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Author Topic: QSC K-Sub  (Read 10787 times)

frank kayser

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QSC K-Sub
« on: May 20, 2011, 01:24:17 pm »

Folks,
I apologize in advance - this question kind of snowballed in my mind, and got a bit more complex than I intended.   It may be a question better suited to the folks at QSC...

In one of the other recent threads on inexpensive subs, some things were said about the QSC K-Sub that I did not get from the user manual - so let me ask more directly - actually three somewhat related questions.

1. Does the K-sub actually have a low-pass filter (either discrete or in DSP)?  It was indicated in the thread (and repeated a couple times without challenge) that the K-sub relied on the K-series tops to provide the high-pass filter (crossover?) to work properly.  The user manual neither stated nor implied that a K-series top was required.  I would assume both the low pass filter and a protective high pass filter would be incorporated into the K-sub DSP.

Which leads to a second question:

2. Can the Q-Sub be wired to run as an aux-fed sub?  Again, the manual was silent on the matter.  It would seem the benefits of an aux fed sub setup would work here, requiring simply an additional return.  It would also seem that stereo tops and a single, mono sub could be run that way -

and finally, assuming I cannot (or choose not to) run the K-sub as aux fed,

3. Seeing that I have only one K-sub, yet run stereo tops, and  how would I set the tops? 

Assume the sub is connected to the right, and the left would not have a matching sub...
The right speaker would be have the DSP set as external sub... (not normal or deep)
Assume I have a double bass fed into a channel - which would be both in the mains and subs based on the frequency

a. I could run mono, and the problem goes away?

Assume stereo tops for the rest...
b. I could pan that channel hard into the right channel, so I would not lose any low freq info that was fed to the left channel?  Not ideal

c. Assuming I did not pan the input hard right... how would I set the Ext Sub, Normal, Deep switch on the left channel? This sceneraio would appear to make the tops mismatch if the normal or deep position were to be used on the left speaker.

d. Finally, I'm guessing I could run an XLR from the left speaker feed-through to the "B" input on the sub, where the sub would mix both L&R signals to mono...

Am I over (under) thinking this?

thanks
frank
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frank kayser

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Re: QSC K-Sub
« Reply #1 on: May 20, 2011, 03:05:38 pm »

Folks,
I apologize in advance - this question kind of snowballed in my mind, and got a bit more complex than I intended.   It may be a question better suited to the folks at QSC...

In one of the other recent threads on inexpensive subs, some things were said about the QSC K-Sub that I did not get from the user manual - so let me ask more directly - actually three somewhat related questions.

1. Does the K-sub actually have a low-pass filter (either discrete or in DSP)?  It was indicated in the thread (and repeated a couple times without challenge) that the K-sub relied on the K-series tops to provide the high-pass filter (crossover?) to work properly.  The user manual neither stated nor implied that a K-series top was required.  I would assume both the low pass filter and a protective high pass filter would be incorporated into the K-sub DSP.

Which leads to a second question:

2. Can the Q-Sub be wired to run as an aux-fed sub?  Again, the manual was silent on the matter.  It would seem the benefits of an aux fed sub setup would work here, requiring simply an additional return.  It would also seem that stereo tops and a single, mono sub could be run that way -

and finally, assuming I cannot (or choose not to) run the K-sub as aux fed,

3. Seeing that I have only one K-sub, yet run stereo tops, and  how would I set the tops? 

Assume the sub is connected to the right, and the left would not have a matching sub...
The right speaker would be have the DSP set as external sub... (not normal or deep)
Assume I have a double bass fed into a channel - which would be both in the mains and subs based on the frequency

a. I could run mono, and the problem goes away?

Assume stereo tops for the rest...
b. I could pan that channel hard into the right channel, so I would not lose any low freq info that was fed to the left channel?  Not ideal

c. Assuming I did not pan the input hard right... how would I set the Ext Sub, Normal, Deep switch on the left channel? This sceneraio would appear to make the tops mismatch if the normal or deep position were to be used on the left speaker.

d. Finally, I'm guessing I could run an XLR from the left speaker feed-through to the "B" input on the sub, where the sub would mix both L&R signals to mono...

Am I over (under) thinking this?

thanks
frank

 :-[ Oops...  Found the answers in the old forums...   :-[

The answers are:
1. Yes, the K-sub has a crossover implemented in DSP. Can be used with any tops.
2. Yes, the K-sub can set up as aux-fed-subs
3. RTFM.

http://srforums.prosoundweb.com/index.php/mv/msg/58589/563288/0/#msg_563303

(from the post for those who do not wish to follow the link)


Rob, the manual certainly isn't clear on this point. I asked QSC to clarify and here is the reply:


Hello Tim,

Sorry for the delayed reply, your email got "stuck" in our spam filter for some reason.

