How many watts per channel to hit reference?

Harkon321

Well-known Member
Thinking of future upgrades, more specifically a Power Amp. This would probably be in the new year, as there are a few things I want to do first.

Currently I run my 7.1.4 system from my Denon 4400 with a smaller Audiolab Mono amp to power the two back surrounds.

Speakers are all M&K Sound.
LCR are M&K IW150 mk3, Surrounds will be MK IW150T (currently using some Monitor Audio as a stop gap), Back surrounds IW95 and Atmos are all IW85s. All effienet speakers I believe.

I imagine the most sensible step is to buy a 3ch amp to power the LCR and leave the rest on the Denon. Alternative would be 5 or 7 ch, as I'm not ready to go the separates route yet.

Is there a layman's way to calculate the wattage needed per channel to hit reference, as I think it could be very easy to over amp surround and atmos channels that don't need it?
 

Conrad

Moderator
Plenty of calculators online, have a look at this one for example: Amplifier, Speaker & SPL Calculator - Geoff the Grey Geek

For me, with my speakers, at my distance I need under 200w to hit reference (105dB from a main). But with 300w I only get 108dB so once you get close to reference you need a lot more watts to increase by even a few dB. To hit 115dB from my mains for example I need 1600w. Although that's in free air.

I think @Mr Wolf has a calculator as well.
 

Mr Wolf

Well-known Member
I have a detailed spreadsheet system power calculator but I'm now finding basic rules of thumb work well for most situations.

There are three components to it:

1. Speaker sensitivity i.e. the SPL that 1W of power (2.83V into 8-Ohms) gives you at a 1M distance

2. Amplifier power gain - the dB gain you will get from the lowest maximum amount of wattage that could be made available to drive that speaker at any point. Using a 5-channel driven test figure is a useful worst case scenario as in practice no more than the equivalent of 4 channels are driven fully at any one point due to surrounds have combined maximum total SPL output of one LCR channel. The dB gain = 10 x LOG (Number of Watts available). Your X4400 will get you about 19dB.

3. The SPL loss between 1M and the MLP due to dispersion. This is 5-7dB in most rooms at typical seating distances.

The maths of THX Ultra certified systems for the LCRs look like this.

They take an 89dB+ sensitivity twin woofer speaker and feed it 100W of clean power which gets it to 109dB. If you're using an D&M AVR, you would need a Denon X6700/X8500/SR8015 to do this. They then take away 6dB for maximum dispersion loss from LCRs to MLP in a 3,000Ft3 room to get 103dB. 103dB is actually true cinema reference - apparently Dolby measured it incorrectly 2dB higher when they came up with it.

Note that this is on a conservative continuous RMS power basis - peak power output would be 3dB higher and, due to capacitance, short term bursts have even more power.

All THX rated LCR speakers seem to have twin woofers that are at least 6.5". Presumably these are to cover the most demanding first octave as it gives them 3dB more sensitivity there. I don't think 100W fed into a bookshelf speaker would work for the bass no matter what the sensitivity rating says as they're usually an average from say 300-3,000Hz.

Obviously if you have a power amp with 200W of clean power available and your speakers can handle it then you could drop back the sensitivity requirement by up to 3dB and still get the same result but that's a harder, hotter and more expensive way to do it.

If you're listening at -12dB on a system like this then you would need only 10W of power per channel which is why AVRs work extremely well for most people that use sensitive speakers in normal sized rooms. This is exactly what I do with 89-90dB twin woofer speakers up front and a beefy 140W/channel AVR.
 
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Harkon321

Well-known Member
If I use a Power Amp for the LCR does this take load away from the Denon and allow more wattage for the surrounds, or are they getting the same amount regardless?

The LCR are 90db sensitivity. The fact that they’re 4ohm makes them harder to drive doesn’t it?
 

Gasp3621

Distinguished Member
I have a detailed spreadsheet system power calculator but I'm now finding basic rules of thumb work well for most situations.

There are three components to it:

1. Speaker sensitivity i.e. the SPL that 1W of power (2.83V into 8-Ohms) gives you at a 1M distance

2. Amplifier power gain - the dB gain you will get from the lowest maximum amount of wattage that could be made available to drive that speaker at any point. Using a 5-channel driven test figure is a useful worst case scenario as in practice no more than the equivalent of 4 channels are driven fully at any one point due to surrounds have combined maximum total SPL output of one LCR channel. The dB gain = 10 x LOG (Number of Watts available). Your X4400 will get you about 19dB.

