roland microcube bass rx cabinet modification

Discussion in 'Amps and Cabs [BG]' started by alleyonemusic, Feb 7, 2022.

  1. alleyonemusic

    alleyonemusic

    Jul 3, 2012
    norcal
    as an owner of a vintage orange roland cube 60 bass amp with the tuned port, i am wondering if this type of tuned port would be feasible on the micro cube bass cabinet?
    any ideas?
    tanx, m)
     
  2. Wasnex

    Wasnex

    Dec 25, 2011
    To answer your question without doing a destructive mod, you need the Thiele-Small (T/S) parameters for the drivers and the internal volume of the chamber(s) in the cab. Insert the data into a speaker modeling program and experiment with different size ports to see what happens. Choose the setup the works best. My guess is the stock, sealed setup will be best. Also, I doubt Roland publishes the T/S parameters.

    My advice: If the Bass RX does not meet your needs, don't devalue/degrade with an experiment. Sell it and use the proceeds to buy something that is more suited to your requirements.
     
    abarson likes this.
  3. alleyonemusic

    alleyonemusic

    Jul 3, 2012
    norcal
    thank you wasnex,
    that's the practical and logical answer i was looking for.
    but i'm always willing to experiment as well.
    m)
     
    Wasnex likes this.
  4. Wasnex

    Wasnex

    Dec 25, 2011
    I think the biggest problem is lack of power. Specs say 2.5W x 2 but I believe this is a peak rating. Continous RMS is either 1.25W x 2 or 0.625W x 2.

    In addition to having low power, my guess is the sensitivity rating of the speakers is low.

    My personal feeling is the amp is only useful for practice in a quiet environment, but a lot of people seem to like them.
     
  5. alleyonemusic

    alleyonemusic

    Jul 3, 2012
    norcal
    hi wasex,
    thanks for your reply.
    i have used this little amp to play bass along with acoustic guitars in open mic and song writer circles. that's it's loud limit. i'm just wondering if porting the cabinet will give a bit more psycho-acoustic sound :)
    the sound from an early (orange) roland cube 60 bass amp seems to do this quite nicely. this cube 60 is about all i use when i play out. if i need to be louder i connect my countryman di and tell the sound person... m)
     
  6. Wasnex

    Wasnex

    Dec 25, 2011

    Not sure what you mean by pyscho-acoustic. Ports reinforce and possibly extend the lows. They do not create any sort of effect. If you want a good sounding cab, you can't just install a random port. You need to consider characteristics of the drivers and use sound engineering practices to design around them.

    Here is sort of a basic explanation for how a port works and is tuned. Above the port tuning frequency, the cab functions essentially as a sealed design, meaning little to no sound emanates from the port. As the frequency goes lower, eventually the drivers start to roll off. The port is tuned so that it starts to become resonant just as this occurs. As the frequency drops below this point, the port becomes more resonant. The most resonant frequency is labeled Fb. At Fb the port is producing most of the sound.

    A benefit of the port resonance is it suppresses driver excursion. This tends to increase power handling within the systems pass band.

    The excursion plot of the driver will have sort of a "S" shape. Generally excursion starts to increase as the frequency drops below about 500hz. Below 100hz, the excursion start to increase quickly. As the port starts to become more resonant, driver excursion decrease until the design hits Fb. Below Fb, the output of the system drops off extremely fast and cone excursion increases drastically, so you don't want to operate the system very far below Fb.

    For example here is the excursion plot for a ported design for the Eminence 2512.
    upload_2022-2-8_15-42-28.png
    Notice how excursion reaches a minimum at Fb (44hz) and then increase to max liner excursion (Xmax = 4.9mm) as the frequency drops below Fb.

    Here is the Frequency Response plot.
    upload_2022-2-8_15-44-51.png

    The design is down by 3dB at 63.69hz. By Fb the output is down by 12dB. You can't correct for the roll off with EQ because it will push the driver beyond Xmax, unless you reduce the power level below 125W. The notes for this design say to use a steep high pass filter set to 35hz, which is approximately where the driver hit's Xmax with 125W.

    Another factor is certain T/S parameters determine if drivers work best in a sealed cab or ported cab. My guess is the drivers in the Micro Bass Cube RX are optimized for a sealed cab, and they may not work well in a ported design.

    Nobody is stopping you from cutting a hole and trying to install a port. But I think you are unlikely to improve on the little amp's performance without the right expertise and skill.

    Most of the Eminence Pro woofers have Cab Design docs that show a variety of tunings. For example I pulled the docus used in this post from: ps://www.eminence.com/speakers/speaker-detail/?model=DeltaliteII_2512
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    If you don't know what driver is in it, you aren't going to be able to do anything but guess. It may be that with the driver in there, no port may give the best results.

    My gut feeling is that with an enclosure so small, the driver selected will probably do just as well in a sealed enclosure as it was designed as a system along with the amp. It's also likely to have an even hung voice coil so displacement linearity is focused around the limited power available.
     
    Wasnex likes this.
  8. alleyonemusic

    alleyonemusic

    Jul 3, 2012
    norcal
    waxnex and agedhorse,

    thank you. you're saving me a lot of time and trouble. good stuff.

    roland does not make the Thiele-Small (T/S) parameters available.

    can't make 5 watts be any louder can ya?

    cheers,

    m)
     
    Wasnex likes this.
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Sometimes, it is what it is.

    For 5 watts to be usable, tradeoffs need to be made in the speaker design, maximizing one variable at the expense of another.
     
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