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Optimum amplifier wattage?

Orbitall

Standard Member
I have recently purchased some new 200W 8ohm floorstanding speakers. Can anyone help me find a cheap amp that will power these at optimum levels? Been looking at skytec range as these seem affordable with half decent spec! should i get-

2 x 300W Max @ 8ohm, so RMS is around 200W?
or is this overkill?
help?
 

pragmatic

Distinguished Member
More important is the efficiency of the speaker, if they are efficient then you'll be able to get away with anything if they aren't then you'll need more power.

The maximum power might be 300W @ 8ohm, but you shouldn't need anywhere near that to enjoy them beyond a comfortable volume.
 

Orbitall

Standard Member
Cheers for the info! I didnt want to under power my speakers n screw them up, ive heard bad things can happen! Im probs going to get the 300W and run it @ 25% so its comfortably powered!
 
M

Maxcherry2

Guest
Hi There,

An amps peak wattage output is mostly irrelevant. RMS wattage in more of an indication of what an amp will happily deliver. Also it is more important to have an amplifier with a power supply capable of supplying the actual amps for peak volume levels. Most speaker damage is caused by amplifies clipping rather then just not having enough wattage.

It is also true a more efficient speaker will produce more volume for any given wattage but that doesn’t mean they will sound better they are just easier to drive.

You also need to have 10 x the wattage to produce twice the volume in DB so in essence a 100watt amp is not twice as loud as a 50watt one.

Mind you I might be wrong :confused:
 

JojoBar

Active Member
10 x the wattage gives +10 dB when 2 x the wattage gives only + 3dB.
Then, in terms of "volume" increase perception, it depends on many factors, the first being the initial volume ...
 

Welwynnick

Distinguished Member
To be pedantic for a moment, there is no such thing as RMS wattage.
The term RMS is generally applied to voltage, not to power.
When you want to know how long something is, do you talk about it's centimetreage?
The appropriate expression is average power.

Nick :)
 
M

Maxcherry2

Guest
To be pedantic for a moment, there is no such thing as RMS wattage.
The term RMS is generally applied to voltage, not to power.
When you want to know how long something is, do you talk about it's centimetreage?
The appropriate expression is average power.

Nick :)

So then the average power is what you might say the Amp is happy to produce without getting into trouble? In other words peak wattge is just that but the amp can't run at this output but might reach it in short bursts.
 

Welwynnick

Distinguished Member
So then the average power is what you might say the Amp is happy to produce without getting into trouble? In other words peak wattge is just that but the amp can't run at this output but might reach it in short bursts.
There are lots of different ways of measuring power, but that's pretty much it.

Nick
 

Alan Mac

Well-known Member
So then the average power is what you might say the Amp is happy to produce without getting into trouble? In other words peak wattge is just that but the amp can't run at this output but might reach it in short bursts.

The average power (Pavg) is the amount of energy (ΔE) transferred from the amplifier to the loudspeaker during a given period of time (Δt).

Pavg = ΔE / Δt

For example:
If 300 joules (J) of energy is transferred in 10 minutes (600 s) then the average power is:

300 J / 600 s

= 0.5 J/s

= 0.5 W


The instantaneous power (P) at time T is the limiting value of the average power as the time period Δt approaches zero.

P(t) = dE / dt

In terms of the voltage applied across the loudspeaker V(t) and the current through the loudspeaker I(t):

P(t) = V(t) x I(t)


The peak power is the maximum value of the instantaneous power.


Alan
 

Normal Bias

Active Member
I think this thread has wandered a bit off topic. To answer the OP's question as best I can:

I agree with the posts so far that you need to look at the average power, and I would choose an amp that can provide what the speaker manufacturer recommends, but to some extent the (average) power of the amp you choose might depend on how you use your speakers.

