How to make my speakers more punchy?

Discussion in 'DJ Gear' started by Djziaelectro, Feb 9, 2018.

  1. steve149

    steve149 Urbane Legend

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    It's only possible to control the crossover point to the extent of the built-in options .. or .. you use an external crossover like the dbx 223/234 or a driverack style DSP and have many more options (in addition to crossover point you may get slope type, slope attenuation, low cut, etc.).

    A low cut at 40Hz is fine for recorded music. The only way you're going lower is with a live bass guitar or kick drum or maybe a good keyboard.
     
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  2. Handinon

    Handinon DJ Extraordinaire

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    OK Grasshopper, we shall walk through the specs together -

    Power Rating 1500 W Maybe. Ratings are all over the place these days, probably by the marketing department.

    AC Power Input 100V - 240V~ 50/60 Hz OK

    Frequency Range (-10 dB) 30 Hz - 103 Hz OK. Note already -10db down at 103 Hz, the subs high end.

    Frequency Response (±3 dB) 35 Hz – 87 Hz Part of the problem

    Internal Crossover Frequency 100 Hz DSP controlled 48 dB filter slope OK

    Loop out Crossover Frequency 120 Hz analog 24 dB filter slope The rest of the the problem - see below.

    Maximum SPL 134 dB peak OK

    Signal indicators Limit: Yellow LED indicates peak output has been reached and dsp ALL good.
    limiter is acting
    Signal: Green LED indicates signal present
    Power/Standby: Blue indicates system has power and ready to pass audio,
    Red indicates system has power but is in a power saving mode and will not
    pass audio.

    Dynamic Control (Input) dbx Type IV™ limiter circuit Good

    Input Impedance 20K Ohms (balanced) OK

    Polarity normal or reverse polarity Good

    LF Driver 1 x JBL 2278H 460 mm (18 in) woofer

    Enclosure Rectangular, 18 mm, plywood How this sucker is made

    Suspension / Mounting M20 threaded pole socket on top

    Transport 2 x injection molded handles with backing cup

    Finish Obsidian DuraFlex™ finish Obsidian - gotta be good, whatever that is!!

    Grille Powder coated, Obsidian, 16 gauge perforated steel with acoustical transparent black cloth backing.

    Input Connectors Two Balanced female XLR/ 1/4" combo connectors

    Output Connectors Two balanced male XLR connectors.

    Dimensions (H x W x D) 690.372 mm x 523.24 mm x 723.9 mm
    (27.18 in x 20.60 in x 28.50 in)

    Net Weight 36.8 kg (81 lb.) Too heavy for dinosaur like me!!



    First off, this is a good sub, so take the following in context.


    The sub itself is always low passed, limiting it's upper frequencies with a 100 Hz @ 48 db/octave filter. It's -3db at 87 Hz and -10db at 103 HZ. What this means in English is there is almost nothing coming out of the sub above 100 Hz.

    The internal high pass filter to the tops is 120 Hz @ 24 db/octave filter. If you use this to feed the tops, they will have greatly limited output below 120 Hz.

    What this means in English is you have almost no system output between 100 Hz and 120 Hz. A 20 Hz hole in a very critical
    frequency range = no punch. This is why you hear such a big difference running your tops full range!

    I suspect JBL chose this 120 Hz value so literally anything can be hooked up to it with no fear of them blowing. JBL tops probably have their own proper filters to work with the through-put option*, your tops do not.

    Using the low cut EQ on your tops is certainly one option. A better option is an external, fully adjustable xover. If you go that route, do not enable the 40Hz high pass sub filter on the xover that cuts everything below 40 HZ - I'm sure JBL already has one enabled internally on your sub**.


    * Edit - No, they don't. Weird!

    **Edit Edit - not so sure about that any more. It's a pretty crazy company that deliberately designs crossovers like this. A PRX712/PRX718 combination has the exact same issue - a 20 Hz hole unless you run the tops full range, and I wouldn't call these inexpensive. Not until you get to the 800 series do you find real xover adjustments. Does JBL expect you to use some kind of speaker management with the 700 series?
     
    Last edited: Feb 12, 2018
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  3. DJ TJ

    DJ TJ DJ Extraordinaire

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    Yeah come to think of it now I think I read about that same "hole" you mentioned on another forum with the prx 6 series so it looks like they havent changed specs or the internal xover freq on the 7 series either.
     
  4. Djziaelectro

    Djziaelectro DJ

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    I read in another forum that You almost never want your subs and tops to have the same crossover frequency, unless they are run at the exact same level. Because subs are typically run a lot louder than mains, you want a gap in between the two crossover points because the subs will 'fill this in'. Overlap is worse ...always run subs with a gap ...usually <80hz ....mains >100hz ...18db slope. If you don't run a gap ...you get a 'summed' peak ...especially with shallower slopes.
     
    Last edited: Feb 13, 2018
  5. Handinon

    Handinon DJ Extraordinaire

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    This would only make sense when using 6 db/octave filters with smooth slopes - it makes no sense with sharp filters.
    You can run that PRX 718 as loud as you want, they'll still be almost nothing above 103 HZ with a 48 db/octave filter. How can you "fill this in" with nothing? If this quote is someone's opinion, IMHO they are wrong.

    I have been running passive speakers for years, both as an audiophile, and a DJ, using 18 db/octave and 24 db/octave active xovers, and have never done this. Do they recommend the 800 series (which are fully adjustable) be set like that? A 20 Hz hole? 1/5 of the frequency spectrum?

    What I do believe is a legal department saying "Since it will be non-adjustable, set it for 120 Hz so we will never be responsible for damaging the tops. Even in the hands of the unknowing, it will never come back to bite us".

    Use sharp adjustable filters. Use the same xover frequency. Get the Polarity correct. Done.
     
    Last edited: Feb 13, 2018
  6. Djziaelectro

    Djziaelectro DJ

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    Agree.. how can something fill a hole in the frequency. Dont know the science behind it. Only JBL engineers will be able to answer it.
     
  7. Handinon

    Handinon DJ Extraordinaire

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    As with everything else in life, there are no absolutes. Here's where a speaker designer might use a crossover with a "hole" in it -
    http://www.eminence.com/img/curves/Delta_Pro_15A.png

    This is the frequency response for an Eminence Delta Pro-15A, a good 15" driver typical of what would be in a good 15" two-way speaker.

    See that rising high end frequency response starting at 700 Hz? It's because of the electrical parameters of the driver, and is best fixed with a Zobel Network. However, instead of using extra parts, almost the same effect can be achieved by simply setting the crossover frequency lower - only on the woofer - to offset it's rising high end.

    What is not shown is that along with this rising high end, the dispersion is narrowing. Can you say "laser beam that hurts my ears", and is the main reason I don't like 15" two-ways. That's right, most of that nasty stuff is not coming from the compression driver horn tweeter, but from the 15" woofer, and is why the EV-SX500 has that disc on the grill*.

    This problem only exists at high frequencies - crossing over from a woofer to a tweeter. No 15", 18", or even 21" woofer has this problem at 100 Hz. IMHO, what JBL is doing is still not logical.

    *I shall preempt the miss-guided conception that modern powered speakers with DSP's can fix the dispersion problem. No, they can't, with the exception of Alto's, who use Unobtanium magnets, and operate outside the constraints of Newtonian Physics!!
     
    Last edited: Feb 13, 2018
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  8. Handinon

    Handinon DJ Extraordinaire

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    I don't think there is science behind it!