House Curve - Properly Implementing in REW

[zorax2]

I'm trying to fully understand how to best implement a house curve within REW and then use REW to properly equalize the subs response.

First, I've followed Bruce's suggestions:

brucek wrote:

Simply put a simple housecurve file into the REW directory. Call it housecurve.txt
A simple one that rises from 80Hz by 5dB until it hits 30Hz would have two entries in the file.
30 5.0
80 0.0
Start REW, select FILE and Load Housecurve. That's it. It has nothing to do with the RadioShack calibration file (other than both files are stored in the REW directory)....
Once the housecurve is loaded you'll see it in the target response.
brucek

The following is my unfiltered response with a standard curve.

zoraxunfiltered.jpg

Now assume the blue line represents a house curve rather than the standard response. Can I simply use REW to move the entire curve up or down within REW using the "Target" control on the lower right side until it intersects nicely (more peaks than dips) with my measured sub response? In this particular case, moving the start of the curve down from its present start of about 75 dB down to about 70 dB would result in the curve more closely intersecting the dips between 40 and 50 Hz. I would then have a lot of cuts to make but no boosting needed.

If so, I would then assume that I could use the "Find Peaks" and "Assign Filters" to adjust my subs response to follow the house curve. Finally, I would export the filters to the BFD and now adjust the volume control (not the trim control on receiver) on my subwoofer to equalize the sound level between speakers to compensate for the cuts made during equalization.

Is this the correct way to implement the house curve?

[Sonnie]

I believe you are on the right track.

I would probably increase my measurement volume up so that my response line is higher up on the graph. IOW's try to get that dip between 40-50hz to where it will be at 80hz after you have ran your mesurement sweep. That would be about 8db louder. Then move your target line with the house curve loaded to 80db and bring everything else down to there. You'll have a little hump below 20hz... but it may sound pretty good. Or you could widen the bw on the filter at 23hz and bring some of that below 20hz down, if you wanted to.

It also want hurt to boost part of an area that was cut. You are ultimately not boosting your response in this case... only fine tuning the cut.

[zorax2]

Sonnie wrote:

I would probably increase my measurement volume up so that my response line is higher up on the graph.

Can this be done either way with the same end result? For example,

A) Increase the measurement volume to fit the house curve, make filter adjustments, adjust the trim control on the amp or receiver to equalize the volume of the speakers (i.e. - calibrate the system at 75 dB or 80 dB).

B) Use the Target Level control to move the house curve to fit the originally measured response, make filter adjustments, adjust the trim control on the amp or receiver to equalize the volume of the speakers (i.e. - calibrate the system at 75 dB or 80 dB).

I ask this in case there would be issues beyond my understanding and secondly to conform with the help files in REW. I would think it would be easiest if there was a set process to implement house curves in REW shown in the help files to aid new users. Creating and importing the house curves is easy and well explained. The more difficult issue in my opinion is how to properly implement the house curve.

The REW help indicates that a user should calibrate at 75 dB. If this measurement should be done at 80 or 85 dB, the help file should be changed. While I'm getting to better understand REW, I'm trying to help make the whole process easier for the next person by trying to indentify the areas where I had trouble or didn't understand why something was done in a certain way.

Sonnie wrote:

It also want hurt to boost part of an area that was cut. You are ultimately not boosting your response in this case... only fine tuning the cut.

Wow - I didn't realize that was the case. Perhaps this tidbit of information can also be added to the help files in REW as it is an extremely beneficial piece of knowledge. I had read all these things about not boosting frequency response for a variety of reasons and had not realized that a boost could be properly used in this circumstance (i.e. - boosting an area of frequency that had been cut to a point no higher than it had started.)

Great information! It'll be nice to get back into REW and do some more tweaking in learning. What a powerful tool and awesome program!

[Sonnie]

I've adjusted the target response both ways as you described and did not get any differences in responses so I don't see why it would really matter which method you used. After you have set your filters and obtained the response you so desire... then you would adjust the volume on your sub to level with your mains. Do not use the sub gain on our recevier or preamp because that has to be set accordingly for the BFD input (in Bypass mode on the BFD).

John states in the help files "around 75db" and I wanna say he may change this to 80db in the next update... he may chime in and correct me on this if different. 80db is easier to match on the SPL meter and also helps prevent the meter needle from pegging out so much one way or the other during the sweep. I've actually measured at 70db, 75db, 80db and 90db and all of my response came out within .5db of each other. Even numbers are easier to use on the SPL meter since it's centered on the db level you set it for and all of those levels are in 10db increments beginning at 60db.

Now... someone may enlighten me too, if there is the possibility of problems with this. I just haven't experienced any of them.


I think it would be logical and technically speaking to say that boosting in this method is perfectly fine. In practice you are simply eliminating some of the cut that you applied and don't want.

I boost my response anyway in certain areas, always have, and again, have never had problems. I suppose my sub amp is okay with it. Well, I take that back... I did experience a problem once when my HT was shared with my great room which had a lot of large openings into other rooms. I tried to boost an area... didn't move... boosted it more and still didn't move and on top of that my sub was making some unwanted noise at that frequency when testing. The amp was trying to make the sub do something it just couldn't do. But since I've been in my HT room, using two different subs, I've not had any problems boosting the frequencies I have boosted. I've even boosted some frequencies between 20-25hz by as much as 6db... just piddling.

[zorax2]

I think it would be very helpful for John to suggest 80 dB as the common set point in the help files. After getting the suggestion from someone else on Home Theater Shack to try this, I also found the 80 dB setting much easier to use.

First, it solved my problem with the "Set Input Volume" on REW maxing out which required changing the Radio Shack SPL level from the 80 dB setting to 70 dB. I think there is maybe a quirk in REW whereas you are calibrating at 75 dB (the 80 dB setting minus 5 dB), you run a greater chance of the calibration not working. Whereas if you start the calibration at 80 dB on the Radio Shack meter, the meter has more room both plus and minus to measure within that scale. Hopefully my explanation of this quirk makes sense. As I was learning to use REW, I ran into this problems a number of times frustrating me. Had I started with all the settings at 80 dB, I don't think I would have run into that problem.

Second, the 80 dB setting, as you have mentioned, is so much easier to read with the needle centered. In my case, all my computer cables to the soundcard, receiver, and BFD are short with the only long cable being the one to the Radio Shack meter at my listening position. It is sure nice to simply see the needle centered at 80 dB as opposed to running back and forth while adjusting to make sure the needle centered at 75 dB.

I'm glad to hear you had already tried calibrating at different volumes. Again, from a newbie's perspective, it's nice to understand what works and doesn't and most importantly to get a consistent methodology for everyone to follow for easy results. It seems a number of folks over at AVS were in fear of the BFD / REW setup - the more clear and concise the instructions we can post, the easier it will be to get folks using either of the BFD equalizers or the SMS-1 to use John's awesome product.