Slopes, X-Overs and Bass

I've never gotten the kind of production I felt I should be getting from the subchannel on my amp and/or my sub.  The other day I was playing around with the x-overs on my head unit's sub out and noticed something interesting.   Going from a 24db slope to a 18db, 12db, 6db, and full pass was like slowly turning the volume down on my sub.  In other words, I was getting pretty good production out of the sub with the 24db slope (regardless of the cutoff frequency), but there was a noticable drop off every time I lowered the slope.

The subchanel on my amp has a fixed low pass 12db filter in place.  I can change the cutoff frequency, but I can't turn the filter off and run full pass (allowing my HU to handle the x-overs).  Since I can't turn it off, I turned it all the way up to 200hz.

What I don't understand is why are the higher slopes making such a big difference?   I thought this might be a phasing issue, but I notice the same difference in production with the front and rear spakers disconnected.  I talking with someone at another forum the other day, and if I understood him correctly, he though this was because the amp's crossovers are inferrior to the HUs and that the higher the slope I used, the more I was "defeating" the amp's built in crossover by sending it less signal to work with (or possibly mangle).

That sounds reasonable to me, but I just wanted to get some other opinions.  If it is the x-over on the amp that's causing me so many problems, it may be time to get a new amp, or at least a new sub amp.

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No, the reason is because if you use a steeper cutoff slope, the headunit can divert more of it's available power to the lower frequencies becase the higher frequencies are cutoff at a more rapid rate.

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My ex once told me I have a perfect face for radio.

Ahh heh there Tom.

Ur STILL playing with this system? hehe...

You seriosuly need to dump that w1 and get a pair of real subs eh?

Hmm... perhaps geepherder has the right idea... with a small correction:

I believe he meant to say:
"No, the reason is because if you use a steeper cutoff slope, the AMPLIFIER can divert more of it's available power to the lower frequencies becase the higher frequencies are cutoff at a more rapid rate."

Either way, what you describe is a bit odd... as you compare increasing slopes to an increasing volume knob... I would be more inclined to describe the sound as.. eh.. "tightening up" not "getting louder" .... generally, with larger subwoofer sizes, (like your 12) a steep subwoofer cutoff is desirable... as your VR's will sound much better producing 150hz than your w1 will.. once you start working more with 10's or 8's, you'll find that getting the cutoff slope down a bit can be blended much more naturally than with larger woofers...

Personnaly, I always use the steepest cutoff available.. anything lower than 18/db/octave leads to seriously displaced woofer in my ears...   I heard a 48/db/octave xover on a Zapco amp a few weeks ago though.... talk about *CLEAN* ....

What kind of car are you driving?

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"I'm finished!" - Daniel Plainview

BTW there Tom,

tomfin wrote:

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I talking with someone at another forum the other day, and if I understood him correctly, he though this was because the amp's crossovers are inferrior to the HUs and that the higher the slope I used, the more I was "defeating" the amp's built in crossover by sending it less signal to work with (or possibly mangle).

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This is retarded. There isn't anything wrong with your amps built in xover (except it's gross inflexibility).. I hate Alpine and even I'll give the amp that.


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"I'm finished!" - Daniel Plainview

What you are describing is probably more an anomaly of your install than anything the HU or amp is doing.  In a properly functioning system, changing the Xover slope will change the power distribution to the amp, but it should not have the effect you describe on the overall loudness.  Indeed, increasing the slope will generally reduce the overall loudness.   I will guess that what you are actually hearing is the resonant frequency of the vehicle being activated by the sub, and when you reduce the Xover slope you are adding information that ends up out of phase with the vehicle's resonance frequency at your listening position, dampening it.  If you want to test this, take the sub out of the vehicle, place it on the ground away from the vehicle (preferably outdoors) and do the same listening test.

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sedate wrote:

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Ur STILL playing with this system? hehe...

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Always, man.  Always. 

I hadn't updated my sig line when I posted this, but I took out the VR650 components up front and had a set of CDT EF63-Neo braxials put in and I LOVE them.   I'm not going to rag on the VR650s because I'm sure a large part of my disatisfaction with them was due to the install (tweeters mounted high in the doors and over a foot away from the mids), but I've got very good imaging, a nice soundstage (although it could be a little higher) and I get no listening fatigue whatsover.  Also, since I didn't feel the need to attenuate the tweets 3db or cut the high frequencies on the EQ, I'm getting a much more natural sounding high end.

[QUOTE]You seriosuly need to dump that w1 and get a pair of real subs eh? [/QUOTE]

Hey, that sounds good to me.   What amp/sub combo would you recommend?  I found a local shop that I've very comfortable dealing with, and they sell JL Audio, Eclipse, and Diamond.   Anything in those lines appeal to you?  I've heard a lot of good things about the Diamond D1s that will be out soon. 

[QUOTE]Hmm... perhaps geepherder has the right idea... with a small correction:

I believe he meant to say:
"No, the reason is because if you use a steeper cutoff slope, the AMPLIFIER can divert more of it's available power to the lower frequencies becase the higher frequencies are cutoff at a more rapid rate." [/QUOTE]

Yeah, that makes sense, but I'm still surprised that I would notice such a big difference between slopes.

[QUOTE]What kind of car are you driving?[/QUOTE]

2004 Honda Civic sedan.  Don't let the sedan part fool you though.  It's a still a very small car.

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DYohn] wrote:

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hat you are describing is probably more an anomaly of your install than anything the HU or amp is doing.  In a properly functioning system, changing the Xover slope will change the power distribution to the amp, but it should not have the effect you describe on the overall loudness.  Indeed, increasing the slope will generally reduce the overall loudness.   I will guess that what you are actually hearing is the resonant frequency of the vehicle being activated by the sub, and when you reduce the Xover slope you are adding information that ends up out of phase with the vehicle's resonance frequency at your listening position, dampening it.  If you want to test this, take the sub out of the vehicle, place it on the ground away from the vehicle (preferably outdoors) and do the same listening test.

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I'll give that a try and see what happens.   If it does turn out to be the car's resonance frequency that's creating the problem, how do you go about correcting something like that?

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tomfin wrote:

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I'm getting a much more natural sounding high end.

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I knew you'd be happier with different componets from ur first post ...! JL Audio componet sets are shrill and sterile speakers, period... accurate sure, but like you said, the CDT's are *much* smoother and warmer eh? I have EF's up front as well (well, did up to very recently, but they'll be back shortly), albiet with a totally different xover setup, but I *love* mine..

tomfin wrote:

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What amp/sub combo would you recommend? I found a local shop that I've very comfortable dealing with, and they sell JL Audio, Eclipse, and Diamond.   Anything in those lines appeal to you?

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All depends on you eh? Honestly, either giving the w1 a partner, or scrapping the thing entirely and starting a bit higher on the totem would both be great ideas.. I really like 'slash' monoblocks from JL, and Eclipse makes outstanding amps as well. Diamond doesn't really blow my horn in quite the way Eclipse or JL do, but I'd turn to them for subs before either Eclipse (efficency numbers are *way* to low for my listenening tastes) or JL (too expensive for what ya get, wierd tonality IMO).. Honestly there are two-dozen combos from those three brands I'd be very comfortable with that all land in the $500 - $1000 range.

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"I'm finished!" - Daniel Plainview