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OT - Stereo Upgrades

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Old 10-30-2002, 11:34 PM
  #61
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Alright, not to reopen a can of worms, but I need to hash out this clipping speaker blowing issue... (which I guess really IS opening up the can, isn't it).

A speaker does not have a set resistance, it has an impedance factor, rated in ohms, and even that is affected by the Q and some other factors which cause the resistance to vary at different frequencies, right?

A voice coil is an electromagnet, right?

Frequency variance causes change in resistance NOT due to any physical change in the electrical circuit through the voice coil, but due to affects of the magnetic flux or field surrounding the voice coil during the dynamic operation or movement of the voice coil across the fixed permanent magnet pole at differing frequencies. Right?

So, if we look at a signal being produced beyond an amp's ability to produce a proper sine wave (which ALL musical sound is comprised of), we see a voltage signal in which the topmost and bottommost quadrants of the wave arc are flattened (or clipped off) where the output section of the amp is saturated and can not produce the peaks of the waveforms anymore. Right?

We all know that an amp running into clipping will run warm, but the amplifier heat has nothing to do with the speaker heat.

A speaker voice coil heats from current passing through it. More current = more heat. A voice coil, however, is a moving component and its motion does truly accomplish an effective air-cooling action that tends to pump air in and out of the "tunnel" that the coil moves within (the spider also helps function as a bellows of sorts). So we see now that a voice coil in motion will typically maintain a safe temperature at a higher current flow than a stationary voice coil would otherwise tolerate.

Now, let's go back to the magnetic flux issue. If we begin sending clipped waveforms to a speaker at substantial power levels, we are asking (powerfully, mind you) the voice coil to follow an impossible path (a sine wave is a smooth reversal of momentum and is the natural motion of an undamped oscillator - or even a damped oscillator). A speaker cone is nothing more than an electrically-driven oscillator. A clipped signal is electrically possible, and is the result of any amplifier pushed beyond its saturation level. A clipped signal, however, is IMPOSSIBLE for an oscillator to faithfully reproduce. There MUST be some curve involved for the accel/decel components... As a speaker cone is fed these clipped (DISTORTED) signals, it attempts diligently to reproduce these waveforms. As it does so, the magnetic field is disturbed and the true resistance through the voice coil can (and usually does) drop which allows the current flow to increase. This increase in current flow can be substantial and can overheat the voice coil.

This can (and DOES) occur in situations where an amplifier rated at less than the safe RMS input wattage is connected to speakers and then run heavily into clipping over a period of time.

Somebody feel free to correct my thinking here, cause I ain't saying I'm right, I'm just presenting it the way I understand it to be.

As far as 1 ohm loads, if you are running an amp that is happy at 1 ohm loads, then you automatically have a built-in safety margin 8 times as high as somebody running an 8-ohm amp into an 8-ohm load. Let's face it: a 1 ohm load ain't got very far to go from "normal" to a "dead short". This means the differential from a speaker reproducing sine waves to a speaker being fed a hideous set of chopped waveforms can't look a whole lot different electrically to the amp (whereas an 8-ohm speaker in heavy clipping could drop as low as an ohm or so - definitely an opportunity for heavy overcurrent, especially on cheaper amps).

Comments???

mike

ps: Apache77 - I just live for your posts with pix of your sweety.
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Old 10-31-2002, 12:17 AM
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quote(A voice coil is an electromagnet, right? )

answer= no actually it does not use magnitism like people think, most people think is does the north south pole thing but they actually use what is called the right hand rule of electron flow. which i do not have time to explain, but it is not magnitism.


quote (. Let's face it: a 1 ohm load ain't got very far to go from "normal" to a "dead short". )

answer= think of it this way if you take 8 ohm how many times do you have to divide it by two to get to 1 ohm, then take 1 and divide it in half and see how long it takes you to get to dead short. you will be there for awhile because it will never actually reach 0. ohms does not mean anything just like the + and - on a speaker do not mean anything, they are just reference. instead of saying + and - on a speaker it could say apache and skater , you can still hook it up correctly.


Quote(whereas an 8-ohm speaker in heavy clipping could drop as low as an ohm or so )


answer= as per my previous answer you can build the amp to make the same power at what ever ohm you want. years ago they picked the ohm rating we use now because of the length of wire and ga. in the coil that was practical to build and then they built amps to work at that ohm.
 
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Old 10-31-2002, 12:18 AM
  #63
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but i did like your post you have a better understanding than most and you spent some time thinking about it instead of just writing
 
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Old 10-31-2002, 12:34 AM
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In a marine environment, voltage is far different than on a test bench that offers 100's of amps of current generated by regulated power supplies. In the real world, a boat idling or parked on an island, generally you have two 12 volt batteries.(bear in mind that most amps are rated at 14.4 volts. If you take an amp rated at 1000 watts at 14.4 at 12 volts it probably only makes 800 watts. As the voltage decreases, the amp draws more current to compensate. This creates additional heat and distortion. A simple test is to put a voltmeter at your amplifier input. Watch the voltage decrease as you demand more from the amp. The more the amp demands the lower the voltage and the draw increases causing even less voltage. How many watts do you think a 1000 watt amp makes at 10 volts. It would not take an electrical degree to calculate that a hungry 1000 watt amp might only make 400 watts in the real world.

Real world= 3 beers worth of tit watching at the island jammin the sound system. The batteries are probably sitting at 10 volts after just over an hour of amp use.

