An improvement?Originally Posted by Beowulf57
It would seem that we are too far down the subjective path here to make that kind of recommendation. It is quite possible you would like them better, but it is also quite possible that you would find the difference modest or even unacceptable.
Your system as you have described it seems to be one that has been dialed in by the owner for his own pleasure. I wouldn't feel confident about making any recommendations.
Widget
Fair enough, though having received and read a number of posts concerning the "problems" of using the LE85/HL91 combo with a 500Hz crossover, I'd like to hear any comments (to be more specific) on the changes in the sonic signature which others have encountered using the longer HL92/2312.
Yes, it is subjective and yes, I have listened to the existing combo for many years with no driver damage (not sure I can say the same for my ears) and enjoyable sound, however we do tend to report on the subjective effects of changes to our systems and seek improvements over time.
A different bass driver may provide more extended bass, leaner upper midbass, a warmer sound, etc.; a midrange driver may sound clean and detailed, rich, hard, bright or have excessive glare, etc.; a tweeter may roll off too soon and lack air, or it may have a sibilant spit, or as in the case of adding the 2405H to my system the high frequencies became more noticeable and there was a distinct improvement in the sense of "air" of the acoustic recording space and in the delicate shimmer and decay of cymbals. As well, a slight hardness/glare diminished.
So, if anyone can comment on the subjective changes in the sound of music noted when switching to the longer horn, I'm all ears.
For want of a detail, polarity was lost.
For want of polarity coherence was lost.
For want of coherence, 25 years of enjoyment was lost.
And all for want of a detail!
Just kidding, I have enjoyed the sound for 25 years, however:
I have been using an LX5 for 20+ years with an LE85/HL91 with the polarity to the HF section reversed. This was based upon a JBL Network Service Bulletin (6-74) I was given when I acquired the LE85/HL91s from a local audio emporium. The components had come from an S7 system. I recently changed the connection so both the LF and HF connections were the same polarity and the sound improved markedly: a lower midrange "suckout" disappeared and the presentation was richer, more coherent and more delineated. Also, less in your face midrange and much better balanced sound. As it seems now, that bulletin referred to the use of the LX5 in the S8R with the 375 and the shorter HL93 horn and not to the use of the LX5 with the LE85/HL91!
So, onwards and upwards I go: thanks to this forum for returning the Kingdom of Wonderful Sound to me through all the excellent advice!
Now, I acquired a pair of 2312 horns and will try them after revisiting the N1200 crossovers...hmm, perhaps I'll reverse the phase and see if that ameliorates the hot midrange.
Replaced my H91/2307 horns with the H92/2312 horns. I had forgotten that years ago I had surrounded the horns with grey, sticky crack insulation putty to dampen the metallic resonance of the cast aluminum horns (flick the inside of the horn with your fingernail and you can hear the ringing. So, off to the hardware store for more putty (11.5" of horn to cover, rather than 8.5").
It took about three hours to remove the cabinets, replace the horns and reconnect. Once everything was in place I settled down for some listening with LPs and SACDs. First impressions: smoother sound, less strident (e.g., massed strings) and less aggressive on vocals. A good start. However, when listening to satellite programming and DVD films, voices sounded muted and a bit muffled. I played with the level control on the LX5 crossovers, and went back and forth between too much midrange and too little. What next?
Hmm...the three drivers are all hooked up in phase which sounded best with the shorter horns, but the new horns are 3" longer which affects the phase response lobes around the crossover (500Hz). I reversed the phase of the connection to the 3106 network: Eh Voila! Much better: the sound was better integrated and richer and I could listen to satellite/DVDs without needing to add sound from the TV speakers to hear dialogue clearly.
Another tweak: I reversed the connections to the 2405H tweeters and the top end was more lively and better balanced with the rest of the audio spectrum. At the moment, I am running the LX5 crossovers at minimum and so far I'm not sure I'll need to add L-pads to the LE85s in order to get more level form the 2405Hs...sounds hot enough on top at the moment.
From the following thread on JBL POLARITY CONVENTION: http://audioheritage.org/vbulletin/s...php?t=9&page=3
"A comment on "correcting" JBL polarity
If you are going to reverse the polarity of a JBL cabinet, it must be done AT EACH COMPONENT in the cabinet. You should not simply hook-up the cabinet red-to-black. That will not have the proper effect, because that will result in the signal being pathed through the transducer before the capacitor(s) - this is a DC circuit, and that is backwards. For the crossover network to work properly, the capacitor(s) must see the signal BEFORE the transducer, regardless of cabinet (and transducer) polarity.
To "correct" or re-phase a vintage JBL cabinet, you need to reverse-wire at each component. Simply alter the signal path AFTER the crossover and before the transducer, at each component binding posts. "
My question: is there really any difference (other than when testing for polarity using a 9V DC battery) between reversing the leads from my LX5 to the 3106 and then reversing the HF so it is in phase with the LF, and leaving the 3106 in phase with the LX5 and reversing the MF alone? The goal is to put the MF 180 degrees out of phase with the LF and HF. Audio is AC and the capacitors are non-polarized, so my common sense tells me the result is the same in both cases. However, perhaps my brain is fogged and missing a crucial point.
No.
Audio is AC.
Information please: what is the effect of adding an 8 ohm l-pad to the LF section of the 3106 network, after the 20 ohm resistor rather than before?
Thanks Grumpy. Perhaps I'll try both then. By the way, what does the "dampening" resistor dampen? The resonant impedance peak?
