Power needed for home theater

[Dj7675]

I am trying to figure out how much power I need in my home theater. I have read a few threads here but want ask if I am on the right track... As a starting point I am using this calculator:
https://myhometheater.homestead.com/splcalculator.html
On that page, it says to enter 3 channels if doing multichannel. So if I put in the following info in the calculator:
93 for speaker sensitivity
60 watts
14 feet distance
Near wall
With this info I get 105.9db spl. It is my understanding, if listening at reference level, I need to get to 105db, so in this scenario it looks like 60w is enough. Is this a correct conclusion, or am I missing something? Thanks

 

[GrimSurfer]

I'd run the calculation with a speaker sensivity in the 87-88 dB/W/m range, becausevthese are the average values of most speakers. Why? Because many speaker efficiency ratings published by manufacturers are quite optimistic. This means that 75W could translate into something closer to 200W.

There is also a difference between dynamic peaks of ~106 dB (which aren't dependent on RMS power) and sustained reference levels of 85 dB (which do).

Also, you're aware that the amp wattage quoted is likely in RMS at 8 ohms nominal, right? Not all amps double their wattage at 4 ohms, so this needs to be taken into account if you ever see a time in which speakers lower than 8 ohms are used.

Next, since seating 14' back suggests a long room, there are sonic benefits to moving the speakers out from the wall. This will drive up power requirements.

Even with all of this taken into account, it is true that people often buy far more wattage than they need (and companies go big on power at the expense of quality, quality sound... this is particularly the case in HT, where many consumer units are of notoriously poor quality or performance). A solid and stable 100Wpc is a lot of power.

 

[Dj7675]

I should mention, speakers are 8ohm. Speakers are Diysoundgroup 893 speakers, and my understanding is the sensitivity is accurate in this case. Would I be correct guess some receivers could do 60w rms all channels? Something like a Denon x7200/x8500 or possibly even the Denon x6300-X6500. Just trying to figure out if I would need external amplification or not.

 

[GrimSurfer]

I wouldn't place any bets wrt the actual sensitivity or impedance of a diy speaker. And that's not even dealing with the issue of impedance curves or phase changes, which can have a massive impact on power needs.

Even if I had the driver specs/test results, so much could change with cabinet size, structure, xover etc.

Look carefully at the specs of what you're shopping. Are they one channel, two channel or all channels driven, RMS? Chances are they're rated at 1 or 2 channels driven.

You can probably tell that I take a conservative approach to all this. My preference is to spend time on nailing down the requirement (needs, not wants), do research, buy and enjoy. I have little time personally for trying to tweak Ill considered purchases to work. And I hate having to buy the same thing twice.

 

[Dj7675]

I wouldn't place any bets wrt the actual sensitivity or impedance of a diy speaker. And that's not even dealing with the issue of impedance curves or phase changes, which can have a massive impact on power needs.

Even if I had the driver specs/test results, so much could change with cabinet size, structure, xover etc.

Look carefully at the specs of what you're shopping. Are they one channel, two channel or all channels driven, RMS? Chances are they're rated at 1 or 2 channels driven.

Manufacturers sure don't make it easy figuring out all channels driven. And yes, the new 1 channel driver/10% distortion spec is completely ridiculous. How is that spec remotely helpful? Marantz/Denon, on their receivers now have a 70% guarantee. What that means I believe is whatever their 2 channel rating is, they guarantee 70% of that in 5 channels driven. It still amazes me that if they are offering a 9/11/13 channel amps in their receivers, why not show all channels driven? Instead you have to search for bench test to try to guess. For example, the Denon x7200 bench test at SV:
https://www.soundandvision.com/content/denon-avr-x7200w-av-receiver-test-bench
It shows:
7 channels driven continuously into 8-ohm loads:
0.1% distortion at 113.7 watts
1% distortion at 124.0 watts
Read more at https://www.soundandvision.com/content/denon-avr-x7200w-av-receiver-test-bench#mAQpSpLmFYMgTW1m.99
It has 9 amps so it seems reasonable that it would do over 60w in 9 channels driven. The latest flagship from Denon, the x8500 has 13 channels but there are no detailed bench tests anywhere. It seems reasonable I think it would do 60w rms with 13 channels, but who knows!

