Behringer DEQ 2496 as an electronic bass trap?

[Arkytype]

Those familiar with the Behringer DEQ 2496 know it is an audio "Swiss Army Knife" with multiple functions. The built-in FeedBack Destroyer (FBD) function may not be the first feature an owner would use in his or her listening room. But it might be one of the most useful.

I discovered the FBD's usefulness after deciding to construct some diaphragmatic bass absorbers to tame some of my room's Eigenmodes. Before buying the materials, I decided to try an experiment to accomplish the same thing electronically.

A Bruel & Kjaer 4133 mike was placed at the listening position and the output was connected to my Ivie IE-30A RTA. The line level output of the Ivie fed an AUX input of my preamp via a "Y" phono adapter.

Since I was only interested in notching out the room modes below 400 Hz or so, I disconnected the squawker and tweeter drivers in my Klipschorns. Starting with the preamp balance control fully counter clockwise, I slowly raised the volume until feedback occured. The Ivie and the DEQ2496 (set to RTA mode) showed a spike at 80 Hz (the floor to ceiling modal frequency). Increasing the volume further brought another mode to life.

At this point, I decided to activate five of the ten FBD filters (there are ten per channel) and let the DEQ 2496 automatically do its "search and destroy" thing. In a matter of a few seconds it had found and notched out four offending room modes!! The great thing about the FBD filters is that they are 1/60 of an octave wide which translates to "inaudible" in their action.

Of course I wasn't content to just sit down and listen to music. I decided to set the FBD filters for manual mode and spent the next half hour accomplishing about the same thing that had been done automatically in a few seconds!!

This is a work in progress. The next step is to place the mike in several locations throughout the room and see if the results change. Since I'm educated beyond my intelligence, doesn't it follow that if the loudspeaker doesn't excite the room modes in the first place, the modes won't be an issue?

Having an open mike and loudspeaker in the sme room can be an invitation to blown fuses, ruptured cones or loss of your lease! Be careful.

Any thoughts or suggestions are welcome.

Lee

[Colin]

don't the bass traps help with the nulls - how can the DEQ fill those in?

(still haven't been able to spend much time playing with mine...)

[mikebse2a3]

This is a work in progress. The next step is to place the mike in several locations throughout the room and see if the results change. Since I'm educated beyond my intelligence, doesn't it follow that if the loudspeaker doesn't excite the room modes in the first place, the modes won't be an issue?

Having an open mike and loudspeaker in the sme room can be an invitation to blown fuses, ruptured cones or loss of your lease! Be careful.

Any thoughts or suggestions are welcome.

Lee

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Thanks and very interesting Lee

I was hesitant to use the FBD feature because of the chance for damage once feedback started so how loud did it get and did the FBD control it quick enough or did you lower the volume quickly before damage could occur?

When I used the (PEQ)Parametric module it took like you said about 30 minutes for me to test and create a couple of filters for two peaks in my room. What I really like about the Behringer was how you can create a filter then just roll it up or down the frequency range of interest till you get the exact correction by tweeking the level and bandwith of the filter while referring back to the RTA to see how good a correction you've done.

Another thing I noticed was my just opening or closing the door to my room shifted the center peak frequency by about 10Hz from 107Hz to 100Hz on one of the room mode peaks that I have. So I created two different PEQ curves and saved them to memory so when I want to listen with the door closed or open the correction fits the needs of the two different conditions. I love the versatility of this Behringer!

I had a really sharp null at 77.8Hz did you spot any sharp nulls?

I believe this null corresponds to the MIC height I used which is my ear level when seated in my listening chair and is the ceiling to floor room mode I believe which I'll check out later when I have more time. If this proves to be the case then I believe changing seating height wouldn't help because it will probably just cause the frequency where this occures to shift slightly. I'm thinking for this null somekind of bass trap or diaphragmatic panel absorber used above the listening position would help.

My experience so far is moving the MIC a foot or two makes a difference in the frequencies/level where the correction filters of the (PEQ) should be applied for the room modes just like opening a door changes things. Luckily I listen in just one position so I'm setting things to sound best from that location. If I had to deal with different listening positions then I guess I would create several curves to match those positions or try some kind of averaging if there are going to be several listeners at one time but I have always preferred to listen from the sweet spot.

As far as your question:

"Since I'm educated beyond my intelligence, doesn't it follow that if the loudspeaker doesn't excite the room modes in the first place, the modes won't be an issue?"

