Cross-Over Slope Question

[elk]

Howdy

First time poster here and had a question regarding how cross over slopes interact with one another?

In my case, I have an external 2way cross over with a 12/db slope and a sub amplifer with a nonadjustable crossover point and 24 db/slope.

The external crossover (low pass) is set lower than the amplifer crossover point (78Hz low pass. Amp is 90Hz fixed).

Currently the Amp crossover isn't active but the question comes what would result by using it? I had several 'ideas' as follows:

1) Is it two cross over points? 90Hz @ 24db/oct and then one acting at 78Hz @ 12db/oct?

2) Does the 24db/oct slope act at the 78Hz crossover point (basically the greatest slope applies to the lowest filter)?

4) Do they combine to get a 36db/oct slope? Would it apply at 78Hz? Act at both points? What sort of resulting phase issues between midbass driver and subs (midbass will still be on a 12db/slope based on the high pass) could I expect to deal with?

5) I'm completely in left field and need me some s-plane-in

All are linkwitz-riley

Utilizing the article pinned to this SQ forums; written by Terry SooHoo, I've been walking myself through phase set ups and before I clean up my midbass/sub blend (midbass was set by the IASCA phase track), I want to understand the effects of activating the amp crossover could result in.

Thanks kindly

elk

[Kevin M]

1) The 90hz 24 db slope would overide the other making the passive x-over more or less redundant. If you are putting alot of power to a comp set I would go with the 24 db slope as it will be better at preventing lower freq being reproduced by the speaker.

2) If it says the x-over point acts at 90 then that is where it starts.

3) X-over sloes do not couple to each other. You won't see a 36db slope from a 12 and a 24 db slope together. You are putting way too much thought into this bro. lol

I would try both and see what you like better. If you are having midbass issues there are over a dozen ways you can try to improve it from enclosure, driver choice, phase as you mentioned, placement, eq, T/A....etc.

What is your current setup, midbass drivers, location, power?

I'll let Randall come in and fill the naughty bits I missed. I'm more like an expert in shaw brothers movies but he is a real martial arts expert. Hope the reference isn't lost on ya.lol He, Wicks, or CleanSierra can probably explain it better than I can.

[elk]

Thanks for the quick response Scottishbear.

To clarify, it's not a passive crossover network for the component set (well there is one, but the high pass is from an actual 2 way
crossover).

As requested - equip and basic signal path

XS Power 5100R
XS Power 2700

Ohio Generator Alternator

Alpine CDA-7949
Alpine CHA-S624

PPI DEQ-230 (x2 one left/one right)

PPI EPX-223 (2/3 way cross over)

PPI PC2100 (Front amp)
PPI PC2350 (Sub amp)
JL Audio XR653-CS (tweet, 4" & 6.5")
10W7AE-3 (x4 both stereo and bridged - 3ohm stereo for 2 and 6ohm mono for 2)

I think mentioning components may help (or I feel I was a bit misleading in my initial post)

The sub amp should only be able to play up to the 78Hz low pass on the EPX-223 crossover and roll off at 12 db/oct. If I activate the amp cross over, is it going to play to 78 Hz, roll off at 12 db/oct and then hit 90 Hz and create a sharper roll off at 24 db/oct? Since they don't combine, I think I still need clarification of my #1 or 2 question(s)?

Highest slope will be active at the lowest filter point (78Hz at the EPX-223 crossover point but using the 24 db/oct slope on the PC2350) or it's two cross over points being active rolling off at 78Hz @12 and then again at 90Hz @ 24.

As for locations - see here

Thanks

elk

[elk]

Anyone?

I'm in the midst of set up out in this fantastic weather (2C yesterday!) and of course no garage.... Then again I am Canadian..... so it's what..... 9 months winter and 3 months road construction? Kinda have to work with what you're dealt ....

Anywho, I'd love to have an understanding of what's happening before I experiment and see if some of the changes I'm considering will help (I'd rather not go through the whole tear down though if I don't have to).

Thanks!

elk

[kirill007]

If both slopes were at the same frequency they would couple perfectly.

The 90hz at 24dB/octave slope will work with the 78hz at 12dB/octave, so you won't hear a lot above 100Hz.

If a slope starts at 70Hz, the signal will already be lower at 70Hz.

1) Yes, in your example the signal will be down a lot before it reaches 90Hz, then that slope makes it a much steeper slope.

2) It will act a little on the other slope, but not as much as the 12dB/octave slope works on the higher frequency.

4) No, it won't be 36dB at 90 Hz, since the first slope isn't at 90Hz. You shouldn't expect any phase issues worth mentioning.

5) Read about RC-designs.