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16 OHM speakers 8 OHM amp, Virtual Instrument Plugins
Old 8th October 2018
  #1
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Jaybird's Avatar
16 OHM speakers 8 OHM amp,

Only asking because iv had offers of $9000 for the speakers and refused it.
So I was told its like having an 8 cylinder car run at 4 cylinder but...

Will it damage the drivers? (Drivers valued at $8000) no rebuild kits, when its gone its gone.

We listen to metal sometimes, sometimes...mostly jazz but there been some metal.
Old 8th October 2018
  #2
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Friedemann's Avatar
 

Assuming these are dynamic drivers, no ESLs and a sloid-state and no tube amp - No risk for the drivers at all. A 16 ohm load just result in slightly less volume. Nothing more.
Old 8th October 2018
  #3
$9000 will buy some rather fine loudspeakers.
Old 12th October 2018
  #4
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Agree with Friedemann. No risk to the drivers, as long as the amp doesn't clip.

Typically, the biggest risk to speakers with dynamic drivers is driving the amp to clipping(driving it beyond it's maximum voltage output capability) because it doesn't have enough power to produce an adequate volume level with the given speakers, room and listener's tastes in volume level.
Old 12th October 2018
  #5
Gear Maniac
 

The concern would be less a matter of impedance loads but of power capability of the loudspeakers and the amplifier.

Mathematically, loading an amplifier capable of driving an 8Ω minimum load with a 16Ω will effectively de-rate the amplifier's power outputs by 3dB but in practice it's less so due to amplifier power rail deflection. This is safe and acceptable provided that the amplifier's power rating and use does not exceed that of the loudspeakers.
Old 12th October 2018
  #6
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Quote:
Originally Posted by Andy Thornton View Post
This is safe and acceptable provided that the amplifier's power rating and use does not exceed that of the loudspeakers.
Have to be careful here.
I would say it's better to overpower the speakers as opposed to under power them. But it does depend on many things.

Assuming the amp doesn't have clipping protection(which many modern amps do), IME more speakers are damaged from under-powering speakers as opposed to overpowering them. IME, a speaker can be driven by an amp several times it's power rating and still be OK. It's when an amp clips and either sends DC power to the tweeters and damages them, or makes a woofer bottom out because there's no damping anymore, is when the damage is done.

A speaker system's(multiple drivers in a box) power rating is not a clear thing. Each driver within the system has an average power level that cannot be exceeded due to thermal limitations of the voice coil. But the typical average power when playing music is something like 10% of the peak power, even with highly compressed pop/rock music. So if the power limitation is a thermal one, then theoretically a 100W rated speaker could be driven by a 1000W amp before damaging the voice coils due to over heating.

The overall system power rating probably makes some assumptions about what kind of music is going to be played through the speakers. A typical tweeter power rating can be as little as 10 or 20 watts in a system that's rated at many hundreds of watts. The system's power spec is assuming most of the power will go to the woofer, which is typical of most music. If it all went to the tweeter, or if one played brassy music that sends a lot of power to the tweeter at high levels, the tweeter could blow. If one played music with extremely low and powerful bass, the excursion limits of the woofer may be reached before the system power rating is exceeded and damage to the woofer could occur.

All this is moot I suppose if music is played at reasonable(many definitions of 'reasonable' depending on who you talk to) volumes. So if OP doesn't like his music cranked, he'll never have an issue with any amplifier of reasonable power.
Old 13th October 2018
  #7
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Quote:
Originally Posted by u87allen View Post
I would say it's better to overpower the speakers as opposed to under power them.
Hmmm. I assume you mean that it is safer to use an amplifier with a higher power rating than the nominal rating of the loudspeakers?
Even so, this is dependent on use, which is why I stated "power rating and USE".
Damage can occur in loudspeaker drivers for different reasons and there are many factors at play. It's a bigger subject than it appears on the face of it and beyond the scope of the OP's question, however.....

Over-excursion causes mechanical/structural damage, most commonly to LF drivers. This manifests as torn cones, torn or detached surround suspension, detached spiders, detached coil formers etc. This can occur almost instantaneously with misuse or accidental use if the amplifier power rating significantly exceeds the loudspeaker's rating, whereas a correctly rated or under-rated amplifier would save it. 'Clipping' a power amplifier is always sonically undesirable but in this scenario, it acts as a crude limiter, preventing transients exceeding the driver's mechanical limits.

