Dual RL-P18 LLT for my 2000 cu ft HT soon

**Blaser** · **06-02-07, 03:43 PM**

I think that any porosity in MDF might be negligeable. But Plywood really seems stronger but at least double cost!!

**aceinc** · **06-02-07, 03:48 PM**

Actually, the amount of breathing that an untreated MDF cabinet with veneer, or some other nice finish on the outside does seems like it would be so minimal as to be meaningless compared to the dynamic changes of pressure induced by a subwoofer. I only paint the inside as a "belt & suspenders/chicken soup" type of approach, in that it doesn't cost much, and it may actually help seal any place I miss with glue & caulking.

I certainly wouldn't call it hermetically sealed, unlike Carnac the Magnificent's mayonaise jar kept on the front porch of Funk & Wagnall's house.

Paul

**Blaser** · **06-02-07, 04:02 PM**

FOR THOSE INTERESTED IN THE RL-P18 TESTING BY ILKKA, THEY ARE WELLCOME TO CHECK THIS:http://www.hometheatershack.com/foru...html#post38201.

I AM POSTING THIS HERE AS ALTHOUGH IT MAKES SOME TIME ILKKA HAD PROPOSED TO TEST THE WOOFER (AS FAR AS DONATION WOULD COVER THE DRIVER FEES), I JUST NEW TODAY, AS I WAS ONLY LOOKING AT THIS DIY FORUM....SO MAYBE SOME OF YOU JUST DON'T KNOW!

**brucek** · **06-02-07, 04:26 PM**

Quote:

According to the modelling softwares, lining the walls does not change the tune but slightly the FR...Anything wrong with it?

I don't think it's bad, it's just that stuffing changes the effective size of the box. I think you can calculate that size change and alter your box size in the modelling software and see what happens.....

brucek

**Blaser** · **06-02-07, 04:33 PM**

Quote:

brucek wrote:

I think you can calculate that size change and alter your box size in the modelling software and see what happens.....
brucek

Insulation is supposed to make the box appear bigger, not smaller....That's the issue: How larger??

**Blaser** · **06-02-07, 06:16 PM**

Cables now...What gauge is required to support 2000 W? Is 16 enough

**brucek** · **06-02-07, 07:22 PM**

Well, I'd use 12 or 10 gauge...........

**planet10** · **06-02-07, 11:33 PM**

Quote:

blaser wrote:

Thank you for your post

, I just need some clarifications pls
What do you mean by dead center?

Do not put a brace exactly in the middle of a panel. A more general statement is that any brace should not divide a panel into 2 (or more) identical sub-panele.

Quote:

How? Pls elaborate, Do you mean that not stuffing would be acceptable?
According to the modelling softwares, lining the walls does not change the tune but slightly the FR...Anything wrong with it?

As far as the frequencies a sub should be producing, damping has no effect. It will thou increase the appartent size of the box. I would not trust a modeler (except maybe MJK within linits) to account properly for the stuffing.

dave

**planet10** · **06-02-07, 11:37 PM**

Quote:

blaser wrote:

I think that any porosity in MDF might be negligeable. But Plywood really seems stronger but at least double cost!!

And what proportion of the total cost is that compared to the cost of the driver(s) and the effort you are putting into it?

Unless you are somewhere where the price of wood is out-of-site (ie BB in Western Australia), arguing about the difference in cost of panel material is penny-wise, pound foolish.

dave

**aceinc** · **06-03-07, 12:19 AM**

Quote:

And what proportion of the total cost is that compared to the cost of the driver(s) and the effort you are putting into it?

Unless you are somewhere where the price of wood is out-of-site (ie BB in Western Australia), arguing about the difference in cost of panel material is penny-wise, pound foolish.

This is what I meant by a religous war...

Some people belive that the mass and uniformity of MDF makes for a better speaker, others believe the strength of BB is better and there are even a few lost souls that believe particle board is best. I have been unable to find a definitive answer by someone that has done empirical, objective testing, and until I do, I will use plywood and MDF interchangeably, as in the speakers I am currently building that have a bit of both.

I have thought a little about a test regime. If I can get around to it what I thought I might do is take a driver (I have some HiVi A5+ 5" drivers laying about) build two cabinets that WinISD says is an optimal for sealed with a 1-1/4" MDF baffle. One cabinet would be 13 ply BB and the other MDF with veneer, braced as similar as I can make it. For testing I would;

1) Do freq tests measuring from one meter on axis, and set amplifier for a reasonable level such as 85db.

2) place the mic face down on each of the panels coupling the mic to the panel, and run the same tests.

3) place the mic about 1-2mm away from each panel and re-reun the above tests.

What I would hope to find is if there are any differences.

Paul

**planet10** · **06-03-07, 11:44 AM**

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)

Quote:

aceinc wrote:

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/showt...threadid=98834

dave

**brucek** · **06-03-07, 12:54 PM**

Quote:

you will need to be able to display waterfalls at a minimum.

Most people here use REW for mesurement software. It has waterfalls......

brucek

**planet10** · **06-03-07, 02:30 PM**

Quote:

brucek wrote:

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

**aceinc** · **06-03-07, 02:47 PM**

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

**brucek** · **06-03-07, 03:45 PM**

[/hijack on]

Quote:

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.............

Name: waterfall.jpg
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brucek

[/hijack off]

**Blaser** · **06-03-07, 04:04 PM**

Quote:

aceinc wrote:

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

. 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.

**Blaser** · **06-03-07, 04:36 PM**

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?

**Blaser** · **06-03-07, 04:51 PM**

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

It is not as easy as I thought

**Blaser** · **06-03-07, 06:36 PM**

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

**planet10** · **06-03-07, 06:38 PM**

Quote:

brucek wrote:

[/hijack on]
...... 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

**planet10** · **06-03-07, 06:42 PM**

Quote:

brucek wrote:

Apple has their own audio class library

CORE Audio is pretty good, and Apple only has so many resources...

dave

**Blaser** · **06-04-07, 04:39 PM**

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?

**planet10** · **06-04-07, 05:14 PM**

A flared port that has the same basic diameter needs to be longer.

dave

**aceinc** · **06-04-07, 05:24 PM**

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

**SteveCallas** · **06-04-07, 05:41 PM**

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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