Is a 7 watt per channel amp enough

[vamper]

Recently I decided to build my own pair of speakers using the Planet_10 mini onken design with alpair 10 drivers. Since this is my first pair of real speakers, I need to get an amplifier.

After looking at some thrift stores (seem to have cheep stuff), I remembered that my dad had an old tube amplifier from my Uncle that he is not using (a Grundig Stereomeister 300). I believe it was a high quality amplifier back in the day, and my dad said it sounded good with his speakers (I have included a link to the model below).

My concern is that this amp only outputs 7 watts per channel. Would this be enough to drive the alpair 10s (87db efficiency)? I live in an apartment and do not need a lot of volume, but don't want to have to strain to hear the speakers either. The room the speakers will be in is ~20' by 14'.

Any insight you could provide will be appreciated.

Stereomeister 300a Radio Grundig Radio-Vertrieb, RVF, Radiow

[cotdt]

If you have the speakers up against the wall, then it's enough power. Problem is, we don't really know if the thing can really deliver 7W.

[Eli Duttman]

Listening room size and musical taste definitely have an impact on power requirements. Having said that, Paul Joppa has provided us with a useful rule of thumb, for assessing amp/speaker combos. Joppa's rule states that in a "typical" listening space and amp/speaker combo should be capable of producing 102 dB. SPL peaks at a 1 meter distance. Unfortunately, it's quite obvious that 7 WPC will be grossly inadequate in combination with 87 dB. sensitive speakers. Mid 90s sensitive speakers are an appropriate match for a 7 WPC amp.

[jrenkin]

Boy, back in the day when the tube really was just another ugly piece of electronics to hide in a case. Now we like out tubes on display.

I think eli's point is good, but you may be able to get away with it if you really don't crank it. Your room isn't too big.

If you listen at 3 meters, you may only get 78 dB with 1 watt at the listening position, not accounting for any room gain. 2 watt = 81dB, 4 watt 84dB, 8 watt only 87dB. If you want 20+ dB headroom for a well recorded piece of music with a good dynamic range, you can't turn it up too loud. Average 65-70 dB at listening position. Higher if you listen to highly compressed modern music.

That being said, I find, in a 10' x 12' listening room, at 6' listening, I don't put it up much beyond 63 dB, I find it loud enough.

[scott17]

I agree with Eli.

I just finished building a 7W RMS (measured) amp and am using it with 97~98dB loudspeakers. It is "just" loud enough for my taste.

Of course I don't listen to it full out all the time.

Scott

[tomchr]

I'm using my 300B amp which delivers 10 W per channel. I have no trouble driving it to ear-splitting volumes (>100 dB SPL at the listening position 1.5 m from the speakers) even with my 87 dB efficient speakers.

Recall, you have two speakers (+3 dB) and the room has some reverberation ("room gain" +4-5 dB) so it only takes about 2-3 W to drive the SPL to 100 dB(A) with those speakers. 100 dB SPL is enough to make my ears ring for hours. I tend to listen at around 80 dB SPL when I'm enjoying the music. Lower for background noise.

~Tom

[TubeHead Johnny]

It all comes down to: "How loud is loud?" I'm sure it will be adequate for background music, but beyond that is subjective. I have a little PP EL84 amp that puts out only 7-10 watts a side. Right now it's powering a pair of "Overnight Sensations" which is a speaker kit put out by Parts Express. Supposedly, the 4" woofers only have a 83 db efficiency and it's more than enough volume for me. They're in a medium sized bedroom.

[counter culture]

Speaking as a solid-state enthusiast, whatever you do, if the amp is on offer, don't turn it down.

[Eli Duttman]

Definitely take the Grundig and do everything necessary, including obtaining appropriate speakers, to put it back doing what it should, playing music. Fine "vintage pieces, like that, do not belong on museum shelves. They were built to play music, not be gawked at!

The ELL80/6HU8 O/P tubes the Grundig uses are scarce. Scrounge up at least 1 set of spares and more sets would be better. At least 1 unit I've seen (by Fisher) competes for the limited stock that's available.

[jjman]

You will not have to strain to hear 7 true watts, promise.