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what is "flat frequency response" and why would i want an amp/cab with it

Discussion in 'Amps and Cabs [BG]' started by muhammadsmith, Jul 5, 2003.


  1. someone mentioned the phrase "flat frequency response" in another post i made. now, keeping in trend with the fact that this forum has been great in helping me learn about bass-related things, i was curious if someone can explain to me what that phrase means and why it would be neat to have an amp or cab that produces it. is there a way i can hear this acoustic trait versus regular amplifiers by going into a music store and doing a demo of amps they have? what brands would carry this feature?
     
  2. "Flat frequency response" means that the whatever you put in to a component is what you get out. In other words, that component doesn't color the sound. This could be referring to a speaker cabinet, a power amp, a preamp, or even pickups. This is sometimes desirable and other times it is not. It really depends on what sound you want.
     
  3. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I normally use the term "flat frequency response" to refer to speaker cabinets which reproduce the entire range of bass frequencies without any EQ being applied.

    If a cab is advertised at "10db down at 40hz" then it would take a 10db positive EQ at 40hz to make it reproduce those low notes at the same volume as the rest of the notes. 10db requires 10x increase in power to achieve (which means you have eaten your headroom).

    The big reason most cabs aren't flat IMO is cost and convenience. For a driver to go low, the cone must have a long excursion. If a driver has a long excursion it will not be very sensitive, and so you need a LOT of power to make noise. To get loud, you would need multiple cabinets with lots of power each.

    I have yet to hear a good argument why a flat response is "bad", except that folks make the personal choice not to amplify those freuqncies because of power and convenience requirements.

    You can turn down the bass EQ on a cab that can cleanly reproduce low notes, but you can't necesarily make a cab cleanly produce low notes just by jacking up the EQ.
     
  4. To elaborate a little, a flat frequency response (FFR) is one that will not "add" or produce any tonality or sound that is not already present in your signal chain. A good example of speakers with a FFR would be high quality studio reference monitors and high quality home audio (HI-FI) systems.

    I really like the way my bass sounds (like when I record in the studio, etc...) and didn't want a set-up that "colored" the sound of my bass at all. I recently bought an Acme Low B-4. Acme's are renowned for their FFR. The sound and character of my bass come through virtually unchanged. I then have a lot more flexibility with EQ as I'm not trying to make up for any type of deficiancy (or false coloration) the speaker enclosure might possess.

    Speaker designs of this nature often pay the price in efficiancy. They require larger amounts of power to create volume levels similar to "regular" cabinet designs. I for one am happy with the trade off because I really enjoy the sound my particular instrument makes. I also like the flexibility it gives me in producing different sounds through my pre-amp as well.

    I hope this helps you out a little. Read up on Acme if you're interested. There's a lot of good information on their site-

    http://www.acmebass.com/
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    True. But as ESP correctly pointed out, Acme are also renowned for their low sensitivity. I believe they're in the Low 90's. Compare that to Eden which do colour the sound but have a sensitivity of 100+. Remember that 10dB is A LOT because dB is a logarithmic unit of measurement. I'd never use an Acme style cab because in the bands I play in, I't would amount to perfect tone that I can't even hear. But there are situations where the Acme aproach works better. Horses for Courses.......
     
  6. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    alot of gents here, do a alot of recording and session work, and love the sound of their bass, its pickups, and onboard preamp as they are, straight into a board and into whatever song mix.

    so, when amplified for the big stage, they dont wanna lose any of that natural goodness the bass itself. thus, they look for live use amps & cabs that can accurately and faithfully reproduce that DI'ed sound, without any coloration.

    amp wise, a simple vocal mic pre or a beefed up DI like an Avalon U5 into a nice power amp, and into a pair of Acme's would do you right for that "flatness".

    i like to think of Acme cabs like a nice piece of white block marble, ready for whatever tonal ideas you want to sculp it into. :bassist:
     
  7. LM Bass

    LM Bass

    Jul 19, 2002
    Vancouver, BC
    Flat response

    My Euphonic Audio cabs are pretty flat. I've
    found that one of the real benefits to that kind of response is less ear fatigue. My old rig had a big ping up around 3 Khz that happened on just about every note. I would get a lot more ringing in my ears at the end of a set. When I first went EA, I thought they were a bit too smooth, but I got used to their flat response, and now I don't want to play without it! Efficiency? Yep, got that too.

    LM
     
  8. I think that by this time you have a good idea of what it means. The next thing is how should it be applied to the bass guitar. When you play a bass guitar through a rig that is flat (pre-amp --> speaker) you will hear every fundamental and it's associated overtone the bass guitar produces in its' correct proportions. The big mistake I think many make is in thinking that this is the best type of bass sound for all type of music. It isn't! The flat, full range, hi-fi sound is great when it doesn't have to compete with a lot of other instrumental sounds. For example, a jazz duo or trio. I think it sounds good in just about any type of sparse musical environment. It doesn't work, however, in a dense musical environment. For example, competing with 2 Marshals a loud drummer and a keyboard. In this environment the bass needs to be EQ'd so the it sits in the frequency gap between the Kick drum, and the Guitar/keys. Using a flat full range bass sound just gets lost in the mix. One of the reasons a 4x10 cab is so popular is because it naturally sits right in the gap. Can a full range cab be EQ'd to sit in the gap? Of course it can. Problem is many players want that full range all the time and in a lot of cases it never makes it past the edge of the stage. I'll shut up now... :smug:
     
  9. LM Bass

    LM Bass

    Jul 19, 2002
    Vancouver, BC
    Point taken,

    I mostly play in situations where no Marshalls are in evidence. When I do occasionally work against a Fender Twin, I usually boost at 1 Khz and cut some low mids.

