Technical Surround Sound Confusion. (1 Viewer)

[AshDrache]

Hello everybody,

My First Post
I am working my way into a surround sound system slowly, very slowly. This may prove best as I clearly have a great deal to learn before I should be putting down the big bucks.

After several years of saving up "Sony Points" I have a rebate worth about $260.00 for any Sony product. I want to initiate a surround sound system with a receiver and two speakers. I am in college and have a low budget. For now, I just want to purchase something that will continue to serve me (even if it is just as a computer surround system when I'm 40.)

I came home from Best Buy with a Sony STR-DG500 receiver and a pair of Yamaha NS-AM370S speakers. The yamaha speakers sounded much better than the sony ones on display, and they were only $55.00 for the pair so I preferred them.

Let the confusion begin. First of all, although nothing is mentioned about speaker compatability in the manual, on the back panel it says "SPEAKERS IMPEDANCE USE 8 - 16 Ohms." Well that is rather unfortunate since my speakers say they average 6 Ohms. Can I even drive these things?

Let's say I can drive these two. What about when I want the full 6 speakers and 1 subwoofer? If they are not matched, won't the lower impedance speakers be much louder than the others. Would it be possible to drive all 7 channels if they all were 6 Ohms on average?

The sales clerk said these speakers were perfect since they were rated at 120 watts max and the receiver offers 110 watts per channel. But on closer look, I don't know who Sony thinks they are kidding since the power supply can sink a maximum of 220 watts. Is this instantaneous watts that they are talking about?

So let's say that I can't fully drive these speakers. What is going to happen? Will I end up clipping and sending square waves into all 7 speakers? Will the volume be so loud prior to this disaster such that this is not really a concern? I live in an apartment so high volume isn't really an option.

Finally, (sorry for all the questions), the sales clerk said that the same power is used by the speaker at high volume as at low volume. This doesn't really agree with my intuition but I don't know that much about speakers (obviously.) To what extent is this true?

In addition to these questions I am looking for advice. Should I take part or all of this purchase back and buy something else? I've tried throughout to make direct questions, as opposed to retorical ones, so that the question marks may serve to direct the answers. Please feel free to respond in part, or in full, and thank you greatly for your time. I have to say that I am taking some interest in this topic and in reading this forum.

Sincerely,
Ash

 

[Nick:G]

A lot of Yamaha speakers are rated at 6 ohms nominal impedance. Cheaper amplifiers often don't have low impedance drive capability, because their power transformers are designed with an emphasis on output voltage (high impedance) rather than current (low impedance). So, can you drive your Yamaha speakers? Probably, but the amplifier will have to work harder to do so, which means it will produce more heat and possibly not be as reliable.

Regarding the rated output of your receiver, Sony is one of the undisputed kings of fudging specs on lower-priced receivers. Unfortunately, marketing has conditioned consumers to buy products based on wattage and not much else! On your model, they rate that 110W/ch at 1 kHz, which is a very easy frequency for any amplifier to drive. It certainly won't output 110W/ch at the reference 20-20,000 Hz frequency range. Neither the owner's manual nor the published spec sheet actually discloses the rated output with ALL channels driven (only two!), because it's likely only capable of outputting MAYBE 40W/ch RMS maximum with all channels driven. Amplifiers that output an honest 100W/ch with ALL channels driven require expensive transformers and capacitors. It's hard to get that at $200, unfortunately.


Your intuitions are correct, as that is totally bogus. Higher volumes require more power (more wattage), especially for low frequencies like bass. This is why amplifiers clip and overheat when driven too hard (the clipping is caused by insufficient power for the desired volume). You can test this with a scope and see for yourself.

Best Buy stores use Yamaha receivers to drive their speaker demos. Most Yamaha receivers are capable of low-impedance drive down to 4 ohms, whereas a lot cheaper Sony receivers aren't really designed for that. Yamaha makes MUCH better receivers in the entry-level $200-500 range; you can get them starting at under $300 I believe.

 

[AshDrache]

Thanks you Nick for all your answers.

Interesting. So "they rate that 110W/ch at 1 kHz," and only on two channels. I suppose that would at least add up to the maximum 220 W sinking power of the power supply. I suppose this is tested with a pure 1 kHz signal.

Is it true that if my OTHER speakers are 8 Ohms, that they will receive less power than these 6 Ohm speakers, or is the receiver intelligent. I doubt it since it isn't even designed for loads below 8 ohms. Perhaps I should take it back, but I need a sony product in order to use my sony rebate. What is the cheapest one that will handle my needs. Or should I purchase 8 ohm speakers? Is there some advantage in lower impedance speakers?

When the specification says
"8 ohms 20 Hz - 20 kHz, THD 0.09%
100 W + 100 W, 110 W/ch"

What does this mean? Do they sweep a sine wave through this frequency range with the volume turned to max and record the power the receiver consumes / the power the speakers consume? Does this mean that at that volume there is no power left over for the other frequencies and we get extreem distortion?

It seems a bit fishy since another line says
"8 ohms 1 kHz, THD 10%
125 W + 125 W, 150 W/ch"
Yet, even if they did just put a 1kHz sine wave in, the power output would exceed that of the supply. Or perhaps they could simply presume this would not happen for long during standard use and the stored energy of the capacitors/inductors could supply this power for a moment.

Interesting (at least to me)
Thanks again,
Ash

 

[Nick:G]

And this is why Sony is reluctant to actually publish ACD (all channels driven) specifications for this model. Unfortunately, the current government regulations are not very stringent on accuracy of ratings, considering that the FCC categorizes anything rated over 5W/ch RMS output as a "high fidelity appliance". Because of this, manufacturers can fudge ratings all they want. They know that the vast majority of consumers in that price bracket aren't going to care anyway. They've already brainswashed their customers into being Sony-centric and those people will probably end up with lackluster Sony speakers to go along with their purchases. Oh, did you know that Sony is the 2nd most recognized speaker manufacturer in the world, right behind Bose? Name recognition goes a long way in this world...

 

[Grant B]

Finally, (sorry for all the questions), the sales clerk said that the same power is used by the speaker at high volume as at low volume. This doesn't really agree with my intuition but I don't know that much about speakers (obviously.) To what extent is this true?

Generally that's true since the volume control is used to attenuate the volume.
Sort of like water coming out of a faucet; it's always there but how much do you want to let out depends on how much you open it up

 

[Arthur S]

Grant

Not sure exactly what you are asking, however, the receiver does not draw as much current from the wall outlet at low volume. If the receiver drew maximum power at low volume, the receiver would be very, very hot all the time.

Hope this answers your question.

Happy Holidays