Bass Traps

[Pitchucold]

Tried the new sub / peaker positions. Initial looks very good. I dont hear the extra unwanted bass anymore. IT looks good.

But when i played the music in pure audio mode, i do hear a echo now, which i earlier missed or was not there.

how do i handle it now?

Regards,
PRasanna KV

 

[Pitchucold]

Thanks Sanjay. I shall position the sub exactly at 5 feet today and try it out.

Personally I would decouple the speakers from the granite top. But if you feel the difference has been marginal in the past (this could be due to a very well made enclosure), then I would not bother.

I have not tried it without granite boxes earlier. I mentioned i tried with DIY Speaker Stands i made with Control 1 as fronts before they sounded better. But i did not hear a difference with monitor audio with my stands. So made the granite top based on earlier recommendations i received.

Let me try without these and update you ?

Now for the minor echoes i am hearing, would a broadband chuncky traps like sash and himadri made would help ?

regards,
Prasanna KV

 

[sdurani]

Absorption in general will reduce the decay time of your room, which will cut down on echos you hear.

I would start by covering as much of the front wall as possible with broadband absorption. This will have another benefit: reflections bouncing off the front wall will be absorbed, so you hear only the sound from your front speakers, with no other sounds coming from that direction to muddy up the soundstage. Imaging should become much cleaner and more articulate/detailed.

The next place I would put absorption is the contra-lateral reflections (i.e., reflections from a speaker on the opposite side wall). Have a friend slide a mirror along the left side wall until you can see your right front speaker in the mirror. Put a large (4'x4') absorber there. Repeate for the right side wall and left front speaker reflection. Again, this will do a couple of things: 1) absorbtion in general in the room will reduce echos, and 2) sounds from the left side of the soundstage won't also be heard (however softly) from the right side of the room (and vice versa). At this point, your front soundstage should sound incredible.

BTW, I keep repeating 'as much as possible' because this isn't an all-or-nothing situation. Don't let 'perfect' be the enemy of 'good'. If you can cover 4 feet of the front wall, then that's better than nothing. If you can do 8 feet of the front wall, then that's better than doing just 4 feet. If you can do front and contra-lateral reflections, then that's better than doing only the front wall. This doesn't have to be done all at once, so work in stages, as time and money allow.

 

[LIZARDKING]

by panelling i meant frame between which is the foam and above the frame there is plywood on which there is fabric the total depth from cloth is 3 to 4 inches. I want to make new bass traps for the corners for there is too much of it there in all corners. I am using a Velodyne dd15+

 

[Pitchucold]

Hi Sdurani,

Thanks for the suggestion. Work kept me really busy and did not get to think about this.

For Broadband Absorption, I can get Rockwool (100CMX50 CM) Slaps, wrap them with Cushion form (as Sash Did) and hang them on the walls without any wooden frame or support. If there an advantage in having a wooden frame to support it ?

How is normally broadband absorption done?

regards,
Prasanna KV

 

[magma]

By broadband absortion the FM meant absorbiton over the spectrum
or all frequencies

Room tuning is a combination os absorbition,diffraction and reflection

in generall bass traps tend to absorb lower frequncies and reflect the upper mids and highs
Bradband absorbers are the easiest to do

Part frequncy absorbtionand reflections are more difficult to curtail

you can do broadband absorbtion usng rockwool or U foam

standing waves are dealt with using wedge or prism shaped cutouts

there is no advantage to using a frame other than supporting

Most of bass traps we have done are to absorb only the lower end below (say ) 100hz and refelct the rest
You need to use a combnation of MDF U foam and compsite wool

 

[jls001]

The next place I would put absorption is the contra-lateral reflections (i.e., reflections from a speaker on the opposite side wall). Have a friend slide a mirror along the left side wall until you can see your right front speaker in the mirror. Put a large (4'x4') absorber there. Repeate for the right side wall and left front speaker reflection. Again, this will do a couple of things: 1) absorbtion in general in the room will reduce echos, and 2) sounds from the left side of the soundstage won't also be heard (however softly) from the right side of the room (and vice versa). At this point, your front soundstage should sound incredible.

For the above exercise, where should the listener be?

 

[hydra]

^^ Sitting in the sweet spot/listening chair.

 

[sdurani]

If there an advantage in having a wooden frame to support it ?

Easier to work with completed panels (they retain shape, corners don't bend, etc).

How is normally broadband absorption done?

Yes. Remember to make them at least 4 inches thick and, if possible, space them 3-4 inches away from the wall.

 

[sdurani]

standing waves are dealt with using wedge or prism shaped cutouts

Or you can place subwoofers and speakers where they cancel standing waves (prevent them from occuring in the room to begin with).

 

[sdurani]

For the above exercise, where should the listener be?

^^ Sitting in the sweet spot/listening chair.

^^^What he said.

 

[Pitchucold]

Or you can place subwoofers and speakers where they cancel standing waves (prevent them from occuring in the room to begin with).

