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How much power do you need?

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#1
Sorry to create a few threads in this forum over the past month as I agonize over what amp to buy.

Current choices are
  • Hypex 100 wpc @ $500
  • Purifi 200 wpc @ $1k
I saw a reddit thread today regarding VU METERS and in it someone speculated that they aren't popular anymore because most people listen at very low volumes and very small percentages of what their amps have to offer. Essentially, It makes one feel kinda like a their big bad amp is a bad investment when most of the time their VU meter is barely tickling.

Besides listening at VERY LOUD, noise complaint volumes, is there a reason to have an amp that can push speakers to the max?

Picture of current setup with jbl l80t (150w rms) and my SMSL sa-36a with it's "honest" 15 wpc for your judgment. This setup still gets loud enough to annoy the person I share a wall with.
IMG_7334.jpeg
 
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#2
AFAIK, power needs ultimately come down to choice of speakers (higher sensitivity = less power needed, and vice-versa), as well as how loud one wishes to listen (i.e - you want lots of power to listen to less efficient speakers at high volumes, but you don't need much at all to drive efficient horn speakers to ear bleeding levels).

Although I'm of the opinion that it's better to have a bit more power than not quite enough (you don't want to amp to clip if you decide to push it), big power is overkill for the vast majority of low to moderate listening level situations. Those JBLs are fairly sensitive, and tbh, 15WPC is probably just fine if you're not playing them loud.
 
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#3
Actually I also try to understand how much power do I need.
I have KEF R3 (87 dB sensitivity) with Denon x3500h and judging by Amir measurements the amp inside is quite good for stereo.
But KEF says 25 - 150 W and there's a lot of different talk around internet how they sound completely different with more power.

Is there any way to estimate if there's enough power without blindly trying different amps ? THe room is 20 sq. m. and I listen below reference volume and hear no distortion.

Maybe there's something I can read about it to get a better feeling of the subject ?

My current understanding is that most power goes to drive the low-frequency driver, so with lower power amplifier there could be not enough bass.
 

NTK

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#4
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J
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Thread Starter #5
Thank you NTK, that document is indeed useful.
1616960241309.png

1616960320336.png


It's amazing to me just how LITTLE power is required for every day listening.

Using https://www.crownaudio.com/en/tools/calculators I'm showing that my setup requires only 10w to stay under the 85db threshold for long term hearing damage.

1616960418645.png

On the other hand, it's also crazy how quickly power levels increase. 3kw at 110db aka "rock concernt / full orchestra (must be drums)

1616960632979.png


That all be said, this doesn't really answer my question. 10w at 85db... but 85db of bass is a different power level than 85db of treble right? So if I wanted to be accurate, I would need to know how much power I needed drive my woofers to the db I wanted.
1616960765751.png


Anyways, at this pointed I'm leaning toward the extra power of the Purifi.
 

abdo123

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#6
An amplifier does not offer the same (max) power at 20 Hz that it delivers at 1KHz.

If you would like to see an example, go and check the Aiyima A07 amplifier review. Amir shows how much Wattage the amplifier can produce at different frequencies. He further explains why this happens on the review’s YouTube video.

One more thing that could alter that number is the fact that a lot of manufactures rate the sensitivity of their speakers at where it is peaking on a Frequency response curve. This is shady business as it means that the speaker doesn’t have a flat anechoic response to begin with.

So while they advertise their speakers to be efficient, it can actually be quite poor in the bass.
 

restorer-john

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#7
An amplifier does not offer the same (max) power at 20 Hz that it delivers at 1KHz.
An amplifier should deliver a flat power response vs frequency or it is a faulty design. Just because a whole bunch of cheap and nasty class Ds cannot do that, in no way normalizes their poor power bandwidth.

The fact that a lot of amplifiers sold these days don't even specify a power bandwidth, is just disgusting if you ask me.
 

abdo123

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#8
An amplifier should deliver a flat power response vs frequency or it is a faulty design. Just because a whole bunch of cheap and nasty class Ds cannot do that, in no way normalizes their poor power bandwidth.

The fact that a lot of amplifiers sold these days don't even specify a power bandwidth, is just disgusting if you ask me.
oh usually the gain structure is very flat / consistent across the entire range, I'm only talking about peak power output.
 

MrPeabody

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#9
... But KEF says 25 - 150 W and there's a lot of different talk around internet how they sound completely different with more power.
It is best to ignore that kind of talk.

