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15/6/1 Full range cab build / crossover(fEARful inspired)

Discussion in 'Amps and Cabs [BG]' started by BoogieZK, Dec 8, 2018.

  1. BoogieZK


    Sep 28, 2008
    Toulouse, France
    Hello everyone,
    I'm currently building an 15/6/1 cab with:
    Eminence Kappa Pro 15LF2
    Eminence Alpha 6CBMRA (closed back 6A)
    Sica Horn HFU6x8/83.26

    It's a bit oversized compared to the 15/6 (150L) and it's based on the Kappa PRO15 LF2 datasheet with 15mm plywood.

    The current question is about crossover points and the discussion started about how much power is thrown into the mid driver as i chose to Xover @ 300Hz/3kHz.

    @agedhorse starded:

    Calculate the power density from 300 to 3kHz and you will see that when combined with the sensitivity and (real) power handling of that driver you are in "danger" territory.

    300-3kHz represents about 20% of the thermal spectrum, the driver is <94dB/1W/1M and the power handling is 100 watts RMS (this is a number to carefully respect on this driver due to limited crossover slope at the very least).

    With an average sensitivity of >97dB/1W/1M on a good LF section, you will need a 3dB power gain to balance levels, which reduces the normalized power handling to 50 watts. Now, take 50 watts divided by 20% and your system power handling is roughly 250 watts. When you power this with say 500-800 watts and subtract crest factor you are pretty close to the driver's limits.

    Where reliability is a concern (ie. you have to warranty thousands of products), these calculations give you an idea of likely reliability issues before they become real, costly warranty issues.

    My reply was:
    I have some knowledge in electronics and stuff but in french, sorry if i don't use correctly technical terms.

    My use of the cab will be limited to bass guitar and maybe some very low power PA use for an acoustic project.
    For bass guitar, i have an amp that doesn't exceed 325Wrms/8ohms.
    I'm never running the amp on full power and even if i do, I think my amp is barely pushing 150Wrms on full blast @8ohms.
    Actually my desk power amp Atoll AM100 feels a lot more powerful than my bass amp (Class D shuttle 6.0).

    My setup is at least 6dB attenuation on the mid driver, and a lot more on the Horn (107dBspl sensitivity).
    You are talking about adding 3dB gain to balance the mid but in fact i'm taking the LF driver as base to calibrate balance between each speaker.

    Agedhorse, what do you think about that? It's really interesting and you have a lot of knowledge on it.

    Having 3 a channel amp and a active filter is simpler and i thought about it.

    If you are crossing over at 300 Hz, that's would be a contributing factor to why you find a 6dB pad necessary for better tone. Assuming that you are not low passing the 15" driver, I would be surprised if the overlap is very predictable in response because both the phase response as well as the group delay will be quite different between the two sources.

    Sure, if you run a lower power rig, and with 6dB of attenuation on the mid driver, the mid driver should survive ok.

    When you say your desk top amp feels more powerful than the Shuttle, are you basing this on knob position?

    My reply:

    Yes and no, Channel volume and master up until it starts to limit on the shuttle poweramp.
    The shuttle and the Atoll amp are drived by the same soundcard.

    The shuttle amp is highpassed a bit high to my taste.

    On the delay, i simulated something like 30° shift on the mid range.

    This is each speaker measured without any filters.
    Baffle sans filtres.
    This is my last attempt of passive filtering:
    Baffle avec filtres.
    HF power is just an exemple because i have an Lpad on it like the 15/6/1 crossover.
    BadExample likes this.
  2. BogeyBass


    Sep 14, 2010
    Really for the money.

    Just a pair of good sounding high power 12" fullrange will stomp all over any squeaky mids from a sealed back.

    Instead of shoving all this contraption in a 3 cubic foot box

    Just build a 4 cubic foot. Shove 2 12s in it
    Call it a day. Mids for days
  3. BoogieZK


    Sep 28, 2008
    Toulouse, France
    Hello BogeyBass,
    I understand the simplicity but I had a Mesa 4x12 for years and something was not right with the sound.

    My 15/6/1 design (mainly a copy of fEARful design but with another speaker) is thought as bass full range rig.
    Meaning that i can use it as practice amp, playing music thru it and still use as a mid to high power bass speaker handling perfectly a B string and a high C string.

