Thank you very much. I won't bother you any further.
I think I understand the power relationship, the SPL max provided from your link is somewhere around 100w value when I calculate it on this
[link], but I lack basic understanding how much SPL I really need.
It says on the site 100 watts increases SPL by +20dB and stereo speakers by +3dB when I pick 1 meter, 85dB SPL, 2 speakers and away from the wall, so 180w vendor specification equates to 100w on the site.
I still don't know if I need 100 watts, or 180 watts rms power for 98.3 dB max when I pick 3 meter listening distance. Good thing it only drops to 88.3dB if I lower power by 10 times. 10-18watts rms power seems plenty loud to me @88dB. Any regular old amp should be able to drive 10-18 watts.
Hi there. I am relatively new to this hobby but I'll do my best to fill you in.
The KEF Q Concerto Meta is rated for 85 dB/2.83 V/m. At 4 ohms, this is 2 Watts. P=V^2/R, = 2.83^2/4 = 2 Watts. This is double the power of a normal sensitivity, in decibels (since it is logarithmic) this doubling equates to 3 dB. So you must subtract 3 dB to convert to W/m. So the sensitivity is actually 82 dB/W/m.
Your question is really about how to size an amp for a speaker. This is a really complicated topic!
The speakers max SPL is 108 dB (at 1 m). To get a 26 dB gain from the amp, you need 400 W. That power will play at that SPL. This does not mean that if you plan on playing your speakers at 108 dB (you shouldn't), that 400 W would be "adequately sized". That also doesn't mean that 400 W is adequately sized for 70dB at 1m. That's because these measures are for a continuous SPL, not a changing SPL like in normal listening.
KEF is saying that when you play music if any dynamic reaches an SPL/1m exceeding 108 dB, it may cause damage to the speaker. If you're reasonably sensible with your volume control I doubt you'd ever hit that.
Here's the catch, when evaluating an A/B amp. As you approach maximum power or current output, almost everything about the amp (in general) will degrade in performance. Response linearity, distortion, etc. So for the amp to perform best, it should be at an average power of significantly less than the minimum required for the desired SPL. This is called "headroom". Maybe 25 dB of headroom would provide peak performance. The specific headroom required is amp/speaker specific (e.g. tolerance of linearity with changes in temperature and power output).
A good listening position is like <10 feet probably (depends on speaker placement and room dimensions). SPL something like 65 dB, so a 100 W RMS would be plenty headroom. However, I will mention sizing an amp for a speaker isn't just about SPL. Current output, damping factor are also relevant. These must be sized to the characteristics of the speaker: Q and impedance response:
https://ca.kef.com/blogs/news/damping-factor-explained
Personally, I also think amp slew rate is something to pay attention to (analogous to speaker instantaneous compression response). In general though the most modern manufacturers probably don't have "lobsided" amps I would think though.
I know this doesn't exactly give you a direct answer, but hopefully it helps you to create a framework for sizing an amp.
Cheers,
lkh
