My graphs - suggestions?

[quenthal]

I just got new speakers and decided to try REW for the first time in my life AND to make my first post here ever.. ;-)

I made few measurements, which can be seen below:
1. Main speakers only, no crossover:


2. Main speakers only, crossover @ 60Hz


3. Subwoofer only, crossover @ 60Hz (sub levels not properly configured yet)


4. Mains+sub, crossover @ 60Hz, phase 0


5. Mains+sub, crossover @ 60Hz, phase 180


Few questions and observations...
The huge drops @ 59Hz (@52Hz with sub) and @ 135Hz with main speakers and peaks at 40 and 80Hz with sub are probably caused by the room? I don't remember moving the speakers closer to the front wall make any big difference. Also the overall level is about 5dB lower below 140Hz with main speakers (when I run the Audyssey setup from my AV, it sets the crossover @120Hz maybe because of this and this is way too high for my taste).

I have played with crossover of 60Hz, but as you can see my subwoofer still gots quite a lot to play between 65Hz and 120Hz. Should I use the low pass filter from the SMS-1 in addition to the one from AV-receiver?

Am I making correct assumption if i say the 180 degree phase is the correct one?

What are your overall recommendations?

[brucek]

The huge drops @ 59Hz (@52Hz with sub) and @ 135Hz with main speakers and peaks at 40 and 80Hz with sub are probably caused by the room?

Yes.

Should I use the low pass filter from the SMS-1 in addition to the one from AV-receiver?

Never..... The sub actually tracks the target quite well as shown in graph 3.

Am I making correct assumption if i say the 180 degree phase is the correct one?

What are your overall recommendations?

Yeah, graph 5 is quite good. You might use the SMS to bring the peak between 25Hz-45Hz down.

brucek

[quenthal]

Thanks for quick comments!

What would be your opinion about the correct crossover?

Am I little worried since I probably need to put sub level 6-8db lower -> dip at 55Hz becomes bigger, and the overall level at 60-140Hz lowers too. I think the reason that pic 5 looks relatively good, is that subwoofer's level is so much higher that main speakers. Because of the it affects to that 55Hz dip and up to 150Hz more than it probably should, considering that I'm currently using 60Hz crossover

[brucek]

I don't feel it's too high at all. Many people use a house curve that results in the sub being quite a bit higher than the sub. Read about house curves here.

I think you may need to reduce the peak at 40Hz and take down the area a bit from 25Hz to 45Hz with a filter while leaving the overall level where it is...

brucek

[quenthal]

What about putting a little bit of gain at near the crossover at 53-54Hz?

The only reason why I wondered about lowering the sub was that it is boosting the frequencies between 80-110Hz nearly 8dB even with 60Hz crossover when comparing pictures 2 and 5 (or is this normal?) Maybe the my AV-receiver (Onkyo 805) is doing only 12dB/octave.

I decided to try house curve -idea too, however it would seem that I'd need even more then to get the subwoofer give more responsibility to the main speakers after crossover point. Using the LPF from SMS-1 achieved nearly this - what are the negative sides in using it in addition to AV-receiver's filter (especially when it drops so slowly as my graphs indicate)? Lower quality?

[brucek]

Maybe the my AV-receiver (Onkyo 805) is doing only 12dB/octave.

That's normal. Usually the LPF is 4th order and the HPF is 2nd order.

You have to be careful with gain to not add more than about 5dB and only if the level responds to it..

brucek

[Wayne A. Pflughaupt]

quenthal wrote:

What are your overall recommendations?

Pretty tough graph you have there. You’ve got fairly flat response between 25-40 Hz; I always hate to see filtering applied to an area that essentially needs nothing, especially when it amounts to more than 2/3 of your total subwoofer range. On the other hand, it’ll require a substantial boost to deal with that 55 Hz hole. Whether or not that’s a problem depends on the limitations of your sub, but I think I’d try to relocate it, if that’s an option, to see if you can get a graph that’s more readily equalizible (don’t look for that word in the dictionary ).

Regards,
Wayne

[HClarkx]

Wayne A. Pflughaupt wrote:

. . . . . I think I’d try to relocate it, if that’s an option, to see if you can get a graph that’s more readily equalizible (don’t look for that word in the dictionary ).

