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Cab design questions

Discussion in 'Amps and Cabs [BG]' started by l0calh05t, Nov 24, 2002.


  1. I am thinking about building a closed 2x12 , as soon as I have enough money, but because I hate wasting money I'm trying to plan everything as exactly as possible.

    I am planning to use Peerless 830669 (SLS 315) drivers in a cab that has an effective volume of 90l , which would be in the low area of the volume suggestet by peerless (45-65l per driver), this would result in a Qtc of approx. .89 (F3=39.6Hz and I play 4-string so it will be low enough to reproduce the fundamental)

    Now my question would it make sense to add 2 Peerless 821615 (M 122) to get more high end, or would it be to difficult to make the crossovers (at approx. 800Hz), or would a simple highpass on the M 122 be enough to have a fairly even sound? (it doesn't have to be perfect just good enough to not have a 6 dB hump in the 800-2k Hz area) ?

    BTW I know the cab will only have an SPL of approx. 91dB
     
  2. geshel

    geshel

    Oct 2, 2001
    Seattle
    Well, it depends on how smooth of a midrange you want. The woofer looks like it breaks up around 2-4kHz. This might not cause much problem with a bass amp but I'm not sure. I'd put at least a first-order low pass on it at 1kHz just to make sure. And match that up with a first-order high-pass at 1kHz on the midrange.

    You could, maybe, first build the box with just the two woofers, straight up. See how that sounds. If the upper midrange is too harsh, or you need more treble, think about putting in a midrange or two. Since they have their own chamber it'll just be a "cut a hole and drop them in" sort of thing, which is handy.

    Man, I love that Peerless web site !
     
  3. what's so special about the peerless website, except that they give all details for their speakers?
     
  4. almost forgot to say what kind of lowpass would you use on the woofers?
     
  5. geshel

    geshel

    Oct 2, 2001
    Seattle
    P.S. I think the Qtc and F3 sound just about perfect - you've got a little bass bump from the Q of .9, and it goes just as deep as you need it. Being a sealed box it'd probably still do pretty well on the low B fundamental too.

    Hmm, I just plotted it in WinISD and it shows the F3 of about 47Hz, -6dB at 39, -10dB at 30Hz. I'd still expect that to do well with a four string.
     
  6. I actually also plotted it with winISD and i got different values
     
  7. heres a screenshot of my winisd plot

    EDIT: I just rechecked the t-s parameters that are saved in my winisd and they are completely wrong! I don't know how this happened, but with the correct values a volume of ~120l is required for a similar freq. response
     
  8. geshel

    geshel

    Oct 2, 2001
    Seattle
    Weird. Here's a screenshot of mine. Are we using the same params?

    For the lowpass, I'd just keep it simple and use a single coil on each woofer. If you're using the midrange that is. Otherwise just leave them as-is.

    As for the Peerless site, I guess I just meant I liked that they had the specs and graps for all their products available online like that.

    edit: can't read it, but that's a Qtc of .90 in that 120 liter box.
     
  9. as i said the parameters i used (also in my screenshot) where somehow completely wrong (might have been my faulty RAM which caused that, EDIT: "Me stupid" the parameters i used where the parameters for the Peerless 830668 SLS 263, except for the radius)

    Do you have an idea which parameters are the correct ones to use, the free-air or the baffled?
     
  10. heres a new screenshot in which the different parameters are compared
     
  11. Link to 830669 Plots

    This Peerless driver is very similar to my 15" subwoofer drivers. It is very inefficient, and requires a LOT of amplifier power to make any noise. I calculate a true 90.7 SPL from the T/S data published by Peerless. Mine are 89 SPL, and I drive two 1x15 with 450 watts each, and it is everything I can do to keep up with a loud band in a bar venue.

    The EBP of this driver is 55 which puts it right into the realm of sealed boxes, but it will also perform very well in a larger BB4 alignment vented box if you need the big bottom. The BB4 requires 172 lites internal volume. This Peerless driver requires big boxes for both sealed and vented applications. I would not build this as a 2x12, but as two 1x12 instead.