3. The SPL loss between 1M and the MLP due to dispersion. This is 5-7dB in most rooms at typical seating distances.

The maths of THX Ultra certified systems for the LCRs look like this.

They take an 89dB+ sensitivity twin woofer speaker and feed it 100W of clean power which gets it to 109dB. If you're using an D&M AVR, you would need a Denon X6700/X8500/SR8015 to do this. They then take away 6dB for maximum dispersion loss from LCRs to MLP in a 3,000Ft3 room to get 103dB. 103dB is actually true cinema reference - apparently Dolby measured it incorrectly 2dB higher when they came up with it.

Note that this is on a conservative continuous RMS power basis - peak power output would be 3dB higher and, due to capacitance, short term bursts have even more power.

All THX rated LCR speakers seem to have twin woofers that are at least 6.5". Presumably these are to cover the most demanding first octave as it gives them 3dB more sensitivity there. I don't think 100W fed into a bookshelf speaker would work for the bass no matter what the sensitivity rating says as they're usually an average from say 300-3,000Hz.

Obviously if you have a power amp with 200W of clean power available and your speakers can handle it then you could drop back the sensitivity requirement by up to 3dB and still get the same result but that's a harder, hotter and more expensive way to do it.

If you're listening at -12dB on a system like this then you would need only 10W of power per channel which is why AVRs work extremely well for most people that use sensitive speakers in normal sized rooms. This is exactly what I do with 89-90dB twin woofer speakers up front and a beefy 140W/channel AVR.

The 6000 range is not really going to make any difference power output wise to 4000. They use same two 15,000uF capacitors in both models and powersupply is not much larger. There is like 10-15w difference at best to 4000 range when comparing 2-7channels continuosly tests. I can see from Audiovision site they tested the X4400H which put out 7ch 99w for 4ohm load. X6500H did 100w for same test. For 5ch 116/123w (6ohm), for 7ch 83/99w (6ohm), for 2ch 207/223w (4ohm). See how tiny the differences are, that is basically within the individual unit/testing protocol margin as i see X4700H measuring ~10w worse than X4400.
 
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rccarguy2

Well-known Member
If I use a Power Amp for the LCR does this take load away from the Denon and allow more wattage for the surrounds, or are they getting the same amount regardless?

The LCR are 90db sensitivity. The fact that they’re 4ohm makes them harder to drive doesn’t it?

Yes the more channels the AVR powers, the more it drops, so if you have power amps driving speakers you get more power from the AVR powered speakers.

Here's the older version of yours, you can see the more you connect the lower it is

 

Mr Wolf

Well-known Member
If I use a Power Amp for the LCR does this take load away from the Denon and allow more wattage for the surrounds, or are they getting the same amount regardless?
Yes, it make more power available to them as it will reduce the current demand on the shared power supply.

The LCR are 90db sensitivity. The fact that they’re 4ohm makes them harder to drive doesn’t it?
Potentially but it's not usually an issue for people that have mid-range upwards AVRs and efficient speakers like you.

First understand that the 4-Ohm rating is just a nominal average. In practice all speakers' impedances vary massively throughout the frequency range - your speakers might range from say 3-16 Ohms. My 90dB B&W mains are 8-Ohm rated but dip as low as 3.1 Ohms at one point (see chart below).

DM603FIG1.jpg


Low impedance dips can draw more current to maintain the amps' output voltage to the speaker and if insufficient is available then you have a problem but this is only ever likely to be at the amp's maximum limits.

In practice, the easiest way to cover off this risk is simply to allow a few dB more headroom. Having 3dB (=100% more watts) power headroom is more than enough to cover a 50% drop in impedance. Most people's AVRs give them way more than this e.g. I have at least 13dB headroom across every speaker channel from my AVR. Using a power amp with twice as much power would only give me 3dB more headroom. Interestingly, in commercial cinema Atmos systems Dolby specifies a minimum 3dB power headroom.
 

DavidT

Well-known Member
Yes, it make more power available to them as it will reduce the current demand on the shared power supply.


Potentially but it's not usually an issue for people that have mid-range upwards AVRs and efficient speakers like you.

First understand that the 4-Ohm rating is just a nominal average. In practice all speakers' impedances vary massively throughout the frequency range - your speakers might range from say 3-16 Ohms. My 90dB B&W mains are 8-Ohm rated but dip as low as 3.1 Ohms at one point (see chart below).

