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jarrods
02-14-2005, 05:49 PM
Consider this; A pair of JBL 4344s, bi-amped with the LF driver having no passive crossover circuitry and the other drivers using a 3134 passive network with the three L-Pads. A dbx DriveRack Studio can provide external EQ.

All three L-Pads are set to 0dB and system EQed up with the DriveRack RTA and amp gains tweaking.

OK. The L-Pad range of control can go up to +5dB on all three drivers. So the amp must be putting in that level to the network but as the LPad is set to 0dB the LPad just dissipates the rest in heat.

So my question is: if you wind all three L-Pads up to +5dB and then reduce amp by 5db (or maybe some other magical number ???) do you have the same sound but your system is now more top end efficient?

Jarrod

Robh3606
02-14-2005, 05:53 PM
Interesting. If you just reduce attenuation I would expect you just saved some power. Like adjusting fixed pads. What happens when you measure with the pads wide open?? You get the same driver to driver balance??

Rob:)

duaneage
02-14-2005, 06:02 PM
If the dbx rack can control the same range of frequencies as the crossover network, gain within the crossover network would amount to a "virtual" L-pad. You should therefore be able to wire over the L-pads and control MF and HF output through the crosover.

jarrods
02-14-2005, 06:04 PM
i thought the idea of an L-Pad was to present a somewhat constant impedance to the driving network independent of the L-Pad setting.

so at one extreme the driver gets none of the signal, it being all dissipated in the resistance windings of the L-Pad and at the other extreme the driver is basically connected directly to the driving network so the L-Pad dissipates no power at all.

jarrod

jarrods
02-14-2005, 06:10 PM
hi duaneage... i do wish to keep the lpads to get the MF/HF/UHF balance about right before i do the final tweak with the dbx. (less digital EQ fiddling that way)

my thought is do i set them at like for example:

0dB, -0.5bB & +1dB
or
+5dB, +4.5dB & +6dB

and just drop the amp driver gain back by +5dB in the DriveRack settings for the top end amp.

jarrod vbmenu_register("postmenu_43101", true);

majick47
02-15-2005, 10:17 AM
Jarrods it was very interesting to read your post re biamping your 4344 speakers with the LF driver having no passive circuitry and the other drivers useing a 3134 passive network with the three L pads balancing the output either via EQ or volume control via your amps. I have recently "experimented" with a pair of L200b that I added 2405 tweeters/3106 crossovers making them quasi L300/4333. The 136a woofers (reconed with 2235) are running straight to a Yamaha MX-2000 130 watt class A amp with no EQ or active crossover in the path. The second MX-2000 amp is powering the MF and HF via the passive crossovers. The LF output to my "ears" now very closely matches the output of the MF/HF and seems to fill in the upper LF. I ran this by a couple of much more experienced people with mixed responses (positive/negative). Am I correct in interpeting that you are doing the same thing as I am with your 4344 15" woofers? I have to admit that I am pleased with the results but I'm open to any and all suggestions/advice. This "biamp" configuration is not etched in stone since I just picked up a second pair of L200b speakers to add to my system. Now thinking of powering each pair of L200b with a single MX-2000 amp. I'd like to keep the signal path simple and clean with the least amount of equipment utilized. Rich.

GordonW
02-15-2005, 02:24 PM
hi duaneage... i do wish to keep the lpads to get the MF/HF/UHF balance about right before i do the final tweak with the dbx. (less digital EQ fiddling that way)

my thought is do i set them at like for example:

0dB, -0.5bB & +1dB
or
+5dB, +4.5dB & +6dB

and just drop the amp driver gain back by +5dB in the DriveRack settings for the top end amp.

jarrod vbmenu_register("postmenu_43101", true);

Sounds reasonable, but remember, due to the way L-pads interact with speaker drivers and other crossover components (they don't have exactly the same "behaviour" as seen by the crossover, at different level settings) you may have to adjust the relative levels between mid/hf/uhf controls, once you crank them up.

You should, almost without any doubt whatsoever, be able to find a "happy balance" at the new range, but it may just be at very slightly different relative settings, than what you might expect (different from just adding 5 dB to all three, one or more may need to be slightly higher or lower by a fraction)...

Regards,
Gordon.

jarrods
02-15-2005, 04:40 PM
Rich, Yes I am running the 2235's directly from the K1 amp with no passive filtering. But the system I use to split the signal to the three amps (subs K2 as well) does do active filtering that bandpasses the signal at 47.5Hz to 280Hz as well as EQ'ing it. The last set of readings had the 2235 EQ at:

63Hz 0dB
80Hz +2dB
100Hz -1dB
125Hz -5dB
160Hz -0.5dB
200Hz -1.5dB
250Hz 3.5dB

so there is still lots digital manipulation going on here in the DriveRack Studio.

http://www.driverack.com/studio.htm

jarrod

jarrods
02-15-2005, 05:05 PM
Gordon, thanks for the positive words. yes i agree that the l-pad/driver combination will not be consistant over the whole range.

i actually decided to have a closer look at the L-Pad. the ones i used were from Parts Express as recommended in these pages. very different to the old car radio fader i used to install back a 100 years ago that was a single 50ohm pot...!

this one was dual wipers with the resistive element facing the network at 8.6R and the resistive element facing the driver at 32R. I hooked up a very accurate model speaker (HAHAHAHA), an 8.2 ohm resistor, to the output and measured the load over the complete range.

CCW 8.5R
1/4 10R
mid 9.9R
3/4 8.8R
CW 8.2R

next to useless experiment as a 8.2R resistor load and measuring purely the resisance of the overall combination does not come close to reality. but even here i can see like 12% changes in the load over the range of the LPad travel.

I'll wind up the LPads all flatout, RTA EQ the system, then look at the boosts/cuts put in place and then use that as a guidance as to which LPad to lower. then re RTA again. (as 75% of the forum members cringe at the thought of my digital hacking... hehehehe.... hmmm wonder how many CD's and DVD's are made now without the signal going though a digital mix desk and a 6ft high rack of digital 'gear'?... anyway that is another thread ;) )

jarrod