Members drenwick Posted June 5, 2008 Members Share Posted June 5, 2008 Considering using a QSC PLX2502 (450W/8 ohms, 750/4 ohms) in the following manner: A pair of JBL MR925s (350W/8 ohms) on one side with 100 hz HPF engaged and a single JBL MRX518 (500W/4 ohms) sub on the other side with 100 hz LPF engaged. My questions are: -Is the power adequate? -Do the filters alleviate the need for an external X-over? -What is your opinion of the MRX518 subwoofer? Rockabilly/Blues trio (guitar, bass, drums), small to medium bars/clubs (50 -200). (A PLX1602 will drive 2 - JBL JRX112s for stage monitoring.) Thanks for sharing your experience folks! Link to comment Share on other sites More sharing options...
Members dboomer Posted June 5, 2008 Members Share Posted June 5, 2008 reasonable ... Will the amp allow you a HPF on the sub side too? Very important to have if you are gonna run this system even "medium" Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 5, 2008 Members Share Posted June 5, 2008 At those power levels, a HPF is essential. The PLX-2 includes 33Hz HPF's on each channel, and a switchable 100Hz LPF/HPF for crossover use. Link to comment Share on other sites More sharing options...
Members witesol Posted June 5, 2008 Members Share Posted June 5, 2008 that'll work well. The MRX sub is a good'n. The only slightly tricky thing might be to get the balances smoothed out between the highs and lows. Hopefully you have at least a 15 band EQ to adjust. Playing a few CDs through the system will help you balance out the subs to tops.. The temptation might be to push that single sub to try and really get things bumpin.. Link to comment Share on other sites More sharing options...
Members drenwick Posted June 5, 2008 Author Members Share Posted June 5, 2008 At those power levels, a HPF is essential. The PLX-2 includes 33Hz HPF's on each channel, and a switchable 100Hz LPF/HPF for crossover use. So the 33Hz HPF is sufficient? Is this the HPF dboomer was looking for? So no X-over needed? Link to comment Share on other sites More sharing options...
Members Not Serial Posted June 5, 2008 Members Share Posted June 5, 2008 IIRC the filters on the amps are 12db/octave. a crossover would usually be around 24db/octave depending. 33hz is usually a little low but doable, i'm not familiar with your sub so i cant say. i usually HP at 40hz or 50 if i am pushing hard. Link to comment Share on other sites More sharing options...
Members dboomer Posted June 5, 2008 Members Share Posted June 5, 2008 IIRC the filters on the amps are 12db/octave. 33hz is usually a little low but doable, If the filters are 12 dB/oct you should try flipping the polarity to the top box. Use whatever works best. 33Hz HPF is low but better than nothing. You should use the cutoff frequency of the box when possible Link to comment Share on other sites More sharing options...
Members witesol Posted June 5, 2008 Members Share Posted June 5, 2008 every filter "reaches" a bit past it's cutoff freq, now matter how steep the slope or Q, so 33hz sounds about right. low-cuts on the board and cutting the 20hz on your graphic go a way towards clean, safe power down low. funny, I still see bands with their gr. eq's 20hz boosted in the classic 'smile' curve...and they have a pair of 12+cabs on sticks Link to comment Share on other sites More sharing options...
Members drenwick Posted June 5, 2008 Author Members Share Posted June 5, 2008 every filter "reaches" a bit past it's cutoff freq, now matter how steep the slope or Q, so 33hz sounds about right. low-cuts on the board and cutting the 20hz on your graphic go a way towards clean, safe power down low. funny, I still see bands with their gr. eq's 20hz boosted in the classic 'smile' curve...and they have a pair of 12+cabs on sticks I won't make that mistake... Thanks for the input! dboomer - you lost me on switching the polarity on the top box... what's the theory? (just my inexperience talking here...) Link to comment Share on other sites More sharing options...
Members dboomer Posted June 5, 2008 Members Share Posted June 5, 2008 You never know for sure. But since each pole in a filter shifts things 90 degrees your tops may be out of polarity with your bottoms. 12 db/oct shifts 180 degrees ... flipping polarity shifts by 180 degrees back. Just turn over the banana plug to the tops and then turn it back. Best if you can play a 100Hz sine wave. Just leave it in whichever position is the loudest. Everybody should be doing this (just to be certain) but few do. Link to comment Share on other sites More sharing options...
Members witesol Posted June 6, 2008 Members Share Posted June 6, 2008 the problem is with a 180 phase shift is it's sort of the lessor of two evils. sound wise, never seems to be just right. That new Radial Phase controller(like the little labs) looks to be an interesting box, especially if anypone is double mic'ing things too... Link to comment Share on other sites More sharing options...
Members drenwick Posted June 6, 2008 Author Members Share Posted June 6, 2008 I don't use bananas but does the fact that both the tops and the bottom are being filtered, one above and one below 100 Hz have any bearing on that? Link to comment Share on other sites More sharing options...
Members agedhorse Posted June 7, 2008 Members Share Posted June 7, 2008 I don't use bananas but does the fact that both the tops and the bottom are being filtered, one above and one below 100 Hz have any bearing on that? Yes, that's where the 360 (acoustical) degrees comes from on 2 x 12dB/octave filters. One leads by 180 and the other lags by 180. This is of course not exact and by the time the signal approaches -6dB (1/4 power) the phase will approach 180 degrees. So you are comparing signals that are different by a spread of say 12dB. It's a continuous phase shift as the signal approaches the filter knee. More importantly, the acoustic responses have their own phase shifts that must also be factored in, then there's the point sources offset delay. All in all, it's impossible to tell without emperical measurement, and maybe the "fix" effort yields little practical results when the point of measurement is moved. Link to comment Share on other sites More sharing options...
Members drenwick Posted June 8, 2008 Author Members Share Posted June 8, 2008 Uhh... OK... Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.