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Help needed, my first diy subwoofer

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20K views 74 replies 9 participants last post by  gperkins_1973 
#1 ·
Hi everyone,

I would like to build a sub woofer for my home theater.

I have read a lot of posts & have quickly become overwhelmed, so would like as much help as possible.

I have found a Mach 5 Audio IXL 18" Subwoofer driver & think would do the job (unless someone has a better idea).
I have heard Behringer is the amplifier to get & have found a Behringer EP 2500 amp but am not sure if it is the right amp to suit the driver.

The cabinet design I like is the slot ported version, there are no size limitations on the cabinet.

Hope I haven't asked to many questions :help:
 
#2 ·
Hi Jeff and welcome to the Shack!

The IXL-18 will definitely get the job done and is known as the 'best bang for the buck' for low end extension in a HT sub. The EP2500 is an excellent match for this. 12.5 cu.ft net volume tuned to 15 hz with a 2.5" X 17" X 35" long slot port would get the most out of this sub. There about a dozen builds in the Database you can have a look at if you need any ideas.

http://www.hometheatershack.com/forums/members-diy-subwoofer-database/24323-mach-5-audio.html


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#6 ·
Thanks everyone for your help it is greatly appreciated.

Before I go & buy all of the components I would like to ask some more questions.

One thing I see a lot of is tuning to get the right sound.

If I build the slot ported cabinet, is then a matter of connecting the sub amp from my main amp via RCA & then running speaker cable to the sub driver?

If not can you please tell me what would need to be done to tune it.

Thanks.
 
#7 ·
Yeah, youv'e got it, alot of folks will use speakon connectors on there sub box cause they are cleaner looking but i prefer using flush mounted binding post cups on my builds.
Keep us posted on the build and put up some pics along the way. Happy building.:sn:
 
#11 ·
No problem with the questions that is why we're here. In post #2 Mike stated your net volume should be 12.5 cu.ft. Net. That is not taking into account driver displacement or bracing, On that very same post (#2) you'll see in Mikes window something like box calculater click on it and it will take you to a section of the forum that will give you all the details you need to properly design a box including port displacment, driver displacement also your displacment for your bracing. Go there and play around for a bit and get back to me if you have anymore question ,i'd love to help.:T
 
#12 ·
Thanks for the reply.

I have had a look there, but it is asking for dimensions of the cabinet & I don't even know what size I need.

I entered the port info Mike sent through & it gave me a total port value.

This area is where I am really lost. :surrender:
 
#14 ·
Ok your getting somewhere.:T Now enter your displacment values that you know (port displacment, and driver displacement). Once you enter those start throwing numbers in the other windows for what sizes you hope will work and to your specs (i.e. do you want it tall, long or deep) then hit calculate if the numbers are nowhere near your needed volume then just keep playing with the numbers hitting calculate each time your done entering untill you get the correct volume. once you have that you'll need to figure out your bracing and add that to the equation and recalculate it and probly having to move some more numbers around till your back to where you need to be.:T Practice and play with it for abit and you'll figure it out. Anymore questions just holler.:T
 
#15 ·
I would second the suggestion of looking at the Easy Button threads because there are a number of Sketchup drawings in there that will help you visualise what you need to do for the construction.

12.5ft³ is 356 litres net. To decide the shape of the box, look at where you want to put it and find a limiting dimension if you have one. For example, you are limited to a min of about 50cm on one side because the driver frame is a bit over 46cm diameter. 356l is 356000 cm³, so 356000/50 = 7120. Lets say you cannot have the enclosure more than 1m tall; 7120/100 = 71.2cm so you now have an enclosure of (internal) 50 x 100 x 71.2cm.

This is your baseline set of dimensions, but we still need to consider driver, port and bracing volumes.

Using Mike's suggestion; "12.5 cu.ft net volume tuned to 15 hz with a 2.5" X 17" X 35" long slot port", the internal volume of the port is 1487.5in³ or 24376cm³, the driver takes about 8 litres and bracing will be (WAG here) 15 litres. The total internal volume needs to be adjusted up to 404 litres and the dimensions jiggled to fit. Then decide do you want the driver on the front or the bottom of the box. Then start sketching to fit it all into place.

The baffle will need to be double thickness if using 18mm because the chassis flange is very thick and you'll need sufficient depth to have somewhere for the T nut inserts to go.

Something else to consider to perhaps make it easier for your first time build would be to use sonotube (called Formatube in Australia). There are plenty of builds using it here, for example this current one. Boral would be able to direct you to a local supplier if interested. because a slot would be hard to do in this type of build, the port can be substituted for one or more round tubes, eg PVC water pipe that equal the cross sectional area of the 2.5 x 17" slot port.

For the EP4000, DJ Warehouse is typically the cheapest in Oz for them.
EP4000

Thinking in non metric units makes my brain squirm, so here's a very useful unit converter that I have used for many years.

There is also an enclosure volume calculator here that will help. Collo's Boxnotes (free) software is also useful to have as is his Sonosub software, and there is a wealth of information and experimental data regarding sub design and construction on his website.
 
#16 ·
Thanks for the info.

I am having a lot of trouble getting my head around all of this.

I have a mac & most of the software doesn't work on it.

What I imagined was a square or rectangle cabinet around 1100 mm high (43") high or there abouts. The width & depth can be whatever the calculations say it will be. Then the driver will be in the front & the slot port either in the bottom or the top.

So if I was to use mike's volume calculator I need to know the cabinet size to work out the bracing etc don't I?
 
#18 ·
Thanks for the info.

