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Frequency response charts

Discussion in 'Amps and Cabs [BG]' started by snowdan, Jan 5, 2007.

  1. snowdan


    Feb 27, 2006
    am i the only one who wonders why there are no freq response charts of amp heads available? has noone over done a such thing? i think such measurements would really help.

    i only know of the measurements of the GK BL600 that fdeck has done.
  2. Interesting post, but not sure that makes sense. I can see it with a 'fixed' cab.... but with tone controls, etc. on amp heads... what would you be measuring. On many amp heads, the 'flat' settings are obviously not in any way flat, but provide a baseline for the inherent tone of that manufacturer or piece of gear?

    I guess 'power delivery' through the entire frequency spectrum might be a good thing, assuming there are amps that 'cheat a little' in the low end department!
  3. snowdan


    Feb 27, 2006
    one could either measure response from the input to speaker out (technically possible i guess)

    or measure the preamp alone, usually the coloration happens there, most poweramp designs are flat more or less, right?

    such measurements would reveal low end boosts, mid scoops, exaggerated treble or whatever.

    whenever i A/B input vs. effects return in an amp, i am stunned by the difference.
  4. +1.... I guess this gets back to the old 'flat' versus voiced sort of thing. I actually want my pre to provide some character and voicing to my instrument (assuming the pre/head is voiced so that it gets me started toward the 'sound in my head'.

    However, there are those that try to find the most 'flat' pre to start with.

    I always viewed my amp/head/cab as a single instrument, so this sort of testing is not that interesting to me. If I plug my bass into a rig, and it doesn't sound good to me with a few quick turns of the knob (or even no turns of the knob), then I usually move on pretty quickly.

    Different approaches though.

    I actually find that the published response curves or at least specs many amp companies provide on the center frequencies of the EQ, the freq's impacted by enhance type circuits, etc. are pretty informative.

    However... I many be missing the point, so I'm in for the ride:)
  5. silky smoove

    silky smoove

    May 19, 2004
    Seattle, WA
    I can understand frequency response charts of cabs measured at a fixed frequency (Bill Fitzmaurice does this with all of his cab designs)... But I'm also not sure of the accuracy or usefulness of charts for heads...
  6. snowdan


    Feb 27, 2006
    i am pretty sure one can mke proper response charts of pretty much everything.
  7. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    I posted some response curves and noise and distortion tests of my DIY preamp a while back. Just download RMAA (Rightmark Audio Analyzer) and do it yourself. Most manufacturers are going to see this as proprietary information and aren't likely to be happy to share their voicing schemes, at least in my experience. I spent many years perfecting tweaks to guitar amps, I sure wouldn't post them to the world.

    Very few bass players actually care about those specs, IMHO. As far as Ken's question: you'd be measuring range of adjustment, voicing centers, interaction or lack thereof of tone controls, and so on. You can measure all of this extremely accurately, and for not much cost if you have a decent soundcard already.

    I understand all that stuff pretty well, but when I'm doing DIY I still always revert to trial and error.;)
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Sure you can...but what would it tell you?

    If you're looking at a frequency response plot of an amp and of a cabinet, are you going to be able to know what the combination is going to sound like?

    And to complicate it further...you'd need to have a fequency response plot of the instrument, the strings, and if you're going all out, better measure the cables too.

    None of that is really going to tell you how it's going to sound in your hands in any particular room. And frequency response plots don't tell you about transient response.

    Seems to me that fdeck offered software to anyone who was willing to measure the frequency response of the preamp section of their amp...
  9. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I did see the measured response of a fairly well respected name combo amp, a 60 watter as I recall, and it was, in a word, gosh-awful. This was done as part of a rebuild project by an audio engineer, who proceeded to upgrade the amp components to bring it up to a reasonable standard of performance by his standards. He did at least manage to get the signal to noise ratio up from an abysmal -70dB to a useable -90dB. But that's still a long way off from what even a cheap stereo receiver will do, let along a quality hi-fi amp.

    Musical instrument amps are by no means hi-fi, and if measured the vast majority of them would probably not fare much better than this example did. But musical instrument amps aren't supposed to be hi-fidelity, and for the most part wouldn't sound very good if they were. This is one case where all that matters is if it sounds good.
  10. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    About the measurements that I did on the GK BL600 head, my motivation was just to find out what the voicing consisted of, and to see if I could dial it out. So I ran some pretty basic curves: Default voicing, EQ curves relative to the default voicing, and a curve representing my best attempt to dial the amp flat.

    I don't really see how an amp maker would be harmed by having their curves published. It's just a strange historical anomaly that they aren't, perhaps because nobody knows how to build a marketing message around the information.
  11. BbbyBld


    Oct 13, 2005
    Meridian, MS
    I don't see how a manufacturer would be helped by publishing response curves.

    The curve is not really secret, the reasons it looks the way it does are the real secrets. Probably the worst thing you could do is publish a curve with no explaination because people could use it against you. I'd like to give an example of that, but I'd give away a secret.

    BTW...none of the following applies to Peavey.

    Many manufacturers lie and say their amps are "transparent" or "flat" when they really aren't, so they won't want to publish a curve.

    The controls on many popular amps don't do what they say they do, so they aren't going to want people to know that.

    It's almost impossible to dial some amps flat, so that could be used against those amps.

    Some amps are copies of others, and the curve can give that away.
  12. seamonkey


    Aug 6, 2004
    It's not much of a secret if it can easily be copied. It's not hard to do these days. In fact publishing would give a better chance of protecting the IP. At least it would keep other's from claiming the curve is unique to their eq.
  13. will33


    May 22, 2006
    I think we'd all be better served to get honest specs from cab makers first of all. I'm no engineer but I have done a whole lot of reading/self-educating and I have built 3 cabs all of which sound better than the ones they replaced. One of the first things you realize when the light bulb comes on is that most manufacturer's are full of crap. There are some honest ones but many more are not. I don't know how much info you could glean from amp head specs like that but graphs on things like eq bandwidth's and interaction would help, does it all have to be marketing fluff? I really like fdeck's idea of testing and providing corrections for popular amps. The result of this would be a cross-reference page with things like for ex. 'On brand X amp to obtain a truly flat sound, turn mid knob to +2 at whatever freq. and set treble at -1 etc. Most all amps tell you what their eq centers are supposed to be but most say nothing about bandwidth or interaction. You'd still just turn knobs until it sounded good but it would help people learn what it really is they like or don't like about certain sounds.

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