Dual box sealed 18" Mal X build begins. - Page 10 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #91 of 99 Old 01-26-11, 09:12 AM Thread Starter
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Re: Dual box sealed 18" Mal X build begins.

That's solid advice!, thanks. Great to hear that you achieved so good results.

My main concern is ringing. It appears that having two subs solved the dip I used to have across the couch, which is great!

The dips I have now occur higher up and caused by the front speakers I suppose. So I think bass trapping can help on that.

Reducing ringing below 40hz seems almost impossible with conventionel broadband absorbers. Or would require a ton of them beyond what I can get acceptance for!

I'll get around to making some measurements for a larger range, up to say 400hz?

Because if I can "live" with EQing the peaks around 30-40 and then treat the higher up peaks and dips I think I will be ok and it will be a real world solution with decent WAF also.
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post #92 of 99 Old 01-26-11, 09:31 AM
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Re: Dual box sealed 18" Mal X build begins.

Claus, I absolutely love how those turned out. Very, very nice work. The finish looks fantastic, and the glossy base is a nice touch. I still love the subtle curve of the top, and I really may steal your design if I'm able to do a dual MalX setup down the road.

So is the plan to replace the MalX's with two LMS if you decide you like it better, or are you going to keep one of each?

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post #93 of 99 Old 01-26-11, 11:04 AM
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Re: Dual box sealed 18" Mal X build begins.

Claus,

I saw an improvement down to about 25 Hz with 3 big floor to ceiling traps. Keep in mind that music exists mostly above 40 Hz, so I'd be concerned most about what happens from 50 - 300 Hz. Your room already looks like one that has been trapped, so I can only guess you are one of the lucky ones.

30 - 40 Hz isn't a huge concern IMO. That's getting into LFE territory and a little extra ringing there that you have will give the impression of a bit more bottom end.

Don't forget you have 20 corners in a rectangular room. So you could pick some corners that get you into less WAF trouble. A bit of creativity might pay off. Here is one trick to make them seem not so big. Place a door so that it straddles the corner (just imagine it). Now move it into the room about 6". That makes it bigger acoustically due to the depth to the corner, but visually it looks like a smaller trap because you see the width more than the depth. Now had you made it a simple triangle shape, it would look much bigger because instead of a width of 820mm you might see 1000mm. I hope that makes sense.

I think with tools like cheap mics and REW floating around, people get fussy with nice flat lines. It's not too difficult to achieve, but the eyes are more fussy than the ears. A ruler flat line looks good on paper, but if the time domain isn't equally pretty then you will still have problems. Instead I'll take +/- 5 dB up to 300 Hz with a well trapped room because I've found that sounds better. Even less flat than that can be a good result.

Here is what I got with bass traps:



You can see my starting point was not as good as yours. I wrote about it here:

http://redspade-audio.blogspot.com/2...trap-test.html

This is my before:


I tried it out with some foam I had around the house because I was not too convinced about the value of bass traps and the need to give up valuable space in my small room. The result got me hooked right away and it was a big turn around. I had considered bass traps the icing on the cake in the ideal perfectionist setup. Talk about a big change of opinion!

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post #94 of 99 Old 01-26-11, 03:20 PM Thread Starter
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Re: Dual box sealed 18" Mal X build begins.

Quote:
Owen Bartley wrote: View Post
Claus, I absolutely love how those turned out. Very, very nice work. The finish looks fantastic, and the glossy base is a nice touch. I still love the subtle curve of the top, and I really may steal your design if I'm able to do a dual MalX setup down the road.

So is the plan to replace the MalX's with two LMS if you decide you like it better, or are you going to keep one of each?
Thanks alot!

Feel free to copy the design, mine's a copy also, with minor tweaks. As someone mentioned earlier, a piece or two of cross bracing might be worthwhile, to further enhance the cabinet.

I will get another LMS down the road for sure, but I think a new larger TV, then possibly a better reciever is better spend right now since my bass is quite good now.
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post #95 of 99 Old 01-26-11, 03:31 PM Thread Starter
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Re: Dual box sealed 18" Mal X build begins.

Paulspencer,

I absolutely agree with not obsessing with a ruler flat response. When I dailed in my new sub + the old one, I focused mainly on reducing decay time.

Alot of trial and error went into the 30-40hz area, but eventually I think I got it as good as I can with my current knowledge and experience!

It's quite interesting to see your waterfall graphs and nice image switching for easy comparison!! Looks like you solved the 25hz, 40-50hz and 70hz problems, and beyond that just looks amazing really. Do you know what's causing your dips from 70hz onwards?

How much acoustical treatment did you end up with? Not sure it states that in your blog? Just those 3 big corner traps?

I think I might be obsessing a little about my 30-40hz ringing and perhaps I'm giving overemphasis to that area in regards to whats causing boomy bass in my room?

Tomorrow, if I get around to it, I'll try and make some more measurements.

Regarding my room. Right hand back corner is actually a double french door style. I think it might act as one big membrane bass trap and it certainly vibrates in some scenes during movies!

Front right corner is a set of double windows on either side, so wouldn't be possible to place traps there.

Front right corner has the one sub in it. Placing a huge bass trap there across the corner would be less a no go. I was thinking one 100mm trap each side of my TV behind the main speakers.

Left back corner is the only really good bass trap corner. However, there are 2 smaller windows there about 1.2' from the corner itself. This means I am unable to construct a large trap there.....

