Dj speaker repair...

[Tann-44]

We've all helped out a friend with speaker replacement's at some point...

Last year I helped a dj friend who got careless with the pa system and you guessed it pop went the speaker's a nice pair of wharfendals 150 rms 300w max...

so we set about getting some replacements speakers and fitted them as they where needed for his friday night gig...any how all went well but 2 months down the line he call's again saying they've blown again oh we did not even turn them up that loud as it was a small venue plus they've only been used 6 times or so...yeah we've heard that one before...

so on checking the damage I found both cone's stiff as board and the smell of crisp burnt coil's...
I called my mate to say these have been push hard for the coil's to be burnt like that...nope your wrong there mate! so my next question was what is the o/p of his amp? turns out to be 200w rms per side and he was told it would be ok to use the wharfendales cos there 300max..

He now thinks he should get free replacement's from the store cos they popped...nope if you use to strong a amplifier on speakers.. A.. keep it to a usable level or B get one's that can cope with the power with some head room to spare...

So who's been down this same old road??

 

[Sceadwian]

Don't try to explain technical issues to a DJ. He screwed up, quote the math and leave him standing there alone. Probably doesn't even realize that even at 75% of their rated power the harmonic distortion is so bad that any nearby audiophile will rise from their grave to chastise him. With any luck they understand the importance of multiple speakers and crossovers.

Given three speakers 5 watts for sub, 5 watts for mid, and 5 for tweeters, it will add up to more than 15 watts total from a given speaker as far as the actual audio output goes compared to a single 15 watt speaker.

Try to explain acoustical membrane to transducer impedance matching to the same person.

 

[Gobbledok]

An underpowered amp which is driven into clipping is just as likely (maybe even more so) to blow speakers than an overpowered amp.

 

[audioguru]

"Max" 0r "peak" power is a lie used by cheap amplifier and speaker manufacturers. It is double the real RMS continuous power rating. "Max music Power" is Max power only for a moment.
A real power rating is RMS power continuously at a low distortion.

When a 200W RMS amplifier is clipping hard then its output is 400 Whats max continuously but with extremely high distortion! Maybe 600 Whats max music power for only a moment.
Of course a speaker rated for 600 Whats max music power for a moment will be fried when it gets 200 Watts RMS continuously.

Some 200 Watts continuous RMS speakers and amplifiers are rated for peak-to-peak music power which is the number doubled again. 1200 Whats peak-to-peak music power!
Lots of lies.

 

[bountyhunter]

so on checking the damage I found both cone's stiff as board and the smell of crisp burnt coil's...

I'd check that amp for DC offset or bias problems.

 

[Nigel Goodwin]

He now thinks he should get free replacement's from the store cos they popped...nope if you use to strong a amplifier on speakers.. A.. keep it to a usable level or B get one's that can cope with the power with some head room to spare...

The speakers were mis-sold, they weren't suitable for the amplifier supplied with them - the store wouldn't have a leg to stand on in court.

For PA/DJ use it's absolutely vital that amps and speakers are fairly well matched, otherwise you ARE going to blow things with normal useage.

 

[Tann-44]

Bountyhunter, that was my next question to him..but, he did say it's ok because he used it on a second pair with clean power.... I would liked to of checked things myself to ensure it was ok as he just plugged a his back up pair straight in...wow!!

 

[Tann-44]

The thing is, he was sold the wharfendales to match his amp...mmm to most of us a 200w rms per channel amp is not matched to a pair of 150w rms speaker's...he was given the old sale's talk 'yes these are able to cope sir..there 300w max and your amp is 200w per side more than able to do the job!.....yeah the job of being hammered to a crisp....

I wish, I was there at the time to hear all this sale's talk!

 

[Tann-44]

"Max" 0r "peak" power is a lie used by cheap amplifier and speaker manufacturers. It is double the real RMS continuous power rating. "Max music Power" is Max power only for a moment.
A real power rating is RMS power continuously at a low distortion.

