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

31K views 182 replies 19 participants last post by  Blaser 
#1 ·
Final design not completed yet, but I will go for 2 boxes 550-600 L effective, 16 Hz tune, 8" or 10" port, powered by EP 2500, dual 2 ohm configuration.

I am not that good in woodworking, so I am only making the design on paper, but will have the job performed by a carpenter.

I have some variables I would like your advice about:

- MDF or not? If MDF, 16mm, 18mm, or 22 mm? Front baffle will bear both the driver and port.
- Is bracing a must? Never read that anybody made an enclosure without bracing, but I did that for my 4cu ft car sub. and it is rock solid and working very very well, I can even stand on it... no problem. Of course at least the port will be internally supported.
- Insulation: Is it a must? If yes, is 1" fiberglass ok? Should the volume be taken into consideration? I never read someone did...

Your inputs are highly appreciated.

Blaser
 
#36 ·
Discussing wood material can start a religous war:devil: and don't even start about glues.

My opinion, for what it is worth is I like MDF. If you want to get wild and crazy and you are using double thickness for things like the baffle, use a layer of good plywood laminated to a layer of MDF on the outside. This among other things will give your screws something to bite into.

If you want to deaden the cabinet really well without spending big bucks buy some 1/4" "HardiBacker" and 30# felt (commonly called Tar Paper). Put one layer of 3/4" MDF two layers of 30# felt and 1 layer of HardiBacker together and screw liberally. This will couple additional mass, a second material with different resonances and add damping to the cabinet. It shouldn't cost much but will add a fair amount of work to the endeavour.
 
#46 ·
for what it is worth is I like MDF
I on the other hand, would follow the advice of the cabinet maker, and build the box out of plywood. You want it to be void free (ie Baltic Birch or ApplePly).

Hopefully, without starting a holy-war, i will state my opinion, that MDF is one of the worst materials for building speaker enclosures. I'll put an exclaimation on that by saying that we get MDF for free, yet still go out and buy BB for making boxes.

For a subwoofer this is even more the case. Even staunch defenders of MDF will admit that the extra stiffness of plywood makes it better for subs. Probably the most important characteristic of a sub box is that it not act like a balloon. (another little realized problem with MDF is that it is not air-tight)

The box needs to be braced (and please do not be tempted to put them dead centre -- that is the worst place for them)

The need for stuffing in a sub is debatable, but the rational was covered pretty well in an earlier post. Do take into consideration that it will change the apparent volume of the box, and thus its impact on the box tuning needs to be considered.

dave
 
#37 · (Edited)
I ordered the RL-p18 s 2 days ago, and the amp yesterday!!:jump:

I should receive them within 10 days. I am already fed-up of:waiting:....But, when they come it will be a big:bigsmile:

I think my last decision is two boxes around 625L each, 14.5 Hz tine with an 8" flared port for practical considerations.

You can expect my impressions and probably some measurments within 2 weeks:yes:

Cheers!
 
#38 · (Edited)
Update: Mike confirmed that the drivers were shipped :jump: Thank you Mike for being so prompt in shipping the units as soon as money transfer was performed:hail: I should receive them around June 11th...:waiting:

For the sake of telling bye bye to my old sub., I performed some listening tests (max SPL at listening position) with music today...

My sub is a Jamo X8 sub, 200W RMS with limiter, 12", (visually) Xmax does not seem to be more than 9mm (maybe even less), 2*3" ports around 40. I blocked a port to lower the tune to be around 34 Hz.

So, I put some good dynamic music (50 cent, Sean Paul, Depeche mode...) and amazingly it could hit 117 db digital RS uncorrected with most of the materials in my 1800 '3 room at listening position (4m) :raped: It seems that I had quite underestimated this sub.. Sound depth was good enough for music, everything was shaking....but I must admit that I never felt the WOTW effects most peoples speak about:rolleyesno:

Comparing the above with the upgrade that should be performed soon (10 times more power, 2 drivers, 18", competely different Xmax....):neener: and guess about the results:flex::devil:

Can't wait:heartbeat:

Edit: I made some more tests and the 117 db was mainly (by ear) between 30-40 Hz (axial room mode), although I have the sub equalized, the room offers lots of headroom at these frequencies.
At higher frequencies where I have dips( above 65Hz) it could only hit 110 db(uncorrected)....Still Great, but I will have some bass traps in the future:reading::neener:
 
#39 ·
In case anyone was wondering what the **** I was prattling on about in an earlier post;

Batting is used in both Quilting, and upholstery. Here is a link to an e-bay sale on some 1-1/4" batting;

http://cgi.ebay.com/Upholstery-Bond...QQihZ007QQcategoryZ116679QQrdZ1QQcmdZViewItem

or a more permanent link;

http://storesonline.com/site/490194/product/BB-CC-1219-ROLL

The advantage of batting is that it can be glued to the walls of the cabinet easily with spray adhesive, and won't bunch up or be pushed around by the air the driver moves.

