Can the BFD fix this? (1 Viewer)

[Ranga]

Finally got the BFD yesterday. Here is the SPL graph for a LARGE setting (with no sub) and a SMALL (80Hz Xover) setting with sub.
My room dimensions are 24'x12'x10'. Here is a pic on my HT setup.
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It looks like I have modes at 47Hz and 94Hz and that corresponds to the peaks in the 45-55Hz and 90-100Hz range with or without the sub.
Before I start experimenting with the BFD, do you have any suggestions regarding speaker placement, sub volume level setting etc..?
Of course, if the experts - Wayne, Sonnie, brucek and others can comment on my graph, it would be great.
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Ranga

 

[John Desmond]

Ranga: the graph and pic don't show up

 

[Ranga]

I am not sure if Yahoo allow cross-posting of links. I had a problem with webshots. Just right-click on the red x, select properties, copy the URL, and paste it into the Address window, go view it, then come back here. Then, it will show up.

I may have to get my own website.

 

[Ranga]

Are you able to view the pics now?

 

[Wayne A. Pflughaupt]

What are the “Metered/Compensated SLP” readings (the one that brick-walls at 36Hz)?

I have some concerns about the sub being right next to the seat. It might be distracting. However, there is an upside: With your seat against the same wall as the sub, you will realize markedly higher SPL levels, which can be helpful in some instances. If it must be there, the corner away from the kitchen is best.

Which brings us back to the readings. They should be taken at the seat location. IF these readings were taken from some other location, you will need new ones when you EQ.

To answer your question, I’ve yet to see a room the BFD couldn’t improve.

It would help to know what the cubic ft. of the kitchen/family room is, to calculate a house curve. Since they appear to open to each other, it’s all space the sub has to fill. It would also be helpful to know what sub you have, how much power, etc.

Regards,

Wayne A. Pflughaupt

 

[Ranga]

Wayne

Here is the info that you requested.

It would also be helpful to know what sub you have, how much power, etc.

My sub is an SVS 25-31PC. My mains are JM Reynaud Twins which go down to 55Hz (-3db) although in this room, they seem to go a bit lower thanks to the room modes.

Ranga

 

[brucek]

Ranga,
I'd like to bring up a couple of points regarding the graph.
Generally, if you're trying to equalize a sub, you'll "only" turn on your sub without any other speakers, then with the processor in stereo and speakers to small, (so your sub is fed its normal low passed signal), perform a frequency response from your normal listening position with any EQ unit in bypassed mode.
Correct for the inadequacies of your SPL meter by whatever means you like and place only those "corrected" unequalized values on your graph. This lets you see what the room and the sub look like unequalized and will give you valuable information on equalization to come later.
The vertical scaling of the graph should not start at zero dB. Although debatable, the vertical scaling should show at least the max and significant min dBSPL readings of the sub. It could be 45dB to 105dB for instance if your sub readings where from 55dB to 95dB. A smaller scaling could be used, and would accentuate the problems, sometimes a good thing - either way, the scale should not start at zero. You might try the Excel graphs from Sonnies site.
You're checking a subs response and perhaps its integration after crossover. In that regard, 20Hz to 160Hz would be perfect for horizontal scaling.
Once you've decided from your single corrected unequalized frequency response curve where you want to add equalization - enter some equalization filters and enable the equalizer in the sub path. Take a new set of readings from 20Hz to 160Hz. Correct for the inadequacies of your SPL meter by whatever means you like and place only those corrected equalized values on your graph.
Uncorrected SPL readings are a confusion factor and shouldn't be put on a graph. The two graphs lines could be labelled "equalized response" and "unequalized response". I've seen so many people lately asking what other peoples graph legends mean..
Now, since during this entire process you haven't disturbed any volume control settings on the sub or processor after initial setup, the two graphs should "lay" right on top of each other and the only difference will be the effect of your EQ filters. Now you can see what you're really doing with your EQ.
If you disturb those volume settings or if you go back another day to play with the filters and do some graphing, make sure you re-do the unequalized readings again, so you'll have the reference.
That said, it doesn't look like you'll have any problem removing those peaks.
brucek

 

[Ranga]

brucek

That was very informative..thanks.

The reason I listed the freq response of both the fronts and the fronts with sub is to highlight what seem to be room modes. I was wondering if I should experiment with the mains placement to reduce the peaks before applying the EQ.

The vertical scaling of the graph should not start at zero dB. Although debatable, the vertical scaling should show at least the max and significant min dBSPL readings of the sub. It could be 45dB to 105dB for instance if your sub readings where from 55dB to 95dB.

This brings to me to another question. I played a 1K tone calibrated at 70db to set the volume on my pre-amp. Shouldn't I also be setting the volume on my sub's amp to establish a baseline db reading to compare with the other frequencies?

I believe that Sonnie did mention this in one of his posts.

Thanks..

Ranga

 

[brucek]

Ranga,

Well, there certainly is a sequence of setting up the levels for the processor and sub, given the fact that you're now going to place a level sensitive digital device between the two. You should do this setup before you start your filter setup. You can read about that on Sonnies site.

Basically you need to get the "sub out" level established from your processor for the optimum level going into the BFD without overdriving it. Once that is set, the wholesale level of your sub amp can be set to whatever you like .i.e. 10dB above mains.

Once you've established that, it's not that critical what volume you use on your processor to do a simple frequency response for the purpose of setting up your filters. Play a tone at 50Hz and adjust the volume of your processor so you read 85dB or so at your listening position. Then don't touch your volume control until your finished.

brucek