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Author Topic: Mixer to crossover to Ksub : benefit to dual balanced inputs?  (Read 395 times)

Jeph Bennett

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Mixer to crossover to Ksub : benefit to dual balanced inputs?
« on: November 28, 2019, 08:59:15 pm »

Hi guys and gals!
   I apologize in advance if this has been covered before, but after an hour searching here (and 2 hours elsewhere), i can't seem to create the correct search string to find these answers.

System: Laptop & 4 mics into a Alesis 8ch mixer -> BBE Max-X3 crossover --> QSC Ksub & stereo powered main cabs.
Application: Mobile DJ & karaoke for small/medium events (corporate, wedding, etc)
Me: Former musician with experience in recording/mixing bands, plus some live sound rigging. *Note: I ALWAYS prefer stereo separation, even in subs.*

Question 1: Since the Ksub has dual (A/B) inputs & dual 500w amps, do I have to run XLRs to both inputs on the Ksub? Would running just one XLR input cause the Ksub to send that signal to both amps/12's? (I don't have the manual, & their online info seems unclear)

Question 2: I want to run everything with balanced cables when possible. My mixer has balanced 1/4" outs, but the crossover only offers balance on the XLR inputs. Do I need TRS-XLR cables to connect these two devices? Or TS-XLR?

Question 3: Since the Ksub has a 100hz lowpass filter, and the main cabs (which I haven't confirmed or bought yet) will likely have a switchable high-pass filter around 100hz (or even better, adjustable), is running the BBE X3 crossover overkill? I have never used an active crossover, but I feel like it would do a better job of separating the lows and highs than relying on the filters in the speakers. Plus, I do like that maximizer sparkle as well. Thoughts?

Thanks for any input, please go easy on my noob questions.  ;D
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Luke Geis

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #1 on: November 29, 2019, 12:46:14 am »

#1. No, you only need to send it one signal. The amp may be two channels, but either input will pass the signal to both channels. If you put an input into both channels, you will just end up with a +3db increase in volume. Just use one input, you get the same peak SPL either way.

#2. Balanced is ideal, so I would go with TRS-XLR if you can. While an unbalanced TS-XLR cable will work, it will lose 3db in level and hum can be introduced ( while hum may be unlikely though ) potentially.

#3. Using it on the subs would be overkill and or counterproductive. If you use a crossover on the subs, you would be stacking the filters on top of one another. This would lead to large phase shifts and no appreciable gain would be acquired. If the tops do in fact have a crossover setting, once again the external crossover would be basically pointless. The only suggestion I make is that if you buy tops, buy ones that are from the same Vendor as the subs. This is because different Vendors use different slopes and crossover frequencies. If you are at least using gear from the same model line, it will work together quite well. Active crossovers are really only useful if you can defeat/turn off the units built-in crossover function. Most all powered speakers subs do not have that option, so it is best to not bother with trying external speaker management with them ( other than EQ perhaps ). Most powered mains do have a full range option and they can be used with an external crossover, but what sthe point if the internal option is just fine.
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Jeph Bennett

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #2 on: November 29, 2019, 02:46:23 am »

#1. No, you only need to send it one signal. The amp may be two channels, but either input will pass the signal to both channels. If you put an input into both channels, you will just end up with a +3db increase in volume. Just use one input, you get the same peak SPL either way.

#2. Balanced is ideal, so I would go with TRS-XLR if you can. While an unbalanced TS-XLR cable will work, it will lose 3db in level and hum can be introduced ( while hum may be unlikely though ) potentially.

#3. Using it on the subs would be overkill and or counterproductive. If you use a crossover on the subs, you would be stacking the filters on top of one another. This would lead to large phase shifts and no appreciable gain would be acquired. If the tops do in fact have a crossover setting, once again the external crossover would be basically pointless. The only suggestion I make is that if you buy tops, buy ones that are from the same Vendor as the subs. This is because different Vendors use different slopes and crossover frequencies. If you are at least using gear from the same model line, it will work together quite well. Active crossovers are really only useful if you can defeat/turn off the units built-in crossover function. Most all powered speakers subs do not have that option, so it is best to not bother with trying external speaker management with them ( other than EQ perhaps ). Most powered mains do have a full range option and they can be used with an external crossover, but what sthe point if the internal option is just fine.

