Will I blow the speaker?

[tauzero]

On 25/01/2024 at 03:23, agedhorse said:

To respond to the message I received calling me a liar, here is where the test conditions for normal conditions are defined in the IEC 62368 regulations (for the EU). The input power to be labeled is defined to be the input power under these normal conditions (or greater if the manufacturer chooses a more stringent duty cycle because of the application). For example, for the amps I design for bass and electric guitar, I typically use more than double the minimum required under the regulations but for acoustic guitar it will be a little less than double:

 

 

Also, may I ask why there's so much rudeness here? For those interested in learning, I'm providing information that most players clearly don't understand or haven't been exposed to. For those of you who don't want to learn, why challenge the facts is such a manner? 

 

 

 

When the standard says "1/8 non-clipped output power", is that 1/8 of the measured maximum non-clipped output power or 1/8 of the claimed maximum output power?

[Baloney Balderdash]

On 25/01/2024 at 20:22, BassmanPaul said:

 

Just as a bit of levity in a somewhat contentious thread;

 

Does this mean you are a Robot??  LOL

No, our never system, including our brain, works by exchanging electric impulses. 

[agedhorse]

3 hours ago, tauzero said:

 

When the standard says "1/8 non-clipped output power", is that 1/8 of the measured maximum non-clipped output power or 1/8 of the claimed maximum output power?

Non-clipped output power in rms metrics. 

[Stub Mandrel]

On 22/01/2024 at 10:00, sandy_r said:

 

Well, we'll obviously have to agree to differ on that then - interestingly we don't disagree on the bottom line that the amp can be used carefully (ie. "less than 200W.") with that speaker, as long as the system is operated below clipping

 

You are obviously very welcome to have your own opinion on why the guideline value of "1/8 max. Power" (which i showed in a photoclip) was chosen by the regulating bodies to be at that level

 

Have a nice day 😊

 

 

No, he's right. I've had that answer before and knowing @agedhorse' backgound it was reluable, but did the research. The 1/8 power is the level written into the standards as an estimate of typical power from an amplifier playing a typical selection of content.  It's a very fair way of estimating the power consumption of something like a hifi that plays content with a wide dynamic range and is not normally used flat out. That's reasonable for helping someone work out how much it will cost to run an electrical item.

 

But we are interested in how much power our amps put out when we run them hard for prolonged periods i.e. whole songs.

 

Amp manufacturers are allowed to use more "realistic" ratings but don't have to. Orange rate the power consumption of the 500W bass terror at 690 VA (Volt Amps are close to Watts). That's a sensible consumption value for something that has two valves being heated, a fan and still pumps OUT at least 500Watts  allowing for inefficiencies.

 

Legally, the Bass Terror could probably be rated at about 150W power consumption or less, while 690W is probably an accurate figure for someone driving it flat out.

 

Note that NEITHER figure is actually an accurate one for how much power the amp can put into a cabinet.

 

 

It's just a shame you can't trust most OUTPUT power figures. Orange's 500W rms is amost certainly accurate. But other manufacturers might give figures at high levels of distortion (typically about double rms) or theoretical instantaneous peak values (up to four times RMS).

 

I applaud Thomann for particular clarity... I  have two of their powered speakers, manufacturer's output rating is 600W peak, but Thomann clearly state RMS 140W in the specs.i

[Bill Fitzmaurice]

1 hour ago, Stub Mandrel said:

 Orange rate the power consumption of the 500W bass terror at 690 VA (Volt Amps are close to Watts).

Volts multiplied by amperes is the very definition of watts. 1/8 power is the benchmark for measuring long term continuous amp performance as that's -9dB from maximum, which is the minimum amount of headroom required to prevent clipping during transient peaks.

[sandy_r]

21 hours ago, Stub Mandrel said:

 

No, he's right. I've had that answer before and knowing @agedhorse' backgound it was reluable, but did the research. The 1/8 power is the level written into the standards as an estimate of typical power from an amplifier playing a typical selection of content.  It's a very fair way of estimating the power consumption of something like a hifi that plays content with a wide dynamic range and is not normally used flat out. That's reasonable for helping someone work out how much it will cost to run an electrical item.

 

But we are interested in how much power our amps put out when we run them hard for prolonged periods i.e. whole songs.

 

Amp manufacturers are allowed to use more "realistic" ratings but don't have to. Orange rate the power consumption of the 500W bass terror at 690 VA (Volt Amps are close to Watts). That's a sensible consumption value for something that has two valves being heated, a fan and still pumps OUT at least 500Watts  allowing for inefficiencies.

 

Legally, the Bass Terror could probably be rated at about 150W power consumption or less, while 690W is probably an accurate figure for someone driving it flat out.

 

Note that NEITHER figure is actually an accurate one for how much power the amp can put into a cabinet.

 

It's just a shame you can't trust most OUTPUT power figures. Orange's 500W rms is amost certainly accurate. But other manufacturers might give figures at high levels of distortion (typically about double rms) or theoretical instantaneous peak values (up to four times RMS).

