Attenuate compression driver output.

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   Hey people....

Just a question.  We've got some JBL SRX series 15" boxes and double 12" boxes.  These can sound really nice bi-amped however when run through the passive crossover inside them they spew out way to much high end from the compression driver/horn.

I've been dealing with it by eq'ing the sh*te out of the boxes, pulling everything after the 1.2Khz crossover point back by 6-12db most times.

With the EQ applied they sound really nice again.

I did start thinking about better solutions and was wondering if there was something I could put in series with the compression driver inside the box that would lower the signal going to it?  A resistor or something?  I'm no expert about things like this but would be interested if anyone had suggestions.

I can deal with it as is with the EQ but would be nice not to have to think about it.

rez.

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rezsbc Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 November 2006 Location: Ireland Status: Offline Points: 352	Post Options Post Reply Quote rezsbc Report Post Thanks(0) Quote Reply Topic: Attenuate compression driver output. Posted: 20 September 2007 at 1:24pm
	Hey people.... Just a question. We've got some JBL SRX series 15" boxes and double 12" boxes. These can sound really nice bi-amped however when run through the passive crossover inside them they spew out way to much high end from the compression driver/horn. I've been dealing with it by eq'ing the sh*te out of the boxes, pulling everything after the 1.2Khz crossover point back by 6-12db most times. With the EQ applied they sound really nice again. I did start thinking about better solutions and was wondering if there was something I could put in series with the compression driver inside the box that would lower the signal going to it? A resistor or something? I'm no expert about things like this but would be interested if anyone had suggestions. I can deal with it as is with the EQ but would be nice not to have to think about it. rez.

matt andrews Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 15 September 2004 Status: Offline Points: 501	Post Options Post Reply Quote matt andrews Report Post Thanks(0) Quote Reply Posted: 20 September 2007 at 1:27pm
	An lpad will do what you require, look here. http://www.lalena.com/Audio/Calculator/LPad/

rezsbc Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 November 2006 Location: Ireland Status: Offline Points: 352	Post Options Post Reply Quote rezsbc Report Post Thanks(0) Quote Reply Posted: 20 September 2007 at 1:35pm
	thanks man exactly what I need!!!!

tb_mike Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 01 October 2004 Location: New Zealand Status: Offline Points: 2744	Post Options Post Reply Quote tb_mike Report Post Thanks(0) Quote Reply Posted: 20 September 2007 at 10:14pm
	Bear in mind that the jbl will have an Lpad,or a version of it,already so youl have to modify the one thats there.Perhaps stuff a sock in the horn flare LOL - Many say that JBLs sound bright. Im not sure if this is due to the program material,or an edgy titchy compression driver with strange resonances on it. DJK might have some input. I dont think JBL would purposely emphasise anything - HIFI speakers do this enough.

_djk_ Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002	Post Options Post Reply Quote _djk_ Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 2:52am
	A specific model number is needed, then I will look at the JBL crossover design and comment.
	djk

rezsbc Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 November 2006 Location: Ireland Status: Offline Points: 352	Post Options Post Reply Quote rezsbc Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 10:45am
	SRX715 and SRX722. I'm sure JBL are doing everything ok... this is probably a matter of my personal taste I don't know but for me the highs are too loud.

HansA Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 07 March 2007 Location: Norway Status: Offline Points: 595	Post Options Post Reply Quote HansA Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 11:44am
	rezsbc: your hearing is to good. Go get some eardamage as the rest of us.
	��o�O�o��: HansA, The FUBAR sound technician :��o�O�o��

_djk_ Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002	Post Options Post Reply Quote _djk_ Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 12:10pm
	I looked at the network designs. They are very complex and NOT compatible with adding an L-pad. I would bi-amp them. The passive crossovers look like they will not work correctly with a resistor or an L-pad added to the highs. Loudspeaker enclosure 'diffraction loss' occurs in the low frequency range of loudspeakers in enclosures that are located in the open, away from walls or other surfaces. The essence of it is this: a speaker radiating into half space plays 6 dB louder than the same speaker radiating into full space. A full range speaker finds itself radiating into half space that the upper frequencies but radiating into full space at lower frequencies. This results in a gradual shift of -6dB from the highs to the lows. This is called the '6 dB baffle step' or the enclosure's 'diffraction loss'. The center frequency of the transition is dependent on the dimensions of the baffle. The smaller the baffle the higher the transition frequency. All enclosure shapes exhibit a basic 6 dB transition or step in the response with the bass ending up 6 dB below the treble. The -3dB point for the 722 is about 300hz, you will need about 3dB of boost there and about 6dB of boost in the 80hz region, and about 1dB of boost around 600hz. The step points for the 715 will be roughly 250hz, 63hz, and 500hz. The JBLs are flat to very high frequencies. Close mic techniques sound un-naturally bright on flat systems. Sound at a distance does not have as much HF content as sound up close does. It is recommended you follow a 'house' curve and do a 3dB/oct roll-off starting about 3Khz. These two combined will give a shift of almost 12dB between 100hz and 10Khz and will probably sound close to what your ear thinks is 'right'.
	djk

HansA Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 07 March 2007 Location: Norway Status: Offline Points: 595	Post Options Post Reply Quote HansA Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 2:33pm
	There shouldnt be a problem adding a serial and parallel resistor right before the tweeter, conserving the correct impedance.. ??
	��o�O�o��: HansA, The FUBAR sound technician :��o�O�o��

rezsbc Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 November 2006 Location: Ireland Status: Offline Points: 352	Post Options Post Reply Quote rezsbc Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 4:18pm
	Thanks DJK... very detailed!!! I'll give what you suggest a try... although the purpose of this was to run them without any EQ but hey. Thanks again!!! rez. and p.s. jokes aside HansA it's not just my hearing trust me stand in front of these bad boys you'll be reaching for that EQ in no time!!!

HansA Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 07 March 2007 Location: Norway Status: Offline Points: 595	Post Options Post Reply Quote HansA Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 4:39pm
	I know. I to feel most untuned JBL systems are to bright.
	��o�O�o��: HansA, The FUBAR sound technician :��o�O�o��

csg Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 17 September 2007 Location: bedford Status: Offline Points: 6047	Post Options Post Reply Quote csg Report Post Thanks(0) Quote Reply Posted: 21 September 2007 at 9:11pm
	if you want to lower the output of the comp driver rather than applying loads of eq all the time ( in my book to much eq always leaves other problems) then you will be able to using a correctly designed L pad network directly before the comp driver and after the passive network in the speaker. Dont go down the simple route using one resistor in series as you will alter the impedence of the comp driver that the passive network sees, hence altering the crossover fequency. An l pad will ensure that the crossover point remains unaffected. Look in the eminence book for l pad resistor values. hope that helps chris