Valve amps, how many watts?!?

[Bill Fitzmaurice]

34 minutes ago, Phil Starr said:

I don't think they are anything more than one person's opinion offered as a guideline but they are based in real world experience.

One of my real world experiences was when a local 6500 seat outdoor amphitheater was on the verge of being shut down by the town due to noise complaints. Prior to contacting me they spent $25,000 with a 'professional' audio consulting firm, who did an analysis of how loud the levels in the surrounding neighborhoods would be based on the level at the FOH. They then installed a computerized SPL measuring system in the FOH, which would turn on a very prominent red light if the levels were exceeded. For the remainder of that concert season the red light seldom, if ever, came on. The complaints not only were not reduced, they increased, especially where the bass was concerned. Before the next season of concerts started they hired me to find out what was wrong. It took me all of five minutes to do so. I looked at their sound standard document and the system, and saw everything was reference to A-Weighting. Their measuring system would only read dBA. The acceptable level standard said that the level in the FOH could not exceed 110dB. On the A-Weighed scale it never did. I had them play some recorded music over the system at 100dBA. It was unbearably loud. I then showed them what my Z-Weighted meter read: 125dBZ. I then ran a 60Hz test tone through the  system, which I measured at 100dBZ. Their measuring system reading was 75dBA. The next day their computer measuring system went into the bin, while I accepted a position as their sound level monitor, at $1k per concert. 😎

I'm talking about a capability of 40dB dynamic range with peaks of 120dB for each instrument.

Real world measured results show that even 20dB of dynamic range is seldom exceeded. That I know from the 200 or so RTA's I took at said concert venue's concerts over a period of a few years. Interestingly that figure remained fairly constant no matter what the genre, save one: Metal. Metal acts tended to compress the content so heavily that they seldom had more than 10dB dynamic range. They also tended to be less loud on peaks, due to that compression. They might average 100dB at the FOH but seldom reached 110dB on peaks. OTOH I measured many country acts at 95dB average that would hit 115dB peaks.

 

[Phil Starr]

14 hours ago, Bill Fitzmaurice said:

 

Real world measured results show that even 20dB of dynamic range is seldom exceeded. That I know from the 200 or so RTA's I took at said concert venue's concerts over a period of a few years. Interestingly that figure remained fairly constant no matter what the genre, save one: Metal. Metal acts tended to compress the content so heavily that they seldom had more than 10dB dynamic range. They also tended to be less loud on peaks, due to that compression. They might average 100dB at the FOH but seldom reached 110dB on peaks. OTOH I measured many country acts at 95dB average that would hit 115dB peaks.

 

That's a really good point. I choose the 40dB range not because anyone is ever likely to need it but because it means you have gear which can cope with most things and for a bassist 20dB over the 'average' gives you a healthy amount of headroom to play with. Your figures of 100dB FOH and peaks of 110dB (so a dynamic range of 20dB) look far more real world to me. It's also interesting (to me) because I think audiences are getting noisier. If they are generating 90dB of crowd noise then 20-30dB of dynamic range is probably all you are left to play with. 

It'll also be interesting for bassists to consider the implication of a band rarely reaching 110db. That won't all be bass of course, but if it was your Barefaced 2x10 would only need 16 watts to produce that sound level at 1m.*  I sometimes wonder at the crazy levels of power people aspire to when most of the time their amps are operating at just about 10W Even then they probably ought to turn down and let the PA do the heavy lifting.

I think what you have here is important for anyone trying to get to grips with decibels and questions of how loud do I need to be. The science gives you extra insight but it can't give an absolute answer. The type of music you play, things like compression eq and so many other things will come in to play. I'm not surprised that the country acts are both louder (on peaks) and quieter (on average) than metal bands but I suspect a lot of people over hear might be a little surprised that a country band would be more demanding of the PA than a metal band.

For the OP who plays in a function band and who wears ear protection we can reasonably assume this is a fairly professional unit where the PA is producing what the audience hears and stage levels are sensible I think that a 100W valve amp would be more than adequate. If you want the audience to hear the same sound you do then you need to chat with your sound engineer about how to relay it on to the audience, or simulate it with tech. 50W would probably be enough depending upon what the rest of your band are doing whether you compress your sound and how you eq and even how far you stand from your amp but I'd start looking at 100W amps. 

*for those of you still looking at the maths: the Two10 gives 98dB for 1W. To make 110dB needs an extra 12 db.

3dB needs double the power and 12db need the power doubled four times which is 16 times the power=16W

 

Edited July 15, 2018 by Phil Starr

[Bill Fitzmaurice]

2 hours ago, Phil Starr said:

I suspect a lot of people over hear might be a little surprised that a country band would be more demanding of the PA than a metal band.

I measured Big & Rich and Montgomery Gentry at an average of 103dB at the FOH.  Deep Purple was the same. Charlie Daniels came in at 104dB. Tim McGraw  and Alice Cooper ran at 105dB.

Quote

It'll also be interesting for bassists to consider the implication of a band rarely reaching 110db. That won't all be bass of course, but if it was your Barefaced 2x10 would only need 16 watts to produce that sound level at 1m.* 

True, although most players are going to be pushing closer to 30w average with 120w peaks. Also consider that the FOH where I took measurements was some 25 meters from the stage. Reaching 110dB there would require some 135dB at one meter, well beyond that capability of almost any backline rig. That's why you size your personal rig to drive the stage, and let the PA drive the room. If all guitar players understood this you'd never see more than a 100w 1x12 guitar amp, and never suffer the result of volume wars.

[Phil Starr]

2 hours ago, Bill Fitzmaurice said:

I measured Big & Rich and Montgomery Gentry at an average of 103dB at the FOH.  Deep Purple was the same. Charlie Daniels came in at 104dB. Tim McGraw  and Alice Cooper ran at 105dB.

True, although most players are going to be pushing closer to 30w average with 120w peaks. Also consider that the FOH where I took measurements was some 25 meters from the stage. Reaching 110dB there would require some 135dB at one meter, well beyond that capability of almost any backline rig. That's why you size your personal rig to drive the stage, and let the PA drive the room. If all guitar players understood this you'd never see more than a 100w 1x12 guitar amp, and never suffer the result of volume wars.

Those figures are interesting, and completely consistent with measurements taken at Glastonbury a few years back.

Oh blessed day when bands learn to turn down and let the tech do the work, and protect their hearing.

[pete.young]

To drag this back onto topic, interesting though the diversion is :

Ask HappyJack if his Matamp is still for sale.

[Bill Fitzmaurice]

It's absolutely on topic. If you understand what's being said you realize how a 30 watt Ampeg B15 is still capable of doing the job, on any stage.