speaker power rating
Mar 29, 2016 at 1:55 AM Thread Starter Post #1 of 6
goodsguys

goodsguys

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Hi and thanks for reading this post
 
I've been offered a pair of speakers which are rated at 300 watts rms each.
Unfortunatly I've been advised not to buy them, as i listen to music at a lowish volume, usually 20-30 watts per channel and was told at that volume the speakers would not sound good, that these speakers probably have a big voice coil that needs a lot of watts to warm it up.
 
What do you think, is this true, i thought a higher wattage rating just meant the speaker could handle more power.
 
Many thanks.
 
Mar 29, 2016 at 10:34 AM Post #2 of 6
 

Quote:
Originally Posted by goodsguys /img/forum/go_quote.gif
 
i thought a higher wattage rating just meant the speaker could handle more power.
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It is, on top of something else: sensitivity (and efficiency). Either it can handle a lot or in some cases, it might also need a lot more than other speakers, which is why you need to look at the sensitivity rating. At the same time there are speakers with low sensitivity but wouldn't be able to handle a lot of power, ie, usually cheaper designs.
 
Basically think of high power handling capability and sensitivity in an automotive sense. The chassis and drivetrain if designed or prepped properly for racing will be able to handle a lot of power, but if it was made for racing (and assuming you don't stuff it with a lot of unnecessary stuff) then technically speaking it also wouldn't need a lot of power to go fast (it's just a question of what the power to weight ratio of your competitors is). Think of something like a Lotus Elise for example - the initial version of the car used a 140hp Toyota engine, then they came up with the 7800rpm version with the TRD engine, and it can hit 60mph at around the same amount of time as a V12 Aston Martin of the era (and go around the corners a lot better); the chassis was so good that, while it can't take a larger engine, some people who don't need to comply with racing rules that even the playing field to focus on settings and driver skill have added a supercharger to get more power out of that TRD engine. By contrast, a chassis and drivetrain that can take a lot of power but along with the body actually needs a lot of power is more like a Bentley - the chassis might be able to handle more torque than a small truck, and the engine also produces as much power as an Aston Martin, but on anything but a very long straight the Lotus Elise will run circles around it because you have a heavy-arse car body that is basically a Rolls Royce focused on sportier driving than sitting in the back with an independent suspension in the champagne glass holder (no seriously Rolls Royce cars can go through a gravel road and not spill the champagne).
 
Quote:
Originally Posted by goodsguys /img/forum/go_quote.gif
 
I've been offered a pair of speakers which are rated at 300 watts rms each.
Unfortunatly I've been advised not to buy them, as i listen to music at a lowish volume, usually 20-30 watts per channel and was told at that volume the speakers would not sound good, that these speakers probably have a big voice coil that needs a lot of watts to warm it up.
Click to expand...

 
It will depend on the sensitivity as well as the amplifier's performance. It's entirely possible to use up 50watts and still end up listening well below 90dB if the sensitivity is low enough, but the question is what amplifier are you using. If the amplifier you plan on driving the speakers with can get those speakers to 87dB and producing the power required to do so doesn't pile on the THD or make the amp run out of headroom for peaks, then it's not a problem. If your amplifier is rated for example 30watts with 0.1% distortion, then chances are good you'll be at 1% THD at 50watts, and probably out of headroom also.
 
Basically it's alright to use low sensitivity speakers as long as your amp can still give it clean power. Of course, the only reason worth it for doing this is if the speakers in question are very large speakers that can go deep into the bass region and extend into the treble with a relatively smooth response, in which case, you get a more fullrange response at lower volumes. In such a scenario if such a speaker can hit a low listening level of 87watts with an amplifier that won't struggle at that level, and you only listen at that level max, then there's no need to get a more powerful amplifier.
 
Of course the noise floor is also a consideration, and personally what I would prefer is a very large speaker that extends past 40hz before it hits its -3dB point, in a very quiet room, which allows the amplifier to operate with very low THD (and in the case of Class A/B amplifiers, you might not get it to switch over to Class B, so you're basically running a Class A amplifier) but I can hear close to a full spectrum (in case what I'm listening to actually has any sound down there). It might be easier to do this with a higher sensitivity speaker, but doesn't mean it's impossible to do on a low sensitivity speaker.
 
Mar 30, 2016 at 12:38 AM Post #3 of 6
Hi Protege Maniac, good to speak to you again.
 
