Why “Peak power”?

[xgsjx]

It might seem like a silly question…
 

Why do PA manufacturers advertise the cabs peak power & not RMS?

 

Is it just marketing, or is there a good reason behind it?

[Newfoundfreedom]

A bit of both. In marketing bigger always sounds better. But as I understand it, there's no industry standard way of measuring power. Even RMS calculations vary across manufacturers. 

[Bill Fitzmaurice]

Marketing. They also use 'music power', 'peak music power', and my favorite, 'peak music power output'. It's all bovine excrement.

[xgsjx]

Thanks guys. 
 

RCF do at least put the SPL for their cabs, but you have to go to the back of the user manual to find out that “2100 watts” is a bi amp with 350 watts for anything above 1.8 kHz & 700 for anything below. 

I would have thought that the non budget PA cabs would have come with some decent specs & would have thought that it would have been demanded by sound engineers, but obvs I was wrong. 😂

[Bill Fitzmaurice]

Non-budget PA cabs do come with semi-decent specs. But 'non-budget' means two thousand quid and up. Even then the numbers don't always add up. For instance, maximum SPL claims are seldom measured. They take the 1w/1m sensitivity and calculate the max SPL from that. But that calc doesn't take into consideration real world issues, like thermal power compression and driver excursion limits. And if they're using peak power for the calculation it's bogus anyway. Experienced acoustical engineers are aware of these shenanigans, and knowing the full driver, enclosure and amp specs can make accurate performance predictions. The other 99.99% of users are at the mercy of the marketeers. 🤥

[Chienmortbb]

It is complicated, at least to the layman, but there are different ways of measuring power in speakers. At the basic level, the RMS voltage across a speaker multiplied by the RMS current through it will give you the AVERAGE power. Don't go on the HIFI forums, though, as many try to promote a different "average" power. The term RMS power is not really correct, but is better understood than average power. Of course, it is around 50 years since my college days.

 

I have never seen a satisfactory explanation of PEAK, INSTANTANEOUS or any other bogus power rating.

 

The AES Audio Engineering Society did create a standard that some driver manufacturers use, but I don't have enough knowledge of it to comment except to say it usually gives a higher figure than RMS.

 

Bill has a good point though, take 6dB off any peak figure, and you may be close to the real SPL.

 

 

[Downunderwonder]

I look at the size of the speaker and the price and divide by 10. Someone could come up with a formula with fudge factors built in so

 

High St Price = P £

Claimed max SPL = C 

Speaker size = S in inches for the main one.

 

Actual maintainable SPL = CxP/BxS/15×F

 

Where B and F are fudge factors to arrive at real world numbers. They could be variable by brand.

[Bill Fitzmaurice]

The actual maximum SPL could be accurately predicted using speaker modeling software if one has the driver Thiele/Small specs, the exact enclosure details, and the thermal and mechanical compression data. Thermal power compression is the result of the heating of the voice coil. When it heats its resistance increases, which causes a loss of efficiency. The hotter it gets the greater the loss. Mechanical factors also reduce driver efficiency as power is increased. The main culprits are the spider and surround, which lose flexibility near the limits of their extension.

 

But thermal and mechanical compression data is by and large unavailable, so we assume that these losses result in 6dB lower maximum SPL than a linear swing voltage to SPL calculation predicts. Manufacturer data is usually even further off, as they never consider the driver mechanical voltage limit, only the thermal limit.

 

Where peak power is concerned that's never a part of the equation. Cone excursion is always calculated using voltage swing, never power.

[xgsjx]

4 hours ago, Bill Fitzmaurice said:

The actual maximum SPL could be accurately predicted using speaker modeling software if one has the driver Thiele/Small specs, the exact enclosure details, and the thermal and mechanical compression data. Thermal power compression is the result of the heating of the voice coil. When it heats its resistance increases, which causes a loss of efficiency. The hotter it gets the greater the loss. Mechanical factors also reduce driver efficiency as power is increased. The main culprits are the spider and surround, which lose flexibility near the limits of their extension.

 

But thermal and mechanical compression data is by and large unavailable, so we assume that these losses result in 6dB lower maximum SPL than a linear swing voltage to SPL calculation predicts. Manufacturer data is usually even further off, as they never consider the driver mechanical voltage limit, only the thermal limit.