Long term use of a system with an over-rated amplifier at levels exceeding the nominal power rating of the drivers (but not clipping the amplifier) will generally put the voicecoils at risk more than the driver's structure. Amplifier power is dissipated in the voicecoils and we hope that some of it is converted to mechanical energy but in reality quite a lot of power simply dissipates as heat. Traditional electromagnetic transducers are inherently inefficient. If heat builds up faster than it can be removed from the voicecoil, coil formers deform, wire enamel is compromised, adhesives are compromised, even solder joints can melt. This is less likely with a correctly rated or under-rated power amplifier.

Using a correctly rated amplifier, or even under-rated, and driving it into long term clipping effectively increases the crest factor of the source material and thus the dissipated power. This means that an under-rated amplifier can in effect cause greater than the rated power to be dissipated in the driver's voicecoil.
Additionally, 'clipping' the ampifier creates near-instantaneous voltage changes. This DOES NOT negate the amplifier's damping factor, in fact the damping factor becomes the enemy. It attempts to near-instantaneously stop the cone travel resulting in its momentum generating back EMF which causes more power to be dissipated as heat in the voicecoil (and to a lesser extent in the amplifier's output devices).
As that happens, the voltage changes when hitting and leaving the clipping points on both positive and negative half cycles are effectively high frequency transients. Suddenly, there is erronious signal generated that will be allowed to pass to the HF driver and increase the power dissipated in its voicecoil. In a passive multiple driver loudspeaker design (most HiFi and many studio monitors) a passive crossover filters the required bandwidth to the 'tweeter' putting it at more risk. This circuit is inherently a DC blocking design, so at no point is DC applied to that driver, even if the amplifier developed a fault that latched a voltage rail to its output.

This is just an overview of what can happen and I should be doing other things! Suffice it to say, loudspeakers are at risk if misused, regardless of the amplifier rating. It depends on the nature of USE as to what the risk is.
Old 13th October 2018
  #8
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Quote:
Originally Posted by Andy Thornton View Post
'Clipping' a power amplifier is always sonically undesirable but in this scenario, it acts as a crude limiter, preventing transients exceeding the driver's mechanical limits.

Additionally, 'clipping' the ampifier creates near-instantaneous voltage changes. This DOES NOT negate the amplifier's damping factor, in fact the damping factor becomes the enemy. It attempts to near-instantaneously stop the cone travel resulting in its momentum generating back EMF which causes more power to be dissipated as heat in the voicecoil (and to a lesser extent in the amplifier's output devices).
Perhaps my mechanism behind what happens in a clip situation is a bit off. Experience tells me when that woofer seems to be flopping around uncontrollably, something in the amplifier has reached it's limit. The exception to this is extremely low frequencies, like <30Hz, played at high power levels.

When an amp clips, we're essentially looking at the impedance of the power supply across the driver, which is probably on the order of a half an Ohm, depending on how large the filter caps in the supply are. This is greater than the typical closed loop output impedance of an amp operating in it's linear region(which is probably <0.1Ω), but still probably enough for sufficient damping.

BUT, remember what the damping does. It locks the cone to a velocity, not to a position. Take a 12V car battery and put a woofer across it. 12V is much less than what that speaker can take when playing music(60V peak for a 200W driver). The 12V car battery has an incredibly low source impedance, probably like 0.01Ω, and is capable of great damping for an 8Ω speaker. But watch that speaker cone go all the way to the compliance limit when connected across the battery.
We're talking about a coil moving in a magnetic field. When the back emf of the coil(which is proportional to how fast the coil is moving relative to the magnet) matches the drive voltage, there will be a steady velocity of the cone.

In a clip situation, we're holding the voltage across the coil steady and high for a long period of time. At high frequencies, the mass of the code typically prevents it from moving too far and too fast, and the clip duration is short. But at low frequencies, mass of the cone is less of a factor and clip duration is longer.

It's also possible for an amp to current-clip before it voltage clips, depending on the amplifier design, load and frequency. A multi-driver speaker system with a complicated crossover can have an impedance that dips pretty low under certain circumstances. And if the amp reaches it's current limit, it is now a Hi-Z current source. And no more damping.

You're right in that this is likely outside the scope of the OP's question. And I think you're right about the fact that lack of damping isn't what causes the speaker cone to go wild in a clipping event. But I disagree with you in the idea that a clip prevents over-excursion.

Last edited by u87allen; 13th October 2018 at 06:48 PM..
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