 

I applaud Thomann for particular clarity... I  have two of their powered speakers, manufacturer's output rating is 600W peak, but Thomann clearly state RMS 140W in the specs.i

 

I appreciate your considered input here, Neill, i really do

 

I'm not sure what you think has been going on here, but latterly it certainly hasn't been about trying to give the OP an answer to the topic question - with a clear and relatable interpretation of supporting evidence from the OP type equipment 

 

I repeat (again, sigh) that, mysteriously, supposedly 'right'/'wrong' proponents are coming out with the same bottom-line advice that: "that the amp can be used carefully (ie. "less than 200W.") with that speaker, as long as the system is operated below clipping" ...something i stated in one of my earliest posts above

 

Cheers, Neill

 

And now for something completely different:

I will just say that after 50+ years working as an engineer in Academic Research, Aerospace and Medical Engineering, and latterly Quality Control, my experience has been that an expert, in any field, is recognised by what they do, and have achieved (ie. evidence-based) - not just by what they say they do

 

I joined this forum to both learn and share any bass, gear and electronics-related  knowledge which i may have picked up in my work and interests - i attempt to do that in as clear and helpful a way as possible for people seeking help - people can take it or leave it as they see fit -  I am not prepared to enter into what i perceive to be 'points-scoring' exercises

 

...And says at last just as the time bell rings
"Goodnight, now it's time to go home"

 

Edited February 23 by sandy_r
for clarification

[Stub Mandrel]

1 hour ago, Bill Fitzmaurice said:

Volts multiplied by amperes is the very definition of watts. 1/8 power is the benchmark for measuring long term continuous amp performance as that's -9dB from maximum, which is the minimum amount of headroom required to prevent clipping during transient peaks.

 

Sorry Bill, for once you are wrong. For a DC load VA = Watts, but for AC if the load is capacitative or inductive the actual wattage is less than the VA figure by the power factor.

[Bill Fitzmaurice]

1 hour ago, Stub Mandrel said:

 

Sorry Bill, for once you are wrong. For a DC load VA = Watts, but for AC if the load is capacitative or inductive the actual wattage is less than the VA figure by the power factor.

The load presented by a speaker has capacitive and inductive components, but it is mainly resistive. Where speakers are concerned capacitance is minor. Voice coil inductance is significant in that it increases impedance, but that reduces current draw, so where power factor issues are concerned it's not an issue. There are instances where a crossover can cause problems with respect to power factor, dropping Z lower than DCR, resulting in what's referred to as a difficult load for an amp, but that's in hi-fi. I've never seen it in pro-sound. 

Edited February 22 by Bill Fitzmaurice

[Stub Mandrel]

1 hour ago, Bill Fitzmaurice said:

The load presented by a speaker has capacitive and inductive components, but it is mainly resistive. Where speakers are concerned capacitance is minor. Voice coil inductance is significant in that it increases impedance, but that reduces current draw, so where power factor issues are concerned it's not an issue. There are instances where a crossover can cause problems with respect to power factor, dropping Z lower than DCR, resulting in what's referred to as a difficult load for an amp, but that's in hi-fi. I've never seen it in pro-sound. 

 

Whatever,  but the readon volt amos exist is because they aren't the same as watts, even if the difference can be nil or negligible in some conditions.

[agedhorse]

For audio output power, the VA term is simplified to watts because the amp is modeled as a close to ideal voltage source and for practical purposes it’s easy to measure RMS voltage, square it and divided by the nominal impedance (simplified to resistance) to calculate power. 
 

 

[Stub Mandrel]

52 minutes ago, agedhorse said:

For audio output power, the VA term is simplified to watts because the amp is modeled as a close to ideal voltage source and for practical purposes it’s easy to measure RMS voltage, square it and divided by the nominal impedance (simplified to resistance) to calculate power. 
 

 

 

Absolutely, the example I gave used VA for the input power of an amp with an SMPSU, the power factor for an SMPSU can range from 0.5 to 0.99, so the VA rating has the potential to be significantly misleading.

But my beef was solely with the assertion "Volts multiplied by amperes is the very definition of watts." which is demonstrably wrong.

You and Bill are experts and sticklers for accuracy; people reading that the two of you consider VA = Watts are likely to assume that this is a fact, regardless of any context.

[agedhorse]

38 minutes ago, Stub Mandrel said:

 

Absolutely, the example I gave used VA for the input power of an amp with an SMPSU, the power factor for an SMPSU can range from 0.5 to 0.99, so the VA rating has the potential to be significantly misleading.

But my beef was solely with the assertion "Volts multiplied by amperes is the very definition of watts." which is demonstrably wrong.

You and Bill are experts and sticklers for accuracy; people reading that the two of you consider VA = Watts are likely to assume that this is a fact, regardless of any context.

Yes, I understand. I was explaining why the simplification is made with regards to the audio output power.

 

The PF of most SMPS used in the audio amps I work with is around .9, which makes watts and VA within ~10%. That's plenty close enough for audio work, nothing precision about audio.

[Chienmortbb]

10 hours ago, Stub Mandrel said:

But my beef was solely with the assertion "Volts multiplied by amperes is the very definition of watts." which is demonstrably wrong.