Is there any way to estimate if there's enough power without blindly trying different amps ? THe room is 20 sq. m. and I listen below reference volume and hear no distortion.
There are a lot of factors that influence the amount of power you need in an amplifier. When the integrated effect of the various factors is taken into account, it is reasonable to expect that the appropriate amount of power for different users will vary by, oh, let's just say 10 dB. This corresponds to an ordinary ratio of 10:1. That is, given a 50 watt amplifier, another amplifier that is more powerful by 10 dB will be a 500 watt amplifier. This is a pretty large difference in amplifier power, and yet the 10 dB number that I picked out of the air really should be bigger, because 10 dB is not even enough to compensate for the different listening volume levels that different people prefer.

The summary statement on the question is that if you listen at a level where you don't hear any distortion, your amplifier is as powerful as you need for it to be. If the amplifier isn't as powerful as you need it to be, the way you would know this is by hearing distortion. (Or else if you turn the volume knob up all the way and it isn't as loud as you want it to be.)

...My current understanding is that most power goes to drive the low-frequency driver, so with lower power amplifier there could be not enough bass.
You are alluding to a notion that is popular but not correct. It is true that loud, deep bass requires a lot of power, and thus a lot of current. That much is true. Nevertheless, if you compare two different amplifiers with very different power ratings, the bass loudness will be the same for both if a few mundane conditions are met. These mundane conditions are that the overall or nominal volume level is matched for the two amplifiers (the same voltage gain), that both amplifiers are operating below the threshold of clipping, and that neither amplifier has entered a protection mode. These conditions are normally sufficient to insure that the bass loudness will be the same for both, but these conditions may not be necessary conditions, i.e., it may be that bass loudness will be the same for both even if one of the amplifiers is clipping or has entered protection mode.

(EDIT: I did the math wrong and had to correct it.)
 
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Beershaun

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#10
How can someone calculate if the amplifier they have can deliver sufficient voltage when needed, and sufficient amperage when needed? The typical statements I see is that a speaker requires a high current amplifier when in a low impedance state and a high voltage amplifier when in a higher impedance state. So how can someone test or confirm through documentation if their amp is capable of producing both the amperage and the current required for the range of their particular speaker? Power ratings by themselves seem insufficient to differentiate between the two.
 

Hiten

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#12
How can someone calculate if the amplifier they have can deliver sufficient voltage when needed, and sufficient amperage when needed? The typical statements I see is that a speaker requires a high current amplifier when in a low impedance state and a high voltage amplifier when in a higher impedance state. So how can someone test or confirm through documentation if their amp is capable of producing both the amperage and the current required for the range of their particular speaker? Power ratings by themselves seem insufficient to differentiate between the two.
This is a good test.
https://www.diyaudio.com/forums/multi-way/204857-test-voltage-power-speakers-125.html
It tells you how much power you need at your listening level.
Regards.
 

peng

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#13
How can someone calculate if the amplifier they have can deliver sufficient voltage when needed, and sufficient amperage when needed? The typical statements I see is that a speaker requires a high current amplifier when in a low impedance state and a high voltage amplifier when in a higher impedance state. So how can someone test or confirm through documentation if their amp is capable of producing both the amperage and the current required for the range of their particular speaker? Power ratings by themselves seem insufficient to differentiate between the two.
Unfortunately you cannot, because amps are typically just rated in WPC into 8 and 4 Ohms. The 4 Ohm rating, if given, would indicate the current capability and the 8 Ohm rating would indicate the voltage capability but only to an extent.

As I posted elsewhere, amps should have been rated more usefully by voltage and current, not power. For example, if an amp rated 100 W/150 W 8 Ohm/4 Ohm is rated instead:

Max. voltage: 28.3 V, Max. current: 5 A, then we can calculate the Max. power output = 28.3 X 5 = 141.3 W and it would be achieved if the load is a 5.65 Ohm resistor by simply using the power formula:

P = (V^2)/R, or (I^2)*R, or V*I

I am simplifying things a lot just to make it easy to follow. In the real world, loudspeakers are not resistors and amplifiers can be rated in many different ways such as continuous indefinitely (very few amps are rated that way), "continuous" to mean just tested with a continuous sine wave, or for a specific duration, short term rating, e.g. 20 ms, 200 ms, 2, 5, 10 minutes etc.... you get the idea. Manufacturers don't, or won't tell you all those things either.

