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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Bob Burke on July 21, 2014, 06:15:12 AM

Title: Sub Question
Post by: Bob Burke on July 21, 2014, 06:15:12 AM
  Hello all. I'm thinking of adding a small powered sub (JBL EON518S) to our passive rig  which consists of 2 Yamaha S115V's,  a Soundcraft EFX8 and a QSC PLX1804. My question regards the output from the mixer. I can't find an answer in the mixer manual.

  Is the Aux 1 signal affected by the channel EQ's, or is it a flat signal? Should I run it Pre or Post? I want to run our backing tracks and the bass guitar (with a direct out from the bass amp) through the sub. Should I roll off the lows from the mains?

  Finally, what's the best way to hook the sub up? The JBL appears to have an internal crossover and a high pass. I've never used a sub, and don't want to mess it up!


Thanks,

Bob
Title: Re: Sub Question
Post by: g'bye, Dick Rees on July 21, 2014, 06:53:54 AM
  Hello all. I'm thinking of adding a small powered sub (JBL EON518S) to our passive rig  which consists of 2 Yamaha S115V's,  a Soundcraft EFX8 and a QSC PLX1804. My question regards the output from the mixer. I can't find an answer in the mixer manual.

  Is the Aux 1 signal affected by the channel EQ's, or is it a flat signal? Should I run it Pre or Post? I want to run our backing tracks and the bass guitar (with a direct out from the bass amp) through the sub. Should I roll off the lows from the mains?

  Finally, what's the best way to hook the sub up? The JBL appears to have an internal crossover and a high pass. I've never used a sub, and don't want to mess it up!


Thanks,

Bob

Use a cross-over to divide the frequencies between the subs and tops.  You can find usable analog units used for very little money. 
Title: Re: Sub Question
Post by: Simon Hutson on July 21, 2014, 07:08:19 AM
Hi Bob.

Personally, I'd keep things simple. Run the LR outputs from your Soundcraft EFX8 into the LR inputs of your JBL EON518S, then run the LR outputs of the JBL into the LR inputs of your QSC PLX1804 and hook up your Yamaha S115Vs as normal. Select the HPF setting on the JBL and turn up the level until you get the right balance between the tops and sub, keeping an eye on the "clip" light to make sure you are not overloading the sub. If things don't sound quite right, try changing the polarity switch on the JBL to see if it makes things sound better/worse.

Best regards, Simon

P.S. According to the schematic in the Soundcraft EFX user guide, Aux 1 is globally switchable for pre or post fader, but will always be affected by the channel EQ regardless of this setting.
Title: Re: Sub Question
Post by: David Allred on July 21, 2014, 07:52:13 AM
You are right, the manual is useless.  I thought I had a definitive answer, but the block diagram is a little unclear.  The mono vs stereo inputs are routed differently as well, so take that into account when you do my recommendation, as they may not be the same functionally.

Connect an amp / speaker to the Aux output and physically test what the fader and EQ do when they are adjusted.   

David
Title: Re: Sub Question
Post by: David Allred on July 21, 2014, 08:00:09 AM
Hi Bob.


P.S. According to the schematic in the Soundcraft EFX user guide, Aux 1 is globally switchable for pre or post fader, but will always be affected by the channel EQ regardless of this setting.

On the mono channels, there is definitely a before and after connection at the EQ, apparently... PK is a switch.  Perplexing... indeed.  Do a test.

David
Title: Re: Sub Question
Post by: Simon Hutson on July 21, 2014, 08:54:16 AM
On the mono channels, there is definitely a before and after connection at the EQ, apparently... PK is a switch.  Perplexing... indeed.  Do a test.

David

Hi David.

I think that's the Channel Peak LED which lights when the signal level approaches clipping at any of the three monitored points:
a) PRE-EQ
b) POST-EQ
c) POST-FADE

Both the pre and post aux 1 signals seem to come after the EQ.

Best regards, Simon
Title: Re: Sub Question
Post by: Bob Burke on July 21, 2014, 09:24:07 AM
Hi Bob.

Personally, I'd keep things simple. Run the LR outputs from your Soundcraft EFX8 into the LR inputs of your JBL EON518S, then run the LR outputs of the JBL into the LR inputs of your QSC PLX1804 and hook up your Yamaha S115Vs as normal. Select the HPF setting on the JBL and turn up the level until you get the right balance between the tops and sub, keeping an eye on the "clip" light to make sure you are not overloading the sub. If things don't sound quite right, try changing the polarity switch on the JBL to see if it makes things sound better/worse.

Best regards, Simon

P.S. According to the schematic in the Soundcraft EFX user guide, Aux 1 is globally switchable for pre or post fader, but will always be affected by the channel EQ regardless of this setting.





Thanks Simon.
Title: Re: Sub Question
Post by: David Allred on July 21, 2014, 10:27:09 AM
Simon, Nice catch.  Why not label it "Peak"?  Pretty of room... and clear. 

