Amp vs Speaker Wattage

[BarryPseudonym]

OK, I've read the FAQ threads (very informative) and done a search (very long) but haven't been able to find a definitive or satisfactory answer for this. So forgive me if I'm treading old ground.

Basically, I'm looking to buy my first decent rig, and after playing an Ampeg SVT-3 Pro in a shop, am pretty much sold on that. I don't want to go overboard on the overall cost, so was looking at a cab to go with it that does the business but doesn't cost the earth. To me, that looks like a BSE-410HLF.

The thing is, the head allegedly kicks out 450w at 4ohms, and the cab is rated to handle 400w RMS. Will this cause any damage/problems? I've read in places that putting more than the rated power into a cab is OK - even good - but that sounds all wrong to me. What's the story?

Am I looking at shelling out extra quids (yeah, I'm a Brit, soz) for an SVT cab, or best off dropping down to 8ohms?

Decisions, decisions. And that's before you all go off recommending other brands to me...

 

[Mcrelly]

thing of your amps ratings like the speedometer on your car. lets say your looking for tires. I'm gonna use Miles per hour MPH in my explaination, but you can substitute KPH o.k.?

when buying tires you don't tell the dealer "hey, but my car goes 120 MPH!, will these tires handle it?" normally you'd drive between 0 and say 70MPH. the amp only puts out as much watts as you tell it to. your gas pedal and volume control are adjusted by you.

now you may ask "how many watts do I need in a typical situation?" I use to wonder "if I play at 105 dB how many watts is my amp putting out?" since physics of electricity and wattage are dependent on so many different variables, its hard to make a consumer friendly "watt usage meter" (just made that up) for your amp.

what am I getting at? don't worry about a cabs rated wattage, in my opinion, just make sure your amp is rated as much or higher than the cabs. now, I just thought about my situation and that is not the case. my amp CAN put out 550w into 4 ohms (two 8 ohm cabs used together) and my cabs are 300w at 8ohms each. this seems to be a good match for my situation: fairly loud echoey church with live drums and several other instruments.

as far as considering the safety of your equipment I think its better to have more amp watts than more cabs watts. i.e. a 100w amp with 300w cab is a more dangerous situation for potential misuse and damage. this situation would be referred to as "underpowering" your cab. what can happen is your volume need might not be met before the amp runs out of juice and distortion is being sent to the cab, possibly damagine the speaker.

a similar situation that could be called "overpowering" happens when a speakers wattage is alot lower than the amps output. i.e. 500w amp and a 100w speaker. its possible that only soo much air is going to be moved by, lets say, a single 10 or 12 speaker. you might be tempted to pump more and more wattage into the speaker until something has to giveout.

wow, this is getting long!

 

[Mcrelly]

rereading your post I think you'll be fine with that cab and amp.

if you need more volume in the future try adding an extra cab first, then consider more watts if that doesn't do the trick

 

[BassIan]

OK, I've read the FAQ threads (very informative) and done a search (very long) but haven't been able to find a definitive or satisfactory answer for this. So forgive me if I'm treading old ground.

The truth is there is no definitive answer when looking at the big picture of this issue. Thus, it may not satisfy you or many others. There are, however, reasonable guidelines that are pretty foolproof.

Basically, I'm looking to buy my first decent rig, and after playing an Ampeg SVT-3 Pro in a shop, am pretty much sold on that. I don't want to go overboard on the overall cost, so was looking at a cab to go with it that does the business but doesn't cost the earth. To me, that looks like a BSE-410HLF.

The thing is, the head allegedly kicks out 450w at 4ohms, and the cab is rated to handle 400w RMS. Will this cause any damage/problems? I've read in places that putting more than the rated power into a cab is OK - even good - but that sounds all wrong to me. What's the story?

Am I looking at shelling out extra quids (yeah, I'm a Brit, soz) for an SVT cab, or best off dropping down to 8ohms?

Decisions, decisions. And that's before you all go off recommending other brands to me...

So, you will have a 450 watt (at 4 ohms) head, and you need to choose a cabinet. Ampeg cabinets are pretty good so you're on a good track there. Feel free to look at others also. You don't need to match your cabinet's power handling to your amplifier power. When choosing the ideal rig, most of the technically trained people here will suggest that an amplifier capable of producing 2X the cabinet's RMS handling is ideal. Many others claim it's best to closely match the ratings. Often, it is seen as forbidden to run an amplifier with less power output than the speaker cabinets can handle.

