Help tuning T48's

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Basshund
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Joined: Sun Sep 28, 2014 5:21 am
Location: Melbourne

Re: Help tuning T48's

#31 Post by Basshund » Thu Apr 20, 2017 9:55 pm

Grant Bunter wrote:
Basshund wrote:Yeah I think the polarity might be reversed out of my amplifier :shock: I will look at it properly tomorrow.

In the meantime it appears the SPL meter was set on some weird setting, reading the bottom end result maybe? With tonights tweaking, this was my final measure...
Don't immediately assume it's the amp output that's the cause of the polarity problem.
It could be one lead from the DJM to the driverack, or the driverack to the amp, on the offending channel.
A multimeter with continuity function will tell you if pin 2 is to pin 2, and pin 3 to pin 3 on each lead, and, not, as sometimes happens, pin 2 to pin 3, on your XLR's.
Check your speaker leads too, ie +1 to +1 and -1 to -1.

If you're getting nearly 130dB now, you must be starting to get that "hell yeah" grin...
Deaf and grinning :D

I've just checked my leads, all the XLR's are good. I'm using 4 pole speakon cables to run out to the subs, which are a bit tricky to test, but given that when I run the two subs daisy chained (parallel), I wasn't having the polarity issue, I'm assuming they're good.

So.... How do I test polarity off the amp, rack, and mixer? I'm putting money on the mixer, as it was a rebuilt Frankenstein we got from a service provider. The Amp was bought new and the drive rack was vgc second hand from someone that had used it without complaint... unless he was fibbing.

As always, many thanks in advance.

Grant Bunter
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Re: Help tuning T48's

#32 Post by Grant Bunter » Fri Apr 21, 2017 4:01 am

Basshund wrote:
Grant Bunter wrote:
Basshund wrote:Yeah I think the polarity might be reversed out of my amplifier :shock: I will look at it properly tomorrow.

In the meantime it appears the SPL meter was set on some weird setting, reading the bottom end result maybe? With tonights tweaking, this was my final measure...
Don't immediately assume it's the amp output that's the cause of the polarity problem.
It could be one lead from the DJM to the driverack, or the driverack to the amp, on the offending channel.
A multimeter with continuity function will tell you if pin 2 is to pin 2, and pin 3 to pin 3 on each lead, and, not, as sometimes happens, pin 2 to pin 3, on your XLR's.
Check your speaker leads too, ie +1 to +1 and -1 to -1.

If you're getting nearly 130dB now, you must be starting to get that "hell yeah" grin...
Deaf and grinning :D

I've just checked my leads, all the XLR's are good. I'm using 4 pole speakon cables to run out to the subs, which are a bit tricky to test, but given that when I run the two subs daisy chained (parallel), I wasn't having the polarity issue, I'm assuming they're good.

So.... How do I test polarity off the amp, rack, and mixer? I'm putting money on the mixer, as it was a rebuilt Frankenstein we got from a service provider. The Amp was bought new and the drive rack was vgc second hand from someone that had used it without complaint... unless he was fibbing.

As always, many thanks in advance.
No worries!

I had a thought. Did you use the setup wizard on the driverack by any chance?
If so, check the polarity settings, in the crossover section, I think, lol.
Check them anyway. Especially if pre loved, it may also have been altered by the last owner.

Errr 4 pole speakons. NL4's are fine, but, you don't need cables with 4 wires.
If you have 4 wire cables, they are simple to test, just undo the blue covers, slide back the cable grip, at both ends, and +1 and -1 and +2 and -2 will be "easy" to see, and to test with continuity tester.
But again, you don't need them. The only reason to use 4 lead speakons would be to drive subs and tops off one cable, and, normally you would hook them up via a breakout box.

Regarding the "Frankenstein DJM, in the immortal words of Pauline Hansen, Please explain...
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

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bitSmasher
Posts: 617
Joined: Fri May 30, 2008 2:55 am
Location: Sydney, Aus.

Re: Help tuning T48's

#33 Post by bitSmasher » Fri Apr 21, 2017 5:51 am

Another Strayan, nice...
What brought you to the T48, and have you seen/heard any BFM in Melbourne?

