Hz vs Db graph.

[troostj]

Hi,

Im a noob at this stuff, just graphed my sub. I cant moove it from its location.. does this graph look pretty bad? Do I definely need an equalizer for the LFE channel?

[white_shadow]

Do you mind me asking what program you used and by which methods you attained your frequency response plot.

[troostj]

Sure,

I used a cd called subtunez.. Basically it had tones from 15Hz to 160Hz.. (plays constant tones at each track.)

I used a radio shack meter and compensated for the values.

I set my receiver at -25, and wrote down each Db for each Hz.

I cant move my sub. Is this curve pretty typical for a standard room? or is it pretty bad? I know it has a big drop in Db at 56Hz, and it also has a few peaks at 22 and 40Hz.

Do I need an equalizer? and If so, which one do you suggest?

[Drew in the desert]

I have the same sub as you and I also have a big valley around 50Hz. I used the DVD Essentials test disc, but I can't get very accurate data since the disc is a frequency sweep and doesn't play a constant tone.

[CECAA850]

An ART-351 is a relitively inexpensive EQ and can (with time) get you to + or - 5Db. A BFD can get within 2-3 Db but is much more complicated to operate. Also, you can try to tame a peak, but the valleys are most likely there to stay. Carl.

[troostj]

"valleys are most likely there to stay"

ok I see, so I cant add anything to boost the valleys to smooth out the curve?

Sorry,noob.

[J.4knee]

Have you tried treating your room, it amy help. You can a free evaluation done over the internet by Auralex. www.auralex.com

[CECAA850]

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ok I see, so I cant add anything to boost the valleys to smooth out the curve?

Sorry,noob.

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Generally speaking, trying to erase a null in the listening position can overdrive the subs amp. EQ's are best used to tame peaks. Carl

[JohnA]

I think your graph is not good, but not really all that bad, depending on what mains you're using. The variations are from room effects. Moving the sub is the only sure cure. Deep valleys in the response are usually cancellation and there is never enough power to compensate. Bass traps may help.

[Champagne taste beer budget]

I'm with John on this one, though I still have a lot to learn, so if I'm all wet I'm sure someone will be more than happy to say so. I'd try and redo the graph with the meter in several more places in the room and see how it comes out. It's possible that the sub is creating good spl at the 50hz freq, but it's getting cancelled out from reflections from the walls/corners at the position you first tested at. If it seems to come back in other areas of the room, you need to check out the threads on bass traps in the Architectural forum. Good luck.

[WMcD]

There is an impossible situation with the nulls in the data.

These occur because a bass signal comes off your sub and then is reflected off the various walls in your room. At a given location, and a given frequency, the reflections are 180 degrees out of phase from the direct signal. They cancel out.

You can experience this if the tones on the test CD are pure tones. If so, they sound like hum. If they are band limited noise, they sound like a rumble, and the following will not work. (This data is so smooth I have to think there have been band limited noise or a lot of smoothing. Raw data in a room shows 40 dB nulls at least.)

Put on a pure tone in the bass region. Walk around the room. You'll find the nulls. At some locations, it will seem that someone turned off the system. Yet some feet away, it seems fine.

Put on another track. The nulls have shifted in location.

It is difficult to believe this unless you do it for yourself.

So you can imagine the situation. People test the system at a listening spot. At some frequencies, a null occurs right there. Again, it is just a matter of reflections arriving out of phase.

Can't we use some electronics to eliminate this? No. If you turn up the output at that frequency, you're also turning up the reflections in exact proportion. If you do the walk around, the nulls occur at the same locations despite the volume setting on the amp. So equalization can't cure them.

You can alter the specific nulls at the listening (measuring) location by moving the speaker. None the less there will be new ones.

As you might infer from the above, all rooms have these nulls. The standing wave effect. It comes to the fore when you do careful testing. On the other hand, many installations sound very good. Maybe yours does.

Gil

[troostj]

Thanks for the reply guys..

Gil, that makes sence. My system sounds fine.. but again, I'm not an expert, you dont know what sounds good until you've heard it.

I wish I could move my sub, but I'm pretty limited due to a WAF factor.

I guess it would be a waste of money to get an equalizer.

[DrWho]

keep in mind that moving your sub around will only result in changing where the peaks and valleys occur. The only real cure is to attempt bass trapping (the concept here is to absorb the reflections that are causing the nulls at your listening position).

As far as your posted frequency response, Anything within +- 10dB in a home environment should sound fairly decent where +-6dB would sound good. A response of +- 3dB would be ideal and a response of +-0dB would be perfect.

Depending on where you draw your reference line, you're sitting at around +-6dBish.

Also keep in mind that a test tone may not result in a -40dB dip like Gil mentioned because your sub is without doubt introducing 2nd and 3rd order harmonics which will be frequencies produced that don't have nulls at your listening position.