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Discussion Starter #1
...well at least from my listening position according to test tones and what I measured with an old analogue radioshack SPL meter. I also used some correction numbers for that meter.

The response graph looks disasterous with a huge HUGE dip around 50Hz, also my output below 40 far exceeds anything higher up. The crossover is supposed to be set at around 90Hz.

Do I worry or just leave it? Is it normal to have such huge variances in a typical rectangular room?

 

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The 50hz is a room mode probably. Be sure to take multiple position measurements in the seating area to get an average.

Ignore everything below 20hz. That can come from anywhere(trains, plain, and automobiles)

Did you have the speakers combined with the sub in this measurement?
 

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Looks like you have gotten good advice about room modes. Keep in mind boundary cancellation factors, as well. They can put a big fat hole right in the middle of the bass response.

Here are a couple of links in case you haven't found them already:

Boundary Cancellation And Room Mode Chart that helps find ideal placement for sub that cancels out room modes at a wide range of frequencies.
http://www.padrick.net/LiveSound/CancellationMode.htm

Harman Room Mode Calculator for Excel. You probably have used something similar to this.
http://www.harman.com/EN-US/OurCompany/Technologyleadership/Pages/Calculators.aspx

Good luck with your system and happy holidays.
 

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Just to test the boundary cancellation factor: Is your sub between 4½ or 5½ feet from the nearest wall?

Thanks and good luck!
 

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Discussion Starter #6
Hi Bill, thanks for the reply. The room is approximated in the picture I drew below. The celing is about 7' high with ceiling tiles. If I remove the a tile, I have another 2' before it actually hits something solid for the floor above.

The listening locations are also approximated. I hope this helps a little bit. I've also attached a pic of the front wall with the sub and speakers so that the picture I drew makes some sense. Much appreciated as any help fixing or reducing that massive dip would be great.






First, we need to know the size of your room to tell if the dip is room related.
Secondly, we need to know the listening position in relation to the loc ation of the speakers.

Cheers,
Bill.
 

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Discussion Starter #7
Thanks Isiberian, the frequencies below 20Hz I measured for sure. It was clear on the meter as soon as I pause and play the tones plus its in a basement so its fairly isolated I'd think. I do think its probably the room but not sure if thre is much I can do to fix it :( When I move the microphone from the seating position forward towards the sub, the 50Hz does start to come back but then the lower frequencies start to lessen and same happens in the other direction. I guess I have to strike some balance with the seating position?

The 50hz is a room mode probably. Be sure to take multiple position measurements in the seating area to get an average.

Ignore everything below 20hz. That can come from anywhere(trains, plain, and automobiles)

Did you have the speakers combined with the sub in this measurement?
 

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Discussion Starter #8
Thanks Synthsayer, I will definitely be looking into the links you provided. Must MUST fix this :)

Looks like you have gotten good advice about room modes. Keep in mind boundary cancellation factors, as well. They can put a big fat hole right in the middle of the bass response.

Here are a couple of links in case you haven't found them already:

Boundary Cancellation And Room Mode Chart that helps find ideal placement for sub that cancels out room modes at a wide range of frequencies.
http://www.padrick.net/LiveSound/CancellationMode.htm

Harman Room Mode Calculator for Excel. You probably have used something similar to this.
http://www.harman.com/EN-US/OurCompany/Technologyleadership/Pages/Calculators.aspx

Good luck with your system and happy holidays.
 

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Factors to consider here since it looks like you have a great system.
Is the wall separating the 2 spaces 2 X 4 and drywall?
Insulated?
How much bass do you hear in the small room area and the rest of the house when your system is at listening volume? Is the adjoining room empty or possibly have things that are absorbing or reflecting sound?
Looking at the overall space it would appear that the subs are somewhat in the corner of a nice large space of about 22 X 18 feet in size. If the ceiling is less than 8 feet some cancellation could come from that, maybe?
Have you tried placing the sub cabinets with the woofers positioned closer together or facing the wall. Could you put the subs in the back of the room where they are further from you? Possibly in the back of the room facing the wall.
Don't worry about answering all these questions; I'm just trying to suggest anything that might solve the frequency dip in the system. EQ helps but isn't the absolut solution, IMHO :)
 

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Discussion Starter #10
I'll see if I can answer all of them :)

The wall dividing the two places is indeed just 2x4's and drywall - no insulation. There are some shelves with boxes and stuff I've stored so its not totally empty but at least empty of things that would be considered sound absorbing I guess. The ceiling is lower than 8 feet (maybe 7) so maybe it could be affecting the sound but then again, not sure because its ceiling tiles so I dont know what the sound characteristics are for those.

I have not tried the subwoofers elsewhere only because I thought it might be aesthetically less pleasing but I guess I could try it. Will be a pain to move them due to the weight. I think they are about 130lbs for each cabinet. I wonder what might happen if i got another two subwoofers (same drivers) and build a cabinet in the back or side wall. Maybe I can place it in such a place where at my seated position, the bass at 50Hz might get bumped up. The drivers are cheap enough (Dayton SD315-88).

Factors to consider here since it looks like you have a great system.
Is the wall separating the 2 spaces 2 X 4 and drywall?
Insulated?
How much bass do you hear in the small room area and the rest of the house when your system is at listening volume? Is the adjoining room empty or possibly have things that are absorbing or reflecting sound?
Looking at the overall space it would appear that the subs are somewhat in the corner of a nice large space of about 22 X 18 feet in size. If the ceiling is less than 8 feet some cancellation could come from that, maybe?
Have you tried placing the sub cabinets with the woofers positioned closer together or facing the wall. Could you put the subs in the back of the room where they are further from you? Possibly in the back of the room facing the wall.
Don't worry about answering all these questions; I'm just trying to suggest anything that might solve the frequency dip in the system. EQ helps but isn't the absolut solution, IMHO :)
 
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