Bruce Weldy
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Re: Help tuning T48's

#34 Post by Bruce Weldy » Fri Apr 21, 2017 8:32 am

Basshund wrote: I'm using 4 pole speakon cables to run out to the subs, which are a bit tricky to test, but given that when I run the two subs daisy chained (parallel), I wasn't having the polarity issue, I'm assuming they're good.
.
While that is probably true, it's not necessarily so. If your cable is wired backwards and your parallel speakon on the cab is wired backwards - they would now send the signal properly. That could account for the bad polarity when running with two sides of the amp vs. one. Bottom line - check every cable and check the input plates on both cabs.
So.... How do I test polarity off the amp, rack, and mixer? I'm putting money on the mixer, as it was a rebuilt Frankenstein we got from a service provider. The Amp was bought new and the drive rack was vgc second hand from someone that had used it without complaint... unless he was fibbing.

As always, many thanks in advance
To test the mixer, hook it all up and let it run. Now, unplug the Left output - did it get louder? If so, there's a problem. However, it's doubtful that is the cause. As far as the amp.....maybe a one in a million chance that it's wired backwards.


More than likely, as Grant mentioned, the problem is in the driverack. So, do these things....

1. Start fresh with a new program.
2. Do NOT use the automatic setup wizard
3. Set everything to CUSTOM
4. Make sure you are running a MONO sub.....regardless of whether the tops are stereo.
I'm pretty sure you aren't doing this since the GX7 can't run a parallel input - you have to be
running a cable to both the left and right inputs. Instead, you should run only one XLR from the
sub out of the driverack to the first channel of the amp, then daisy chain from the first input to
the second input with a short jumper or build a Y at the end.
5. Now set your crossover, limiter, etc.

At this point, my bets are on there being an incorrect setup in the driverack and your wiring scheme to the amp. Give that a try.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

Grant Bunter
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Re: Help tuning T48's

#35 Post by Grant Bunter » Fri Apr 21, 2017 4:58 pm

+1 to Bruce's post.

Just checked out the GX7 user manual. Doesn't have a version on it, but on page 7 it specifically states to use only 2 wire speakon leads.

In Australia, more often than not, Pre made 4 wire speakon leads have 4 wires, each with a wire surface area of 1.5mm squared. That's around 16G, and only allows for maximum lead length of say 5m before losses occur.
2.5mm squared (around 12G) wire allows 10-15m cable lengths. Heaps better and more practical when it comes to setting up...
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

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Bill Fitzmaurice
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Re: Help tuning T48's

#36 Post by Bill Fitzmaurice » Fri Apr 21, 2017 5:12 pm

Grant Bunter wrote: 16G...only allows for maximum lead length of say 5m before losses occur.
A lot longer than that. In most cases with pro-sound the wire current capacity will be more of a problem than resistance. Use this to find out what's actually required:
http://www.bcae1.com/images/swfs/speake ... istant.swf

Bruce Weldy
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Location: New Braunfels, TX

Re: Help tuning T48's

#37 Post by Bruce Weldy » Fri Apr 21, 2017 5:26 pm

Bill Fitzmaurice wrote:
Grant Bunter wrote: 16G...only allows for maximum lead length of say 5m before losses occur.
A lot longer than that. In most cases with pro-sound the wire current capacity will be more of a problem than resistance. Use this to find out what's actually required:
http://www.bcae1.com/images/swfs/speake ... istant.swf
And I just remove all doubt by building all 12ga. all the time.

You spend thousands on a PA system, why scrimp on the cables? Good 12ga. cable with a good jacket, if rolled properly, will lay flat and never let you down.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

Grant Bunter
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Location: Ilfracombe Queensland Australia
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Re: Help tuning T48's

#38 Post by Grant Bunter » Fri Apr 21, 2017 6:18 pm

Bill Fitzmaurice wrote:
Grant Bunter wrote: 16G...only allows for maximum lead length of say 5m before losses occur.
A lot longer than that. In most cases with pro-sound the wire current capacity will be more of a problem than resistance. Use this to find out what's actually required:
http://www.bcae1.com/images/swfs/speake ... istant.swf
True. Sorry if my post is at all misleading.

I'm with Bruce, I only run 12G speaker leads. Higher current carrying capability, similar losses to 16G, but over longer lengths. Win Win.
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

Basshund
Posts: 25
Joined: Sun Sep 28, 2014 5:21 am
Location: Melbourne

Re: Help tuning T48's

#39 Post by Basshund » Fri Apr 21, 2017 10:20 pm

Rightio. So as per advice, I got my myself an XLR Y-lead for the subs and put it to the test. Still had cancellation (winding back 1 channel on the amp had an instant increase in volume, so I new I still have reverse polarity somewhere in/after the amp.)

