Low Pass Filter Question

[radioeng]

This isn't particularly relevant. In any case this is only a parasitic loss. It can be made insignificant. Even if it weren't, what does it matter?

To tweaky audiophiles it matters. But if you prefer listening to 128k MP3's it makes no difference. Heck, why bother with a sub-woofer?

 

[AllenB]

Are you suggesting it causes a sound quality issue? Do you have evidence?

I always get the same results with any style of filter system. Your overall argument has to be based on usage, because the quality of the end result is not a factor when given the chance.

 

[radioeng]

As with all thing's audio, it is a matter of personal perception. Although back in the 70's when I was building Discos in Hollywood. They could clearly and evidently perceive a difference between passive and active bi amped subwoofers. It put the shake in shake your booty. ROFL

 

[AllenB]

I'd need to see the implementation to verify it was the same. It's easy to believe it was different due to it not being set up to be the same. This doesn't reflect on the type of system.

It was much harder to implement the active than the passive.

But I have never found a substantial audible or measurable improvement from active. In fact, it is a small enough audible change that I cannot say that it is better or worse, or if I am even imagining the difference (knowing that there is a small measurable advantage.) So I am very suspicious of claims of substantial improvements.

 

[radioeng]

I am old school. When I started in audio I sill used a slide rule for my calculations. Even when computer calculations became available I soon discovered that real world conditions invalidated much of the computer modeling. I fondly remember hauling around my Apple 2+ based spectrum analyzer. It only took about 10 minutes to generate a 1024 waterfall plot showing group delay (yeah, I am that old) early FFT analyzers were heavy! But that was very helpful in getting the phasing correct. Much of this stuff still needs to be done by ear in the environment where it will ultimately live. After all "If it does not sound good to you. It does not sound good" Sound is something we should all enjoy. Do not become a slave to engineering masturbation, it takes the fun out of everything. FYI, I prefer active networks and bi amping for one simple reason. You can easily adjust the gain and Fc of your subwoofer. Something you cannot easily do with a passive. This is important in getting the right sound and timing in your listening room.

 

[Veleric]

I did a simulation for a 100 Hz LR lowpass filter designed for an 8 ohm load, to see what would actually happen to the speaker signal and if (and how much) it actually is "heavily" 🙂 affected by the speaker impedance
1) with 8 ohm ideal load
2) with 4 ohm ideal load
3) with a loudspeaker impedance model (8 Ohm, Fs = 25 Hz, no enclosure/infinite baffle for simplicity)
attached the results and the circuit.

edit: I could do a impedance graph later, and a version with 4-ohm filter.

stv,
Thanks for the simulation, that's interesting.
Concerning the loudspeaker simulation: You may recall from my original post that this is for a DML (panel with exciter) subwoofer. I have no idea if the impedance follows anything like what a piston loudspeaker's impedance.....
Eric

 

[stv]

Hi eric,
yes, i suppose DMLs will have a low resonance frequency and if it's far enough from the x-over frequenc it may be perfectly ok.
I did the simulation mainly to check, whether my claims ("heavily affected response") were actually true ...