Someone please correct me if I'm wrong, but this is how I look at it:

The source signal/wave represents how the microphone diaphragm moved when the recording was originally mastered, and as such describes how the cones of your speakers should also move. The Y axis corresponds to the potential difference (voltage) that the amplifier applies to its outputs in an attempt to put the cone where it should be. I like the term potential (difference), it implies there is something to be exploited, rather than a guarantee of the outcome. Now think of the power of the amp as the current it is able to provide at a particular voltage - the degree to which it can guarantee that voltage - in order to get the cone to where it should be - the force as it were, to get the cone moving. Bear in mind a moving coil in a magnet generates resistant force (back EMF) as well as the cone mass inertia and the elastic properties of the cone suspension (did I say off topic? Lol) but on the whole, the greater the force (current) the more closely the cone position will follow the signal. For this reason, upping the power and available current of the amplifier will improve the accuracy (sound quality) of any speaker, which may be particularly noticeable at lower listening volumes, where some much needed force/authority to move the cone may have been lacking. But one can only raise the available current so much before increases cease to have any effect. The speaker is a resistance (a load) which will only draw so much current from the amp (which is why you can play 50w speakers with a 1000w amp at low volumes) but as the volume and hence voltage rises, the power (current x voltage) rises and the ability of the coil to dissipate heat may start to lag behind the heat being generated. This will give distortion and may damage the driver. Also the cone can be driven beyond its limits which will also damage the driver.

So to simplify, an over-specified amp (average power compared with the power rating of the speakers) will give you more accuracy up to the limits of your speakers but you could damage them thermally or physically by turning the volume up too high.

Just to complicate matters, an underpowered amp can also (is probably more likely to?) damage your speakers if it clips and sends nasty discontinuous voltages to your speakers.

That's my take, I look forward to correction from the gurus :)
 

Alan Mac

Well-known Member
So to simplify, an over-specified amp (average power compared with the power rating of the speakers) will give you more accuracy up to the limits of your speakers but you could damage them thermally or physically by turning the volume up too high.

No, a higher-power rated amplifier gives no more accuracy than a lower powered amplifier, provided they are both working within their linear region of operation.

In fact, as a higher power amplifier normally has more voltage gain than a low power amplifier it will have an inferior signal to noise ratio, which could be viewed as being (slightly) less accurate.

Any “control over the loudspeaker cone” is determined by the output impedance of the amplifier (the lower the impedance the better) though the effect is fairly limited. However low power amplifiers can (and do) have just as low output impedances as high power amplifiers.


Alan
 

lbstyling

Active Member
conventional crossovers largely soak up the controling effect of output imp leaving little effect on the cone.
this effect is mainly the result of amplifier feedback and not power stages or the sise of them- meaning as alan says that the power of the amp gives no indication of its effectiveness.
This is largely why NFB amps work well with HES speakers- they dont require the damping factor because they center to rest position entirely by the spider/suspention mechanism.

other than that im impressed this kind of knowledge is on the forum these days.- good stuff!

pd is used in electical/electronic terms mainly because 3 phase (and earthing) require the distinction between power sources that are at different phase positions and also due to the use of 'floating earth' points (like in a car) where the power is say 14.4v above the car chassis, and in turn the chassis is a certain value above the actual ground (this is why you can get a shock when you get out of a car- connecting the PD between the car and ground)
 
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IWC Dopplel

Distinguished Member
It's probably a better question to as which amps would potentially work well with a certain speaker.

If you have a pair of Apogee's (very low impedance and low sensitivity) or a pair of Audio Note E's (high efficiency easy load) the choice of amp will be very, very different.

However most AV is typically more straightforward. I would not only look at quoted power but also measured power, many if not most quoted figures fall short for multichannel amps (especially receivers).

Without knowing I would look at 100w per channel plus, unless you are running monoblocks with very big power supplies :smashin:
 

lbstyling

Active Member
11w rms is fine if the peak value was 200w.

for stereo use, you can get away with comparitively little power, but for modern surround the dynamics reach 20db+ above average level constantly, in which case you will likely clip a 11w amp often.

a TRUE 95db/1w speaker will probably be happy on this amount of power in a typical living room.- if thats what you have- then your sorted.
 

cy1984

Standard Member
Looking at amps for big, classical music. What published specs give me the "headroom", "dynamic power", in other words, how do I read specs to determine AMPs vs WATTs in terms of power, speaker matching, richness at lower volumes, etc.? What are the relative measures I see published for Dynamic Headroom in db's? Can someone point me to a primer on the subject?
 

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