Checked the speakons which are actually 2 pole, and 2.5mm wire, so about 13 gauge (somehow got confused, the jacks in the cabs are 4 pole. It has been some time since I built these). Anyway cable were good.

Finally went digging in the cabs, continuity was good between jacks, but on closer inspection some moron had reverse wired the line from jack to driver... :wall:

Pulled the driver, flipped the polarity, hey presto. :hyper: :noob:

SPL meter stops at 130db, so I think I'm above that now judging by the vibration in my ribcage. Very lucky to have not cooked a driver or two... +1 Eminence.

Basshund
Posts: 25
Joined: Sun Sep 28, 2014 5:21 am
Location: Melbourne

Re: Help tuning T48's

#40 Post by Basshund » Fri Apr 21, 2017 10:28 pm

Grant Bunter wrote: Regarding the "Frankenstein DJM, in the immortal words of Pauline Hansen, Please explain...
Dear old Pauline... A buddy and I bought a pair of CDJ 900's from a pioneer service agent, and he had enough spares parts lying around to build us a DJM800 mixer to go with. Thus the Frankenstein.

And in answer to bitSmasher, I haven't heard any other BFM's, so this has been a bit tricky. I've never had a reference for what they can do, I just felt like mine could be a lot better...

Grant Bunter
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Re: Help tuning T48's

#41 Post by Grant Bunter » Sat Apr 22, 2017 1:31 am

Basshund wrote:Rightio. So as per advice, I got my myself an XLR Y-lead for the subs and put it to the test. Still had cancellation (winding back 1 channel on the amp had an instant increase in volume, so I new I still have reverse polarity somewhere in/after the amp.)

Checked the speakons which are actually 2 pole, and 2.5mm wire, so about 13 gauge (somehow got confused, the jacks in the cabs are 4 pole. It has been some time since I built these). Anyway cable were good.

Finally went digging in the cabs, continuity was good between jacks, but on closer inspection some moron had reverse wired the line from jack to driver... :wall:

Pulled the driver, flipped the polarity, hey presto. :hyper: :noob:

SPL meter stops at 130db, so I think I'm above that now judging by the vibration in my ribcage. Very lucky to have not cooked a driver or two... +1 Eminence.
Awesome, problem solved! :hyper: :clap:
On all levels.

Get out and enjoy them now...
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

CoronaOperator
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Location: Medicine Hat, Alberta, Canada

Re: Help tuning T48's

#42 Post by CoronaOperator » Sat Apr 22, 2017 7:43 am

Basshund wrote: SPL meter stops at 130db, so I think I'm above that now judging by the vibration in my ribcage. Very lucky to have not cooked a driver or two... +1 Eminence.
Measure just one titan at max volume which should be within the meters range, then add +6 dB's to calculate the value it would be at with both boxes going.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

Basshund
Posts: 25
Joined: Sun Sep 28, 2014 5:21 am
Location: Melbourne

Re: Help tuning T48's

#43 Post by Basshund » Thu Apr 27, 2017 4:13 am

CoronaOperator wrote:
Basshund wrote: SPL meter stops at 130db, so I think I'm above that now judging by the vibration in my ribcage. Very lucky to have not cooked a driver or two... +1 Eminence.
Measure just one titan at max volume which should be within the meters range, then add +6 dB's to calculate the value it would be at with both boxes going.
128dbc at 2 metres, 50mm off the ground, inside the workshop.

Grant Bunter
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Re: Help tuning T48's

#44 Post by Grant Bunter » Thu Apr 27, 2017 4:32 am

Basshund wrote: 128dbc at 2 metres, 50mm off the ground, inside the workshop.
Ok
This, for me, is where it gets a bit antsy.
I'm simply not familiar enough with driveracks.

128dBC (or 134dbC at 1m) has suddenly become irrelevant. You need to know which frequency was the peak frequency in order to determine relevance.

Hopefully someone who is driverack savvy will chime in, can the driverack be used as a spectrum analyser? Or is it "just" RTA?

134dbC at 100Hz is one thing. 134dbC at 50Hz is quite another...
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

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