Why Big Amplifiers

nheather

Distinguished Member
I'm trying to understand why general advice is to get as powerful an amplifier as possible.

Say my chosen speakers have a sensitivity of 87dB/W and a maximum SPL of 102 dB.

Now theory says that I need 1W to get 87dB (isn't that more than enough).

Given dB is a logarithmic scale I assume I have to double the power for every 3dB increase. So

87dB = 1W
90dB = 2W
93dB = 4W
96dB = 8W
99dB = 16W
102dB = 32W

So even I push the speakers to their maximum I only need 32W.

So why do I need 100W plus?

I can appreciate that bigger amps are often associated with better components (transformers etc).

But if I consider two amps which are neighbours in the range e.g. Denon 1906 and Denon 2106, build quality doesn't seem that different (given the internal pictures on the website) so the difference appears to be down to 80W vs 90W.

Specs would suggest that neither would break into a sweat driving the speakers to the full extent so why would I spend extra on the 2106?

I assume I am missing something important?

Cheers,

Nigel
 

Jules

Well-known Member
I think its more to do with an amps ability to deliver sufficent current which does requires a big beast. Watts don't mean much.
There are better experts than I on here, but I'll try to explain..........

The lower your speakers impedance the more current it draws.
Now whilst your speakers may be rated as 8 ohms, that rating will be at a specific frequency. At some frequencies the speakers impedance will be lower (perhaps very low) and draw loads more current from the amp.

A big amp will therefore drive your speakers with far more authority and control.
 

pragmatic

Well-known Member
Yep its not about loudness but control, even if you don't use the more power its there for the little times when it spikes too, i.e. a real bass note that lower powered amps would really strugle with.
 

nheather

Distinguished Member
I do understand that. I can appreciate the difference between a £300 amp and a £1000 amp.

What I'm not sure about is the difference between a £300 and a £400 amp from the same range.

For example, does the Denon 2106 offer more control than the 1906? It doesn't have that much more power (90W compared with 80W) and the build looks virtually identical given the pictures on the Denon web site.

Cheers,

Nigel
 

pragmatic

Well-known Member
It used to be the case that features and build quality aswell s internals would improve, so each model you went up had a clear advantage over the previous models, this doesn't seem to be the case so much anymore though. There is alot more to the build quality and the components than what you can see on a picture and the differences inside may be the biggest change, if these actualy make any difference to its perfromance is for the ear of the behonder to decide.
 

Knyght_byte

Well-known Member
also that 10 watt difference could be useful....its generally worse for the speakers lifecycle to underpower them......(altho obviously dont stupidly overpower them...lol)

so having that extra 10 watts could give you an extra bit of safety if your speakers are reasonably power hungry......as explained above, sometimes certain notes will draw more current for a very short period of time that could be well above what they generally draw, not having that power available means the speaker wont function so well and could even in worst case scenario cause damage....certainly over the long term....
 
K

koshatnik

Guest
What I'm not sure about is the difference between a £300 and a £400 amp from the same range.

For example, does the Denon 2106 offer more control than the 1906? It doesn't have that much more power (90W compared with 80W) and the build looks virtually identical given the pictures on the Denon web site.



The difference between the amps probably comes down to 2 main things; its ability to keep mains and source current 'clean' and the ability to take that signal and drive the speakers well. Amps that sound good are better at maintaining the integrity of the source signal and feeding it with clean mains power - hence no degradation in signal=better sound. It may be that the model at £300 isn't as good as the model priced at £400 at doing that, hence its cheaper. I've certainly noticed with some amp ranges that subtle differences in spec don't justify the price hike, but when it came to listening to them, it was clear that the price difference was down to sound quality rather than added features or added power.
 

nheather

Distinguished Member
Okay but what am I missing in my original post.

My calcs suggest that to acheive the maximum SPL requires 32W.

The specs for the amps are

1906: 80W into 8 ohm, 110W into 6 ohm
2106: 90W into 8 ohm, 125W into 6 ohm

The speakers in my example are Canton CD50s which have impedance of 4-8 ohm and power rating of 50W nominal, 100W music.

Looking at the Denon website, the differences appear to be

10W increase in power
different remote control (don't care)
more inputs (don't care)

the build quality from the pictures appears to be very similar.

Whilst I accept that 10W may be a useful increase, does it really come into play with these particular speakers?

Cheers,

Nigel
 

pragmatic

Well-known Member
Test them your self!

Going on the given availible volume is like compairing two cars on there max speed, they may both be able to get there but how fast, well and comftably should be better with the more expensive model.

Specs alone never tell the story with AV equipment, if you don't know this yet it will become evident over time, espeialy if you become a video/audiophile.
 

Knyght_byte

Well-known Member
nheather said:
Okay but what am I missing in my original post.

My calcs suggest that to acheive the maximum SPL requires 32W.

The specs for the amps are

1906: 80W into 8 ohm, 110W into 6 ohm
2106: 90W into 8 ohm, 125W into 6 ohm

The speakers in my example are Canton CD50s which have impedance of 4-8 ohm and power rating of 50W nominal, 100W music.

Looking at the Denon website, the differences appear to be

10W increase in power
different remote control (don't care)
more inputs (don't care)

the build quality from the pictures appears to be very similar.

Whilst I accept that 10W may be a useful increase, does it really come into play with these particular speakers?

