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How Much Power Do I Need ?

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All,

Just remember;

3 dB is a just noticeable increase in volume

10 dB is generally to be twice as loud.

Alanh

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Just a bit of a correction

0.25bd - 0.5dB is regarded as just noticable (theshold of being able to pass a blind test)

3dB is easily noticable

10dB is equivalent to twice as loud

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Drizt,

3 dB is for the general public who are not trained to detect differences. It also depends on whether it is measured on noise excluding headphones or with background sound, it also depends also on the nature of the sound under test ie tone music or speech.

All,

For those who don't know 10 dB is 10 times the power

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A 3db change in level represents the smallest significant change that can be heard by a person with normal hearing..

It is not the least audible change in sound level one might notice .

C.M

Edited by Tweet

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A good thread and would be very helpful to a lot of folks I'm sure.

But in regards to how much power is needed, I'm wondering how much do people allow for dynamic headroom/transient peaks on average. For live music some things I've read they say transient peaks can be as much as 25dB while recorded/compressed can still be upto as much as 10dB. Depending listening distance and speaker sensitivity this can start getting crazy in terms of power needs from a amp if you like reference levels or higher. Classical can have some pretty decent transients.

EG: myself I often tend to be a bit of a loud listener lol, though it depends on what I'm playing and my mood. While my room isn't large the listening distance is 5m-6m, my speakers are fairly sensitive but I tend to learn towards quite powerful amps because of my listening habbits and I don't like to overdrive a amp for obvious reasons. I tend to err on as much power as possible with the idea to work the amp as little as possible and using common sense to not just crank the volume to insane levels. Too little or too much power can be a issue either way.

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The dynamic range of an orchestra is very wide indeed, in the range of 70db to 100 db above ambient noise levels so you are never going to have sufficient power reserves to compete with that, let alone the amplifier and the loudspeakers to deliver it.

Most modern loudspeakers have an efficiency of about .1 to .2% at best unless one goes to horn loading, but then two of such monsters in your room may make it a little difficult for other amusements.

Most 'quality' amplifiers usually only boast a 2 - 3 db headroom over their rated power levels and at possibly elevated distortion levels too, so don't expect anything substantial in power reserves.

Remember your ears do not have a linear frequency response, and neither linear in dynamic range.

So, in the end one has to ask one's self this question ..." What is HiFi anyway ?"

C.M

Edited by Tweet

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The dynamic range of an orchestra is very wide indeed, in the range of 70db to 100 db above ambient noise levels so you are never going to have sufficient power reserves to compete with that, let alone the amplifier and the loudspeakers to deliver it.

Most modern loudspeakers have an efficiency of about 1 to 2% at best unless one goes to horn loading, but then two of such monsters in your room may make it a little difficult for other amusements.

Most 'quality' amplifiers usually only boast a 2 - 3 db headroom over their rated power levels and at possibly elevated distortion levels too, so don't expect anything substantial in power reserves.

Remember your ears do not have a linear frequency response, and neither linear in dynamic range.

So, in the end one has to ask one's self this question ..." What is HiFi anyway ?"

C.M

It seems to have as many meanings as there are enthusiasts.

Literally its quite difficult to acheive especially when dynamics and scale are required. Efficiency, power and power handling all add to the end result though

But for many it's a nice colored presentation which to them is nicer than even the original performance is all thats wanted. :) .

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A 3db change in level represents the smallest significant change that can be heard by a person with normal hearing..

It is not the least audible change in sound level one might notice .

C.M

I'm surprised re 3dB.

2dB is easily noticeable IMO. But I'm old.

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I'm surprised re 3dB.

2dB is easily noticeable IMO. But I'm old.

:D ...Well, I'm not a spring chicken either.

Yes, a 2 db change is quite noticeable but it is also dependent on the frequency one is listening to and the SPL being heard.

At 20Kc/s, a 20db change in level is irrelevant to almost everyone I would think, but at 4Kc/s where the ear is most sensitive a 0.5 db change may be noticeable to some, while a 1db change might be noticeable to almost every person with normal hearing.

Because the sensitivity of the ear varies in accord with frequency and the average SPL of the sound being heard, a 3 db change apparently represents the smallest significant change in level across most of the audible range for the average person.

How they actually arrived at that conclusion I do not know, but possibly it was through testing the hearing of multitudes of people, and of all ages.

It ties up with all kinds of audio equipment design so it must relate to the sensitivity of human hearing in general.

C.M

Edited by Tweet

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Great post, this answered a question I've had for a long time, but I have a few more: Is the SPL calculated, the theoretical volume at 0dB on the amp, assuming the source is mixed "properly", at reference, etc? And also, how does this relate to speaker power handling? I assume this calculation is purely the amp's possible SPL for a given speaker sensitivity. Obviously, if the speaker's rated power is less than the amp, the speaker will give right?