    I would also say that fundamentals aren't THAT important to a bass tone. Most of what we hear are the harmonics, from the second partial up. I'm a bit spoiled though, and I like my flatness.
    LM
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That's what I was trying to say :)
     
  11. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Maybe I'm splitting hairs here, but this is my $0.02 on this subject. There seems to be somewhat of a misconception regarding FFR, relative to "what goes in is what comes out only louder". This statement is only true with respect to relative decibel levels. Almost every different sound reproduction system put together is going to sound tonally different even if they all had FFR. One of the biggest source of the difference is the speaker system used. For instance, Speaker driver cone material: there are various types of paper cone materials, there is also Kevlar reinforced paper cone drivers, there's polypropylene cones, carbon fiber reinforced cones, etc. Each type will have a different tonal coloration. Then there's different cabinet designs which will also affect the tone produced: a folded horn, a sealed box, a thiel-small ported cab (shelf or tubed port), passive radiators, transmission-line cabs are all going to introduce different colorations to the reproduced sound.

    Some people want the sound of their bass to go into an amp and come out the speaker the same only louder.

    Some people like to have certain tonal colorations to be added by their preamp &/or amp &/or speaker cab.

    It all depends on the synergy of your whole system, including the bass guitar (or DB) and what tonal pallete your after in your sound.

    Until I ran across the cab I have now, I thought that if I wanted to add any color to my overall sound that it should be done at the bass &/or preamp (or head), and definitely not at the power amp or speaker cab.

    I still feel the same way about the power amp.
    [Only possible caveat to the foregoing statement would be a vintage SVT 300W for certain types of music.]

    But that's just me and my taste..., YMMV.
    [Maybe I should say YGMV (Your Groove May Vary).]

    May you have a fruitful quest for your own tone.
     
  12. All of those things affect the frequency response. That is one of the reasons they sound different.
     
  13. My friend(s), there's so much more to it! All those things also affect phase response, phase distortion, group delay, harmonic distortion, baffle reflections, etc etc. There's a whole world of sound characteristics very few people are aware of...

    The frequency response is the easiest wat to measure a loudspeaker system, and it says a lot about it. But hardly everything.

    Why does the Bag End ELF system go down to 8 Hz? There really is no need to reproduce 8 Hz, humans can't hear it. But it allows for minimum phase shift at frequencies we CAN hear, making the bass response VERY direct and VERY tight. Once you heard something like THAT (even I can only imagine), you'll know what it means.
     
  14. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Yes they do, but my point was if you achieve multiple FFR systems using different components/methods, they will still sound different, producing different colorations (tones).
     
  15. I'm not an engineer and I was wondering:
    Can 2 speakers with IDENTICLE response graphs sound different? If so, how?

    Can 2 speakers with DIFFERENT response graphs sound the same? If so, how? :confused:
     
  16. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    A more accurate way of depicting how a speaker sounds would be to have a 5 dimensional graph, with acoustic output power on the V-axis, electrical input power on the W-axis, frequency on the X-axis, time (i.e. transient response) on the Y-axis, and phase on the Z-axis. Unfortunately this would be near impossible to either measure or interpret (humans aren't good at thinking in more than 3 dimensions, and printing it on 2D paper would be challenging to say the least).

    An easier to read approach would be to have three 3D graphs of frequency/sensitivity against transient time, phase and input power respectively. That would really show how different designs compare. But would that be definitive?

    Alex
     
  17. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Have someone speak these words to you, "The rain in Spain falls mainly on the plain".

    Have them put their hands beside their mouth like a bullhorn and say them again.

    You will get an idea of the difference of how a horn loaded cab affects tone (even if they speak more softly, the sound coming off their hands affects the way their vocal chords sound).

    Sound coming off a paper cone, sounds different than a kevlar cone, etc, etc.

    It would be good to have John (or Gary) from EA chime in here.
     
  18. Would that not change the frequency response of the sounds, especially off axis?
     
  19. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    OK; both of you stand in the middle of an anechoic chamber (or a big pasture with lush grass) so there no off-axis reflections reaching your ears.

    [I think we're getting off into the bushes here.]
     
  20. EAJohn

    EAJohn Euphonic Audio

    Dec 4, 2002
    A single on axis frequency plot does not characterize a loudspeaker cabinet. A cabinet with a wide dispersion pattern(-3dB polar points horizontally: +/- 30degrees) and vertically: +/-15degrees) with an on axis response that has small downward tilt starting at 800Hz can sound brighter than a cabinet that has a narrow with a flat on axis response.

    It takes about 40 meausrements To quantify a loudpeaker cabinet with a reasonable degree of accuracy. You need to take 1 on axis frequency plot, 4 vertical polar plots(-20, -10, +10, +20degrees), 6 horizontal polar plots(-45, -30, -15, +15, +30, +45 degrees). The 11 frequency plots should be performed with the input power at 1/4watt, 1watt and 50watts. Impedance measurements should also be performed at these 3 different power levels. Harmonic and Intermodulation Distortion Tests should be run at 1 and 50 watts. After running all these tests you could develop a transfer function that characterizes the loudspeaker cabinet.

    John Dong/Euphonic Audio Inc