This last guideline there is VERY incorrect. You can run whatever amplifier you like into your speaker cabinet. The cabinet doesn't notice or "care". It just converts electrical energy into heat (mostly) and sound, and is rated to dissipate a certain amount of it, and create a certain quantity of sound.

So, your best bet to make the most of your power is to find the cabinet that sounds best to you with the highest Sensitivity rating. That is the measured sound pressure level at 1 watt input into the cabinet and 1 meter away. Typically, this is given as 1 figure and measured at 1000hz. This is a poor sign of how a bass cabinet will respond, since many cabinets have peaks around that range and are several decibels lower on a broadband scale. Better would be to have a graph plotting sensitivity across the passband of the cabinet - but this is only given by billfitzmaurice and Phil Jones for their cabinets.

So, go try out lots of cabinets and see which suit you the best. Whatever the power rating is, it doesn't matter because if you have the right tool for the job, you won't have to worry about exceeding the limits of your amplifier's capability.

 

[galore]

What's the peak power of your cab and head? If you have these the same, don't worry. Usually some players like to have a bit more powerful head than cab, but it's not a rule. SVT classic and 810E have totally different wattage rating, but people use that rig. With 450w head and 400w cab you'll be just fine.

 

[billfitzmaurice]

You can turn the amp down to 5, you can't turn it up to 15. If the amp has more power than one cab can use then you have the option to add another later. Better to be muscle bound than anemic.

 

[TonyJZ]

......The thing is, the head allegedly kicks out 450w at 4ohms, and the cab is rated to handle 400w RMS. Will this cause any damage/problems? I've read in places that putting more than the rated power into a cab is OK - even good - but that sounds all wrong to me. What's the story?

Am I looking at shelling out extra quids (yeah, I'm a Brit, soz) for an SVT cab, or best off dropping down to 8ohms?

Decisions, decisions. And that's before you all go off recommending other brands to me...

Hey dude, I am running an SVT4 Pro (similar to your SVT3 Pro) along side a SVT 410hlf (at 500watts RMS). I run it bridged sending out 1200watts (900watts continous) to the cab....So far I've had no problems other that It does not seem to be as loud as I thought it would be. (Could just be that I am chicken and dont push up the volume) But I can hear myself when we play outside....we just need PA for audience.

 

[TonyJZ]

........So, your best bet to make the most of your power is to find the cabinet that sounds best to you with the highest Sensitivity rating.......

Hi,

As I mentioned before, I am running an SVT4 Pro and an SVT 410hlf 500watt RMS cab @ 4 ohms with a sensitivity of 98dB......Does that mean that, say a Gallien Krueger RBH 410 @400watts @ 8ohms with a sensitivity of 103dB will give me MORE volume because of dB?

 

[BassIan]

Hi,

As I mentioned before, I am running an SVT4 Pro and an SVT 410hlf 500watt RMS cab @ 4 ohms with a sensitivity of 98dB......Does that mean that, say a Gallien Krueger RBH 410 @400watts @ 8ohms with a sensitivity of 103dB will give me MORE volume because of dB?

Absoultely it does. Here's some math you can use that makes the sensitivity rating clear. 3dB is the increase you'll get from doubling the power (in the ideal case where power compression and other factors are ignored).

So, take the Ampeg cabinet at 98dB with 1 watt input. Let's assume (incorrectly) that this applies across the frequency range you're concerned with. Now you get the following output at the following power levels:

2 watts... 101dB
4 watts... 104dB
8 watts... 107dB
16 watts... 110dB
32 watts... 113dB
64 watts... 116dB
128 watts... 119dB
256 watts... 122dB
512 watts... 125dB

Apply same logic to the G-K cabinet and you get the following:

2 watts... 106dB
4 watts... 109dB
8 watts... 112dB
16 watts... 115dB
32 watts... 118dB
64 watts... 121dB
128 watts... 124dB
256 watts... 127dB
512 watts... 130dB

We can observe a few things here. First, let's say you have to reach 120dB for your mix (remember, this is 1m away). With the G-K cabinet, you'll need just under 64 watts from your amplifier to sustain that. Note that if 120dB is the maximum volume you need, most of your content requires much less (volume). With the Ampeg cabinet, reaching 120dB requires a bit over 128 watts from your amplifier.

