How much power do I need?

[Leerlaufprozess]

Hey everyone and sorry for this rather primitive question but I'm new to the world of diy audio.

I was thinkin about buying the suppo audio Golden voice EL84 but I'm a bit worried about how much power I will get from it. I'm planning to build my own speakers (probably these) and I don't really know whether the amp can sufficiently power them. They seem to be rather efficient (91 db) but I always thought the maximum power intake of the speakers should be about 30% above what the amp delivers and every set of speakers I've seen so far are far above the 2x8W the amp delivers.

I'm not trying to use them for anything big, just a standard-sized room.

Thanks in advance to everyone taking the time to answer my question

[rotaspec]

You may be surprised just how loud the little 8W amp will be into speakers of that efficiency. 91dB for 1W means 100dB for 8W.
I have a Meng Yue amp that is around the same power, and it goes fairly loud with my 87dB speakers.

Gary

[Yvesm]

There is no "minimal required power" for any loudspeaker.
The restitued sound level depend ONLY on the speakers efficiency, any 91 dB system will produce the same acoustic energy what could be its size or power rating.

Of course, feeding a 10W LSP system with 100W will probably destoy it
But driving a 100W LSP with "only" 10W will surely produce less distortion.

Yves.

[Glowbug]

What kind of music do you usually listen to?

[jrenkin]

I was sitting in my listening/living room enjoying a Brahms piece at my usual, comfortable listening volume and pondered this general question. So I pulled out my trusty SPL meter (my iPhone) and measured the decibles at one meter.

It was about 70dB. Not that much. 80dB is a LOT louder and acounting for all sorts of error in my very rough measure, it seems that all I need to drive my 86dB Zen Adagios to comfortable to loud listening is 1 watt or less.

91dB speakers at full 8W = 100dB as above. Damn that's loud in my book. Of course, you won't want to drive your amp at the full 8W. But it seems to me you will be fine for most relaxed listening.

If you need the 115dB rock concert levels, get a big SS amp and plan on early loss of high frequency hearing. Gentle listening means more years of appreciating.

[tomchr]

I believe the US NIH (National Institute of Health) recommends that you wear ear protection if you subject yourself to SPL's above 75 dB(A) for an extended period of time. So using this yardstick, let's do a little math...

Ignoring room reflections and reverberation time, the SPL will decay exponentially as you move away from the speaker. I.e. the SPL gets 3 dB lower every time you double the distance to the speaker. So... 91 dB @ 1W, 1m. You're using two speakers, so for 1 W dissipated in each, you'll get a total SPL of 94 dB. Let's say you're 4 meters away from the speakers. So you'd be experiencing an SPL of 88 dB with 1 W dissipated in each speaker. To get below the NIH recommendation, you'll need to cut the power by 13 dB. So at 0.05 W = 50 mW you'll get an SPL of 75 dB at the listening position. And this does NOT count room reverb or reflections!!

I've been using a small tube amp that delivers 4.5-ish W per channel for a while in my fairly live 20-ish sq. meter living room. My speakers are 87 dB/W*m efficient. I've been measuring the output power by watching the oscilloscope and assuming the speakers are 8 ohm loads. When the peak output is 1 W, it's really quite loud. At 2 W peak power, I start turning down the volume. It won't rock the house off the foundation, but it's certainly enough power to play at a reasonably loud level.

~Tom

[Eli Duttman]

Paul Joppa has provided us with a useful rule of thumb. For a "typical" sized listening space, Joppa's Rule states an amp/speaker combo should be capable of 102 dB. SPL peaks, at a 1 M. distance. So, 15+ WPC are needed in combination with 91 dB. sensitive speakers. PP triode wired EL84s and 6V6s will not do, sorry. OTOH, PP triode wired EL34s and 7591s are fine.

BTW, music IS transients and the peak SPL indicated by Joppa's Rule is necessary to handle the dynamics.

[wahab]

2 X 8 W is plenty of power...
i use currently a 2 X 5 W class A amp for tests,
and it s never used over 2 X 1 W in my 91dbm speakers...

[bigjppop]

Originally Posted by Eli Duttman

Paul Joppa has provided us with a useful rule of thumb. For a "typical" sized listening space, Joppa's Rule states an amp/speaker combo should be capable of 102 dB. SPL peaks, at a 1 M. distance. So, 15+ WPC are needed in combination with 91 dB. sensitive speakers. PP triode wired EL84s and 6V6s will not do, sorry. OTOH, PP triode wired EL34s and 7591s are fine.

BTW, music IS transients and the peak SPL indicated by Joppa's Rule is necessary to handle the dynamics.

I've read this multiple times and I try to buy/build my speakers/amps to abide by this idea. That being said, I've been shocked how much volume I've gotten out of some pretty inefficient speakers with some pretty low power amps. For example, with my little Suppo Audio EL84 based amp (claims around 8 WPC but might be a little more) I've been able to listen to my Quad 12L2's without any problem. I believe the Quads are sitting at 86-87 dB. That amp is a better match to my 93 dB Omega speakers but its not a volume issue. I think the Quad sounds a little "looser" with this amp @ 8WPC as opposed to when I've heard them driven with 40+ WPC.

So, while I'm far from an expert, I think when talking power and "how much do I need" volume is the easy part

[Leerlaufprozess]

Thanks everyone, just ordered the amp. Looking forward to building my speakers