    The advantage of the Kappa PRO15LF2 is high power capacity and ferrite magnet. I think that this is what I didn't like with the Mesa.
  4. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    Hi, if I may ask, what simulator programme are you using?
  5. BoogieZK


    Sep 28, 2008
    Toulouse, France
    Of course, Room EQ wizard for acoustic measurement with a soundcard and a ECM8000 ref mic.
    I also use Proteus 8 for the electrical simulation simply because i used it in school and liked the interface.
  6. BadExample


    Jan 21, 2016
    Looks great on paper. Is the 15 LPF'd?

    Ready to build?
    Last edited: Dec 10, 2018
    Dean N likes this.
  7. I don't have any experience with these specific drivers, but I have designed and built a lot of full-range systems for sound reinforcement applications and my initial reaction is that the lower crossover point is too low, by at least an octave. It's difficult to imagine that the 6" driver would be able to keep up with the other components at 300 Hz, regardless of the manufacturer's spec's. It also puts the crossover point right in the middle of where the richest overtones of the instrument are. That would inevitably lead to some distortion where it is least desirable, or at least give you another set of variables (obstacles) to have to deal with. The first graph presented seems to indicate the 15" driver has usable response to above 1KHz--what would happen if you were to move the crossover point up to 600 or even 800 Hz? That would ease up the thermal demands on the mid driver considerably.

    But then, I'm an old guy and don't really see the need for a "full range" cabinet for bass in the first place. Good luck with your project.
    agedhorse and rogypop like this.
  8. BoogieZK


    Sep 28, 2008
    Toulouse, France
    I did not explained my self well. The cab is already build and those measurements are from the actual cab with real drivers.

    I understand, AgedHorse is following your thought as well.
    I gonna try again to hook 3 amps to my soundcard and run some digital crossovers to set points higher than it is now.
    The major issue with the Kappa PRO15 LF2 is the high peak @ 1,2kHz even is in my cab, this peak is not this much prominent.

    But, for what I understand in signal analysis, i have a different vision of the power spread into the frequency span.
    Lets suppose, the LF speaker is capable of 600Wrms.
    So the maximum power into 20kHz is 600Wrms

    The Mid driver uses a 2,7kHz span so 13,5% of the total span.
    So if the power is continuous on 20kHz, the mid driver will receive 13,5% of 600Wrms = 81,5Wrms.

    It's not the case with a bass guitar, Fundamentals on a 6string bass goes from 30,9Hz to 523Hz.
  9. Well, your 13.5% calculation works for white noise yes. But music is more like pink noise, and bass probably more like brown noise (hah!).

    Consider that, for white noise, the bandwidth of the LF is only about 270 Hz or 1.4% of the total power, and that the HF then accounts for 17 kHz of bandwidth or 85% of the power. You would need to send 510 W to your horn!

    Pink noise is equal power per octave and in the case of the mid from 300-3000 Hz that is more than 3 octaves, the same as 30-300 Hz for the Kappa. So then you need to send 600 W into the Alpha.

    YMMV with bass guitar, but certainly for most basses you will get a lot of harmonic content above 300 Hz. You may, in fact, end up with more power going to the Alpha than the Kappa which would certainly be a bad thing!

    Consider using the Eighteen Sound 6ND410 at 102 dB@1W/1m efficiency, EQ'd to provide flat response, and you will be in much better shape.
    BoogieZK likes this.
  10. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Or simply choose a more appropriate crossover frequency.

    How confident are you with your measurement numbers? I ask because it's VERY easy to have confidence in numbers that have little accuracy.
    el murdoque, BoogieZK and ThisBass like this.
  11. ThisBass


    Aug 29, 2012
    Nope, you can't predict those average numbers right behind the decimal point.
    I guess some lack of understaning in basics cause audio program material acts somewhat different versus your expectation.
    Last edited: Dec 11, 2018
  12. BoogieZK


    Sep 28, 2008
    Toulouse, France
    Ok, Thank you for the explanation. I understand power consistence into frequency span. What i don't know is the audio signal spectrum.
    I'm working with Spectrum analyzer and complex signals at work but usually, those signals are even in term of power in a given F span. And i know how much harmonics or carrier there is in a given span, so it's easy to calculate.

