4 ohm and fried

  • Thread starter Thread starter CoolCat
  • Start date Start date
CoolCat

CoolCat

Well-known member
I bought some JBL Control 5 not too long ago, $25 pair, they retail at GC for $350 pair.

One turned out to be blown, the foam is fried and theres no audio. the tweeter too.

The other is ok.

Along time ago I tried using 4ohm car speakers and they both had their foam destroyed and the cone became brittle and fell apart.

I assume both cases these 4ohm speakers were destroyed/blown because they were hooked up to a high powered 8ohm output.
Is this a good guess?

I also wonder what a repair might cost on the JBL C5? Anyone have a guess?
Buying replacements is far too expensive and these speakers were a CL purchase, I dont need them.
 
The amplifier doesn't have an impedance rating, the speaker does. You do need to realize that the amp will put out more cottage at a lower impedance than it does at a higher one. but, yes, running way too much power through a speaker will create too much heat and screw up the speaker.
 
Well, amps actually DO have an impedance rating (sort of) but it works the other way around. An amp should specify the minimum impedance it can drive safely because, the way Ohm's law works, the lower the impedance rating of the speakers, the more power the amp will try to put out.

Hooking 4 ohm speakers to an amp rated for a minimum of 8 ohms will result in the speakers trying to draw double the rated power of amp. The all-to-common result of this is the amp itself dying. If you're lucky, the amp will have overload protection and not destroy itself. If you're unlucky, you may get a nice smoke effect.

Either way, it's worth paying attention to the matching of speakers and amps. Not doing so can be an expensive hobby.
 
CoolCat said:
I assume both cases these 4ohm speakers were destroyed/blown because they were hooked up to a high powered 8ohm output.
Is this a good guess?

.
Click to expand...
nope ....... .... first off, the foam wouldn't be damaged by that at all ..... that's a matter of UV deteriorating the foam usually, and heat too like in a car in the sun.
Further, not all amps put out significantly more into a 4 ohm load than an 8 ohm load.
Some do but some don't ..... and certainly it's nothing like 2 times more or even more than that.

All you have to do is look at specs.
Virtually none of the amps we guys use double power into a 4 ohm load.
Expensive stuff like Bobbsy uses for his sound reinforcement gigs might but the cheaper stuff we all use doesn't.
And some amps (like my Ampegs) put out the same regardless of impedance because they're switchable to match the load they're going into.
 
In order for an amp to put out twice its rated power on half the rated load you still have to turn it way up.

Overpowering a speaker will result in either mechanical damage (torn suspension etc.) or thermal damage (burnt coil etc.). Disintegrated foam is caused by age and/or exposure to the elements.
 
bouldersoundguy said:
In order for an amp to put out twice its rated power on half the rated load you still have to turn it way up.

.
Click to expand...
doesn't change the fact that most amps do NOT double power into half a load regardless of how much you turn them up.
That's a truisim that's constantly repeated around here and it's simply not true.

A quick perusal of amp specs will show that with the exceptions of quite expensive amps that have robust enough power supplies to pull it off, the vast majority of amps don't.

For example ..... the very first Crown specs I found for one amp was 500 watts@8 ohms, 800 watts @ 4 ohms and 1050 @ 2ohms.
That's more like a 60% increase from 8 to 4 ohms and only a 25% increase from 4 to 2 ohms.
This is fairly typical of common amps.
Now a $5000 Crown I found did go from 1250 a side into 8 ohms to 2500 a side into 4 ohms so it did double but then it actually dropped in power into 2 ohms.
It's all about the power supply.
And this gets talked about most in the guitar amp section and guitar amps especially don't tend to double output if you halve the load.
 
Amps can generally put out way more than their rated power, even at 8 ohms. Rated power is limited by distortion specs and thermal limits. That is, an amp can exceed its rated power when driven past acceptable levels of distortion or to a level that causes thermal overload. If an amp's 4 ohm rating is much less than double the 8 ohm rating it's to keep it within distortion specs or thermal limits. It will still put out something like twice the power into half the load. It may sound bad or the amp may overheat more easily but for a while there will be double the power.
 
Lt. Bob said:
Further, not all amps put out significantly more into a 4 ohm load than an 8 ohm load.
Some do but some don't ..... and certainly it's nothing like 2 times more or even more than that.
Click to expand...