I guess Soundcraft is assuming that operators would never use the strip EQs for feedback control or speaker tone control(undesirable as it may be).

david
Title: Re: Sub Question
Post by: Simon Hutson on July 21, 2014, 01:39:27 PM
Thanks Simon.

No problem. Enjoy your new purchase.

Best regards, Simon.
Title: Re: Sub Question
Post by: Bob Burke on August 17, 2014, 08:06:55 AM
Sorry to resurrect this thread, but I'm confused about the specs JBL provides for this sub, particularly the frequency range(s).

(http://www.sweetwater.com/store/detail/EON518S/)


System Type: Self powered 18", bass-reflex design
Frequency Range (-10 dB): 36 Hz - 130 Hz
Frequency Response (±3 dB): 42 Hz - 100 Hz

Crossover Frequency: 120 Hz (HPF switchable on outputs)
System Power Rating: 500 W continuous, 1000 W peak


  What is the difference between the -10 dB and the  +  3 dB rating? Does this sub produce down to 36 Hz or 42 Hz? I know that I should know, but I've forgotten half of what I did know already! ;D


Thanks.


Bob
Title: Re: Sub Question
Post by: Mark McFarlane on August 17, 2014, 01:01:22 PM
In essence it is saying that 42Hz is 3db softer than whatever the peak of the sub is, and 36Hz is another 7 db (i.e. a lot) softer.
Title: Re: Sub Question
Post by: Bob Burke on August 17, 2014, 01:48:18 PM
Thanks Mark.
Title: Re: Sub Question
Post by: Scott Holtzman on August 17, 2014, 04:40:39 PM
Sorry to resurrect this thread, but I'm confused about the specs JBL provides for this sub, particularly the frequency range(s).

(http://www.sweetwater.com/store/detail/EON518S/)


System Type: Self powered 18", bass-reflex design
Frequency Range (-10 dB): 36 Hz - 130 Hz
Frequency Response (±3 dB): 42 Hz - 100 Hz

Crossover Frequency: 120 Hz (HPF switchable on outputs)
System Power Rating: 500 W continuous, 1000 W peak


  What is the difference between the -10 dB and the  +  3 dB rating? Does this sub produce down to 36 Hz or 42 Hz? I know that I should know, but I've forgotten half of what I did know already! ;D


Thanks.


Bob

The -10 is a sloppier spec.  It means that within the stated frequency range the driver can reproduce that frequency with -10db(spl I think) of 0.  That's a big swing, more than three orders of magnitude.

Title: Re: Sub Question
Post by: Mac Kerr on August 17, 2014, 04:45:12 PM
The -10 is a sloppier spec.

It is a looser spec, being equivalent to +-5dB instead of the +-3dB we see most often in specs.

Mac
Title: Re: Sub Question
Post by: Bob Burke on August 17, 2014, 04:54:32 PM
Thanks for the info guys. I just ordered the sub, so.... fingers crossed.
Title: Re: Sub Question
Post by: Ivan Beaver on August 17, 2014, 06:18:41 PM
Does this sub produce down to 36 Hz or 42 Hz?

ANY loudspeaker (ever tweeters) will easily "produce down to" 1Hz.  No problem.

NOW HOW LOUD it is at that freq is a TOTALLY different story!

There are all sorts of different "games" that manufacturers "play" with specs.  Some more than others.

In MY opinion (others are willing to differ), the low freq response HAS to be tied to the rated sensitivity-or else it has very little meaning.

For example (I'm just making this spec up) let's say the rated sensitivity is 100dB.

The freq at which the response in 3dB down (97dB) should be the -3dB point.  The point at which the level is 10dB down (90dB) is the -10dB rating.

If these are not tied together-then you can come up with all sorts of specs that don't mean anything.

In the above example let's say that there is a peak in the response at 500Hz (we are talking about a sub here).  The manufacturer could rate that peak as being the "sensitivity", but it would be VERY misleading as to how loud the speaker would be in the intended range it would be used.

Let's say this peak is 6dB higher (106dB) than the "realistic" rating of 100dB (as measured down in the sub range).  This would mean that you would need twice as many subs to get the levels you would "think" you would be getting-based on the rating at 500Hz.

Yes the numbers MATTER-and it is VERY important to not only look at the "simple number" but ALSO the measured response-to get an idea where the numbers came from.

If you don't see a measured response then you have no idea where the numbers came from or how realistic they are.

There is no standard-so you HAVE to look a bit closer when comparing specs to see how well they REALLY stand up to each other.

Of course none of the specs even begin to tell what the speaker actually SOUNDS like.

That is a totally different subject-for which I am not sure there is any metric or spec-other than subjective.

