How do you determine how much power is enough?

[BuglerBass]

Always a discussion with Keyboard players and vocalist.
Since default solution or theory was more power would be
higher levels.
Nope, more important was speakers.
Often they would upgrade the amplifiers
to find out the speakers hit distortion at the same old
levels.
Never really needed much more than 300 to 400 watts.
For Bass. Enough Speaker was more important.
Speaker will distort or feel compressed usually way before
the amplifier runs out of steam.

Rehearsal levels was the standard to reach most the time
for drum levels. Or if adding vocals or keyboard.
Stage levels usually about the same or lower.
Only exception usually large outdoor stages.
Wind direction can change and just sweep sound
away in strange cycles . Odd thing to experience.
Having speakers higher up at ear level. Then be able
to push cabinets little more than rehearsal levels
helps a lot.

 

[CallMeAl]

It was just trial and error for me. Volume comes from the cabs mainly. But I’d say the extra wattage gives me a heft, bite, attack… je ne sais quoi… that’s not there at lower wattages. Something comforting about leaving the master volume at about 9 or 10:00 all night

As for numbers, 100 was too little. 500 was my sweet spot where I never thought about it anymore. I had a 350 for backup, which most likely could have covered any gig the 500 did. But the 500 became my fave.

 

[Wasnex]

We all know that less power = less clean headroom.

Sorry but this is an erroneous assumptions and, as a result, you are asking the wrong question.

The correct answer is how much SPL is necessary? This is something you are going to have to decide for yourself. My magic number is at least 124dB, based on the calculated SPL the rig is rated to produce.

How much power you need depends on two factors: 1. The SPL you require, and 2. the sensitivity rating of your cab(s).

Here' a formula you can use.

Calculated SPL = [Log(Usable Power) x 10] + Sensitivity Rating​

Where:
- Usable power is the minimum between how much power your amp makes and how much power your speakers can handle. Use the RMS power ratings.
- Speaker Sensitivity is expressed in terms of 1W applied and the SPL measured at 1m​

Let's do an example. We'll assume usable power is 400W and our speaker's sensitivity rating is 97dB 1W/1m

Calculated SPL = [Log(400) x 10] + 97 = ~123dB
​

This almost meets my minimum .

If you add a matching cab, the sensitivity goes up +3dB. So: 97 + 3 = 100dB 1W/1m. Also most solid state amps make more power as the impedance goes down. So let's a assume our amp makes 600W with two cabs, and each cab can handle 400W. This means total power handling of both cabs is 800, but our usable power is 600W.

Calculated SPL = [Log(600) x 10] + 100 = ~128dB
​

This significantly exceeds my minimum .

In reality this may not be enough headroom for every circumstance. But I am only willing to turn up so much.

For the record, my last touring was rated for a calculated SPL of 127dB. AFAIK I never pushed it to clipping. There were times where I could not hear very well, but refused to turn up further.

 

[Hounddog409]

3 - 4 times the total wattage of the other amplified instruments, or 3 times the combined wattage of all over-powered guitar rigs on the stage.

Meaningless mumbo jumbo. So 1x10 cab is ok?

Power rating of amp is not the starting point. Number and size of speakers is where you start.

Then Enough amp to lower said speakers.

 

[Tim Skaggs]

Pretty much what the title says. More specifically, if you like:

If you’re currently rocking an 800+ watt rig, what kinds of gigs would you no longer be able to do, or what kind of musical compromises would you have to accept, if you had to make do with a 500 watt rig? (Or transpose the question to 500 —> 350, 350 —> 200, 200 —> 100.)

We all know that less power = less clean headroom. But how does that actually manifest as a limitation in real-world gig situations for you? Is it little tonal infelicities that only you would notice? Gross farting? Speaker damage?

I hope the thread premise makes sense, and I’m looking forward to hearing your responses. (I don’t have any agenda except to learn, I promise.)

There is no way to answer this without at least some info on the band instrumentation and type of music being played. If you are playing in a duet with one acoustic guitarist doing songs by the Eagles, a 25 watt amp & one 10” cabinet would probably work. If you are in a band with a couple guitarists, keys, a horn section and a few percussionists doing Chicago songs in heavy metal style, you might need a little more, unless the PA did all the amplification.

The gig I played last Sat. 8/19 with a four piece rock & blues band was done with a 75 watt amp with a single 12” speaker for the first half of the gig. I turned the amp off for the last couple sets. IEMs were used by me. I don’t know if the other band members added me into their monitors or just heard me through the mains. I probably won’t take an amp to the next gig.

 

[Altitude]

This feels like it’s more about the size of the room than anything else. You can play 200 gigs in clubs using a 500 watt head and a 212 cabinet and have a great experience. But if you then find yourself in a 1500 seat theater one time, that amp might not produce enough output.

 

[Wasnex]

As I mentioned, my last touring rig was rated to produce about 127dB. This is with only 260W. The key is my speaker had a 103dB 1W/1m sensitivity rating.

[Log(260) x 10] + 103 = ~127dB.

 

[Jazzdogg]

This feels like it’s more about the size of the room than anything else. You can play 200 gigs in clubs using a 500 watt head and a 212 cabinet and have a great experience. But if you then find yourself in a 1500 seat theater one time, that amp might not produce enough output.

