# is phase adjustment possible with BFD1124P?



## zheka (Jun 11, 2010)

Is it possible to adjust phase or delay in BFD1124P?

if not, are there any cheap stand alone devices that can do this and, ideally, set HPF?

I am trying to play with Geddes multisub technique and my supplemental subs only have 0/180 phase switch.

thank you


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## proaudio (Sep 17, 2008)

The DSP1124P doesn't have a delay function.

The control on your subs marked "phase" would be better called polarity as phase is a function of time and wavelength but polarity is purely in the amplitude domain. Both can affect how waves interact, but in drastically different ways.

It looks like the Geddes technique simply averages out room modes. For that it shouldn't be necessary to do delay if the polarity matches and the subs are all reasonably close to the same distance from the listening position. But rooms can do funny things. Still, polarity switching and moving subs around ought to be enough to get them all working together.


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## zheka (Jun 11, 2010)

proaudio said:


> The DSP1124P doesn't have a delay function.
> 
> The control on your subs marked "phase" would be better called polarity as phase is a function of time and wavelength but polarity is purely in the amplitude domain. Both can affect how waves interact, but in drastically different ways.
> 
> It looks like the Geddes technique simply averages out room modes. For that it shouldn't be necessary to do delay if the polarity matches and the subs are all reasonably close to the same distance from the listening position. But rooms can do funny things. Still, polarity switching and moving subs around ought to be enough to get them all working together.


thank you for the reply. I suspected as much.

the subs will not be reasonably close. The idea is to spread them through out the room, hence the need for the phase fine tuning. 
i'll be using BFD for bandpassing the supplemental subs. hopefully this, in combination with polarity switching and moving the subs around the room, will give me enough flexibility.


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## proaudio (Sep 17, 2008)

zheka said:


> thank you for the reply. I suspected as much.
> 
> the subs will not be reasonably close. The idea is to spread them through out the room, hence the need for the phase fine tuning.
> i'll be using BFD for bandpassing the supplemental subs. hopefully this, in combination with polarity switching and moving the subs around the room, will give me enough flexibility.


They don't have to be close together or close to the listening position, they all just need to be about the same distance from the listening position. Then you wouldn't need to delay anything. If your crossover frequency is 100Hz then the distances from the listening position could within a range of about 2.5'. If there is more than 2.5' of variation you might want to delay the closer one(s), but then you have the issue of time aligning the full range speakers as well.

If you want to get into that a good tool might be the DCX2496. That has eq, proper crossover filters and delay functions and it has three inputs and six outputs. The DSP1124P doesn't really have filters designed for bandpass.


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## zheka (Jun 11, 2010)

proaudio said:


> They don't have to be close together or close to the listening position, they all just need to be about the same distance from the listening position. Then you wouldn't need to delay anything. If your crossover frequency is 100Hz then the distances from the listening position could within a range of about 2.5'. If there is more than 2.5' of variation you might want to delay the closer one(s), but then you have the issue of time aligning the full range speakers as well.
> 
> If you want to get into that a good tool might be the DCX2496. That has eq, proper crossover filters and delay functions and it has three inputs and six outputs. The DSP1124P doesn't really have filters designed for bandpass.


good stuff, thank you. I did not know about the 2.5 feet threshold. 

I already own the BFD but I have not worked with it yet. This gives me an opportunity. Would i be able to simulate a high pass filter with it?


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## proaudio (Sep 17, 2008)

zheka said:


> good stuff, thank you. I did not know about the 2.5 feet threshold.


The 2.5' number I used relates to a 100Hz crossover point. If the subs are all within a 1/4 wavelength of the same distance from the listening point then they won't interfere destructively. At 100Hz the wavelength is about 10' so a quarter of that is about 2.5'. A higher crossover frequency would narrow that window.



zheka said:


> I already own the BFD but I have not worked with it yet. This gives me an opportunity. Would i be able to simulate a high pass filter with it?


Sort of. But I don't think you can set a filter center below 20Hz so there are limits. It won't be a true high pass filter because its response rises below the center frequency. If your target rolloff frequency is high enough you could stack a number of filters to get a semblance of a high pass filter.

By the way, I own a DSP1100P (the first version), a DSP1124P and a DCX2496. A studio I work in has a DEQ2496 that I set up, and another studio has a DSP1124P that I set up.


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## zheka (Jun 11, 2010)

thank you very much, it was very informative.


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