Low frequency suck out, what can'I do?

bpape · « **Reply #80 on:** 31 May 2011, 10:49 pm »

There is so little content at 25hz, I'd not worry too much about it. Tuned Helmholz absorbers that low can cause their own problems. From what I see in the graph, I see +/-6db which indeed could get better but hardly +/-10. Realistically, in room, if you can get to +/-4, you're doing pretty well.

Bryan

McTwins · « **Reply #81 on:** 1 Jun 2011, 01:39 pm »

Hi
If the content at 25Hz isin't important then what's the point of using a sub. I see +/- 10dB from 16-63 Hz. It schould be 20-100 Hz +/- 2,5 dB in a dedicated listening room. I have this in my room and done it myself.

Audioblazer....
The best thing for you to do is,
Highpass the sub at 30Hz then take a measurement and see if the resonant minimizes and boost the suckout with EQ.

or...

Contact Rives audio and tell them to fix your resonance problem.

Good luck.

Thanks

bpape · « **Reply #82 on:** 1 Jun 2011, 02:48 pm »

I'm just saying for music, there isn't much there. Yes - if you go down to 20Hz and below, it's more than +/-6. I'm just talking the range were 99.999% of the music lives. Also, for the overall +/-, I'm talking with zero EQ applied.

The point of a sub is not only extension. It's also to allow movement of the sub for best bass response independent of the mains position as well as taking the load off the main speakers and amps to give more headroom.

Bryan

rollo · « **Reply #83 on:** 1 Jun 2011, 02:56 pm »

A little more to the right please.

charles

jtwrace · « **Reply #84 on:** 1 Jun 2011, 03:02 pm »

Quote from: McTwins on 1 Jun 2011, 01:39 pm

Contact Rives audio and tell them to fix your resonance problem.
Good luck.
Thanks

I'm not so sure that you would need to do that.

audioblazer · « **Reply #85 on:** 1 Jun 2011, 04:05 pm »

room measurement with front wall passive resonator removed, 4 panel bass trap removed and 3 placed at the center of rear wall, sillk carpet in front of listening position removed.
U can see that it measured better now particular at around 110 hz. RT60 increased slightly

Initial measurement

McTwins · « **Reply #86 on:** 1 Jun 2011, 05:56 pm »

Hi
The first axiell mode must be taken care of, if not,
Bastones a little bit higher in frequences will trigger the mode and you sit with false music information and a boomy room (and with Murpys law a dip in the sweetspot).

Room resonances shift the phase of the low frequences and makes its very difficult to integrate the sub with the main speakers.

Matts Odenmalm, SMT AB from Sweden is travelling around the world and can tune your room to your liking with local carpenter.

I highly recommend him and he will fix your room.

Here is a brochure I got from a hi-end show.

http://i1223.photobucket.com/albums/dd505/mctwins1/sidan1-1.jpg

http://i1223.photobucket.com/albums/dd505/mctwins1/sidan2.jpg

Thanks

oboaudio · « **Reply #87 on:** 1 Jun 2011, 08:26 pm »

Brick walls and concrete floors are great for isolation but are more difficult to get uniform and well controlled bass.
I use 36 ASC bass and midrange tube traps, some GIK bass traps and other homemade traps.
Here is a drawing of my room showing placement of all the bass and midrange traps.

Nyal Mellor · « **Reply #88 on:** 2 Jun 2011, 12:30 am »

Quote from: audioblazer on 31 May 2011, 02:45 am

Nyal , thanks for your suggestion. The graphs shown are for measurements without integrating the sub to the front speakers .
Can I use XTC to measure 2 channel + sub ? To integrate the sub ( a pair of fathom 113) , I connect it thru the output of the preamplifier . So if I were to unplug the RCA connectors at amp side & plug in the y connector at the amp & take measurement with preamplifier driving the active sub & amp driving the front speaker would that be the right way to go about it.
I removed the front passive resonator , removed 6 panel bass traps & add 3 traps to the center of my rear wall behind the LP rack, my room measures
better. Will continue to experiment & see how things turn out.

I think you've got it - plug the XTZ with a y adaptor into an input on your pre-amp. Then unplug the speaker cable or rcas for the other channels. That way you should measure the front channels plus the sub.

Nyal Mellor · « **Reply #89 on:** 2 Jun 2011, 12:42 am »

Mctwins

In reference to the thick absorbers I was referring to using them to kill a boundary interference related suckout, not for general bass trapping.

It is more important to get low decay times across the bass range than to get flat frequency response. Frequency response variations after getting low decay times are mostly boundary interference related.

I agree that targeting that resonance at 25Hz is a good idea. A single parametric EQ filter would most likely do the job.

