Too little power?

[The Geoff]

I've always wondered (well, at least for the last year), How much power does it really take to drive a speaker properly.

 

I suspect there will be a difference in opinion between bassists and guitarists.

 

I have a 15" Celestion rated at 250W/8 Ohm, and a 12" Beyma rated the same.

 

I have a 200W Marshall 3520 Integrated Bass System head.

 

My guitarist head tells me that is safe, my bassist head tells me I am underpowered.

 

How much drive do you need in relation to handling capacity to make a speaker sound OK?

 

G.

[Pappy P]

Bump. I can't believe there aren't any answers to this.

[BillWelcome Home Studios]

That is because the "answer" differs.

 

Any PA guy will tell you that he wants 10dB more amp headroom than the speakers will handle.

 

Most home studio guys will tell you that it is important that the amp and speaker wattage match (that is totally incorrect, by the way... and accounts for a bunch of blown tweeters due to square waves, and a lot of guys listening to distorted music and not even knowing it.)

 

Guitar players want to push a speaker until it is begining to break up and guitar speaker driver design is adjusted to accomodate this without blowing up the speaker.

 

A bass player wants something similar to the PA guy... clean reproduction of what he is putting into it.

 

A guitar player will run a 20 or 30 watt amp flat out and love the tone, a bass player will run his 350 watt bass amp at much more conservative levels, be quite loud, and have more accurate reproduction of what he is putting in to the speakers.

 

In terms of 'properly driving' a speaker, it is not just the speaker in question, but also the efficency of the cabinet. Yes, speakers have sensitivities. But the response varies and the acoustical output varies depending upon the cabinet.

 

I started out using PA speakers (Gauss, JBL) in guitar cabs, and had to push the darned things to 'stun' level to get a 'good' guitar tone. Moved to cheaper, low wattage speakers and got the tone at much more sensible levels for much less money.

 

If you are really interested in the science of the process, there are many books on the subject of speaker response and there is (or at least, used to be...) a magazine devoted to speakers and speaker issues (cabinets, crossovers, etc.) I forget the title, but I'll bet that you could google it.

 

Strictly speaking, or correctly speaking if you prefer, you are grossly underpowered for the system that you describe. That doesn't mean that you will damage anything, but you sure have the right setup for producing square waves and burning out speakers.

 

Bill

[fantasticsound]

So long as you provide a clean, rms power output at or less than your speaker is rated you will not damage it.

 

As you don't know what that rms level is with real world program material, the typical power to speaker rating is 1.2 or 1.3 to 1. For every watt your speaker is rated to handle you can safely provide an amp that can deliver 1/5th to 1/3rd more power than that rating, for headroom.

 

This is because peaks, depending on the rigor of the testing method, can easily be 2x or 4x the rms power rating without damaging the speaker.

 

Bass frequencies pull far more power than high frequencies. If you play at your amp's capacity to deliver instant power for bass peaks, you'll either clip the amp or send it into compression, the modern power amplifier's protection for your speakers.

 

Also, if an amp is rated to deliver 100 watts and your speaker can handle it, but the amp cannot recover quickly enough (slew rate), it will also clip or trigger compression to protect your speakers.

 

Typically, in guitar applications this is usually less important because bass peaks aren't nearly as power hungry as with bass guitars' bass peaks.

[The Geoff]

Yes, I was aware that it's underpowered as a bass rig, but it's what I can afford, so I'm careful not to overdrive.

 

I suppose this sort of underlines what I really thought..

 

However, I *have* found that putting the Digitech Genesis in front of all this makes a hell of a good guitar rig.

 

G.