What’s up with watts?

[UncleJoe]

I’m struggling here. I’m trying to build a simple 2.1 or 2.2 system for a medium sized living room in an open floor plan. Before getting into all the specific preferences and requirements I have, I’m struggling to figure out how much power is necessary. (I know there is some mathematical formula involving desired db and speaker efficiency etc.) Looking at integrated amps, they all seem to have 70-100/ch. All the reviews I watch swear this is enough power to push nearly any speaker. Plenty of people will say 30 watts is enough. But when I look at powered speakers, they’ll have a 100 watt amp just for a tweeter. Per channel these speakers will have 400-700 watts. Can someone please explain this massive disparity? It seems odd that if a speaker only needs 50 watts that a company would add in tons of extra power for no reason. Thanks in advance.

 

[ahofer]

I’m not the right person to explain it, but certainly the dramatically lower price of compact, limited bandwidth, class D amplification is part of the picture, probably eliminating design trade offs active speaker designers had to make in the past.

 

[kemmler3D]

I’m struggling here. I’m trying to build a simple 2.1 or 2.2 system for a medium sized living room in an open floor plan. Before getting into all the specific preferences and requirements I have, I’m struggling to figure out how much power is necessary. (I know there is some mathematical formula involving desired db and speaker efficiency etc.) Looking at integrated amps, they all seem to have 70-100/ch. All the reviews I watch swear this is enough power to push nearly any speaker. Plenty of people will say 30 watts is enough. But when I look at powered speakers, they’ll have a 100 watt amp just for a tweeter. Per channel these speakers will have 400-700 watts. Can someone please explain this massive disparity? It seems odd that if a speaker only needs 50 watts that a company would add in tons of extra power for no reason. Thanks in advance.

For starters, depending on the manufacturer, you have to read the fine print when it comes to wattage ratings. Sometimes they're inflated quite a bit.

When it comes to active DSP speakers like the KEF LS60, there's a ton of wattage packed into the speaker for a few reasons.

1) Sealed design with extended bass via DSP is one of the most power-hungry designs
2) They're meant to go loud (ish)
3) They're meant to go deep

Other very good speakers don't have a ton of amplification built in. E.g. the Genelec 8030c, a professional-grade unit if there ever was one, only has 100w built in. It's a ported design, and my guess is they don't really need 50w for the tweeter but it was cheaper to buy a single 2-channel 100w amp than find a smaller one just to avoid having "wasted" power in there.

As for how much power you actually need personally, you'll need to know:

1. How loud you want to listen on a continuous basis (subjectively for me: 75dB is okay but not loud, 85dB is reasonably loud, 95dB is really loud, 105dB is super duper loud)
2. How loud do you want the peaks to get? Some say you need 20dB for peaks.
3. How far away do you want to sit from the speakers?
4. What speakers are you using, and what is their sensitivity rating?

Knowing all that, you can use a calculator like this and figure out the necessary wattage: http://www.hometheaterengineering.com/splcalculator.html

Sensitivity rating is very important. If you start at 90dB vs. 83dB, that's going to be a very noticeable difference and you don't need nearly as big an amp.

Welcome to ASR!

 

[Doodski]

Hi @UncleJoe. What is your budget looking like and what speakers do you have or want to have?

 

[Cbdb2]

For starters, depending on the manufacturer, you have to read the fine print when it comes to wattage ratings. Sometimes they're inflated quite a bit.

When it comes to active DSP speakers like the KEF LS60, there's a ton of wattage packed into the speaker for a few reasons.

1) Sealed design with extended bass via DSP is one of the most power-hungry designs
2) They're meant to go loud
3) They're meant to go deep

Other very good speakers don't have a ton of amplification built in. E.g. the Genelec 8030c, a professional-grade unit if there ever was one, only has 100w built in. It's a ported design, and my guess is they don't really need 50w for the tweeter but it was cheaper to buy a single 2-channel 100w amp than find a smaller one just to avoid having "wasted" power in there.

As for how much power you actually need personally, you'll need to know:

1. How loud you want to listen on a continuous basis (subjectively for me: 75dB is okay but not loud, 85dB is reasonably loud, 95dB is really loud, 105dB is super duper loud)
2. How loud do you want the peaks to get? Some say you need 20dB for peaks.
3. How far away do you want to sit from the speakers?
4. What speakers are you using, and what is their sensitivity rating?

Knowing all that, you can use a calculator like this and figure out the necessary wattage: http://www.hometheaterengineering.com/splcalculator.html

Sensitivity rating is very important. If you start at 90dB vs. 83dB, that's going to be a very noticeable difference and you don't need nearly as big an amp.

Welcome to ASR!

Room gain and speaker directivity can also make a level difference.

 

[DVDdoug]

But when I look at powered speakers, they’ll have a 100 watt amp just for a tweeter.

That would be a lot for "home listening". In pro studios they often listen loud and the space is usually "dead" (sound absorbing). And with PA systems the sound-power requirements can be enormous for a large audience.