Thank you very much, that makes perfect sense.

I would love to grab a pair of QSC K10s to match this sub, but due to budget crunch, I will likely be going with a pair of RCF ART 322A's, which I found nearby for only $225/each!
The good news is that the 322a's should sound better than anything else I can get for that price. The bad news is they don't have a sub mode to filter the low end, so i'm back to thinking the crossover should be in the chain.

So, new question (#4): If I send 90hz & up to the RCF's, and then 90hz & below to the Ksub, doesn't that mean i've effectively "bypassed" the Ksub's 100hz filter? (in theory, the ksub's filter would have no sound in the 90-100hz range to filter, so it would just play all of the 30-90hz frequencies it's being fed, no?

Off topic / question #5:   I heard some rattle on deep bass hits, so I opened up the Ksub and found one of the 12's magnets is separating from the basket. It's like 60% attached, 40% separated. So, that seems unfixable, right? (tempted to try JBwelding it back together)
It's $128 for the OEM replacement...any other beefier options I should consider? I see Daytons & Eminence with larger magnets for $50-$80....or for $120 I could pop in a Emm Delta Pro, but i cant find the TS parameters for the OEM, so I have no idea if it's a fit for this Ksub box..... (i know, I'm out in left field at this point...)

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Steve M Smith

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #3 on: November 29, 2019, 04:15:57 am »

I heard some rattle on deep bass hits, so I opened up the Ksub and found one of the 12's magnets is separating from the basket. It's like 60% attached, 40% separated. So, that seems unfixable, right? (tempted to try JBwelding it back together)


If the cone moves ok without the voice coil rubbing on the sides and is generally working ok, then you have nothing to lose with running in a bit of glue.  It's what I would do.  Worst case scenrio, you have to replace it.


Steve.
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Debbie Dunkley

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #4 on: November 29, 2019, 10:28:55 am »

Thank you very much, that makes perfect sense.

I would love to grab a pair of QSC K10s to match this sub, but due to budget crunch, I will likely be going with a pair of RCF ART 322A's, which I found nearby for only $225/each!
The good news is that the 322a's should sound better than anything else I can get for that price. The bad news is they don't have a sub mode to filter the low end, so i'm back to thinking the crossover should be in the chain.

So, new question (#4): If I send 90hz & up to the RCF's, and then 90hz & below to the Ksub, doesn't that mean i've effectively "bypassed" the Ksub's 100hz filter? (in theory, the ksub's filter would have no sound in the 90-100hz range to filter, so it would just play all of the 30-90hz frequencies it's being fed, no?

Off topic / question #5:   I heard some rattle on deep bass hits, so I opened up the Ksub and found one of the 12's magnets is separating from the basket. It's like 60% attached, 40% separated. So, that seems unfixable, right? (tempted to try JBwelding it back together)
It's $128 for the OEM replacement...any other beefier options I should consider? I see Daytons & Eminence with larger magnets for $50-$80....or for $120 I could pop in a Emm Delta Pro, but i cant find the TS parameters for the OEM, so I have no idea if it's a fit for this Ksub box..... (i know, I'm out in left field at this point...)

The K - sub throughs are full range so when using tops that do not have HP filters, a crossover is necessary.
I used to have to use a crossover when I ran a K-Sub / PRX612 set up because the JBL PRX series house the HP filter in the subs - not the tops and QSC is the other way round.
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Brian Jojade

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #5 on: November 29, 2019, 04:39:45 pm »

1. Answered

2. TRS to XLR cables would be ideal. For short runs though, unbalanced connections should be fine. Sound quality shouldn't be different, only possible noise/buzzing from external interference. Any signal differences could be compensated for by turning a gain knob.

3. Using an external crossover simply gives you more control as to where you want that crossover point to be and what the slope is.  Relying on internal crossovers from different manufactures could produce undesirable results, as they may have picked different crossover parameters that don't play well together. This is one where you try it, and if it works to your liking, then you don't need the external unit.
Now, personally, I've never been a fan of anything with a BBE sonic maximizer in the signal path.  On some of their gear, the 'bypass' function is a 'make the sound suck horribly' function that magically improves if you simply remove the entire unit from the signal path. It does make it seem like the BBE is doing a lot more than it really is. :)  Haven't used your particular crossover, so I can't say if it has that same 'feature' or not.

