15" subwoofers

[Mindset]

I think "saturated" may be a better word for the magnet, not "overheated". No power is passed through the magnet, it only acts as a heat sink to help cool the voice coil, which is what generates all the heat. Voice coils get hot because they have all the voltage and current from the amp passing through them, if they can't cool down, they will fail.

Actually the magnet is part of sound reproduction. When the voice coil is powered up, and it enters the magnetic field, the neutrons move to x place etc & it's part of how sound itself is created. Just like microphones.

The current reaches the voice coil inside the speaker, creating an electro-magnet that will either be repelled, or attracted by the fixed magnet at the bottom of the speaker. That causes heat, generated by both the voice coil's and the fixed magnet.

The current goes to the voice coil and changes + to - to + rapidly, which it's polarity from + to -, and of course magnets attract opposites, which then either pushes or pulls the voice coil which causes the cone to move which then causes air pressure to change, and that is sound.

 

[boingoman]

The current reaches the voice coil inside the speaker, creating an electro-magnet that will either be repelled, or attracted by the fixed magnet at the bottom of the speaker. That causes heat, generated by both the voice coil's and the fixed magnet.

The heat is generated by the current moving through the wire, not by the magnetic fields interacting. I have never, for instance, noticed my guitar pickups getting hot when I play.

I will need some kind of proof that a magnet gets hot when something passes through it's field. Even if it does heat, I would bet the temperature rise will be in millionths of a degree, or at least not enough to affect the voice coil at all.

So when I said the magnet acts only as a heat sink, I meant it does not generate any significant heat by itself.

 

[Mindset]

Well, application has something to do with it. Your playing a guitar. I sometimes do car audio competitions (many back in the day) The moments of the subs & frequencies it's responding to will differ from yours being not hot, and mine that's banging out bass.

I agree that the magnets itself do not create heat altogether , but my point was that they do heat up because

Anyways, for the thing about blowing subs because of less power thing...

"It should also be mentioned that it can sometimes be easier to blow a speaker with an amp that puts out less power than the speaker is designed to handle! The reason for this is that an amp that is being overdriven can generate a lot of distortion and the RMS level of the amplifier output will be a lot higher than what the operator thinks it might be, and the speaker can blow." Taken off this site...
http://www.rocketroberts.com/techart/spkr.htm


Ok, here you go http://www.patentstorm.us/patents/5802189-description.html

The rotor is constructed so that it may be submersed in oil to provide greater heat dissipation. A motor will generate heat as a result of the excess energy that is not converted to mechanical energy as the power is applied to the motor. The motor will eventually burn out because as the power increases, the motor cannot dissipate the heat fast enough, therefore the available power handling is lowered to compensate for the excess heat. The present design can be completely submersed in oil because the shaft can be sealed. Conventional systems with longer excursion and high power using voice coils are not capable of being submersed in oil because there is no way to seal them. The Ferro fluid normally used with voice coils is insufficient because the oil will be blown out of the magnetic gap at high power with long excursions. The presence of oil also increases the damping of the unit, reducing distortion.

Motor = basically the magnet & parts

http://www.criticalmassaudio.com/catalog/index.php?act=viewProd&productId=20
http://www.tcsounds.com/tcmotor.htm Buy yourself a good mag and high power handling coils, and Kevlar coated cones, etc and build a sub, they are great.... if you do it right

Also, my subs in competition were very hot to the touch.

 

[boingoman]

Anyways, for the thing about blowing subs because of less power thing...

"It should also be mentioned that it can sometimes be easier to blow a speaker with an amp that puts out less power than the speaker is designed to handle! The reason for this is that an amp that is being overdriven can generate a lot of distortion and the RMS level of the amplifier output will be a lot higher than what the operator thinks it might be, and the speaker can blow." Taken off this site...
http://www.rocketroberts.com/techart/spkr.htm
.

Yup, that's right. The main thing to take away is that an amp that is rated below the power rating for your speakers may be able to produce enough RMS power when clipped to fry your speakers. Too much power, in other words. All you have to do is have a little restraint, and not clip your amp.

The part about distortion isn't right, though. If distortion killed speakers, a lot of guitar amp companies would be out of business, and rock music would be a lot less awesome.

Sorry to be so picky about the voice coil thing, I just wanted to make sure it's understood that the voice coil is the source of heat in a speaker, not the magnet.

Interesting link to the speaker patent. Seems like a take on Tom Danley's Servodrive stuff, but capable of much greater excursion.

 

[firby]

If you are a DJ looking for PA speakers try JBL and then EV. Really if you have mid level JBLs you are ahead of the game for DJing. Just buy them, cry, then have a drink and spin records. It gets better.

 

[CoolCat]

Yup, that's right. The main thing to take away is that an amp that is rated below the power rating for your speakers may be able to produce enough RMS power when clipped to fry your speakers. Too much power, in other words. All you have to do is have a little restraint, and not clip your amp.

The part about distortion isn't right, though. If distortion killed speakers, a lot of guitar amp companies would be out of business, and rock music would be a lot less awesome.

Sorry to be so picky about the voice coil thing, I just wanted to make sure it's understood that the voice coil is the source of heat in a speaker, not the magnet.

.

the terminology thing, clipping & distortion..clipping kills. flat line, pop bam boom good point.

I've never tried that amp test. So if I had some 100Watt speakers and a 10Watt RMS amp....if I clipped it it wouldn't blow the speaker? interesting.
makes sense I think?hmm?


the coil is the source of heat. Terminology thing..
Source being the key word, the magnet does get hot, its just not the "source"....

in other words, the electrons and atoms running into each other create the heat making them the "source" in relation to the coil, at a molecular level.
Its always the molecules and crap...damn things are everywhere causing problems.

JBL
The gear I had or have of theirs has never been a problem and takes abuse as well as Peavey....but I like the JBL sound better. But pricey.


Still, IMO, If the THROW goes too far out, the precision placed coil gets out of whack and thats usually the scratchy, popping, blown speaker sound....we hear.

So with that said...how does one best match up a amp and speaker that will NOT have the ability to THROW THE SPEAKER OUT of Alignment? Isn't that the real issue..er..goal?


woof.

 

[CoolCat]

I found this, I guess I was wrong...seems heat is more common to trashing the coil than extending..talking about a blown sub but the effects the same.

This type failure can happen at any frequency, not just the bass range. When people talk about blowing a speaker up they usually mean that excessive wattage caused a thermal failure of the voice coil. That type failure means that part of the voice coil became short circuited, or open, or deformed so that continued movement is impossible or very noisy. EVERY speaker voice coil can be burned up.

What does a burned (charred) coil look like? You can't tell until the cone and spider are cut out and the coil pulled out of the gap for inspection. However, sometimes the dust cap can be removed and you can see a melted Kapton voice coil former (It goes at 750 degrees.), or bubbles in a paper or aluminum former, or even charred wire. A new voice coil is a neat little cylinder of bright copper colored wire. When operated at its rated power it turns brown. When operated above its rated power it turns black. The coil could delaminate (come unglued from itself) before it turns black. THIS SHOULD BE COVERED BY THE MANUFACTURER'S WARRANTY. But once it turns black, it s ABUSE. Excessive heat can expand the voice coil wire and the little cylinder will not be neat anymore. Eventually the wire may become unbonded and create a short or open circuit.

Thermal overload cannot be fixed in watts. A speaker takes in heat (watts), and it can dissipate heat into the air. If the air is HOT the speaker can't handle as many watts. Power handling goes way down in the summer with a speaker in the trunk. Don't put a hot amp under a speaker or in the enclosure with it.