AVR crossover question

[pearsall001]

I know that crossover settings are not brick walls & have a gradual slope. For instance, if the AVR crossover setting is at 85hz how much is still bledding thru below & above that point. Set at 85hz would it go as low as say 75hz & as high as 95hz? Or maybe my numbers are way off. Curiousity has the best of me. Thanks.

 

[TLS Guy]

I know that crossover settings are not brick walls & have a gradual slope. For instance, if the AVR crossover setting is at 85hz how much is still bledding thru below & above that point. Set at 85hz would it go as low as say 75hz & as high as 95hz? Or maybe my numbers are way off. Curiousity has the best of me. Thanks.

It depends on the order. AVR crossovers are usually second order. That means they roll off 12 db per octave above and below the crossover point.

So if the crossover is at 80 Hz, the high pass will be down 12 db at 40 Hz and 24 db at 20 Hz. The low pass driver will be down 12 db at 160 Hz and 24db at 320 Hz.

First order crossovers roll off at 6 db per octave, second at 12 db per octave, third at 18 db per octave and fourth at 24 db per octave and so on. In other words there is 6db per octave roll off per order of the filter.

 

[pearsall001]

It depends on the order. AVR crossovers are usually second order. That means they roll off 12 db per octave above and below the crossover point.

So if the crossover is at 80 Hz, the high pass will be down 12 db at 40 Hz and 24 db at 20 Hz. The low pass driver will be down 12 db at 160 Hz and 24db at 320 Hz.

First order crossovers roll off at 6 db per octave, second at 12 db per octave, third at 18 db per octave and fourth at 24 db per octave and so on. In other words there is 6db per octave roll off per order of the filter.

Thanks for the info...& confusing me even further. Is there any way you can rephrase that so I might catch on. I notice that you mention 12db down at 40Hz, but isn't that volumn related since you have db in the info? This is all new to me. I was just assuming that the filter would let 75Hz-95Hz pass thru at the 80Hz point. Am I far off? Thanks.

 

[highfigh]

I know that crossover settings are not brick walls & have a gradual slope. For instance, if the AVR crossover setting is at 85hz how much is still bledding thru below & above that point. Set at 85hz would it go as low as say 75hz & as high as 95hz? Or maybe my numbers are way off. Curiousity has the best of me. Thanks.

Crossovers don't stop the signal below the "crossover point" like the edge of a brick. That would cause all kinds of problems with the sound and it's difficult to do it that steeply in certain cases (like low impedance circuits). Also, where it crosses over isn't a point, it's the frequency where the high and low pass signal is at specific level, like -3dB (summed Butterworth filter) or even better, because the net result is flat response, -6dB (summed Linkwitz-Reilly filter).

These filters have a characteristic of decreasing the level at a certain rate. A first-order (like a capacitor or coil in series with a woofer, mid-range or tweeter) works at 6dB/octave- an octave is the same in music or speaker building and is double or half of the original frequency. A second-order filter works at 12dB/octave and for each additional order, 6dB/octave is added. This works out to -12dB at 40Hz for a second-order high pass filter that has a crossover point of 80Hz and an 80Hz low pass filter will be -12dB at 160Hz.

 

[M Code]

It depends on the order. AVR crossovers are usually second order. That means they roll off 12 db per octave above and below the crossover point.

So if the crossover is at 80 Hz, the high pass will be down 12 db at 40 Hz and 24 db at 20 Hz. The low pass driver will be down 12 db at 160 Hz and 24db at 320 Hz.

First order crossovers roll off at 6 db per octave, second at 12 db per octave, third at 18 db per octave and fourth at 24 db per octave and so on. In other words there is 6db per octave roll off per order of the filter.

Partially correct..
2nd order (12dB/Octave) filters are typically used for the high pass filter, however for the subwoofer out 3rd (18dB/Octave) or 4th order (24dB/Octave) steeper filters are used. Primary reason for the subwoofer filter is steeper is to minimize any higher frequencies being passed through. Also note that included in the subwoofer out are 2 groups of audio if any channels is set to Small. 1 group is the redirected bass of any channels set to Small and this is summed with the LFE (.1) track.

Just my $0.01..

 

[TLS Guy]

Thanks for the info...& confusing me even further. Is there any way you can rephrase that so I might catch on. I notice that you mention 12db down at 40Hz, but isn't that volumn related since you have db in the info? This is all new to me. I was just assuming that the filter would let 75Hz-95Hz pass thru at the 80Hz point. Am I far off? Thanks.

Take a look at this.

For every 3db reduction power at that frequency is halved. However it is a log scale, because human perception of loudness is log. So if a sound is 10 db below another it is half as loud. So when a driver is 10 db below at a frequency where it is at 0 db it is half as loud at that frequency as the frequency at 0 db.

I'm leaving now so sort yourself out. If you don't understand, plug it in and be happy.

 

[pearsall001]

Thanks for the link!