Cheers,

Nigel
ok, so you dont care about the different remote, but another buyer might find that useful....

more inputs, again someone else might have a wider array of equipment to plug in so to them its a useful addition.....

i cant remember, are both the amps 7.1? or is the cheaper 6.1? this will also give a reason for price hike (ignore this comment if both 7.1...lol)


and as for the speakers you mention, not everyone uses those speakers, so again the 10 watt difference is relevant, my MA S6's are rated up to 120 watt, and at higher volume levels seem to demand a decent amount of power.......

so to you the difference isnt necessary, theres your answer, buy the cheaper amp.......to someone else the difference between the amps may be worth the money or even be necessary from the point of view of inputs...
 

davehk

Novice Member
the 87dB/W is at 1m away. Remember that the sound level drops with the inverse square of the distance - double the distance, 4 times (+6dB) the power for the same SPL is needed. I doubt you are sitting 1m from the speakers.

32W gives you 102dB at 1m. At 2m you need 128W at 4m you need 512W etc

More info here: http://www.octasound.com/pdf/bulletins/kdm_sound_solution.pdf
 

nheather

Distinguished Member
davehk

Thanks for the info - informative site.

Agree with everything you are saying but rather than try and maintain the SPL at distance, let's let it fall away

32W give 102dB at 1M

SPL falls away at 6dB each time the distance doubles. So

102dB at 1M
96dB at 2M
90dB at 4M

Now viewing distance is no more than 4M and 90dB at this distance is still pretty load and still only requires 32W (less than half the capability of the 1906).

Cheers,

Nigel
 

Welwynnick

Well-known Member
Manufacturers of AV amplifiers tend to exagerate power outputs to a much greater extent than with stereo or power amplifiers. For example, they will use figures for just one frequency, or for a high distortion level, or with some channels being undriven, or for a low impedance, or for short term signals rather than continuous. All these things conspire to give higher power figures, and the differences can be considerable. This means that you generally get less power than you would expect.

100 real watts per channel is enough for most people, and the diffeence between 90 and 100w is probably inaudible. Remember, sound quality is usually invcersely proportional to the number of buttons, knobs and lights!

Nick
 

Knightshade

Active Member
Forgeting the technical aspect for a moment.
87DB speakers aren't the most sensitive in the world. They will try to suck the amps power resevoirs dry on the lower frequencies. Not only will this sound bad it won't be doing your speakers any favours either. Also worth bearing in mind that at 16 ohms you'll probably only have about 10-20 watts if your lucky.
It's not just a case of the wattage. How good the power supply is will have a major effect. Listening at low volumes I doubt you'll notice the problems but start turning it up a bit and the music will start to fall apart. Not saying the dearer amp will be hugely better but I would expect some improvment.
As for the two Denons? At a guess I'd say a lot of the improvments would be to the power supply stage. The extra 10w output is incidental.
 

Ekko Star

Well-known Member
Knightshade said:
It's not just a case of the wattage. How good the power supply is will have a major effect. Listening at low volumes I doubt you'll notice the problems but start turning it up a bit and the music will start to fall apart. Not saying the dearer amp will be hugely better but I would expect some improvment.
As for the two Denons? At a guess I'd say a lot of the improvments would be to the power supply stage. The extra 10w output is incidental.
Yes Power supply is key. Low volumes you probably won't be able to tell the difference. Start cranking it up and the lower model will probably start to show tednacies of the sound becoming tinny, bright and distortion will set in far earlier on.

Both will go loud but I would expect the upper model will keep the integrity of the sound far better at higher levels. That is generally why you pay more for a better amp. You want it loud and crystal clear, not loud and distorted.

A top quality amp can go seriously loud but one thing you will notice is it reamins awesome throughout the volume scale. At top volumes the sound remains completely refined and very listenable. A lower quality amp becomes unbearable over extended listening when driven hard for long periods.

Secondly a better amp will draw out detail far better. Once again when the action gets loud most amps handle the crash bang wallop side of things. However, when it's going some, the better amps will still draw out all the detail consistently as well as all the other sounds as well.

Test both with the Cantons and hear the difference for yourself.
 

Reiner

Active Member
It is true that at normal levels only a few Watt are required but for an AV setup (and hifi to some extend) I would always get as much power as you can to provide for sufficient headroom / dynamics. It's just no fun if what should be a loud bang comes out as a 'puff' only. ;)

Manufacturers of AV amplifiers tend to exagerate power outputs to a much greater extent than with stereo or power amplifiers. For example, they will use figures for just one frequency, or for a high distortion level, or with some channels being undriven, or for a low impedance, or for short term signals rather than continuous. All these things conspire to give higher power figures, and the differences can be considerable. This means that you generally get less power than you would expect.
Also very true, unfortunately. And even the ratings are given under proper conditions 5x100 Watt for example doesn't equal 5x100 Watts simultaenously, especially budget AV amps may deliver 100 Watts to two channels only due to their weak power supplies (though technically every channel can handle 100 Watt, but just not at the same time).
However hardly any soundtrack requires such, so while it may not be that tragic you are somewhat cheated.
 

nheather

Distinguished Member
Test both with the Cantons and hear the difference for yourself.
That would be great if I could find a retailer who could do this.

However, I fear that I would have more chance buying a scratchcard, winning £10,000 and buying top of the range.

Cheers,

Nigel
 

pragmatic

Well-known Member
If you feel the extra £100 would be better spend else where, and there is no chance for you to demo then, get the cheaper one.

We have all given reasons why the bigger one may possibly be better, but the 10w may be all the difference and denon are charging over the odds. Or it could be that it has a totaly redesigned internels and the 10w extra is only a little bit to it, as it has high quality DACs and preamp section, and better capacitors and overall all change inside (althoguh the fore is probably a lot more likley).
 

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