Some material on boundary interference http://www.acousticfrontiers.com/Speaker-Boundary-Interference.html

audioblazer · « **Reply #90 on:** 2 Jun 2011, 01:44 am »

Oboaudio,
That is a hugh no of bass trap. How big is your room? I suppose with my room being constructed of concrete brick wall, it should retain much more bass energy. However from my experience with only 10 panel trap, 3 soffit bass trap around 30" x 18" x 12" & 4 corner bass trap abt 33" across , it seems to damp my room too much. I suppose there is no 1 formula fit all room treatment . From this experience I realised that for proper room treatment , experimenting by moving traps around may be necessary.
I have a friend whose room is filled with 1D diffuser with acrylic fins for 3/4 quarter of his room & ave size bass trap & did final tweaking by moving around a small 20x30" x 7" (only filled 4" with 80kg/m3 rock wool like material) bass trap & the room sounded 1st class .

audioblazer · « **Reply #91 on:** 2 Jun 2011, 02:00 am »

Nyal , plug the y adapter of the xtz to 1 of the preamp input ( not output) and unplug speaker cable to measure both front channel + sub? How would it work with speaker cable unplug ?

oboaudio · « **Reply #92 on:** 2 Jun 2011, 02:11 am »

My room is 29'-3" long x 19'-2" wide x 11' high cathedral ceiling. All the ASC bass
and midrange tubetraps have a reflective membrane that prevents over damping the highs, but
provides bass that is powerful and detailed. As Ethan Winer of Real Traps has said many times, one can never have too much bass trapping, and I agree. The traps are spaced evenly around the
perimeter of the room with 3' between each trap that reduces comb filtering and the
result is voice reproduction that is very detailed and imaging that is extraordinary. The overall
sound is very spacious and one feels like there in the hall (venue) where the recording was made.

audioblazer · « **Reply #93 on:** 2 Jun 2011, 03:02 am »

Oboaudio,
I suppose Asc basstrap with reflective surface will not overdamp the room. I believe there are many ways to skin a cat. Looking at performanceacousticslab.com gallery, I noticed that most rooms are mainly treated with diffusers & I hardly see any bass trap unless its build into the room. I believe there is no such thing as 1 formula suits all room treatment. For those who likes to DIY, plenty of info in gearslutz.com, a site which make me realize making diffuser is pretty simple with a good carpenter
Anyway thks for your feedback

McTwins · « **Reply #94 on:** 2 Jun 2011, 05:59 am »

Hi
Audioblazer....
Performanceacousticslabs use Helmholtz resonators that is integrated in the room, it does not look like basstraps.

I really don't see any difference in those measurement you are showing either before or after, it looks the same. You removed some stuff, how does it sound now compared with the treatments?

Nyal Mellor....
I understand how the SBIR works but it can't remove the resonances in a room no matter how the speakers is position in that room. About the decaytime, how do you fix this?

To EQ the 25Hz won't help much, I suggested him to remove or highpass 30Hz.

oboaudio....
I would like to see some measurements of your room. I have not seen any from ASC, Realtraps or any other real measurements in a room they have treated. Still waiting on this.

Thanks

audioblazer · « **Reply #95 on:** 2 Jun 2011, 06:47 am »

Well it's sounded sharp & slightly blurry. Can't really hear the suck out issue , probably not much musical content around the region fr my Lp or cd. However it's still sounded boomy eg with Jennifer Wearnes Way down deep. If u look at the RT60 graph u will noticed that it has increase & that shows that the room is less damp now. I hope my interpretation of the graph is correct

McTwins · « **Reply #96 on:** 2 Jun 2011, 07:14 am »

Hi
Your interpretaion is correct, if you raize the volume a little higher so you are around 100 dB you will have better measurements readings for your RT60. You are measuring in the noise floor region and this can affect the measuring results.

You have to be 30 dB above your room noise floor.

So, if I understand you correctly there is no different.

You still have to kill the first axial mode and it has nothing to do if you have brick wall or soft wall, it will still have this problem in your room. This boomy sound you hear is from your strong peak at 25Hz and you can't hear a suckout, our ears don't hear this.
Your friends room have different room dimension than yours and maybe he does not have strong modal ringing that he can hear, but the principal is still the same.

And also, this first axial mode if you don't kill it it will also affect their mutiples along the way up in the freq in the same way as the first axial mode.

Thanks

audioblazer · « **Reply #97 on:** 2 Jun 2011, 07:23 am »

Let's see what happen when I put up 11 2d prd diffuser , 3 at front wall & 4 at each side wall & 2 portable bass trap around front wall , then I will see how it measure & move from them . Hopefully I should have it done 2 weeks from now

McTwins · « **Reply #98 on:** 2 Jun 2011, 11:10 am »

Quote from: Nyal Mellor on 2 Jun 2011, 12:42 am

Mctwins

In reference to the thick absorbers I was referring to using them to kill a boundary interference related suckout, not for general bass trapping.

In this case its not only a SBIR. If it had been, were should you put a 10feet thick absorber for the big suck out ?

It is more important to get low decay times across the bass range than to get flat frequency response. Frequency response variations after getting low decay times are mostly boundary interference related.

It's NESSECERY to lower the first axiell resonance that appears in a room as much as possible. Check out SMT and PAL case studies and see how the frequence respons flattend out
Here is one VERY similar example

http://i386.photobucket.com/albums/oo303/smtab/audio.jpg

I agree that targeting that resonance at 25Hz is a good idea. A single parametric EQ filter would most likely do the job.

A parametetric EQ will just lower the level of the problem frequence, it will NOT do anything with the dip just above

Some material on boundary interference http://www.acousticfrontiers.com/Speaker-Boundary-Interference.html

Nyal Mellor · « **Reply #99 on:** 2 Jun 2011, 05:13 pm »

Quote from: audioblazer on 2 Jun 2011, 02:00 am

Nyal , plug the y adapter of the xtz to 1 of the preamp input ( not output) and unplug speaker cable to measure both front channel + sub? How would it work with speaker cable unplug ?

Sorry something must be getting lost in translation! I mean unplug the surrounds and center or choose a mode on your pre/pro that doesn't upmix stereo to HT but keeps the bass management; that way you will have the front L and R speakers playing with the sub.