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Figuring out port tuning on a vintage speaker cabinet.

Discussion in 'Amps and Cabs [BG]' started by Rock&Roll, Aug 7, 2004.

  1. Rock&Roll


    Jul 21, 2002
    I've been jumping around on the internet all day today reading this and that about bass speaker cabinet calculations. The stuff i've come across hasn't lead me to any sort of clearity in understanding things yet. I'm proving to be quite inept at the current time.

    Basically, I'm trying to get a grasp on the abilities of the 2x15 Acoustic made cabinet I have. It is ported, but I don't know for what frequency. I have taken measurements and calculated the internal volume (thanks Autocad). As well, I've gotten Perfect Box and another DOS based speaker buider program. I've been playing around with these programs, but I really don't know what to put in for the vent frequency, so my graphs are about worthless.

    So here's what I'm looking to find out. How can I figure out the port tuning from the given size? Here is a screen shot of the autocad drawing I made. The organe color represents the inside surfaces of the cabinet.


    I'll probably wake up tomorrow and find that I've just asked the most stupid question in the world. If so, just slap me, and I'll go on my merry way.
  2. Petebass


    Dec 22, 2002
    QLD Australia
    I just ran a dummy speaker simulation through WinISO Pro, using the supplied cab volume and port dimensions. It spat out a value of 42.5Hz as the tuning frequency.

    There's a couple of ways to check this. The easiest if to use a sine wave generator and play every single frequency through the speaker one at a time (I use a CD instead, one that has a sine wave of every frequency between 20Hz and 100Hz. Speakers are rarely tuned higher than this). When you've got the tuning frequency, the speaker cone movement will be virtually Zero. I find if helps to put a small dot of white liquid paper in the middle of the speaker, on the dust cap, just to make it easier to see exactly how much the speaker is moving.

    I've also got some info on how measure it with a multimeter lying around somewhere. I can dig it up if needed, but 42.5Hz sounds about right for that sort of cab.