# BFD filter help



## Guest (Jun 13, 2006)

Hello All

I have recently completed a sweep of my subwoofers in room response using REW.

I have attached an image of my graph.
Can anyone make some filter suggestion on how i can achieve my target response (blue line)


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## brucek (Apr 11, 2006)

Something is not right.

Do you have the correct meter calibration file loaded?

Measure just the sub only.

Why is your sweep cut off at 160Hz? Sweep from 20Hz to 200Hz.

brucek


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## Guest (Jun 13, 2006)

Yes i loaded the correct file

I set the sweep to run up to 160Hz.

cheers


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## JohnM (Apr 11, 2006)

Are you connected directly to the sub? If that is the sub response alone, looks like any crossover in the sub is bypassed or set to its highest frequency (normal assuming your processor is handling the bass management) hence the extended response. For that situation the target is a flat line rather than the usual low pass, set the speaker type to "Full Range" and the target level to 72dB, then use the "Find Peaks", "Assign Filters" and "Optimise PK Gain & Q" buttons to let REW suggest and optimise some filter settings.


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## Guest (Jun 13, 2006)

Thank john

I will try that. Is there any reason why i should set the target level to be 72Db?

Is a flat target respose better than a house curve?



thanks


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## brucek (Apr 11, 2006)

> Is a flat target respose better than a house curve?


Depends on the sound you like.

Is the signal into the BFD directly and not through your processor?

If so, is the crossover in the sub disabled?

What type of sub is it?

You need to fill us in on the situation before we can respond properly....

brucek


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## Guest (Jun 13, 2006)

brucek said:


> Depends on the sound you like.
> 
> Is the signal into the BFD directly and not through your processor?
> 
> ...



Hi there

The sub is a Monolith its made by a British manufacturer called BK electronics.

http://www.bkelec.com/HiFi/Sub_Woofers/monolith-df.htm

The crossover on the sub is disabled. 
For measuring the room respose, the BFD was connected directly to the sub and not through the my receiver

I can't think of anymore info to give, hope this helps


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## JohnM (Apr 11, 2006)

dongagon said:


> Is there any reason why i should set the target level to be 72Db?


I picked 72dB as from the response that looks to be the level the sub is achieving without the influence of modal resonances. The sub rolls off much faster at the low end than would be expected from the info in the link you posted, is it placed away from the walls? If so, try placing it against a wall or in a corner, should substantially lift the low end and give you enough output at the bottom to be considering a house curve.


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## Guest (Jun 14, 2006)

JohnM said:


> I picked 72dB as from the response that looks to be the level the sub is achieving without the influence of modal resonances. The sub rolls off much faster at the low end than would be expected from the info in the link you posted, is it placed away from the walls? If so, try placing it against a wall or in a corner, should substantially lift the low end and give you enough output at the bottom to be considering a house curve.



I Jonh

Once i have applied the filters should i calibrate my sub to 75Db the same as my other speakers?

The sub is to one side of a bay window, this is the only place i can go in my room so i am limited. It is as close the walls as it can be.

Cheers


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## JohnM (Apr 11, 2006)

Calibrate as usual once your filters are in place. Whether that should be 75dB or lower or higher is a topic that tends to attract lively discussion. A good way to set the sub level is to make a full range measurement through your AV processor with both the sub and a main speaker running, see how the sub level compares with the general level of the main speaker through the 500Hz to 1.5kHz range and tweak the sub level accordingly.


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## Guest (Jun 14, 2006)

JohnM said:


> Calibrate as usual once your filters are in place. Whether that should be 75dB or lower or higher is a topic that tends to attract lively discussion. A good way to set the sub level is to make a full range measurement through your AV processor with both the sub and a main speaker running, see how the sub level compares with the general level of the main speaker through the 500Hz to 1.5kHz range and tweak the sub level accordingly.


Sounds good.

One problem though i initially wanted to connect the external sound card to my receiver, and perform the test that way. However, using the method described in the online REW help files i was getting lots of feedback (i check all of the connections and cables), so much so, i had to use connection method 1 bypassing the av receiver.

With this i mind i am not sure how to perform a sweep to see how my main speakers and sub are running together


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## JohnM (Apr 11, 2006)

If you get feedback with either connection method it indicates there is something wrongly set in the soundcard providing a path from input to output - e.g. line in not muted in the replay volume control, or monitoring enabled in the soundcard or similar. Even if this doesn't cause obvious feedback when going directly to the sub it will affect the measurements, so needs to be resolved. Can track this down using a local loopback from line out to line in so don't have to risk damaging anything through feedback howl.


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