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  • Intentionally Mistuning Cabinet

    I'm looking at building some speakers that are flat down to at least 24Hz. I was planning to use 12" Ultimaxes but there are a couple of high end 15" drivers (Acoustic Elegance) I'm also considering which don't really go down past 30Hz in a ported box.

    I'm wondering if it would be OK to build a box tuned to around 24Hz anyways. When I model it, it starts to roll off similarly to a sealed enclosure and then has a steeper rolloff from the port. My idea would be to then EQ it flat down to 26Hz or so. Basically lowering everything to match where it is at 26Hz. In terms of power handling and excursion, the driver is fine.

    Are the any reasons I shouldn't do this?

    Here's an example -

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  • #2
    Some JBL speakers did that. EQ boost is fine as long as it's above the port resonance. Below there, you stand a chance of exceeding xmax. Of course, because of room gain you may find that EQ is unnecessary.
    Francis

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    • #3
      Originally posted by gerhardw View Post
      I'm looking at building some speakers that are flat down to at least 24Hz. I was planning to use 12" Ultimaxes but there are a couple of high end 15" drivers (Acoustic Elegance) I'm also considering which don't really go down past 30Hz in a ported box.

      I'm wondering if it would be OK to build a box tuned to around 24Hz anyways. When I model it, it starts to roll off similarly to a sealed enclosure and then has a steeper rolloff from the port. My idea would be to then EQ it flat down to 26Hz or so. Basically lowering everything to match where it is at 26Hz. In terms of power handling and excursion, the driver is fine.

      Are the any reasons I shouldn't do this?

      Here's an example -

      Click image for larger version  Name:	Subs2.PNG Views:	16 Size:	126.5 KB ID:	1429835
      There's another option! This option doesn't play as loud as ported, but goes as deep. I modeled an RS270P-4 in 1 cu-ft sealed. The f3 is about 62hz. When you add a 60hz low-pass, the f3 drops to about 25hz. I posted a jpeg in a recent sub-woofer discussion thread showing the sim.

      I was going to port my box, but after using it as described, I decided to keep it sealed.

      Comment


      • #4
        And just for the record. Adjusting the port tuning like you are contemplating is a normal part of the design process. I usually tune mine similarly to get the minimum possible group delay and best transient behavior. So what I'm saying is that "flat" is a perfectly valid choice, but there is a lot of latitude depending on personal preference.
        Francis

        Comment


        • #5
          +1. If it gives the results you want it's tuned correctly.
          www.billfitzmaurice.com
          www.billfitzmaurice.info/forum

          Comment


          • #6
            You absolutely want to take room gain into consideration. I redesigned a pair of dual 15" bass bins from ported "flat" to much smaller sealed boxes with a much higher roll off because in-room response was just awful. They got just as low as before but we took the boom out of the room. YMMV. They sound so much better and will still rattle your guts (and everything else).

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            • #7
              +2 I also agree. I mentioned the sealed option just in case a smaller box was a plus.

              Comment


              • #8
                In my case, my room drops off below 30Hz (well, in the side of the room that I sit) so having more power down there is desired. My current 10" Titanic subs were designed to be flat and tuned to around 28Hz. They play fine without too much correction needed so I think I should be aiming for something similarly flat (as a starting point before actually tuning these in the room).

                My main concern is that while my plan is to attenuate everything down to where the speaker is tuned, that's essentially the same thing as boosting around the port by quite a bit (~8dB). As far as I can tell, xmax isn't an issue until I get down below 20Hz so I'm just worried about any sort of side effects or weirdness from boosting the port.

                I have modeled sealed but it can't handle the SPL I need (can only down to 30Hz). I'd need to double the number of drivers to get the same output down to 20Hz. Box would end up basically the same but it would add another $1300 to this project plus the price of another amp. Going with these drivers has already added $1300 to my project which is no small feat. If you tell me that my idea won't turn out well and that going with the dual sealed is what I should do then I would seriously consider it but otherwise I'd obviously like to not spend that much more.

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                • #9
                  Here's what I managed to come up with. F3 ends up at 23Hz and that obviously doesn't include any room gain.

                  It seems to be able to handle the highest SPL I'd ever need (105 @ 4m) for if I ever move to a larger room (right now my full-band max SPL is 100 @ 2m). Group delay doesn't look very good. Can anyone comment on if I should move forward with this? Any input is greatly appreciated.

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                  Comment


                  • #10
                    Don't forget to add a low pass filter to your WinISD filters. Set it to whatever F3 and Slope order you plan to cross it over to your mains. This will make a big difference in your planning.

                    -Bob
                    -Bob

                    The PEDS 2.1 mini system
                    My A7 Project - another small desktop speaker
                    The B3 Hybrid Dipole - thread incomplete and outdated

                    Comment


                    • #11
                      Originally posted by BOBinGA View Post
                      Don't forget to add a low pass filter to your WinISD filters. Set it to whatever F3 and Slope order you plan to cross it over to your mains. This will make a big difference in your planning.

                      -Bob
                      Can you clarify how this would impact my planning? I'll be doing at least a 4th order linear phase crossover probably at around 120Hz. Definitely above 80Hz. I'm not sure what difference entering that in to WinISD would make. It seems high enough that it wouldn't really have any impact on the region that I'm playing around with.

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                      • #12
                        What you're saying (Fc up near 120) seems true enough.

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                        • #13
                          It might not affect it much, but its simple to do and you can see if it allows you to lower the tuning a little bit.
                          -Bob
                          -Bob

                          The PEDS 2.1 mini system
                          My A7 Project - another small desktop speaker
                          The B3 Hybrid Dipole - thread incomplete and outdated

                          Comment


                          • #14
                            Sometimes the only way to tell is something is going to work out well is to go ahead and try it. Either way, you'll learn something in the process. If we always did things according to rules of how they were intended to be we'd be putting artificial limits where they don't need to exist.
                            Screw it, let’s do it. Richard Branson

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                            • #15
                              Originally posted by Trendytech85 View Post
                              Sometimes the only way to tell is something is going to work out well is to go ahead and try it. Either way, you'll learn something in the process. If we always did things according to rules of how they were intended to be we'd be putting artificial limits where they don't need to exist.
                              True. Although in this case it's established tech, used in some commercial speakers. And to get a "regular" tuning all you need to do is shorten the port, and perhaps place some filler material in the box to take up volume.
                              Francis

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