And even THAT is very different.  Some people like a smooth response-others like the "agressive ice pick in the forehead" type sound.  Yes I have had a good number of people tell me over the years they want the system to "hurt" the audience and "drill through" the audience.  So they prefer a system with "an edge" to it.

Oh well-------------------
Title: Re: Sub Question
Post by: Tim Padrick on August 17, 2014, 10:25:09 PM
Lets not forget distortion.  At the -10 freq I'll bet it's very high, so don't bother trying to get more out of the sub with an EQ boost.
Title: Re: Sub Question
Post by: Mark McFarlane on August 17, 2014, 11:43:58 PM
...
If you don't see a measured response then you have no idea where the numbers came from or how realistic they are.....

And, unfortunately, the measured response 'graph' that is published may be smoothed so much as to be misleading.
Title: Re: Sub Question
Post by: Bob Burke on August 18, 2014, 07:04:58 AM
  Man, I learn so much here it's incredible. I'm just a ham and egger, but through all the advice I've received here at PSW, I've managed to put together a nice little, good sounding rig. This JBL sub will give us some boom, and help keep people on the dance floor.

  Thanks again to you all.


Regards,

Bob
Title: Re: Sub Question
Post by: Bob Burke on August 18, 2014, 08:27:18 AM
Just when you thought this tedious thread was over...... ::)  I  need advice on hooking this sub up.

This is the sub:

http://www.sweetwater.com/store/detail/EON518S/

 I have a Soundcraft EFX8 (http://www.sweetwater.com/store/detail/EFX8/) into a Dbx 1231 (http://www.sweetwater.com/store/detail/1231) into a QSC PLX 1804 (http://www.sweetwater.com/store/detail/PLX1804/).

  Normally, I run the main outs from the mixer into the EQ, then to the power amp, then to my passive Yamaha S115V mains. What is the correct method of hooking the JBL sub into this system? I have to buy the cabling, and want to make sure that I get the right stuff.


Thanks,

Bob
Title: Re: Sub Question
Post by: Bill McIntosh on August 18, 2014, 08:49:28 AM
Just when you thought this tedious thread was over...... ::)  I  need advice on hooking this sub up.

This is the sub:

http://www.sweetwater.com/store/detail/EON518S/

 I have a Soundcraft EFX8 (http://www.sweetwater.com/store/detail/EFX8/) into a Dbx 1231 (http://www.sweetwater.com/store/detail/1231) into a QSC PLX 1804 (http://www.sweetwater.com/store/detail/PLX1804/).

  Normally, I run the main outs from the mixer into the EQ, then to the power amp, then to my passive Yamaha S115V mains. What is the correct method of hooking the JBL sub into this system? I have to buy the cabling, and want to make sure that I get the right stuff.


Thanks,

Bob
There are two approaches, aux-fed or post-EQ.

If you have a spare aux output from the mixer, connect one XLR from that to an input on the sub.  Then on the channel strips, send only the signals with low frequency content (bass and backing tracks probably) to that aux send.  The sub will handle the rest.  Yes, you would also roll off at about 120 Hz from the mains.

Or, you can insert the sub between the EQ and the QSC amp.  Send both channels to the sub, then right output from the sub to the right top, left to the left top.  Engage the high pass filter on the sub outputs -- this will keep the low stuff out of the tops. 

Aux-fed is simpler and gives you more control, but requires one available post-fade aux output from your mixer.  Post-EQ is easier to picture, but a little more difficult to get the levels correct between tops and sub. 

You didn't mention the make/model of the EQ unit.  Some of these have dedicated sub outputs, use that if it is present.

FWIW I use the post-EQ, but I am using a DR260 so I can easily change the relative levels between tops and sub from my laptop at FOH.
Title: Re: Sub Question
Post by: Bob Burke on August 18, 2014, 09:00:11 AM
Excellent! Thanks Bill. I have a Dbx 1231 (http://www.sweetwater.com/store/detail/1231), and it does have a low pass filter. I do have an Aux that I can use as well, so maybe I'll try both methods.

You guys are the best!
Title: Re: Sub Question
Post by: Bob Burke on August 18, 2014, 09:49:44 AM
p.s.


  If I use the Aux Out from the mixer, which is 1/4" phone plug,  how do I connect that to the sub input, which is XLR? Adapter? Special cable?
Title: Re: Sub Question
Post by: Bill McIntosh on August 18, 2014, 10:24:09 AM
p.s.


  If I use the Aux Out from the mixer, which is 1/4" phone plug,  how do I connect that to the sub input, which is XLR? Adapter? Special cable?

Either a 1/4" balanced adapter + a regular XLR, or an adapter cable.

http://www.audiopile.net/products/Mic_Instr_Cables/MP_Adaptor_Cbls/Adaptor_Cables_2.shtml
http://www.audiopile.net/products/Adaptors_Connectors/Adaptors/Quarter_Inch_Adaptors/QuarterInch_Adaptors.shtml