DM603FIG1.jpg


Low impedance dips can draw more current to maintain the amps' output voltage to the speaker and if insufficient is available then you have a problem but this is only ever likely to be at the amp's maximum limits.

In practice, the easiest way to cover off this risk is simply to allow a few dB more headroom. Having 3dB (=100% more watts) power headroom is more than enough to cover a 50% drop in impedance. Most people's AVRs give them way more than this e.g. I have at least 13dB headroom across every speaker channel from my AVR. Using a power amp with twice as much power would only give me 3dB more headroom. Interestingly, in commercial cinema Atmos systems Dolby specifies a minimum 3dB power headroom.
How do I calculate the headroom on my 5.1 system?
 

Mr Wolf

Well-known Member
You need to take away 105 from the output capability at your listening position and compare this capability to your listening level.

Output capability at MLP = Speaker sensitivity @1W (usually 85-90dB) PLUS Amplifier gain (use 5 channels driven which is usually 18-20dB for mid to upper AVRs) MINUS Dispersion loss from 1M to MLP (usually 5-7dB depending on distance/room size).

Example:

89dB speaker sensitivity + 18dB amp gain (e.g. Denon X3700) - 6dB (3,000Ft3 room) = 101dB.

101dB - 105dB = -4dB capability

At a typical -15dB maximum listening level you would have 11dB of dynamic headroom.
 

rccarguy2

Well-known Member
I get this from my audiolab 8000sx amps and Dali alteco.

With svs prime elevation it's 99.5db
 

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Fred777

Active Member
So, just to check my understanding and application @Mr Wolf ....

My KEFs are rated at 87dB (2.83V/1m) sensitivity (8 ohms) and I'm running a Denon x1500H which is rated a measly 80W for 2ch driven 8 ohm. Running 5.1 all KEFs.

For simplicity's sake, we'll say my MLP is ~6 feet from the speakers (it's actually 7.2 feet).

That means, at 3 feet (1m) 87dB of SPL is achieved with 1 watt of power. If I take that measurement (and go off the ~4dB decrease for every doubling of distance in a typical room) I would have 83dB (87dB - 4dB) of SPL at a distance of 6 feet?

Building on from that, every doubling of power (watts) is about a 3dB increase in SPL? So, it looks like this at 6 feet from the speaker:

83dB with 1 watt
86db with 2 watts
89db with 4 watts
92db with 8 watts
95db with 16 watts
98db with 32 watts
102db with 64 watts
105db with 128 watts

So to hit 85db is no real issue, but to hit big peaks (say 105db) at that level is basically impossible for my AVR without quite a bit of distortion (not that I'd want to anyway, be deafening).

If I never listen to movies above say, -10dB to -15db from reference, that means my AVR is fine power wise? I can't find specs for my AVR with 5 channels being driven, but assuming peaks of 95dB, it sounds like it's ok (although nearing it limit with all 5 channels I'd assume).
 

Mr Wolf

Well-known Member
Your general understanding is correct but there is a bit more to it.

D&M's higher range models tend to have larger power supplies relative to their amplifiers so they guarantee these to have at least 70% of the quoted 2 channel power output still available when 5 channels are driven. Your X1500 is not one of these higher range models so it's fair to assume that the power is probably less than 56W (70% x 80W) with 5-channels driven. Let's say it's 50W into an 8-Ohm load.

50W of power gets you exactly 17dB of amplifier gain over 1W. So your 87dB speaker should generate 104dB at 1 metre in a ground-plane environment (e.g. outside, or in a quasi-anechoic chamber).

If you took that speaker and put it in a room close to a wall (say within 1 metre) like most people do you should get at least 3dB more SPL at 1 metre due to additional sound reflected back from the boundary. So now your speaker is producing 107dB at 1 metre in a room with a wall behind it.

When you move away from the speaker you get dispersion loss as the sound waves spread out and pressure reduces. If the only sound you were hearing was from the speaker and the wall behind it you then would lose 6dB per doubling of distance and in an extremely large room this figure may be accurate (6dB is the assumption required when system power specifying to Dolby's Atmos commercial cinema standards).

In smaller domestic rooms that loss per distance doubling is typically 3-5dB and varies according to the size of the room, the listening position's proximity to boundaries and how reflective the boundaries are. A well treated room will have less boundary reflections and greater dispersion losses. Anyway, let's say the dispersion loss is 4dB at your circa 2 metre MLP position.

