# Dynamic Headroom Measurement **URL:** \ **Category:** QA40x\ **Created:** [January 3, 2026, 4:50pm UTC](https://forum.quantasylum.com/t/dynamic-headroom-measurement/2144 "2026-01-03T16:50:41Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![VAR](https://yyz2.discourse-cdn.com/flex032/user_avatar/forum.quantasylum.com/var/32/959_2.png) [@VAR](https://forum.quantasylum.com/u/VAR)\ **Post date:** [January 3, 2026, 4:50pm UTC](https://forum.quantasylum.com/t/dynamic-headroom-measurement/2144/1 "2026-01-03T16:50:41Z")
Much of the vintage gear that runs across my bench has a _Dynamic Headroom_ specification. While the QA40x has an Amp Dynamics automated test which can provide useful information, it does not provide a _Dynamic Headroom_ measurement. I thought I would share how I have been making this measurement- criticisms welcomed. Since a lot of the gear probably used the old IHF-A-202 definition for the Dynamic Headroom, that is what I have used (paragraph 3.2). For this example, I am using a receiver that is rated for 60w/8ohms, so I started by setting it for that at 1khz- the response shown below: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/a/a33c7430c597f41a4fb5e52082e8809975a3668a.jpeg) I now switch the DISPLAY to TIME: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/f/fccab98e44acf7a8e6ea73e976dfce708d48ee42.jpeg) Next, I drag a “zoom window” around a small area of the beginning of the wave form and get this: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/9/92832646c85662e77f7b82b3fbc5da478cf0d87b.jpeg) I turn the cursors on and put them at the min and max of the waveform: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/1/16626b5fd6559a97253f208e21e46bc19c2b6b61.jpeg) The delta Y (62v) gives me the 1st voltage I enter into the spreadsheet for the Vpp for Pnom: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/c/c0b3430a5e2b3184ce04fcb5ecec1f8e9af7b4dc.jpeg) I will come back to the spreadsheet in a bit. I now select the AmpDynamics automated test and populate it with these settings, and run the test: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/3/3270f2d45e27a78ed775e09607c2e9bbada365db.jpeg) The resulting waveform will be something like this: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/0/0a3b1b8e9189b32b49eb592dce353705aedf412c.jpeg) I then zoom in on the larger waveform at .5 sec and end up with something like: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/b/b2f61c2b23ce2d4d24b03dbe30462ad5ffa44aff.jpeg) There is no clipping of the waveform so I go back to the AmpDynamics automated test and increase the amplitude of input signal (note that 1.75dBV was the input level that yielded 60w) Levels 1 & 3 by 1dB (you can go more or less to start with, of course). You must also increase Level 2 by the same amount ( 1dB): ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/6/64e1a565eecee1ed096e6b34c78d196525d8f52c.jpeg) Press OK to run the test, repeating until you see some clipping of the waveform- remember to change the values of each such that levels 1 & 3 are the same and 20dB less than Level 2- eventually you will get a plot something like this that shows some clipping: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/9/917f6291f08b6d0b87595ad77a6931ebbd528090.jpeg) Placing the cursors at the maximum & minimum of the waveform gives a delta of 76.12V, which gets entered in the spreadsheet as the Vpp for Pmax: ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/6/6426f01184b030c82cca27887524d2de301c27a1.png) The dynamic headroom is then calculated to be 1.78dB, which was close to the spec. I will paste the equation below in case anyone wants to try this (and check my work): =10\*LOG10(((((B2/2)/1.414214)^2)/D2)/((((B3/2)/1.414214)^2)/D2)) ---
**Author:** ![restorer-john](https://avatars.discourse-cdn.com/v4/letter/r/b5a626/32.png) [@restorer-john](https://forum.quantasylum.com/u/restorer-john)\ **Post date:** [January 6, 2026, 3:24am UTC](https://forum.quantasylum.com/t/dynamic-headroom-measurement/2144/2 "2026-01-06T03:24:59Z")
This is all very good work Scott. I’ll have to have a go myself, as I found the dynamics plugin a bit awkward to use. I’ve always done dynamic headroom manually as it is very fast, repeatable and doesn’t need an analyzer. A CD source playing a standard EIA (20mS@0dB/480mS@-20dB) or EIAJ/JIS (8mS@0dB/24mS@zero) toneburst for Japanese gear (they are different) and a scope. Only takes a few seconds to ramp up the volume/level until the bursted cycles get clipped and you back it off, read the value and calculate the power/headroom. A DSO makes it even easier as you can have it trigger on the bursts and do the math for you. I can email the standard .wav files I use if you want. They are off one of my test discs. ---
**Author:** ![VAR](https://yyz2.discourse-cdn.com/flex032/user_avatar/forum.quantasylum.com/var/32/959_2.png) [@VAR](https://forum.quantasylum.com/u/VAR)\ **Post date:** [January 6, 2026, 4:33am UTC](https://forum.quantasylum.com/t/dynamic-headroom-measurement/2144/3 "2026-01-06T04:33:14Z")
@restorer-john Thanks for your comments and yes I would like to try out your .wav file. The old IHF spec I referenced used 480ms and 0/-20dB. It would be nice if there was a Dynamic Headroom automated test that set the defaults up for the method you want- I am sure I mentioned that at some point in the forum. I am not sure I follow about how you would trigger the scope, but I like the idea of using the volume control. More stuff to play around with and learn about.