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Large Cab Natural Low End vs. Small Cab + EQ'd low end

Discussion in 'Amps and Cabs [BG]' started by zac2944, Sep 16, 2008.


  1. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    Here's a question for all you cab design guys.

    What are the pros and cons of getting natural low end from a larger volume cab vs. EQing in the low end with a smaller volume cab?

    Assuming everything other than cab volume being the same, you should be able to use EQ to achieve similar (not identical, but similar) low end in a small cab that would occur naturally in a larger cab.

    Take for example the Eminence 3015LF, in a V[SUB]b[/SUB]=4ft[SUP]3[/SUP] vs one in a V[SUB]b[/SUB]=2.5ft[SUP]3[/SUP] with both cabs tuned to F[SUB]b[/SUB]=50Hz. Then add a parametric EQ (F[SUB]c[/SUB]=50Hz, Q=2.00, Gain=3.00dB) to boost the low end of the smaller cab. Here's what you get:

    3015lfeqvssize.

    3015lfeqvssize2.

    They're not identical, but pretty close. What am I missing here? I know there is no such thing as a free lunch when designing speakers, so what's the catch here? Why not just use a smaller cab and EQ in the low end?

    So far here is what I could come up with:

    1. Boosting EQ on your amp could add distortion, and reduce headroom, but if your amp had enough clean power available this might not be an issue.

    2. Do the same EQ boost on the larger cab and it totally crushes the low end of the EQ'd smaller box.

    So, what else am I missing?
     
  2. You'll have to feed the smaller cab more power, wich will introduce power compression earlier.
     
  3. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    OK. That makes sense. I'm not sure how much extra power the 3db bump in the EQ is going to add though. Is that really enough to make an audible difference?
     
  4. Kindness

    Kindness

    Oct 1, 2003
    Chicago
    Not if he's looking at the Max SPL chart he's posted.
     
  5. Yeah, I missed the major point:rollno: I was interpreting that as, for example, a 110 versus a 212. Duh. I understand now that it's box size with the same driver.

    I'll erase my posts. Thanks.

    K
     
  6. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    I understand what you are saying, but I don't think that is the case in the situation I've presented here.

    That's sort of what I'm talking about, but the two cabs here have the same drivers and are tuned the same (50Hz). I'm trying to compare larger apples to smaller apples. I'm not really concerned with the "absolute" sense. I know the larger box will have more output down low in the absolute sense. I'm trying to understand the differences if we EQ in the low end in the smaller box to match the larger. Like you say:
    The SPL and MaxSPL show output over the frequency range, and they are quite similar. There is a 3dB drop in low end with the smaller cab on the MaxSPL graph though, and I'm not sure why that happens. Hopefully someone might chime in with an explanation.
     
  7. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    No big deal. ;) I appreciate your input either way.
     
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The maximum SPL chart says it all.
     
  9. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    Thanks for chiming in Bill. Any chance you could help me better understand where the 3dB drop in low end comes from in the MaxSPL graph for the smaller cab?

    I've read into MaxSPL on the WinISD Help file, but is doesn't make much sense.
    The SPL and MaxPower graphs look pretty similar when comparing the two designs. Are the small defferences seen in these two plots more significant when looking at the big picture (MaxSPL)? How exactly are they combined to determine MaxSPL?

    One interesting thing to note is that adding EQ in WinISD doesn't seem to effect MaxPower or MaxSPL. You can togle the EQ on and off, but there is no change in either graph. The change seems to be there in every other graph though. :meh:Hmmm?
     
  10. Kindness

    Kindness

    Oct 1, 2003
    Chicago
    Those are the limits of the cabinet. You can play with the voicing of a cabinet within the limits of the maximum power and SPL limits, but you can't exceed them.

    The reason the max SPL on the smaller cabinet is lower is because it is less efficient than the larger cabinet, but it is still limited by the same (more or less) maximum power.
     
  11. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    It requires the amp to make double the power at the EQ center point, and do it cleanly. It also requires the driver to handle double the power at the EQ center frequency without distorting or going into power compression. Or to look at it the other way, it cuts available clean power in half out of the EQ band, which represents your 3dB drop in the low end max SPL. In my experience that can be very audible in many cases.

    I currently have my 3015LF in a smallish box, ~3.3 cu ft, tuned at 39Hz. It sounds great for my purposes with EUB where I want the gradual low end rolloff that alignment produces. Max SPL is almost never what I'm most concerned about in my DIY cabs, but many other guys seem to rate it as job one.;)
     
  12. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    OK, I think I get you. Since the smaller cab requires more power to hit the same SPL as the larger cab in the low end due to its inefficency, you hit the thermal limit or mechanical limit of the driver sooner. Would that be another way to describe it?
     
  13. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    Yes.

    And you push the amp harder, which requires a bigger amp.
     
  14. spode master

    spode master

    Jan 21, 2007
    When you boost the Eq on the smaller Cab, Xmax increases, distortion increases, and yes thermal compression is an issue too (Coils changing Z).

    If you tune to low in a smaller box, your vent velocity can get too high, and chaufing occurs.

    If its a smaller box tuned "optimally" You loose control of the cone bellow tunning.

    If its a well designend sealed box, you will have a predictable 12dB per octave roll off, that you can EQ against.
    The right drivers in the right sealed box will stay within xmax across rated power, but distortion increases with Excursion.
     
  15. Kindness

    Kindness

    Oct 1, 2003
    Chicago
    Exactly.
     
  16. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    3 dB means double the wattage for same SPL.

    You might say "it's only at the lowest freqs!!!!" well, if you play notes that generate them you'll need double the wattage.
     
  17. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    That makes sense. I don't have much experience with power compression, but I've read a bit about it. I'd love to do some SPL testing some day to get my ears used to what the numbers tell me I'm hearing.

    I'm infatuated with small loud (and light) boxes, true low end vs. perceived low end, and training my ears to understand what empirical and theoretical data tells me I'm hearing. I've got the cab design/build "bug", but the deeper I get the more there is to learn. I love it.
     
  18. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    I know nothing, really. And I love it too!:cool:
     
  19. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    I hear what you're saying. In my first post I made an assumption "if your amp had enough clean power available this might not be an issue", but as others pointed out under this assumption it is the thermal limit of the driver that will determine the MaxSPL.
     
  20. What a mess

    What a mess

    Aug 20, 2008
    Valdosta Ga.
    It is harder to achieve (building fart syndrome) with a smaller box. That is where people approaching the building from outside can hear the building make groaning creaking sounds from outdoors.
     

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