The Wattage Game

[Kdogg]

Okay, I've been playing bass for the past ten years or so, and I am currently playing in an originals rock band. The band consists of me, the drummer, two guitars, and a lead singer. I've just purchased an SWR SM-500 off ebay, and I am trying to decide on the appropriate cab to use with it. My dilemna is trying to figure what wattage cab I should be considering. The SM-500 puts out 500 watts at 4 ohms, and 400 watts at 8 ohms, this according to the owners manual. I'm interested in the Goliath III 4x10 cabinet. However, this particular cabinet is rated at 700 watts and is 8 ohms.

 

Would I be under powering this cab? The owners manual suggests 2 Goliath III's with this head, but I can't understand how that would not tax the amplifier, even though it would give you a 4 ohm load and so run the amp at 500 watts. Am I misunderstanding the whole amps/ohms/watts thing? Is there some kind of ratio one should use to determine how much power you will need for a given cabinet? What would be the optimal amplifier for an 8 ohm 700 watt cabinet?

 

My current rig is an SWR Silverado 2x12 combo. It's running 350 watts into a 4 ohm cabinet. I love the sound and tone, but I'm finding I need a bit more volume during our live shows.

 

I hope this post makes a little sense...

[sunburstbasser]

There is no such thing as under-powering. What you can do is clip the amp, but this happens when you run a solid state amp around 9 or 10 for a while. With the proper EQ, running the 4x10 and maybe a 1x15 underneath it will be plenty of volume.

 

The cab wattage is, I believe, more a general estimate as to where it'll run best at more than a DO NOT EXCEED wattage.

[Emprov]

You know, I've had a ton of cabs and have never really realized any underpowering. Sure, some cabs love more watts behind them but everyone can't own a 2000w rig to satisfy a few cabs. You're also not going to hurt the head, it doesn't care how many watts the cab will handle, it only cares about the ohms so move forward with confidence.

 

Oh, and welcome to the forum!

[timmerz]

Greetings, Kdogg....

 

Just look for a Goliath that was wired to 4-ohms.

Like this one here:

 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7357471492&fromMakeTrack=true

 

Then you'll get your full 500 rms out of the SM500, and you'll be happy, trust me!

 

Or, even better yet, jump on this Goliath Senior, which I believe they only made in 4 ohms, and get yourself a hell of a cab for very little...

 

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7357467836&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

[Zeromus-X]

The difference between the 8 ohm cab and the 4 ohm cab will only translate to less than 3dB. You'd be better off getting the 8 ohm cab, that way you'll be able to add on later. Granted, doubling the speakers is going to net you 3dB (so you'll be at the same power level according to paper), more speaker surface area is going to be perceived as a lot louder. Plus, having one cabinet on each side of the stage works really well.

 

/IMO

[mike fitzwell]

I've gigged my 800W Ampeg 8x10 with either a 100W tube head or a 1400W poweramp pushing it and both have worked great. Bottom line is be smart about it--don't mismatch the ohm ratings and don't clip your amp. And if you start to hear something weird coming from your cab turn the amp down.

 

This line of reasoning has served me well all these years.

[Gfunkk44]

The goliath III works fine with less power.. my main amp went down for a short time, and I had to use a little 100 watt amp to power the cab for a few gigs and practices.. It worked fine, you won't get the volume outta the cab, but it certainly won't hurt the cab, and the difference between a 400 watts, and 700 wats, isn't huge.

 

Remember to double your sound in terms of watts you need nearly 10 times the amount. Better to just get the 8ohm cab for now.. 4-5 hundread watts is good enough. Just don't clip the power amp, but the difference between 8 and 9 on that amp, won't matter much anyway.

 

Also, in a band setting alot of times your EQ, can give you more presence with less power... I used to practice with my amp set at 6. But I started playing with my EQ, and now find im louder than I was at 6, and had to turn down to 5. Im sure you know all this stuff as well though.

 

OR, you could always turn your amp up to 11 for that extra little bit

[hasbeen]

 

Originally posted by sunburstbasser There is no such thing as under-powering. What you can do is clip the amp, but this happens when you run a solid state amp around 9 or 10 for a while. With the proper EQ, running the 4x10 and maybe a 1x15 underneath it will be plenty of volume. The cab wattage is, I believe, more a general estimate as to where it'll run best at more than a DO NOT EXCEED wattage.