 

[GrimSurfer]

Manufacturers sure don't make it easy figuring out all channels driven. And yes, the new 1 channel driver/10% distortion spec is completely ridiculous. How is that spec remotely helpful? Marantz/Denon, on their receivers now have a 70% guarantee. What that means I believe is whatever their 2 channel rating is, they guarantee 70% of that in 5 channels driven. It still amazes me that if they are offering a 9/11/13 channel amps in their receivers, why not show all channels driven? Instead you have to search for bench test to try to guess. For example, the Denon x7200 bench test at SV:
https://www.soundandvision.com/content/denon-avr-x7200w-av-receiver-test-bench
It shows:
7 channels driven continuously into 8-ohm loads:
0.1% distortion at 113.7 watts
1% distortion at 124.0 watts
Read more at https://www.soundandvision.com/content/denon-avr-x7200w-av-receiver-test-bench#mAQpSpLmFYMgTW1m.99
It has 9 amps so it seems reasonable that it would do over 60w in 9 channels driven. The latest flagship from Denon, the x8500 has 13 channels but there are no detailed bench tests anywhere. It seems reasonable I think it would do 60w rms with 13 channels, but who knows!

No, Sir, they definitely don't make it easy.

7x124=868W of power. AB amps have an electrical efficiency of 40-50%. Class D amps, 70% or so. So I would call bullshit on that power rating if it has an AB amp. If it's a class D, it's possible (~1240W consumption). But this isn't counting the power for the DAC, equalization circuitry, video etc.

If we raise the channel count to 13, then the power output at ACD at 60W would be 780. That's equates to a power requirement of about 1600W for an AB amp. Right at the edge of a 15A circuit, not counting the ancillaries. Possible under class D. Still tight with inrush current etc.

I wouldn't use amperage as an indicator of anything but amperage and, perhaps, capacity to drive difficult loads. Heck, I have a 30W 2ch amp that is capable of 30A. Never had an issue driving speakers that dip to 3.7 ohms at 45 degree phase angle. But using that same 30A peak figure to guess what the amp's RMS output is wouldn't be yield anything bankable.

You gotta watch AVR ratings and the manufacturer's who publish them.

 

[Dj7675]

I don't quite follow. The 7x124 is what was measured at SV. The spec from Denon is Power Output (8 ohm, 20 Hz - 20 kHz, 0.05% 2ch Drive)150 W . The amps in the Denon are A/B. Are you saying the measured output from the benchtest at SV can't be accurate (7x124)? A lot of this is new to me but I am learning a lot as I go.

 

[GrimSurfer]

I'm not familiar with the product but, like I said, entirely possible with class D topology. Not apparently feasible if the amp and preamp are class AB.

Was the amp preconditioned or tested cold? Was the amp section tested while running signals thru the other sections or was it run in bypass/direct mode? How long was the full power test? Was the device plugged into a 15A circuit? These things can make a huge difference in the outcome of a test.

Sound and Vision makes money on ad revenue. It doesn't mean that they would intentionally be blatantly dishonest. But there are perfectly legitimate ways to test a component that avoids embarrassing a manufacturer with whom you have a big ad contract.

Now it could be capable of 7x124, but you better not put a lamp or turntable, etc. on that 15A circuit when running at max or something is going to pop. Why? Well, my rough ciphering tells me that it would be drawing over 1736W on a circuit that trips at 1800W. And that's assuming an AB amp with an electrical efficiency of 50%.

 

[KozmoNaut]

Denon is somewhat less deceptive than most in their power ratings. They aren't perfect, but they do publish ratings at "8 ohm, 20 Hz - 20 kHz, 0.08% 2ch", rather than "6 ohm, 1 kHz, 10% 1ch", which I've seen before.

For my Denon AVR-1911, they rate it as such:

While it's not super detailed, they do give you a somewhat decent spec, and then a slightly more marketing fluff spec to compare with.

