Question Watt calculations and Do I need an amplifier?


Active Member
Hello folks,

  • AVR Denon X4100W
  • Monitor Audio RX6 L/R
  • Monitor Audio RXC
  • Monitor Audio RXFX (Side Surrounds, Dipole)
  • Sub - BK XXLS400 DF
I have recently picked up a C weighter SPL meter and have been balancing channels for 75db with the internal Denon test tones.

As I was looking into SPL meters I also stumbled across watt calculators and the discussions around how many watts are needed for certain db levels and so on.

My first question being is my system, as it is, capable of reference level. With that being 75db and peaks of 105db. I also read that I should have 3db headroom to be on the safe side, so 108db. I am not going to be looking to listen at reference level, most likely - 10db max. But would like to know how powerful or weak my current system is.

Listening position/information - Front Left, RX6

I am only calculating the required watts for my furthest speaker as the rest should require less.



Are the above calculations accurate-ish for the SPL levels I would get from the front left speaker. I included two calculations as the Denon AVR specs (attached below) state 125W 8 ohms and 165W 6 ohms, I wasn't sure if I could take the stated watts at face value for 6 ohms.

Also the AVR, has a 'Dynamic Power' section. Am I correct in thinking this is extra Watts that can be tapped into? Or is it for some other purpose?

If it is extra juice when using the calculator, for my calculations above to reach 108 peak db levels (3db headroom). Would I add on say between 130 - 190 watts, as my speakers are 6ohms, to the amplifier power in the calculator?


If that is how Dynamic power is used would the below calculation be correct?


First cacluation is for the 125w 8 ohm rating on the denon reciever + 160w of Dynamic power.
Second is for the 165w 6ohm rating on the denon reciever + 160w of Dynamic power.

(I split the difference between the Dynamic power ratings of 130w 8 ohms and 190w 4 ohms to get 160w 6 ohms. No clue if that's correct but thought I would ask).

I included both calculations for 8 + 6 ohms just to save the time of me asking again would this calculation now be correct.

The ultimate question!!!

Also, Monitor Audio RX6's state a power handling (RMS) of 125w. If I have understood correctly, it's safer to have a higher W rating on the amp than the speaker, just be careful with the volume.

So given everything am I safe to play my system at a 75db reference level with peaks of 108db (3db headroom) using my Denon AVR and current speakers?

Appreciate any help as I have been doubting what db levels I can play my system at, it's sucking the enjoyment out of movies contemplating this over and over :D


Denon X4100W amp specs:


Monitor Audio RX6 specs:



  • 1607865452385.png
    97.9 KB · Views: 6


The quoted figures for the Denon are for two channels driven. Using all available speakers will considerably dilute that power and would more than likely be in the 70 watts per channel at 8 ohms, maybe even lower. With a full speaker load in a fairly big room in a very active scene the amp could simply run out of puff. At 90dB sensitivity your speakers are quite easy for the receiver to drive under normal circumstances.

Dynamic Power? Not confusing this with Dynamic Volume as I've never seen that on any Denon amp I've owned. There is no hidden power what you hear is what you get.

If you are driving a fully loaded system then many will use a power amp to drive the front three as these are the most important speakers in the set up. The saved output is then shared around the remaining speakers connected to the Denon. A win win situation. A power amp can easily be incorporated into the system as the 4100 has a full set of pre-outs.

If you are using the 4100 for music as well as cinema work then a stereo amp with HT by-pass would be of more benefit than a power amp. Again the saved stereo power output would be shared between the remaining speakers.


Active Member
Ah okay, I didn't realise I was running at such a low wattage with only the receiver when fully loaded.

If I wanted to drive my speakers at their best. Would I be right in thinking I would need a power amp that could supply 125 Watts per channel. So for the L, R and C. That would be a total of 375 Watts for the power amp?

As you said that then mean my surrounds would receive more Watts from the Denon. Would that relieve them enough for them to play at their RMS capabilities with the Denon alone?

Sorry for all the questions, very new to this! :)

I've given myself a budget of £ 2/300, for upgrades. Hopefully that's enough, if not willing to stretch.

Taking the budget into account would it be best for me to get a power amp or stereo amp (with HT by-pass).

Would you also have any recommendations or what I'm looking for in the power amp/stereo amp. I'm finding the specifications they publish very confusing and sly :)

I'll most likely look at used amps to get the best value for money.

Edit: thank you for the help! :thumbsup:


Don't take any notice of the watts required for speakers. There is little point in trying to match the maximum wattage of any speaker to a given amp. The figures that are important is the sensitivity, ohm loading and minimum wattage requirement.

The amp needs to be able to drive the speakers without clipping and this is where the sensitivity comes into play. The higher the dB number the easier for the amp to drive. With most amps and speakers your ears will cry foul long before the speakers actually do.

With a good amp it's how it handles the low end performance of the speaker, that when the ohm loading drops, some 8 ohm speakers can drop as low as 3.2 ohms and the amp needs to be able to sustain these drops without distortion.

All in all you don't have to worry about specifications and for some extent with receiver under full load it goes out of the window. Power amps tend to be more powerful than an integrated amp with HT by-pass as well as considerably cheaper. I would only consider a stereo amp with HT by-pass if you are seriously into music.

I'm running a Denon X6500 which is slightly more powerful than the 4100 with speakers that are somewhat harder to drive than the MAs and I would not have considered a power amp with a 5.1.2 set up as there is certainly enough power on tap for it to fill the room to reference levels. I do though run a stereo amp to drive the fronts for music purposes as I feel the Denon is very poor in this regard.


Active Member
Damn, they really like to milk their specifications.

I definitely won't consider a HT By-pass, not worth it for me at the moment.

I may put the power amp idea to the side for now. But I do like the idea of a stereo amp to drive the fronts. Maybe that's what I was hearing when listening to the odd bit of music through the Denon, when demoing them they sound better.

Thanks for the advice and Happy Holidays!! 🎄

The latest video from AVForums

LG G1 OLED Evo TV and SVS SB-1000 Pro subwoofer reviews, Samsung OLED rumours and more...
Subscribe to our YouTube channel
Support AVForums with Patreon

Top Bottom