Insane SPL levels at 30-50 Hz - Countermeasures ?

[Kolia]

So I'm testing 2 subs this weekend and using the AVIA setup DVD.

Martin Logan Abyss (Down firing, 12in driver, 300W)
Martin Logan Grotto (Front firing, 10in driver, 250W)

I've yet to play with different placement (two locations done) .

Using the lower frequency LFE sweep test tone (a tone that goes from 100Hz don to 20Hz), the SPL level will jump +10dB at about 50Hz and then an other +2-3 dB at 30Hz. It's pretty loud (cats going crazy and ears feeling "pressure"). I've moved around the room and I get similar results.

Are there any countermeasures I could try to blanace the sound levels ? Ideas ?

 

[dave1490]

So I'm testing 2 subs this weekend and using the AVIA setup DVD.

Martin Logan Abyss (Down firing, 12in driver, 300W)
Martin Logan Grotto (Front firing, 10in driver, 250W)

I've yet to play with different placement (two locations done) .

Using the lower frequency LFE sweep test tone (a tone that goes from 100Hz don to 20Hz), the SPL level will jump +10dB at about 50Hz and then an other +2-3 dB at 30Hz. It's pretty loud (cats going crazy and ears feeling "pressure"). I've moved around the room and I get similar results.

Are there any countermeasures I could try to blanace the sound levels ? Ideas ?

get a eq,you,ll need a 1/3 octive eq for that narrow band.

 

[no. 5]

Room placement, and or, treatments will work too. As will running two subs.

Some subs have a parametric EQ for just such problems, and this has been recommended for taming room modes too.

 

[mtrycrafts]

So I'm testing 2 subs this weekend and using the AVIA setup DVD.

Martin Logan Abyss (Down firing, 12in driver, 300W)
Martin Logan Grotto (Front firing, 10in driver, 250W)

I've yet to play with different placement (two locations done) .

Using the lower frequency LFE sweep test tone (a tone that goes from 100Hz don to 20Hz), the SPL level will jump +10dB at about 50Hz and then an other +2-3 dB at 30Hz. It's pretty loud (cats going crazy and ears feeling "pressure"). I've moved around the room and I get similar results.

Are there any countermeasures I could try to blanace the sound levels ? Ideas ?

How is the sub volume when you are using the internal test tones on
the receiver?
Rooms are notorious for such peaks and valleys in the sub band; that is the nature of the beast, unfortunately. Some are even much more.

I would suggest that Behringer feedback destroyer as you can select any frequency and shape it to what width you need tamed by how much. I think it will cut up to 48 dB and it works in the digital domain at 24 bits.

But, you would need a better test cd than what you have as you would need to have better frequency resolution than you can estimate from a sweep tone; that is just pure guessing.
There are low frequency test tones at 1 cycle increments from 10Hz-99Hz. You could check the full spectrum, plot it, apply meter correction as the RS meter is not linear by any means, then, with that Behringer, you can have it FLAT, maybe. It takes time.

 

[Kolia]

Thanks, that was good info all.

I'll shop some more and up my budget a bit to try and find a sub with a built in equalizer. I know the SVS' have one. The Martin Logan Grotto also, but "fixed" to 25Hz.

 

[tbewick]

I think you can have some difficulties using time-invariant equalisers, because with music signals in room environments, steady-state conditions are rarely met. I think this is due to there being some time required for resonances to take full effect. There is also the problem of achieving a flat response over a large listening area which is probably only possible with acoustic treatment.

There is also the difficulty in actually getting a balanced sound, because there will be all kinds of reflections in the higher frequencies which will give a more lively sound. This means that you may find a slight excess of bass produces a more balanced sound.

Just on the point of obtaining balanced sound, this AES paper has quite useful information:

'Some standard recommendations for level alignment recommend the use of broad-band pink noise, or pink noise band limited from 200 Hz to 20 kHz. This has been criticized by some for involving too much low-frequency content, and thereby making the measurement highly dependent on room mode response, as well as being very direction-dependent at high frequency. Such measurements, though, are normally made with A-weighting filters, which reduce the extreme low- and high frequency components considerably.

...Recent research attempted to find correlations between the subjective alignment of channel loudness and a variety of objective measurements, using a wide range of different test signals [13 {see paper}]. There is some evidence that the low-frequency content of test signals is ignored when subjectively aligning channel gain, and that constant specific loudness noise signals may be preferred over other noise signals with regard to subjective/objective correlation. Further work is required to determine what high-frequency roll-off (if any) is ideal for noise signals to be used in system alignment.'

AES Technical Council, 'Multichannel Sound Systems and Operations', page 21
http://www.aes.org/technical/documents/AESTD1001.pdf

 

[Kolia]

Goddamit more data!!!

Lol

Thanks

 

[crewst]

How is the sub volume when you are using the internal test tones on
the receiver?
Rooms are notorious for such peaks and valleys in the sub band; that is the nature of the beast, unfortunately. Some are even much more.

I would suggest that Behringer feedback destroyer as you can select any frequency and shape it to what width you need tamed by how much. I think it will cut up to 48 dB and it works in the digital domain at 24 bits.

But, you would need a better test cd than what you have as you would need to have better frequency resolution than you can estimate from a sweep tone; that is just pure guessing.
There are low frequency test tones at 1 cycle increments from 10Hz-99Hz. You could check the full spectrum, plot it, apply meter correction as the RS meter is not linear by any means, then, with that Behringer, you can have it FLAT, maybe. It takes time.

I'm trying to pinpoint a similar problem (peak from 60-85 roughly). Can you tell me where I could get a disk with 1 cycle test tones and how I could go about plotting the frequency response? I have noticed quite a difference in the RS meter's "A" and "C" modes, and would like to have something more reliable when trying to flatten my response.

 

[mtrycrafts]

I'm trying to pinpoint a similar problem (peak from 60-85 roughly). Can you tell me where I could get a disk with 1 cycle test tones and how I could go about plotting the frequency response? I have noticed quite a difference in the RS meter's "A" and "C" modes, and would like to have something more reliable when trying to flatten my response.

Use 'C' weight on the RS meter.
The test tones are on Autosound 2000 Test CD 101, tr10-98. 1-800795-1830.

Send me an email, should be at my profile, so I can pass on an Excell worksheet that is in 1/6th octave with built in compensation for the RS meter. So, you just plug in your meter reading and the corrected spl is shown and 'plotted.' Cool program found it somewhere on the net