Regards,
Wayne

I agree. I've found moving a sub can provide remarkable improvements. The better the starting point, the better the equalized result. I have two subs and played with their locations independently so that they were highly complementary when combined. I found that my ear's ability to pinpoint the sub location(s) was reduced when the subs were placed so they tested well without EQ and integrated well with the mains. The Audyssey filters do remarkable things, but they really sparkle when the starting condition is good. Further, try different crossovers. Audyssey may suggest a crossover, but will accept your choice and do well with it. I usually start at 80Hz and try moving up and down from there.

Harrison (HClarkx)

[DrWho]

I think I would start by turning down the subwoofer ~10dB so that it's output is more in line with that of your mains. This will push the interaction point of the relative phase between your mains and sub closer to 60Hz, which is where you've got some nasty modes happening. In other words, right now you're running an electrical 60Hz crossover, but are seeing an acoustic crossover of 75Hz.

Another alternative would be to lower the crossover frequency to 50Hz so that you're seeing closer to a 60Hz acoustic crossover. You would probably still need to reduce the output of the sub, again, the goal being to see if your phase switch can help fill that 60Hz null.

If neither of the above approaches work, then your best bet will be to reposition the subwoofer (in fact, you might as well just start with moving the subwoofer). Don't forget the option of moving the listening position too. The position of nulls in the room are mostly the result of the standing waves that build up...moving the speakers around doesn't change the dimensions of the room, which is to say that the standing waves generally want to happen in the same location. For instance, take a measurement in the rear corner of your room and note how different the response is...

[HClarkx]

DrWho wrote:

If neither of the above approaches work, then your best bet will be to reposition the subwoofer (in fact, you might as well just start with moving the subwoofer). Don't forget the option of moving the listening position too. The position of nulls in the room are mostly the result of the standing waves that build up...moving the speakers around doesn't change the dimensions of the room, which is to say that the standing waves generally want to happen in the same location. For instance, take a measurement in the rear corner of your room and note how different the response is...

I agree. The mains and sub both have a nasty dip at nearly the same frequency. Nothing short of moving speakers is going to fix that (or as the Dr. suggests, moving your seats out of the area where that occurs). If your mains and sub are in about the same location, it is probably the same surface reflecting a wave that is weaker but out of phase with the direct waves from the main and sub at your listening position. That suggests the possibility of having to move both mains and the sub to fully eliminate the dip.

The worst thing you can do is put mains and a sub centered on a wall facing the wall opposite them, and then sit between the two walls. Unfortunately, that's a typical room layout. Say the room is 20 feet from front to back and you are sitting five feet from the back wall. The direct wave will travel 15 feet to your ears. The reflected wave will travel 20 feet to the back wall and bounce forward to your nears, an extra 10 feet. Unfortunately, that 10 feet will put the reflected wave out of phase with the direct wave at your seat at about 55 Hz. Likewise, if your sub is to the right of your seating position and there is wall 5 feet to the left, the same result occurs. The further you are from the back wall, the lower the frequency where the dip appears (and vice versa).

One of the best locations for a sub is the corner nearest your mains (so long as you aren't sitting in the diagonally opposite corner. Where that doesn't work, put your sub 1/3 the distance from the corner to the left of your mains or the corner to the right of your mains, but not where you will be sitting directly in front of it. You want the sub well off to the left or right and at the 1/3 or 2/3 point along the wall (assuming you want the sub on the same wall as your mains). If the sub is on a side wall, the same rule applies, 1/3 or 2/3 and not on a perpendicular from your seat to that wall.

If the sub can be away from any wall, that's also a potential solution, but in that case the sub should be 1/3 1/3 ... that is, 1/3 the distance from each closest wall to the opposite wall. And, again, you don't want to sit on a perpendicular between the sub and a wall. That is, you don't want sound passing directly past your ears, hitting a wall at 90 degrees and bouncing back to your ears. You will have a dip at the frequency where the distance to the wall and back is 1/2 wave length.

At least these are starting points.

Good luck. And, it does take some luck!

Let us know how it's working out.

Harrison