Subsonic filter madness!

[TheMonolith2001]

Ive been searching all over the place here and everywhere on the internet and I just can't figure this out. There is too much conflicting information. I'm just trying to figure out what to set my subsonic filter to or if I even need one. This is such a huge pain in the ass because my amp doesn't have one built in. You guys have been such a huge help and there are a ton of gurus on here so here we go!

I am using:

-Pioneer DEH80PRS Head Unit

-Kicker ZR1000 amplifier

-Fi Q 18

-8 cubic foot box tuned to 28hz

Tons of info on my box in this thread: http://www.stevemeadedesigns.com/board/topic/151485-fi-q-18-box/

-Harrison Labs HP-SUB PFMOD Subsonic Filter. This little box allows you to select 20,25,30,35hz as the subsonic filter. It looks like it is discontinued now because I cannot find it on the website, however the website is pretty crappy so maybe thats why. Anyway here is the manual http://www.hlabs.com/manuals/CROSSOVER/HPSUB/index.htm

The first issue is how the setting should relate to your box tuning. Most people seem to agree on 5hz below box tuning, which for me would be 23hz. However some people (including Fi, I recently emailed them) say 2hz below box tuning, which for me would be 26hz. Meanwhile others with 28hz tuning seem to think you shouldn't even bother unless your messing around with bass mekanik CDs and the like because your never going to run into anything that low anyway. I'd rather be safe than sorry and not blow up my beloved subwoofer.

Then I came across a thread where someone had modeled their setup in WinISD to see exactly when they would bottom out. They came to the conclusion that because of the amount of power they where giving the sub was much less than the sub was rated for, they would actually never bottom out. (Came across another similar thread where the guy would never bottom out because he had something crazy like 14hz tuning - Damn!) What a great idea! I went ahead and modeled my setup to see if this was a possibility with me. Now I admit I am not the greatest at WinISD so I'm trying to find someone to double check my work (which I didn't save unfortunately) but I found if I only give it 1200 watts instead of rated 1500 I wouldn't bottom out until about 21-22hz.

It seems like I have to choose between the 20hz and 25hz setting. The 25hz setting seems safer but here is the thing, when I set it to 25hz I lose TONS of the real low sounding bass. I notice my dash doesn't vibrate anymore too. I'd like to fix that with sound dampening rather than not playing as low! Even on old school albums where the bass isn't reaching anywhere near 20-25hz it just doesn't sound as deep as before. This leads me to believe that this subsonic filter is introducing distortion. At 20hz it sounds much better. I tried it without the lowpass filter for a little bit and I believe it even sounded better than with it on the 20hz setting, but I cannot say for sure because I only tried it very shortly because I don't want to break anything. Maybe I should buy an audiocontrol crossover/epicenter/etc just to use as a subsonic filter instead but man that's not cheap! I have seen quite a few people using the FMOD filters from harrison complain about distortion. These are the non adjustable subsonic filters that come in either 20 or 30hz. Maybe this harrison stuff just isn't very good?

The other option I considered but haven't tried yet is to just use the equalizer on my head unit. I have a 20hz band. If I am not going to bottom out till 21-22hz then why not just dial the 20hz band down a bit and call it done? I am aware that this 20hz band isn't a cutoff and it probably effects something like 15-25hz with less effect as you go farther away from the center 20hz but is this not good enough? I mean 14hz and below? I don't even think bass mekanik type stuff even goes that low. I mean there probably are a few tracks that do but it seems like with normal music the chances of going this low are next to impossible and even if it did it would be with very little volume. I couldn't find the exact spec for my head unit but I have a home CD player that says it can only output down to 15hz. I imagine something similar is going on with the head unit?

I own an SPL meter, I COULD play some tones to see how it is effecting the frequencies above cutoff but I don't know if it is necessary since I can for sure hear a difference. I also own an oscilloscope but I am still waiting on new probes to come in the mail so I can use it which won't be for another few weeks. When I get them I'm definitely hooking the oscope to this subsonic filter and posting the results. That way we will know for sure if it is introducing distortion or just limiting more frequencies than it should or what. That way none of you guys waste your money. Too bad if it turns out to be crap ill never be able to sell it!

Should have made a damn sealed box....too late now haha.

[Joe X]

The Kicker ZR1000.1 has a built-in variable 0-25Hz subsonic filter not sure if you are using that but anyways that low tuning will make it hard for the sub to bottom out and more so since you are not likely pushing rated, I wouldn't actually worry. BTW I see you finished and pictured your build, missed that when it was posted.