I believe your right and I guess some large Dipole Speakers such as a Electrostatic might have an advantage by having a null in their response at there sides which might help mitigate floor to ceiling and sidewall to sidewall modes. But so far any rooms I have had there where modes that needed to be delt with.

As Lee said any thoughts are appreciated.

mike

[mikebse2a3]

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On 2/3/2005 11:08:07 PM Colin wrote:

don't the bass traps help with the nulls - how can the DEQ fill those in?

(still haven't been able to spend much time playing with mine...)

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Colin I wasn't sure if you saw my experience with a null in the other Behringer Thread so here it is.

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NOW for the Null in Response I mentioned earlier at (71Hz & 80Hz & 89Hz):

I created a Peak filter curve to try and counter this Null

I choose center frequency of (77.8Hz)

The Bandwidth chosen was (1/8 octave)

The Level chosen was (+8db)

The results of trying to bring the Sharp Null in the response up was less than an increase of (+.5db) for a filter calling for a (+8db boost). This goes to show if using an EQ and an adjustment to a trough/null in the response shows no improvement its best to leave it alone as far as using the EQ adjustments are concerned.

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I believe sharp nulls such as this are not correctable by the Behringer(or any EQ) as confirmed by only a (+.5db) improvement for a (+8db) boost from the Behringer but should be dealt with by Bass Traps or other acoustical devices designed for this purpose and placed in the correct location. This small increase in level seems to me to be a good indicator of when one would not want to use the Behringer for such a problem.

mike

[Daddy Dee]

Lee,

Sounds interesting. was wondering how you'd describe the difference with what you hear, or don't hear with your ears, after adjustments.

wow, zzounds.com has these units for $249 B-stock

[76scalas]

Need some help here! The Behringer manual kinda sucks. When I run auto EQ it looks like this. Does this make sense?

On page 2 of the auto eq menu where should I set "max"?

On page 3 of the auto eq menu where should I set "max" and max span?

When do I push the "done" button?

Thanks!

Keith

[Arkytype]

Mike,

Are you saying there is a null centered around 77.8 Hz after running the FBD in AUTO? If so, then that's normal and, as you suggested, is the floor to ceiling frequency. Frequency of mode = 565 Ft/Sec//8 feet= 70.6 Hz mas o menos.

If you are measuring a null at 77.8 Hz without any filter engaged, try moving the mike up or down or left or right. Peaks are a lot more common than nulls.

Colin,

The general rule of thumb (or ear) is that you can't fill a hole or notch in the response. Besides, you can't hear them anyway.

Keith,

Your AUTO EQ settings don't look too bad. You've wisely disabled the lower frequencies in AUTO mode.

Try miking about a meter from each loudspeaker and don't forget to mute the one not being EQ'd. "Flat" measured response at the listening position is usually too bright. Using one meter measurement distance will allow the woofer, squawker and tweeter to meld their outputs and will also minimize room contributions. Get the loudspeaker "flat" at one meter, and it'll be 'bout right ten or fifteen feet away.

Daddy Dee,

That a good price. FWIW, Behringer has updated the firmware for the DEQ2496. Check your manual to see how to determine your unit's version. You can download and update your unit using the MIDI port.

Lee

[mikebse2a3]

Mike,

Are you saying there is a null centered around 77.8 Hz after running the FBD in AUTO? If so, then that's normal and, as you suggested, is the floor to ceiling frequency. Frequency of mode = 565 Ft/Sec//8 feet= 70.6 Hz mas o menos.

If you are measuring a null at 77.8 Hz without any filter engaged, try moving the mike up or down or left or right. Peaks are a lot more common than nulls.

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Thanks for the reply Lee

Yes the Null was measured without any GEQ or PEQ activated. I was looking at the raw curve to decide where to start designing the PEQ Parametric Filters I was going to use to correct the two peaks in response I had identified and to see what would happen to a Null I saw if I tried to counter it with the Behringer like some had been asking about.

I do believe this will turn out to be related to the Height(which is my actual listening Height) of the MIC position I was using and is a result of a vertical room mode. So when I get a good day to spend some time at it I'll check this out more to see if this is actually whats happening.

My room is on the small side and my listening seat is off axis of the Khorns so I chose to just use my listening position for MIC location and In my particular situation it seems to be working very good. I do intend to try the method you suggested about using a 1 meter position above 400Hz and then moving back to the listening location for adjustments below 400Hz when I can get a good day to spend some time at it.

