Cross over slopes

[kgveteran]

Why is it that manufacturers use 12db/oct for mains and 24db/oct for the subwoofer XO ? Should they be symetrical ? Does this cause a phase shift between the two ?
I'm sure the more expensive preamps like the B&K Ref 50 ( actually I know they give you a choice ).

[ThomasW]

12dB/octave cause phase shift, 24dB LR are phase coherent.

They do this to void having a hole in the frequency response between the mains and the sub. It saves money to have only a 12dB slope, since fewer parts are needed.

[kgveteran]

Would this method also apply to passive XO's ? If I look at the response of each driver in a threeway it would appear to have holes at the XO point but the end product looks great.

[Karma]

12dB/octave cause phase shift, 24dB LR are phase coherent.

HI Thomas,
Please explain how a 24dB/octave filter differs in phase shift and coherence from a 12dB/octave filter other than phase magnitude. Remember, a 24dB/octave fiter could be constructed with two 12dB/octave filters of identical design for a given frequency.

Sparky

[Paul H]

HI Thomas,
Please explain how a 24dB/octave filter differs in phase shift and coherence from a 12dB/octave filter other than phase magnitude. Remember, a 24dB/octave fiter could be constructed with two 12dB/octave filters of identical design for a given frequency.

Sparky

12dB/octave filters shift phase by 180 degrees, 2 12dB filters shift phase by 2 x 180 = 360 degrees, which is extremely similar to no phase shift.

Paul

[kgveteran]

12dB/octave cause phase shift, 24dB LR are phase coherent.

They do this to void having a hole in the frequency response between the mains and the sub. It saves money to have only a 12dB slope, since fewer parts are needed.

What would be the lesser of two evils, the phase shift or the hole in the respose?

[engr_dave]

Search revealed this thread on receiver crossover slopes, but not much else.

I'm trying to find out what the crossover slopes are on a Yamaha HTR-5890 receiver I purchased. The manual discusses setting frequency: 60, 80 (THX), 90, 100, 110, etc. but doesn't mention slopes.

I contacted Yamaha technical support and they didn't know :blink: .

I suppose I could measure it, but I was hoping that someone would know.

My Lexicon MC-12 specifies symmetrical 12dB/oct for the 80Hz THX setting and 24dB/oct for all others.

However, this thread seems to imply that most manufacturers use asymmetrical slopes.

Help! This will affect how I design speakers for this "Theater #2" system. Thomas feel free to move to the DIY forum if that's more appropriate

[whoaru99]

What would be the lesser of two evils, the phase shift...

Isn't the driver receiving the phase shift signal usually wired in reverse polarity to address it?

So, in effect, it's not as ominous as it sounds?