Setting a subwoofer’s crossover

Where do you guys have your sub's crossover set?  What is the equation again that shows you how power declines after the cutoff point?  I may have phrased that wrong - I lost my CA&E magazine that talks about it.

Thanks!

-------------

Anyone have any suggestions?

-------------

Subs are usually low-passed anywhere between 70Hz and 200Hz, depending on the setup and what you're trying to accomplish.  What "equation" are you talking about?

-------------
Support the12volt.com

something to do with the efficiency below the crossover point.  I'll research

-------------

A crossover filter reduces the signal strength above (for a low-pass) or below (for a high-pass) the cut-off frequency depending on the slope.  Crossovers can have several slopes, generally in multiples of 6db per octave.  (6, 12, 18, 24, 36 being the most common.)  An octave is a doubling of frequency.  So, a 12db/oct low pass filter set at, say, 100Hz will reduce the incoming signal strength so it is down by 12db at 200Hz, and by 24db at 400Hz, etc.  A 10db reduction in signal strength is 10 times less amplifier power.  20db is 100 times less.  You could take this data and create an equation if you like.  Here's a page with simple xover curves illustrated for you.

-------------
Support the12volt.com

Thats right! 

In most music what is the frequency of most of the bass.  On this CD I have it starts at 320Hz and goes down to 10Hz and my bass seems to be the strongest at about 100 - 120 Hz.  Would changing the x-over frequency help with the low end bass reproduction?

-------------

Yes, the first four octaves (20-40Hz, 40-80Hz, 80-160Hz, 160-320Hz) are generally called the "bass" region.  The purpose of a sub-woofer is to reinforce the first two octaves (and a little higher sometimes, plus the lower sub-20Hz tones that we cannot really hear but that we can most certainly feel.)  Where is your subwoofer low-pass set now, and where is your main speaker high-pass set?  Whatever crossover frequency you use, these settings should be the same.

-------------
Support the12volt.com

I've been playing with it, it is at about 80 right now - is that what you recommend?

-------------

coppellstereo wrote:

---

I've been playing with it, it is at about 80 right now - is that what you recommend?

---

That's where I recomend.

-------------
Support the12volt.com

Are there any disadvantages to turning my subwoofers lpf to the upper extent of the range and using my HU's subwoofer crossover?  This is much easier to set.  I can adjust between 50, 80, and 135

-------------

Any crossover should be set while you're listening to recorded test tones...rather than using a switch.  With that, the variable crossover on the amp allows finer adjustment than the three choices of the switch.  But, as in all things, there is more to consider.  One of the two crossovers is most likely better than the other one, and it is a matter of testing and listening to find which one provides the sound that is best with your system.  I would look at the steepness of the slope with each, and if one is steeper than the other, give that one my full attention.  If that doesn' suit, try the other.  But don't try to set both at the same frequency.  Which is to say, as you stated above with the comment that you would turn the amp's crossover range up high, what you stated is correct.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

cool - i appreciate it.  What is a good test tone for reference?  Are tones downloaded from sites, such as realofexcursion.com a decent choice, or should I purchase a CD?

-------------

coppellstereo wrote:

---

Are there any disadvantages to turning my subwoofers lpf to the upper extent of the range and using my HU's subwoofer crossover?  This is much easier to set.  I can adjust between 50, 80, and 135

---

That works just fine.

-------------
Support the12volt.com

The main thing I have found over the years is to set it at what works for the particular woofer/enclosure/car/etc. What does this mean??

Well....

The LPF (Low pass filter) for a sub really depends on several things:

1) LF cutoff of the highs. If those 3.5" in your car only play down to 400Hz.... invest in some midbass to get the overall response down to the 60Hz range. Crossing your sub at even 120Hz without some midbass/low mid in there leaves a pretty huge hole in the response....

2) What is the sub? If it is an 8", it isn't going to be very happy hanging out from 50Hz and below providing decent output. A 15" on the other hand, would be perfectly fine with it.

3) What kind of box? A 12" in a ported box that is tuned to 60Hz would obviously require a pass point above the tuning freq. of the enclosure..... say 80Hz or so.

The most important thing to take note of are the two most important tuning devices you have.... your ears. Listen to the sub.... typically, it should be hard to locate the actual position of it. You want it to be more of a feel thing than a noisey thing. If the sub sounds like it is peaking far too easily, try lowering the pass point. Reduce the midbass to it, allow it to reproduce the lower bass that it is designed for.

For example..... in my own personal system, there is a PPI DCX124 in a ported enclosure that is tuned to around 28Hz. My LPF is hanging out somewhere between 48-55Hz. 24db/oct (I change it once in a while because I like to fiddle with it..... easily done with a laptop on my system). It is very very hard to locate the sub in this system, acoustically it sounds like it is in the center console (it isn't.... it's about 6 feet back in the spare tire well), but you can definately feel it moving your hair, and it gives that lovely thump in the chest feel you get at a concert. Luckily, my front stage plays easily down to about 50Hz no problem, so therefore, I can have a low cutoff point for the sub. Many of the customer cars we do on a daily basis are typically subs with factory speakers..... we tend to cross them higher, closer to 80Hz, listening to things we are familiar with to get the most output out of the sub with the least amount of stress on it. Once again, it really depends on the rest of the system, and what you think sounds good. There really is no right, and there is typically not a wrong crossover point (within reason.... lowpassing subs at 200Hz doesn't work too well... they just don't reproduce those frequencies very well at all.)

Play with it.... find the setting that works well for your car, with your system, with the music you listen to.

HTH....

Gus


-------------
Wherever I go, that is where I end up......

nice post - thanks!

When setting the x-over point, I should play a test tone and start the xover high, then adjust it until the sub plays the note, then it is set at that point - correct?

-------------

It's not nearly that cut-and-dried.  A crossover reduces the output on a slope, so when setting a sub you will be listening for a softer output above the target point.  When setting the same crossover point on the mids, you'll be listening for a softer output below the target frequency.  It's very subtle close to the point you're after.  Usually a few sweeps with the adjustment will help narrow it in.  And I like to turn the volume down low for this because I find it easier to hear the change in output volume.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Cool, thanks!  You are all over this forum - And i'm glad!

-------------

I just adjusted my xover - I started it at 320Hz while playing the 80Hz test tone I lowered the xover until the 80Hz tone faded in, then I found where the tone was full (not attenuated) and then set the xover about halfway in between.  Good strategy?

-------------

What you have there is one actual reference point, the 80 Hz tone.  With much fiddling you can probably get the sub/midbass crossover set to your liking, but it could take a few tries.  Rough-guessing will give you an "almost-maybe" crossover point.

If you were to record several more frequencies on both sides of the 80 Hz reference you could dial the point in much more precisely.  A CD will hold 99 tracks, so I made a test CD with a sequence of freqs around the common target crossover points.  For the 80 Hz target, I recorded tones from 70 to 95 Hz (with track numbers labelled as to what freq. they are).  These are relatively short tracks that are listened to in sequence several times while adjusting the LP.  With the volume at just above a whisper, I can find where 85 Hz is very noticeably softer than 80...and at the same time find that 80 and 75 are the same volume.  That zeros the crossover point  of 80 Hz very precisely (or at least as precisely as my ears can allow!)  You can do slight tweaking later, listening to your normal CDs, to get the final sound just right.

Thanks for the kind words, good luck and have fun with it.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.