You also have to keep in mind that your front and center speakers are going to do most of the work. They handle the majority of the signal and all of the main action will be happening at the front, correlated with what you see on screen. The rear and surround speakers are for flavor and ambience, they hardly ever get driven particularly hard.

That is figured into the overall power consumption figure of the AVR, they have a standardized use case, which is assumed to cover the way the vast majority of users will actually use their receivers. Yes, the back/surround speakers can be driven at 90w continuous, but that never happens unless you're specifically running test signals through them. No movie soundtrack puts that much power through anything other than the front+center speakers. The overall power consumption is meant to be a real-world figure, not a theoretical "all channels driven to maximum power" figure.

Putting in my speakers for my 2.1 setup (90dB @ 1w/1m) and my distance (~3.4m), 90w brings me to 105dB continuous, which is solid amount of headroom over the 85dB with 105dB peaks reference level.

I would prefer not to dip below 75w per channel when/if I need to replace my AVR.

 

[GrimSurfer]

Denon is somewhat less deceptive than most in their power ratings. They aren't perfect, but they do publish ratings at "8 ohm, 20 Hz - 20 kHz, 0.08% 2ch", rather than "6 ohm, 1 kHz, 10% 1ch", which I've seen before.

For my Denon AVR-1911, they rate it as such:
View attachment 36822

While it's not super detailed, they do give you a somewhat decent spec, and then a slightly more marketing fluff spec to compare with.

You also have to keep in mind that your front and center speakers are going to do most of the work. They handle the majority of the signal and all of the main action will be happening at the front, correlated with what you see on screen. The rear and surround speakers are for flavor and ambience, they hardly ever get driven particularly hard.

That is figured into the overall power consumption figure of the AVR, they have a standardized use case, which is assumed to cover the way the vast majority of users will actually use their receivers. Yes, the back/surround speakers can be driven at 90w continuous, but that never happens unless you're specifically running test signals through them. No movie soundtrack puts that much power through anything other than the front+center speakers. The overall power consumption is meant to be a real-world figure, not a theoretical "all channels driven to maximum power" figure.

Putting in my speakers for my 2.1 setup (90dB @ 1w/1m) and my distance (~3.4m), 90w brings me to 105dB continuous, which is solid amount of headroom over the 85dB with 105dB peaks reference level.

I would prefer not to dip below 75w per channel when/if I need to replace my AVR.

Excellent post. 100% "good oil", as they say.

I'd be delighted if Denon and others could include terms like "RMS" or continuous in their ratings. That said, I do accept honest statements/specs that show biasing wrt front channel ratings because the rear and height effects speakers aren't equally driven (or need to be).

As for "real world", if only we had some assurance that Denon's "real world" was the same as Yamaha, Anthem, Panasonic et al....

 

[Dj7675]

Thanks for the comments and the real world practical use thought that only in bench tests will the surround channels be needing that much power. Also, another upper end marantz receiver that Audioholics reviewed.
https://www.audioholics.com/av-receiver-reviews/marantz-sr8012-receiver/marantz-sr8012-bench-tests
Here were his results:
7 channels 1kHz Psweep 97 watts 8-ohms 1%
Interesting that he noted that it was tested on his 15amp line and that results are generally 5-10% higher with this kind of unit if tested on a 20A circuit vs a 15amp circuit.
Right now I have the NAD T758 V3. It is rated at 60w with 7 channels driven. I don't find it lacking in volume output. On higher volumes I don't think it sounds as good as I would like. Looking at the measurements of the unit I sent in, regarding both the amp and dac measurements, I can see why this might be the case. Or maybe a big case of confirmation bias.. It appears I could get away with 60W, but wouldn't turn away more.

 

[GrimSurfer]

Yeah, using a 20A line is one of the older tricks in the testing book.

Now I get how such a line can offset the need for regulated power to avoid dips etc., but it does result in higher than typical outputs and sometimes prevent the power supply from sagging.

Having a 20A circuit run in a home isn't a big deal. I have several such circuits. It's just a matter of having space on the panel, capacity on your service and paying an electrician to run 10ga instead of 12ga wire. The heavier wire doesn't snake easily, but that's the electricians problem. Don't worry, you'll get the bill. Ha ha.

