Hello, maybe a noob question but I’ll ask it anyway.
I recently took a look at allpassfilters with a few webinars and now I’m wondering if you could possibly „change“ group Delay with a 2nd order allpassfilter with high Q factor.
Allpassfilters shift the time delay of the lower frequency’s where the filter is applied.
If you use a high Q factor it would shift the time at the frequency where the filter is applied even more than below that. I attached a picture to show what I mean.
Following situation:
Subwoofer with high group Delay at for example 40hz, with a downward sloping group Delay to 80hz. (Tapped horn)
Wouldn’t it be possible to introduce an 2nd order allpassfilter with high Q at 80hz to shorten the time distance between 40hz and 80hz? I know this would result in an overall higher group Delay. But isn’t it better to have for example 50ms at 40hz and 20ms at 80hz with a 20ms difference than 40ms at 40hz and only 5ms at 80hz with 35ms? Of course you would have to delay your mains more, but my main question is if you can get tighter bass out of a sub with this method?
I recently took a look at allpassfilters with a few webinars and now I’m wondering if you could possibly „change“ group Delay with a 2nd order allpassfilter with high Q factor.
Allpassfilters shift the time delay of the lower frequency’s where the filter is applied.
If you use a high Q factor it would shift the time at the frequency where the filter is applied even more than below that. I attached a picture to show what I mean.
Following situation:
Subwoofer with high group Delay at for example 40hz, with a downward sloping group Delay to 80hz. (Tapped horn)
Wouldn’t it be possible to introduce an 2nd order allpassfilter with high Q at 80hz to shorten the time distance between 40hz and 80hz? I know this would result in an overall higher group Delay. But isn’t it better to have for example 50ms at 40hz and 20ms at 80hz with a 20ms difference than 40ms at 40hz and only 5ms at 80hz with 35ms? Of course you would have to delay your mains more, but my main question is if you can get tighter bass out of a sub with this method?
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Why don't you set on biquad filters and fotget all this delay thing? You talk about 40 and 80 Hz which involves waves several meters long
Yes the overall phase shift characteristics (and therefore the group delay) of an existing filter could be changed by using an allpass filter in cascade with it.
Yes.
Ideally, you'd want to have a constant delay (linear phase) across all frequencies in order to maintain perfect phase coherence. That would also simplify the adjustments required to the other channels. The following gives an idea of how it could be done.
https://www.diyaudio.com/community/...earization-by-fir.393435/page-23#post-7240102
No, you can't. The tightness is usually due a faster transient response, which is not a characteristic of low bandwidth (low-frequency) drivers.
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Thanks for the answer.
I know that ideally the group Delay should be constant, but in most designs that isn’t the case. So what’s the explanation on why it isn’t better to do this with an allpass filter?
Shouldnt that make the Impulse response shorter? And therefore „tighter“ 🤔
In my simple understanding where 80hz and up is Kick and 40hz is for example that rumble of the kick. Putting 80hz and 40hz closer together should result in a „tighter“ feeling bass? Or am I completely wrong here
I know that ideally the group Delay should be constant, but in most designs that isn’t the case. So what’s the explanation on why it isn’t better to do this with an allpass filter?
Shouldnt that make the Impulse response shorter? And therefore „tighter“ 🤔
In my simple understanding where 80hz and up is Kick and 40hz is for example that rumble of the kick. Putting 80hz and 40hz closer together should result in a „tighter“ feeling bass? Or am I completely wrong here
The best explanation would be that it does not preserve the phase coherence of frequency components in the original signal.
For a faster response, the system needs to have a wider bandwidth. Simply changing the phase relationships between frequencies does not increase the bandwidth of the system.
just wondering about the subs response when for example playing a kick only to the subs.
Imma post 2 examples. The first picture is with only a highpass and lowpass Filter Applied.
The second picture is a highpass, lowpass and an allpass applied. With the allpass set with a high Q factor so the frequency’s at 80hz get delayed more than those at lower frequency’s. If you’d play a single kick through both of those subwoofer with different settings, shouldn’t the second one sound tighter? Or are there any major disadvantages on allpass filters that I miss?
I know Hornresp can’t set allpasses but since we’re only looking at group Delay and not magnitude a normal filter should do the same to Phase and group Delay.
Imma post 2 examples. The first picture is with only a highpass and lowpass Filter Applied.
The second picture is a highpass, lowpass and an allpass applied. With the allpass set with a high Q factor so the frequency’s at 80hz get delayed more than those at lower frequency’s. If you’d play a single kick through both of those subwoofer with different settings, shouldn’t the second one sound tighter? Or are there any major disadvantages on allpass filters that I miss?
I know Hornresp can’t set allpasses but since we’re only looking at group Delay and not magnitude a normal filter should do the same to Phase and group Delay.
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Your conclusions appear to be based on subjective hearing. Why don't ask for this thread to be moved to the musical instruments sub-forum? You could actually get much better responses that way.
