Low frequency suck out, what can'I do?

McTwins · « **Reply #60 on:** 29 May 2011, 12:07 pm »

Hi
Put your diffusors on the first reflection points to start with. Place five of them behind the speakers in the middle and three on each side to get first and second reflection points. 20 to 25 inch from the floor is OK.

Have you tried to put your subwoofers together in the middle as mentioned before. If not, please do this first and report back with the result.

Please, post some pictures

Thanks

audioblazer · « **Reply #61 on:** 29 May 2011, 12:12 pm »

Mctwins, 1st I can't put the sub at the middle due to space constraint. 2nd I don't seems to be able the integrate the fathom with vr4sr well without using an external crossover.
My question was is it ok to put some diffuser at 24" and some at 30" fr floor due to presence of sub panel or must it all be place uniformly ie at 30"? Thks

McTwins · « **Reply #62 on:** 29 May 2011, 12:31 pm »

Hi
Ok I understand. I just whant you to try it out and I am 99% certain that you will fix your suckout problem. Can you put the sub behind the gear and do a freq response measurement. You don't need a external crossover just leave the VR4SR fullrange and cut the sub at 80 to begin with. I asume it is active subs you have.

It's OK to put the diffusors as you are suggesting.

Thanks

audioblazer · « **Reply #63 on:** 29 May 2011, 12:59 pm »

I tried that with my fathom 113 which is active . Didn't like what I hear. Too much low bass

bpape · « **Reply #64 on:** 29 May 2011, 01:03 pm »

If it's better but just too much low bass, tweak the level adjustment and play with slight movements away from the front wall to tweak how much boundary gain you're getting.

Bryan

McTwins · « **Reply #65 on:** 29 May 2011, 01:09 pm »

Hi
Just do a measurement, please. I would like to see how the response looks like. I am suprized that you haven't done any measurments when you tried it in the first place.

bpape.... you are absolutely right, TURN DOWN THE LEVEL on the subs and it will be fixed.

Thanks

audioblazer · « **Reply #66 on:** 30 May 2011, 03:13 pm »

Would love to measure but with an Xtz analyser I do not know how it's done. To measure front speaker I connect the y cable fr Xtz to the RCA input of the amp. To measure both the front speaker + sub , how do I measure?
To integrate the twin sub with the front speaker, I connect 1 RCA from the out put of the preamp to each of the sub for 2 channel . For HT , I use preamp bypass for front channel & a processor & 5 channel amp for the surround & center speaker.
So how do u propose I measure the front channel + sub using XTZ analyzer?

McTwins · « **Reply #67 on:** 30 May 2011, 05:20 pm »

Hi
Now I don't understand. On page one in this thread you did a measurement, what was that? only the VR + subs or only the subs. I hope you didin't measure with you hometheater with all of your speakers.

Can't you connect the xtz to input of your preamp and only measure the VR seperatly or only the subs or all together. If you can't do this then I don't know what the measurement on page on is telling.

Let's take it from beginning, I just want you too measure only with VR + subs, if you can only VR seperatly and only the subs seperatly(subs in the middle and as far back to the wall if possible). Your mic at listening position.

I just want to see the freq response.

Read the manual of the xtz and see what say there.

Let me now if you can do this.

Thanks

audioblazer · « **Reply #68 on:** 30 May 2011, 05:50 pm »

Let me try to sort it out. Page 1 shows measurement of the VR only.

McTwins · « **Reply #69 on:** 30 May 2011, 05:59 pm »

Hi
Ok now I follow, that's good.
Measure only the subs as mentioned before. That will be enough for me too see how it looks.

I just read the manual, dosen't say much how you schould connect.

I am measuring mine thru the preamp and not the amplifier, little bit easier.

Thanks

Nyal Mellor · « **Reply #70 on:** 31 May 2011, 02:03 am »

If I understand you correctly to measure your subs only in your two channel system you would plug in XTZ into your preamp but unplug the cable between preamp and power amp hence only subs would be playing.

In any event +- 2.5dB in the bass is going to be VERY difficult to achieve. I don't think your graph looks too bad. There is visible room mode ringing at one frequency in particular - 25Hz? (you can see it in the time domain graph where the red / yellow tail is greatly extended in the time domain) that will be audible and you should try and deal with further. Unfortunately it is at such a low frequency that modifying your room construction or a tuned bass trap is going to be the only way to deal with it. Passive bass traps are not going to have any effect at that frequency.

