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There are some studies that do objectively test panels... one good one is linked to in the thread below (which has some good waterfalls -- included in the thread below is an overlay of MDF & ply which shows why ply has an edge). Another is buried in an old AES article -- i have been tasked to try and find it (this one IIRC, clearly showed the superiority of particle board over MDF)

What I would hope to find is if there are any differences.
Have a look at this thread so that you can refine your procedure to give it enuff resolution to detect the panel resonances at all... you will need to be able to isolate the front of the cab from the measured panels, and you will need to be able to display waterfalls at a minimum.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=98834

dave
 

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Most people here use REW for mesurement software. It has waterfalls......
Now that is cool... it will run on my Mac. I just got my Pismo fixed (it is a Frankenstien) and had planned on using Fuzzmeasure, but this is the 1st alternative to that that i have seen.

I'll have to dig into the help files, but can anyone tell me if in the waterfalls, you can specify msec or periods for the "time" axis?

dave
 

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A waterfall plot will be useful, but before looking at it, I want to see which material will vibrate more, hence coupling the mic to the panel, and lets sound through, the reason for the close mic to the panel. I suspect if there is a difference in these tests, there will also be a difference in the waterfall plot.

I have not tried, but I have bought something for my next cabinets, and that is "Thick Grip" shelf liner, and HardiBacker tile backing board. The former is a foam waffle like shelf liner, the latter is a concrete like 1/4" board type material. My concept is to use contact cement to attach the shelf liner to the inside of the cabinet, and another coat of CC to attach the cement board to the shelf liner. this should add about 3/8" thickness to the cabinet wall. I think the best approach would be to not compress the foam by screwing, but I am not sure on this point.

At any rate we are drifting far afield from Blaser's intent to build a subwoofer.

Paul
 

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[/hijack on]

but can anyone tell me if in the waterfalls, you can specify msec or periods for the "time" axis?
Yes - here's a pic showing the adjustments. All the screens are of course derived from the impulse response.

There are some issues with REW and MACs. JohnM (author) indicates he may have to supply a MAC-specific version eventually to get around the problems. The usual benefit of cross platform capability relies on the platform providers supporting it, but Apple has their own audio class library instead of using the existing JavaSound classes, and so some people report problems when using REW. Others are OK, so give it a try...... or come on over to Windows like the rest of us............. :)

waterfall.jpg

brucek

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Discussion Starter #66
At any rate we are drifting far afield from Blaser's intent to build a subwoofer.

Paul
No Problem, feel free to have any constructive discussion:bigsmile:. I only wish your tests were soon enough, I should be building these subs within 10 days approx.

By thye way I found 15mm plywood (7 ply BB I think), and it was not as expensive as I thought...If any benefit ever I would go with it.:nerd:
 

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Discussion Starter #67 (Edited)
I need your opinion Guys....would you go for a 16 Hz Tune with with a 10" port, no port compression ever and no need for a flare (a bit less wood also), or a 14 Hz tune but with only a practical 8" flared port? Is there any benefit on real material?

By the way, the use of a 10" port will not leave 10" everywhere around the port entrance and may probably lead to a lower tune. Any comments?
 

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Discussion Starter #68
What's quite amazing is at time of thinking of going DYI, everything appeared to be very easy, and choices seemed obvious .... Now that I ordered and I am about to receive the equipments every small detail is very hard and time consuming to think about and I change my mind 5 times an hour:coocoo:

It is not as easy as I thought:dumbcrazy:
 

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Discussion Starter #69
By the way, here is a cross section photo of the 15 mm plywood I found here. Looks good enough?
 

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...... or come on over to Windows like the rest of us............. :)
I am not going to downgrade to Windows, i have too much work to get done on my computer... I will thou be getting an Intel Mac sometime in the future and will be running either Parallels or Cross-over Mac (WINE) on it so that i can run Windows programs (that don't yet have Mac equivalents) and have as little as possible to do with Windows as i can...

dave
 

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Discussion Starter #72
I think I will go for 8" port because of too low a port resonance with a 10" port. Nevertheless, I have noted something weird to me between Winisd and Unibox concerning the ports:

- I think I will do flared ports (both inside and outside).
Winisd says flanged (is it same as flared?).... port length decreases by swiching to flanged
- In Unibox, we have either flush or flared, but port length increases by switching to flared

Could anybody help pls?
 

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I thought it is the same length, but you measure from half way down the flare. This means the entire port is longer, but you can use the calculations for a non-flared, by adding this amount.

Paul
 

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If you need say 30" of port length for example, and want to use flared ends, the actual length of the cylindrical port will be less than 30", as half the length of each flare needs to be taken into consideration. If you do not use flared ends, the actual length of the cylindrical port would need to be 30" on its own.

As for MDF vs Plywood, while a more rigid enclosure is always better, realize that a LLT is one of the least demanding subwoofer enclosure applications, as the force created by the driver is spread out over such a large area (large enclosure), meaning lower pressure than say a small sealed sub using the same driver. MDF with bracing every 12" or so should be just fine.
 

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Discussion Starter #76 (Edited)
So why when swiching to Flanged in Winisd, the length decreases?
 

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Discussion Starter #77
Hi Steve....Nice to see you around and thanks for your generous help in this world :T... The problem I have with MDF is of a complete different nature from strength or SQ.... I don't know how I will get it to my house due to it's weight:dumbcrazy::bigsmile::R....I am really not joking, the boxes will be bigger than getting into the lift (yes it is a small one for my private building), and both of them will have to be carried-up through the stairs to the third flour:boxer:(boxmaker expects them to be 300 Lb+ with 3 layers front baffle):surrender: And I do not want to start with scratches or so either:rolleyes:
 

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So why when swiching to Flanged in Winisd, the length decreases?
I think that member collo has a good site about flares

He says:

The generally accepted adjustment is to subtract half the flare radius from the physical length to obtain the effective length. If both ends of the port are flared, the adjustment is done for each flare.

These ports have a flare radius of about 1 inch, so your design length of 17 inches means you build a port that is 18 inches from end to end.




So if you have a length in WinISD and you add a flare, you need to shorten that length to accomodate the flare length.

brucek
 

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Discussion Starter #79
Thanks Brucek!! and maybe Unibox takes the flare length into account so that the indicated length of the port increases....This might be the diference.
 

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Discussion Starter #80
Guys....The subs arrived today!!!!:jump: They are huge....I knew they are, but it is a completely different feel to see them...I must admit I was a bit afraid:holycow: These drivers are for my tiny 1800 cuft room??:raped:

I bought some accessories: 8 binding posts, 15m 14 gauge cable, 8" PVC pipes, and I also ordered the insulation material....(it is 1" corrugated sheets of polyfill....the seller qualified it as an "acoustic sponge"....and it is a sponge material isn't it). see photo.

Tomorrow should begin the fabrication with either 22 mm MDF(veneered maybe) or 18mm plywood (whichever is available), while the insulation material should be received on Thursday....Painting to be applied Thursday/Friday, and Hopefully you should see the first FR Saturday.

Note: 8" are huge really:bigsmile:, I don't know how on earth I could hear any shuffing, or reaching core velocity....But concerning the drivers that's another story....I am pretty certain only one driver would reach RL quite easily....We'll see:yes:
 

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