Passive Lo Pass with Active Crossover?

[cheapbasslovin]

Originally Posted by 1958Bassman

Yes, it does. Passive filter components cause insertion loss and that does "waste" power- it's one of the main reasons active filters are superior.

This isn't really true. It increases the impedance above the filter point, which reduces current running through the speaker at a given frequency. That isn't wasting power, that is reducing power consumption. Like putting a 50W bulb in instead of a 60W.

Active filters are better because they occur in the signal path and not the power path, reducing the likelyhood of catastrophic failure that will destroy amps and cabinets.

My opinion, leaving the filter in is only creating a sharper slope above 125hz. It's not doing any harm and if you are using both crossovers you aren't putting any stress on it, you are good to just leave it.

I suspect if you experiment you will find that with the active and without the passive it will sound very similar to the way it sounds now, maybe a little bleed, but barely perceptible. Without either it will sound terrible.

[MrLeadFoot]

To be clear, the filter is not a Parts Express filter. I just linked to a PE filter to give an idea as to the construction of the filter, however, it is supposed to cut at 125hz.

This a Seismic Audio Enforcer II 18" sub. Before anyone says they suck, know that this is the model with the all-birch cabinet, not the lower pressboard model. The speaker is rated at 1000 watts RMS, and as always, I take all specs with a grain of salt. ;-) Lest anyone thinks I am an idiot for getting one of these, I also have a Mackie SRS1500 sub, and I wanted something beefier, with better tone. And, I must say the Seismic Audio sub does indeed produce what I wanted, in that regard, and I am now trying to dial it in using the amp I currently have.

[MrLeadFoot]

OK, I just got a Rane AC22B crossover, and I gotta say, "WOW!" I can't BELIEVE the difference this thing makes. If you recall, I was previously using either the sub's passive lo-pass filter, and/or the Mackie amp's built-in "subwoofer" option. Regardless of combination, it seemed like I had no choice but to run the amp in bridge mode (850-1000 watts) to get enough power to the sub. And, even then, I was pushing the amp near max, which was indeed surprising, especially since my Mackie SRS1500 powered 15" sub is only 350 watts.

I don't understand it, but I installed the Rane crossover in the signal chain, turned the amp's Subwoofer option OFF, and I seem to be getting the same output level (measured with my ears) at the sub with the amp UNBRIDGED, and when not bridged the amp is rated at only 250-300 watts at 8ohms!

I couldn't believe what I was hearing, so for grins, with the Rane still installed, I engaged the Mackie Subwoofer switch, and sure enough, the output was significantly dimished. I'm thinking that the lo-pass filter built into the Mackie amp must be a simple passive filter, which is convenient, but it is not even a close substiture to having an active crossover.

Moreover, and more directly related to the topic of this thread, if the Mackie Subwoofer function reduces the speaker's output that noticably, I am willing to bet that the passive lo-pass filter in the sub is also indeed significantly degrading the signal to the subwoofer. Any takers?

I'm going to remove the passive lo-pass filter from the sub, and see what happens. I will post my findings to settle the controversy once and for all.

Oh, and did I mention that the 850-1000 bridged watts sent to this Seismic Audio (not Mackie, JBL, EV, etc.) sub seems like it will blow the windows out of all the cars in my garage? You won't believe how happy I am right now having taken the chance on spending $300 for this beast, especially since the Rane crossover was basically given to me today!

[MrLeadFoot]

OK, I removed the passive lo-pass filter from the sub, and while I didn't notice an appreciable change in volume or punch, I do notice that the sound seems "bigger", if that makes sense. Not sure if that's a good or bad thing. Comments?