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An attempt to build K-402-MEH clone in wood


StabMe

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33 minutes ago, Chris A said:

I use double Owens-Corning 703 fiberglass panels (total 4" thick each) in ATS Acoustic bags. They are placed across the room corners and are closed on one end (sitting on top of the TH-SPUD DIY subwoofers in each front corner). 

 

Any potential benefit in obtaining higher density material like OC 705 (6 pcf, 96km/m3)?

 

34 minutes ago, Chris A said:

It's important that one end is closed off in order to make it a 1/4 wavelength trap (down to ~70 Hz based on the panel length).  If you leave both ends open, then it becomes a half wavelength trap (i.e., 140 Hz).

 

Would this picture be a good visualization of correct placement?

 

image.png.7bbc57d7f8f81cf3825ec5d112eba1df.png

 

21 minutes ago, Chris A said:

If you place the horn mouths within 2 feet (0.6 m) of a side wall, I then recommend a line of 1" (2.5 cm) thick laundry-lint-type (Roxul, etc.) squares of 2 feet by 2 feet dimensions (0.6 x 0.6 m) place just adjacent to the horn mouth exits.  This will dramatically help to recapture the phantom center stereo image, in my experience. 

 

Currently have a panel 2x4 panel with 2" fiberglass standing near each of the side edge of the horn. It does indeed improve phantom center. 

 

I've read Corner Horn FAQ over at DIYAudio and I can see that you advice in favor of using absorption and against diffusion at least near on the front wall and side walls near the horn edges. Would you advise against using diffusors in the rest of the room if the goal is to deal with large reverberation time? I will probably be placing diffusors on the ceiling and back wall and was also going to place them on the side walls at listening position. But now I am thinking if it is better to use absorption at the sides of listening position.

 

I can place 3 2x4 panels at this location:

 

image.png.2373595c315bb3072c9962b52b076cef.png

 

Room size is It is 10m x 6m. Or 32.8 by 19.6 feet. Currently have a TV with desk, horns, sofa and that's about it.

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1 hour ago, StabMe said:

Any potential benefit in obtaining higher density material like OC 705 (6 pcf, 96km/m3)?

I haven't looked at the absorption coefficients vs. frequency of the 703 vs. 705 in many years.  In general, you're looking for relatively equal absorption vs. frequency (flat absorption plot lines).  If your room's RT values look like the 705 would be a better fit (i.e., the absorption values of 705 increase at frequencies where the RT values also increase), then the 705 material might be a better choice.  Also, be mindful its lower frequency absorption coefficients, too, in the midbass and lower treble range.

 

1 hour ago, StabMe said:

Would this picture be a good visualization of correct placement?

Yes.

 

1 hour ago, StabMe said:

I can see that you advice in favor of using absorption and against diffusion at least near on the front wall and side walls near the horn edges.

The problem with using diffusors in this critical area near the horn mouths is that it's difficult to get really broad band diffusion of high enough efficiency.  I find it easier to use the 0.6x0.6 m squares to make sure that all early reflections are effectively controlled. 

 

1 hour ago, StabMe said:

Would you advise against using diffusors in the rest of the room if the goal is to deal with large reverberation time?

You have to use enough absorption somewhere (or have a large enough room wall area) to get the high RT values down to reasonable values.  You can place these absorption panels spaced out among diffusion panels, even alternating with absorption/diffusion, etc.

 

Chris

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9 hours ago, Chris A said:

If you place the horn mouths within 2 feet (0.6 m) of a side wall, I then recommend a line of 1" (2.5 cm) thick laundry-lint-type squares of 2 feet by 2 feet dimensions (0.6 x 0.6 m) placed just adjacent to the horn mouth exits.  This will dramatically help to recapture the phantom center stereo image, in my experience.  You can experiment using more squares just around the horn mouths--out to perhaps 6 feet (2 m) radially.  You may need to place more absorption along the side walls, carpet on the floor, etc. to help control the nearfield reflections to the loudspeakers--and the listening positions.

 

Chris

I made some 2' x 4' x 6"  (stuffed with 2 Roxul R60 2" layers) for each side of the horn mouth. We will see how much of a difference it makes next time I take measurements.