That's what I'd expect... that and cut down the level a smidge, since the source
impedance feeding the resistor and driver in parallel is non-zero. Other effects
such as giving a low-ish DC path for driver EMF have been posited, but this is
more than I know.
More simply, that it sounds better with the resistor in place seems
to be the repeatedly conveyed experience here. I can't honestly say
I've bothered testing audibility of this, but have no reason to doubt
the folks here with direct/years of hands-on experience.
Well, to start I simply hung the 8 ohm L-pad across the network output terminals to the LE85s. So far I like the LX5 set to the "mid" attenuation which gives a nice degree of HF output from the 2405Hs (max is too hot and with the mid setting, I can set the HF (3106) L-pad to max and it is effectively out of the circuit). The MF needs a little attenuation and I dialed in approximately -2dB with the external L-pad. Sounds nicely balanced...but I have more listening to do to check this out.
What is interesting is that at the -2dB setting, the L-pad measures approximately 4.5 ohms in series and 17.5 ohms in parallel with the LE85 driver (impedance~12 ohms). The impedance flattening resistor is 20 ohms. So by my calculations, I get ~7.4 ohm load on the network. Without the L-pad it is ~7.5 ohms. Pretty close and the LE85 still has 17.5 ohms across it to flatten that impedance peak. On the other hand, if I try the L-pad before the 20 ohm resistor (and assuming that I finally settle upon the -2dB setting) the load seen by the network would rise to 9.8 ohms, 30% higher than the original nominal load.
Now...I don't know all the implications of this? Perhaps with the higher load, the network response would rise and show less attenuation (I recall a JBL network instruction manual which showed that placing a lower than nominal load on a network resulted in a response dip in the crossover region, so possibly a higher load would raise it), thus requiring a higher degree of attenuation to reach the desired MF level. A higher L-pad setting (when placed before the 20 ohm resistor) would actually increase the overall load slightly.
All this leads me to wonder if (in my case) placing the L-pad right across the driver is optimum from the point of view of the network configuration?
I'm not sure what you're measuring... or what your -2dB is indicated on, so itAll this leads me to wonder if (in my case) placing the L-pad right across the driver is optimum from the point of view of the network configuration?
might be worth confirming a few things:
http://www.apicsllc.com/apics/Misc/filter2.html ... go to the bottom and plug in
driver impedance (in this case, use "8", as that's the L-pad you're using) and
"2" as the attenuation; with the l-pad knob set to "-2" you should be able to
measure R1 between the Lpad input and speaker output, and R2 between the
speaker output and ground/common, with nothing else attached.
...but the point of an L-pad is to approximate a consistent load as viewed by
the circuit upstream, while being able to vary the attenuation as seen at the output.
If you use an L-pad that isn't roughly close to the speaker load (or speaker plus
resistor load), the impedance seen by the upstream circuit (L-pad plus speaker)
will change with attenuation, and in a passive crossover, also affect the frequency
response. Dropping the 20 ohm resistor and finding a single optimized setting
for the 8ohm L-pad (attenuation - and parallel resistance) was just lucky.
If the upstream circuit is expecting the parallel load of 20ohms plus driver
(or a nominal 7.5 ohms if you make the -assumption- of a 12ohm driver), then
inserting an 8ohm L-pad seems appropriate. In setting up the 3133A network
though, JBL decided to use a 16ohm L-pad, so perhaps the 12ohm assumption
isn't the best. Do you have an impedance plot of an LE85/2420 on the horn
you're using? If not, I think I can set one up at home this weekend (no lens though).
Thanks Grumpy...I don't have an impedance curve on the LE85/2312 combination. Curves I've seen seem to suggest around a 12 ohm AC impedance...so, I used that as a guesstimate. If you can do a curve with the 2312 horn, that would be great.
I didn't remove the 20 ohm resistor, and my L-pad values were drawn simply from the resistance measurements I made once I found a setting I liked (with the L-pad out of circuit of course). My "dB" calculations were wrong if I go by the examples from http://www.apicsllc.com/apics/Misc/filter2.html. Extrapolating from the values possible using the calculator (in this case with a load of 12 ohms since the L-pad is right on the LE85 input), I think my attenuation with the two L-pad legs measured (4.5 & 17.5 ohms) comes out more like ~-4.0-4.5 dB. I tried to use 10*log [(R2/R1+R2)^2], which comes out to -1.98dB...got it wrong I guess.
In any case, I calculated the load on the network simply using the series and parallel resistance values in the circuit. Gosh, I hope I got that right at least!
Equation is OK, if you first combine Rload in parallel with "R2" -as- R2 in
the equation. (not simply the L-pad R1, R2 voltage divider).
(then, realize that this isn't exact either as the source impedance feeding
this from a passive network isn't zero, but ignore that for now).
Personally, I'd show the equation as 20log... for voltage ratios and drop the ^2,
(just so it's more obvious to those still sorting this stuff out) but it's the same result.
Weird L-pad reading combination though...
I'll try to do a sweep. It'll give me motivation to try out the new (as of September)
S&LA WooferTester2 v4.0.
If someone has a plot handy and can post before I get to it... great.
Meanwhile, here's one on a 2370A:
http://www.audioheritage.org/vbullet...84&postcount=9
Looks like in the target crossover range, the driver impedance is a bit higher than 12 ohms
(on that horn, probably not on a baffle).
Last edited by grumpy; 10-16-2008 at 02:27 PM. Reason: Noticed WT2 update is available
Right.... I forgot to include Rload in the calculation of the attenuation. Now I get -4.25dB which makes much more sense. The load impedances seen by the network still work out pretty much as per my first calculations. My horn has the lens and sits on a baffle.
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