    My setup is simple:
    Calibrated Mic into a calibrated soundcard. What i can't control is room and amp influence on the measurement.
    The simulation I run uses Spice model, simple enough and i can verify my simulation by quickly setting up the crossover and measure it with my setup.
    Don't get me wrong, i mainly do it be ears. I just want to predict what i solder with Proteus.
    Plus, I use T attenuation and T filters to have a better control on how it will react with a source and load.

    So how confident? I trust my ears, that's all.

    I guess.

    Yesterday i tried moving the crossover point to around 500Hz but the cab sounded too middy.
    I want to try to filter the LF lower but with 1st or 2nd order filter just to tame this 1,2kHz peak.

    I will keep the mid driver highpass filter higher to avoid any damage.
  13. Matthijs


    Jul 3, 2006
    I lost a 6cbmra twice in a cab with a much higher xover frequency. It is just not the right driver for this kind of work. Ime it is to sensitive for real life transients and starts to sound harsh when pushed a little. I changed over to a 5” faital thats better suited for the job.

    A xover at 300 or 500 is really low and cals for a very carefully selected mid driver imho. If you goal is to control the whole 300 to 3k range this waythere might be other ways to do that.
  14. BoogieZK


    Sep 28, 2008
    Toulouse, France
    Yes, i experimented that with my digital crossover setup on this cab.
    I could just run the LF driver without any filter and the horn with an high pass suited to the LF response.
    It works.
  15. Matthijs


    Jul 3, 2006
    I think it is an interesting experiment,but you need a mid that can handle a whole lot in range and power. You might even consider combining 2 8” speakers, or two of those 6” for that matter.
    Jeff Siddall likes this.
  16. Getting rid of a peak is a good job for an equalizer. You can also, to some extent at least, do a bit of level matching with an EQ (ex: if you switched to a more sensitive mid driver) so it might be something to consider.

    Since I already setup a pink noise calculator for my 12/6/1 I ran your LF/mid drivers through. Even if you change to 500/3000 Hz crossover points you still end up needing about 380 W into your Alpha. It would never survive. Keeping the crossover point at 500/3000 Hz but using two of those Alphas would allow you to run at just under 100 W each but of course give you a 4 ohm equivalent load.

    However, switching to a single 6ND410, and dropping the mid power by about 4 dB, would let you keep that 500/3000 Hz crossover and require only 145 W into the midrange.

    Bottom line: an Alpha 6 is barely able to keep up to a 450 W Kappalite and will never keep up to 15" Kappa Pro running 600 W with more than 2 dB better efficiency.

    Again, all that is based on pink noise which will have much more HF content than probably anything but an extremely distorted bass guitar, so if you only need it for bass guitar work you might still be OK with an underperforming mid. It all depends on the tone you want so no one can predict that for you. You would probably need choose the most "mid-y" tone you like, run it through a spectrum analyzer, then decide if what you have will provide what you need.
    Matthijs and ThisBass like this.
  17. Matthijs


    Jul 3, 2006
    I think pink noise is a good tool. It might not represent the average bass sound, but in practice our gear has to deal with divergent sounds. It’s not all about bass. Otherwise a single slap, click or pop can blow your mids or tweeter to pieces.
  18. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Experience is even better than pink noise.
    Bill Whitehurst likes this.
  19. BoogieZK


    Sep 28, 2008
    Toulouse, France
    Well, i experienced a bit yesterday with L, C and highpower R on the filtering of my cab.
    The cab is fully build and i wired each speaker with a cable passing through the vent.

    I ended up with L=12mH in serie with the LF, something like 500Hz/4kHz on the mid and an HPF on the HF @ around 4kHz.
    It sounds good but the 12mH L on the LF is a bit low. It is actually 2*6mH inductors, so i will continue experiencing with the Xover to obtain the better sound to my ears.

    Again, I think i will not exceed 200Wrms on the input, most of the time, my amp is not very powerful (shuttle 6.0).
    BadExample and Stumbo like this.
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Your shuttle is 300 watts RMS at 8 ohms.

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