PA - Watts Vs Watts

paulphoenix · November 2017

Sounds silly even saying this but, is there a difference between one manufacturers 400W and anothers' 400W?

I have been using a powered mixer for ages rated at 400W per side (all be it a budget brand), and was relatively happy with the sound.

But then I borrowed a friends Studiomaster powered mixer rated at 350W per side (using my own speakers) for a gig last weekend and it had so much more punch and presence (even seemed louder?) to which even the other band members commented.

So is there a difference between budget brand X's 400W and decent brand X's 400W output?

ESBlonde · November 2017

OK there are a number of caviats here.

Watts are measured and quoted as Peak power, RMS, or several other catagories. For our practical purposes the only meaningful one always quoted is RMS so ignore all the others as sales pitch.
Next that quoted RMS power is for a given impedence of the loudspeaker load (think losely of a resistance). This is measured in Ohms with a funny upturned horse shoe characture. For PA purposes we shall assume they are all solid state (no valves) so the lower the impedence (resistance) the greater the output....but there are limits. Most musician grade PA amplifiers will range down to 4 Ohms, any lower and they will risk overheating with potential catastrophic results. A typical output might be spec'd as 180Watts RMS at 4 Ohms, 100 Watts RMS at 8 Ohms, and 60 Watts RMS at 16 Ohms. Al of these from the same amp output.
Not all manufacturers are totally honest and nobody would sell an amp with 237W RMS per chan because 250W is the sort of sales pitch desirable. So one amp might be capable of 246W RMS and another 262W RMS and both would be sold in the same catagory of 250w per Ch. Now a few watts might make little difference and then a lot depends on how that rating is measured. It is always assumed that a small amount of distortion is allowed, for some makers that might be 3% or 0.3% or .03%. The lower the distortion used to measure the more 'spare' distorted signal that can come through and 'seem' louder.
Also the question of the internal gain structure withing the mixer/effects/crossover chain will dramaticly effect the perceived punch in the final sound. So if the first mic amp passes the signal full and clear to the Eq section, to the Buss routing, to the Main outputs then the signal going to the power amp has all the headroom and punch available. If this 'gain structure' is not optimised, the power amp section is at a disadvantage before it starts.

I've tried to put this into non technical words so I hope some people can get something from it.

paulphoenix · November 2017

thanks @ESBlonde ;

quite helpful - i guess different brands quote different figures for sales purposes....

So would say a Peavey 300W per channel or a Soundcraft 300W per channel be enough for a pub covers band playing to small crowds of <100?

ESBlonde · November 2017

Vocal only? Those Peavey units have a great reliability reputation and seem to take abuse well. Pay attention to setting the ch gain nice and clean so the master volume does the work. Soundcraft may have a slightly better sound (subjective) and either really depend very heavily on the quality and sensitivity of the speakers.
Peavey no longer have a proper UK parts and service centre, but the older stuff is reasonably fixable anyway.
I would have either unit provided you are vocal only and get good speakers above peoples heads safely. Go for 10" or 12" cones with vocals rather than 15" becuase they generally sound punchier in the right range.

maltingsaudio · November 2017

@ESBlonde ; has kind of nailed the advertised power rating against the actual RMS power. Behringer for one is shocking at this for example the iNuke 3000watt power amp which is actually 440 watts at 8ohms if you look at the specs and even then you have to hunt hard to find them hidden in the user manual http://www.music-group.com/Categories/Behringer/Power-Amplifiers/Portable-Amplifiers/NU3000/p/P0B1P.

As to using the PA for vocals again spot on, get the gain structure properly set up and avoid using too much bass on the channel. Try setting up your PA then rolling off the bass frequency and you'll see how it increases the clarity, this is because the amplifier is trying to increase the volume of what isn't there instead of what is

ICBM · November 2017

paulphoenix said:

Sounds silly even saying this but, is there a difference between one manufacturers 400W and anothers' 400W?

I have been using a powered mixer for ages rated at 400W per side (all be it a budget brand), and was relatively happy with the sound.

But then I borrowed a friends Studiomaster powered mixer rated at 350W per side (using my own speakers) for a gig last weekend and it had so much more punch and presence (even seemed louder?) to which even the other band members commented.