That is why it is important to use speakers that match the amp as well. A sub rated to handle 1000 watts is generally less efficient than one rated to handle 400 watts. A ported enclosure also adds to sound output efficiency. If you combine the correct enclosure, subwoofer and amplifier ultimately you can achieve far better results than concentrating on the bench ratings or opinions.

Proper system design is the key to sound performance. Each application has its challenges and its tricks to achieving the desired results. The true test is how it sounds when it is done and how long it performs without failure.

Generally, when I suggest a brand or combination of products, it is because the package has worked well repeatedly for many customers and therefore I can confidently offer that advice to others. There are many choices consumers have when choosing electronics. I offer items at all price points and promote what will ultimately lead to a satisfied customer.
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Old 10-31-2002, 12:46 AM
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Quote:
Originally posted by mcollinstn
A speaker does not have a set resistance, it has an impedance factor, rated in ohms, and even that is affected by the Q and some other factors which cause the resistance to vary at different frequencies, right?

A voice coil is an electromagnet, right?

Frequency variance causes change in resistance NOT due to any physical change in the electrical circuit through the voice coil, but due to affects of the magnetic flux or field surrounding the voice coil during the dynamic operation or movement of the voice coil across the fixed permanent magnet pole at differing frequencies. Right?
I think you're trying to point out the difference between a resistive and a reactive load. Most amp bench tests are done a a resistive load (w/ a series of resistors)...a speaker is a reactive load.

Quote:
Originally posted by mcollinstn
So, if we look at a signal being produced beyond an amp's ability to produce a proper sine wave (which ALL musical sound is comprised of), we see a voltage signal in which the topmost and bottommost quadrants of the wave arc are flattened (or clipped off) where the output section of the amp is saturated and can not produce the peaks of the waveforms anymore. Right?
Yes.

Quote:
Originally posted by mcollinstn
This can (and DOES) occur in situations where an amplifier rated at less than the safe RMS input wattage is connected to speakers and then run heavily into clipping over a period of time.
I think the true discrepancy is where a speaker's thermal threshold is. It's generally agreed upon that most speakers can reproduce a clipped sine wave (or square wave) as long as the wattage supplied is within it's thermal limits, or ability to cool itself.

If the wattage is exceeded, overexcursion of the voice coil will cause overheating, and the V/C will meltdown. I believe you are correct on the V/C resistance, but it's the overexcursion that will decrease resistance, as the current tries to jump the increased gap.

Remember, most speakers are not meant to be abused by a sine wave. Most amplifiers only put out a small percentage of their cabability when playing music (dynamic), but full power when fed a sine wave.

So the big debate is...do you overdrive your speakers, or underdrive your speakers?

Either one can destroy your speaker. But both are related...it's not the signal that will melt the V/C, it's the watts, and exceeding the thermal limits of the speaker.

I think the debate started when I mentioned that I don't see how you can melt a V/C with an amp rated less than the speaker's rating. IMHO, you can send it a distorted signal all day long with no consequences.

Remember, these are theories, and people are still publishing articles today on both sides of the fence.

Quote:
Originally posted by mcollinstn
As far as 1 ohm loads, if you are running an amp that is happy at 1 ohm loads, then you automatically have a built-in safety margin 8 times as high as somebody running an 8-ohm amp into an 8-ohm load. Let's face it: a 1 ohm load ain't got very far to go from "normal" to a "dead short". This means the differential from a speaker reproducing sine waves to a speaker being fed a hideous set of chopped waveforms can't look a whole lot different electrically to the amp (whereas an 8-ohm speaker in heavy clipping could drop as low as an ohm or so - definitely an opportunity for heavy overcurrent, especially on cheaper amps).
Yes, a 1 ohm (reactive load capable) amp is a thing of beauty. Car audio has come a long way...but like apache77 pointed out, you can regulate the output...JL's amps are rated the same at 4 ohm or 1 ohm...clever since some of their woofers match this configuration...

I also agree with Andy...watts = amps x volts...if one drops, we turn up the volume to make up for it...some of the best systems I've seen work together...no weak links...
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Old 10-31-2002, 01:05 AM
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quote
(If the wattage is exceeded, overexcursion of the voice coil will cause overheating, and the V/C will meltdown. I believe you are correct on the V/C resistance, but it's the overexcursion that will decrease resistance, as the current tries to jump the increased gap. )


answer= what the hell is overexcursion? that has nothing to do with the price of apples in europe around the third century B.C.
we are talking about speakers not spark plugs.
apparently you have never seen the inside of a speaker.
 
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Old 10-31-2002, 01:14 AM
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sorry i just had to reply to that one again. where is this mythical gap that current has to jump. could you draw me a picture.
 
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Old 10-31-2002, 01:16 AM
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come on, some of you guys that actually know about speakers have got to think that was funny
 
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Old 10-31-2002, 01:58 AM
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There is no gap for the current to jump. In one end of the voicecoil conductor wire, roundy roundy for a handfull of turns, then back out the other end of the conductor. No gap.

I've "over excursion-ed" plenty of cheap paper speakers in my days, tearing the paper surrounds without melting the voicecoils.

I've also "over-excursioned" a nice Pyle 12" woofer in a vented box when I played a low frequency test CD that went below the port frequency, unloaded the woofer, and the voice coil went past the center pole and the cardboard tube of the voicecoil hung on the pole.

I'm not challenging any views, I just enjoy throwing stuff out there..

M
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Old 10-31-2002, 02:05 AM
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this is the back of my (over)excursion does that count
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