Yeah, sounds like the "should my speakers be rated higher or lower than the amp" question...

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Great post, this answered a question I've had for a long time, but I have a few more: Is the SPL calculated, the theoretical volume at 0dB on the amp, assuming the source is mixed "properly", at reference, etc? And also, how does this relate to speaker power handling? I assume this calculation is purely the amp's possible SPL for a given speaker sensitivity. Obviously, if the speaker's rated power is less than the amp, the speaker will give right?

Yeah, sounds like the "should my speakers be rated higher or lower than the amp" question...

SPL is calculated base on the real power output of the power amp and AVR, db value on an AVR does not reflect how much power you are pumping out to your speakers and if you are turning the volume tab way above 0db you may be sending serious level of distortion which may damage your speakers. I think you are safe to stay below 0db on your AVR. The calculation of spl is more about how loud you can go with speakers at certain sensitivity with certain amplifier. It is perfectly fine to have speakers with higher power handling figure matching up with a lower output amplifier or speakers with lower power handing figure driving by a more powerful amp.

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Thanks for that. There's no real hard and fast rules after all.

So is there any significance to the volume readout on the avr/amp? Or is that pretty arbitrary?

Eg, if the amp is rated at 125W per channel, it doesnt mean at 0db the output will be 125W per channel, all things being equal, right?

Edited by Sanguinicus

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Thanks for that. There's no real hard and fast rules after all.

So is there any significance to the volume readout on the avr/amp? Or is that pretty arbitrary?

Eg, if the amp is rated at 125W per channel, it doesnt mean at 0db the output will be 125W per channel, all things being equal, right?

No, it doesn't. The volume read out at 0db does not indicate the amp is pumping at full power. And also with most of AVRs they usually don't quote their power output figure across the whole audible spectrum across 5 or 7 channels. An AVR which specced by manufacturer at 100 watts may actually been pumping out about 30 watts a channel. So take manufacturer quoted power with a grain of salt specially when you see them quote a power figure at 1khz or single or two channel driven. Other misleading way of quoting power output are pmpo, peak musical power.

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So take manufacturer quoted power with a grain of salt specially when you see them quote a power figure at 1khz or single or two channel driven. Other misleading way of quoting power output are pmpo, peak musical power.

Yeah, problem I've got with the Denon 3313 is that It's got 20Hz-20kHz@8ohms per channel, 1kHz@6ohms per channel and maximum power output. I'm guessing that max power is peak-to-peak because it's about 1.7 times greater than the 1kHz rating, which looks like it's the RMS power.

I don't know which way is up :hmm:

Edited by Sanguinicus

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Yeah, problem I've got with the Denon 3313 is that It's got 20Hz-20kHz@8ohms per channel, 1kHz@6ohms per channel and maximum power output. I'm guessing that max power is peak-to-peak because it's about 1.7 times greater than the 1kHz rating, which looks like it's the RMS power.

I don't know which way is up :hmm:

Big pinch of salt with amp power ratings. Some manufacturers quote several power ratings and attempt to be honest :hyper: .

As an example I own a NAD T757 with the following numbers:

Stereo mode 110W into 8ohm within 0.08%THD.

IHF dynamic power into 8ohm 130W

IHF dynamic power into 4ohm 243W

All channels driven 7*60W

I now ignore published values and concentrate on the sound.

hornblower

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Ah gotcha.

What do you think of the 3313, btw?

You can get a rough estimate of the real power output by looking at the power consumption figure. For an AVR with class AB amplification you can estimate the real output by multiply power consumption figure by 0.7 (general efficiency of this type of amp) then divide by 7 (if it is 7.1 or 7.2 receiver. Take the exmaple of Denon 3313, the max power consumption is 670 W, so estimate power output is 67 watts per channel.

Edited by jliang70

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Yes ..... that's about the truth of it, of course if one invests a little more in loudspeakers that are much more sensitive than the typical 85db/watt/metre offerings, one can make proper use of the power available from one's AVR.

50 watts /channel is more than enough to drive high sensitivity speakers to ear shattering levels. The problem is that db's in sensitivity are easily lost in the dampening down of resonances in loudspeaker designs but are then hard to win back by the powerful magnet/voice coil combinations that drive them.

My complaint is not with the amplifier manufacturers themselves but rather with loudspeaker driver manufacturers producing highly damped drivers for use in small cabinets. This kills sensitivity, efficiency and dynamics and puts more strain on the amplifier to compensate.

The little speaker box on its pedestal in the corner for the sake of WAF just kills the life out of music and movie soundtracks, having no air to breath in internally.