You don't need the DriveRack to feed these boxes! They are already "voiced" with internal DSP with LOTS more DSP horsepower than what is in the DriveRack! Just feed them directly from the mixer/console outputs.
I don't know if you are doing stereo (I assume you are), so refer to the diagram at the bottom of page 18 in the user's manual. For just one
(mono) signal, refer to the top of page 17. If you've misplaced your manual, you can download and view (and print) a new copy from here:

http://media.qscaudio.com/pdfs/manuals/K_Series_User_Manual_ EN_revA.pdf

Just make sure you set the top box "LF" switches (on the rear of the
K-12's) for "EXT SUB" so the K-12's do not try to pass any of the sub signals, they let the subwoofer handle those signals below 100Hz.

Now, some folks like to drive Left and Right tops directly from the board, and use a third AUX output of the board to send Subs (to get a little more control over the sub signal). This is fine, just feed the Subs directly, again no DriveRack is needed -- the Subs have their proper built-in DSP crossover settings. Of course, in this case you would NOT have the K-12's patched down to the Subs as well.

Now, in either case (L/R feeds, or L/R/Aux feeds) you COULD put the DriveRack in line just to do some "room EQ" to taste, but this is usually accomplished right on the mixing console, just before the signal leaves the console. Use such EQ very sparingly, sort of like "seasoning to taste" when cooking -- a little goes a long way, too much seasoning is bad!

I hope this answers your question. Let me know if I can be of further assistance.

Regards,
=============================
Fred Thomke
Technical Services Group
Manager - Engineered Systems
QSC Audio Products, LLC
fred_thomke@qscaudio.com
Skype: qsc.eng.systems.support
(714) 957-7169 direct
(800) 772-2834 Tech Support
(714) 269-7151 cell
(714) 754-6173 fax
www.qscaudio.com

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Kirby Yarbrough

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Re: QSC K-Sub
« Reply #2 on: May 20, 2011, 05:58:10 pm »

1. Yes, the K-sub has a crossover implemented in DSP. Can be used with any tops.

Sorry, the KSUb does not have an internal crossover:

Connectors    Dual balanced female XLR/¼" line level input, Dual Balanced male XLR full range line level out, Remote gain control, Locking IEC power connector

(from here: http://www.qscaudio.com/products/speakers/k_series/series_specifications.php)

You'd have to use an external crossover or a top cabinet with an HPF.
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frank kayser

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Re: QSC K-Sub
« Reply #3 on: May 23, 2011, 09:52:50 am »

Kirby,
Thanks for keeping me in line.  It is obvious that I was missusing the term "crossover".  :-[ :-[

What QSC implemented in the K-sub was a low-pass filter in DSP - which I termed crossover incorrectly.
 
And you are correct - the use of any top used in conjunction with the K-sub should run some type of high-pass filter to eliminate the frequencies the sub will reproduce (redundant, weak signals from the tops).  The K-tops do implelent a high-pass filter, also in DSP, which is complementary to the K-sub, but are completely independent.  Whether another active or passive top uses a "protective" high pass filter or not is more or less moot - unless the HPF is tunable or at a frequency that harmonizes with the k-sub frequency and rolloff characteristics - hence the need for an external DSP
 
The K-subs can be run aux-fed quite successfully along with the k-tops with the DSP switch in the "ext sub" position.

frank
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Nate Armstrong

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Re: QSC K-Sub
« Reply #4 on: May 26, 2011, 09:10:15 pm »

this post and some info from a qsc retailer has really confused me.  I own 3 k10's and 3 ksubs  and normally just use a driverack. . 

1) if i go direct out from my mixer  main out to a ksub  will the sub reproduce sounds above 100 hz ?

2) if i go from the Ksub out to a full range speaker directly. will the full range speaker produce sounds 100 hz and below.

sorry if this seems redundant.
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Peter Morris

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Re: QSC K-Sub
« Reply #5 on: May 27, 2011, 07:14:06 am »

this post and some info from a qsc retailer has really confused me.  I own 3 k10's and 3 ksubs  and normally just use a driverack. . 

1) if i go direct out from my mixer  main out to a ksub  will the sub reproduce sounds above 100 hz ?

2) if i go from the Ksub out to a full range speaker directly. will the full range speaker produce sounds 100 hz and below.

sorry if this seems redundant.
Q1

From the K series manual - “The K Series features advanced DSP (digital signal processing) circuitry that performs many functions. Some functions are set at the design/production level and are not user accessible. These functions include crossovers, time alignment, limiting and protection, thermal management and a number of proprietary features. QSC has designed exclusive DSP functions that greatly enhance the capabilities and performance of the K Series systems.”

“When using one of the top boxes with a subwoofer, the switch should be moved to the “EXT SUB” position to engage the 100 Hz high-pass filter. It is also recommended that the 100 Hz high-pass filter be engaged when using the K10 or K12 as a floor monitor to prevent excessive bass build up on the stage.”

I think quite reasonable to assume that the subs will have a complimentary 100 hz crossover -3db @100hz

Q2

"Both Channel A and Channel B have discrete direct outputs on female XLR connectors. The signal on this output is exactly equivalent to the signal from the corresponding input. The level of the output signal is not affected by the gain set on the subwoofer gain knob."
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