4. Crossovers are not hard numbers, they create slopes. When you stack crossovers, those slopes go from nice and smooth to weird and random.  Definitely not advised unless the second crossover is many octaves away from the first. One at 90 and one at 100 will likely give undesirable results.

5. Speakers and cabinets paired together give different results. If you replace your internal speaker with any different model, the outcome may not be what you expected.  While it may seem better to have a beefier speaker, it also may sound worse.  Unless you're into designing and experimenting, it's usually best to stick with stock designs.  This is especially true with powered speakers, as the amplifier and any processing in the amplifier is designed around the stock speaker.
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Brian Jojade

Paul G. OBrien

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #6 on: November 29, 2019, 09:22:07 pm »

So, new question (#4): If I send 90hz & up to the RCF's, and then 90hz & below to the Ksub, doesn't that mean i've effectively "bypassed" the Ksub's 100hz filter?
No, the filter in the ksub is not defeatable and also not a brick wall filter.. lots of content above the crossover frequency still gets past so there is always some mixing going on. This is normal and why it's always recommended to use speaker/crossover combos that are designed to work together, the total is always a sum of it's parts which in this case means the total output from the whole speaker system is a combination of output from the subwoofer, mid/high boxes and whatever crossovers are involved.
If you do get the RCFs I suggest you use the crossover for them only, the subs should get a direct line from the mixer totally bypassing the crossover.

Off topic / question #5:   I heard some rattle on deep bass hits, so I opened up the Ksub and found one of the 12's magnets is separating from the basket. It's like 60% attached, 40% separated. So, that seems unfixable, right? (tempted to try JBwelding it back together) It's $128 for the OEM replacement...any other beefier options I should consider? I see Daytons & Eminence with larger magnets for $50-$80....or for $120 I could pop in a Emm Delta Pro, but i cant find the TS parameters for the OEM, so I have no idea if it's a fit for this Ksub box..... (i know, I'm out in left field at this point...)
That OEM driver has either been damaged in use(dropped) or has a factory defect, if the box no longer has warranty the best option is to replace it with another of the same. The bandpass enclosure design of the ksub requires a driver with very specific specs, there is no way to know if another driver is suitable without modelling it and those that aren't suitable will perform very poorly despite potentially looking "beefier", so don't go there.
« Last Edit: November 29, 2019, 09:24:36 pm by Paul G. OBrien »
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Jeph Bennett

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #7 on: November 30, 2019, 07:10:38 am »

Thanks for all the detailed & knowledgeable advice, guys.

As for the broken sub, I clamped it with JBweld in the crack overnight, reinstalled, it sounds MUCH better, I don't know what the sub is typically like, but this is deeper & louder (but a bit whompier) than my 350w home infinity sub and just fine for a used speaker.

As for crossover, I now plan to send my main mixer outs to the crossover's 100hz HPF, then to the RCF's. Then I will send my control room outs to the sub, so I can control it's volume without crawling under the table.

As for BBE, i think their 1st gen (and maybe 2nd gen) had a poor unbalanced signal chain, and this caused many to hate their sound when bypassed. I do recall running old 4-track demo tapes thru the maximiser, back into the computer for archiving onto CD, and they DID actually sound better than the original tapes. So it's not all BS. just partly. lol

Thanks again for the expertise. I love when information and communication produce better results. Cheers!
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Steve M Smith

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #8 on: December 03, 2019, 03:53:21 am »

the JBL PRX series house the HP filter in the subs - not the tops and QSC is the other way round.


With KSubs and K12s, both have crossovers.




Steve.
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Debbie Dunkley

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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #9 on: December 03, 2019, 10:09:37 am »


With KSubs and K12s, both have crossovers.




Steve.

The K subs are full range pass through. When I got mine I found the paperwork provided by QSC to be a little confusing and other folks seemed unsure too from what I read so I called QSC to make sure.  I was told that the K subs do not offer HP pass through. They have low pass but the outputs are parallel to input.  The K tops offer the HP.
« Last Edit: December 03, 2019, 10:13:45 am by Debbie Dunkley »
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Re: Mixer to crossover to Ksub : benefit to dual balanced inputs?
« Reply #9 on: December 03, 2019, 10:09:37 am »


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