 

[Julf]

Yeah, using a 20A line is one of the older tricks in the testing book.

I assume that is US 110 V (so 1650 W vs. 2200 W)? Here in continental Europe the standard domestic connection is 10 or 16 A 230V, so 2300 or 3680W.

 

[GrimSurfer]

I assume that is US 110 V (so 1650 W vs. 2200 W)? Here in continental Europe the standard domestic connection is 10 or 16 A 230V, so 2300 or 3680W.

110-120. Some utilities in North America quote 115V plus or minus a certain percentage. In Japan, it's a bit lower... 100V if my memory serves.

Europe is, as you very correctly point out, roughly double the voltage of North America with a reduction in amperage.

 

[Putter]

I would prefer not to dip below 75w per channel when/if I need to replace my AVR.

I would prefer my AV receiver had preamp outputs so I could use a separate power amp for some or all of the 5/7/9/11/13?!!! channels.

Dj7675's analysis doesn't take into account the fact that in most cases there is a separate power amp in the subwoofer(s) to do the heavy lifting in the bass frequencies where the power demand is greatest. This is not to excuse AV receiver makers (although obviously most users find them to be adequately powered), but rather to indicate that the picture is more complex than simple ACD, RMS or any of silly measures makers use to inflate power ratings.

 

[Dj7675]

I would prefer not to dip below 75w per channel when/if I need to replace my AVR.

I would prefer my AV receiver had preamp outputs so I could use a separate power amp for some or all of the 5/7/9/11/13?!!! channels.

Dj7675's analysis doesn't take into account the fact that in most cases there is a separate power amp in the subwoofer(s) to do the heavy lifting in the bass frequencies where the power demand is greatest. This is not to excuse AV receiver makers (although obviously most users find them to be adequately powered), but rather to indicate that the picture is more complex than simple ACD, RMS or any of silly measures makers use to inflate power ratings.

Thanks for bringing that up. For me, I have 2 18 inch sealed subs and they would be crossed at 70-80hz.

 

[amirm]

Having a 20A circuit run in a home isn't a big deal. I have several such circuits. It's just a matter of having space on the panel, capacity on your service and paying an electrician to run 10ga instead of 12ga wire. The heavier wire doesn't snake easily, but that's the electricians problem. Don't worry, you'll get the bill. Ha ha.

14 gauge is for 15 amp and 12 gauge is for 20 amp in US for typical domestic runs. I had my entire home run as 20 amp against grumbling from my electrician as you indicate.

 

[KozmoNaut]

I would prefer my AV receiver had preamp outputs so I could use a separate power amp for some or all of the 5/7/9/11/13?!!! channels.

Yes. You have to go way too high in price to get pre-outs.

Actually, I would prefer if preprocessors with no power amplification were available as widely as one-box receivers, and at lower prices to reflect the reduced complexity.

I don't need to buy new power amplification, just because I want support for a new codec or streaming service or something. And I certainly don't need a full 7 channels of amplification for my 2.1 setup.

But no, they're "premium segment products", and are generally neglected when it comes to updating product lines.

 

[GrimSurfer]

14 gauge is for 15 amp and 12 gauge is for 20 amp in US for typical domestic runs. I had my entire home run as 20 amp against grumbling from my electrician as you indicate.

You're right, @amirm. I was more conservative than the National Electrical Code, which is conservative enough already!

No wonder my electrician grumbles! (although he did recommend 2 x 10 ga wires for my hw heater, which is a 2 x 20A circuit)

20A sockets are becoming more common in new builds and renos. My kitchen reno a few years ago had to be all 20A to meet local code.

 

[MZKM]

Keep in mind that calculator assumes -6dB per doubling of distance, which is true for outdoors/anechoic, indoors it is more like -3dB to -4dB (room dependent). Use something like 2/3 or 5/8 the actual distance for a more accurate calculation.

This calculator does not account for room acoustics, amplifier dynamic headroom or off axis listening positions.