Newbie on speaker/amp matching

[bitofagiggle]

Hey guys. So I've built myself a 1400W NJD system using 2 tops @ 300wrms and 2 subs @ 400wrms. My amp is an AH1800 which is 900w @4Ohms per side.

 

It's mainly vocals that run through the PA, so I never feel the need for any more bass, but was considering replacing the tops with something more powerful. For example, have 400w sub and 500w top so it's 900w load on a 900w channel.

 

But.. I've heard lots of different opinions about loadings.

 

Opinion 1: You should always have your tops slightly more powerful than the amp so you know you're never going to blow the speakers

 

Opinion 2: Your amp should be about 25% more powerful than the speakers so it's never running at full capacity, this will increase the life of it

 

Opinion 3: Your amp should be anything between 2 and 4 times more powerful than your speakers as then will draw more power in peaks than the amp can handle

 

 

Now... I'm gonna go ahead and guess none of these are bang on the nail and as a young 'wanna be' sound engineer I've had to pretty much learn everything I know by watching literally hundreds of youtube self teach videos and trial and error. I have no formal qualifications other than a level 3 diploma in Production Arts. (tech theatre)

 

I'm pretty sure I've got it fairly right so far, but I'm at the point now that I don't feel comfortable going my system any more until I have this very basic concept completely confirmed with a wax stamp on it in my head, so I've come to the pros!

 

Can you please bust some common myths about amp/speaker matching for me so I can start to plan safely building a larger system!

[pete10uk]

Hey guys. So I've built myself a 1400W NJD system using 2 tops @ 300wrms and 2 subs @ 400wrms. My amp is an AH1800 which is 900w @4Ohms per side.

 

It's mainly vocals that run through the PA, so I never feel the need for any more bass, but was considering replacing the tops with something more powerful. For example, have 400w sub and 500w top so it's 900w load on a 900w channel.

 

But.. I've heard lots of different opinions about loadings.

 

Opinion 1: You should always have your tops slightly more powerful than the amp so you know you're never going to blow the speakers

 

Opinion 2: Your amp should be about 25% more powerful than the speakers so it's never running at full capacity, this will increase the life of it

 

Opinion 3: Your amp should be anything between 2 and 4 times more powerful than your speakers as then will draw more power in peaks than the amp can handle

 

 

Now... I'm gonna go ahead and guess none of these are bang on the nail and as a young 'wanna be' sound engineer I've had to pretty much learn everything I know by watching literally hundreds of youtube self teach videos and trial and error. I have no formal qualifications other than a level 3 diploma in Production Arts. (tech theatre)

 

I'm pretty sure I've got it fairly right so far, but I'm at the point now that I don't feel comfortable going my system any more until I have this very basic concept completely confirmed with a wax stamp on it in my head, so I've come to the pros!

 

Can you please bust some common myths about amp/speaker matching for me so I can start to plan safely building a larger system!

 

As you say non of them are completely right as a lot of it is down to personal preference. option 2 and 3 are more to my liking but having said that I'm just listening to a set of speakers with an amp half the rated power of the speakers, I'm pushing it to full in order to test the concept before placing them in an install.

 

The theory is that over powering speakers rarely blows them, they tend to tell you that your pushing them too hard first, if you ignore the warning then thats when you blow them. If the amplifier is under rated what tends to happen is the system is pushed too much, until something is clipping and in effect the the square wave you are now sending to the speakers can rip them apart.

 

In terms of your system you don't mention exactly what your speakers are I.e 4 or 8 ohm but I would look at introducing a crossover and a second amp for either the tops or the subs. This gives you much more control over how hard you need to push the amps and speakers.

[TonyMitchell]

Before we moved completely over to d&b systems, I also sat somewhere between your "option 2" and "option 3".

 

Option 1 is a definite "no no". You wouldn't buy a car with an absolute maximum speed of 68mph, to ensure you never exceeded the speed limit.

 

 

[pete10uk]

Option 1 is a definite "no no". You wouldn't buy a car with an absolute maximum speed of 68mph, to ensure you never exceeded the speed limit.

 

Nice analogy, might use that one myself if I may.

[sam.spoons]

+1 to all above.

 

The received wisdom is to rate your amps at 1.5-2.0 times your speakers (as you say) though it's to give "headroom" for peaks rather than destroying the amps. Nothing is set in stone in this game though and if you use your ears you can probably employ pretty much any combination of speakers and amps without destroying either. A second amp (another AH1800 would do fine) teamed with an active crossover (Behr*&@er springs to mind) would probably be a better way to spend your cash. It's worth adding that your Audiohead AH1800 is rated it's full output into 4 ohms (and it's a fairly budget amp at £199), running it into a pair of 8 ohm loads would generate less stress on the amp so you'd expect better reliability that way.

[pete10uk]

If you bare in mind that the amp is rated at 900 watt @ 4 ohm, if your speakers are rated at 8 ohm you are in effect halving the amps power to 450 watts, making it perfect for the tops with 50% headroom.

[bitofagiggle]

This is really useful! Thanks guys!

 

So, I should be looking for about 150-200% power on my amp then. But does that mean I need to keep the gain setting on the amp 25-50% rolled off or will the amps 'full' power only be delivered in peaks even if turned right up?

 

So say I wanted to get another AH1800, then run the subs off one amp (550w into 400w per side) at 8Ohms and used the extra amp to run 4 tops (900w into 600W per side) at 4Ohms. Would that be a reasonable set up or have I not quite got the balance right? (obviously idealy the amp for the subs would be slightly more powerful but based on working with what I already have)

 

 

Thanks again for the help guys, glad to finally get this written in pen in my head rather than having a rough idea!

[Electrolytic]

amps always run a full power all the time.

 

those dials on the front are only input signal attenuators.

 

they're there to let you set up the right gain structure. master fader at nominal, then 'dial back' the attenuators until the appropriate dB SPL is achieved +plus some headroom.

 

if however there was a drive-rack pre power amp, use that to set the gain structure attenuation and password it out, run the amps 100%, so no one has the ability to mess with/crank your system / force more power out.

[Bobbsy]

I can't argue with most of the above. I'm in the "amp power rating at around 150% of stated speaker power handling camp" myself but I've seen well reasoned arguments for most of your three options.

 

However, a couple of comments:

 

First, although we know what you mean, it's not really correct to refer to "speaker power" unless it's a speaker with an inbuilt amp. It's power handling you're talking about.

 

Second, looking at the power handling isn't really a way to get the "more powerful" system you desire. There are huge variations in speaker sensitivity/efficiency. This is normally specified at the level (in dB(SPL) you get for a 1 watt input, measured at 1 metre range with a frequency for the measurement given. I've seen speakers with sensitivities ranging from around 85db @ 1W/1m up to about 110db @ 1W/1m. Clearly, the second speaker is going to be hugely louder than the first even if the power handling spec is the same.