So going by the information provided, here's a quick example.
- 8 ft avg listening distance (average sized liviing room?)
- 5.1 speaker setup with 89db/1w/1m (anechoic) sensitivity
- Assumed 85db nominal listening SPL
- No accounting for room gain
So for this example 0.5W output is needed for 85db SPL and only 50W is required to reach ~105db. Now correct me if I'm wrong but most mid-level AVRs can handle short term all channels driven to 50W without clipping right? And if so, with this information why do people buy external amps for their setups?
Steve
8 feet is over 2.4 meters, and the sound is coming from multiple speakers, not just one (though one does not simply add the numbers in dB from the different channels), so your numbers are off from the start. But your conclusion, that most people do not need external amplifiers, is correct. External amplifiers are needed if the speakers are a difficult load (low impedance, keeping in mind that "nominal" impedance ratings do not tell the impedance at every frequency) that the receiver cannot handle, or if one needs more power than the receiver can put out (which will depend on the speakers, how loud one likes it, etc.).
Sometimes, when people use external amplifiers, they are actually degrading their sound, as being an external amplifier does not mean that it is better in every way from something built in (see
this for a popular example, though in this case it depends on how the amplifier is used, and obviously the particular receiver under consideration).
To directly answer your question, for most people, buying external amplifiers would be wasting money. Though certainly not in all cases. People who have difficult to drive speakers, or who listen very loud (and who don't have high sensitivity speakers) require more power than most people. People with larger rooms than most require more power than other people with the same speakers in a smaller room (that is acoustically otherwise similar).
Also, your idea of keeping with "mid-level" receivers is a good one, as the budget models can involve too many sacrifices in quality (as well as features). I think most people don't need to spend more than about $600 for a receiver. And if they need more power, typically it would be best to still buy the $600 receiver (with preamp outputs for all channels) and buy external power amplifiers instead of a more powerful receiver, for two reasons. First, one can get more power with an external amplifier, and second, when new features come out that they need or want, they just replace the $600 receiver and keep the external amplifiers.
I used to use a receiver that retailed for about $600, but because I wanted more features (and the old one was too old to have things like HDMI), I replaced it with a receiver that retails for about $1700. Unless I engage a feature that affects the sound, it sounds the same as the $600 receiver. Now, it could matter in some cases, as the more expensive one can put out about twice the power of the old one, but the old one could drive my speakers to levels I found painful with crystal clarity, so the extra power is useless in my case. (The only reason I bought such a high model receiver was because I got it at a great discount as a discontinued model from an authorized dealer; I paid about 1/4 of its retail price. On the other hand, I have thousands invested in my speakers, because there one will hear differences. If sound quality is what you want, put your money in your speakers.)
