active sub in serial conection with a passive sub

[eto1976]

Hi,
I have a LG (main reason is the SimpLink to the LG lcd) ht752 lacking a true bass sound ( the only weakness), partially due to the passive system and partially due to the lack of proper engineering. today i bumped into an old Sony active subwoofer that has only a rca plug (for the sub out on the Sony receiver ).the LG Ht does not have a sub out port, nor ANY audio output(besides those for speakers and passive sub). After a careful thinking (and a few beers) i stripped a RCA connection cable and I hooked up the active sub in serial connection with the passive one. I adjusted the level on the Sony at almost min and turned it on. for my surprise, just as I thought, the passive sub acts like a line output converter, the bass sound is coming only from the active sub (i think), and it really works great.
Question: should anything go bad in the future? I didn't tested the HT to the max, but I did go up the volume and the actve sub reacted quite normal.
PS. i also turned the Bass level to -5 db in audio settings menu before starting.

 

[Adam]

Welcome to the forum, eto1976!

Interesting. I honestly wouldn't have expected that to work very well, so maybe I'm misunderstanding. How did you connect the stripped RCA cable to the passive sub?

The amount of power that is carried by speaker wires is much higher than what would be transferred through the RCA cable between a receiver's subwoofer output jack and an active sub. So, I would expect that connecting the active subwoofer's RCA input to the speaker-level signal being sent to the passive sub would cause the active sub to either overload or just sound amazingly loud and/or distorted. That doesn't seem to be the case with you, though, so I'm wondering how you connected everything.

Thanks.

Adam

 

[eto1976]

simple serial connection

I did a simple serial connection, like two bulbs or two batteries. I had a old 1 plug (mono) RCA cable, already cut (i used the other Rca plug somewhere else in the past). I just stripped the isolation and I plugged the Negative(black, ground) of the original cable coming from HT(bass high output) in the black connector at the base of the passive sub; I inserted the RCA ground wire (running from the active sub) in the red connector on the passive sub and joined the red from HT with the center wire in the RCA cable( the RCA cable is the shielded type where it actually has inside one wire that goes to the pin in center and a shield wire that goes to the rim of the RCA plug). I plugged in the active sub and the circuit closes. The impedance of the passive filter is 3 Ohms at ????500W... and the active sub has almost no impedance at low level input (actually it should have about 0.3-0.5 Ohms). The serial resistors add values(Ohm's law) so the circuit should be at 99% like it was, the passive sub draws the high power and protects the active input, I think. The thing that I don't know for sure (because I'm just a dentist) is the voltage range that the input on the active sub expects.
BTW: the level knob at the active is set close to min, the bass output is also set to -5 (I'm repeating myself here, sorry) but the sound is great over the whole range of volume, no distortion that I can pick up with my ears. I just hope it works until I find something to replace the passive sub and filter the high output. Any ideas?