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Mid driver in a cab?

Discussion in 'Amps and Cabs [BG]' started by jock, May 23, 2004.


  1. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Ive got an almost done cab based on the Eminence Omega Pro 12 driver. I was thinking of putting a 5" or something to give some more highs and mids. How do I choose one that will fit? Can I use a simple cap to protect the mid from low frequencies and leave the 12 "uncrossovered"?
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    What do you mean by "fit"...physically or acoustically?

    Acoustically, I guess you'd need to choose one with a lower frequency response below where that 12 starts to get weak and cross it over there. Eminence posts nice frequency response plots on the web so you should get an idea from there.

    Yes, you can run the 12 full range. That seems to be how most bass cabinet manufacturers do it anyway...run the woofers full range and run the tweeters with just a high-pass filter on them to block the lows.

    Yes, a cap in series with the mid will block lows and roll them off at 6 dB per octave. Probably no real need to so steeper unless you're crossing over the midrange really low.

    You might want to PM or email Petebass...IIRC, he did something similar.
     
  3. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Thanks!
    Yes, I ment fit acoustically.
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Good memory Billy! But the project in question never went ahead. I was looking to revamp an existing cab but couldn't really find any woofers that would suit, so the project has been put on hold.

    The challenge here is adding the 5" in such a way that your 8 ohm cab remains an 8 ohm cab. Personally i'd be putting a High pass filter that is at least 12dB/octave, and I'd cross it over at least one full octave above the 5" drivers resonant frequency. This will prevent the 5" driver from reaching an impedance that's low enough to alter the nominal impedance of the cab. A 6dB/octave will also work but you'd have to cross it over even higher, 2 octaves above Fs would do it.

    The other issue is sensitivities. The 5" will probably be more efficient than the 12", so it may come on a bit too loud. If so, you may have grab a couple of resistors and add an attenuation cell to turn it down and balance the volumes. Resistor values will vary depending on how much attenuation is required. Experimentation may be needed to get the right balance.

    Have you got a 5" driver in mind?
     
  5. You definitely need a full crossover for a 12 to a 5. And 12 dB/oct is IMO the minimum steepness. Which means a cap and a coil on both speakers. A 6 dB/oct filter on a 5" (iow. a pretty big cone mid speaker with a strong resonance) will get you into trouble, as you will be doing far from 6 dB/oct in practise, because of the inductance of its voice coil.

    But do you think the 12 doesn't have a good midrange? It's the most popular driver for PA midrange, and should at least reach as far as 4 kHz. Maybe a 5" will get you to 8 kHz.

    I've done a 15" design with a 6" midrange x-overed at around 600 Hz, which works pretty well, but the 15 was too sluggish for midrange.
     
  6. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Thanks guys. This sounds a bit more complicated than I hoped for. Im about to put the last screws into my Omega Pro 12 cab today. Dont know how it sound yet. It might have enough mids/highs as it is. But it was just a thought to ad some 5" to widen the frequency response if it comes out too muddy.

    The Omega Pro 12 is one biiiig driver BTW. Biggest magnet and casing Ive ever seen. Looks super solid. Cant wait to get this cab running... :hyper:
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Keep us posted. Let us know how it sounds.
     
  8. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Well, tis done! :bassist:
    The cab is wired up and I tried it using the head in my 60W Behringer combo. Not the best but my poweramp is at our rehersal space. What I can say is that it sounds really true to my bass´ sound. Its fat yet really pronounced and has enough mids and highs for my taste (Ive never liked tweeters). It sounds a lot like my EBS 210 but deeper and not so harsh on the topend. Im really pleased so far. We´ll have to see how it sounds in the band next week when bridging 1500W into it. BTW Im using a Jack Casady bass and like fat, non-scooped-mids rootsy rock´n´roll sounds that are clear (not muddy like Ampeg :bag: ).
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Great stuff!

    12's are not common in Australia. I've considered building one and I like the Omega Pro 12 on paper. Let me know how it goes with the big amp at ear bleeding volumes.
     
  10. Jock,

    Look into an Eminence Alpha 6 and pxb2:800 crossover.

    The driver sensitivity between the Alpha and Omega Pro is virtually identical, so there will be a smooth transition at the crossover point. The slope is 18dB for the Alpha and 12dB for the Omega. The 800 Hz crossover point offers more than 1 octave headroom at the crossover point for both drivers.
     
  11. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Thanks a lot!
    I was looking at that driver but since its in Eminences lowest range I kind of backed away. Is it good quality?

    Also, could I put it in a separate box? I dont think there is enough volume in the cab unless I would be willing to steal some volume from the 12". Would that make a big difference for the 12´s sound? Its now in an SBB4 tuned cab.

    Edit no 2: Should I tune the Alfa 6 to an SBB4 alignment too or put it into a closed box?
     
  12. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Great. I know a store that has such mid-speaker-bowls. I´ll check it out.
     
  13. Cheap speakers have little Xmax and no bottom end. Neither matters if using the Alpha for 800 Hz and higher. Its response curve shows it will carry the upper end out to 10 KHz or higher.

    The Beta and higher series do not have the high end response. The crossover frequency is too low to use an Eminence horn driver, plus the horn is significantly more sensitive (louder) than the Omega 12. The Alpha 6 is a perfect match.