Phase in JBL dual 18” |
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serioussound
Registered User Joined: 01 December 2013 Status: Offline Points: 443 |
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Posted: 17 April 2019 at 10:44am |
I have a pair of JBL 2241H dual 18”.
1 driver was bad so I changed it.
After changed it I was so confused since 1 cab sound pretty much nothing compared to the other cab which gave nice full bass. I then realised I wired the new driver out of phase. (Damn JBL color marking) Please help why was this effecting the sound so brutally much? |
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toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
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Tonskulus
Registered User Joined: 15 September 2017 Location: Finland Status: Offline Points: 425 |
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Think about car and two equally strong persons trying to move it by pulling or pushing. 180 degree phase cancellation: one person is pulling and another one pushing at the same side. Car is not moving at all, no work is done no matter how hard they are trying. 0 degree phase cancellation: Both persons are pushing OR pulling at same time - now the car is moving by power of two persons. Edited by Tonskulus - 17 April 2019 at 12:14pm |
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studio45
Old Croc Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3863 |
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One was suckin' while the other was blowin' - so no pressure resulting...
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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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serioussound
Registered User Joined: 01 December 2013 Status: Offline Points: 443 |
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I see never tested this before but it was crazy before I realised it ..
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bob4
Old Croc Joined: 29 February 2004 Location: Finland/Germany Status: Offline Points: 1842 |
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Aaaaargh......... Why does everyone use wrong and outdated terminology? It is an issue of reversed POLARITY!
Don't perpetuate incorrect and sloppy terminology! |
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studio45
Old Croc Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3863 |
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If you walk up to a system - especially a bespoke build - and there's not as much bass as you were expecting, it's the No 1 thing to check. Usually the culprit is a short XLR link in the amp rack that should have been labelled as a polarity reverser, but isn't... or a Speakon link that the work-experience guy made.
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Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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Boxes-R-Blue
Registered User Joined: 11 December 2018 Status: Offline Points: 147 |
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Also, just for shits and giggles be aware JBL tend to run Red Back, black forward, IE the DEAD opposite polarity/phase/motor aspect to any other manufacture so you kinda need a Phase Popper to check the box is in line with the rest of your rig...
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partya
Registered User Joined: 06 September 2013 Location: New Zealand Status: Offline Points: 105 |
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JBL standardised their polarity conventions in the early 90's, here is an older link to a list of positive / negative transducers --
Cheers
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Turn it up! Turn what up?
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Robbo
Old Croc Joined: 05 December 2005 Location: Shropshire Status: Offline Points: 4221 |
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This caused us loads of problems in the early 1970s when we used to hire in extra bass and mid cabinets to augment our own systems on some of the larger tours--I can remember crawling inside Martin 115 horns to feel which way the cone was moving when another crew member applied a 9v battery to a plugged in adaptor lead that we used for phase checking.
Back in those days a lot of companies including ours used a mix of JBL and Gauss in both bass and mid cabinets so from that day, I have always double checked drivers with a battery to ensure matched phasing---JBL reconed drivers were a common problem and very often moved in the wrong direction when non genuine kits were fitted. I bet there are loads ofJBL HF drivers being used out there in the field that are fitted with copy diaphragms that are wrongly phased and no-one has ever noticed it. |
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madboffin
Old Croc Joined: 03 July 2009 Location: Milton Keynes Status: Offline Points: 1537 |
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For some obscure reason, JBL driver magnets were the opposite way round to everyone else's, hence the nonconformist polarity.
If you put a JBL next to another manufacturer's driver on the bench (same way up), it was a bad idea to get your fingers between the two! |
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mojofilters
Registered User Joined: 13 January 2018 Location: Tyne and Wear Status: Offline Points: 19 |
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Is it true that the old JBL polarity inversion standard was intended to mitigate potential damage from the cone moving forwards, if an amp getting turned on produced sufficient movement?
I was never sure if that was the audio equivalent of an old wives tale, or actually a pertinent problem back when such drivers were used with much less sophisticated amps etc? If it was correct, wouldn't backwards cone movement of equivalent force potentially cause another type of damage?
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