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ELIActually5: Headroom.

Discussion in 'Amps and Cabs [BG]' started by DeaconBlues09, Apr 20, 2016.


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  1. OK guys, I know. There are hundreds of posts explaining the concept of headroom, and I've read through dozens of pages and only got more confused.

    So I'm borrowing a format from Reddit Explain Like I'm Actually 5. (Yes, there is the more well known ELI5 [explain like I'm five], but, since people were explaining things with too much jargon, they created a new sub with the addition of the word "Actually"!)

    One thing that confused me more than the rest, with the limited understanding I gleaned, was the concept of "peak." I mean, we are talking about machines here, right?

    A car can either go 110 MPH or it can't, why would a car be able to go 110 for short spurts only? Unless they are limited due to overheating concerns? What are the concerns of pushing the power of an amp if that were the case? Overheating? Ruptured Speakers? If the former, why not just install an extra fan, and get rid if the "Peak" rating.

    TIA for your indulgence!
     
  2. What are you, 5?
     
  3. Kidding of course, DB09; love you, and you know it. You're a G&L guy!
    I'd have to try and explain headroom from my own simple experience. Years ago, I used a 150W amp into an abundance of speakers. The crappy band got loud enough to where I'd simply stomp the accelerator to the floor ("10" it). I suppose the amp would play at 10 all night like that, if I wanted, but somewhere beyond the 5 volume, the amp only put out a signal that the speakers heard (and translated) as "someone wadding up wax paper" all night. It was a special tone of its own... and it plunged my image into the toilet.

    I learned a lot about headroom from that poor overdriven amp.
     
    DeaconBlues09 likes this.
  4. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Because most roads have corners?

    Because most music has peaks and valleys? It's all about optimizing the tool to the job.
     
    mbelue likes this.
  5. "Headroom" is really pretty simple, but constantly miss-used as a "buzz word".
    First used as a studio term it was the amount of room left in the gain of a mixer. Stated simply it is the USABLE amount of "volume" still available. If you have a 300 watt amp with cabs that can handle that power cleanly you have 300 electrical watts of headroom before you apply a signal. If these cabs that can only handle 300 watts input are driven by a 2000 watt amp you still have only 300 watts of headroom. Anything above 300 watts is not usable and therefore waste, NOT HEADROOM.

    If you walk into a room with 8 foot ceilings, you have 8 feet of headroom even if there are 100 floors above you.
    "Headroom" is what is usable from the floor to ceiling. Whatever limits that ceiling determines the amount of headroom available.
     
    VigierUSA and DeaconBlues09 like this.
  6. BassmanPaul

    BassmanPaul SUSPENDED

    Drive that car down a steep hill and you will indeed surpass it’s 110 MPH rating.
     
  7. Applying power to sucessively lower frequency generates less and less resulting loudness. Both from lack of lf hearing sensitivity in humans and needing more power to push a given SPL as the response sensitivity of a cab generally worsens markedly below 80hz. Google "spl response chart".

    It can also send a speaker into a different mode of operation which you can hear as 'fartout' if you push too hard too low. So power headroom is dependent on frequency.
     
    DeaconBlues09 likes this.
  8. If you have enough power to "fartout" a speaker cab you already ran out of headroom before that point.
     
  9. Depends what you mean by run out. You could change the EQ or apply a hpf and then be back in business with room to turn up even more.
     
  10. Then you have just shifted the amount of headroom to a different band, possibly to the point of power compression onset. Once in power compression you are again out of headroom. Limits to headroom come by either the amp, cab(s), playing style or any combination of these.
     
  11. Yep. That about sums it up. OP head spinnng yet?
     
  12. ELIACtually5!

    Actually, dammit! Lol,

    As a matter of fact, until the power compression bit, these were some of the most simple yet lucid explanations of the matter I have read yet!

    This is why I love TB and TBers! :smug:
     
  13. Power compression is the loss of headroom caused by the motor heating up at higher power level thereby increasing resistance to electron flow through the coil. That's high school physics at work.

    Leading on from power compression you can get a runaway condition where the motor gets so hot it gets quieter. The runaway happens when you don't recognise what's going on and dig in more, or worse, reach for more volume from the master. Oops, you fry the woofer.
     
    DeaconBlues09 likes this.
  14. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    Power compression loss of a 450 Watt AES driver
    upload_2016-4-21_22-15-59.png
    Power compression loss is caused by average power.
    Presumed the crest of an "random" audio signal is 6dB which is already lots of dynamic supression to the signal, a signal that shall produce 250 Watt average demands a power amp of 1000 Watt at least.
     
  15. Jules Meuffels

    Jules Meuffels Commercial User

    Apr 14, 2016
    The Netherlands
    Custom Shop Bass Cabinets
    In laymans terms (correct me if I'm wrong TB'ers):

    -There's the Gain and Volume knob. The gain is like the firtst stage of amplifying. Always find the clipping point of your incoming signal/bass with your gain. (Google clipping soundsignal). If you own a transistor amp, stay below this point! If you own a tube amp you may like the signal to clip, for it gives you an overdriven sound. If gain is set, you can use volume however you like.

    -How much Ω your driver/speaker/cab has and will do to your amp is discussed earlier here; Ohms - How do they work?

    -Then there's the discussion about amp-watts vs cab-watts. If your amp is to strong for your cab, you might 'fart-out'- or even worse blow up your speakers. If your amp is too light, it has to work to hard all the time to a point where it overheats and dies.

    :D
     
  16. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    Maybe this is a workable super-oversimplification of headroom?

    If you're at the gig, playing along, and the drummer and guitar player keep getting louder
    headroom is "how much more ability to keep getting louder with them before bad things happen to your rig"
     
    DeaconBlues09 likes this.
  17. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    I'm more at science side that Headroom is the remaining reserve (if present) at transients/dynamics.
    Bass players most of the time think different cause clipped transients remain inaudible.
    Strictly speaking there is no more Headroom if transients are already clipped.
    It has nothing to do with gainable loudness till the amplifier signals an "audible" clipping.
    Amplifier clipping at transients and audible clipping are very different kinds of animals, thus different interpretation of Headroom.

    Major importance of Headroom comes with all kinds of digital signal processing cause a clipped but very short transient does cause very nasty "clipping" artifacts.
     
    Last edited: Apr 21, 2016
  18. seamonkey

    seamonkey

    Aug 6, 2004
    That I agree 100%
    No peak, just true power
    Problem is there are very few amp makers that publish true power, they can't even agree on a standard way to measure it. Which implies they also don't agree on a standard way to measure "peak power".
    If you look at most amp ratings they don't say any standard next two "watts" they just say "watts" and you can't know what they mean.
     
    DeaconBlues09 likes this.
  19. that's one side covered. The other is when you play with a light to lighter touch and headroom is how well you can take over the mix aka "bring the thunder" with a single thump from time to time.
     
  20. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I can ELI5 the reason the car analogy means nothing when it comes to music...because the idea behind getting a car to a certain speed is to keep it there as long as possible, whereas music is full of instantaneous stops and starts.
     
    DeaconBlues09 likes this.

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