If we take away the assumption that the sensitivity ratings are correct (this is a bad assumption anyway), then we're back to the crapshoot. Some here say that since everybody fudges the sensitivity ratings, perhaps they still work to compare cabinets in a relative way. I don't think this is true, and I believe full disclosure gives shoppers a much better way of comparing, but the day a manufacturer posts frequency vs. sound level plots for each cabinet is not near. In most cases, they don't even have such plots because they've never tested their cabinets.

Keep in mind, your 8 ohm cabinet will draw less power from your amplifier.

As I say, your best bet is to try the setup in the loudest setting you see yourself being in. Please realize the limitations of my comparision above, since that's using a purely mathematical relation and ignoring real-life effects (power compression, impedance that shifts with frequency, non-flat speaker response, etc). It's a good concept to use but is not useful as any more than that.

Also, a speaker cabinet may well be able to handle its rated RMS handling and beyond in terms of thermal capacity, but it is possible to cause mechanical failure of a driver at power levels well below its RMS rating. Keep this in mind when setting your EQ - it's usually bad to boost lows since these require tons of power to reproduce. Remember, if you ask you amplifier to boost by even 3dB (a small increase - most knobs can do 12dB of boost/cut), you're asking it to double the power to reproduce those frequencies. Boosting 3dB at your bass, 3dB on a pedal, and 3dB on your amplifier at some really low frequency is asking for 9dB of boost, which is 8 times the power. These things add up!

Hopefully this helps out a bit.

 

[billfitzmaurice]

Hi,

As I mentioned before, I am running an SVT4 Pro and an SVT 410hlf 500watt RMS cab @ 4 ohms with a sensitivity of 98dB......Does that mean that, say a Gallien Krueger RBH 410 @400watts @ 8ohms with a sensitivity of 103dB will give me MORE volume because of dB?

It would if all things were equal, and that sensitivity was measured at a frequency of consequence where electric bass is concerned, such as 100 Hz. Unfortunately neither Ampeg nor G-K reveal at what frequency those ratings were measured. About all you can assume with any certainty is that it was not 100 Hz.

 

[BarryPseudonym]

Cheers for all your replies, I'll probably go with that setup then. Bye bye bank balance.

Incidentally, I'm not worried about live volume as I'll be going through the PA at most/all gigs, it's more for rehearsing, recording and on-stage monitoring.

Oh, and Mcrelly- us Brits still use miles over Km, it's just the rest of Europe that have properly gone metric. Bit of useless info for you there.

 

[MarkMyWordsXx]

this always confuses me, and scares me cuz i have a 1200w avatar. im putting 350w into it. am i gunna damage it?

 

[BassIan]

this always confuses me, and scares me cuz i have a 1200w avatar. im putting 350w into it. am i gunna damage it?

No. Read my post. It doesn't care whether you put 1 watt into it or 5, or 350. Your Avater is rated, most likely, at 1200 watts peak, meaning 600 watts RMS. Even if you crank your amplifier to the ugliest point of clipping where it generates well over 350 watts, you still will not likely damage your cabinet UNLESS you cause overexcursion.

It's not like your Avater will explode the moment you plug your 350 watt amplifier into it.

There is no such thing as "underpowering". If there was, cabinets would be blowing everywhere because of sitting around with 0 watts driving them. It'd be like the movie Speed: If you go below 350 watts, the cab will explode.

There is nothing magical about speaker cabinets that makes them different than any other electrical device.

 

[No Profile]

There is no such thing as "underpowering". If there was, cabinets would be blowing everywhere because of sitting around with 0 watts driving them. It'd be like the movie Speed: If you go below 350 watts, the cab will explode.

funiest thing ive heard all week, but defo true.

 

[BarryPseudonym]

OK, I thought I'd get an answer from the horse's mouth as well, and it seems you were all correct about it being better to over- than under-power a cab. Thanks again for the help, and in case anyone's interested:

From: Ampeg Support [mailto:[email protected]]
Sent: 06 September 2006 23:08
To: Marc
Subject: Re: Ampeg Question

Hi Marc,

Not a stupid question at all. In fact a very good question!
In a nutshell, you always want to have MORE power in the head than what the cab will handle. Here's why......

It is far easier to blow a speaker by underpowering it than it is by overpowering it. When an amplifier is underpowered for the cab it's pushing, (ie: a 200 watt head into say a 400 watt cab) it will basically dump all of its power into that cab and the cab will still be looking for more power to run efficiently. Eventually that head is going to square-wave. This means its putting out as much as it can and now it's sending DC current to the speakers which is very bad. DC will easily blow a speaker. It's essentially power amp distortion. This is why there are limiters on some of our amps, to prevent this. Think of it like this. Would you rather have a V8 in a Volkswagon or a small 4 cylinder in a Cadillac? It's kinda the same premise.