I am having a lot of trouble getting my head around all of this.
Don't over think it: it's simply a box.

What I imagined was a square or rectangle cabinet around 1100 mm high (43") high or there abouts. The width & depth can be whatever the calculations say it will be. Then the driver will be in the front & the slot port either in the bottom or the top.
Here are two examples of how I would do it; both are side cross section. The first has the port exiting the front below the driver, the second straight out the bottom, with the entire box being raised on feet to allow the port to breathe. You could have the port exit the top, but I don't like that as for sure some foreign object will end up inside the enclosure. You could also use 4 100mm round water pipes 91cm long instead of the slot port.

The bend in the first design is to minimise turbulence in the port by not having a 90° bend and it's length becomes the centreline of the port.





So if I was to use mike's volume calculator I need to know the cabinet size to work out the bracing etc don't I?
I already did it for you. Should be close enough and with a box this large, a couple of percent difference doesn't matter anyway.
 
#17 ·
To answer your question, yes that is how i do it then i might have to change a number here or there to get the volume back to where i need it. Just for fun i typed in 24X24X44 inches and came up with a volume of 12.4cu.ft. now that was without adding bracing, port or sub displacement.
So if you throw tose numbers around a bit and add find your dimensions then you can determan your bracing and add it just remeber you'll have to move some more numbers around to get it right and it isn't totally critical to get it exact but very close will do. Play around some more and you will get it.:T
 
#20 ·
Hi there,

To get a 12.5 cu ft net you will need a bigger box than 24" x 24" x 44" as this will only give you a net box volume off 11 cu ft but this will make no difference to the amount off spl you will get. You won't even loose 0.5db at 20hz. Attached are two pics, one is off the calculations I have worked out on the box size above. I have put 400 cubic inches for the bracing which is what I roughly put in my 11 cu ft boxes and the other pic is to show you what sort off bracing I put in mine which would be similar to yours. It makes the box very solid and rigid. I cut out slots in mine and slotted it in which also makes it stronger too.

What mike has suggested would be great in a dual set up too.

With Mikes winisd plot you will only need 700 watts to get that spl, otherwise you will go over max excursion but my drivers are 1000 watts rated and I run mine 2 ohms stereo with 1000 watts rms and even at full tilt it still doesn't bother the drivers.

I used a 90 degree bend in my ports and dont get any port noise at all and I am currently tuned to 13hz with quite a narrow port so you will be fine without having the hassle off putting a 45 degree angle bend in.

Looking forward to seeing your pics when you start.

cheers

Graham
 

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#21 ·
I am still having trouble with the design of my cabinet.
There have been people that have been nice enough to help me & worked out formulas etc.
But it makes it hard for me to make any adjustments to the sizes as I'm still not sure how to calculate the volumes yet.
One trouble I am having is that I can't find the driver volume of the Mach 5 Audio IXL 18" sub woofer.

I have found a design that I like & would like to do something similar.
Loudspeaker Subwoofer Audio equipment Brown Wood


How do I work out the internal bracing that is shown in that cabinet.

It doesn't have to be as elaborate as per the drawing if it doesn't have to be.

I am happy to have the port at the front in the top or bottom position or even at the back, it doesn't really worry me.

The other thing is at the very beginning Mike suggested a slot port size of 2.5" x 17" x 35"
What does that mean?
Is it 2.5" high x 17" wide?
If so what if the cabinet is wider than 17"
Then what is the 35" dimension come into it?

Thanks again for all of your patience with me on this topic. :wave:
 
#22 ·
For the bracing you subtract the volume of how many squares you cut out of the panel.

The driver volume of the IXL-18 is .25 cu.ft.

The internal dimensions of the port need to be 2.5" high x 17" wide. The port length is 35" long.

If the internal width of the cabinet is wider then 17" inches then the port needs to have sides on it so it's only 17" wide.

When figuring out the port volume you need to add the thickness of the building material if the cabinet is wider then 17".
 
#23 ·
Hi there,

That was my design. If you give me the dimensions off the box you would like or the space you have I can model you a drawing in sketchup and work out the measurements for you on the bracing.

My boxes are 11 cu ft so they won't be too different to mine.

My subs are 42" high by 22" wide by 28" deep.

cheers

Graham
 
#24 ·
Hi Graham,

Thanks for the offer, it is greatly appreciated.

The cabinet size I would like is 22" wide x 22" Deep & the height can be what ever it works out to be.

Please let me know if this size is ok or if you think it should be a different size.

Many thanks again for the offer.

Regards,
Jeff
 
#27 ·
Jeff,

Roughly you will be looking at a 22" wide by 24" deep by 54" high to get you a net off 12.5 cu ft.

Attached is roughly what you will be looking at. I need to double check your port size when I get home but remember you won't loose much if you go down to 11 cu ft in spl. 11 cu ft comes out at 48" high.

I would then stick with a 20.5" width port as it will make the build easier. I think from memory you could get away with a either a 2" or 2.5" port height by what ever the determind port length is.

Do you want me to sketchup something for you later.

cheers

Graham
 
#30 ·
Thanks Graham / Mike.
The cabinet dimensions Graham has done above look good to me.
Thanks Mike if you could re jig the port dimensions for the above cabinet would be great.
Do I have to make the front face material thicker for the sub woofer driver?

Graham If you could do a sketch for me & the details on where the bracing is to go & the details of any cut outs that need to be done.
And also the port length details that Mike mentions.

Thanks for all of your help, I really do appreciate it.

Regards,
Jeff.
 
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