How many watts do you need?

poldo

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Dec 23, 2009
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Hi,

I had a discussion on another forum.

I own the Audiovector S3 Signature with the Moon i1 amp + cd player. Many people were saying I need an amp with more watts. Because the Moon only offers 50 watt per channel.

My speakers have 91 dB sensitivity so I think quality is better then quantity. The Moon is a very high quality amp and in Holland it is cheaper then Naim XS and Cyrus 8v2 and performance is in the same league.

Do I need a bigger amp for my speakers?
 

CnoEvil

New member
Aug 21, 2009
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It depends on the current that the amp can produce. If it can keep doubling the Watts as the Ohms of the speaker halve, then you can get away with a 25 to 35W amp.
 

chebby

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Jun 2, 2008
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poldo said:
Do I need a bigger amp for my speakers?

Depends on room size, distance from speakers, and your preferred level of volume when listening.

If you want concert levels in an open-plan barn conversion (and prefer to listen from 30 feet away) then I would plan to get a bigger amp. Whereas - for instance - I listen across the 15 foot width of our living room from about 8 - 9 feet distance and prefer volume levels that most would describe as 'moderate' or 'neighbour friendly'. (For a point of reference I used to have the volume control on my 50wpc Nait 5i at around 9 o'clock to 9:30 when feeding 89db speakers and a smidge higher with 87db sealed enclosure speakers.)
 
A

Anonymous

Guest
poldo said:
I had a discussion on another forum.

I own the Audiovector S3 Signature with the Moon i1 amp + cd player. Many people were saying I need an amp with more watts. Because the Moon only offers 50 watt per channel.

My speakers have 91 dB sensitivity so I think quality is better then quantity. The Moon is a very high quality amp and in Holland it is cheaper then Naim XS and Cyrus 8v2 and performance is in the same league.

Do I need a bigger amp for my speakers?

It all depends how much volume you want.

Sound level increases by 3dB every time you double the power. At 1W you have 91dB. 91dB is surprisingly loud, but you have 50 Watts, to estimate you just double to 2,4,8,16,32,64 Watts, which is 6 doublings so you get 91 + 3x6 = 109dB.

The maths to get the precise number for 50W is 91 + 3 x Log2(50) = 108dB.

NB: If you do not have the Log2 function then you can use Log(50)/Log(2).

BTW people usually listen to the First Watt and little else unless they want to go deaf fairly quickly.

http://www.hse.gov.uk/noise/
 

poldo

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Dec 23, 2009
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Thank you very much for the responses, I sit at 3 meters from the speakers, I usually listen at 9-10 o'clock on the Moon amp. At 11-12 o'clock it is extreme loud and I don't like the sound anymore, it is a bit harsh then.
 

matthewpiano

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Nov 23, 2007
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I personally think 45wpc or thereabouts is ample for many domestic situations. Certainly I've not had any problems with amps of that sort of rating. I don't listen at loud listening levels most of the time - about 8 o'clock most of the time, sometimes rising to 9 o'clock, but hardly ever any further. On amps of around 45wpc I've never had any issues with transients or dynamic peaks at these levels. I find excessively loud listening uncomfortable and not at all enjoyable, and I've often found that much more powerful amps struggle to convince at my lower listening levels (Yamaha A-S700 at 90wpc, A-S500 similar, Cambridge Audio 740A).
 

poldo

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Dec 23, 2009
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True, Primare had the same problem for me, at low volume the sound was not very involving.

The Moon dealer told me that the i1 has a very big power supply and it doubles the watts in 4 ohm to 100 watt.

Maybe I will try the Moon i3.3 against the i1 and if it makes difference i can upgrade.

cheers

rob
 

chebby

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Jun 2, 2008
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Globs said:
The maths to get the precise number for 50W is 91 + 3 x Log2(50) = 108dB.

Hmm. So my Marantz (I will call it 40 wpc rather than it's rated 50 wpc just to err on the 'conservative' side) will produce up to 105db peaks @ 1 metre* with my 89db 6 ohm speakers?

So if I listen at around 2.5 metres distance, is that about 97 - 98 db maximum? (That still seems scarily loud in an enclosed space.)

*Using your second method of 89 + [ 3 x Log(40)/Log(2) ] (No Log2 on my iPhone scientific calculator.)
 
A

Anonymous

Guest
chebby said:
Globs said:
The maths to get the precise number for 50W is 91 + 3 x Log2(50) = 108dB.