The greatest difference, IME, is between indoor and outdoor gigs, and their respective acoustic environments.

For outdoor gigs I stacked cabs, two high, with the upper cab aimed at me, and the lower cab aimed to suit my band mates. Usually a 1x15 on bottom, and a 2x12 or 2x15 on top; indoors, a single cab sufficed most of the time.

Outdoor gigs without enough oomph are not happy experiences for me. Usually, this means I need to add more cabs, and be tactical about their placement; the power requirements are established by venue conditions.

 

[Wasnex]

If you know your target SPL and your speaker system's 1W/1m sensitivity rating, you can use this form of the formula.

Let's say you want 126dB and your cabs sensitivity rating is 99dB 1W/1m

So for 126dB calculated, you need about 500W. Keep in mind, the speaker needs to be able to handle at least 500W for this to work.

To check the answer, let's use the previous formula.

Calculated SPL = [Log(501.2) x 10] + 99 = ~126dB​

 

[ezstep]

I used a 150 wt head as my main amp on top of a 2x15 for about 19 years. I now use the D-800+ regularly and I would estimate that I run it around 300 watts in a medium to large venue (on a 2x12 or two 1x15's). Absolutely no scientific proof though.

 

[nightchef]

Let's say you want 126dB and your cabs sensitivity rating is 99dB 1W/1m

But how do you know you want 126 dB? I realize it sounds like a dumb question, but it's sincere. I don't know how to derive specific dB requirements from the empirical experience of playing in various band/venue combinations. Should I just bring an SPL meter to my next soundcheck and have somebody hold it 1M away from the cab when I'm playing my loudest? (Well hey, maybe I should.)

 

[seamonkey]

Say you have a speaker cabinet rated at 100dB at 1W at 1 Meter and there is no clipping or bass compression,
Here's what the different watt ratings could be at 1 Meter:
Input power (W), SPL (dB)
1w, 100 dB
100w, 103.2 dB
200w, 106.4 dB
300w, 109.6 dB
500w, 112.8 dB
800w, 114.4 dB

But above 100dB, human hearing can hardly hear a 3dB difference. So differences between 500w and 800w at 112.9dB and 114.4dB is hard for any human to detect.
If you find a 500w head you like, don't worry about the difference a 800w may bring.

If your cabinet is putting out 110db at 1 meter, and you're that close, you can suffer permanent hearing loss if you're exposed for several minutes, so beware.

Let the FOH carry the grunt, and the FOH engineer will monitor the levels for the audience. Line arrays help spread the sound out, so the audience doesn't get over exposed to high dB levels.

 

[mikewalker]

Are those 800 watts available into 2 ohms?? That should provide plenty of decibels, assuming reasonably sensitive speakers.
(and lots of them!)

 

[Wasnex]

But how do you know you want 126 dB?

Experience and awareness. I know a rig rated for at least 124dB is enough for me, because I pay attention to this sort of stuff.

You can use these formulas to do sort of crude comparisons between different gear. The comparisons are somewhat crude because the way the specs are derived is not standardized or consistent from one product line to the next. So the calculated SPL is only a ballpark figure.

The idea is if you find one rig that is loud enough, you can figure out the calculated SPL and then look for other gear combinations that can make at least the same calculated SPL. Since the comparisons are crude, it's good to look for the calculated SPL rating of gear you are considering to exceed your expectations by a few dB. For example, I think my number is 124dB, but my last touring rig was rated for 127dB. This rig always met my needs.

 

[Wasnex]

Input power (W), SPL (dB)
1w, 100 dB
100w, 103.2 dB
200w, 106.4 dB
300w, 109.6 dB
500w, 112.8 dB
800w, 114.4 dB

???

1w, 100 dB
100w, 120 dB
200w, 123 dB
300w, 124.8 dB
500w, 127 dB
800w, 129 dB

 

[Mastiff_5]

Meaningless mumbo jumbo. So 1x10 cab is ok?

Power rating of amp is not the starting point. Number and size of speakers is where you start.

Then Enough amp to lower said speakers.

Meaningless mumbo jumbo. Cool. Be a jerk. At least I have variables in my offering to the OP that aren’t completely arbitrary. I gave him a number to compete against. Way to be a jerk.

 

[Eminor3rd]

I feel like the answer is just roughly 500w, and any cab that works with 500w

 

[sawzalot]

At a certain point you will hopefully have PA support with big powered subwoofers. At that point you just need enough amp to hear yourself onstage.

 

[57pbass]

I played countless shows all over Chicago with nothing but an SWR Working Mans 12.
Sure, I wish I had my Demeter/Berg rig back then when I was playing 3-4 shows a week, but having a crappy rig never stopped me.
Disclaimer: I did have a much larger Hartke 210/115 rig, but I didn’t have a car, so I typically ran with the SWR via taxi cabs. Lol

The ultimate test of portability.. if you get into a cab with your bass and amp.. it’s good to go !
Living in metro NYC I’ve done this many times.

 

[agedhorse]

More power is always the answer; you can always turn down the volume & gain knobs.

Until you don't or have an accident and then it becomes more (working) speakers and repairs to those you just damaged.