit, not a disco/club/prosound sort of amp. Also, you didn’t specify what size your Infinities are (8/10/12/15 inch woofers?). Just guessing here, but if she’s doing club/disco/DJ type of mixing, she’s got the bass turned up to 11 (or even higher). That’s why the tweets are OK, they aren’t being used as much.
Look at the wires she’s using to hook the speakers to the amp. If there are some “Y” connections in there, then she has them wired in parallel and that’s the problem–a reduced load will cause the output transistors to over heat and melt, sometimes sending DC into the speakers. That’ll do it!
Suggestions:
Get a whole different kind of gear (meaning, have HER get…). Pro DJ stuff is built to take that sort of abuse where audiophile gear is not. For the same $800 you spent on your lovely Infinities you could have a power amp (not a receiver) and club speakers that will shatter the windows in her room.
Not that daughters will listen to their parents (I have 15 and 17 year old girls living at home) but mention the hearing thing. I’m losing the hearing in my left because that’s the one I keep towards the drummer.
If she ignores the hearing advice, get her headphones. If she is hoping for the professional DJ gig, she’ll need some anyway.
Since the woofers were destroyed in all of the speakers and the tweeters are ok I would look at clipping last.
Clipping usually destroys the tweets first since the voice coils don’t have the cooling capacity to dissipate the heat produced from the artificial tones created by the clipping.
If the Denon is common to all of the speaker destruction then I would look for DC voltage at the speaker outputs produced by a blown transistor, as previously mentioned.
As for overdriving an amp to the point of destroying the woofers; I commonly overdrive the amp in my office listening area and have yet to destroy any speakers although the top of the amp ove the transformer will get hot enough to make a CD turn limp and floppy.
I say look at the Denon first. Hook up a disposable speaker to the speaker outputs and look for the woofer to jump to either end of it’s travel and stay there. If this happens, you have a DC current and any speaker you hook up to the amp will be destroyed.