I can’t find a schematic for an L-Pad on a second order series crossover for a woofer and tweeter. Every source I have uses a parallel crossover as an example. Can someone point me to a schematic or post an example? Thanks!
Right. Tony has / had a few in his archive. Here's one: https://www.humblehomemadehifi.com/download/Humble Homemade Hifi_HATT Mk-I + Mk-II.pdf
Yes , sorry, I deleted the post thinking it might be better to start a new thread instead making it easier to find in a search "Series First Order 2 Way Crossover with L-Pad", which is what I was looking for when I found it through a Google search. The exchange above cast some doubt until I figured that's what it must be.
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I was showing the application of an Lpad in an AR-SXO 12dB network. It would also work in a 1st order electrical application. The schematic is not wrong or incorrect. It is just another way to do it.
The schematic makes it look as though it can be done with an off the shelf L-pad. Is that wishful thinking? It would sure be easier than swapping resistors in and out if it can work that way.
How is the total resistance calculated and is there any range for adjustment with a single value?
Thanks !
How is the total resistance calculated and is there any range for adjustment with a single value?
Thanks !
Resistance in attenuation circuits isn't really calculated when the software.does it for you in a model. That said, you could wire a variable Lpad as a rheostat and use it in Rabbitz schematic, or you could also use it conventionally in the first posted Lpad schematic.
I would use the Lpad as the testing phase, and then place final resistors after you are happy.
I would use the Lpad as the testing phase, and then place final resistors after you are happy.
I don't use modeling. I 'm just trying something out with a couple of drivers - 12" unknown woofer in plywood boxes with AMT sitting Heil on top. Using L and C values I have on hand and using the pad as shown in AllenB's posted image. The woffer and AMT seem to be about the same sensitivity but amt just slightly hot.
With online basic calculators , values for Rparallel can vary within a relatively large range. I have been fine tuning it for the AMT with impedance at crossover point of about 3.7 Ohms. So far Rparallel has varied from 9 Ohms to 30. My conclusion is that the easiest way to do it would be to have a couple of pots wired as rheostats connected in series .
I wondered about your posted circuit - whether it would be in the same resistive territory or a different kettle of fish. I also wonder how its placement between the L and C might make for a difference in performance compared to the one more local to the tweeter.
With online basic calculators , values for Rparallel can vary within a relatively large range. I have been fine tuning it for the AMT with impedance at crossover point of about 3.7 Ohms. So far Rparallel has varied from 9 Ohms to 30. My conclusion is that the easiest way to do it would be to have a couple of pots wired as rheostats connected in series .
I wondered about your posted circuit - whether it would be in the same resistive territory or a different kettle of fish. I also wonder how its placement between the L and C might make for a difference in performance compared to the one more local to the tweeter.
Do you find the AMT has a resistive looking impedance? For a small reduction you might find the single resistor easier.
While it can be done with either 1 or 2 resistors, any variations to the filter damping (meaning the drivers plus resistors) may require changes to the reactive components, eg the capacitor. An L pad might also be a choice where you are trying to deal with tweeter impedance variations. Even though variations are already somewhat smoothed with a series crossover, when you're tweaking without measurement you may want to make things easier.
While it can be done with either 1 or 2 resistors, any variations to the filter damping (meaning the drivers plus resistors) may require changes to the reactive components, eg the capacitor. An L pad might also be a choice where you are trying to deal with tweeter impedance variations. Even though variations are already somewhat smoothed with a series crossover, when you're tweaking without measurement you may want to make things easier.
With Series 1st order XO there's no real benefit when using an L-pad. All the damping for the HF driver, being that a tweeter or a full range, is provided by the inductor.
The only "positive" is that the impedance is flatter.
In most cases a single resistor is what's required.
And in the case of a 4ohm tweeter it's actually the preferred option.
Disclaimer:
I only use Series filters, and only 1st order, so I'm biased.
The only "positive" is that the impedance is flatter.
In most cases a single resistor is what's required.
And in the case of a 4ohm tweeter it's actually the preferred option.
Disclaimer:
I only use Series filters, and only 1st order, so I'm biased.
The biggest variation is right at present crossover point. Here are the impedance graphs done on a borrowed CLIO set up for me by its owner and handed over with the helpful instruction "You'll figure it out."
The FR shown here was done at 1 Metre with series xo of 1.3mH and 47uF and no padding. It sounded very nice (I like the AMT) but the slope was too shallow at 3dB/ Oct. and at volume the AMT was distorting.
Increasing slopes with 2.2mH (not sure how I got to that value now) and 24uF (2 x 47uF in series) and was still good but the Heil a bit too hot. Thus started L-pad school.
The roughly 1KHz point was chosen mostly with quick listen to driver combo with the scavenged inductors I alsready have. It's not meant to be a permanent build project but just something to try for a few weeks while I have the space to play it and learn in
Right now pad is down 2dB with Rseries 0.76 Ohm and Rparallel 15. Level Ok but sounds a bit wrong.I wouldn't keep it.
Proabaly best to recalc the XO proper. I found a few small value inductors I can combine for a larger value.
I also hear the message about single resistor in series only. I'll give it a try.
I do hear a qualitative difference though not sure yet what exactly it is. The diference with padding is not just a matter of level and so far I don't like the change that I hear.
Thanks