One big issue is we usually don't know what dB level we want/need. And the power we want/need depends on the peaks, and the peaks depend on the dynamics of the music. How Loud is Loud

100W is usually more than enough for "home listening" but doubling the power only gets 3dB louder and as you turn it up, power requirements go up exponentially.

Bass can also require lots of power.

A powered subwoofer (with enough power & "size") can help a LOT with "loudness". You can crank-up the bass to get the "feel" of a lot of power without much power to your main speakers and without hurting/damaging your ears.

Speakers are supposed to be rated to handle an amplifier of the same rating that's hitting full-power on the peaks (without clipping) and it's usually safe to match amplifier power and the speaker's maximum power rating. But that's "statistical" (depending on the dynamics of the music). And manufacturers don't always follow the standards and they aren't always honest. (Amplifier power ratings aren't always honest either.) If you push the amplifier into clipping the average power goes-up even though the peaks are clipped, and that can damage the speaker. (There's a very-popular myth that clipping is worse than a higher-powered amplifier, but either way you can damage a speaker by over-driving it.)

It's usually OK to use an over-powered amplifier as long as you don't go crazy at a party (or during "testing") and blow your speakers. (Extra power is OK if you don't actually use it! )

Sometimes a speaker manufacturer gives a maximum & recommended minimum power rating. You can ignore the minimum recommendation and use the sensitivity spec if you want to calculate/estimate your minimum requirement.

 

[Head_Unit]

Amplifier power ratings aren't always honest either.) If you push the amplifier into clipping the average power goes-up even though the peaks are clipped, and that can damage the speaker.

And amplifiers are only tested into resistors, which are not much like real speakers. The speaker power ratings, meaningless drivel says this loudspeaker engineer and once upon a time marketing shill.

The damage, let's suppose you're playing an amp which clips at 100 watts. Your volume is set to 50 watt peaks, and 2 watts of that is high treble. Turn up the volume x10 (10 dB), the 48W bass peaks try to become 480W which does not happen because the amp clips at 100W. BUT the treble peaks do actually hit 20W and your tweeter vaporizes. Amplifiers can also output DC or other weird effects when they clip if not well designed.

I agree as you don't go crazy" is the important part!

 

[UncleJoe]

Hi @UncleJoe. What is your budget looking like and what speakers do you have or want to have?

I’m a bit all over the place. Max budget probably $7k ish. I’m interested in the Mofi Sourcepoint 8, Kef R3 Meta (perhaps used R7meta). Unfortunately I haven’t been able to audition any of these. I did listen to some Sonus Faber towers and didn’t like them. Listened to the B&W 704 S3 and really liked how wide the stereo image was. But they seemed to struggle a bit in the low mids. Just don’t think 5.25in drivers are big enough. I’d like to hear the 703 S3 with the 6.5inch drivers.

 

[UncleJoe]

That would be a lot for "home listening". In pro studios they often listen loud and the space is usually "dead" (sound absorbing). And with PA systems the sound-power requirements can be enormous for a large audience.

One big issue is we usually don't know what dB level we want/need. And the power we want/need depends on the peaks, and the peaks depend on the dynamics of the music. How Loud is Loud

100W is usually more than enough for "home listening" but doubling the power only gets 3dB louder and as you turn it up, power requirements go up exponentially.

Bass can also require lots of power.

A powered subwoofer (with enough power & "size") can help a LOT with "loudness". You can crank-up the bass to get the "feel" of a lot of power without much power to your main speakers and without hurting/damaging your ears.

Speakers are supposed to be rated to handle an amplifier of the same rating that's hitting full-power on the peaks (without clipping) and it's usually safe to match amplifier power and the speaker's maximum power rating. But that's "statistical" (depending on the dynamics of the music). And manufacturers don't always follow the standards and they aren't always honest. (Amplifier power ratings aren't always honest either.) If you push the amplifier into clipping the average power goes-up even though the peaks are clipped, and that can damage the speaker. (There's a very-popular myth that clipping is worse than a higher-powered amplifier, but either way you can damage a speaker by over-driving it.)

It's usually OK to use an over-powered amplifier as long as you don't go crazy at a party (or during "testing") and blow your speakers. (Extra power is OK if you don't actually use it! )

Sometimes a speaker manufacturer gives a maximum & recommended minimum power rating. You can ignore the minimum recommendation and use the sensitivity spec if you want to calculate/estimate your minimum requirement.

Thanks for the reply. I usually listen at modest volume. On occasion I do like to listen a bit louder but nothing crazy, 90db ish. I will also be adding 1-2 subs. I just don’t like the idea of pushing amps to their limits. I’d rather have extra power I don’t use and have the amp easily do what I ask of it.

 

[UncleJoe]

For starters, depending on the manufacturer, you have to read the fine print when it comes to wattage ratings. Sometimes they're inflated quite a bit.

