Wattage on speakers and amplifiers? [Archive] - Audio & Video Forums


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11-21-2010, 08:35 AM
Hi everyone,

Just wondering.....If i had a set of speakers that had a range of say 130 - 150 watts, and an amplifier that produced 70 watts per channel, would it mean that my speakers would only ever run at a peak of 70 watts? So they don't get their full potential volume? Sorry if it is a stupid question but i'm kinda confused...

Thanks - Jack :)

11-21-2010, 09:15 AM
Hi everyone,

Just wondering.....If i had a set of speakers that had a range of say 130 - 150 watts, and an amplifier that produced 70 watts per channel, would it mean that my speakers would only ever run at a peak of 70 watts? So they don't get their full potential volume? Sorry if it is a stupid question but i'm kinda confused...

Thanks - Jack :)

It's more than confusing, it's really for the most part useless. Speakers can never have a too "low" wattage range, only a do not exceed top range. That being said your more likely to fry your speakers with an underpowered amp if you push it too hard because of driving the amp into clipping. A 1000w amp driving a speaker that is rated for 100w max is perfectly fine if you don't go crazy with the volume control. How loud your speakers can play is a function of how efficient they are, ie. SPL/Watt of input, and how much power they can take.

You should also try to match your speakers to the size room they will play in. A small "mini-monitor" might be driven past it's design specs and not fill a large room, but can sound excellent and reach a decent SPL in a smaller room.

Finally the difference between 70 watts and 150 watts is really not that much when it comes to SPL. Depending on the speaker it may be as little as just a couple dB of output. Also, your talking about using the speaker at it's very end of it's usable volume. Unless you intend to listen to music at rock concert levels your never going to reach that point.

11-21-2010, 11:34 AM
Good points. Some people get WAY too hung up on wattage ratings for speakers and trying to "match" an amplifier. There are two ways to damage a speaker: (with an amp - we're not getting into things like lighting on fire, feeding into wood chipper, etc) One is to exceed it's physical excursion capabilities, and the other is to exceed its thermal dissipation capabilities. On point one, it is possible to just crank them up past their design limits and cause audible distortion. As Geoffcin pointed out, however, most people actually do this by clipping an underpowered amp and sending square waves to the speakers. Frankly, if you care at all how our speakers sound you'll hear this happening and know to back off the volume. As far as thermal limits, the vast majority of speakers can handle quite a bit more than their rated wattage as long as you don't clip somewhere up the line since the material you play has much higher peaks than what the average level is. (and many woofers have excess thermal dissipation capacity anyway)

So, your 70w amplifier will put out its available wattage (at max volume) into any speaker, and the sensitivity of the speaker will determine how loud that is. If that loudness is more than the speaker can physically handle you'll get distortion. If that wattage is more than the drivers can dissipate thermally, you'll damage a voice coil. If the loudness you want is more than the amplifier can deliver you'll get distortion from the amp.

What does all that mean? It means that depending on how loud you want it those 130-150w rated speakers are probably fine anywhere between 50w and 300w. Just pay attention to the limits of your gear when you crank it.

11-21-2010, 02:02 PM
Long time ago I stopped to look at the speakers wattage! Even on some receivers too!

You can have a Marantz 30W per channel that will blow 150W speakers.

12-10-2010, 10:14 AM
I agree with the others. One thing to keep in mind is the clarity of the sugnal you are feeding your speakers. The old addage is true "garbage in... garbage out." Don't get too hung up on how loud a speaker will play, or how much an amp can push. In the final analysis you will damane one or both of them. Be best speakers and amps I have ever heard carry full range at lower volumes. I would be asking questions like " do the speakers hiss at lower volume levels and what is causing it?" Does the amp hum? Are there things in the circuit that produce noise in the output signal? Are my power lines and interconnect cables too close together? If your objective is to listen to your music / movier really loud, may I suggest Peavey or Cerwin Vega products. Not the cleanest things out there, but they are designed to be played loud.

12-13-2010, 10:04 AM
Watts does not equal volume level. SPL is volume expressed in decibels (dB). In general the numbers on speakers mean little because there numerous factors involved and the standard measurements factor in "most" but not all speakers and somewhat unfairly treat certain designs - corner loaded and dipole speakers for a start.

What you want to look at in a speaker if "loud" is you're thing is the sensitivity of the speaker and the maximum continuous watts (not peak) that the speaker is capable of producing (and it would be nice to have that number without "dynamic compression"

I'll give you an idea of my two speakers. My main speakers are 93db sensitive at 1 watt/meter. This means that at 1 watt of amplifier power at a distance of 1 meter from the speakers I should get 93dB. This is considered loud. Now we listen at 2-4 meters away typically from a speaker so in our listening chair we are not going to get 93db - we may get 82-90db depending on several factors. But keeping it simple we'll keep apples to apples and use the 1 meter distance.