LEE I haven't tried the FBD option. I was hesitant to use the FBD feature because of the chance for damage once feedback started so how loud did it get and did the FBD control it quick enough or did you lower the volume quickly before damage could occur?

Thanks mike

[artto]

Sorry, but this thread gets the BIG YELLOW BUTTON. Colin's question hits it right on the head. Glad to see someone starting to understand what room modes are (not intended as any kind of insult Colin).

You cannot correct room modes electronically!!!!! You might be able to "compensate", to some extent, but just like any kind of EQ, its only good for one, and ONLY one set of conditions, in one location. It does NOT smooth out or eliminate room modes. These effects are strictly related to the dimensions of the room itself, and more specifically, applied to "simple" shaped rooms and those whose dimensions are shorter than that of the wavelengths of the lowest frequencies being produced. Any attempt by anyone to do otherwise, electronically, simply demonstrates that they do not yet understand the underlying physics principals at work here.

Sorry if all this sounds a bit harsh, but there have been a number of posts recently regarding this subject, on its own, or related to other topics. I'm probably as responsible as anyone for bringing this subject up a long time ago. And I know it takes a long time for most to comprehend what is going on with a subject this (me included).

[mikebse2a3]

artto said:

You cannot correct room modes electronically!!!!! You might be able to "compensate", to some extent, but just like any kind of EQ, its only good for one, and ONLY one set of conditions, in one location. It does NOT smooth out or eliminate room modes. These effects are strictly related to the dimensions of the room itself, and more specifically, applied to "simple" shaped rooms and those whose dimensions are shorter than that of the wavelengths of the lowest frequencies being produced.

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Yes I have to agree with arrto I do not consider the Behringer as an Electronic Bass Trap and would hate for anyone to get the wrong idea about using it for that purpose.

To be honest I hadn't really paid attention to the Threads Title. I was mostly observing what Lee was acomplishing with the EQ which as arrto said I believe would better be described as compensating for the room mode problems at the listeners location and not traping them electronically.

What Lee has accomplished is still a VERY IMPORTANT ACHIEVEMENT in Lee's situation(I don't intend to put words in Lee's mouth and I would like to hear what he thinks but I'm pretty confident that he has achieved a very worth while improvement in tonal balance and clarity from his listening position by doing this). I know this to be true in my on listening room.

I would like to make clear for this thread and for the other Behringer thread in Mods section. I definitly would advocate room treatment as well as bass traps(properly installed) to deal with acoustical problems as the first thing to do when possible. I also want to make it clear that I listen from one location but if I was interested in listening from other locations I would run a different correction EQ Setting which could easly be stored in the Behringer's memory. If a person has multiple listeners say in a home theater situation then (maybe) an average of these curves would be a good compromise. I agree with arrto that we cannot eleminate room modes with an EQ but if a room mode is causing an audible boost in a certain frequency range at our listening position then the EQ if adjusted properly (can audibly improve that situation in some instances) but as you said the user must decide if the EQ adjustments are acceptable at other listening locations if you have multiple listeners.

Look I wish we all could have correctly sized and properly acoustically treated rooms but for the large majority of us thats not possible for various reasons. I have had my Khorns in (3) different rooms since I've owned them and heard Khorns in a couple of other situations so I do know how much the sound we hear is determined by the room our speakers are in. My point in starting the Behringer thread in the MODs section was a curosity that in difficult or limited room situations and especially if after reasonable room treatments had been used that maybe one of the new Digital EQUALIZER might be worth while and anyone who has listened to my system has noticed the improvements very easly.

Nothing is perfect and I would hate to be responsible for anyone buying the Behringer and not being satisfied thats one reason why I suggested getting a trial period before buying(Musician Friends in my area gave me 30day trail but it only took (1)day for me to know in my situation that I would be keeping it). There is a learning curve to using the Behringer and no one claims it will cure everything but so many people are swapping and buying expensive equipment trying to fix their problems that IMHO they actually would be better off dealt with by acoustical treatments(Often Expensive at Times) and if necessary with something of the quality of the Behringer EQ when used properly. Heck the RTA feature alone is worth the cost to me.

mike

[mikebse2a3]

arrto speaking of room modes said:

These effects are strictly related to the dimensions of the room itself, and more specifically, applied to "simple" shaped rooms and those whose dimensions are shorter than that of the wavelengths of the lowest frequencies being produced.

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Even "odd" shaped rooms that have dimensions that are shorter than that of the lowest frequencies wavelengths being reproduced will still exhibit room modes but they are more unpredictable in their distribution in the room.

mike