When it comes to active DSP speakers like the KEF LS60, there's a ton of wattage packed into the speaker for a few reasons.

1) Sealed design with extended bass via DSP is one of the most power-hungry designs
2) They're meant to go loud (ish)
3) They're meant to go deep

Other very good speakers don't have a ton of amplification built in. E.g. the Genelec 8030c, a professional-grade unit if there ever was one, only has 100w built in. It's a ported design, and my guess is they don't really need 50w for the tweeter but it was cheaper to buy a single 2-channel 100w amp than find a smaller one just to avoid having "wasted" power in there.

As for how much power you actually need personally, you'll need to know:

1. How loud you want to listen on a continuous basis (subjectively for me: 75dB is okay but not loud, 85dB is reasonably loud, 95dB is really loud, 105dB is super duper loud)
2. How loud do you want the peaks to get? Some say you need 20dB for peaks.
3. How far away do you want to sit from the speakers?
4. What speakers are you using, and what is their sensitivity rating?

Knowing all that, you can use a calculator like this and figure out the necessary wattage: http://www.hometheaterengineering.com/splcalculator.html

Sensitivity rating is very important. If you start at 90dB vs. 83dB, that's going to be a very noticeable difference and you don't need nearly as big an amp.

Welcome to ASR!

The difference with Genelec as I understand is they are near field monitors. Usually placed just a couple feet from your ears.

 

[Mnyb]

I’m of the opinion that you need more power than you think for dynamic peaks and handling speaker impedance , so get yourself some modern class D amp and you be packing the same power as an active speaker

And it’s very big difference between sensitivity in some speakers.

I also own the kef LS60 with 500 +100 +100 watts the bass section is very inefficient being closed and small midrange and treble have more normal power rating .

But if you bring on some of these big horn speakers with very high sensitivity , they will probably outperform my kef’s in loudness with 1 watt.

Small closed subwoofers are another example you can get bass out of these with a 1kW of power if you put a large 18” driver in a several hundred litre bass reflex enclosure you need a handful of watts to remove your wallpaper

You can see this trend in passive speakers to the latest very well performing ascend bookshelf has a sensitivity of 82dB I would certainly always use more than 100 watts with them I would get some 250w class D amp .

Some larger floorstander migth be fine with a typical 100w amp .

Decibel is logarithmic .

+3dB a little bit louder demands double the power .

+10dB a significant jump in loudness means ten times the power .

Also the level decreases with distance to the speakers, so a large well damped room demands more power than sitting next to desktop monitors.

I would always use the speaker manufacturers power rating as a min spec for amp shopping that way the speakers always sounds nice and clean within their capacity.

 

[Doodski]

@UncleJoe chose your speakers based on spec and what feels the best for your ears. Then chose the amp you need. Class D is available in nice devices and so is AB and H.

 

[Chrispy]

I’m struggling here. I’m trying to build a simple 2.1 or 2.2 system for a medium sized living room in an open floor plan. Before getting into all the specific preferences and requirements I have, I’m struggling to figure out how much power is necessary. (I know there is some mathematical formula involving desired db and speaker efficiency etc.) Looking at integrated amps, they all seem to have 70-100/ch. All the reviews I watch swear this is enough power to push nearly any speaker. Plenty of people will say 30 watts is enough. But when I look at powered speakers, they’ll have a 100 watt amp just for a tweeter. Per channel these speakers will have 400-700 watts. Can someone please explain this massive disparity? It seems odd that if a speaker only needs 50 watts that a company would add in tons of extra power for no reason. Thanks in advance.

With a traditional amp that would likely be more about what speakers you intend to use at what distance and to what spl. That said, usually a good 100wpc at 8 ohm amp is going to work well for a lot of people with a lot of speakers. As to your passive/active speaker comparisons with "watts", what's the "cost" differences particularly involved?

 

[kemmler3D]

The difference with Genelec as I understand is they are near field monitors. Usually placed just a couple feet from your ears.

The 8030s are meant to be used within a few meters... some of them are suitable for longer listening distances, but I couldn't tell you the wattages off the top of my head.

 

[TonyJZX]

you're not making note of speaker sensitivity

i think with avg. speakers with say 6" woofer and 85dB+ sensitivity a 50w amp would fill the room nay to ear splitting levels

i have been able to get brand name bookshelfs for as low as $200 usd and matched with any of the TPA3255s you get more vol. than you would realistically ever need

and this is BEFORE you add a sub... the weakest sub I have, a cheapo 8" 100w DJ store affair matched with something very middling like an SMSL A300 + my test speakers which is the JBL Arena 130 w/ 7" drivers would put out enough clean effortless volume to make people leave the room, because you are shaking the room...


if you get speakers that are very insensitive say well below 80dB then you will need a big amp to push them

if you get horns above 90dB well then you're golden...

 

[Doodski]

@TonyJZX the OP has stated, "Max budget probably $7k ish." I think he can afford and wants something better than a TPA3255 design amp. A class D monster amp would fit his range very well.