M-Audio Transit and REW... a success!

[JohnM]

The level at which REW was calibrated doesn't really matter, that process just allows REW to relate the size of the signal on its input to a corresponding dB SPL level so that it can draw the measurements at the right level on the graph.

The target level adjustment is used to set a reference where the response would lie if there were no resonance contribution from the room. It is something of a best guess, as it is very difficult to separate the contrubutions of the resonances from the underlying output of the speaker being measured. The target level can be set manually, looking at the response and estimating where it should lie, or by letting REW make its best estimate using the "Set Target Level..." option in the Target Settings - REW does it by generating a test signal and measuring its level, which may or may not be more accurate than using your own judgement.

The target level is important because the gains and bandwidths of the correction filters are adjusted to bring the measurement on to the target line. The filters should be countering the effects of the room's resonances, if the target level is too high the filters would be taking out too little of the resonance, if it is too low they take out too much.

This process is a bit too manual at present, I'll be looking at providing further automation and more accurate determination of the contributions of the room's resonances and the best filter settings to counter them in a forthcoming release. That will also include features to automatically determine the settings for filters that shape the response to bring it to a preferred characteristic, such as a desired house curve.

[m-fine]

I think you are missing the point.

You raise or lower the target level to select the best filters to get the subwoofer SHAPE the way you want it with minimal EQ. Once the sub shape is as desired it is a simple matter to adjust the output level on the receiver, EQ, or the sub's amp to set the output level relative to the mains.

[jagman]

m-fine wrote:

I think you are missing the point.

You raise or lower the target level to select the best filters to get the subwoofer SHAPE the way you want it with minimal EQ. Once the sub shape is as desired it is a simple matter to adjust the output level on the receiver, EQ, or the sub's amp to set the output level relative to the mains.

How is that different than creating a house curve manually. In my case, I had the target curve set to 75dB, but added a house curve that deviated from the original. There is a linear 8dB increase (on the log chart) from 60Hz to 30Hz. It then stays flat at 30Hz below that. I've created the shape that I wanted while only using 5 filters. Isn't that the point?

Edit: I forgot to put in a new graph I did last night. It's a little different than the one above. I also moved the seating position back to try and alter the low end and trough at 44 Hz. It did a pretty good job at both:

[m-fine]

I think what Jonh was trying to tell you was to make one house curve and then adjust the level up and down with the target level adjustment. Yes you can change the house curve to achieve the same thing but that is a lot of work. The 75 db target starting point is completely arbitrary at this stage of calibration.

Once you have your filters set, you can put the target level back at 75 (and not have to adjust your house curve) and then adjust the subwoofer level on your electronics until the sweep best matches your target.

[brucek]

Others have tried to make this point, but you haven't really taken the advice to heart, but the fact is, you're using the BFD as a level control for your sub.

A big clue is that your target (even with an exaggerated house curve) doesn't touch the uncorrected response, and at its worst you require -30dB filtering.



brucek

[Wayne A. Pflughaupt]

Hi Krister,

It looks to me like there’s been something of a "breakdown in communication" here.

From what I can see, based on your posts above: (a) you’re trying to avoid any boosting filters, and (b) you have a highly-capable IB system with two 18" drivers, (which you mentioned in your PM to me, but I don’t think here, so this is news to John, brucek et. al.).

From what I understand this is a fairly typical response for an IB, being "weak" on the low end, coupled with excessive upper-bass energy (at least I think that’s correct – the guys at our DIY Subwoofer forum could qualify that).

So - no two ways about it, the levels below 30 Hz needs to be boosted, and the levels above 30 Hz need to be reduced.

Taking to heart all the stuff you’ve no doubt seen about "boosting is bad," you’ve cut everything above 30 Hz to avoid boosting below 30 Hz. But notice in your graph what the others have pointed out, the difference in overall level between your baseline vs. equalized response. Equalized response is nearly 15 dB lower at 35 Hz.

So, what’s going to happen when you fire your full system back up? You’ll find that the subs now sound really weak compared to the mains (you’ve noted that you like the subs 5-10 dB hot). So, you naturally raise the sub level up to compensate.

To get what I’m talking about, mentally move your equalized Target Curve line up to 95 dB, where the unequalized peak at 35 Hz is. That's about where your sub level will end up once you turn them back up to reclaim the lost volume. Of course, you can see that you’ve succeeded in boosting down low, even though you used only cutting filters.

