Spec Me A Receiver....

oHUTCHYo · 13 Jun 2015 at 21:38

I'm in the process of buying components for my new system. I'm planning a 5.1 system built around the Monitor Audio Bronze BX system.

For the fronts I'm using the Monitor Audio BX6. They are rated 150rms @ 4 ohms, 90db sensitivity.

Which AVR do I need to power them and the other components (e.g. BXW10 sub, centre and likely BX1 or BX2 rears)?

I like the look of the Sony STRDN1060, it's specs state;

7.2 Ch. 1155W A/V Receiver (165 W x 7 @ 6 ohms, 1 kHz, THD 0.9%)
(6Ohms, 1kHz, 2ch driven) THD : 1%
(6Ohms, 1kHz, 1ch driven) THD : 0.9%
6ohms, 20-20kHz, 2ch driven : 100 W + 100 W (6 ohms, 0.09% THD)
6Ohms, 1kHz, 2ch driven : 165 W (6 ohms, 0.9% THD)

I fear this may not be powerful enough? I was hoping to budget £500 but will adjust upwards if it otherwise means having an underpowered system overall and wasting the speaker potential.

lucid · 13 Jun 2015 at 22:31

First things first, your impedance figure for the BX6's is wrong. They're 8 Ohm, not 4 Ohm.

Second, any amp will drive the speakers. Most of the time you'll be using relatively modest amounts of power. Think of it this way, your BX6's are rated at 90dB per 1 Watt of power measured from a distance of 1 metre. 90dB is flippin' loud. To be sure, you don't sit just 1 metre from your speakers, and sound does dissipate with distance, but there's also the reinforcing effect of room boundaries to consider. What it all means is that you won't need as much power as you think to drive the speakers to a decent level. That's good news because AV receivers aren't as powerful as the paper spec suggests, but a 1060 will do okay.

More power from an amp will give you greater dynamics (goes louder without distortion). More powerful or higher quality amps are likely to be able to drive all the speakers to louder levels because of superior current delivery thanks to larger power supplies and bigger power reserve capacitors.

oHUTCHYo · 13 Jun 2015 at 22:41

Damn helpful, thanks Lucid.

It's criminal the AVR manufacturers can get away with stating over optimistic RMS ratings.

The main attraction to the Sony was purely on brand and aesthetics, perhaps a I should be looking at the better regarded Yamaha/Onkyo/Denon et al.

lucid · 14 Jun 2015 at 10:07

All the mainstream manufacturers play the same game. That's because the general public has been brainwashed in to believing more watts is better, hence why all the all-in-one home cinema kits have stupidly high wattage figures from tiny power supplies that can't possibly sustain those numbers.

To be fair, the AV receiver market doesn't quite go to such extreme lengths to deceive. However, if you look at the specs for the Sony then the most realistic power figure is: 6 Ohms, 20-20kHz, 2ch driven : 100 W + 100 W (6 ohms, 0.09% THD). That's because the audio signal is full range (20Hz-20kHz) rather than the 1kHz single frequency tone, and the THD figure is roughly on par with how a Hi-Fi amp would be measured. Higher THD figures such as 0.1% and 1% are where the amp is starting to get towards the limits of the power supply performance. I have seen specs for all-in-one kits where they are measured at 10% which is speaker-wrecking territory. :eek:

If AV amps in this category were measured for sustained power, all channels driven, 20-20kHz, 0.09THD then it's likely that they'd yield around 40-50W per channel, but the marketing departments would never allow those figures to be published because of the historic confusion about power. If you really want to find out how loud a Watt of power can be then go have a chat with the serious valve amp boys. They'll couple very high efficiency speakers with amps producing fewer than 5 Watts but produce sound that's equivalent to 60 Watts from a Class A/B transistor amp. Last year at the Cranage Hi-Fi show I listened to several such systems in rooms seating 15-20 folk where the music played at volumes that would have my wife shouting "turn it down"