Hi Sanjay,

I am not sure if i got it. Could you please elaborate.

I was re reading the entire thread. Thats when i realised you have mentioned behind the speaker broadband absorption can be done in parts like 4 ft first and then can add on as well.

What should be my first focus area behind the speaker. I have also have TV mounted right in between the speakers. Any suggestions here.

Based on the positive experience i had in moving the subwoofer (right in line with Center channel) to the middle of the room, I am planning to invest in speaker stands and then take room treatments.

I shall be opting for Magma's / Sound foundation's Nexus or Optimus Stands. waiting for some clarification from him.

regards,
Prasanna KV

 

[sdurani]

I am not sure if i got it. Could you please elaborate.

I already did earlier in this thread:

If you blow across an empty Coke bottle, you can get that small chamber to resonate (make that foooooh sound). If you enlarge that chamber to the size of your room, it will still resonate (produce large peaks & dips at certain frequencies).

For your 10' width, the first 5 of those resonant frequencies will be 57Hz, 113Hz, 170Hz, 226Hz, 283Hz. You can cancel the first one by placing your subwoofer at the midpoint of room width. By comparison, the bass trap needed to absorb a peak in the 50Hz range would have to be a couple feet thick. More practical to do it with subwoofer placement.

The other 4 width modes are above the crossover point, so you can't use subwoofer placement to fix them. However, placing your L/R speakers 20 inches in from your side walls (assuming centre speaker is exactly in the middle) will cancel the remaining 4 resonances. This should get you much smoother frequency response across your entire seating area.

So if you place you L/R speakers where I mentioned in the earlier post, it will cancel the standing waves at the resonant frequencies listed above. Then you won't need to absorb them since they won't be occuring in the first place.

What should be my first focus area behind the speaker. I have also have TV mounted right in between the speakers. Any suggestions here.

Start by covering the bare wall between the L/R speakers and TV with absorbtion. If you can cover all the way out to the edges of the front wall, then all the better. The only thing you want coming from that direction is the direct sound from your L/C/R speakers, not a bunch of reflections muddying the front soundstage.

 

[Pitchucold]

hi All,

I was checking with one other FM who was interested in similar setup. He has mentioned about BURLAP and Hessian Cloth.

I was not aware of it earlier until i searched the forum . I was originally planning to have it like
1. 10 CM Wooden Frame
2. cheap cloth as support on top of it
3. 2 layers of 5 CM Rockwool Covered by U foam
4. Fabric on top of it.

How important is it to have burlap on top of U FORM and underneath the fabric. Is it important really important??.

I was planning to have some thin natural fabric. Is Burlap exactly used for this ?

regards,
Prasanna KV

 

[IndianEars]

Hi Sdurani,

Thanks for a VERY Informative post.

Can you please run me thru the Math (or is there a Look up table ? ) for calculating:

1. The Resonant Freqs of a room. (Ideally for a rectangular room )

2. Exact location of the speaker based on the resonant Freq and the room Dime3nsions.

MANY, MANY Thanks !

 

[sdurani]

If you have a PC with Microsoft Excel, then you can download a free room mode calculator from Harman (see link below) and enter your room dimensions.

Harman - Calculators

If you post your room dimensions, I'll let you know where good placement would be.

 

[IndianEars]

Thanks a TON sdurani.

My Room Dimensions are :
Length 14.5 feet ( The speakers fire in this dimension )
Width 10.5 feet
Height 9 feet


I have a 2 channel stereo ( no Sub ).

I have run the Excel file. Would appreciate your help in interpreting....

The second (Centre ) Graph shows 108 Hz at 2 2/4 is that 2.5 feet ?

I presume that these distance are from the back wall ?

What about the distance from the side walls ?

Thanks for your feedback. MUCH appreciated.

 

[sdurani]

The second (Centre ) Graph shows 108 Hz at 2 2/4 is that 2.5 feet ?

Your room's first 3 width modes are 53Hz, 108Hz and 161Hz (you'll see those numbers in the second/width graph).

You can cancel all three modes by placing your speakers 1/4 of room width in from the side walls (the text on the mode calculator rounds up, which is why it says 2.5 feet).

If you toe-in the speakers (point them at the sweet spot), then make sure to double check that the centre of their woofers are exactly 31.5 inches (1/4 room width) from the side walls.

The science behind this is explained in one paragraph and one diagram (just substitute subwoofer with speaker).

 

[IndianEars]

You can cancel all three modes by placing your speakers 1/4 of room width in from the side walls (the text on the mode calculator rounds up, which is why it says 2.5 feet).

That will result in my speakers being Just 5 feet apart ! Not a happy situation for imaging ....

 

[sdurani]

That will result in my speakers being Just 5 feet apart ! Not a happy situation for imaging ....

Imaging should be razor sharp. If you want a wider soundstage, move closer to the speakers or move the speakers closer to you.

I can answer your question of where to place your speakers to get smoothest frequency response. I can't guarantee you'll be happy with the answer.