# peaks vs nulls



## jstefano (Jan 2, 2008)

What type of items in a room cause peaks and nulls ?

Which one of these graphs (different positions) would be best to start with ?


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## Ricci (May 23, 2007)

Usually the major peaks and nulls in a room result from reinforcement or cancellation of freq's due to standing waves or room nodes. These are determined by the dimensions of your room and also the placement of the microphone and the speakers inside the room. I'm not particularily strong on this subject so maybe someone else will chime in. 

The 2nd graph is a much better starting place.


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## weverb (Aug 15, 2008)

You need to switch your graphs from linear to logarithmic. You may also want to contain all your questions in one thread so we do not have jump around to see how you are progressing. Just a thought.


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## jstefano (Jan 2, 2008)

What frequency's would I target if I want to decrease the "boomyness" of my sub ?


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## weverb (Aug 15, 2008)

jstefano said:


> What frequency's would I target if I want to decrease the "boomyness" of my sub ?


Looks like you have a major boost at 45Hz.


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## thewire (Jun 28, 2007)

I like to deal with all of them, but I would recommend that you try and shoot for dealing with the lower fequencies and those possible peaks or dips. These are the lower room modes that can cause potential for coloration. Once you have delt with the axial (left to right, front to back, top, to bottom) room modes, the tangential room modes which are much lower in amplitude, tend to follow.


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## thewire (Jun 28, 2007)

jstefano said:


> What type of items in a room cause peaks and nulls ?


You can do an experement to demonstrate how having something in the room will change the measurement. Here a simple program I wrote that will do a left mouse click after around 15 seconds. Get the measurement window up in REW and point the arrow over the button to start the measurement and double click the file. Leave the room quickly moving away as far as you can, and wait for the measurement to occcur. Now do the same measurement again while you are at the computer. See how it is changed? You might need to look very close. This is just some practice and no need to post graphs. This should show that the measurement is sensitive to what is inside the room.


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## jstefano (Jan 2, 2008)

*Questions*

1. Jamo A340 Speaker freq range 50 Hz-20 kHz would you consider this a "Full range" or "Bass limited" ?

2. Denon 3806 AVR, if the crossover freq for the LFE is set at 80 Hz does it matter what the sub's crossover freq is set at ?

3. My AVR has an option for "LFE" or "LFE+MAINS" what would be the correct setting and what is the difference ?


4. Why don't you treat "Nulls" more aggressively with filters ?

5. If I want to run 2 subs do I split my LFE out from my AVR ?

Please see my signature for the list of my equipment


Thanks for your knowledge
Joe


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## brucek (Apr 11, 2006)

> 1. Jamo A340 Speaker freq range 50 Hz-20 kHz would you consider this a "Full range" or "Bass limited" ?


Bass limited. But all main speakers should be used as 'small' when it comes to bass management.



> 2. Denon 3806 AVR, if the crossover freq for the LFE is set at 80 Hz does it matter what the sub's crossover freq is set at ?


The subs own crossover should be disabled.



> 3. My AVR has an option for "LFE" or "LFE+MAINS" what would be the correct setting and what is the difference ?


I believe this sends the LFE track to the mains. Best to send it to the sub.



> 4. Why don't you treat "Nulls" more aggressively with filters ?


Nulls are often created by a reflection arriving out of phase with the main signal and so causing a null. If you increase the level of the main signal with a filter, you will also increase the level of the out of phase signal. The result is that nothing changes. All you're doing is decreasing headroom. It doesn't work..



> 5. What would you do with this graph ?


Change the presentation to LOG from LIN as already suggested so we can better evaluate it.

brucek


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## jstefano (Jan 2, 2008)

Thanks for your input Bruce,

Here is the graph I would like some advice on, It is My sub and mains. I am just looking to see how you would interpret this graph.









There is also a ? regarding 2 subs on the other post
I went to Tweeters today and bought a Polk Pro 500 Sub 

Thanks again


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## jstefano (Jan 2, 2008)

*My Media Room & Setup*

Here are some Pic's of my room and calibration setup


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## brucek (Apr 11, 2006)

> Here is the graph I would like some advice on


Can we see the waterfall?
Use the standard Vertical graph axis of (45dB - 105dB) and the Horizontal graph axis of (15Hz - 200Hz) using the Graph Limits button in the top right corner of REW. 
Set the mode to LOG rather than LIN using the Freq Axis button in the top right corner of REW.
Best to set the time range to 600msec and leave the Window at 300msec.
Set the X=1, Y=50, Z=150.
Select the measurement in the REW left pane you want to look at, and Generate the waterfall.

brucek


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## jstefano (Jan 2, 2008)

*Waterfall*

Here you go.
I also want to know the best way to hook 2 subs to my BFD. Is it ok to split the LFE output of my AVR and run 1 sub on the Lch and 1 sub on the Rch of the BFD ?


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## Wayne A. Pflughaupt (Apr 13, 2006)

A couple of things. I once tried experimenting with various placement options with two subs in a rectangular room, and I got the absolute _worse_ results with them catty-cornered like you have in your picture above. Most of the time the best approach is use REW to find the best location, and put both subs together there.

Second, it's usually not a good idea to use mismatched subs. Typically what you'll find is that the weaker one will "dumb down" overall performance (to use a great phrase brucek coined).

Regards,
Wayne


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## jstefano (Jan 2, 2008)

If my LFE crossover is set at 80 Hz do I need to filter this peak at 115 Hz ? and how does the rest look ?


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## brucek (Apr 11, 2006)

> If my LFE crossover is set at 80 Hz do I need to filter this peak at 115 Hz ? and how does the rest look ?


Normally, you would add the mains and see how that transition area looks before you tackle the peak at 115Hz.

brucek


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## jstefano (Jan 2, 2008)

Here is the mains added


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## brucek (Apr 11, 2006)

Looks fine.....


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