When a 200W RMS amplifier is clipping hard then its output is 400 Whats max continuously but with extremely high distortion! Maybe 600 Whats max music power for only a moment.
Of course a speaker rated for 600 Whats max music power for a moment will be fried when it gets 200 Watts RMS continuously.

Some 200 Watts continuous RMS speakers and amplifiers are rated for peak-to-peak music power which is the number doubled again. 1200 Whats peak-to-peak music power!
Lots of lies.

Agree..

 

[Sceadwian]

Avoid the salesman. ANYONE trying to sell you something has only one thing in mind, to sell you something, otherwise they wouldn't even be trying, they'd just provide you with information and let you decide.

I've come close at least a half dozen times in the last year alone to throw a punch at a so called 'expert' in a store. I have not to this date once EVER run across someone in a store that sells anything betray any fundamental truth or knowledge to the consumer that might benefit them if it could reduce their profit margin by even the smallest fraction.

The few stores I've been to that don't have a hard commission base and go for customer satisfaction do only one thing better, they sell whatever anyone else buys and comments on positivly, this is nothing more than a social effect of experience and shows not one iota of actual product knowledge.

 

[audioguru]

There are two computer store chains in Canada owed by the same company. Best Buy from the US came to Canada and bought Future Shop.

Future Shop has commissioned sales people who JUMP on you and want you to buy the most expensive thing they have plus all the options.
Best Buy has sallaried sales people who are friendlier and sell what you want.

I bought my first computer from a commissioned sales HAWK at Future Shop then bought my second computer from a friendly sales guy at Best Buy.

 

[Nigel Goodwin]

Best Buy from the US came to Canada and bought Future Shop.

Best Buy tried in the UK, they lasted about 12 months, then pulled out with millions in debts!.

 

[Tann-44]

I'd check that amp for DC offset or bias problems.

I've checked his amp and all it fine....I even connection it to my 12'' 300watt rms cab's in the local studio and did not even have to turn up that loud to hear the difference ... he's reaction was mmm, well we did play at a loud level before the speaker's sounded rough and breaking up!!

I rest my case.. some Dj's use under rated system's and think it can be pushed hard!! .....wait for the smoke to appear...

 

[unclejed613]

i've seen many examples of sales people selling amplifiers with more power than the speakers can handle. one of my customers kept bringing the same pair of very expensive speakers in with melted voice coils. the manufacturer's policy was to void the warranty for burned out speakers. i asked the customer what they had for an amp. it turned out to be a 250W/channel (rms), and the speakers were rated at 100Wrms. the speakers cost more than the amplifier. i asked the customer whether or not it really mattered to him that he had these nice pieces of expensive furniture, or he wanted speakers that could handle the power of his amp. i also explained that his expensive speakers had a sensitivity of 80db@1m@1W, which meant to get a SPL of 100db required 100W. i showed him a pair of professional stage monitors rated at 800Wrms with a sensitivity of 95db@1m@1W..... at 40% the cost of the nice cherry wood towers (and which would provide a 105db SPL at 10W). he was very happy with the new speakers (i don't know for sure, but i suspect he got his money back on the expensive speakers because the store salesperson "created" the mismatch to begin with).

good pro-audio speakers are the best kept secret of the audio business. they are more efficient than home audio speakers, and so can be operated at lower power levels and get the same amount of sound. the efficiency is as important as the power handling.

as far as wharfedales go, what he SHOULD have got with his system is this model **broken link removed**

 

[Nigel Goodwin]

good pro-audio speakers are the best kept secret of the audio business. they are more efficient than home audio speakers, and so can be operated at lower power levels and get the same amount of sound. the efficiency is as important as the power handling.

But are also far lower quality, HiFi speakers are about quality, not raw power.

But if the guy you mentioned was running his system that hard, he wanted PA and not HiFi.

 

[Tann-44]

Here's the latest on things....he's now brought more speakers, no, there not burnt like that last pair! but working as they should be... as for the amp it's doing the job after a service and soak test to ensure all is well...