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F3 of 100 Hz, too high?

Discussion in 'Amps and Cabs [BG]' started by fdeck, Feb 1, 2006.


  1. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I have a DIY cab with a calculated F3 of about 100 Hz. The midrange hump is minimal. So far I am quite happy with the sound, but it leaves me curious as to what people think is a reasonable range of F3 values for bass cabs. Mine is a sealed box. I ask before I build a smaller cab with roughly the same response curve.

    Am I in good company at all, or is such a high tuning out of the ordinary?
     
  2. permagrin

    permagrin

    May 1, 2003
    San Pedro, CA
    If i'm not mistaken, a few recent GK cabs' -3db point is around that same frequency.
     
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It's not out of the ordinary at all. Many cabs loaded even with 15s typically have f3s around 60 Hz. I'm not saying that it gives the best tone, but it is quite common.
     
  4. There's a bit of a diff between 100 and 60 though...

    It depends an awful lot on your rolloff, but I would personally want to go lower, or your E string will lose all its balls (fo for an E is 42Hz, so you will be missing a lot of fundamental at f3 of 100Hz).

    Don't even think about a 5 string - the B is 33Hz or so.

    But as I said before, it depends a lot on the rolloff and whether you can compensate with EQ on the amp.
     
  5. A somewhat higher F3 in a sealed cab is less of a problem than a relatively high F3 in a bassreflex cab since a sealed cab responds better to EQ-ing than a bassreflex cab.
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Sometimes, but not as a general rule. Adding EQ below fb is verboten, but fb and f3 are seldom the same, with fb often a half octave or more below f3. A 100Hz fb would be very problematic, but also very rare.
     
  7. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    But it's done all the time....... with folks boosting the "low" control "to get some fundamental", and then complaining that the cabinet farts out........... or that they run out of power, or that they blew a speaker.....

    I suspect that 100Hz is just a bit too high..... I think it will cause the sound to be missing the specific harmonics that keep it audibly "mixed" lower than guitar.... But it might work.......just.....

    You will have to stay off the low EQ if it's ported, and stay conservative with EQ even if it isn't.
     
  8. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I guess that a privelege of being a geezer is that I don't have a powerful amp. At 180 Watts, my tentative design shows an excursion plot that is safely below Xmax down to 40 Hz. You guys with 600+ Watts have a harder job with speaker design.

    My design is a B&C 12HPL64 in a 19 liter box with a 50 Hz port. That puts Fb at about 130 Hz, and F3 at 100 Hz. The port is not doing much -- just raising the response curve below cutoff by about 2 dB, and helping out on excursion at the lowest frequencies. The only drawback I can see to EQ'ing the bass is that it might not be the most efficient possible use of amp power. But I have been happy with the sound of an existing speaker that has roughly the same response curve, albeit with a 15-inch driver.

    Anyway, I still have to decide if I really want to do this, but at least I am grateful for all of the good advice.
     
  9. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I don't think you'll find the response curve all that bad, but with only a single ten you won't get much output. OK perhaps for practice, not up to the job onstage.
     
  10. etnops

    etnops

    Nov 6, 2005
    absolutely not! for a lot of the home subwoofers i do, i apply LIBERAL amounts of EQ/filtering to boost response below cabinet resonance. as a matter of fact, i like to actually try to get system resonance up as high as i can. makes for implementing EQ much easier when impedance is relatively flat.
    take a look at some of the bag end "infrasub" products for a good example.

    delve into the home subwoofer market, where you'll see roughly 80% of all products with EQ applied below Fb to boost response.
    now that all assumes you've got enough excursion to keep up with SPL demand, and you've got a high current amplifier to drive it.......

    that's an old myth. a very old myth.

    just for kicks, i did a small sealed subwoofer a couple of months ago where i used a transform filter which had about 25dB of boost @ 20Hz...and system resonance was about 70Hz.

    oh, and guys, keep in mind that if you've got a sealed system, it will always have a 2nd order roll-off (12dB/oct) below resonance. vented systems will always be 24dB/oct.
    if you look at the F6 bandwidth and it's specific roll off, you can correlate that to the step/impulse response (system ringing). kinda neat to make that connection....