So now you're at 103dB at your MLP but this is without any dynamic headroom and running a system to its limit is not recommended. The minimum headroom that is recommended by Dolby is 3dB so this takes your maximum output down to 100dB at the MLP. In your case I would allow an extra 6dB of headroom beyond this, being 3dB more for the fact that your Q350's mains' minimum impedance is 3.7-Ohms and your AVR will probably be current limited due to the size of its PSU and a further 3dB due them having a single woofer (single woofer speakers are not capable of maintaining their sensitivity/efficiency at lower octaves and have 3dB less sensitivity in this region compared to a twin woofer speaker). This total 9dB headroom takes your safe maximum output down to 94dB.

If your AVR is calibrated to 85dB reference at 0dB volume, 94dB peak output equates to -11dB maximum volume which for most people is enough.
 
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Gasp3621

Distinguished Member
Your general understanding is correct but there is a bit more to it.

D&M's higher range models tend to have larger power supplies relative to their amplifiers so they guarantee these to have at least 70% of the quoted 2 channel power output still available when 5 channels are driven. Your X1500 is not one of these higher range models so it's fair to assume that the power is probably less than 56W (70% x 80W) with 5-channels driven. Let's say it's 50W into an 8-Ohm load.

It´s still the X serie range (Denon doesn´t sell many S range receivers in UK/EU which has lower quality components), so the 70% guarantee should be applied to this aswell. Example Marantz SR5015 is identical to Denon X2700H and Marantz gives the 70% guarantee for it so it applies to Denon aswell. Now if we compare Denon X1x00H and X2700H there is almost nothing between them. Same powersupply and slightly larger caps (12,000uF vs. 10,000 uF) on the 2000 serie.

Denon X1200W measured (0,1% THD) this would apply to that X1500H aswell:

5 Channels Continuously Driven, 8-ohm Loads 69.9 watts
7 Channels Continuously Driven, 8-ohm Loads 47.4 watts


Denon X1500H - 5channels driven 4ohm - 84w, 5channels driven 6ohm - 79w (Audiovision)
 

Mr Wolf

Well-known Member
It´s still the X serie range (Denon doesn´t sell many S range receivers in UK/EU which has lower quality components), so the 70% guarantee should be applied to this aswell. Example Marantz SR5015 is identical to Denon X2700H and Marantz gives the 70% guarantee for it so it applies to Denon aswell. Now if we compare Denon X1x00H and X2700H there is almost nothing between them. Same powersupply and slightly larger caps (12,000uF vs. 10,000 uF) on the 2000 serie.

Denon X1200W measured (0,1% THD) this would apply to that X1500H aswell:

5 Channels Continuously Driven, 8-ohm Loads 69.9 watts
7 Channels Continuously Driven, 8-ohm Loads 47.4 watts
Thanks, that's good to know although 7-channels driven test results are meaningless as in practice no more than the equivalent of 4-channels are ever driven to their limits simultaneously by the source material. Anyway, using 56W (70% x 80W) or 69.9W in the calculations would generate 0.5dB and 1.5dB more output than 50W so maybe a -10dB maximum safe volume setting is more accurate here.

Power capacitance has no impact at all on continuous power output results but in practice helps provide current to cover short transient peaks so reduces risk of compression. Interestingly, I saw a video recently in which Anthony Grimani said that he's currently working with CEDIA on a proposal to introduce CEA-2010 style burst testing for amplifiers similar to subwoofers which should better reflect real world output performance capability. This is test where power capacitance should have a major impact. They're also trying to get away from watts as its confuses people due to how it varies with speaker impedance. Under the proposal, amps may receive maximum dB gain ratings for bursts at different impedances which you simply need to add to the speaker sensitivity ratings to get 1M ground-plane output figures. I really like the idea as the value of all channels driven testing is very limited and misunderstood.
 

Gasp3621

Distinguished Member
Yep, Gene is proposing this as he knows the ACD has very little to do with real world usage:

“In addition to a 2CH driven, full bandwidth rating, we'd like to take the power spec one step further by proposing an additional power rating as follows for AV receivers:

3CH driven, full power bandwidth, 8 ohms, at specified % THD+N (max 0.1% THD+N) with remaining channels driven at 1/8th power.

Alternatively, the manufacturer could provide a guarantee that their product can produce 70% of their 2CH driven figure with up to five channels driven. This is currently what Sound United specs for their Denon and Marantz AV receiver products.

Having this data will prove that the AVR has enough juice in its internal power supply to handle a real load condition while maintaining at least 70% power rating across the 3 front LCR channels.”



