# Newbie Rew Assist



## Evolvo (Mar 6, 2009)

First off the letter after o on my keyboard doesn't work so if you see it missing thats why. Anyway I just setu rew and I have a grah, but the subwoofer seems to be rolling off quite badly around 45hz. When I go to the eq anel and try to match resonse to target It only returns like 3 or 4 filter values for my BFD. All the values are above 45 hz becaue it won't give values below target db of 75db's, so since all frequencies under 45 hz are close to 60db it won't give values. I think it said it was to rotect driver. Does this mean that the subwoofer amlifier is to bad and can't be equed or should I just set the target value around 64db so that I get eq filters for most of the curve.

Also should the target db be the same as the calibration value used in the check levels section, in my case it was 75db so both match, but not sure if they have too.

Also how far off DB wise should any eq adjustment be in order to not create distortion or cause roblems.


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

Welcome to the Forum, Evolvo!

What kind of subwoofer are you using? What measurement mic and calibration file? With this information perhaps we can help out.

Regards,
Wayne


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## Evolvo (Mar 6, 2009)

I have a Tuba HT subwoofer from bill fitzmaurice. It's a diy folded horn design. The graph is showing the sub being used with a 1999 JBL 75 watt rms amp I pulled out of a JBL 125a 8" subwoofer. It's a horn loaded design so I can use a low watt rms amp cause sub is so efficient. I do not intend to keep this week amp as apart of this sub, but I would just like to know the questions from the post above incase I run into problems like this in the future. I'm actually using an behringer EP2500 for the most part to power this sub which has a flatter curve and the db only move about 10db from 20 to 80hz, but I stilll slightly run into the problems above even with the behringer. Not as much because the difference is not 25db. But I would like to know what I should do for the above problem. 

Also I do not have my BFD yet, I'm just taking measurements now to figure out how to use everything before I get it in a few days.


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## JohnM (Apr 11, 2006)

REW will not suggest filters in an area that appears to be below the lower limit of the sub. That may in part be because the target level is higher than it should be, and the target shape (particularly the LF Cutoff) need adjusting to better match the natural response of the sub. That doesn't stop you manually entering filters to see what effect they would have on the response, but that response does seem to roll off quite early - applying a lot of boost would risk clipping the amplifier and/or over-driving the drive unit.


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

Evolvo said:


> The graph is showing the sub being used with a 1999 JBL 75 watt rms amp I pulled out of a JBL 125a 8" subwoofer.
> 
> I'm actually using an behringer EP2500 for the most part to power this sub which has a flatter curve and the db only move about 10db from 20 to 80hz...


Since you’re getting better results from the EP2500, that suggests that perhaps the JBL amp had a built-in high pass filter to protect it’s little 8” driver. There will be no problem equalizing response within a 10 dB window.

Regards,
Wayne


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## Evolvo (Mar 6, 2009)

What do you mean by I may be setting the target too low. My question of does the target level have to match the set level in the preferences menu was not answered. Does my target level have to be the same as my set levels measurement? 

Also can the target level be whatever you want it to be?

Also Also how far off DB wise should any eq adjustment be in order to not create distortion or cause roblems.

Could someone please answer the questions listed in OP. I learn best when people answer the questions I ask directly and point for point. You gave responses but I don't fully understand the response cause the initial question which was created so I would understand what was going on was never answered, so my basis to understand your response is somewhat hindered. 

Although I will take a wild stab in the dark. I believe that the the set levels doesn't really effect what the target level should be. From what it sounds like the target level should be within 10 DB's of the upper highest DB on the frequency curve. It also sounds like the target level can be adjustable so that the target curve is within a certain DB range of the frequency curve, in which in this case I would have to lower the target curve down to 63 or 64 db so that the 20hz dB's would be close to matching, but doing this because of the 25 db swing in one frequency to the next might cause over excursion of the driver. What I would say is that this driver can handle high db's at low frequencies, so I don't think I would damage the driver, because the curve from the ep 2500 looks great and high. So my only real concern is if adjusting the eq DB's with a higher than 10db swing would cause distortion or problems as far as listening goes.

