I'd like to increase the attenuation on the HF section of my current speakers. These speakers have a rotary switch on the back with 3 separate positions, -1db , flat and +1db. A rather useless amount of attentuation. I would like to increase attenuation to at least -3db and -6db. Does anyone with passive crossover knowledge know which parts I need to change and to roughly what values?
How are you running them?? Simple way would be to passive bi-amp them and attenuate the HF amp using the sensitivity control on the HF amp. Providing they use jumpers you could remove and separate the LF HF inputs.
Modifying the passive network will not be easy you are changing both the resistors and the HF bypass cap values. You would have to work out the values changes in LEAP or equivalent as an example.
You might be able to work it out using a dummy load without measurements but measurements would be preferred.
Rob
"I could be arguing in my spare time"
If you put a fixed pad on the horn with 6.2 ohm resistance in series and in parallel with the horn compression driver it will help. But you will need to experiment. My is to use a variable 8 ohm L pad. Once you have the right setting swap out the L pad with fixed resistors.
You talking a pad before the input connectors? That 0db looks like a 62? Strange?Originally Posted by Ian Mackenzie
Rob
"I could be arguing in my spare time"
It’s on the driver not the input of the horn network. We use it as a simple pad for biamping. It’s 6.2R in series with the driver and a 6.2R resistance in parallel with the actual driver.
Based on an average 10 ohm driver impedance this is a consistent impedance for the network
Calculation
For driver impedance of 10R (1/x) = 0.1 in parallel with 6.2R (1/x) => 0.16
Then 0.26 (1/x ) = 3.84 R,
Then add 6.2 R + 3.84 R = 10 ohms.
Greg had been using this pad for years on compression drivers.
It’s a starting point in the absence of real measurements in this situation.
I may pop down and check it out.
To be clear this is a fixed constant impedance attenuation. Place it on the driver after the network. Before the network will not work.
It 1.00 am over there.You talking a pad before the input connectors? That 0db looks like a 62? Strange?
Rob
Yes you right. I think the schematic has a mistake in it. Not the first time unfortunately. Between that and the BS JBL marketing it’s no wonder there are a few disagreements….Lol. I stumped my little toe this morning so l am a bit slow.
*Hey, Check out the feedback from Greg on the Array 1400 in the imaging thread. I’m gona build a poor man’s diy Array…Lol.
Hello Ian
Hey heads up. Looking at the 3100 Mk 2 it uses the 8 ohm version. Apparently there are an H and J versions.
DCR is 3.2 ohms
Rob
"I could be arguing in my spare time"
I simmed the basics of that 3100 Mk11 network ( I left out the 3 notch-filters ) .
The values for R3a + R3b resistors ( 24R & 62R ) do ( actually ) make sense since they end up being paralleled with the ( always in circuit 12R ) R3_ resistor.
It's a padding trick used within a few other higher-end networks from JBL .
The way the resistors add together allows the horns output in the 750hz ( crossover ) area to be virtually untouched ( since what gets attenuated is mostly over 1K ).
FWIW, placing an Lpad right by the driver will certainly attenuate any desired amount >> the problem is, it'll also attenuate the crossover region which wasn't part of the original network design ( from what I see ).
OTOH, increasing R3_ from 12R to 15R ( while holding everything else the same ) will give another 1.2db of mid-band horn attenuation ( while still keeping the crossover region mostly untouched ).
I have to believe the initial desire for 3 to 6 db more attenuation is a bit over-stated.
Hello Earl
Glad you looked at it with a simulation. Damn I missed the 12 ohm parallel at zero! That does make sense.
What's you take on the cap value changes??
They go from 2uf to + 2.6 and - 1.5. That's changing the hinge point for the HF bypass. Did you sim that as well??
Rob
"I could be arguing in my spare time"
Yes I simmed the changing cap values.Hello Earl
Glad you looked at it with a simulation. Damn I missed the 12 ohm parallel at zero! That does make sense.
What's you take on the cap value changes??
They go from 2uf to + 2.6 and - 1.5. That's changing the hinge point for the HF bypass. Did you sim that as well??
Rob
They change values so that they can offer the listener a very ad-hoc, variable, Fletcher-Munson curve ( iow, when the mid-band of the horn is more aggressively attenuated >> the HF of the horn is only moderately attenuated >> each Cap & Resistor combo alters the balance between Mid-Band & HF ).
OK So it not linear attenuation through the compression drivers full range. Odd wonder if the presence of the notches linearizes it?Yes I simmed the changing cap values.
They change values so that they can offer the listener a very ad-hoc, variable, Fletcher-Munson curve ( iow, when the mid-band of the horn is more aggressively attenuated >> the HF of the horn is only moderately attenuated >> each Cap & Resistor combo alters the balance between Mid-Band & HF ).
Thanks
Rob
"I could be arguing in my spare time"
I just re-simmed it but this time including the ( first @ ) 1450hz notch.OK So it not linear attenuation through the compression drivers full range. Odd wonder if the presence of the notches linearizes it?
Thanks
Rob
As expected ( by me at least ) , the attenuation still isn't linear ( with that notch in place )
I wouldn't expect the differing values of the HF contour capacitors to have much influence due to R4 ( 10 ohms ) really dominating the actual "loop-impedance" that the 3 notches are working within//against ( one needs to study a little bit of transmission-line theory to understand that last bit ).
From my perspective, the original design is done very well ( keeping the crossover region smooth ) while still offering mid-band// lower-treble attenuation ( FYI, this is a long-standing feature of the network in the Altec M19 ).
Thanks
Rob
"I could be arguing in my spare time"
Do the right thing... through a DSP in the system and you can fix a lot of other issues too.
Analog and passive have their place, but this is 2024 and adding a little contemporary tech in there is really the right answer.
Widget
dumb thought... Treble knob?
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