    -SDP
     
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The ELF system uses a 12dB/octave boost to compensate for the 12dB/octave rolloff below fb of its sealed box, and requires both very high excursion and power handling capabilities to do so, not to mention very high current capable amplification. But that has nothing in common with Link Wray's post, and my reply to it, which dealt specifically with using EQ below fb in a vented box, not sealed.
     
  12. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    It's a twelve, but your point is well taken. I play mostly jazz, and mostly upright, but this forum seems to have a more lively discussion of DIY speaker design -- perhaps thanks to you and a couple other real speaker experts. My GK MB150E combo is sufficient for about 80% of my gigs. For the other 20%, I bought a GK Backline 600 head (180 W into 8 Ohms) and was using it with my 15" speaker.

    I have a 1x12 made from a surplus driver, whose sensitivity I can compute, and I can also do a comparative measurement of its response against the GK combo. But it has an evil midrange hump. Based on measurements and calculations, I estimate that my proposed 1x12 will be noticeably louder than the combo, especially with the BL600 head, while affording much better portability than the 1x15.

    Long story short, I was converging on this new design, but wanted to make sure I am not making some gross conceptual error.

    Also, truth be told, I do my practicing on stage. :bag:
     
  13. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Not to be a contrarian, but in my limited experience, sensitivity is more critical in bass speakers. If you artificially give up 6 dB in low end response (for instance) and make it up with EQ, then you need a lot more amplifier power to get the same tone quality and volume.

    Granted, I might end up doing exactly this with my new design, but I am trying to make sure that I only have to do it in moderation, if at all.

    I am getting 12 dB/oct with my vented design, according to the response curves in WinISD. Sadly, I don't have a name for this "alignment," but the port is acting only minimally on the response curve. It adds a flat 2 dB to the low end response, and its main benefit seems to be that it takes some load off the cone at the lowest frequencies where I might otherwise run into the excursion limit. Maybe I have invented something, though it seems unlikely.
     
  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I can't say what you've got, but I can assure it's not new. Don't confuse fb and f3, they're totally different, and in the case of pro-sound drivers in small cabinets very often at widely spaced intervals. f3 is where axial reponse is down 3dB from f0, f0 being the lowest frequency of flat response, but even determining where f0 is can be daunting with some alignments. If your plot shows 12dB rolloff in a vented alignment that rolloff is actually taking place below f3 but above fb. Below fb the rolloff rate will be 24dB/octave, or close to it.
    Not at all. My DR250 has a nominal f3 of about 90Hz, so from that spec alone one might conclude it to be too high for the bass. But with sensitivity of104dB at 90Hz and 93dB at 60Hz it's got game. An f3 at 40 Hz sounds impressive in and of itself, but if that's coming off a base sensitivity of 90dB then you're going to need a lot of drivers and a lot of watts behind them to be heard.
     
  15. etnops

    etnops

    Nov 6, 2005
    OK. I'll bite.

    I already mentioned the power and excursion requirements for such a system. Is there an echo in here?

    Boosting below system resonance in a vented box is usually not a good idea, but with any high SPL demands from a vented system certianly requires EQ/filtering. All of the vented systems I do, incorporate a 2nd order High Pass filter, which will ALWAYS give a boost (depending on the Q of the filter) at Fc. Effectively making for a 6th order system, and if you look at the raw response curve and the filter's transfer function, you'll see there is a bit of boost below system resonance.....
    So......I have the feeling you don't like me, Bill. Am I cramping your style?

    Don't trust WinISD. It's a small signal lump number simulation. As many of us know, there is quite a big difference between prediction and real-world. Vented systems will always be 4th order, and roll-off at 24dB/oct.


