Phase problem? Will an EQ help?

**01-05-07, 03:54 PM**

Subwoofer crossover is set to 80Hz. Subwoofer has switchable 0/180 phase control.

The graph on the left with phase set to 180 shows a steep valley at 70Hz, while the graph on the right with phase set to 0 shows a steep valley at 87Hz.

Which is the more appropriate setting, 0 or 180? And is there anything a BFD could do to help?

Thanks,
Ron

**Josuah** · **01-05-07, 03:57 PM**

The DCX2496 has a phase adjustment which would let you pick stuff between 0 and 180. But you should try adjusting your crossover point first.

**01-05-07, 04:24 PM**

Here are the measurements for the same 0/180 phase settings with the crossover set to 100Hz.

**brucek** · **01-05-07, 04:27 PM**

Those narrow spikey dips won't be audible. I don't think you need to address them at all.

The BFD is used with wide peaks associated with room resonances.

Why not post your response from 15Hz to 200Hz with a vertical resolution of 45dB to 105dB and let us have a look....

brucek

**01-05-07, 05:04 PM**

Quote:

brucek wrote:

Those narrow spikey dips won't be audible. I don't think you need to address them at all.

The BFD is used with wide peaks associated with room resonances.

Why not post your response from 15Hz to 200Hz with a vertical resolution of 45dB to 105dB and let us have a look....

brucek

bruce,

Are you sure that hole at 69-70Hz won't be audible? I listen to a lot of classical music.

I just put the cables and SPL meter away (I run 50 foot cables from my computer to my HT), but I'll post the other graphs tomorrow. The response below 50Hz was pretty good -- around 72-75dB from 30-60Hz, with 15-30Hz in the 75-80dB range. I'm using the Radio Shack SPL meter (with appropriate correction file) so I figured the results below 30Hz probably weren't very accurate.

I do have another dip around 175Hz.

The room has plaster walls and wooden floors (with an area rug), so I know my response will never be perfect.

**brucek** · **01-05-07, 06:14 PM**

Quote:

Are you sure that hole at 69-70Hz won't be audible?

It's quite sharp and fairly narrow. Usually you add some smoothing to the raw data to make the graph more representative of what we hear. I usually use 1/3 octave smoothing (a selectable feature in REW). It's better to see raw data when you post, but for your own viewing, I would add smoothing. You'll see the spike clear up quite a bit.

You didn't post your 15Hz to 200Hz response......

brucek

**Hakka** · **01-05-07, 07:27 PM**

Try changing the subwoofer distance setting in your AVR, this will adust the phase in small increments, it might give a better result than the 0deg and 180deg sttings.

**01-05-07, 09:09 PM**

Quote:

Try changing the subwoofer distance setting in your AVR, this will adust the phase in small increments, it might give a better result than the 0deg and 180deg sttings.

Unfortunately, I am using the Panasonic SA-XR57 which has no distance setting for the subwoofer.

**DrWho** · **01-06-07, 03:26 PM**

Are your mains set to large or small?

**Josuah** · **01-06-07, 05:11 PM**

Must be small, otherwise changing his crossover wouldn't do anything when running an L/R signal.

**DrWho** · **01-08-07, 07:25 PM**

Quote:

Josuah wrote:

Must be small, otherwise changing his crossover wouldn't do anything when running an L/R signal.

Explain? I think you're implying that the subwoofer won't be playing when the mains are set to large? I know you can set it so that both play the material below the crossover. Setting to large increases the amount of interactions below the crossover point whereas setting to small will decrease the amount of interaction.

Also, how high off the floor is the mic when you're doing these measurements? And how far are the mains and subwoofer from the walls? Distances around 4 feet would correlate to the 70Hz dip and distances around 3 feet would be 88Hz.

**blekenbleu** · **01-08-07, 08:27 PM**

Quote:

RonLF wrote:

Unfortunately, I am using the Panasonic SA-XR57 which has no distance setting for the subwoofer.

Does your sub have a low-pass / crossover adjustment?
I was able to fill a similar notch by juggling that and sub gain...

**Josuah** · **01-08-07, 10:12 PM**

Right, if set to large, the subwoofer won't get used with a pure stereo signal.

The situation where both subwoofer and mains get the absolute same signal is if your receiver sets the bass output to BOTH (or something similar) and you are playing back the LFE channel. Large implies no crossover in use.

I believe the 70Hz dip is common in many rooms because that's the room height of 8', and your head is usually about half and half. If I'm remembering things correctly. Doesn't really matter where the speakers are for that dip. But since changing the crossover point reduced the dip, looks like phase is contributing to it.

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