Open Baffle designs, well designed, generally run rings around the boxed speaker for sensitivity and dynamics but they do need the space to breathe and are usually much larger too. Bass equalization is also easily applied electronically to balance the bass response. You will be surprised how good your amplifier actually is once you liberate your speakers from that overly damped sound we usually get from manufacturers.

Here's a good read if it is of interest to you.......

http://www.audioholics.com/loudspeaker-design/loudspeaker-drivers

C.M

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Hi all,

I was hoping someone could help me wrap my head around this concept a little better, especially with regards to amp wattage vs speaker wattage.

My speakers are rated to 150W @ 4 Ohms, with a sensitivity of 90dB / 2.83v / 1m.

My receiver has several supposed power ratings:

Maximum Effective Output Power (1kHz, 1ch driven) (JEITA): 175W x 7

Dynamic Power per Channel (8/6/4/2 ohms): 160/195/255/335 W

Min. RMS Power (8 ohms, 20Hz-20kHz) [THD]: 130W x 7 [0.04%]

So which figure should I be paying attention to when trying to determine how much actual power the amp can deliver to 2 channels at 4 Ohms?

Also I've been told before that you should try and have an amp that can deliver at least 1.5x the power your speakers are rated to, to allow for headroom etc. Seeing as my speakers are rated to 150W @ 4Ohms, does this mean I'd run into issues if using an amp which only delivers 40w (8 Ohms) per channel (like the Cyrus 6A, for example)? Would I be running the risk of damaging the amp, or only if I had it running at insane volumes?

Is there any easy way to figure out how 40w @ 8 Ohms translates into wattage at 4 Ohms?

Thanks!

Ben

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Hi all,

I was hoping someone could help me wrap my head around this concept a little better, especially with regards to amp wattage vs speaker wattage.

My speakers are rated to 150W @ 4 Ohms, with a sensitivity of 90dB / 2.83v / 1m.

My receiver has several supposed power ratings:

Maximum Effective Output Power (1kHz, 1ch driven) (JEITA): 175W x 7

Dynamic Power per Channel (8/6/4/2 ohms): 160/195/255/335 W

Min. RMS Power (8 ohms, 20Hz-20kHz) [THD]: 130W x 7 [0.04%]

So which figure should I be paying attention to when trying to determine how much actual power the amp can deliver to 2 channels at 4 Ohms?

Also I've been told before that you should try and have an amp that can deliver at least 1.5x the power your speakers are rated to, to allow for headroom etc. Seeing as my speakers are rated to 150W @ 4Ohms, does this mean I'd run into issues if using an amp which only delivers 40w (8 Ohms) per channel (like the Cyrus 6A, for example)? Would I be running the risk of damaging the amp, or only if I had it running at insane volumes?

Is there any easy way to figure out how 40w @ 8 Ohms translates into wattage at 4 Ohms?

Thanks!

Ben

Most receivers and speakers overstate the power they produce / can handle - at best these tend to be for transients of a fraction of a second and in the case of receivers only driving one or two channels. Jliang's comment below gives a better indication of calculating real power levels.

In the ideal world an amplifier would "double down" i.e. produce twice the watts if the impedance halves. In the real world, thermal constraints and design/cost compromises come in the way - how much depends on the particular amp. And before someone jumps in to say their amp doubles down, this usually means the nominal output for the higher impedance is understated.

A real 40W/channel with 90 dB sensitivity speakers should provide ample volume in a medium sized room. You can run the numbers in the link Al put in the first post in this thread.

You can get a rough estimate of the real power output by looking at the power consumption figure. For an AVR with class AB amplification you can estimate the real output by multiply power consumption figure by 0.7 (general efficiency of this type of amp) then divide by 7 (if it is 7.1 or 7.2 receiver. Take the exmaple of Denon 3313, the max power consumption is 670 W, so estimate power output is 67 watts per channel.

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Interesting. So if I'm getting this right then my receiver probably realistically only delivers ~125W per channel @ 8 Ohms and somewhere under 250W @ 8 Ohms.

And a 40w stereo amp with my speakers could probably still exceed 100dB at my listening position, which is plenty loud.

Thanks for the clarification!

Cheers,

Ben

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Do you need a power amp that has 1.5x the power handling of your speakers ? The answer is no, you don't. My speakers have power handling figure of 375 watts, the power amps I have are rated at 8 watts, 20 watts and 400 watts a channel. They all work fine with these speakers which has an impedance of 91 db/6ohm. Musically I prefer the 8 watts amp and it is more than enough to deliver a good audio experience. With the low power amp my volume dial on pre will not go beyond 75% of full power. You don't need to go for the most powerful amp you can afford, My suggestion for you is to listen to a few different amps with your speakers

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That's right, one might own a racing car of enormous power but there is generally little need to use that capability to go to the local shop, so it is with high power amplifiers and small rooms.

C.M

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