You can use EQ to deal with the lump - XTZ has a 'simulation mode' which you can access by right clicking on the low frequency graph and dragging it until it is flat. The correct EQ values will appear in the table to the right.

For the dip you will need to figure out if it is speaker boundary interference related. If it is then the dip frequency will vary as you move the sub around the room. If the dip stays in the same place then you can use EQ (it'll be where there is not a reinforcing room mode at that frequency). If it is then you will need to use thick absorbers at the boundary that is causing the cancellation. Again it's going to require serious thickness to do the job due to the low frequency.

Rives should be able to fix this or else consult with a professional acoustician such as myself (my company is Acoustic Frontiers).

audioblazer · « **Reply #71 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.

McTwins · « **Reply #72 on:** 31 May 2011, 09:28 am »

Quote from: Nyal Mellor on 31 May 2011, 02:03 am

In any event +- 2.5dB in the bass is going to be VERY difficult to achieve. I don't think your graph looks too bad.

To bad to hear this from an professional acoustians. How was I been able to do it, I my self are not an proffesional. It's really to bad to hear this.

There is visible room mode ringing at one frequency in particular - 25Hz? (you can see it in the time domain graph where the red / yellow tail is greatly extended in the time domain) that will be audible and you should try and deal with further. Unfortunately it is at such a low frequency that modifying your room construction or a tuned bass trap is going to be the only way to deal with it. Passive bass traps are not going to have any effect at that frequency.

I agree on this one.

If it is then you will need to use thick absorbers at the boundary that is causing the cancellation. Again it's going to require serious thickness to do the job due to the low frequency.

Thick absorbers will not do it, sorry. Not in his room

Rives should be able to fix this or else consult with a professional acoustician such as myself (my company is Acoustic Frontiers).

Why should Rives Audio be able to fix it when they didn't fix it in the first place. Shame on Rives Audio.

audioblazer · « **Reply #73 on:** 31 May 2011, 09:37 am »

To be fair to rives audio, it may not be due to design fault. Could be construction issues. My corner bass trap suppose to have stretched pond liner - suppose to be v tightly stretch but unfortunately it was not well done as well. That could account for some of my room problem. My only grouse is that why no diffuser was recommended

McTwins · « **Reply #74 on:** 31 May 2011, 09:55 am »

Hi
It's good that you have notice that it is better without basspanels. Reasaon that you hear more bass is becasue you have to much absorbtion that kills high freq.

Still waiting for you to take some measurement.

Thanks

bpape · « **Reply #75 on:** 31 May 2011, 11:36 am »

Over-absorbing highs isn't going to account for an appartent excess in deep bass. If anything it would just make the sound dull and lackluster. In addition, Rives' designs I have seen rarely even come close to having too much absorption in the upper frequencies. They use a combination of diffusion along with membrane and tuned type absorbers with very little broadband.

Bryan

audioblazer · « **Reply #76 on:** 31 May 2011, 11:57 am »

Well if u see the 2& 3rd graph on 1st page u maybe able to see that from 10kz - 20khz , the freq dips by 10-15db. My room used to have 12 panel bass trap -2", 60kg/m3, 4 corner trap- width 33", about 8 ceiling traps, & 2 silk carpet. Based on what I heard & measure its certainly over absorbing . There is no diffuser designed into the room except 1 helmholtz resonator at 1st reflection. From my experience I thk whatever we do to our audio room, mobility of the room treatment is essential

McTwins · « **Reply #77 on:** 31 May 2011, 12:06 pm »

Hi
You seem to get the point, that's good.

I am still amazed that they coulden't take that resonanse at 25Hz for you. This is the major problem that has to be fixed for you. I bet that Rives audio can't fix it, they schould be solving that problem for you with no charge. If they can't this is very bad.
Thanks

audioblazer · « **Reply #78 on:** 31 May 2011, 04:21 pm »

Mctwins,

single subwoofer freq response

McTwins · « **Reply #79 on:** 31 May 2011, 05:06 pm »

Hi
Thanks,
Is the bass in the middle? I asume it is just for some clarity.

Take a measurement with the mic as far back as possible, record bookshelf wall(behind the listening position).

As far as I can see the suckout around 50 Hz is better now, +/-10dB now.

That nasty resonace is very bad, indeed. You can boost up that suckout around 31Hz and if possible try to reduce that peak at 25Hz, with EQ.

Remember that if you are measure just keep the mic at one place, don't move it, when you are adjusting something. So you see what's happens.

Thanks