Hope this helps, feel free to drop me a line anytime.....

Thanks for your support in Ampeg

Dino Monoxelos
Global Ampeg Product Specialist
LOUD Technologies Inc.
[email protected]
www.ampeg.com


> Hello,
>
> Sorry if this is a stupid question, but it's something that's been
> bugging me, and I don't want to spend a lot of money on good equipment
> if I'm just going to damage it.
>
> Basically, I'm buying a new rig- I'm sold on the SVT-3 PRO, and am
> just looking at what cab(s) to use with it. When I played the amp in
> my local music shop, it went through a BSE-410HLF and sounded tip-top.
> The thing is, the head is kicking out 450w, while the cab is only
> rated at 400 (both at 4ohms)...If I was to use this set-up would I not
> be risking damaging the speakers? I always figured that the cab
> should be rated well above the power the amp is putting out, but I've
> read in a few places where people say it's OK (even good) to have it
> the other way round. This doesn't make sense to me.
>
> Any help/guidance would be appreciated.
>
> Cheers,
> Marc
>
> P.S. If there is a definitive answer to this, maybe it'd be an idea
> to have some recommended head-cab configurations on the website FAQ
> page?

 

[12bass]

Sorry, but that response from Ampeg sounds incorrect, especially the part about the amp producing DC when clipping. That should never happen in a properly designed amplifier.

Short answer: It depends. The safety of your speakers depends on how hard you push the amp and whether or not your amp overdrives the speakers beyond their mechanical or thermal limits.

If you want a proper answer, do a search for previous posts on this topic from Mark Reccord, Bob Lee, and Richard Lindsey.

Here's a good start: http://www.talkbass.com/forum/showthread.php?t=243009

 

[BarryPseudonym]

Yeah- I'm still sceptical, but in any case, I think either a 400 or 500w cab with a 450w amp will be fine, so I'm not gonna lose sleep over it.

The weird thing is, if they're gonna give out false info, you'd think they'd do it in favour of me having to buy a more expensive cab...

 

[12bass]

I doubt that giving out false information is intentional.

The key to keeping your speakers safe isn't in matching specs. The best way is simply to listen for the signs of them being pushed too hard. If the amp starts clipping or the speakers are bottoming out, then back off on the volume. Also keep in mind that cutting the deep lows helps maximize clean volume.

 

[Kulcha]

so basically Im trying to build a rig. Got a speaker box (no big name company, Alumi-Pro) with a 800 watt busted speaker cone. Took the cone out and put a new 400 watt/4ohm Carvin 15 inch woofer in it. Got a nice Craigslist steal with a Carvin BX500 head, rated of course at 500 watts. Hooked them together nice, now its clipping when I play certain notes, especially around the 7th-12 frets. For some reason the woofer cant handle it and I get a warped metallic clipping sound . Contacted Carvin and got the whole spiel on how I must be doing something wrong BECAUSE OF COURSE THE 400 WATT WOOFER CAN HANDLE 800 WATTS....(hmmm). Plays good at low volumes....but if I crank some kHz on the low end (I play alot of reggae) the warped clipping sound occurs. Help?

 

[Bass_Pounder]

so basically Im trying to build a rig. Got a speaker box (no big name company, Alumi-Pro) with a 800 watt busted speaker cone. Took the cone out and put a new 400 watt/4ohm Carvin 15 inch woofer in it. Got a nice Craigslist steal with a Carvin BX500 head, rated of course at 500 watts. Hooked them together nice, now its clipping when I play certain notes, especially around the 7th-12 frets. For some reason the woofer cant handle it and I get a warped metallic clipping sound . Contacted Carvin and got the whole spiel on how I must be doing something wrong BECAUSE OF COURSE THE 400 WATT WOOFER CAN HANDLE 800 WATTS....(hmmm). Plays good at low volumes....but if I crank some kHz on the low end (I play alot of reggae) the warped clipping sound occurs. Help?

You just learned two valuable lessons......

1 - You CANNOT just throw any speaker into a cab because it is the "right size". There is science used in cabinet design, and the cabs interior dimensions and porting need to be done around the speaker being used.

2 - Wattage ratings on speakers are thermal limits. Real world results are about 1/2 the wattge rating depending on use of low end EQ.