Cabs built to Fletcher-Munson curve

Discussion in 'Amps and Cabs [BG]' started by RichSnyder, Apr 6, 2012.

  1. RichSnyder

    RichSnyder Columbia, MD Supporting Member

    Jun 19, 2003
    There seems to be a lot of attempt to make cabs "flat" to the spectrum analyzer, but has anyone made a cab with an attempt to make it "flat" to human hearing? That is it would reflect an inverse of the Fletcher-Munson curve at the intended playing sound level. I hesitate to post this in case spectrum analyzes already reflect Fletcher-Munson and I look like an idiot. But it won't be the first or last. :smug:
  2. lowfreq33

    lowfreq33 Guest

    Jan 27, 2010
    Endorsing Artist: Genz Benz Amplification
    Fletcher-Munson is volume dependent, it flattens out as you get louder. So it wouldn't be very practical even if you could do it.
  3. WingKL


    May 12, 2007
    I would think it would be easier to build an amp that has a DSP that reflects the fletcher munson curves in EQ as the volume goes up since playing level can vary from bedroom to loud rock gig. The amp will probably have to to matched to a particular cab like in a combo for the scheme to work consistently. Since there isn't great demand for something like that and unless demand can be introduced with marketing, it probably won't happen.
  4. will33


    May 22, 2006
    You don't look like an idiot at all. I've wondered the same thing before when reading up on sound stuff/speakers, etc. Cabs that sound like "fat bass" seem to sound that way not because of greatly enhanced deep frequencies, but rather good output in the 80-300hz range combined with not a scooped mid section, but rather a subdued topend. Cabs that have big response humps in the midbass (100-150hz) compared to the middle and upper response (on a graph) sound boomy, indestinct, and in the worst cases, can even mask your sense of pitch to the notes.

    I think if someone designed a speaker system that mirrored the Fletcher-Munson curve, it would likely sound like crap, at least with an electric bass. The curve has truth in it, but seems extreme to me. It can have greater effect in eq'ing PA speakers, where a small dip in the midrange makes them sound more musical and less like they're yelling at you. But still, in that case as well, mirroring the curve would sound bad.

    It's important to note, when Bell came up with the bell/decibel scale, it was for the telephone system more than 100 years ago. He was figuring with fairly quiet volumes and generally the middle range of frequencies, where our speaking voices are.

    The ears act differently when exposed to higher volumes, especially for any length of time, and the extremes shown in the Fletcher-Munson curve become less drastic. I think Bell was dealing with frequencies around 500-1000hz and at only 75db or so. Anything we play can go louder than that with 1 watt of input.

    Great question and should be an interesting discussion we all may learn from.
  5. wcriley


    Apr 5, 2010
    Western PA
    I have a digital EQ in my PA rack that has a "Dynamic EQ" function. I've wondered if this is what it's for. The manual isn't very clear (Behringer).
  6. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    The DSP in my plate amp has a pretty workable loudness compensation algorithm that I've messed around with a bit, although really I have barely scratched the surface of its capabilities. I think that sort of approach is probably more useful than targeting one specific sound pressure level and baking compensation into the cab for just that specific level.
  7. RichSnyder

    RichSnyder Columbia, MD Supporting Member

    Jun 19, 2003
    I agree that DSP is the way to go to get the can to full Fletcher-Munson "certification", but what about designing the cab so that it's more naturally F-M at higher SPL. Then you're just doing a little tweaking at the higher volumes when the cab is working its booty off. Then at lower volumes it's more of a cut in certain frequencies to keep it flat to the ear. The thought being that it's easier to cut frequencies at lower volumes than to boost them at higher volumes.
  8. billfitzmaurice

    billfitzmaurice Guest Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    He didn't. What became Bell Labs did. And the reason was to determine how far telephone signals could be transmitted before signal losses rendered voices unintelligible, to know the maximum distance allowable between repeater stations.

    As to the original question, lowfreq 33 is correct. However, while equal loudness is impractical where speakers are concerned, amps have always had equal loudness compensation devices. They're called tone controls, or EQ, which were originally devised for the express purpose of realizing equal loudness playback on hi-fi systems.
  9. Interceptor


    Mar 29, 2005
    Madison, WI
    Not at all a bad idea.

    I've thought about this in the past. The F/M set of curves are volume dependent. Mid cut (enhance) controls are usually voiced about right to match the cut range needed for F/M.

    Try this; start with a good amount of enhance at low volume. EQ the rig to taste. Use less enhance as your volume increases. It takes some trial and error to find out just how much enhance will be needed at different levels.

    The upside is you can sound pretty much the same at different rig volumes. The downside is it introduces another thing to think about.
  10. RichSnyder

    RichSnyder Columbia, MD Supporting Member

    Jun 19, 2003
    I probably did a poor job of explaining. Totally understand about EQ/tone controls but it seems that we should be building towards a F-M compensated frequency response in cabs instead of building towards flat response being the ideal. Instead of building to make the spectrum analyzer happy, make the ear happy.

    I wonder what a F-M compensated cab would look like? Two 18", two 15", an array of tweeters and a 6".
  11. billfitzmaurice

    billfitzmaurice Guest Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It wouldn't look any different than any other cab. You can do it with a single driver, using a compensation filter consisting of a parallel capacitor and inductor.
  12. RichSnyder

    RichSnyder Columbia, MD Supporting Member

    Jun 19, 2003
    Your missing my point. Select drivers, dimensions, ports, etc with the goal being something more closely resembling a Fletcher-Munson curve rather than a flat response to an analyzer. Would that cabinet (compensated cab) be able to give a higher spl with a sound that is flatter to the ears than taking a cab that is designed to be flat to an analyzer and then applying EQ curves to end up with roughly the same thing as a compensated cab? I guess it's easier with PA systems than a single cab because you can add as many subs as you want to the system. Of course other factors come into play.

