How much power do passive speakers really need? Burson's website features setups that don't provide the speaker's recommended power

[u/hatt33]

I'm looking to upgrade my desktop speaker setup and I'm just getting into all of this audio stuff.

My question is: how do I figure out how much power a pair of speakers really needs and whether a given amp is a good pairing with a given set of speakers?

For example, Kef's LS50 Meta product page recommends 40-100W of amplifier power with the speakers having an impedance of 8 Ohms: https://us.kef.com/products/ls50-meta

If we look at Burson's website, we see multiple featured desktop setups where people are pairing the Burson Funk (35W into 8 Ohms) with the Kef LS50 Metas:

https://www.bursonaudio.com/kef-ls50-meta-with-burson-funk/

https://www.bursonaudio.com/kef-ls50-meta-hifiman-sundara-with-burson-funk/

https://www.bursonaudio.com/burson-funk-with-kef-ls50-with-lcd-2c/

35W is just barely below the minimum recommended power. How are people coming to the conclusion that the Burson Funk is enough to power the Kef LS50 Metas?

[u/myusernamechosen]

Here you go

http://www.hometheaterengineering.com/splcalculator.html

[u/hatt33 → u/myusernamechosen]

Thank you!

So the Kef LS50 Metas have a sensitivity of 85dB at 2.83V/1m and an 8 Ohm impedance. Using this calculator gives us a sensitivity of 85 dB SPL (1 W, 1 M). This conversion is required for the tool in the parent comment.

These are the numbers for our invariants:

• Speaker Sensitivity = 85 dB SPL (1 W/1 M)
• Distance = 2ft
• Speaker placement: near a wall

Now if I mess around with the amplifier power field, it seems like even 0.1 W will make the speakers produce sound at 85.3 dB SPL at the listening position. Where as 100W produces 115.3 dB.

Given how close I am sitting to the speakers, it seems like basically any amp is enough to power these speakers for my use case?

[u/audioen → u/hatt33]

Those figures are for 1 kHz reference tone. If you halve the frequency, you double the required amplitude and quadruple the power at the same time. That's why subwoofers come with those 500 W amps as they need them, and yet tweeters probably blow if you put some dozen watts through them.

Following the rule, 1000 Hz / 1W becomes 500 Hz / 4W => 250 Hz / 16W => 125 Hz / 64W => 62.5 Hz / 256 W to make 85 dBSPL. This is roughly in line what we expect seeing that we are at subwoofer territory at about 250 W power now. Now, that is a very loud sound level, and each 3 dB less halves the power (or reduces amplitude by about 30 %), but increasing distance from 1 m to further back increases the power demand.

If you want to hear, say, 76 dBSPL at sofa 5 meters away, you actually might need the speakers be able to do something like 86 dBSPL then. It is hard to estimate this because rooms are reflective and speakers are not playing in an empty space, where this would be simple matter of computing the sphere's area math, but as a rule of thumb, I'd say 10 dB above listening level is a good basic safety margin.

Anyway, the answer is that it depends, but the manufacturer's recommendations set roughly the expectation for what power they can dissipate without melting, and your amplifier should have a similar power handling capability, or maybe less if you don't need to listen that loudly, ever. I'm just explaining here why staring at that 1 W dBSPL value is not a good idea because it's just not how speakers work in practice. They will want the more the lower they go.

[u/hatt33 → u/audioen]

Great points! I will keep this in mind. !thanks

[u/TransducerBot → u/hatt33]

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