[mrd6]

I wouldnt run a subsonic for your application if you love lows like ypu seem to. It is not necessary with low tuning if you know your system well and are careful with song choice.

Just be careful when playing a song for the first time and dont go full tilt unless you know your sub will handle it. It's going to be a lot harder to bottom out that sub than you think. I would almost bet you could full tilt a 20hz sine wave and be okay.

[BoomZoom808]

Going with a sealed box you will lose output especially if it is underpowered. The benefit of a sub sonic filter is not only for sound if you were overpowering the sub it would make more a difference in that scenario to protect the sub from over excursion but it also helps current draw. You could set it low enough that it does not effect the output but it will help your electrical a little bit.

[TheMonolith2001]

awesome! I'll remove it then. I still want to put it to the oscope to get the full scoop on that filter though. Just for fun I guess since I don't get to use the oscope often.

You say it is a variable subsonic filter though? Is it inside or something? This amp has no knobs at all except for gain. Here are some pictures, Not mine but looks the same:

http://i1232.photobucket.com/albums/ff375/extremechevyman67/003-1.jpg

http://www.the12volt.com/installbay/uploads/fall_2009_001.jpg

Right now the module that is in there is just a basic board with a wire on it bridging two terminals that makes it so all the outputs are bridged. I have a remote gain but for some reason it doesn't work, maybe I have the wrong knob or something, I just soldered together a pot and some wires to make a volume knob for the RCAs.

[Joe X]

That was a spec on sonicelectronix, as it turns out the have it wrong, the subsonic filter is built-in and engaged to 25Hz 24dB/octave rolloff according to the amp's manual, that's why there are no controls for it I assume, so with that setup if you don't clip you can't do a thing to the sub.

I think you don't need that DIY attenuation device, the amp has it's own input gain, in any case find someone to borrow you a DD-1 or a scope to set those gains and monitor your input voltage to the amp making sure you are at least above 13V at all times while playing. That's it I think until you decide upgrade.

[TheMonolith2001]

Wow I've read that manual a bunch of times and somehow missed that. Well cool like I said my oscope probes are on the way and I'll double check my gain setting and remove that device. I set mine with a DMM for the time being.

My head unit has a voltage readout. Not sure how accurate that is being as its so far away from the amp and the amp has its own 0 gauge power wire and the head unit is off the factory wiring though. I'm usually between 13.5-14.1 on that. I've seen it hit 12.8 for a split second but its pretty rare since I did my big 3 upgrade. Isn't the ZR1000 pretty stiffly regulated? I saw someone say it was good down to like 10 volts so I was more worried about my mids/highs amp. My amp has been modified for up to 18v. I wish I knew what exactly that meant in terms of what was actually modified. It could mean it just sucks power faster, might have more voltage fluctuation tolerance. Who knows until I get the oscope probes I guess.

[Joe X]

It's better to read the voltage at the input terminals of the amp to exclude any issues in the power wiring, once your system is troubleshooted I guess the one in the HU is an ok reference. That HU has a large pre-out voltage so yes, a proper gain setting procedure is in order, other than that you are being very careful to keep your system in good health.

[TheMonolith2001]

Makes sense. So maybe get something like this:

http://www.sonicelectronix.com/item_46311_Stinger-SVMB.html

And then run the wires all the way to the back and into the amp terminals? There are nicer models on there. Including a pretty nice looking SMD one that plugs into the cigarette lighter. But that seems to introduce some of the same problems. If I got that I guess I could chop that piece off and wire it to the amp the same way.

Then I saw this:

http://www.sonicelectronix.com/item_68051_PAC-BG-12.html

Probably a little overkill but a neat idea!

EDIT: Just a quick note. When I removed the subsonic filter and reset my gains without it I noticed it introduced quite a bit of resistance to the signal. My output voltage on the amp should be 69.2v for 1200 watts, after removing the filter it was reading 80.2v which would be 1600 watts! (4 Ohm Load) I didn't think to take a reading of the RCA voltage (Its insanely hot outside today, was trying to work quickly) but that seems like it would be a significant amount! I know WITH the subsonic filter I had previously read 2.7v in another thread at the same volume level. Simple cross multiplication means this would be about a .4v decrease, but I'm not sure if it works that way.

[Joe X]

If your wiring and electrical are good and you have troubleshooted your system I don't think you need any of those, the second one seems it would be good for fellows running their system in bad electrical as a temporary solution.