Firstly I must apologise to the OP for overcomplicating the original question, but such is forum life.

 

It is demonstrably right. Volts X Amps = Power in Watts, or P=V x I. That is for DC.

 

In AC, it is the same, but in the early days, it was hard to measure the Voltage and Current (Amps) at exactly the same point in time using simple analog(ue) meters.  Once impedance comes into play, current and voltage are not in phase and therefore is it incorrect to use Ohms law when measure voltage and current (amps) with separate meters and declare them as watts. So it was commonplace to measure each and multiply them as VA or simply Volts X Amps. Modern test equipment allows us to measure the precise voltage and current simultaneously. 

 

I have just deleted a large amount of text as I had almost ridden my hobby horse off into the sunset. Happy to answer, argue, correct anything that is demonstrably untrue however as my College learning was now 50+ years ago............although as far as I know Ohms law has not been repealed.
 

 

 

 

[Bill Fitzmaurice]

The issue with respect to speakers is that impedance isn't a constant figure, it varies with frequency. Volts x amps= watts, but since amps vary with impedance which varies with frequency power also varies across the spectrum. Even if you have the gear required to simultaneously measure both voltage and current across the audio bandwidth the result looks like this, a 2.83v signal into an 8 ohm speaker. That's nominally 1 watt, but as the chart shows there are only four frequencies out of fifteen thousand where it's actually 1 watt.

 

 

[Chienmortbb]

Yes, one of the reasons amplifier power is usually measure using a resistive* load and that speaker power ratings are a guide only.

 

*There is no such thing as a purely resistive load as every component has resistance, inductance and capacitance to varying degrees.

[Lfalex v1.1]

[Thinks back to hifi days...]

 

Modulus of impedance?

[agedhorse]

1 hour ago, Bill Fitzmaurice said:

The issue with respect to speakers is that impedance isn't a constant figure, it varies with frequency. Volts x amps= watts, but since amps vary with impedance which varies with frequency power also varies across the spectrum. Even if you have the gear required to simultaneously measure both voltage and current across the audio bandwidth the result looks like this, a 2.83v signal into an 8 ohm speaker. That's nominally 1 watt, but as the chart shows there are only four frequencies out of fifteen thousand where it's actually 1 watt.

 

 

This reinforces my earlier comment about nominal impedance for the discussion of power being close enough, for this LF driver, if you take the average between 40 Hz to 1kHz, it’s close enough to 1W for most purposes. For power purposes, the area under the curve method is the most convenient way to visualize this for most people.
 

Amp designers however, need to be aware of the data in this plot because it affects the absolute current through the components for a given voltage and frequency. This affects how protection circuits work as well as the demands places on the active devices themselves. 

[tauzero]

On 22/02/2024 at 16:30, Stub Mandrel said:

 

Whatever,  but the readon volt amos exist is because they aren't the same as watts, even if the difference can be nil or negligible in some conditions.

 

I put the question to Mrs Zero a little while ago because she works at a plant hire company that hires generators, which are quoted in kVA not kW. Although she couldn't tell me why they weren't the same, she could tell me that they weren't, and there was a formula for getting kW from kVA. I've just been spurred on to find out why, and I have an answer, at least for transformers. 

https://www.electricaltechnology.org/2012/02/why-transformer-rating-in-kva-not-in-kw.html

 

What it boils down to is that a transformer converts an input voltage and current into an output voltage and current depending on the ratio of primary and secondary windings - that's the VA bit as the product of the input V and A will always equal the product of the output V and A. However, the power output from the transformer will be dependent on the power factor of the load.

[agedhorse]

VA is apparent power which is different than watts which is real power. Real power does work, apparent power x power factor = real power. 
 

Real power is the apparent power x the cosine of the phase angle. When the load is resistive, voltage and current are in phase and the cosine of zero degrees is 1, so VA = watts.  
 

Since a speaker or resistive plus reactive, both electrically as well as mechanically, the phase angle is generally mostly inductive and his the current lags the voltage. The cosine of this lagging phase shift is less than 1, therefore the real power is less than the apparent power. By how much depends on how reactive. 
 

This is all basic electrical engineering stuff, something every amplifier designer should know inside and out. It’s also something that a speaker designer should have at least a basic working knowledge of. 

[Bill Fitzmaurice]

Where it comes into play with respect to speakers has to do with the potential for damaging the amp. With sufficient phase shift between current and voltage the current and voltage can both be at a maximum. Combine that with low impedance and the result can be magic smoke.

[agedhorse]

19 minutes ago, Bill Fitzmaurice said:

Where it comes into play with respect to speakers has to do with the potential for damaging the amp. With sufficient phase shift between current and voltage the current and voltage can both be at a maximum. Combine that with low impedance and the result can be magic smoke.

Current and voltage will be simultaneously at the maximum into a resistive load where the phase shift is zero degrees. 
 

Where phase shift gets tricky and particularly dangerous is where it’s leading (capacitive) which is difficult to compensate for. 
 

With highly reactive loads it’s possible to have the highest currents where the voltage is not the maximum. This has to be accounted for in VI protective limiters and SOA calculations for linear amps. For class D amps this is not as difficult.