I have to say it's pretty awesome to have the author of the program chime in. Help doesn't get much better than that.

Thank You.


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## Evolvo (Mar 6, 2009)

I do not own the ep 2500 and will have to give it back soon so may have to use the jbl amp for a while, that is why I'm asking about it and because I still don't quite understand a few things. 

Thanks again for the help.


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

Evolvo said:


> What do you mean by I may be setting the target too low. My question of does the target level have to match the set level in the preferences menu was not answered. Does my target level have to be the same as my set levels measurement?
> 
> Also can the target level be whatever you want it to be?


Ideally, the Target should approximately center between the measurement extremities (i.e., the worst peaks and troughs). Despite the initial calibration process, it’s not uncommon for the actual measurement to end up being largely above or below the Target. The Target can (and should) be re-aligned in the Target Settings function before equalizing.




> Also Also how far off DB wise should any eq adjustment be in order to not create distortion or cause roblems.


I have no idea what you mean about the EQing being “off.” Any potential distortion or “problems” are equal parts the amount (severity) of the equalization and the capabilities of the subwoofer. As a couple of extreme examples, if you have twelve 18-inch subs powered by 30,000 watts you can probably get away with any kind of equalization you want to throw at it. But if your sub is a 50-watt 8-incher, you’re probably limited to mild EQ at best, as it has limited output and headroom. Make sense?




> Could someone please answer the questions listed in OP. I learn best when people answer the questions I ask directly and point for point. You gave responses but I don't understand the response cause the initial question which was created so I would understand what was going on was never answered, so I have no basis to understand the your response.


You repeated all those questions in your last post, which I’ve answered here. Except this one, which was answered in Post #5:


> Does this mean that the subwoofer amlifier is to bad and can't be equed


Regards,
Wayne


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## Evolvo (Mar 6, 2009)

Thank you that helped alot. What I meant in the questions you didn't understand was when you use the BFD to adjust the DB's at any given frequency, would it be bad if you say increased the DB's 15db's at 30 hz because you have a massive dip in the eq curve. So I'm wondering would this cause any kind of distortion with the increase in sound at that frequency. 

It sounds like as long as my amp is powerful enough and there is still head room left I'm good, as long as the sub can handle it. You say that a 10db was fine, is that considered around the limit you would want to swing any particular frequency.


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

> What I meant in the questions you didn't understand was when you use the BFD to adjust the DB's at any given frequency, would it be bad if you say increased the DB's 15db's at 30 hz because you have a massive dip in the eq curve.


Again, “it depends.” Dips that severe are usually nulls, and nulls don’t respond to equalization. It’s a waste of power and headroom trying to equalize an area that doesn’t result in an improvement. Severe dips or troughs in response should be addressed by re-locating the sub, if that’s an option.

However, if you’re talking about boosting to deal with the droop in response at the low end that your graphs shows, the “can the sub /amp take it” mentioned previously comes into play.

I Googled you sub and it looks like it should have no problem getting response out to 20 Hz or lower. The EP2500 has high pass filters that will roll out the low end, so make sure those are turned off.

Regards,
Wayne


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## Evolvo (Mar 6, 2009)

If you use a radio shack meter with a .cal file loaded into the mic/meter preferences do you still need to calibrate the microphone on the main rew page.


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

The SPL meter calibration file is only needed if you’re going to use it to take the measurements. If you’re going to use a separate mic for the measurements, a calibration file for that mic is what’s needed instead. :T

Regards,
Wayne


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## JohnM (Apr 11, 2006)

You do still need to calibrate the REW SPL meter reading though, so that REW can show the graphs at the correct SPL levels.


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## Evolvo (Mar 6, 2009)

Ok I have some measurements and was wondering how do they look. I have a pic of how the curve looked before equing and one of how it looked after a 6db equed house curve was applied. I notice I have a 6db dip between 58 and 64db will this have much of an effect. Also overall does it look like the filters did a good job.


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## Evolvo (Mar 6, 2009)

Here they go, let me know what you think.


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## JohnM (Apr 11, 2006)

That looks good, I wouldn't worry about the little wiggle around 60Hz.


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