The things to remember about volume is that a 3db difference doesn't mean much. You will barely notice it. However to get the 3db gain will require "double" the watts. When you go up 10db it is considered a doubling of the "perceived" volume level. So 90db is twice as loud as 80db with 1 watt.

So my 93dB speaker at 1 watt will give me 93db @ 1 meter
to get 96dB I will need 2 watts
to get 99dB I will need 4 watts
to get 102dB I will need 8 watts
to get 105dB I will need 16 watts
to get 108dB I will need 32 Watts

Now my main speaker has a maximum SPL of 108db without compression which is deafeningly loud. My amplifier is about 10 watts so in theory the max volume I can get is about 103 dB. 85dB is more than I usually ever play. As you can see it would be utterly pointless to buy an amplifier with more than 32 watts since it will never be used. In fact 10 watts is more than enough for the above speaker unless I want to damage my hearing. In most sessions I would not even be using the full 1 watt.

My bigger floorstanders are 95db and can handle a continuous 175Watts.
1w =95dB
2w = 98dB
4 w= 101dB
8w= 104dB
16w = 107dB
32w =110dB
64w = 113dB
128w = 116dB
256w = 119dB

As you may notice the amplifier power is in most cases "overrated" and typically an easy sell for the mass market makers who like to say out amp is 70 watts versus the other guys' at 50 watts. But if you choose a high sensitive speaker which can also handle a lot of watts you will win the loudness war.

Compare for an example my speakers above to a typical 85db measuring speakers
1w = 85dB
2w =88dB
4w =91dB
8w= 93dB (this speaker needs to draw 8 watts to what my first speaker needs to draw with watt)
16w = 96dB
32W = 99dB
64w = 102dB
128w = 105dB (This speaker needs a whopping 128 watts of big amplifier power to get the same volume that my speaker will put out with 10 watts).
256w =108db (To get what my speakers will do with a less than 20 watt amp).

And if this were not bad enough most of the speakers out there can't handle 256 watts. Speakers have a max rating (often a peak max rating not a continuous rating) so it is far more likely to be 150 watts max or maybe 120 watts so even if you buy 500 watt amps if the speaker can't handle that power you are not getting the volume levels.

There are issues around impedance - as impedance halves the power demand of the speaker doubles. This is not generally provided in the product literature but certain frequencies - usually bass and sometimes treble the impedance will dip. Most speakers that claim 8ohms will be easy enough to drive but at certain frequencies the impedance will drop to say 4ohms and require twice the amplifier power. So it is possible that a speaker rated 95db 1 watt would need 2 watts in the bass frequencies. This is no problem at low volume but if I am playing very loud and pushing my system and suddenly there is a synthesizer playing a very low note and my amp is running at 10 watts it will want 20 watts to play the note properly - if the amp is only 10 watts then it will run into distortion because it simply can't produce the level required. Most amps though can handle a short demand of many times it's rated power. Further many tube amps when it does run into distortion is an innocuous kind of distortion that will simply soften the frequency extremes so the bass will be a little flabbier and the treble will be reduced in volume. Other kinds of amps will hard clip and sound very bad indeed.

So it very much helps to know the minimum impedance of your speaker. My main speaker's minimum is 5ohms and it is rated as a 6ohm speaker. At no frequency will my speaker request a doubling of the amplifier power so I can play loud without worrying. Also, if you have a 4ohm tap on your amplifier and your speakers are rated as 8ohms but you know it dips to 3ohms - you can run it from the 4 ohm tap and not worry about this issue either.

As an aside - speakers blow from distortion and that occurs with high power or medium power but rarely from very low powered amps. Most tweeters for example can handle 10 watts of distortion. You could conceivably run a 3 watt SET to full distortion and never blow a speaker - ever. It simply can't produce enough distorted power to blow a competently designed driver (however a 20 watt amp into high distortion could certainly blow a speaker). It would depend on the limits of the drivers in question of course. And full distortion is not great to listen to of course. If you hear distortion - turn it down.

So four: High sensitivity, High Power handling, gentle impedance (not dipping down to low or too high) and knowing where the speakers start to compress will equal a very loud very stable sound not requiring a lot of amplifier power. Horn speakers tend to offer this which is why virtually all night clubs use some sort of Horn loudspeaker or other high sensitive design. Typically the trade-offs for this high sensitivity is size, and bass depth. Speakers that keep the bass tend to be very large and the ones that also retain good sound quality (using quality drivers etc) will then be very expensive.