Questions about HP and LP filters, among other things

[keezy235 0]

Hello everyone,

I currently have a pair of Image Dynamics CTX65CS components in my front door speakers and Type S's in my rear doors that're being powered off of my alpine headunit. I will soon be ordering the 12" Dcon Single 4 ohm to place in the 2.0 cubic foot box I have that has a port tuned to 32hz. I thought I got a pretty good deal on it, and it looks sturdy enough to hold the DCON with it's double baffled front! The amp i'm using to power my front components and the subwoofer is the Cadence DCA 4100 which I also linked below. Correct me if i'm wrong, But I have to bridge two channels of this amplifier together if I want my subwoofer to be seeing roughly 250 RMS at 4 ohms. I'm confused on how to set my subsonic filter and LPF for this setup. Can someone please share some knowledge! Thanks.

Box - http://www.ebay.com/itm/200761346811?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_4542wt_1397

Cadence4 channel Amplifier - http://www.amazon.com/DCA-4100-Cadence-Daytona-Competition-Amplifier/dp/B00481S6UI

[///M5 2,833]

Is the SSF adjustable? No specs on the Amazon page (or I can't read in the AM).

As for LP that depends on the installation of your front stage and how low you can (and want) them to play. Typically starting low and working up until it blends nice is what I'd do with the expectation that you will be between 50-120Hz on the LP and probably closer to the higher end depending on your listening preferences. The higher the sub plays the more likely it will pull your stage back, but of course subs are rather efficient in the midbass range so the benefit of course is more.

[keezy235 0]

Is the SSF adjustable? No specs on the Amazon page (or I can't read in the AM).

As for LP that depends on the installation of your front stage and how low you can (and want) them to play. Typically starting low and working up until it blends nice is what I'd do with the expectation that you will be between 50-120Hz on the LP and probably closer to the higher end depending on your listening preferences. The higher the sub plays the more likely it will pull your stage back, but of course subs are rather efficient in the midbass range so the benefit of course is more.

Thanks for the reply!

Well since my front speakers have quite a bit of mounting depth, I don't want them to play too low because they flex and hit the inside of my door panel when playing the deep notes I've noticed. If I want to set my LP filter at say 80hz, could I just download an 80hz test tone and play it through my speakers and set my LP filter by seeing when my front speakers do and don't play the 80 hz test tone. Does that make sense?

Also, there is Subsonic filter as well as a phase control knob. What exactly are these and should I mess with them ? Thanks for your help!

[///M5 2,833]

Phase can help with blending. I realize there is a SSF but I asked if it was adjustable or just on/off

And 80Hz crossover will only be down 3dB at 80Hz so it won't be so audible. If you truly want to "know" where you set it you'll need to measure the voltage drop with a dmm. Of course knowing exactly where it is is pointless since you should set it by ear to blend and not by number.

[keezy235 0]

Phase can help with blending. I realize there is a SSF but I asked if it was adjustable or just on/off

And 80Hz crossover will only be down 3dB at 80Hz so it won't be so audible. If you truly want to "know" where you set it you'll need to measure the voltage drop with a dmm. Of course knowing exactly where it is is pointless since you should set it by ear to blend and not by number.

Ok, mistake me if I'm wrong, but you're saying I should wait until I install my woofer so I can blend the front speakers with my subwoofer using the LPF. Also, The SSF is adjustable. What exactly is this SSF and what does it do? Thanks so much for your help.

[Impious 1,476]

Correct, set the LPF by ear after everything is installed. Setting it to a specific frequency isn't important, all that really matters is how it sounds once you're done. Whether that means it's set to 80hz, 84hz, 73hz, 68hz, etc doesn't matter as long as you're happy with the sound of the results.

A SSF is a subsonic filter. It is literally nothing more than a highpass filter with a really low crossover frequency and typically a steep slope (24db/oct). The intent of the SSF is to reduce the excursion of the subwoofer at low frequencies where it's possible the driver can potentially over-excurt and become damaged. When a subwoofer plays frequencies below the tuning frequency of a ported enclosure, a condition called "unloading" begins to occur where excursion isn't controlled by the enclosure. This leads to the possibility of over-driving the subwoofer and causing damage, with the risk increasing the further below tuning the subwoofer is playing. The SSF will increasingly limit the amount of power going to the driver and hence maintain a safe level of excursion.

There are a lot of theories on where to set the SSF. Some will say to set it to the same frequency as the enclosure tuning. I disagree with this as it potentially unnecessarily limits the output within the intended passband (i.e. you'll lose some output where you probably didn't want to lose output, unless you are intentionally using it as a form of equalization....which isn't a bad idea either). Generally a safe setting is around 1/2 octave below tuning....to figure out where that is, multiply your tuning frequency by .75. Or load the enclosure and subwoofer into a modeling program, input the power you'll be using, look at the excursion graph and see where excursion begins to exceed Xmax (though this is generally around 1/2 octave below tuning, which is why that's a fairly safe setting).

