Speakers w/ Different Impedances - Power Differential

Discussion in 'Amps and Cabs [BG]' started by batflash, Jun 6, 2020.

  1. batflash

    batflash

    May 11, 2020
    Hi all,

    Here's the scenario.
    Amp into 800hz crossover
    8ohm woofer (amp power 350w, 97db sens)
    16 ohm HF Driver (amp power 175w, 99db sens)
    Total 525w@ 5.3ohms

    Am I right in thinking that the HF Driver will be approximately 3db less due to the power differential?

    Thanks for the help.

    J
     
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Yes and no, but it's likely that the HF driver will have a higher sensitivity than this in its passband.

    The sensitivity will be about the same, but depending on the program material you might run out of HF power before the LF power. In practice this is VERY unlikely due to the energy density versus frequency characteristics of the program material (especially bass gtr)

    The system impedance would be more or less 8 ohms, the HF driver doesn't factor into the impedance below 800Hz and the LF driver impedance will be rising while the HF impedance will be dropping above 800Hz.

    What drivers are you talking about?
     
  3. batflash

    batflash

    May 11, 2020

    As always, thanks for your response. I'm still toying with a design concept using those Genz Faital 12350's and the FaitalPRO M5N8-80. I'm not quite there with the concept. The idea is is to emulate a guitar speaker with smooth response, extended lows, with a tapered top end.

    I'll be building a cab, larger than what I have(marshall 2x12). Maybe 4.5 to 4.75 cuft.

    Again, using it for bass and guitar duties.

    I appreciate your feedback. Thanks again.
     
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Ok, there are some complications that apply.

    1. The GNX-12350 was only available in 8 ohms, so if you are planning on a 212, you will have a 4 ohm low frequency section. For constant drive voltage of 2.83V, that would 1 watt into 8 ohms or 2 watts into 4 ohms. The sensitivity will increase by about a dB and a half with 2 drivers, and you will also need to add 3dB to the sensitivity to account for the 4 ohm load.

    2. IF you are planning on low passing the 12's, you will need to account for the 4 ohm impedance of this section.

    3. The mid driver that you are looking at is about 99dB/1W/1M, it's available in 8 or 12 ohms but not 16 ohms (unless OEM). You will need to compare the sensitivities using the drive voltage, if the MF driver is 8 ohms, this would be ~99dB. At the same drive voltage, the pair of GNX-123350's will be about 102dB.

    This may not be a bad thing, but the information is important to understand.
     
  5. batflash

    batflash

    May 11, 2020
    So, you kinda played into what I was hoping for l, which was broaden my perspective on other scenarios and how to apply the same logic. For example, I'd like to first have a go at a 1x12 with the mid range speaker. Mainly because it would be a cheaper learning experience than do the 2x12. Plus it'd be nice to have a smallish rig.

    So in the case of using the same crossover with an 8ohm LF and HF drivers, the LF is going up roughly by half and the HF is going down, roughly by half. In this scenario, is the HF taking the brunt end of the power?

    Is there something in the response charts I could utilize to better understand what to expect from combining drivers? Do you have any recommended reading material that approaches this from a simple approach?

    Also, with form in mind, keeping my cab limited to a smaller size, but no less than 4.5 cuft, however with flexibility with round porting, so you see an issue with a box that size?

    Could building any large-ish box wih the right porting, suffice for the use of the 12350's? I could I flex on box size, if so, by what margin?

    Thanks again.
     
  6. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Power distribution in a bass guitar signal decreases as frequency increases. This is a fundamentally important concept.

    4.5 CF internal air space for a single 12" driver may be too large to achieve good tuning. I don't remember exactly, but I recall the driver being optimized for a smaller box.

    Also, it's critical for the mid driver to be in its own sealed enclosure. Otherwise the 12 will tear it apart, and the tuning of the 12 will also be impacted.
     
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  7. batflash

    batflash

    May 11, 2020
    I had intended to seal the smaller driver off with its own slightly angled baffle for better upward projection. Also toying with the idea of a side firing port to throw some air back as the drummer on small stages. Not sure if that's a good idea being that I'm one of two guitarists in the band and the other won't be employing the same method. I'm certain I'll come off as louder.

    Also, typically, what suffers from too large of an enclosure? What about too small of an enclosure?
    I imagine overexcursion is very possible in both scenarios. Too much space in one cab and too big of a port to achieve lower tuning in the other.
    Probably something that's been covereddd a million times on the forums, huh?

    Thanks again.
     
  8. batflash

    batflash

    May 11, 2020
    I'm seeing a lot of "mid range" speakers that extend well passed 10khz and in some cases bump up in response from 6khz and up. In your experience, do these response charts decently represent the actual response of the speaker? Particatly the high end.

    Note, I'm still trying to find a decent mid range speaker that has a natural high end roll off around 6 or 7khz that I can crossover somewhere around 800hz with the LF driver. Again, no tweater involved in the speaker network.

    Thanks.
     
  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
    I wouldn't bother with a side firing port, the (potential) benefits are very limited.

    When a cabinet becomes too large for the driver, the air is too compliant and the acoustic loading of the driver tends to fall apart. It's not just overexcursion, but poor low end response.
     
    batflash likes this.
  10. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Some do have extended response, and the plots are generally accurate but you need to differentiate on axis from off axis response. Some of the boost occurs because the pattern starts to decrease... think of it as energy density, decrease the area for a constant input and the density increases.

    You are using the mid driver in place of a tweeter.

    I think you may be overthinking this a bit.
     
  11. I use these drivers in their original cab, the Genz-Benz NX2 2x12T and use it for guitar also and think you do not need a mid speaker.
    Though I do have the tweeter on at the 50% mark so that may need to be into play giving my recommendation. :cautious:
     
  12. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I agree, the mid extension is good and pretty smooth by comparison to many.
     
  13. batflash

    batflash

    May 11, 2020
    I agree, however I'm looking for a little more high end extension for cleanish guitar work. Thanks for the feedback everybody.
     
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Than frankly I would be looking at a different driver, either the JBL K/E120 or the EVM-12S/L. There are some others in the Neo world but I can't recall any that I have tested. The JBL would be my first choice.
     
  15. batflash

    batflash

    May 11, 2020
    Don't you think the excursion limits are kind of low on those drivers, especially for a loud heavy, sometimes doomy, rock band playing in low tunings?