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Amp Head Peak Wattage or RMS

Crazyman582

Crazyman582

Guest
Dec 8, 2015
83
32
#1
This may have been asked, if so just drop a link but I couldn't find it.
Anyway I am planning on buying my first non-combo amp soon. The cab I am planning on getting has an 400 watt RMS and an 800 watt peak. Should I get a head over 800 watts for the peak?
Oh and if you could suggest a cheap head in said wattage that would be great
Thanks
 
#2
Get an amp rated at 400 - 500 watts RMS or below. The peak rating of the cabinet is all it can handle at top volume. A 400 watt amp can reach that 800 watt peak easily. Right after that the speakers break.
Make sure the impedance of the cabinet matches the output impedance of the amp. These ratings are expressed in ohms.
Carvin is a good brand and pretty reasonable. If you search budget bass amp in Talkbass amplifier forum you'll find MANY opinions.
 
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#3
old spice said:
Get an amp rated at 400 - 500 watts RMS or below. The peak rating of the cabinet is all it can handle at top volume. A 400 watt amp can reach that 800 watt peak easily. Right after that the speakers break.
Make sure the impedance of the cabinet matches the output impedance of the amp. These ratings are expressed in ohms.
Carvin is a good brand and pretty reasonable. If you search budget bass amp in Talkbass amplifier forum you'll find MANY opinions.
Click to expand...
If the cab can easily reach 800 watts, wouldn't you want a head with similar watts ( Icould be completely off here)
 
#4
Cabs don't make watts. They take watts.

Think of it like this. You have a half liter glass. You can pour a quarter liter of water in it and it will be fine. You can put a half liter of water in it, but it may spill all down your shirt when you lift it up to take a drink. You can not pour a liter of water in.

Now substitute cab for glass, and watts for water and it should make sense.
 
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#5
Crazyman582 said:
If the cab can easily reach 800 watts, wouldn't you want a head with similar watts ( Icould be completely off here)
Click to expand...

Now to really confuse you.

The wattage rating for a speaker is the power it takes to melt the voice coil, NOT the power it takes to cause physical damage.

Depending on your use of low end EQ, *most* commercial cabs can only handle around 1/2 their thermal RMS rating before farting out (don't even worry about "peak" numbers, they are BS).
 
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#11
In general
Cab makers exaggerate how much power their cabs can take.
Amp makers exaggerate how much power their amp puts out.

It's not a bad thing to get a higher power amp, at the same time don't assume a lower power amp will somehow protect your speakers.
Use your brain and ears to hear if the speaker is stressing and back off the volume.

Some DSP enabled FOH rack mount power amps do have limiters that do actually limit power to the speakers, but you still can't know from a bass cabinet maker what their cabinets can actually handle.
 
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#12
seamonkey said:
In general
Cab makers exaggerate how much power their cabs can take.
Amp makers exaggerate how much power their amp puts out.

It's not a bad thing to get a higher power amp, at the same time don't assume a lower power amp will somehow protect your speakers.
Use your brain and ears to hear if the speaker is stressing and back off the volume.

Some DSP enabled FOH rack mount power amps do have limiters that do actually limit power to the speakers, but you still can't know from a bass cabinet maker what their cabinets can actually handle.
Click to expand...
Wouldn't the exaggeration cancel each other then :)
 
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#13
Seismic is one that likes to exaggerate power handling a bit for bass guitar use. What ever amp you do get the volume and EQ will determine how hard your speaker system (cab) will be pushed as well as how "hard" you play.

Most of us don't agree with amp makers "overstating power" although there are brands that make it a standard practice.
 
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#15
Crazyman582 said:
Wouldn't the exaggeration cancel each other then :)
Click to expand...

That's the hope.
Until an honest maker comes along. An honest maker may rate their cabinet and honest 200w but someone is going to think they can get a 400w Seismic for much less $$$. The honest maker has a lot bigger challenge to make a sale. And of course, it's only my assumption that Seismic is exaggerating. And for the amp side, you'll find 200 to 2000w amps in the same price range.
 
#16
Let's all step back for a little dose of reality please...

1. RMS is a measurement based on the RMS voltage of the output of the amp into it's rated load and has nothing to do with continuous. The "RMS" power is also considered the thermal power because it's the area under the power curve.

2. Peak power is exactly 2x the "RMS" power because it is generally (there are some exceptions) based on the peak voltage of the undistorted sine wave used for the thermal or "RMS" power defined in #1.

3. Once you recognize the above, any comparisons made must be with equivalent units... ie. peak to peak or RMS to RMS... EXCEPT that the speaker industry has chosen another arbitrary rating called "program power" which is also defined as 2x the "RMS" power, so then USUALLY BUT NOT ALWAYS, the peak power is taken to be 2x the program power or 4x the RMS power.

4. Now that you are aware of the totally screwed up (different) rating methods used by the two industries, there's another "gottcha", that is most speakers give thermal ratings (RMS) that do not consider the mechanical limitations of the speaker... which DECREASE a lower frequencies (ie. the lowest octave of its rated bandwidth).

With all of that said, I would in general recommend roughly matching the RMS rating of the head with no more than the RMS rating of the speaker, that will get you reasonably close, reasonably safely. Yes, you may be able to drive the speaker harder IF you know more about the specific products, but I wouldn't feel comfortable making that recommendation without knowing a lot more about the amp and speaker involved.

Also, note that the amp's ratings apply only to the speaker impedance presented to it, so those units must be the same also (ie. compare the 8 ohm rated power of the amp to an 8 ohm speaker and the 4 ohm rated power of the amp with a 4 ohm speaker (or 2 paralleled 8 ohm speakers).

Hope this helps.
 
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#17
beans-on-toast said:
A good rule of thumb to follow is to pair a cabinet with an amp that has at least twice the RMS rating of the amp. For an amp that is rated to deliver 400 W RMS, look for a cabinet that is rated to take at least 800W RMS.
Click to expand...

Yes, I agree this would generally be a safer recommendation.
 
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#18
In reality, no bass amp manufacturer or bass cabinet manufacturer agree on any ratings. They don't have to because bass gear consumers don't demand it.

Eminence rates their speaker drivers in EIA 426A
Somehow, when these drivers end up in cabinets, the cabinet manufacturer makes up a "RMS" ratings.
"RMS" is a totally erroneous term for speakers, and for amplifiers.
 
#19
RMS power is understood to be based on RMS voltage and current. Though not correct by definition, it's a pretty easy concept to sort out in reality.
 
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#20
Without getting into the old over/under power debate, i will simply say to the OP go to a music store and try as many amps as you can. There are amps that weigh under 5 Lbs and produce 1000 watts @ 4 Ohms, what a time to be alive! If you don't find an agreeable tone in a class d amp look at a hybrid like a SVT lll (tube pre-amp, SS power section) look at all SS like Gallien-Kruger 400, 700 or 800RB, look at an all tube like an Ampeg V4B or Fender 100T. Generally speaking, see if you like 10, 12 or 15 inch drivers. After trying a bunch of stuff in a music store search the classifieds here, as buying used will get you quality gear at a fraction of the price. Few amp heads go down to 2 Ohms stable, so you have to ask yourself before you buy your first cab if you are going to lock yourself into a 4 Ohm 4x10 or 2x12 as examples, or if you are going to accept putting a few less watts into an 8 Ohm cab now and in future allow yourself the chance to expand into 2 matching 8 Ohm cabs for a 4 Ohm total load. Hope that helps! Cheers.
 

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