Also note that loudspeakers are voltage sensitive device, the spl it produces is proportional to the input voltage, as long as the amplifier driving it is not current limited. So when we say the speaker takes 100 W, it actually may take/consume much less, as a good part of it would be dissipated in the amp's output stage, that's why the heatsinks and fans are there to keep the output devices from overheating.
 
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#15
Picture of current setup with jbl l80t (150w rms) and my SMSL sa-36a with it's "honest" 15 wpc for your judgment. This setup still gets loud enough to annoy the person I share a wall with. View attachment 120576
Wow, beauties. My first "hifi" speakers were the L100T's that looked exactly like yours. Sold them thinking the t3's would be better (nope), and then got the L7's (what a joke in cabinetry). Kicked myself for a long time. Had the 4312B monitors when J&R Music World blew them out decades ago before moving to Japan. I do miss the "furniture grade" L80T/L100T.
 

gags11

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#16
Here is my McIntosh MC462 driving KEF R11s. This is loud rock. Does look like we need lots of power for content like this. ...and these are relatively efficient speakers.

 

peng

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#17
Sorry to create a few threads in this forum over the past month as I agonize over what amp to buy.

Current choices are
  • Hypex 100 wpc @ $500
  • Purifi 200 wpc @ $1k
I saw a reddit thread today regarding VU METERS and in it someone speculated that they aren't popular anymore because most people listen at very low volumes and very small percentages of what their amps have to offer. Essentially, It makes one feel kinda like a their big bad amp is a bad investment when most of the time their VU meter is barely tickling.
I can related to that because I auditioned a pair of KEF blade a few years ago, powered by 2X Mc1.2kW monoblocks (might have been 1.25 kW, not sure now. The Watt-meters stay most of the time between a few watts to 10-15 W iirc, and peaking to about 120 W maximum occasionally. That's just going by memory. I was not totally surprised at the time but I took some pictures that captured the peaks, would post it if I could find it. It was a large demo room and we were using classical and jazz music at reasonably loud level, I would guess higher than 80 dB on average from 4 meters.

In my own set up, I have a Marantz SM-7 powering a pair of 1028 Be and the watt-meters needles rarely hit more than the 25 W mark.

Besides listening at VERY LOUD, noise complaint volumes, is there a reason to have an amp that can push speakers to the max?
Probably not for practical reasons but it's nice to be able to push the speakers to their limit regardless even if that means you have to put on some hearing protection or step outside.:D It may be reasonable to get an amp that can get you reference level even if you can't even stand such high level, and then on top allow for an extra 3 dB and you should be covered, such that under no circumstances the amp would "clip".
 

eddantes

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#18
This is how I answered this question for myself (please correct me if I'm wrong):

The dynamic range in music varies greatly, but a rule of thumb I've seen is ~10LU with 1LU ~ 1.3db soooo - lets just say 12db of padding to be really safe.

I enjoy listening with average DB around 80-85... add to that the head room and it equals 92 - 97db.

Next we examine efficiency of the speakers - mine are 85db at 1W at 1m.

Next we figure out what it would take to get to 97db with my speakers (keeping in mind that we need double the power for every 3db) 88db = 2W, 91db = 4W, 94 = 8W, 97db = 16W ...... at 1 meter, but I don't listen at 1 meter...

So next we need to add the listening distance (wich I believe quadruples the power for double the distance) so at 2M = 64W and at 4M = 256W...

And all of that assumes into 8ohm speakers... (some amps produce 2x power into 4ohm speakers, and some AV receivers actually lose power into 4 ohm speakers).... yadayadayada

Annnnnyyyways - you can see by the quick calculation - to be confident of not having clipping - it's not unreasonable to have a 200W amp or bigger.
 

AdamG247

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#19
I have read the on average music has transient peaks that are 6 to 25 dB above the average level. To me this directly suggests that you may need up to 25 db of headroom. Of course this is dependent on the type of music and the depth of the dynamic range of the specific source recording.
 

RayDunzl

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#20
I have read the on average music has transient peaks that are 6 to 25 dB above the average level.
I use 20dB fudge factor.

If the tunes average 75dBLeq the peaks will push 95dBSPL - both unweighted.

More loud = more voltage = more current, and the "power" number goes up much faster than either of those since it can be calculated as the product (multiplication) of the voltage and current.

Simplistic Example:

1617666274066.png
 
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