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Old 4th May 2009, 02:43   #1
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Default Slope? Active v/s Passive???

I was just reading about Slopes on Basic Car Audio Electronics, and I got mighty confused. Can someone clear the concept of Slopes and explain what roll off means?
Also, I wanted this knowledge to apply to my present setup.
What slope settings are considered ok?
In my 9887, I set the fronts, the rears and the sub to 12dB.
what does this mean? I just did what Bass&Trouble instructed me to do and it sounded awesome. BUT i want to know what it exactly means.

One more question!
We do not have an Active V/S Passive thread on team-bhp, and with so many of us owning some decently respectable equipment, we MUST speak of the pros and cons of each, thus prompting many of us here to take the plunge and go active.


PS: While answering questions, can we keep our first few explanatory posts a little simple, and then have the knowledge gradient go up slowly? We don't want to scare everyone away


PS: This didnt help much
http://www.team-bhp.com/forum/ask-gu...ng-active.html

Last edited by frankmehta : 4th May 2009 at 02:56.
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Old 4th May 2009, 08:10   #2
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In general any slope made by a passive filter can be duplicated using small signal components (aka an active filter). This includes Butterworth, Linkwitz-Riley, Bessel, Chebyshev, Sallen-Key, inverse Chebyshev, etc..

A fiilter (high pass or low pass) has a cut off point point and a roll off. The cutoff point for most filters (except L-R) is accepted as the point at which the filter is -3db below it's nominal voltage.

A designer chooses a filter topology (Bessel, Butterworth, etc..) based on thier needs. In addition to the "standard" topologys" there are various other topologies that are created just to compensate for the anamolies of a particular component (in this case in the audio chain). VMPS for example uses slopes that are variable meaning that the slope is -6db/octave for about 1/2 an octave and then fall faster after that.

In general
Butterworth
1. flat amplitude response
2. Phase response is NOT linear
3. phase shift is nonlinearly with frequency
4. each frequency have a different time delay
5. ringing in step response due to overshoot

Chebyshev
1. overshoot and ripples - more than butterworth or bessel
2. Linear phase response

Bessel
1. Linear phase response
2. phase shifts are linear with frequency
3. slower roll off hence little driver protection

Linkwitz-Riley
Effectively a modified Butterworth filter where the cut off point is -6db down. This filter has a flat power response (not the same as flat amplitude response as amplitude often refers just to the voltage).

In addition to the regular high pass and low pass filters are special filters such as ladder networks used to time align drivers (See John "Zaph" Krutke's ZD5 design)
Zaph|Audio - ZD5 - Scan Speak 15W8530K00 and Vifa XT25

This link explains things in more detail
Filter Solutions Descriptions

Active filter design is explained here
Design and Dimensioning of Active Filters
Free Filter calculators, active filter design, chebyshev filters, Bessel filters, butterworth filters

and heres a quick design helper but it is not complete
Butterworth / Bessel / Chebyshev Filters
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Old 4th May 2009, 09:34   #3
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Read in http://www.team-bhp.com/forum/ask-gu...ng-active.html that active means having HIGH, MIDS and LOWS, but there is also said that no rear fills can be possible, but if we set tweeters at 3KHz LPF, Midbass at 3KHz HPF and 80Hz at LPF and the sub at 80Hz HPF, so the tweeters play the highs so can t we use 4 midbass? just a question.
Also related to what you had said, all are flat amplitude and flat power response, so does this mean we are running the equlizer at 0 for all? i prefer to have alot of bass and a bit more of midbass and almost equal but a little more of highs, so what is that called?
Sorry for being such a noob
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Old 4th May 2009, 10:21   #4
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Quote:
Originally Posted by abhayshanu View Post
Read in http://www.team-bhp.com/forum/ask-gu...ng-active.html that active means having HIGH, MIDS and LOWS, but there is also said that no rear fills can be possible,
not this is not related. you can have high, mids and low for both rear or front or both speakers. a few HUs give you the option of choosing 2 way front and rear OR 3 way front outputs but that does not mean you have to sacrifice rears if you want an all active front.It only means that you will need an external electronic crossover for the front. B&T's description on the same link explains it in pictorial format.

Last edited by navin : 4th May 2009 at 10:24.
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