Hmm. So my Marantz (I will call it 40 wpc rather than it's rated 50 wpc just to err on the 'conservative' side) will produce up to 105db peaks @ 1 metre* with my 89db 6 ohm speakers?

So if I listen at around 2.5 metres distance, is that about 97 - 98 db maximum? (That still seems scarily loud in an enclosed space.)

*Using your second method of 89 + [ 3 x Log(40)/Log(2) ] (No Log2 on my iPhone scientific calculator.)

You'd just use your speakers sensetivity instead of the one he used. So 1 watt at 1 metre is 89dB, 2 watts is 92dB and so on...

90 something dB in a small room (think 4x4m) is very loud. My room is quite small at 2.5mx3.5m and I generally can't go above 87 or so dB without it being unbearable.
 

chebby

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Jun 2, 2008
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A pneumatic drill is supposed to be about 100 db at 1 metre. So 97 db would be about the same as a pneumatic drill at 2 metres!

I know a pneumatic drill is constant noise whereas we are talking about peaks (at least I hope we are) but even so, the idea of sounds approaching anything like that intensity - even if just for peaks - in an enclosed space would make me fear for my ears.
 
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Anonymous

Guest
If you use an AC voltmeter to measure your voltage into the speaker you can estimate how much power you use. Obviously a Fluke RMS meter would be best, but any meter will give an indication when set to the lowest V(ac) scale.

For many a 2W amp would be fine (in fact I built a 2W amp one and it was quite loud enough). My Usher amp is 100WPC and I swapped that out for my SE at an estimated 10WPC, and I still can't clip it on very loud thumping music or thundering crescendos.

Also bear in mind most manufacturers quote power at 1kHz, getting that same power from 20Hz to 20kHz is not always so possible. Additionally many people get sucked into thinking about a 'servo' amplifier with brute force current capability and many watts. This has the following issues: a) The First Watt (the watt you listen to most) is ignored, so most stuff you listen too is not handled well and b) By locking the amplifier onto the speaker you are also locking the speaker onto the amplifier, and the amplifier behaviour is then influenced by that speaker. To achieve a natural sound you have to have the speaker 'listen' to the amplifier, and the amplifier listen to the source. Mixing them all up together does the sound no favours. Another reason for easy to drive speakers..
 
T

the record spot

Guest
How many watts you need is very few, assuming the speaker doesn't require plenty of oomph. What's ideal, however and IMO, is plenty on tap. Like Matthewpiano earlier, I've had some success with lower powered amps but my experience differed as more powerful amps were simply better at playing music. They controlled the speakers but you get what you pay for. I'm not convinced by the AS 500 or the CA 740A as the speakers they're typically stuck with usually tend towards brightness (an annoying trend IMO). I'd like to see how they'd do with the likes of the recent Castle Knight 2s as a less shrill alternative.

The likes of Harman's HK980 amp or the HK3490 receiver might give more capability at budget level.

Having lived with low and highnpowered amps, the latter is the only way to go for me.
 

jaxwired

Well-known member
Feb 7, 2009
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In my experience there is no substitute for lots of power. I've read that most of the time our systems only use a few watts, but having listened extensively to mid powered integrateds (60 to 80 watts) and high powered amps (150 and up), the high powered amps sound more like real music. I'm sure there are exceptions and my experience is too limited to be sure this is always true, but personally I will stick with high power.
 
T

the record spot

Guest
That's it n a nutshell for me; the comment around music sounding more real. That's my experience with my current amp and likewise with some others of a similar mould.
 
A

Anonymous

Guest
poldo said:
Thank you very much for the responses, I sit at 3 meters from the speakers, I usually listen at 9-10 o'clock on the Moon amp. At 11-12 o'clock it is extreme loud and I don't like the sound anymore, it is a bit harsh then.

This sentence does sound like you are overdriving your amp. Ergo, a more powerful one will help I have used low powered amps to great effect, but only at modest volumes.
 

shooter

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May 4, 2008
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I've used this SPL calculator: http://myhometheater.homestead.com/splcalculator.html

My SPL at 12ft is 104.5db at listening position or 115.7 @ 3.3ft. :D

Plenty loud enough and my amp will drive my speakers well at loud volumes. Infact the speaker gives in before the amp does which is good news as there is no clipping occuring.

