Need help matching my receiver with speakers. Watts? Ohms?

Question

I recently bought a Sony 5.1 HTiB HT-7200DH. I know I should have just bought the receiver and speakers separately, but it's too late now. I pulled the following information out of the manual:

POWER OUTPUT AND TOTAL HARMONIC DISTORTION:

With 6 ohm loads, both channels driven, from 120 - 20,000 Hz; rated 90 watts per channel minimum RMS power, with no more than 1% total harmonic distortion from 250 milliwatts to rated output.

AMPLIFIER SECTION

Power Output (Measured under 120 V AC, 60Hz)

Stero mode (rated)

(6 ohms 1 kHz, THD 1%)

90 W + 90 W

Surround mode (reference)

(6 ohms 1kHz, THD 10%)

RMS Output

FRONT: 140 W per channel

CENTER: 140 W

SURROUND: 140 W per channel

Am I really getting 140 W output to all 5 channels?

If I bought 200 W, 8 ohm speakers to replace the wimpy speakers that were included, would I have any problems?

Is an 8 ohm receiver better than 6 ohms?

What about the THD?

I don't want to buy great speakers if this receiver is no good.

Answer 1

I'm afraid this receiver is rather low end. And you actually damage speakers by under-powering them instead of over-powering.

Power is non linear which is why it is so confusing.

Fact - an 8 ohm speaker is "8 ohms nominal/average".  it actually swings from about 4 ohms to 30 depending on the sounds it is playing.

Fact - On average your receiver puts out 10-15 watts per speaker throughout a movie.  But to increase the volume by 1 db, the power must double.  This is why 80,90 watt receivers are the norm.

Fact - a single receiver will produce these types of power numbers:

- 50 watts into 8 ohm load

- 75 watts into a 6 ohm load

- 100 watts into a 4 ohm load

To 'fool' Joe Public, the power output for 6 or 4 ohms is usually prominently displayed.  This makes the cheap electronics compare to Yamaha, Denon, Pioneer who all tend to put 8 ohm power numbers first.

HOW TO READ RECEIVER POWER NUMBERS:

There is no standards for power measurements and by choosing different options, the receiver can appear more powerful than it really is. You have to read the fine print:

Here is what Yamaha, Denon, Pioneer (good receiver companies) typically state:

A) All channels driven. (The sony rating says "Stereo Mode - only 2 speakers attached to make the unit look more powerful.  Add 3 more power-sucking speakers and the available power drops.

B) 8 ohm resistive or non-inductive load (This is common to remove the variable of a speaker changing impedance during the measurement.  Good companies publish separate power numbers for 8, 6 and 4 ohm receivers.)

C) Frequency: 20-20,000 hz.  Lower frequency sounds take more power.  Cheap companies measure power with a 1 Khz sine wave, good companies promise the power with a large swing of sounds.

D) RMS vs Peak: Good companies use RMS which can be thought of as the average power during the sine-wave of the sound. Cheap companies measure peak or 'peak envelope power' which looks about ... 27% more powerful.

E) THD less than 0.07%:  All receivers can & will produce more power than they are rated at.  But distortion climbs up very fast and I think it becomes audible around 0.8%.  Good amps promise to keep distortion below about 0.1%.

Hope this helps.

Answer 2

I would be suspect of the wattage ratings and would anticipate real-world figures to be up to 60 watts, maybe 65 if you want to be really optimistic, with an 8 ohm load.  With exception of the ES line, Sony tends to exaggerate their wattage ratings.

The 140 watts on all channels may be peak wattage on one channel only, if that, and not indicative of real-world operation.

The frequency response of 120Hz-20kHz is rather poor; it should be 20Hz-20KHz and most of the amplifier's power goes towards driving the lower to low-mid frequencies. It is possible that the 120Hz is to allow the 90 watt claim.

1% THD is also a rather poor rating.

Buying 200W speakers may not be a problem if the drivers themselves are efficient, not requiring that much power to make good sound.  Otherwise, I would recommend getting a better quality amplifier to avoid the risk of damaging the speakers.  An underpowered amplifier may be more prone to clipping when pushed hard enough on speakers that require a higher RMS wattage than the amplifier is capable of providing.

Or, get speakers that do not require as much wattage and have good efficiency. A set of two-way or three-way bookshelf speakers by a respectable manufacturer will be a better choice than the stock speakers that came with your HTiB.

Answer 3

You get up to 90 W from left/right and up to 140W for the other 3.

You can put 200W speakers, but the max you can get from your amp is 90 (and maybe even less if you put 8 ohm speakers), so you don't really get anything extra.

Stick with what you have. Unless you have a huge room, I am sure the power you have is more than enough.