Determining required headroom

I’ve heard Paul say that you want some headroom in your amp—at least 20%. I have some very basic questions.

How do you know how much wattage you need and how much headroom is left? For example, I listen to mainly vocal or non-symphonic classical music and jazz. I have a First Watt J2 amp which I think produces 20wpc driving my relatively efficient Tannoy loudspeakers (spec is 92dB sensitivity). So my question is: do I need more power? How can I tell?

In a separate email Paul had said “Our FR30s are 88dB when you put in 1 watts. When a speaker is this sensitive or more, you’ll rarely ever exceed 100 watts.” So with 92dB I’d need at most 40W or so.

So to leave 20%, that means I need an amp that can do 50W. Is my analysis correct?

Thank you.

I’m not accustomed to seeing headroom discussed in terms of steady state power delivery. Headroom in the context I’ve seen it discussed is dynamic, which is a very different question. Many amps can deliver short bursts of power over the nominal steady state power spec, and that can be quite design specific. The J2 is a Nelson Pass design (I’m a former M2 owner). Might make sense to consult with Nelson via First Watt. He’s known for being generous with his time and talent. He can tell you everything about the dynamic power delivery characteristics of the J2 you’d ever want to know, for sure. My two cents …

Do you have a dB meter or a dB app on a smartphone?? Do you listen at 92dB? (You shouldn’t)
There are so many factors. How big is your room? How close do you sit to your speakers? Is your system dynamic enough for your taste? Do you regularly end listening sessions because of listening fatigue?

Yes I wouldn’t want to listen at 92dB. But I don’t understand what your comment has to do with figuring out how much headroom I need. Let’s say I listen at 80dB (that’s approx 16x less loud), what should my amp rating be?

Sorry. I didn’t think you were specifically asking about “headroom”—whatever that is.
I think of headroom as the ability to achieve an ultimate (maximum, but rarely desired) volume without audible clipping.
You quite likely have all you need with your J2/Tannoy pairing.

So why do we have these giant 200wpc amps? To drive inefficient 80 dB sensitivity speakers?

Well, yes. Or to fill large rooms, etc.
I have found that in many cases, but not all, higher wattage amps can produce more dynamics within a given volume–if that makes sense.
That said, I recently went from 500 Class AB watts to 50 Class A watts and I absolutely prefer the little amp. (Both amps are Pass Labs.)

1 Like

This may not be of much help but I spent $30 on a Kill A Watt meter to help assess regenerator sizing. A pair of M1200s (stupid overkill but sounds good), a GCD, and an 11W source barely pull 85W at listening levels much higher than I’d typically listen to driving 90dB speakers.
You might find plugging just your amp into something like the Kill A Watt can provide insight into your needs. The J2 manual specs 200W power consumption, which I assume is at the rated output 30W @ 8 ohms. I don’t know if power in vs out is linear but you might find you’re using less of the amp than you think.

Does the kill 0 watt meter measure dynamic peaks or just rms, I ask because when I ran a Sunfire sub and my apogee duetta 2 speakers powered by my krell amp the lights in the room were blinking just a little at high volumes, with dedicated 20 amp circuits with 10awg wire to each piece of equipment. I’m sure the Sunfire sub had a lot to do with power consumption with the type of power supply that’s used.

Paul likes rules. I’ve heard classic Tannoy speakers with 8w EL84 amps sound wonderful with without running out of gas. The First Watt J2 (25w Class A) seems like an ideal amplifier.

If it sounds good, I wouldn’t worry about it.

1 Like

Well you know how it is… you wonder whether the sound could be better with a different amp :grinning:

FWIW, I recently bought Pass Labs X260.8s but seriously considered XA60.8s. Same chassis size, was critical to me. The 60.8 being 60w class A and the 260.8 being 260w a/b with the first 34w, or so, class a. I have never seen the needle move out of class a yet, not a squiggle. Now, I’m more than happy. I’ll never know for sure what would have been best. Doesn’t matter now, still interesting.


When I have headroom issues,
no problemo…
time to call in the Pro! (…sorry, couldn’t resist) :blush:


RMS only

The XA60.8s are not as dynamic as the X260.8s. After listening to both, I found the bass deeper and tighter at any volume on the X260.8s


I’ve stopped wondering about such things. There’s always something better, don’t need to have it.


Ah you’re a wiser man than I!

For me, the best method is:
A) figure out how far you amp + speaker system can go. To do this, bear in mind that each 3dB increment or decrease, doubles or halves the watts your amp is outputting. So, if our amp is 18watt rated, and your speaker is 92dB efficient at 1meter, then you could theoretically up to 105SPL (92 is 1w, 95 is 2w, 98 is 4w, 101 is 8w, 104 is 16w).
B) measure the SPL at normal listening measures. To do this, use a SPL meter or a phone app. Begin playing music at normal levels at your listening position. Then, turn one speaker off, and measure the level of the other speaker at a distance of 1 meter from that speaker
C) calculate how many watts you are using, taking into account your speaker sensitivity. For instance, should you measure 81dB, and your speaker is 92dB at 1watt, then you are using 0.125watt (92db is 1watt, 89dB is 0.5watt, 86dB is 0.250watt, and 81dB is 0.125watt)
D) Calculate your headroom, as the difference between your listening level and the max SPL. In my example, it would be roughly 15dB, which is a lot. In your real conditions, it should be even more, as normally you would measure around 75dB at listening level, leading to roughly 20dB of headroom.

There are some trick questions regarding how your speaker sensitivity is rated (as per watt, ou as per 2.83v, which is 1watt only at 8ohms impedance). But I think the method above should give you a sufficient estimate.

Hope it helps.