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is there anything wrong with this cab

Discussion in 'Amps and Cabs [BG]' started by bassman454, Jun 19, 2002.

  1. i have a 15 and a 10 in a ported cabinet, the cab i about 2 feet by 2 feet and 1 foot deep, there are 2 ports of about 3 inches diameter and 10 inches long...would you say this is over ported or underported...and what affect would this have on the sound of the cab
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    This is impossible to say without having the spec sheets of the speaker(s).
  3. ZuluFunk

    ZuluFunk Supporting Member

    Apr 14, 2001
    I agree with JMX.

    Who made the cab?

    BTW, JMX, in reference to your signature. I had a Lacrosse Coach in High School. Notorious for Yogi-isms like that. He used to say things and we'd just look around at each other wondering...These are all the God's honest truth.

    "Practice is not an option. Therefore it is mandatory" No-duh.

    "Everytime you get the ball down there you can't get the ball down there." Umm, wait, so, so should we even try to get the ball down there once we've gotten the ba... or do we have to get the.. ummm, forget it.

    And my favorite, which I used as a quote in my yearbook: "Everything I told you not to do you're doing wrong." I guess it would be worse if we correctly executed everything you told us not to do. That would still be better than screwing up everything you told us TO DO!

    Good old Coach Dick!!!
  4. 44me


    Jun 17, 2002
    Bedford, NH USA
    If I understand you correctly, and both the 10 and 15 inch drivers share the same enclosure volume, it won’t be possible to determine whether it is ported “correctly”. The reason for this is that it is highly unlikely that the 10 and 15 inch drivers have the same design parameters, so standard bass reflex design theory cannot be used to determine ideal porting, or enclosure size for that matter. Your cabinet was probably developed experimentally (or a couple drivers were thrown in a box that someone had lying around).

    Forgetting for a second that you have two different drivers, a cabinet tuned to a higher than ideal frequency (ideal meaning an alignment that gives as flat response as possible, for discussion’s sake) will have a mid-bass hump. That is, it will sound a little stronger until you get down to the low notes, where volume will drop off quickly. A lot of small home stereo speakers are intentionally designed this way because it makes them sound bigger to the untrained ear. This also has the undesirable side effect of reducing the peak power that the speaker can handle at low frequency before the driver bottoms out.

    On the other hand, tuning to too low a frequency causes a dip in response just before the low frequency roll-off (it actually pops back up a little just before it rolls off). A side effect of this sort of tuning is that the driver’s resonance is not well damped and you get poorer transient response (notes become poorly defined – might be good for reggae). Unless the tuning is extreme, bottoming out the driver is much less likely. This type of tuning is sometimes done intentionally to get as low a frequency response as possible from a small enclosure.

    So, what makes you think something is wrong with your cabinet? How does it sound? At the end of the day, that’s what really counts.
  5. umm ok, it started as a single 15" cab which was 4 ohms. i had a 10" lying around so i decided to put it in the cab aswell as the 15" and wire them in series to give me an 8 ohm cab.
    i used the same ports that were allready in the cab, but i just rearanged them in the new baffle to fit the combination of the 10", 15" and the 2 ports.
    it just sounds really dull, so i am going to turn it back into a single 15" cab, but i just don't know what is wrong with it weather its underported or overported.
  6. 44me


    Jun 17, 2002
    Bedford, NH USA
    I think your cabinet problems are much more than porting. First, if we assume the cabinet was sized appropriately for the 15” driver, it’s now too small for the 15 plus the 10. Second, wiring two drivers with different characteristics in series is going to give you a very undesirable side effect. Driver impedance peaks significantly at it’s resonant frequency. This means that neither driver will be driven correctly at low frequencies. That is, driver resonance will be very poorly damped. Combined with the small enclosure, low bass is going to be very undefined, and the response will likely roll off at a higher frequency than either driver alone – just the opposite of what you want.

    As a side note, I’ve had issues running two properly designed cabinets with different drivers (2X10 and a 15) in series. Both cabinets sounded fine alone, but wired in series, both became muddy, especially the 15 (this was a recommended configuration by a reputable manufacturer!). Both were 4 ohms, and my amp couldn’t handle them in parallel, but as an experiment, I borrowed an amp from a friend that could drive 2 ohms – they sounded fine. I also tried running one cabinet with one amp, and the second cabinet with the other – almost the same. I then hooked them back up in series with my amplifier, and looked at the driver voltages with an oscilloscope while feeding a constant tone into the amp with a signal generator. Sure enough, the speakers shared the load well above 80Hz or so (roughly E on the 12th fret of the E string), but at low frequencies they did not. At low frequencies, each cabinet was being driven by a much higher impedance than the speaker designer had intended. The only cabinets I will hook up in series now are those that are identical.

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