If they CAN'T that's down to limitations within the amp. They at least TRY to, hence the risk of damage to the amp if you connect speakers of lower than rated impedance. In the live sound arena, most amps these days are rated down to 4 ohms and a good many even claim to drive a 2 ohm load (though even the best seem to be working damn hard--as judged by heating--and I'd have real fears about what I was doing to the service life at such a low impedance). However, the "truism" about amp power doubling as impedance halves is more than a truism. It's mathematics. Even if an amp can't manage it, it's what it's trying to do and risking an amp heart attack in the process--just like me trying to run a marathon!

bouldersoundguy said:
In order for an amp to put out twice its rated power on half the rated load you still have to turn it way up.
Click to expand...

No! Turning an amp up or down isn't changing the gain; it's attenuating the input. The amplifier stage simply adds a certain number of dB gain to the input signal and is always capable of putting out the full rated power if it get an input signal high enough--but with the volume on the amp turned down, you're risking a clipped input. There's huge debate about whether a clipped input is more likely to damage a speaker at high levels, so lets not get into that here! However, turning down your amp to protect your speakers is based on a misunderstanding and most PA amps are run with the input attenuators at full up (11 in moresound's case :) ).
 
Bobbsy said:
If they CAN'T that's down to limitations within the amp. .
Click to expand...
absolutely ...... which I said. If the power supply isn't robust enough it can't put out the doubling of power, I SAID that. Did you read it?

Except for pretty expensive amps the vast majority of amps these days don't have robust enough power supllies to double output into half the load regardless of what they TRY to do.
All you have to do is look at amp specs. Until you get up to stuff like a 5000 dollar Crown NONE of them spec out to doubling power into a halved load.
Yes .... it's absolutely the power supply that limits it ....... but that still doesn't change the fact here and that's that most amps do not have a good enough power supply to accomplish it.

Further ..... in an amp with adjustable loads like my Ampegs ..... if I run my V2 into a 8 ohm load it puts out about 60 watts ...... if I switch it to a 4 ohm load and run it into a 4 ohm speaker it puts out about 60 watts and if I change it to 2 ohm output and run it into a 2 ohm load it puts out about 60 watts.
The truism doesn't even come close to being true.
 
Fine. Most amateur amps can't put out double the power at 4 ohms than at 8 ohms.

However, did you get MY point which was that an amp driven into a load it's not specified for will TRY to do that and risk death in the attempt--therefore users should be aware of the ratings?
 
Since we're talking about speaker damage the rated power doesn't matter as much as the actual power delivered to the speakers, clean or not. Amps can put out more than their rated power if driven hard enough. Of course they'll sound bad doing it and might overheat.

Guitar amps are different. Distortion is part of the sound so the limiting factors are power supply and heat.
 
Bobbsy said:
No! Turning an amp up or down isn't changing the gain; it's attenuating the input. The amplifier stage simply adds a certain number of dB gain to the input signal and is always capable of putting out the full rated power if it get an input signal high enough--but with the volume on the amp turned down, you're risking a clipped input. There's huge debate about whether a clipped input is more likely to damage a speaker at high levels, so lets not get into that here! However, turning down your amp to protect your speakers is based on a misunderstanding and most PA amps are run with the input attenuators at full up (11 in moresound's case :) ).
Click to expand...

I wasn't talking about the input gains but about the overall system gain and the high SPL that follows. That is, if the amp was really putting out so much power that it damaged the speakers there was too much overall gain and it must have gotten pretty dang loud. So, did it get really loud at some point? If no then the speakers probably didn't suffer too much power.
 
Can't you damage a transducer with insufficient power?
 
I've heard some claim that, if you have an underpowered (more accurately since speaker efficiency is greatly variable, just too quiet) system and try to compensate by pushing the input level far into clipping, the almost-square-wave signal can damage a transducer. I have to say, I'm a sceptic but maybe I'm less willing to put up with ugly clipping noises than some DJs!
 
Well that's what I had thought.

I've heard DJ just push the poop out of their small systems and it just sounds terrible - that and using low bit MP3's make for an even worst experience.
 
moresound said:
Can't you damage a transducer with insufficient power?
Click to expand...

The consensus of people I trust on this is that "too little" power or square waves don't damage speakers. If the amp is moderately undersized it's still possible to drive it well past its power ratings and damage a speaker. Although the waveform will be heavily clipped (and approaching square wave) it is the power (area under the curve) that damages the speaker. The shape of the wave is incidental.

I think there's a psychological side to this. The clipped waveform is less satisfying than an unclipped waveform which induces PA operators to push even more level trying to get that punch. Pretty soon their 500 watt amp is putting out 1000 watts into their 700 watt speakers and the voice coils let out the magic smoke. What they remember is that the amp was clipping the whole time so that becomes their explanation when it was really a matter of not enough rig for the gig.
 
You must log in or register to reply here.
Back
Top