So is there a difference between budget brand X's 400W and decent brand X's 400W output?

Yes, there can be drastic differences - it's a guide only. That still applies even if both are truly rated the same for continuous clean power at the point of clipping - the dynamic response can make a substantial difference to the perceived volume and 'punch'.

This is one reason valve guitar amps are so much louder than equivalently-rated analogue solid-state or digital ones - by a factor of at least four times in many cases. (ie a 20W valve amp can sound louder than an 80W solid-state/modelling amp, even with comparable speakers.)

On top of that, there are differences in the interpretation of what 'power output' actually means, even among reputable companies. For PA it's normal to quote programme power rather than 'RMS' (continuous clean power).

paulphoenix said:

So would say a Peavey 300W per channel or a Soundcraft 300W per channel be enough for a pub covers band playing to small crowds of <100?

Yes, easily.

ESBlonde said:

Go for 10" or 12" cones with vocals rather than 15" becuase they generally sound punchier in the right range.

This. Although the trend has been for 15"+horn speakers from the 90s onwards, in my opinion it's a mistake. They generally have a 'hole' in the midrange so they lack punch, and they still don't have enough deep bass - not helped by the speakers being up on poles. If you need to put bass through the PA, get a sub.

I did PA for an outdoor gig a couple of months ago - admittedly only a couple of acoustic musicians, and a jazz band where only some of the instruments were going through the PA, although that included a digital piano and a double bass so full frequency range - with a Peavey amp of only 200W per channel, two 1x10" Celestion speakers and a 250W Wharfedale 15" powered sub. It was loud and clear enough to hear over a reasonable sized park, although it was pretty much at the limit I think.

jpfamps · November 2017

Power rating is one of the criterion used to judge power amp value, and hence marketing departments love to inflate these, as a 400W amp has to be better than a 300W amp.

The usual area manufacturers skip on parts is in the power supply as this is where the more expensive parts are used.

For example using a smaller mains transformer will make a significant cost saving and so your product will look better value, assuming the power rating is the same.

There was a photo knocking around the interweb showing a well known brand of amp and the cheaper Behringer knock off which had a substantially smaller transformer.

A smaller transformer will not be able to hold up the power rails under heavy loading, will run hotter which will reduce continuous power rating, and is more prone to failure.

The many wheezes employed to increase power rating include: using peak power (ie the instantaneous power the amp can produce for a very short space of time); as ESBlonde says, being more relaxed about the distortion figure that power is rated at (amps put out more power when distorted but don't sounds as good); only driving one channel at a time (which stresses the power supply less); or simply lying.

As ever the devil is in the detail.........

ICBM · November 2017

jpfamps said:

Power rating is one of the criterion used to judge power amp value, and hence marketing departments love to inflate these, as a 400W amp has to be better than a 300W amp.

The many wheezes employed to increase power rating include: using peak power (ie the instantaneous power the amp can produce for a very short space of time); as ESBlonde says, being more relaxed about the distortion figure that power is rated at (amps put out more power when distorted but don't sounds as good); only driving one channel at a time (which stresses the power supply less); or simply lying.

As ever the devil is in the detail.........

"Peak Music Power Output", as car stereos and cheap 'hi-fi' systems used to be rated in.

Otherwise known as "Pure Bullshit Power Output"...

Danny1969 · November 2017

Aside from the actual RMS versus peak to peak etc it's worth pointing out that with professional PA equipment your more concerned with the sound pressure level and coverage it can provide rather than thinking about it in terms of watts. For example my own company 2020 has a couple of HK systems that are modestly rated at 400 watts for the highs and 500 watts for the bins .... which is less in terms of watts then a typical RCF, QSC bin and top system which are often 750 watts for bins and 600 watts for the tops etc. However in terms of volume and coverage the HK system will outperform the higher wattage systems due to design.

Be careful with that Studiomaster 350 watt, if it's an ol skool "Power House" model design .... that is loud, punchy for it's size but likely to go wrong if used near it's max ratings. Fixed quite a few of them luckily they are very basic inside and all common parts

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