So you see, in the end boosting or cutting is often academic: If you had sagging response below 30 Hz before, and now you don’t, then you’ve boosted up the sagging area. It’s as simple as that. It doesn’t matter which way you accomplished it, by boosting it outright, or by cutting everything else and then raising the sub volume, the end result is the same. Does that make sense?

Now, with that in mind, let’s take a look at REW and its role in equalization. As we’ve established, you’re going to have to re-adjust your sub level after you equalize to get the correct blend with the mains. So all the levels and stuff you set up in REW before generating the sweep tone, that’s merely for the program’s sake. Once you’re done equalizing, your system levels (including the subs) are going to be adjusted up or down depending on whether you want things quiet or blasting.

Therefore, the purpose of the Target Curve is merely for the sake of properly equalizing. That’s why John, brucek and the others have been encouraging you to re-align it up in range of your base response curve. By keeping it low, yes you’ve successfully flattened response, but you’ve also accomplished wholesale gain reduction.

Normally this isn’t a good thing (as I noted under the “Compelled to Excess” heading of the Hard Knee article, near the bottom of the first post). But in your case things may be different (I’ll get to that shortly). The reason brucek and John et. al. have been encouraging you not to cut gain so much with the equalizer is that we’ve seen cases where people cut so much that they didn’t have enough signal left to drive their sub amp! No kidding, they couldn’t even get a reading on the amp’s meters!

So – back to your graph: If flat response all the way down to 15 Hz is what you’re after, you’ve accomplished it, as long as you have enough of a signal left to drive your amps to max (or at least get the volume levels you need). It’s unfortunate that it took cutting 30 dB at 100 Hz to accomplish it, but if that’s the before-EQ response you have to work with with your crossover engaged (it is, right?), then so be it.

As noted, I think the significantly high levels of upper frequency energy you have is not uncommon for an IB. Raising the Target Curve (as would normally be done) will require some boosting below 35 Hz, but the lowest filter setting on the BFD is 20 Hz. So, equalizing “correctly” with a re-adjusted Target Curve may well result in response sagging below 20 Hz, instead of being flat down to 15 like it is now. It’s up to you to decide if that’s acceptable or not.

So, don’t worry about boosting, if you feel you need to raise the Target Curve and try again. It’s only an issue if your sub drivers and amplifiers don’t have enough headroom to handle it. You’ll find out soon enough if that’s the case. Anyway you cut it (no pun intended), when you’re done equalizing, the depressed areas will be raised, so any equalization will place additional demands on your system. Therefore, you have to have enough headroom going in.

Regards,
Wayne

[jagman]

Thank you for the very thorough reply. What you are saying makes sense. I am surprised how much upper bass the IB puts out. I'll try raising the target level and work with the amp gain to find a nice compromise. One of the issues I have is my integrated amp has a non-adjustable crossover at 80Hz. I plan on getting the Sherwood/Newcastle R-972 receiver after it's release, so I will be able to adjust the crossover down a bit. I think I'll end up crossing it over around 60Hz or so... that should help tame the upper bass a bit without the use of EQ. We'll see.

[m-fine]

You could also benefit from a step up in EQ that allows a low shelf filter such as the DCX2496 or a QSC DSP30. If you put a 6-8 db low shelf boost at 20 hz it will level out the region from 30 on down. You can't do much with positioning the IB to solve the 44hz dip but you did say moving the seats helped, and maybe a small boost in that region paired will smaller cuts on either side will flatten that area. You could also setup a low pass at 80-100 on the DCX until you get a receiver with a 60hz crossover option.

That should give you good results with just 3 PEQ's a low shelf and crossover. You may even be able to do it with just 2 PEQ's.

[Wayne A. Pflughaupt]

Another option would be to get an analog pro-audio electronic crossover and install it in front of the Behringer EQ. I think this would work better than shelving. A shelving filter will only drop and then flatten the level by the amount you cut it, not infinitely like a low pass filter will. The crossover will also have level controls to maintain a good signal for the EQ and amps downstream. An ouboard crossover would also allow you to keep an 80-90 Hz setting on your receiver for your main speakers, which you probably want.

The Behringer CX 2310 is probably ideal for you. It has a dedicated subwoofer output that you can set as low as 10 Hz. So you can set in anywhere you need to tame those upper frequencies. You could even cascade the mains low pass on top of it, if needed, for additional upper bass signal reduction. You can find the 2310 for pocket change on eBay.

Regards,
Wayne

[jagman]

Thanks guys... that may do the trick. Some major networking issues came up at work today so this will have to go on the back burner until next week. I'll think about it and keep all of the recommended equipment in mind. All of you have been very helpful.