 

 

thank you for saying this. I read so many posts here about people stating that "underpowering" a cab is bad. ....I don't get it.

 

Like sunburst says, just don't run the amp into clipping all the time.

[FreestyleIntruder]

 

Originally posted by hasbeen thank you for saying this. I read so many posts here about people stating that "underpowering" a cab is bad. ....I don't get it. Like sunburst says, just don't run the amp into clipping all the time.

 

 

Yep, the worst you'll get by 'underpowering' a cab is that some cabs (eg Peavey) just really like a lot of power to be at their best.

[Craig Vecchione]

 

Originally posted by Kdogg Okay, I've been playing bass for the past ten years or so, and I am currently playing in an originals rock band. The band consists of me, the drummer, two guitars, and a lead singer. I've just purchased an SWR SM-500 off ebay, and I am trying to decide on the appropriate cab to use with it. My dilemna is trying to figure what wattage cab I should be considering. The SM-500 puts out 500 watts at 4 ohms, and 400 watts at 8 ohms, this according to the owners manual. I'm interested in the Goliath III 4x10 cabinet. However, this particular cabinet is rated at 700 watts and is 8 ohms. Would I be under powering this cab? The owners manual suggests 2 Goliath III's with this head, but I can't understand how that would not tax the amplifier, even though it would give you a 4 ohm load and so run the amp at 500 watts. Am I misunderstanding the whole amps/ohms/watts thing? Is there some kind of ratio one should use to determine how much power you will need for a given cabinet? What would be the optimal amplifier for an 8 ohm 700 watt cabinet? My current rig is an SWR Silverado 2x12 combo. It's running 350 watts into a 4 ohm cabinet. I love the sound and tone, but I'm finding I need a bit more volume during our live shows. I hope this post makes a little sense...

 

 

Well, yes, you are misunderstanding how amplifiers and speakers work. As noted previously, the term "underpowering" is completely wrong. You will hear people insist on this underpowering theory, and they are wrong.

 

A speaker is rated to 'handle' a given amount of power, in watts. What this means is that the speaker will dissipate, or use, a certain amount of power up to a limit, above which it will fail...the higher the power, the faster the failure. It presents impedance to that power, expressed in ohms.

 

In general solid state amps will produce more power into a lower impedance load. The tradeoff is that the amp's circuitry is passing more current to deliver that power. The amp can only handle a certain amount of current before the components get too hot and begin to fail. So there's a limit there too.

 

So now you have a speaker that will handle 700 watts, and an amp that produces 400 watts into the impedance that the speaker presents. The 'underpowering' disciples will tell you that you'll damage the speaker with this setup. Well, it's possible, but not because you're underpowering, but because of another thing with amps....they can produce more power than they are rated for. The rating is for 400 watts at less than 1% distortion. But if you really push the amp, it could produce 800 watts with much higher distortion. So if that rig doesn't give you the volume you need, and you crank it to '11', you aren't underpowering the speaker, you're overpowering it....it can handle 700 watts, but you're making it handle 800 watts. That extra 100 watts is heating the voice coil hotter than it can get rid of the heat, and it will eventually fail.

 

Now to address your issue. The Silverado is a great amp. 350 watts is plenty of power. Another phenomenon of sound is that the difference in power between 350 and 400 watts is maybe 15%, but the difference in added sound volume.....maybe 5%. It takes a lot of power to make a noticeable increase in sound. It takes about 6-10 times more power to give a perceived doubling of volume. So even going to a rig that delivers 500 watts won't make that much difference. You'd need about 3000 watts...and the corresponding number of speakers, to double the volume of that Silverado.

 

A single Goliath III will be fine with the SRM500. Yes, you'll get a bit more volume from a 4 ohm cabinet, but the Goliath is efficient and loud.

[Kdogg]

Thanks everyone, especially Mr. Craigv! It's amazing how hard it is to find concise answers to technical questions these days, and I really appreciate everyone taking the time to help a brother out.

[Crescent Seven]

Originally posted by Kdogg Thanks everyone, especially Mr. Craigv! It's amazing how hard it is to find concise answers to technical questions these days, and I really appreciate everyone taking the time to help a brother out.

 

The guys on this forum have always answered my questions.

 

I run 300w, and I can make my singer weightless with a 4x10 and a 1x15 under it. Sure, I'd like more power, but who wouldn't? I just don't need it, especially with a PA.

C7