[keezy235 0]

Correct, set the LPF by ear after everything is installed. Setting it to a specific frequency isn't important, all that really matters is how it sounds once you're done. Whether that means it's set to 80hz, 84hz, 73hz, 68hz, etc doesn't matter as long as you're happy with the sound of the results.

A SSF is a subsonic filter. It is literally nothing more than a highpass filter with a really low crossover frequency and typically a steep slope (24db/oct). The intent of the SSF is to reduce the excursion of the subwoofer at low frequencies where it's possible the driver can potentially over-excurt and become damaged. When a subwoofer plays frequencies below the tuning frequency of a ported enclosure, a condition called "unloading" begins to occur where excursion isn't controlled by the enclosure. This leads to the possibility of over-driving the subwoofer and causing damage, with the risk increasing the further below tuning the subwoofer is playing. The SSF will increasingly limit the amount of power going to the driver and hence maintain a safe level of excursion.

There are a lot of theories on where to set the SSF. Some will say to set it to the same frequency as the enclosure tuning. I disagree with this as it potentially unnecessarily limits the output within the intended passband (i.e. you'll lose some output where you probably didn't want to lose output, unless you are intentionally using it as a form of equalization....which isn't a bad idea either). Generally a safe setting is around 1/2 octave below tuning....to figure out where that is, multiply your tuning frequency by .75. Or load the enclosure and subwoofer into a modeling program, input the power you'll be using, look at the excursion graph and see where excursion begins to exceed Xmax (though this is generally around 1/2 octave below tuning, which is why that's a fairly safe setting).

thanks so much for the explanatory response! I'm a noob but am slowly but surely catching on to everything in the car audio scene What's your thought on bass boost?! I have kept it all the way down for my speakers but may be tempting to mess around with once I get my DCON. Also, my amplifier has a phase knob that starts at 0 and ends at 180. I seem to find a new knob everytime i look

[Impious 1,476]

DO NOT USE BASS BOOST.

Improperly using the bass boost can lead to clipping which can potentially be damaging to the subwoofer in certain circumstances. Really in car audio there is almost zero need to use any type of bass boost with a properly designed enclosure. Bass is the easiest thing to create in car audio, it comes naturally due to the environment.

[keezy235 0]

DO NOT USE BASS BOOST.

Improperly using the bass boost can lead to clipping which can potentially be damaging to the subwoofer in certain circumstances. Really in car audio there is almost zero need to use any type of bass boost with a properly designed enclosure. Bass is the easiest thing to create in car audio, it comes naturally due to the environment.

ok cool, I also have a phase knob on my amplifier that I'm curious about. Care to fill me in? Also, will my amp automatically know to filter the two channels that're powering my front door speakers so they don't receive low frequencies and not the two channels powering my subwooofer? Does this make sense? Thanks so much for your help!

[///M5 2,833]

Phase is a type of delay. If you google a sine wave you'll see that it has a phase from 0-360. Where you choose to start the wave in time alters its phase in comparison to the other signals in the car. It is added so that you can play around with different phase to minimize cancellation and improve the blending. In reality the knob is labeled incorrectly as it is more of a small time alignment adjustment than truly phase since it is centered at a frequency. You can hurt nothing by playing with this and may improve the frequency response. Only your ears can tell

And yes, bass boost is a terrible thing. I seriously hate car audio marketing departments.

[keezy235 0]

Phase is a type of delay. If you google a sine wave you'll see that it has a phase from 0-360. Where you choose to start the wave in time alters its phase in comparison to the other signals in the car. It is added so that you can play around with different phase to minimize cancellation and improve the blending. In reality the knob is labeled incorrectly as it is more of a small time alignment adjustment than truly phase since it is centered at a frequency. You can hurt nothing by playing with this and may improve the frequency response. Only your ears can tell And yes, bass boost is a terrible thing. I seriously hate car audio marketing departments.

sweeet! I'll definitely have to start twisting some knobs(other than the bass boost) when I get my sub in there This may sound like yet another dumb question, but how does my amplifier know to filter lower frequencies for my front two channels (powering my door speakers) but not my rear two channels (eventually going to be powering my DCON). Does that make sense? I'm curious about the same questions for SSF too! YOU GUYS HAVE BEEN SUCH A HELP!! thanks for empowering me with so much knowledge

edit: random, do you drive an M5? my dream car, after the m3

Edited July 11, 2012 by keezy235

[Impious 1,476]

It doesn't "know" anything. The amplifier has separate crossover controls for channels 1 & 2 and channels 3 & 4. You will need to set the crossover controls for the channels as you intend to use them. I.E. for the front speakers you'll need to set the crossover to HPF on channels 1 & 2, then for channels 3 & 4 you'll need to set the crossover to LPF for the subwoofer.

[///M5 2,833]

The M5 in my avatar was mine. I should probably change my screen name to AMG ML63 now, but history is worth something. I almost replaced the E39 with the new M5, but wanted to get rid of one vehicle as I need something to tow my boat and snowmobile trailer. Add to that being 6'7" and having a 1 and 3 year old and car seat space and such changed my priorities.

If I don't hurry up and buy a new house though a fun car of some sort will be coming my way.