Combination low-powered amp with high-powered speakers

[TOATOA]

High all,
I am considering buying speakers and amplifier which i can have for very very low price.
Speakers: Sony SS-MB250H: 2x120W @8ohm, sensitivity 87dB (1W, 1m)
Amplifier: Renkforce SAP-702: 2x20W @8ohm

Both were selected not only for their very cheap price (respectively 30€ and 25€) but also because of space restrictions (should fit in cabinet, so amplifier cannot be more than 25cm deep and 43cm wide).
Objective: upgrade the sound of the TV from its internal speaker to a stereo sound. Not really loud or much bass, simply get a stereo sound.

What are your opinions, is the difference in power too much (i.e. are the speakers going to be 'underpowered' if such thing exists?) ?
Will i have to put the amplifier's volume knob to the maximum level all the time, or not?

Oh yes, I estimate the distance between listener and speaker around 3m20cm (320cm).

Reason why i post it in this category (newbie) is because i consider myself a noobie, and i have no idea if my questions are stupid or not.

Thanks in advance!!

 

[RayDunzl]

Most of the time you'l be using a watt or less for typical listening.

20W will be enough to go "pretty loud".

But there will be a limit where the amplifier begins clipping on peaks.

Crude estimate:

 

[JeremyFife]

Hi, and welcome
Can I start by saying that I don't know anything about those speakers or the amp - so I have no idea what they will sound like. Have you heard them before you buy? Some inexpensive gear is just fine, some is unlistenable.

Don't worry about the amp being underpowered for the speakers, that's hardly ever relevant. If you push your amplifier too hard (too loud, for too long) then it might "clip" or distort because you are using it outside levels that it was designed for. A clipping amp is not good for speakers - but it will sound horrible anyway and you are not likely to want to listen to it at all like that.

It is possible that those speakers can't handle going loud - but again, they will crackle and distort and you will turn the sound down before anything causes problems.
Don't expect much bass - but then you've said you don't so that's cool

There is a handy calculator for the amount of power needed that I like: https://www.crownaudio.com/en/tools/calculators#amp_power_required

Speakers with the same sensitivity as yours, at 3.2m, need 13W to delivery 85 dB SPL (a measurement of loudness) which is the threshold for hearing damage! It should all be plenty loud enough. Don't worry about where you have to turn the volume knob to either - just turn it to where it's loud enough but still sounds clean.

Give it a shot - at that price the only obvious alternative is a soundbar, so why not

Good luck

 

[AnalogSteph]

Going by the frequency response spec of 60 Hz to 50,000 Hz (!), I would bet the specs of this speaker are a tad on the optimistic side anyway.

Also, a rated power spec just tells you how much power with a standard frequency spectrum they will sustain without taking damage, nothing more.

The thing you are interested in is how loud things will go with the power provided. And by the looks of it, that's about 100 dB SPL peak @ 1 m anechoic. Maybe a tad under 100 dB peak at listening position per pair. Should do for TV audio, I'd think.

Had a look at the amp's schematic, a rated 20 W / 8 ohms appears plausible. It's a good thing you're not sitting super close, the TDA7265 is configured for 45 dB of gain and an output noise floor of around 500 µV(A) is expected. That's likely to be quite audible. Should be an easy mod if required (assuming the TV signal is plenty loud enough) since the chip is stable down to 25 dB - swap out R320 and R322 (100k) for something smaller or solder another resistor in parallel. A 20 wpc amplifier realistically doesn't need more than 39 dB of gain, that would be 47k or 51k or 100k||100k. I'd start there and see where this takes you. You could go down further with 47k||100k (~35 dB) if need be.

 

[TOATOA]

Wow thanks a lot for the Quick and extensive replies guys !
Cheers