    I guess I'm just wondering why we want cabs to be flat to an analyzer instead of flat to our ears? Home stereo or theatre I guess it's because we're reproducing a performance and want the reproduction to be close to the live sound. Take an orchestra for example. I'm going hear less string bass than viola if sitting in the audience so I don't want my home speakers to Fletcher Munson the string bass into 10x the actual recording. Well, maybe we do here. It is TalkBass. Heh.

    But now with a cabinet designed to amplify my instrument, shouldn't the goal be Fletcher-Munson compensation rather than a flat frequency response? Flat response makes sense for reproduction of a recorded event, assuming the recording was recorded flat. For for amplification of an instrument flat response seems to be a pointless goal.
  13. will33


    May 22, 2006
    See...I knew it would be something we could learn from.:p

    The loss in voice intellegibility and distance between repeater stations (amplifiers, or rather "re-amplifiers") would have to do with power loss and inductance in a few miles of wire, no?
  14. Joebone

    Joebone Supporting Member

    Oct 31, 2005
    California Republic
    I've always understood the "Fletcher-Munson Curve" to be about the way we hear bass and treble differently at low volume. Namely, at low volume, the frequency extremes -- low and high -- are attenuated.

    In bass land, the most direct manifestation I've seen is the bass and treble pushbuttons on the Eden WT-405 (a great amp!), intended to boost lows or highs in some ratio respective of Fletcher-Munson, so as to provide a wide-range sound at low volume. They work great at low volume, but sound weird if you get loud. Which makes sense!

    This phenomenon is also the reason for many of the "loudness" buttons on home hi-fi. Regrettably, most of those stink out loud because they boost bass without addressing the treble side, and were way, way overdone so as to add boom beyond reason.

    I also recall some number of hi-fi amps/preamps designed to deal with this through a smarter approach. The ones I found most interesting were on Nakamichi and Yamaha pieces from the 1980's, which featured a variable "boost" knob, for which the Fletcher-Munson adjustment could be boosted or lowered relative to the setting on the volume knob. IME, these can work quite well.

    As for whether it makes sense to implement this sort of thing at the speaker level...I don't think so, unless you've built in some sort of preamp or filter function, which would be way expensive in order to be effective. OTOH, the amp seems the logical place to attack the issue, as with the Eden WT 330/405 series. Consider the home entertainment world, where Fletcher-Munson might be addressed via the electronics, but I've never seen it in a passive speaker box.
  15. Bassamatic

    Bassamatic keepin' the beat since the 60's

    It is usually the goal of the equipment maker - be it electronics or cabs - to make the unit as colorless as possible with flat response. That allows the user to add or subtract color as desired via tone controls, effects, etc.

    Stereo gear in the early days had a "Loudness" control in addition to the Volume control to allow you to compensate for F-M. Later units had this function built into the volume control, and even later, it became a button, which has pretty much disappeared from modern gear - not sure why. Most likely they were cheaply designed and mis-used as a bass boost, and did not vary the compensation with volume level, so had a poor end result.
  16. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    I would consider that an exception to the more common goal of the manufacturer coming up with a voicing they like for their product, and baking it into the amp, cab, preamp, effects unit, etc.

    Whether or not it's the goal of the manufacturer, there are very few, specifically in the bass amplification world, who put out products that are anywhere near flat when in the default setting (i.e. knobs at noon, 10-2-10, or whatever the case may be given a particular piece of equipment).
  17. billfitzmaurice

    billfitzmaurice Guest Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    No, I didn't. Your method is impractical to realize, and even with multiple drivers still could not be achieved without an extensive passive network.
    You left out capacitance. :p
    Loudness controls worked well, and were simple to implement with analog potentiometer volume control circuitry. They disappeared when hi-fi volume controls went away from pots to electronic/VCA.
  18. JHAz

    JHAz Guest

    Jun 29, 2011
    FWIW, while loudness curve compensation is theoretically a good thing, a couple of points.

    We always hear with the fletcher munson curvesw in effect. You don't want to correct for the base case (wherever you choose to put it on an SPL basis) because it would sound weird (too much bass). Because we are used to hearing acoustic instruments as well as electric basses and the like with our actual ears that are less sensitive to the bass than midrange, "correcting" for that natural phenomenon would make the sound unnatural.

    Thus the compensation needs to be between the curve for whatever level one thinks of as the "correct" loudness and whatever loudness the sound is perceived at. But in a big room, how loud the bass (instrument) sounds depends a lot on where a person is standing (gets quieter as you get farther away as long as you aren't near boundaries). If you correct at the speaker for the volume difference between the stage level and the level toward the back of the room, somebody in the middle or close to the stage will have too meuch bass.

    Almost all of us have experienced this, though, if we've dialed in a "perfect" tone at or near bedroom levels at home and found the settings don't work at all in the context of the band because they're mushy etc.
    downlowuponit likes this.
  19. I can build a cab like this easy.
    I would start with a good flat cab like a fEarful
    add in a DSP, and power amp.
    A wireless calibrated mic would be placed out in the audience at the point I want the FM curve to be heard.
    The DSP would monitor the signal to the built in amps compared to what the mic in the audience heres, and adjust the EQ as needed.
    People sitting near the mic would hear perfect


    ooops - this is already invented and in FOH use.
  20. RichSnyder

    RichSnyder Columbia, MD Supporting Member

    Jun 19, 2003
    Thanks Bill. Just a late night "wondering". Spurred by reading where someone said that they like completely flat cabs do that it brings out the natural sound of their instrument. But then I thought, wait wouldn't they really need some compensation to get a flat sound to their ears?

    Appreciate the feedback.