Basicly I'm stuck with the walls.

Ceiling is slanted, with 8 feet near the walls and 10 feet in the middle.

Last edited by clausdk; 01-26-11 at 03:37 PM.
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post #96 of 99 Old 01-26-11, 04:36 PM
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Re: Dual box sealed 18" Mal X build begins.

these are my favorite looking DIY subs i have seen yet. i would really love to build a couple myself as i think they are good looking enough to get past SWMBO!!

is anyone able to pen up some cut sheets??? i have tried using sketch up but i cant figure it out.

great work again.
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post #97 of 99 Old 01-26-11, 07:09 PM
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Re: Dual box sealed 18" Mal X build begins.

Quote:
Alot of trial and error went into the 30-40hz area, but eventually I think I got it as good as I can with my current knowledge and experience!
My guess is that if you reduce it with traps, it will give the impression of less weight on the bass. When I first tried traps, I noticed two things in particular. Firstly, it sounded like the bass had moved outdoors! It no longer sounds like that but comparatively it was the initial impression. It's a bit like when you suddenly notice the air conditioning noise in a room only when it stops. Secondly, it sounded like there was less bass, but I recognised that this was a time domain issue. It's hard to keep track when you keep changing EQ and crossover like I do, but I find I tend to run the bass a little higher. This increases the sense of punchiness and oomph in the bass and it becomes more visceral yet does not seem louder than before, even though it is. I find this more satisfying. Yesterday I had a session with some rock music and the improvement in bass punch is startling. Kick drums just have that extra attack. I think some might even find it underwhelming, the impression of less bass and as a result turn it up like I did.

Quote:
It's quite interesting to see your waterfall graphs and nice image switching for easy comparison!! Looks like you solved the 25hz, 40-50hz and 70hz problems, and beyond that just looks amazing really. Do you know what's causing your dips from 70hz onwards?
Yep, that's easy .... the room!

As you probably know already, the modal range is about 40 - 300 Hz. Above that the modes are spaced so close that they smooth out. So we call that point where they are close enough not to matter the Shroeder frequency.

Quote:
How much acoustical treatment did you end up with? Not sure it states that in your blog? Just those 3 big corner traps?
Just those 3 huge and horrendously ugly things. The rear one is now covered with a sheet. They are all about 2.4m high and about a foot thick to make up for being foam. All made out of what I had on hand. I'm going to experiment a little with seeing what happens if I squash the foam together to make it more dense. I may soon get some rigid fibreglass and see how it compares. Unlike most bass traps, I plan to use mine as midrange absorbers as well. The two front traps - one has a foam single mattress on the front and the other a small double. That's a lot bigger than most folks use where about 600mm would be more common.

It's a bit hard to visualise your room, but I have this habit of walking into an audio room and immediately seeing all the spots you could put bass traps. It sounds like you have a lot of "free bass traps" as your room has some lossy elements. Less work to get good bass, but more neighbour issues! So you have a cathedral ceiling? What about the lower corners? Could you run some along the length? Bulkheads that a lot of guys use could make good bass traps.

When I first tried bass traps, I measured things like opening doors and windows. Surprisingly it made little difference - I could measure it but not hear it.

Another interesting thing is that a couch moved out slightly from a wall acts as a bass trap. Moving it out moves the bottom corner of effectiveness down. You can think of it as a trap that takes care of the floor the wall corner. Remember at least 20 corners in a room!

Quote:
I think it might act as one big membrane bass trap and it certainly vibrates in some scenes during movies!
I'd think of it as a leak. As a membrane trap it would not be very effective because they are pressure mode and need to sit right at a boundary to work.

Quote:
I was thinking one 100mm trap each side of my TV behind the main speakers.
That would be a membrane trap, like the ones on Ethan Winers old site. I believe those are much less effective as they are narrow band traps with a centre frequency of about 90 Hz. Handy in that they are unobtrusive, but fairly limited. I plan to add some as well, but I'd consider them "bonus traps." You'll find that Ethan himself pretty much suggests that people put in the broadband traps, as many as people can fit, and no longer strongly recommends the membrane traps. A typical room is actually like one big membrane trap, but generally not a well designed one and also one in which it works only over a narrow range. They need to be tuned at different points to extend their range. There is a good BBC paper online about modular membrane traps where you can see their range. Ethan recommends 6" broadband with a 6" air gap over a membrane if you can allow the extra space or 4" membrane if that's as big as it gets.

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post #98 of 99 Old 01-27-11, 06:42 AM
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Re: Dual box sealed 18" Mal X build begins.

Quote:
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these are my favorite looking DIY subs i have seen yet. i would really love to build a couple myself as i think they are good looking enough to get past SWMBO!!

is anyone able to pen up some cut sheets??? i have tried using sketch up but i cant figure it out.
Try a free program like Cutlist. It should be able to put together what you need, if you have the rough dimensions.

- OJ -

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post #99 of 99 Old 01-27-11, 08:22 AM Thread Starter
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Re: Dual box sealed 18" Mal X build begins.

My dimensions are 53x53x46 (HxWxD) in cm. Then add 2-3cm for the curved top. The base plate is simply 22mm MDF cut slanted. Also the corners are also cut in 45 degree angles. This hides assembly points as well.

Internal volume, minus bracing, is 90 liters in mine.
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