Amplifier Selection: Things that matter

[My adventures in stereo]

I have been putting together a Stereo system over the past few years
It is a book shelf sub system
I have been building up a collection of high dynamic range media & have often felt a need for more head room
Noticed that with a single NAD c298, aiming for roughly 85 db, as I pushed the volume higher, the sound was getting harsh

Had similar experiences with Audiophonics MPA 400 ET, hence I switched to NAD c298, with a marginal improvement in head room
The specifications provided by the manufacturer for my speakers recommended of 50- 150 Watts
Which my amplifiers exceeded
My SVS PB 2000x3 provided the bass grunt below 80 hz, hence the lack of head room was frustrating

Going through the NAD C298 review on ASR, Kal Rubinson was an early adopter & was using them in bridged mode with good results
This had got me interested in going that route
I was advised by many here against going this route, as an expensive misadventure with no audible benefits

Recently picked picked up a second c 298 & got it setup in bridged mode
I had a 3-6 db advantage in head room, depending on the recording
The transients & micro dynamics were much more discernible
I was enjoying the system much more

This got me thinking about how much head room you need, with high dynamic range source material
A few youtube videos were very useful, found through threads in ASR

1 Audioholics : What Specs Really matter in Audio amplifiers
This is a 3 part series, which provides a lot of insight in to amplifier ratings
2 Erin : How much power do you really need?
3 Harbeth How much Power do I Really need
4 Crown Power Calculator

Dynamic power requirements can be much higher than stated in the specs
The maximum quoted power for a speaker, is vaguely stated, objectively poorly calculated & defined
You need to pick a amplifier which has good basic characteristics like
- Flat Frequency response
- High SNR
- Have adequate power output based on your listening distance, speaker sensitivity, desired listening level and have enough head room to support the dynamic range of your listening material

This was the calculation, I got for my speakers

I hope this will be useful to others, planning a system


Present System
Revel M 126 Be
NAD c298 x2 Power amps ( the second power amp, is my latest acquisition)
MInidsp SHD
SVS PB 2000x3

Input is through
CD's
SACD
Vinyl
Tidal/ spotify

 

[Titurel]

To answer this question sensibly, it would helpful to know what your taste in source material is. "Classical" music, with its wider dynamic range, may need that much headroom, whereas popular probably doesn't. Of course, with Classical you'd likely want lower average levels, and reducing average levels to around 70db gets you into much saner territory for your rig.

I also wonder, with big current events (like big bass transients) being diverted to your subs, whether the harshness you're hearing is actually from over-driving your stereo pair (or your ears or room) not from the amp running out of steam. Just a thought...

 

[My adventures in stereo]

I have solved my issues, my approach to the solution
Is what I wished to share here

I listen to a wide range of music, pretty eclectic taste

I had picked up a bunch of living stereo CD & SACD, never enjoyed them till I started using bridged NAD's

 

[DonH56]

Amplifier headroom requirements have been stated many times on ASR and were published several decades ago by the AES, IHF, etc. The rule of thumb I remember and have always used is 17 dB, a factor of 50 times the average power for music. More recent studies indicate 20+ dB, a factor of 100+ in power, for movies, although the loudest parts are likely to be explosions and such wherein clipping is probably unnoticeable. Knowing one's average power needs can be a bit tricky, especially with varying room treatments and speaker impedance over frequency. I designed my system to handle 105 dB/speaker peaks to match the Dolby/THX guidelines, though they assume 85 dB average which is way more than my normal listening level.

What I and many others have stated many times is that most people overestimate their average power and underestimate their peaks.

 

[My adventures in stereo]

I decided to go with 20 dB headroom, to be on the safe side

Manufacturer recommended speaker ratings are misleading
Especially, since they dont mention, how they come across this number
Have not seen any reviews testing for how much power a speaker can safely handle, that would be a useful measurement

 

[amper42]

It's pretty easy to overthink how much power is needed for headroom. If you have a 200W amp like the Purifi design there's no need to worry. Purifi offers all you need for indoor listening in a large residential room. You can navel gaze with the available SPL calculators but if you're exceeding 200W on peaks your next stop is likely the ear doctor.

 

[MaxwellsEq]

Have not seen any reviews testing for how much power a speaker can safely handle, that would be a useful measurement

But unfortunately potentially destructive!

 

[DanielT]

If you don't have a measuring microphone, download a free dB app and measure the sound level at different distances from the speaker. That to see if the listening distance in your listening room matters so much. In most cases, a normally furnished room works like a reverb chamber so there are usually not that big differences. That in itself has a big impact on how much amp power you need.

Edit:
Is your calculation based on one speaker or two?

You have three subwoofers with power on them of 3x 500 watts RMS continuous (1100 watts peak dynamic) working from 80 Hz and down. You have a decent amount of sub amp power.

Do you have HP filter connected so the speakers and your NAD amp take care of everything above 80Hz?

 

[Sokel]

What's left out of the equation most of the times is not only music's dynamic range,distance,needs,desired SLP,etc but also gain losses like EQ,etc.

Subs (if you're into them) help but one must observe the 100-300Hz area (the main bulk of energy) and their absolute seamless integration with the rest of the spectrum above and below.

 

[My adventures in stereo]

If you don't have a measuring microphone, download a free dB app and measure the sound level at different distances from the speaker. That to see if the listening distance in your listening room matters so much. In most cases, a normally furnished room works like a reverb chamber so there are usually not that big differences. That in itself has a big impact on how much amp power you need.

Edit:
Is your calculation based on one speaker or two?

You have three subwoofers with power on them of 3x 500 watts RMS continuous (1100 watts peak dynamic) working from 80 Hz and down. You have a decent amount of sub amp power.

Do you have HP filter connected so the speakers and your NAD amp take care of everything above 80Hz?

I have a spl meter
it is a normally furnished room

My calculation is based on one speaker, the second speaker should add 6 to 9 db of gain

yup , enough sub power there

What's left out of the equation most of the times is not only music's dynamic range,distance,needs,desired SLP,etc but also gain losses like EQ,etc.

Subs (if you're into them) help but one must observe the 100-300Hz area (the main bulk of energy) and their absolute seamless integration with the rest of the spectrum above and below.

The 100 -300 Hz shows smooth response on REW curve

 

[Sokel]

The 100 -300 Hz shows smooth response on REW curve

REW is brilliant but it needs a Multitone test to show that,like the ones Erin does.

Take a look at the Morel speaker he reviewed last.It's FR or compression test does not indicate anything suspicious but the Multitone test exposes these little weaknesses (small in the Morel one) as levels go up.

 

[DanielT]

I have a spl meter

Okay, what does it look like if you measure at 1, 2 or 3 meters from the speakers?

Then compare the results how it looks in theory if you enter 1.2 or 3 meters in your calculator?

 

[Sokel]

Okay, what does it look like if you measure at 1, 2 or 3 meters from the speakers?

Better still,use REW for that,it has an excellent SLP real time chart when calibrated,showing all the parameters and one can use all weightings (except for peaks,that is always Z weighting) .

 

[DanielT]

Smart REW tip.

In any case. The calculator that the OP put in the starting post has the listening distance of great importance because it seems to be based on a theoretical model where no relexes occur, which is not the case in a normal listening room. The results may be more in line with reality if you listen outside, but that's a different scenario.

Thus it becomes very confusing to rely on the amp power calculator if you are to start from the results it gives for what amp power you need for a normal listening room.

I am calculating with 17 dB amplifier headroom instead of 20 dB to get closer to reality when two speakers are used:

Crown Audio - Professional Power Amplifiers | English (US)

www.crownaudio.com