    You can reduce the sealed box size 30% by stuffing the box with 0.455 kilos of fiber fill material per 28 liters of actual box volume. For example, using 120 liters for a Qtc = 0.707 box, you can reduce the box volume to 92 liters with 1.5 kilos of fiber fill.
     
  12. geshel

    geshel

    Oct 2, 2001
    Seattle
    I tried a couple quick ported layouts with that driver and the transient response was pretty yucky. Well, not bad for a bass cab probably but compared to the sealed, 2x the group delay.

    I just discovered that in WinISD you can click in the box picture and move the mouse around, and it adjusts the box size and tuning frequency (right-click for the rear chamber of a bandpass). That's kind of handy. Doing that with a 4th order bandpass helps get an intuitive grasp on the effect of the volumes and front tuning frequency has.
     
  13. As I already said in my first post, I know it will not be very loud. I would still use it in the sealed alignment with Qtc at approx. .89

    I was also aware of the fact that damping will reduce req. volume by up to 20-30% depending on amount. Is there any specific reason for you saying that you would build two 1x12s except that they are more portable (which of course is already a fairly good reason)?

    Also could you answer one of my first questions:


    EDIT: Why would a volume of 120l give a Qtc of .707 I calculated a Qtc of .9 for that volume (which is pretty exactly what I wanted to use)
     
  14. 120 liters is 4.25 cubic feet. The 830669 driver in 4.25 cubic feet, sealed, is Qtc = 0.707. I double checked the math in several places.

    Vas = 205 L or 7.25 cubic feet
    Qts = 0.43
    Fs = 25.7 Hz

    I suggested a pair of 1x12 because a 2x12 requires double the internal volume: 240 L or 8.5 cubic feet. This is getting pretty big and hard to move around.

    Stuffing a sealed box converts it from adiabatic to isothermal operation and changes the speed of sound inside the cabinet. You can reduce a sealed box by 30% using 1 to 1.5 pound per cubic foot of fill material. This has been demonstrated and measured by Tom Nousaine and is a nice trick for reducing the box size.

    If it were my project, I would reduce the 120 L box to 92 L by using the correct amount of fiber fill stuffing.
     
  15. Ah now I understand! It is a simple misunderstanding , I was talking about 120l for both drivers together (Qtc = .9 F3=44.96Hz which is of course a little bit higher than 41.2 Hz but the difference should be fairly small [approx. 1.2 dB]), so it would be 92l with fill material, although I might still make it a slight bit larger
     
  16. 92 liters for *each* driver.
     
  17. to get a Qtc of .707, but 92 (with damping) for both will give a Qtc of .9
     
  18. to show what I am talking about
     
  19. I hope you have watts to spare on your amp, because you might not like the max. SPL of the cab(s).

    I have built and used 2 hifi cabs (each 1x12 with added 5" midrange and 1" tweeter, real-life efficiency 93 dB), and while they have massive amounts of low end, the power I put in them (160 watts each and clipping occasionally) is far from enough to get by on stage. My other home built rig, with PA speakers (1x15+6 and a 2x10+horn) completely blows the others away, SPL-wise. The real-life efficiency of the 1x15 is 100 dB and the 2x10 is 102dB

    You can see the cabs at my site, should you be interested.

    Regards,
    Joris.
     
  20. I have already seen your cabs on your website and they look quite nice.

    Bassically I am looking for a sealed cab (better transient response) which can reproduce my low E (I play 4-string) without great difficulty, and I also don't like the way how the highs from a tweeter sound (I sometimes use slight distortion on the top end of my sound and leave the bass frequencies clean), that was the reason for thinking about using M 122s (together with the SLS 315) because I still want some high end.

    If you know any other speakers that can give me this at an enclosure volume of lets say max. 180l for both drivers together (90l per driver) and with a higher SPL I am open to suggestions :)

    EDIT: It can also be 10" drivers, but I don't want to use 15" drivers