These are the specs for the bass-midrange unit, couldn't find specs for the tweeters:
 
Nominal power 300 W
Sensitivity (2.83V/m) 86.5 dB
Cone  Surround Rubber
Nom. impedance 4 ohm
DC resistance 3.4 ohm
VC diameter 50 mm
VC height 25 mm
Former Aluminum
Layers 2
Wire Copper
inductance 1.13 mH
Xmax 8.5 mm
Magnet (12 units) 15x45 mm
Magnet weight 1.3 kg
Flux density 0.85 T
Gap height 8 mm
Net weight 4 kg
The cabinet volume is 0.75 cubic feet
 
Hope that means something.
 
You lost me a little in your reply, fortunatly your grasp of the subject goes way beyond mine
 
I usually only go up to 20 watts per channel, but today i went up to 50 watts, 100 watts in total, and the sound was uncomfortably loud, no way could i listen to it this loud on a regular basis, but i did not notice an increase in distortion, so do not feel the amp is struggling
 
Mar 30, 2016 at 8:53 AM Post #4 of 6
Quote:
Originally Posted by goodsguys /img/forum/go_quote.gif
 
These are the specs for the bass-midrange unit, couldn't find specs for the tweeters:
 
Nominal power 300 W
Sensitivity (2.83V/m) 86.5 dB
Cone  Surround Rubber
Click to expand...

 
These are the most relevant specs. You mgiht not have anything on the tweeter, but chances are the passive crossover is designed to attenuate its output anyway to match the midwoofer, so in all likelihood this is the one for the entire speaker. Still, what speaker is it anyway? It will be more telling if you can get the spec sheet for the overall speaker.
 
In any case the way it says "nominal power" likely means that the maximum continuous power it can take is up to 300watts, while the sensitivity at 2.83volts (forgot the math on how to convert that to watts at 4ohms, last I had to think of that was way back in HS senior year physics) is 86.5dB. Basically, for 2.83volts of output, you get that loud with it. Chances are that if that is roughly 1watt then you only need roughly 20watts to get it to 89dB - that's already loud enough to get your neighbors angry with you depending on how your walls leak sound, and that assumes a detached house, not an apartment.
 
Put another way, ignore the "nominal power - 300w" spec and just look at the sensitivity, where 30watts can blow your eardrums off. Of course, note that the sensitivity for the overall speaker as well as the impedance might be a little different depending on the crossover design, which again is why I'd rather look at the overall speaker specs, not the specs for each driver.
 
Quote:
Originally Posted by goodsguys /img/forum/go_quote.gif
 
I usually only go up to 20 watts per channel, but today i went up to 50 watts, 100 watts in total, and the sound was uncomfortably loud, no way could i listen to it this loud on a regular basis, but i did not notice an increase in distortion, so do not feel the amp is struggling
Click to expand...

 
How do you know how much power your amp is kicking out? What equipment are you using? It mght not be that accurate, and depending on what it is, you might be interpreting the data wrong.
 
That said, again, it doesn't really matter as much. If it's loud enough for your listening level then it doesn't matter that it's rated for 300watts, and likewise, if it's loud enough and you can't hear distortion, then chances are there might not be much to gain (or not much that would be audible to you) by using a more expensive amplifier. It might in some cases have better channel separation, current delivery, etc, but again it all still hinges more on how loud you listen more than how good the amp is. For example if you're in a highly isolated room then any decent amp will have decent channel separation and will never be near its audible distortion and noise levels anyway, which is why I emphasize on noise isolation more than power - think of how a CIEM with a decent though low power player can in some cases sound better than a giant headphone rig, where the latter is still dealing with non-distinct but otherwise audible noise floor.
 
Apr 2, 2016 at 6:20 PM Post #6 of 6
The 300W rating you refer to is the maximum input power that the speaker can handle without damage. The specs for the driver don't mean much without the the tweeter, cabinet and crossover taken into account. You say you listen at 20-30 watts. How do you know? Volume pots are NOT linear.
 
Low-ish volume for most people in an average sized room is about 60dB to 65dB with peaks of 80dB. Average sensitivity for most speakers is between 85 and 90 dB measured one meter away with one watt of power at 1000Hz. Another important measurement is impedance referred to as efficiency. Impedance is frequency dependent. Impedance can be as low as .5 ohm even though the speaker's nominal impedance is 4 or 8 ohms.
 
The closer minimum impedance is to the nominal the more efficient, therefore the easier the speaker is to drive. 
 
A speaker that is both sensitive and efficient only needs a few watts to get to high sound pressure levels.
 
What is the brand and model of the speaker?
 
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