Subwoofer Crossfrequency

[stoneson2]

Hello,

First I have to say two things: Im a beginner in this field and im very impressed by your app.

The lowest crossfrequency which i can install on my subwoofer is 80hz. I measured that my satellites can play around 58 Hz perfectly linear. So I would like to have a lower crossoverfrequency by software. I got also a strange problem by the subwoofer. If I measure my satellites alone i dont get a dip at 110Hz (-10db). With the subwoofer i get this dip. The subwoofer has this configuration:
80Hz LP and 80Hz HP (24db/decade)

I heard that this is possible with virtual audio cable. Is it true?
Is there a description anywhere how to setup it for this purpose? I could not handle that.

I read that:
"Attention:
Although it might be tempting to assign low frequency filters only to the subwoofer channel, this might not lead to the expected results. Many audio systems apply bass redirection after Equalizer APO has processed the signal, so filters applied to the subwoofer channel won't be effective for redirected sound. Furthermore, as crossover filters only gradually fade in, the low frequency audio might be played over multiple speakers, not just the subwoofer, reducing the effectivity of subwoofer-only filters. Therefore, to avoid these problems, it's recommended to apply low frequency filters to all channels. "

Is this still correct? Or is it not true anymore because of the post-mix stage update?

regards stoneson

[Glenn Odagawa]

I hope you mean 80Hz LPF 24dB/octave with no (or a lower) HPF. A dip @110Hz could be simply the physical distance you have between the satellites and the sub. Also, have you tried reversing the phase of the sub. If distance is an issue you may get a slight broad bump @ 110Hz which is easier to correct using eq, than the (possibly narrow) dip that you are experiencing now.

[Jonas Dahlinger]

I guess that your subwoofer is currently fed with the input signal for two speakers and it outputs a (high-pass) filtered signal to the satellites while playing the low frequency part by itself. This way, the crossover frequency can be completely controlled by the subwoofer.

To do the crossover using Equalizer APO, the crossover filter of the subwoofer must be bypassed: The signal for the satellites should go directly to them, without the subwoofer in between and the subwoofer gets its own signal from a separate channel (normally the LFE channel). Then, this configuration would do the crossover:

Copy: SUB=L+R
Channel: SUB
Filter: ON LP Fc 58 Hz
Channel: L R
Filter: ON HP Fc 58 Hz

You must make sure that your sound card driver does not perform bass redirection.

I read that:
[...]
Is this still correct? Or is it not true anymore because of the post-mix stage update?

This hint was meant for the normal use case, which is room correction. In that case, you don't necessarily need to address individual speakers but just correct the frequency response. In the lower frequencies, this is even more true, as the location of low frequencies can hardly be distinguished by humans. So, it is safer to just apply the filtering to all channels in case that there is a further processing stage (like your subwoofer currently) which redirects audio to the subwoofer channel. If only the subwoofer channel was filtered, the lower frequencies for the main channels would go unfiltered to the subwoofer because of the redirection.

In your case however, it is necessary to filter the subwoofer individually to get the desired effect.

[stoneson2]

"I guess that your subwoofer is currently fed with the input signal for two speakers and it outputs a (high-pass) filtered signal to the satellites while playing the low frequency part by itself. This way, the crossover frequency can be completely controlled by the subwoofer."

Yes, that is right.

"To do the crossover using Equalizer APO, the crossover filter of the subwoofer must be bypassed: The signal for the satellites should go directly to them, without the subwoofer in between and the subwoofer gets its own signal from a separate channel (normally the LFE channel). Then, this configuration would do the crossover:"

Yes, this was also my plan. I`m new to this and confused how to setup it.
Here is my interface setup:
https://www.dropbox.com/s/frw2yfh29d11i81/subwoofer.png?dl=0
Now I have to assign the lp for the subwoofer to output 3 and 4 and the hp to output 1 and 2, right?
Or do i have to assign my outputs instead of mix (l) and (r) to mix1 (mono), 2, 3 and 4? But there is no audio signal on it. I hope you can understand my problem.
Do i have to setup an 5.1 configuration? I never had this before.

I can`t bypass my hardware lp but i can set it to 120Hz, which I think should be fine. (sub)

"In the lower frequencies, this is even more true, as the location of low frequencies can hardly be distinguished by humans."

Im not an expert but i learned a lot about acoustic in the last months. Yes, that is correct. It is also in wikipedia. There is also in the german version of wikipedia a sentence which mean that location and "roomy hearing"=stereohearing are two different things. Location will be fine with a crossover of 80hz. For "roomy hearing" it should be as low as possible. So that is another reason why i want to try this with Eq-APO.
But I dont expect that much difference. By the way it is used for my home studio as room correction. I installed a lot of acoustic also. What are the limits of EQing. I mean how many db and which bandwith or quality factor q are recommanded ? I heard 5-6db are the limit but i cant confirm, my phase graphs in REW are the same with 8db change or without it.

I know a lot of questions! I`m really curious.

Thanks for your reply. I hope you can help me.

regards
stoneson

[Jonas Dahlinger]

Now I have to assign the lp for the subwoofer to output 3 and 4 and the hp to output 1 and 2, right?
Or do i have to assign my outputs instead of mix (l) and (r) to mix1 (mono), 2, 3 and 4? But there is no audio signal on it. I hope you can understand my problem.
Do i have to setup an 5.1 configuration? I never had this before.

It sounds like you are using multiple outputs on your soundcard (line output and 2xSPDIF in parallel). Normally, E-APO operates on just one output with multiple channels, like 5.1. If you are really using multiple outputs simultaneously, you use the Device command to distinguish between them. In that case, they also should be visible as multiple entries in the Configurator. If you only get a signal on one of the outputs, you either need to find a solution to have the audio being routed to the other outputs, or you should reconfigure your output to have at least 4 channels (e.g. 5.1), so that you have the audio for all speakers on one output. I don't know if this is actually possible for you if you have only stereo outputs and SPDIF (which also only supports stereo for uncompressed audio) available.

Im not an expert but i learned a lot about acoustic in the last months. [...] What are the limits of EQing. I mean how many db and which bandwith or quality factor q are recommanded ? I heard 5-6db are the limit but i cant confirm, my phase graphs in REW are the same with 8db change or without it.

I am also not an expert when it comes to filter properties. The higher your filter gain, the more phase distortion you might get, but I don't know how much is acceptable. I read some time ago, that filters with negative gain should be preferred because of how room acoustics work, but I don't know the exact reason for this anymore.

[Krister Stuns]

I have two soundcards. Is it possible to play all frequencies below 80 hz on one of the sound cards and all frequencies above 80 Hz on the other?

[Jonas Dahlinger]

If it is possible to have the audio being output to both sound cards in parallel, this would be possible. Then you could use the Device command to have a separate configuration for each sound card, like:

Device: Soundcard A
Filter:ON LP Fc 80 Hz
Device: Soundcard B
Filter:ON HP Fc 80 Hz

You can generate the Device commands using the Configurator application.

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