Gene is already using CEA-2006 Dynamic Power measurements with av-receiver measurements and said it`s more closer to real world program material than ACD tests.
  • Dynamic PWR - 1kHz CEA-2006 Burst Method testing. This is a dynamic power measurement adopted from the car industry similar to IHF method only a bit more difficult for an amplifier and more representative of real musical content.


Gene:

The average consumer may be tempted to look for the two-channel rating system to simply apply to all channels, resulting in an ACD (All Channels Driven) power rating. While this is understandable, it’s unlikely you’ll ever need to drive all channels at full range simultaneously in real world conditions. Rear channels in a surround format generally only receive a fraction of the information or range of the critical front and center channels. As Audioholic’s founder Gene DellaSala has pointed out:

“It's particularly impractical to rate ACD, especially in products with more than 7 channels of internal amplification because they will often exceed the available power from your wall outlet even if they were capable of delivering it.”
 

Mr Wolf

Well-known Member
Gene is already using CEA-2006 Dynamic Power measurements with av-receiver measurements and said it`s more closer to real world program material than ACD tests.
Yes I know, he's been doing that for ages and it's very revealing. For example, in his review of the 1st generation Yamaha Aventage RX-A3000 he found it to have more real world dynamic power output than a 7-channel Emotiva UPA-7 power amp.


I was really pleased to see this because I'm fairly sure this AVR it has a similar amp section as my RX-V3900 from the previous model year.
 

Fred777

Active Member
Your general understanding is correct but there is a bit more to it.
Thanks for that detailed explanation, very helpful. So essentially, assuming a movie is mastered 'correctly' in relation to '0' (85dB) reference, I would likely start to introduce compression/distortion if I push the volume beyond say, -10dB from reference, during scenes with volume peaks?

Also, I always though that Audyssey calibrates to a 75dB reference, instead of 85db? Whenever I play a test tone via the AVR on '0' my SPL meter reads ~75dB.
Or are the internal test tones set to 75dB, but when you play a movie, it is actually ~85dB on reference?


It´s still the X serie range (Denon doesn´t sell many S range receivers in UK/EU which has lower quality components), so the 70% guarantee should be applied to this aswell.
Good to know this info as well, cheers.
 

Mr Wolf

Well-known Member
Thanks for that detailed explanation, very helpful. So essentially, assuming a movie is mastered 'correctly' in relation to '0' (85dB) reference, I would likely start to introduce compression/distortion if I push the volume beyond say, -10dB from reference, during scenes with volume peaks?
Yes.

Or are the internal test tones set to 75dB, but when you play a movie, it is actually ~85dB on reference?
This is correct. In effect, Audyssey calibrates the -10dB volume setting to 75dB by playing a -30dBFS input signal. It does this because 85dB would be too loud to be comfortable in practice.

Note that the calculations I illustrated were for your front LCR channels as these are capable of the largest 20dB (i.e. 105dB at reference) peaks so are usually (but not always) the limiting factor on system output capability. Bed level surrounds are capable of 17dB peaks and are usually closer to the MLP so their maximum peak power demands are less. Atmos channels have maximum 14dB peaks so need even less power. This is why it usually makes sense to use high sensitivity, twin woofer speakers on the front channels if you want to listen at loud levels.
 

Fred777

Active Member
This is correct. In effect, Audyssey calibrates the -10dB volume setting to 75dB by playing a -30dBFS input signal. It does this because 85dB would be too loud to be comfortable in practice.
I read somewhere that they used to run the test tone during setup at 85dB but got complaints that it was too loud, so they altered it to 75dB. What is super confusing to most, and me for a while, is that whenever you run a test tone out of the AVR to 'check levels' it does so at 75dB at 'reference', but as you affirmed, movies actually play 85dB at reference during playback...

I think this means that some people (not knowing this) then go in after auto setup and increase the individual speaker levels to read 85dB, up from 75dB, on their SPL meters, which means their new 'reference' is actually 95dB... If this is the case, it makes sense why some people say they never listen past -20 to -30 as they actually have increased everything by 10dB!
This is why it usually makes sense to use high sensitivity, twin woofer speakers on the front channels if you want to listen at loud levels.
Sure does. Even though my KEFs are less sensitive than my previous set (Monitor Audios), I find that I don't actually have to crank it as much because of the added clarity/detail, especially the centre channel, which is now a 6.5" compared to the previous 5.5". But a more powerful AVR is definitely on my list for the future (mostly to run .4 Atmos, subject to WAF of course ;) )
 

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