 

Where peak power is concerned that's never a part of the equation. Cone excursion is always calculated using voltage swing, never power.

When discussing PA a few months back with a chap I know who’s a computing science professor, I asked the same question (but more of a statement) “Why just give peak” & his response was along the lines of “it’s relevant to any spikes in volume”. 
 

I suppose “if” the manufacturer measured peak using voltage swing, then it would be relevant?

 

[Phil Starr]

I’m going to be controversial and say that this is the result of weak, dysfunctional politics.

 

The facts are clear, it’s possible to measure the power of an amp or a speaker at home with basic equipment but we allow manufacturers to lie about it in print all the time. Governments in the past have legislated to protect consumers. Germany with the DIN standards, America with AES, British Standards and so on. This is then identified as being “nanny state”, “red tape gone mad” etc. and funding for regulatory enforcement is slashed. The lies and disinformation then continue. We are complicit in this by voting for politicians who tell us we can have it all without having to contribute to a well run and funded society.

 

So, getting back to the question ‘ they’  give you peak power because they can get away with it. Because everyone else is doing it. Because you can’t sell a 200W AES amp if you don’t describe it as 400 W peak, 800W music or 1600W PMPO. Mainly though because it isn’t illegal to try and deliberately deceive you. It should be the role of government to protect people from vested interests and not to be scooped up and owned by them.

[xgsjx]

The thing is though, when the product is already really good, sounds great & is loud enough, why?

 

I can understand the cheap crappers such as KAM, QTX, etc doing it, as they need to have something that looks good, but QSC & RCF?

 

Other than TCE, bass rig manufacturers don’t use “peak”.  Are soundies less technically inquisitive than bassists?

[Bill Fitzmaurice]

Why? Because the competition does it. No one wants to lose a sale because they didn't play the same numbers game as the rest. 

[xgsjx]

Just now, Bill Fitzmaurice said:

Why? Because the competition does it. No one wants to lose a sale because they didn't play the same numbers game as the rest. 

Haha, that’s a very good point. 
But then, wouldn’t a sound engineer want to go with a company that shows more realistic numbers?

[Bill Fitzmaurice]

Someone who really really knows what he's doing isn't fooled by the smoke and mirrors. You actually can cheat an honest man, but it's very difficult to cheat a man who's well informed.

[Chienmortbb]

9 hours ago, xgsjx said:

The thing is though, when the product is already really good, sounds great & is loud enough, why?

 

I can understand the cheap crappers such as KAM, QTX, etc doing it, as they need to have something that looks good, but QSC & RCF?

 

Other than TCE, bass rig manufacturers don’t use “peak”.  Are soundies less technically inquisitive than bassists?

No, many makers exaggerate, take Behringer/Bugera. They make good stuff but 2000 watts? There are people using ICEPower modules that are quoting between 50 and 100 watts more than ICEPower quote for the modules.

[Bill Fitzmaurice]

And you've got TC Watts, where their lame explanation for the blatant exaggeration was 'Well, no, it's not actually 450 watts, but it sounds like 450 watts'. 😒

[tauzero]

It's worth having a look on Ebay for PMPO in titles and descriptions, just for a laugh.

 

https://www.ebay.co.uk/itm/125986388583

 

Output power: 600 watts PMPO

RMS: 2x 2.5W
 

[xgsjx]

Yes, that’s what I meant by TCE, I remember their “but it’s a loud 236 watts”. 🤣

 

But only a couple of makers do that in the bass rig world. 
 

They do this in the budget sound system market, but even better. E.g. a 2:1 system could be advertised as having 3600 watts & breaks it down as 30w+30w satellites x 60w sub. 😂

[Bill Fitzmaurice]

Technically speaking the difference between 236 and 450 watts is less than 3dB, which is audible, but just, so TC thought they'd get away with their subterfuge. TC engages in this specmanship for no other reason than greed, wanting to maximize sales through false advertising. They didn't anticipate anyone actually testing their amps. Not at all surprisingly many actually came to their defense, in effect saying they didn't care if they were lied to so long as the amps sounded good. The idea that people don't care if they're lied to so long as they hear what they want to hear is hardly confined to audio. 😒