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12 hours ago, Chris A said:

I haven't looked at the absorption coefficients vs. frequency of the 703 vs. 705 in many years.  In general, you're looking for relatively equal absorption vs. frequency (flat absorption plot lines).  If your room's RT values look like the 705 would be a better fit (i.e., the absorption values of 705 increase at frequencies where the RT values also increase), then the 705 material might be a better choice.  Also, be mindful its lower frequency absorption coefficients, too, in the midbass and lower treble range.

 

Agree on matching absorption coefficients vs. frequency of material with RT values.

 

I was thinking about using OC705 (which is of double density) for the corner straddled traps and whether increasing the density of the material may somehow improve performance in the bass-midbass region. Don't get the mechanism of this kind of trap completely, so still have questions :)

 

I have some confusion WRT placing a trap behind the corner horn. From what i understand, corners are used as extensions for the horns. But when we place a trap behind, don't we negate the purpose? I know this is probably a silly question, just want to understand what's happening more clearly.

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1 hour ago, StabMe said:

I have some confusion WRT placing a trap behind the corner horn. From what i understand, corners are used as extensions for the horns. But when we place a trap behind, don't we negate the purpose?

 

Any corner of the room will do for placement. 

 

In my instance, it has to be the front corners on top of the TH subs.  I squeeze down on the space behind the traps by shifting them slightly toward the middle of the room (while their edges remain in contact with the corner's walls) in order to reduce their effectiveness a bit.  This is a nice way to adjust just how much they are absorbing via listening and shifting them around.

 

The bass traps are only good down to 70 Hz (the 1/4 wavelength corresponding to the length of the panels), below which in frequency they don't do any effective absorbing.  So most of the corner-horn boundary gain is still intact (i.e., below 70 Hz) even with the traps in the same corners.  The "boominess" of the 100-200 Hz band is however controlled in room, which is their main purpose.

 

Below 70 Hz, the room modes and drywall flex are the main controlling elements of the bass response.  In fact, I have to place stiffeners along the side walls next to the corner-located TH sub mouths in order to reduce drywall flexing.  This really improves the in-room response below 30-35 Hz and down to 16.5 Hz, where a room-width mode appears to attenuate at that frequency.

 

Chris

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Since the room i am planning to place the MEHs in is kinda big and has very little furniture in it, i was thinkiong about placing diffusers on the walls. As of now, the room is very echoey.
 
I already have 6 Leanfusers prebuilt and i was contemplating on making 4 more. Here is how i am going to place them:
 
image.thumb.png.a4a8e8ff4e7187ce23c5115dea2da852.png
 
image.thumb.png.172e1503c293459a3dea96a791f58a86.png
 
The room is about 6 meters wide and 12 meters long. Ceiling height is about 3.1 meters. Listening position is about 3.5 meters from the front wall.
 
I was also thinking about placing filling a 3x3 meters space on the ceiling that is between listening position and front wall with 2D 60x60cm diffusers in a chess fashion. To make them lighter weight, i was thinking about making them out of XPS of maximum density i could find.
 
image.png.64ef681d2f9e14c8be44ed51dd3cd0d3.png 
 
Of course, i will put a carpet on the floor.
 
What do you think? This is what can be done relatively easy. Should i expect some nice results?
In my last house I used the mirror trick and did my first reflection points for the side walls and the ceiling with 4" of Roxul R60. We also put 2" Roxul on the front wall, and had a bass trap in all 4 corners and the rear wall with Roxul R90...it was right on the edge of being too dead. I had a friend of a friend over 1 night and we listened to Steely Dan Aja and he said it was the best he had ever heard outside of the studio. He was a musician and also had his own studio...plus he was in the Studio when Steely Dan recorded Aja. We really loved that old 2 car garage room in a room build. Now i have a room that will be impossible for me to ever get to sound the same, but at the same time the cubic feet dimensions are 4 times larger, and walls, ceiling and floor are all concrete, windows, and marble. I def have a much livelier presentation that sounds like a club, now. Hopefully I will be able to get the reflections down more with my panels and rugs...we will see when I tune again.

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When I am listening at high levels, I usually feel the floor vibrating. 

Looking at the waterfall graphs, I see very long decay times on some frequencies.

 

So I figured what if it is the floor that is ringing having its own resonances?

