Why such a huge dip at 30hz and below? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 7 Old 08-15-11, 10:05 PM Thread Starter
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Why such a huge dip at 30hz and below?

Why such a huge dip at 30hz and below?-081511cal.jpg

Horrible dip below 30hz and not sure why...Ive got early reflection panels, a ceiling cloud (about 10ft overhead...hanging 1ft from ceiling), and 3" corner traps. Do I have too much bass trapping? My HS80Ms are about 1' away from the back wall. If I remember correctly, when I first started using REW I didn't have this dip...lord knows I don't know what I did that would have made it drop so low!!

Why such a huge dip at 30hz and below?-studio-120-jml.jpg

I have my room specs on another thread..I'll go dig it up sometime later tonite...but in the meantime...any ideas off the top of anyones head?

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post #2 of 7 Old 08-16-11, 01:04 AM
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Re: Why such a huge dip at 30hz and below?

Well, none of your basstraps reach that low, so it's not that.

Is that the room from the '30 panels' thread in the gear-something-something forum, btw? Thought I recognize the panels.
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post #3 of 7 Old 08-16-11, 09:14 AM
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Re: Why such a huge dip at 30hz and below?

Horrible dip below 30hz and not sure why...Ive got early reflection panels, a ceiling cloud (about 10ft overhead...hanging 1ft from ceiling), and 3" corner traps. Do I have too much bass trapping? ,,,,,snip,,,,,

You're asking "acoustic treatment" questions within the wrong forum / & most likely, on the wrong website .

But FYI ;

Overall ( IMHO ) you're concerned about the wrong things ( on this REW capture ) .

- That curve looks really quite good to me / though if mine ( for critical mixing ) I would want to deal with that 100hz peak ( if it's occuring across a large area of your mix position ) .

A 4db high peak at 100hz will colorize everything that you hear and commit to "tape" / & if you react to that "color" accordingly ( by subtracting some if it from your final mixed tracks ), you'll end up with mixes that don't translate that well in other systems.

I suggest that you go back to GS and ask the GearSlutz guys what can be done ( acoustically ) to surgically remove that 100hz peak ( maybe first ask to see if you can get a consensus on whether or not others think it's necessary to flatten 100 hz ) .

- Also , the bumps just above 2K & at 7K could use some attention . You'll likely need to get into some DSP EQing ( just before the speakers ) to fix those anamolies .
- ( I'm skeptical that at this point in treating your space , that any more baffling will give the necessary attenuation that high up ).

Something like this ( can really help above a few hundred hertz ) ;

<> EarlK

PS ; You can always add a sub ( or change out what you have ), if you need more bass response below 35 hz .

Last edited by EarlK; 08-16-11 at 10:15 AM.
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post #4 of 7 Old 08-16-11, 09:40 AM
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Re: Why such a huge dip at 30hz and below?

At the risk of offending...

You do know that the speakers frequency response is rated by Yamaha as being from 42Hz - 20kHz! Right?

Now I realize we would like to have a response from DC to gamma rays, but do you expect room treatment to supply that which the speakers do not?

And while many things in the universe remain a mystery, I might suggest that the drop in response below 30 Hz is not one of them.
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post #5 of 7 Old 08-16-11, 09:58 AM
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Re: Why such a huge dip at 30hz and below?

Additionally, while the control of first order reflections from side walls, ceiling AND the worksurface due to bridge mounting speakers is very important to imaging, localization, intelligibility and avoiding polar lobing that results in frequency response comb filtering, none of these issues will result in a sub=30 Hz anomaly.

For these issues you would want to perform a before treatment/after treatment L/R ETC in order to ascertain the specular behavior of the space.

Moving on to a separate issue...

For modal analysis of the space you will want to look at the waterfall plot, not simply the frequency response.

And I will also suggest that 3" half space bass traps in the front corners are not sufficient to address modal issues in a small nearly square room. Typically, superchunk style porous corner bass traps typically employ a volume defined by wall unions of 2' each with a face ~34 inches wide running from floor to ceiling and completely filled with porous material. And even they are severely challenged below 50 Hz, if that gives you a comparative indication.

And that assumes the dip is modal in nature...(which I think is an error at this point considering the other factors such as fundamental speaker response!)

For comparison sake, you might want to perform a near field measurement of the speaker in order to determine its frequency response - which I think you will discover that the speaker does not have significant sub 30 Hz output - considering its rated at 42 Hz as its -3 dB down extension point.

And all of this ignores any contribution that SBIR might make, as one can reasonably discount any suspicion that it will be a significant issue below the speakers' rated frequency output.

In this case, I suspect the sub 30 Hz rolloff is a case of the speakers performing exactly as designed! ...There are worst problems.... ;-)

Good luck.

Last edited by SAC; 08-16-11 at 10:06 AM.
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post #6 of 7 Old 08-16-11, 07:21 PM
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Re: Why such a huge dip at 30hz and below?

If it where only the speakers they wouldn't be louder at 17Hz
And that they are rated from 42Hz only means that they are flat from then, there shouldn't be such a fast gap.
use the tone generator to play that 23Hz or 24Hz and move around in the room to here if its a null in the room or if it is realy existend or a measure/microfone problem
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post #7 of 7 Old 08-17-11, 10:53 AM
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Re: Why such a huge dip at 30hz and below?

Just to add and correct one point expressed above...

The HS8M, utilizing as it does a bass reflex tuning, which generally features 3rd or 4th order 18-24 dB/octave slopes.

Instead of being disappointed, one should instead be quite pleased at the low frequency response given that Yamaha has seen fit to dispense with the conventional specification standard of citing low frequency extension at a -3 dB point and instead specifies the 42 Hz extension at -10 dB. Thus the LF roll off is already well underway at the rated 42 Hz!!

Suffice it to say that one is lucky to have the existent extended low frequency response complete with the limitations of the bass reflect which are increased ripple in the passband and a slightly degraded transient response due to its being underdamped compared to a sealed box.

If one expects LF response to 30 Hz, Yamaha specifically makes a complementary subwoofer unit, the H10W, specified by Yamaha for a passband of from 30Hz to 120 Hz.
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