    Remember guys, as soon as you actually make the cabinet, drop the speakers in, play with any settings on your amp - and most importantly: use the cab in anything other than in 2Pi, 4Pi, or an anechoic chamber, throw all of those predictions out of the window. Your environment has a MUCH bigger impact on the "sound" than the alignment of your system.

    WinISD is old news, and not very thorough (IMHO) for a small signal simulation program. A bit more in-depth freeware is UniBox. It's still not great, but it'll do a bit more than WinISD, and is excel based....


    Just a thought.



    -SDP
     
  16. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Thanks for the tip. I will try UniBox. Also, I sat down once and derived the formulas, but have not gotten over the activation barrier to actually writing a program.

    For my purposes, I don't mind a small signal approximation. Is any mainstream program taking nonlinearity into account?
     
  17. etnops

    etnops

    Nov 6, 2005
    Oh yes. But none of it is freeware. And even so, you'd have to know the non-linear parameters somehow, or at least simulate them with a comprehensive program (FEMM) like Opera2D or such. Not a real easy task I'm afraid.

    "Easiest" thing is to pay $100 for a DUMAX evaluation (www.dlcdesignaudio.com) or $500 + shipping to Germany for a Klippel analysis. www.klippel.de
    Meaning, you'd have to have physically send in a driver to be measured.....

    Small signal gets you an idea. Dynamic analysis lets you know for sure. But in the DIY speaker world, none of it is really critical. I say let the table saw rip, and have some fun!


    -SDP
     
  18. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I downloaded UniBox. Nice. It pretty much confirms the WinISD results, but the graphs are better, and you can pull out the numbers. I like numbers.

    But I am still sticking to my guns about the 12 db/oct rolloff. Both UniBox and WinISD confirm this. My port is tuned to 52 Hz, which I assume means there could be a 24 db/oct rolloff somewhere below low E.

    Details of proposed design:
    Fs = 52 Hz
    Re = 5.8 Ohm
    Qes = 0.35
    Qms = 3.3
    Vas = 85 l
    Sd = 522 cm^2
    Xmax = 4 mm
    BL = 14.9 T*m
    Le = 1.1 mH

    Box volume = 19 l
    Port frequency = 52 Hz
    Amp power = 180 W at 10% THD

    I agree that small-signal analysis gets me where I need to go. While I am not a speaker expert, I have analyzed electromechanical and linear dynamic systems in general. So I won't dispute that the system is 4th order.
     
  19. etnops

    etnops

    Nov 6, 2005

    Just for kicks, try to not look at the T/S parameters by themselves. They are too inter-related, and inter-dependent. In other words, when one shifts, they all shift. IMHO, they don't give the user an accurate picture. Faulted by nature.

    I like to stick to the electro-mechanical parameters only. They are all independent, and give you a better clearer idea of the speaker itself. Concentrate on Cms, Rms, Bl, Mmd, Sd and Re only. From those, all T/S are derived, and you can model with these alone. Le is good to know, but because it's not a static parameter, it also changes with position as well.

    My favorite quick and dirty modeling programs are WinSPEAK and SpeaD and ReverseSpeaD (check out www.gedlee.com and www.redrockacoustics.com both Earl and Pat are both very talented engineers, and have a nifty platform to work off of). Both take into account non-linearities, if you've got the parameters....

    Keep in mind these programs only are predictions of the driver while in the pistonic domain.


    -SDP
     
  20. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I agree... the only reason for using the T/S parameters is that they seem to be the typical mode of data entry for the design software. Admittedly, I have a bit more of a scattershot approach, which is to model a bunch of candidate drivers in realistic boxes and see which ones have the curves that I am looking for. Thus I am not really looking for trends in the parameters. And I don't have the luxury of designing a driver.

    My derivations of the equations sit in a folder on a high shelf, in case I want to make sure I am not straying from a reasonable conceptual understanding.

    I will probably order the driver next week. We'll see how it plays in Peoria, as they say.