# Any way to measure sub excursion?



## VERTIGGO (Feb 20, 2009)

Hello, I've been testing my first build for a few weeks now, and I have a BFD, Reckhorn B1 and EP2500. These all have the capability to manage the subsonic range, but I'm not sure how to be sure. When I measure in REW it is measuring the SPL which includes ports and room gain, so I'm not sure where my actual High-Pass is working at. I recently bottomed out or came close playing some Daft Punk with a house curve, even though the B1 subsonic was around 15-20Hz, and I don't know a way to keep that from happening since it's different with every media and config.

What am I supposed to do to make sure I don't bottom out; is there a way to measure and or simply limit the signal sent at each frequency?


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## brucek (Apr 11, 2006)

> is there a way to measure


You can certainly use REW to measure the frequency response of the BFD and Reckhorn.
First measure a loopback cable from line-out to line-in of your soundcard to be sure you get a flat straight line response. Then simply include the BFD and Reckhorn in that loop and take a response measure.

brucek


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

> I have a BFD, Reckhorn B1 and EP2500. These all have the capability to manage the subsonic range...


Not really. The BFD has no subsonic filter. The EP2500’s lowest setting is 30 Hz. I doubt you want that, even if you could measure it.

That leaves the Reckhorn. You might measure it with REW using the method brucek mentioned, and mark the dial for increments between 10-25 Hz to give you a better idea of where it’s working.

In the end this may not do much for you, because there are so many variables. A subsonic filter won’t necessarily “save the day” because its rated slope assumes a flat incoming signal. Problem is, you’re seldom feeding the system a flat signal. 

For instance, say you have a 20 Hz high pass filter. A 20 Hz one-octave filter from an equalizer boosted 12 dB will essentially blow out the high pass filter and easily extend its rollout point a full half-octave (to 15 Hz).

Don’t think you’re out of the woods if you don’t use any boosting filters. Cutting filters can also be used to extend a sub’s acoustic response. Basically, anything you do with an equalizer to make your sub “dig deeper” will override a high pass filter to a certain extent.

Even if you don’t use an equalizer to extend response, you still have the issue of equalization from the program material. The movie studios mix their programming on systems that are tailored to the X curve, which rolls out the bass response below _63 Hz_ at 3 db/octave. That’s going to put response at their dubbing stage down 5 dB at 20 Hz. How do you think they overcome that if the producer wants some room-shaking bass? They equalize, of course, to overcome the X curve. Take that DVD to a home system that’s flat below 63 Hz you end up with another 5 dB of boost at 20 Hz for "free," on top of whatever they dialed in. 

Basically, it looks like you possibly don’t have enough headroom. Short of upgrading your sub, my suggestion is to replay that Daft Punk CD and dial up the Reckhorn’s high pass filter until the sub no longer bottoms out. 

Regards,
Wayne


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## VERTIGGO (Feb 20, 2009)

Thanks for the help! What I meant by the Ep2500 and BFD, is that I had been using them in concert (30Hz HPF and BFD 20Hz boost) to create a roll-off at 17Hz. The real issue, however, is I don't know exactly what frequency was bottoming it out, since the Reckhorn seems to all a bit more subsonic through than the aforementioned method, and it could be just sending too much 5Hz or 10Hz or whatever, and I just need a more precise cutoff point. BTW the test was much higher than comfortable; I'm not complaining!

I just don't know exactly what the driver can handle, so I can't create the correct roll-off until I know where it should be. Am I supposed to just look at the WinISD model and treat it literally for my HPF; is that the only way to know what you should expect it to handle?


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

> What I meant by the Ep2500 and BFD, is that I had been using them in concert (30Hz HPF and BFD 20Hz boost) to create a roll-off at 17Hz.


It would require a pretty wide filter with a substantial boost to pull that off. 




> I just need a more precise cutoff point.


Judging from the graphs on your build thread, it looks like your sub is “done” at about 20 Hz. The 20 Hz BFD filter is essentially over-riding the EP’s subsonic filter, so the actual boost you’re getting down low will be substantially less than what the BFD indicates. Still, you have no way of predicting (or measuring) what the BFD is actually doing down there. It will depend on the width of the filter and the level of boost, none of which you can effectively measure. If it ends up that you’re actually electronically boosting response below 20 Hz – well, I understand that’s a big no-no with a ported sub that’s tuned to 19-22 Hz. (You aren’t supposed to boost below the port tuning point.)

Aside from that – and I hope I don’t come off as a jerk here - but it strikes me as silly to use the EP and BFD to “manufacture” an unpredictable high pass when you have the Reckhorn. I suggest using REW on the B1 to determine where it establishes a 20 Hz HP and go with that, since 20 Hz is the in-room limitation of your sub. That plus eliminating that stuff with the EP and BFD should take care of the problem.

I have a few more thoughts that I’ll post on your build thread (they’d be off-topic here).

Regards,
Wayne


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