Any comments on my measurements - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 19 Old 01-14-13, 05:21 AM
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Re: Any comments on my measurements

Quote:
eclipse911t wrote: View Post

Can you really effect 40Hz with a 24x24" corner bass trap?
Not really. Wavelengths are very long at lower frequencies. I put 5 GIK Monster Traps in my 12x20x8 room 3 years ago. It helped greatly above about 60-70Hz or so, but did almost nothing for a 26Hz room mode. IIRC, bpape said some type of large membrane absorber is needed for the lowest bass notes.

Don't get me wrong, the GIK Monster Traps made a HUGE difference in my room, but the laws of physics tells us that treating the lowest bass is a challenge.

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post #12 of 19 Old 01-15-13, 09:22 PM Thread Starter
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I'm considering 8 additional panels of 3" thick rigid fiberglass on the rear wall. This would put my rear wall at roughly 45% absorption 55% reflective. I'm currently at 8% coverage back there. I am thinking I could use Certainteed CertaPro 3" CB150 for the panels and use a spray adhesive to attach a black muslin for aesthetics directly to the panels. Any experience with this method?

I'm also considering 12' long super chunks along the wall-ceiling corners down each side of the room filled with 24x24x34 6" thick mineral fiber.

Do you guys think this would be money well spent?

I'm currently traveling but will get some good no EQ measurements when I return later this week.

One of my concerns about my current measurements is that I have been using a Dell laptop's built in sound card for the audio output. I'll order a USB extension tonight which will allow for HDMI output of the audio signal to my DTC-9.8.

PS: I'm also eager to pull down the panels and measure the room without them. The chunks are a bit more difficult to remove, so they'll likely stay.

Comments always appreciated.
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post #13 of 19 Old 01-17-13, 08:12 AM
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Re: Any comments on my measurements

I would think about spacing the panels off the wall to increase their efficiency, 3" panel + 3" space is like a 6" panel. I would watch the adhesive spray with muslin, as you are creating something that is pretty flammable, I'm not sure if the adhesive impedes the airflow either. You should plan to cover whatever the wall surface needs to flatten the low end, not go by a "percentage." Once that is done you can choose to select fabric or covering that will reflect highs to get your high end back, but I would not make the decision to cover a certain percentage of the surface based on looks or surface area, you need to measure as you add to see what works. If you can make your panels and move them around (before covering them)while you measure that will help you. For low end, thicker is better.
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post #14 of 19 Old 01-17-13, 05:54 PM Thread Starter
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Here are the no EQ no smoothing plots for the sub and mains. I believe there was an 80Hz crossover on the mains. They roll off at 40ish on their own.

I also posted an ETC response for the front left speaker, but know little about how to interpret it. I can see my RT60 is at roughly 200ms, but haven't a clue if that's good or not.

I did also run a test on my rears (no sub) and noticed the waterfalls looked much worse on the low end. I'm definitely treating my rear wall with 3" Certainteed Certapro Commercial Board CB150. I'm starting with 7 2'x4' panels high up along the rear wall.

Unfortunately the walk ways in my theater are all specifically 30" wide and will only afford a 2 or 3 inch panel, but not 6".

My next addition will be the two 12' long 34" face super chunks down the side wall-ceiling corners. The materials have been ordered and construction should begin this weekend. I can buy a 4 pack of 24x48x6" SAFB mineral wool for $34. Why not get 3 bags and build these things for about $160 framed, covered and mounted.
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Any comments on my measurements-image-1208200877.jpg  

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post #15 of 19 Old 01-17-13, 05:58 PM
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Re: Any comments on my measurements

Show the ETC out to only say 60ms. Its the early returns that count
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post #16 of 19 Old 01-17-13, 06:03 PM Thread Starter
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Quote:
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Show the ETC out to only say 60ms. Its the early returns that count
Here we are.
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post #17 of 19 Old 01-17-13, 07:02 PM
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Re: Any comments on my measurements

Now I see. Thanks.

I would try to get those reflections arriving in the first 15ms down to -20db. Even -15db would be a noticeable improvement. You have 4 peaks in the -10db range. Most likely 1st reflection points. If you can do this, your FR will smooth out some and you will get clearer images.

Last edited by jim1961; 01-18-13 at 09:12 AM.
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post #18 of 19 Old 01-18-13, 07:41 PM Thread Starter
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Re: Any comments on my measurements

So I did some shuffling and took some additional measurements today. The first I took was the black trace below.

As you can see in the pictures I have 3 2" Auralex Wedge 2'x2' panels not doing much on the rear wall. I measured the location of my first reflection on the ceiling and simply placed the panels right on top of the diffusor and took the measurement in red.

I then removed my two rear panels and set them on top of the two front panels as shown in the picture below drawn in paint as a grey triangle and the result was the blue trace. I think this proves my theory about needing the wall-ceiling corner super chunks.

My plan for the rear wall is also drawn out below using 7 2'x4' 3" rigid fiberglass 3.0pcf panels.

Is this looking better? Thanks much!
Attached Thumbnails
Any comments on my measurements-img_9633-small.jpg  

Any comments on my measurements-img_9634-small.jpg  

Any comments on my measurements-img_9638-small-w-panel.jpg  

Any comments on my measurements-etc-comparison-notes.jpg  

Any comments on my measurements-rear-panel-layout.jpg  

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post #19 of 19 Old 01-19-13, 10:08 AM
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Re: Any comments on my measurements

I am having a little problem sorting out what all the colors mean. But if I am getting it right, it looks like some progress has been made. How does it sound in comparison to before?

You still have some areas to deal with, but if in listening you prefer the now to the before, I would treat the remaining peaks.

Nice work!
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