How loud will my amp go?

[cloth-ears]

As I've said before I’m not a trained electronics engineer, my subject is physics but I did have to learn a little bit on the way. I was trying to explain to a friend the correlation between relative loudness and amplifier/speaker efficiency. I tried to explain SPL, db and VRMS but I could see his eyes glazing over. He’s not very good with technology and asked me to dumb it down as best I could. If any real engineers out there think I’m wrong please tell me.

If amplifiers were petrol producers and speakers were cars then an amp producing only one gallon of petrol would need a Nissan Micra to travel 60 miles whereas a Range Rover would need one producing three gallons to go the same distance. If you were to swap amps then the Nissan would travel 180 miles and the poor Range Rover only 20. There is nothing wrong with either the Nissan or Range Rover, or indeed the two amplifiers. They just need to be carefully partnered. He understood this, I hope I’m right.

I don’t know about anybody else but personally I have found that to play music at the level I most like then the amp has to be running at about 35% efficiency and the speakers at about 45-50%. This has always given me the best results.

[mimoser]

First thing to consider is speaker efficiency in db. 10W will go a long way on 98db efficiency speakers.
Second thing to consider is watt. Low efficiency speakers will require higher watt amplifiers.
Third thing is current. If you run our 30cm rubber surround Wharfedale driver speakers from a 30W Yamaha amp you get some shy and not very controlled bass. The same speakers run from a 100W Toshiba SA-7100 Monster receiver put out a very defined and controlled bass. Loudnesswise everything still takes place below the .5W mark on the Toshies output meters 1W gets pretty loud. The main difference between the Yamaha and the toshiba is the size of their transformers and suppose the kind of current they continuously provide; tbh you could run three of the small Yammies from the Toshies transformer.
:-)
Michael

[cloth-ears]

First thing to consider is speaker efficiency in db. 10W will go a long way on 98db efficiency speakers.
Second thing to consider is watt. Low efficiency speakers will require higher watt amplifiers.
Third thing is current. If you run our 30cm rubber surround Wharfedale driver speakers from a 30W Yamaha amp you get some shy and not very controlled bass. The same speakers run from a 100W Toshiba SA-7100 Monster receiver put out a very defined and controlled bass. Loudnesswise everything still takes place below the .5W mark on the Toshies output meters 1W gets pretty loud. The main difference between the Yamaha and the toshiba is the size of their transformers and suppose the kind of current they continuously provide; tbh you could run three of the small Yammies from the Toshies transformer.
:-)
Michael
Isn’t bass control relative to output impedance? (Damping factor). I would guess that the Tosh has a higher damping factor. The lower the amps output impedance the greater its resistance to reverse current effect of speaker coil return, hence tighter bass.

[sq225917]

The simple explanation.

Amplifiers provide power, speakers consume power. A more efficient speaker consumes less power for a given output level and as such will play louder than a less efficient speaker driven by the same amp.

No cars, no damping factor.

[Reffc]

Is efficiency being confused with sensitivity here. Efficiency is measured in % terms and sensitivity is measured in dB pink noise produced for 1 W (2.83V) of input power at 1m.

Efficiency is a ratio between used (useful) output power to input power. In the case of 'speakers, it's a function of emitted sound Power to electrical input power. Efficiency is very rarely stated by manufacturers, but sensitivity is (usually measured with a 1kHz test tone and not across the spectrum).