On Sunday, October 11, 2015 at 12:45:31 AM UTC-4, veek wrote:
Hi, I have some really old speakers Phillips DH415 that were
gathering dust. I want to re-purpose them and use them with my
TV/computer - i got to buy an Amplifier for them.

(here's an image: subwoofer+bass reflex+tweeter is what i suspect)
http://imgur.com/a/Mt9Hw

I can't figure out what rating amp to buy.

If that's 20W PMPO x 2-speakers, then I need to buy: 30W RMS amp?
That seems like not a lot of power and I don't remember this set
being very loud. So is my assumption correct?

Are there any modern features I could look for in an amp. My TV is a
Samsung 4003 720p and it has Component Ports for audio/video.

OK - a few basics on speakers - at least as they were sold in the US under FTC regulations (sit on your fingers, Phil!):

a) Rated power is based on CONTINUOUS power into the speaker. So, a "20-watt" speaker should be designed to accept 20 watts of continuous power at some mix of frequencies, usually specified, for some specific period of time, also usually specified.

b) Rated Power is not Average Power. Assuming a speaker that produces 90dB of noise at 1 watt at one meter on-axis. Assume a normal peak-to-average of 20dB on the incoming signal, and assume it is running at one watt average (quite loud). Then the speaker will be getting momentary peaks of up to 100 watts (assuming the amp is capable of such). This will do NO damage to the speakers whatsoever as-described.

c) Low cost, low-wattage amplifiers are much more likely to cause speaker damage than large amplifiers. What can happen with some solid-state designs is that when the amplifier clips (called to produce more power than it can), it may send straight DC into the speaker - which will destroy voice coils in short order. So, the larger the amp, the less this may be an issue. As one example, I run 30-watt rated speakers with a 200-watt-per-channel amp, and have done so for years with no issues at all.

So, unless you wish to listen at ear-bleeding volume with an audio-quality source with full-orchestral signal (none of which are likely from a computer source), 30 watts is far more than enough. Another exampleL I run 86dB speakers from a 60 watt-per-channel amp at moderate levels, no problems and no clipping. The speakers are rated at 100 watts, as it happens. The key is *moderate levels*.

This issue is far less so from a tube amp - the simplistic explanation is that it is harder for a transformer to pass DC, so tube amps clip softly. There is much more too it, but for this situation, that is enough.

Peter Wieck
Melrose Park, PA