 

Here is an overlay of full range signal (before correction) and an RTA signal of me hitting the floor with my heel. Purple is full range sweep, red is floor:

 

image.png.72af54cdfae179f7194d280c22f68161.png

 

Waterfall of the full signal:

image.png.690e04140a7b7b8de6642ffaf37167fa.png

 

 

With a bit more smoothing:

 

image.thumb.png.4ba6fe3ca5af90767061d2b65484a615.png

 

Full signal was measured at 1m distance from the speaker while floor hits were produced at LP. 

 

May I conclude that those long decays are produced by floor (18cm concrete) and there is nothing I can do about it?

 

OTOH, could it still be modes that get activated by me beating the floor? :)

I looked closely on the waterfall graphs and room simulation and find that a lot of peaks correlate.

 

 

 

 

image.png

Edited by StabMe
Mistakenly posted several identical images
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Sorry,  but no...in my last setup we never did a before acoustic treatment measurement, and in my current setup we will be, but currently my system is still down while I am rebuilding the amps, and configuring the speakers for one amp per woofer.  I hope to have the amps done soon.

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  • 4 weeks later...
  • 2 weeks later...

First step in room treatment complete - installed ceiling duffusers.

 

1185589439_Diffusersontheceiling.thumb.jpg.46e0b5bc922a68fe54466ed833754186.jpg

 

It is an area of 3 by 3 meters. Half of it (13 pieces) is filled with 2D diffusers (600Hz-2200Hz diffusion) and the rest (12 pieces) are 1D diffusers which should work between 2200-6800Hz.

 

Hope, that mixing 1D and 2D diffusion is not a big deal.

 

The reason i decided to go this way is cost savings. Building 2D diffusors with 23 wells to necessary to cover the whole bandwidth would cost a lot more for me than to build half as much 7 well 2D diffusers and the rest 1D diffusers.

 

Next up are bas traps and back wall diffusers. Oh and a carpet.

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On 10/31/2021 at 6:12 PM, Seadoc said:

Very Nice !!  I too wanted to build my own horns.  And did with the help of forum members, who offered point data, on dimensions for the K-400 horns.  

 

Hey! Did you document build process here on the forum? Wasn't able to find a thread.

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13 hours ago, Khornukopia said:

 

Looks good. What is the material used to construct the diffuser blocks?

 

I used XPS at 35 kg/m3 density. Diffuser geometry was calculated in QRDude. I bought XPS insulation and used a local workshop with CNC hot wire. Then diffusers were painted. I used foam glue when attaching those to the ceiling.

 

Hope that the material is dense enough to reflect sound at frequencies it is supposed to work. And i am not terribly against some absorption if it happens as well, especially at lower frequencies.

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11 hours ago, StabMe said:

 

I used XPS at 35 kg/m3 density. Diffuser geometry was calculated in QRDude. I bought XPS insulation and used a local workshop with CNC hot wire. Then diffusers were painted. I used foam glue when attaching those to the ceiling.

 

Hope that the material is dense enough to reflect sound at frequencies it is supposed to work. And i am not terribly against some absorption if it happens as well, especially at lower frequencies.

 

The painted surfaces should be effective for the diffusers to function the way you want. Nice work.

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8 hours ago, parlophone1 said:

What are the speaker stands made of?

I seems like they might vibrate.

 

It is painted rectangular steel tube. I should have filled them with sand, actually. But since the weight of the speakers is really huge (I expect about 60-70 kilos each), that should damp vibration.

 

20 hours ago, Khornukopia said:

 

The painted surfaces should be effective for the diffusers to function the way you want. Nice work.

 

Thanks! Already hear huge difference in how much easier it is to listen and comprehend dialogues in movies.

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Square room?  That's going to be rough.
Best luck I had there was with taking down the corner tiles in a suspended ceiling. I guess the space above the ceiling acted as a 'resonator' to bleed off the nodes below the ceiling.  The difference was NOT subtle.

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13 hours ago, StabMe said:

 

It is painted rectangular steel tube. I should have filled them with sand, actually. But since the weight of the speakers is really huge (I expect about 60-70 kilos each), that should damp vibration.

 

 

Thanks! Already hear huge difference in how much easier it is to listen and comprehend dialogues in movies.

I would fill them with sand... I had a rectangular stand built that I designed years zgo and if you rap it...it would ring. I filled them with sand and they did not ring anymore...not sure if it would affect the sound, but the good speaker stands are sand filled.

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