My suggestion on the bracing is if you are going to brace in the middle of the cabinet with 1"x4" or similar instead of placing the braces parallel to the walls of the cabinet put them at an angle. See the top down view drawing attached. When bracing make the braces a hair bigger than the cabinert width/height so that when you dry fit them they will stay by themselves, but not so big as to distort the walls of the cabinet.
 

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#41 ·
My suggestion on the bracing is if you are going to brace in the middle of the cabinet with 1"x4" or similar instead of placing the braces parallel to the walls of the cabinet put them at an angle.
What's the benefit of putting them at an angle?
 
#40 ·
Yes, I needed these clarifications!

Thanks Paul!:T
 
#42 ·
My thoughts are that if braces are needed to reinforce the cabinet and increase the frequency at which the cabinet resonates (as well as reduce the tendency to resonate) placing them as non-symmetrically located as possible and oriented so that they break the cabinet into a number of non rectilinear sections may be beneficial. I can see at least 3 benefits;

1) oddly shaped spaces will discourage standing waves.

2) panels whose braces are assymetrical and oriented "randomly" will tend to have fewer reinforced resonances. In other words if there are multiple panels with the same geometry and bracing they will tend to resonate at the same frequency, reinforcing (amplifying) the resonated sound.

3) reflecting high frequencies at an angle will increase the amount of travel before they will go through the speaker cone, (as opposed to hitting a flat piece of wood and bouncing right back) decreasing their amplitude, and increasing the amount of polyfill they will travel through, reducing their amplitude futher.

These are my ideas, I do not have test data, or other empirical evidence to substantiate them. Perhaps some heavyweights can weigh in on these concepts.

I would not expect a large difference, but with a little effort you may get some benefit.

Paul
 
#43 ·
Paul,

Your thoughts seem very logical... And anyway I think that if the benefits are only minimal, there is no drawback!!
 
#44 ·
Regarding standing waves, I have a set of Atlantic Technology speakers (System 8200) where the cabinets have sloped backs that is suppose to help with standing waves.

Would the same design benefit subwoofers?? Any guesses how much slope would be correct??
 
#45 ·
Of course this would help for subs also. I applied such a shape for my car's, but for the monsters I will be building I have to keep the rectangular shape for better utilization of volume and save some space.

I do not think the slope is so critical....remember that all these are hepling factors but not basics IMO...

B Rgds
 
#48 ·
Some of the cabinets that are built based on the LLT design defined elsewhere on this site can have dimensions exceeding 5'. Wouldn't this start causing problems around 113hz? Not out of the range of some subs.

Cost is one reason for some of us to be involved in this "hobby" and the difference between 13 ply, void-free BB and MDF can make or break a project.

Regarding MDF being airtight, I use what I believe to be a simple, effective, and low cost option to resolve this;

After the cabinet is built, but before finishing the outside I slop a thick coat or two of latex paint on the inside of the cabinet. To maximize my funds, I only buy "oops" paint from the local Home Depot/Lowes at $5.00 per gallon. I try to get semi-gloss, as this tends to be quite rubbery when dry, my current cabinets that I am building using a design from planet10's Frugal-horn.com web site, have a rather garish purple interior.:sick:

Paul
 
#51 ·
I think that any porosity in MDF might be negligeable. But Plywood really seems stronger but at least double cost!!
 
#59 ·
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
 
#52 ·
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
 
#53 ·
#54 ·
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
 
#55 ·
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??
 
#56 · (Edited)
Cables now...What gauge is required to support 2000 W? Is 16 enough
 
#60 ·
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
 
#61 ·
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
 
#63 ·
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
 
#64 ·
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
 
#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:
 
#65 ·
[/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............. :)

Green Text Plot Slope Line


brucek

[/hijack off]
 
#70 ·
[/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
 
#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?
 
#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:
 
#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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#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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