Underpowering your speakers can cause allsorts of issues including voice coils or tweeters going, when you push the amp to hard the available power from it at its peak just collapses, that is the distortion you hear. If you have plenty of power on tap this doeasnt happen, the sound is under control and you can control it too.

@ poldo. I'd say if its your amp clipping at 11-12 o'clock then i'd say yes your speakers arent getting the power thery need too operate at those levels, if you happy and all of your listening is low level then it should be fine.
 

eggontoast

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Feb 23, 2011
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Quite an interesting read.

But I would suggest that rather than use an rms multimeter to measure the voltage across your speaker terminal connect an oscilloscope instead. The dvm doesn't react fast enough, if you set the time base correctly on the scope you will be able to see the short bass transients eating up your 50 watt output very quickly.
 
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Anonymous

Guest
An oscilloscope will be far better - but more people have a meter ;)

An issue is also 'what is true power'? Most transistor amps have deep feedback loops inside that need headroom to work, so at max output power there isn't much room left for them to keep control.

Also there is the power bandwidth issue - how much power is available at 30Hz compare to 1kHz?

Then there is compression - look inside a modern amp and see the size of the power transformer, it's usually pretty small. You can have an amp that can deliver it's supply rail power with ease, and one that is straining at every point at the power rail level. They have the same power on paper, but one will sound far more powerful than the other.

Tube amps are a case in point, a 40Watt tube amp will sound far louder, with far better bass and far more dynamic than a 40Watt solid state amp, because it's generally going to have a 300VA power transformer rather than an 80 or 100VA one. My 10W(ish) SEP amp's transformer is about the size of a 60W solid state transformer.

The only time you'll need more power is with less efficient speakers - where the designer has traded bass response for efficiency. Take a typical 85dB/Watt speaker with a 50W amp - you get 102dB max (with 1kW you'd get 115dB). Compare that to a pro-audio 96dB/Watt speaker - you will get the same volume with 4W. That's FOUR Watts! To reach 115dB you'd need 80.6W - rather than 1kW. Speaker efficiency is king, your amp choice is a lot better and bigger with efficient speakers, which is one reason I like the big Tannoy dual concentrics etc!
 

nopiano

Well-known member
As a hugely sweeping statement, more is often better. Once you've heard the effortlessness of a big amp it is hard to resist, but 50 watts per channel is fine for reasonably sensitive speakers in the majority of domestic situations, especially if the amp is basically good (as the OP's is).

Whether the unpleasantness as the volume is increased is the beginning of clipping, the speakers compressing, or a room artefact (even acoustic feedback) I cannot tell from here!
 

Mooly

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Jun 10, 2011
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The meter method in my link works and gives a very conservative value if the method is followed correctly. It's knowing that from CD no transient can ever exceed the 0db level. Everything on a disc is below that level.

A 'scope will show transients in music but these again are all below the Odb point.

So with your favourite track blasting out (which must be from CD or a digital format that has an absolute limit on output) you know for certain that the maximum voltage across the speaker (including the transients in that music) must be at the 0db level or below.

We now leave the volume setting alone and play a 0db test tone at a frequency that all meters can handle. That will be in the 50 to 400hz range usually. The speakers are disconnected because this will be LOUD otherwise. The AC voltage is measured (which will be an RMS value on a normal DVM) and this corresponds to the highest voltage that the speaker can ever see at that volume control setting off CD. That value can be calculated to give an RMS value for wattage. And so at that particular volume setting you will NEVER need an amplifier capable of more powwr than the figure you have just calculated. Transients are withinn that value and the value is very conservative precisely because of that. You have calculated the power needed to maintain the transients in your "favourite track" that you used as a full power RMS level.

Hope that makes sense :)
 

tim92gts

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Sep 24, 2010
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Hi Poldo,

How much amplifier power do I need?

gives a pretty good estimate as a starting point.

i allow 25dB headroom and a typical listening level of 85dB.

It's interesting to put some figures in and see how much each variable affects

the power requirement.

If on a poor, compressed recording with minimal dynamic range you might only need

3dB headroom, but you won't like that recording.

Live classical needs plenty of power for correct reproduction, dance can be very peaky and any

large amount of percussion needs range to do the peaks.

i run 4 x 900W into a nominal 4 Ohms and it's about right (i.e. the amps very rarely clip).

You're amp might be up to the job, but if so you probably didn't need speakers with anything like that power handling capacity.
 

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