Need help designing Sub - Need to go down to 17Hz for 'Earthquake' Project

[s162216]

Is the port volume the volume of just the wood, or the wood and the internal volume of the port? I am starting to think about dimensions now.

Do you definently think this will rumble a room at 250W RMS?

 

[TLS Guy]

Is the port volume the volume of just the wood, or the wood and the internal volume of the port? I am starting to think about dimensions now.

Do you definently think this will rumble a room at 250W RMS?

The volume of the wood. Don't forget to flare the port exit slightly. It will rumble OK. I think that driver is rated at 150 watts RMS, so be careful. It produces over 100 db at 20 Hz with a 150 watt amp, so it will do what you want. I hope you live in a detached house!

I grew up here, so I could produce a lot of spl! I had the room with the left dormer window, and the room went all the way to the back of the house.

 

[s162216]

O.k this driver can handle up to about 250W rms safely, checked JL Audios site,

http://mobile.jlaudio.com/products_subs.php?series_id=15

Look at bottom of page for chart, 250W is just about in the danger zone.

I live in a semi detached house, but I will have other venues such as the scout hut my mum runs her cub scout group at where I should be able to play it full volume, will be especially good when they have the christmas party, that will rock the hut!

I will proberly at home never turn it up too much as I don't want complaints or getting my speakers confiscated.

When I get my first house, I am going to get a shed and soundproof it just for my HT, then no one can complain.

What I would really dream of doing is having a cinema in my shed, I remember reading about a guy in Wales who opened the worlds 'smallest cinema' in his shed in his back garden and had a 35mm film projector with digiital surround sound as well as proper seats that were getting thrown out of the local Odeon.

Now that would be a HT!

 

[s162216]

O.k so this is what the port should look like on the turn up the back.

Does the port have to built out of 0.75" MDF like the main case or can I use some cheaper, thinner wood instead? 18mm MDF costs a fortune, £14 for 2.4m x 1.2m. Theres bound to be some off cuts though so I could use for the port if needed.

Sorry, will have to attach picture later, stupid schools blocking the attachment.

 

[TLS Guy]

O.k so this is what the port should look like on the turn up the back.

Does the port have to built out of 0.75" MDF like the main case or can I use some cheaper, thinner wood instead? 18mm MDF costs a fortune, £14 for 2.4m x 1.2m. Theres bound to be some off cuts though so I could use for the port if needed.

Sorry, will have to attach picture later, stupid schools blocking the attachment.

The port needs to be of the same material. You can build your box from 3/4" plywood or MDF whichever is cheapest.

 

[s162216]

MDF, plywood costs about £20 more for a single sheet the same size.

Heres the circuit for the rumble generator, will this need preamping or would I ahve to just connect it?

When you say flare the exit port slightly, by about how much as I don't have a router I will have to sand it.

 

[TLS Guy]

MDF, plywood costs about £20 more for a single sheet the same size.

Heres the circuit for the rumble generator, will this need preamping or would I ahve to just connect it?

When you say flare the exit port slightly, by about how much as I don't have a router I will have to sand it.

That should be able to connect to the amp directly. Just sand a good convex bell on the port at the exit.

 

[lsiberian]

MDF, plywood costs about £20 more for a single sheet the same size.

Heres the circuit for the rumble generator, will this need preamping or would I ahve to just connect it?

You bring back memories of college.

 

[s162216]

TLS Guy, when you gave the volume that I should use, did you definently include the volume of the driver? (0.025 cubic feet)
I am going to work out the relavent volumes of the port and bracing on Saturday, so that I can then work out how big sub will be.
If I can keep the height under 600mm (23.6") as then I can make two or three sides from one MDF sheet of 2400mmx1200mm then that would be good.
Hopefully I will only need at the most 2 sheets and I can get half size ones if needed.

By the way I may be in luck about a router as my dad is thinking of getting one as he could do a better job with one in the kitchen he is building at the moment

 

[lsiberian]

For volumes it takes a huge change to make a noticeable difference. So don't worry about the driver's volume too much. Just make sure you brace and dampen it with cloth wrapped high density 4" fiber or mineral wool. Behind the driver to reduce mechanical noise.

As far as router goes get a plunge base one they are the most versatile.

Ply is a lot lighter than MDF. So consider that for transporting.

 

[s162216]

Is there anything else that can be used apart from mineral wool or fibre which is cheaper? I can't find 100mm (4") mineral wool anywhere for less than £30.
Should I line all the walls with it or just the back and sides?

 

[TLS Guy]

Is there anything else that can be used apart from mineral wool or fibre which is cheaper? I can't find 100mm (4") mineral wool anywhere for less than £30.
Should I line all the walls with it or just the back and sides?

Yes, I did allow for the volume of the driver, Vd, which according to my data is 71 lt, which works out to be 0.03 cu.ft. You will see that in the pdf I sent you the link to.

You need to use mineral wool. You will see that the design calls for minimal fill, that means no more than 50% of the internal surface should be covered. The main purpose is to stop reflections. In that case make sure the back wall is covered and the other surfaces just around the driver. So a little less than 50% of the other surfaces will be covered.

If you put in too much fill you will kill the box resonance and the speaker will not work.

 

[s162216]

http://soundproofingforum.co.uk/?products/amw_soundproofing.htm

Found some cheap - only £8 for 1200mmx600mmx100mm, top of the list

Most of the stuff I found was so expensive as it was a massive great role designed for loft insulation.

So its only the back and around the driver?

 

[TLS Guy]

http://soundproofingforum.co.uk/?products/amw_soundproofing.htm

Found some cheap - only £8 for 1200mmx600mmx100mm, top of the list

Most of the stuff I found was so expensive as it was a massive great role designed for loft insulation.

So its only the back and around the driver?

Yes, you have it. Just cover 50% like you stated. Make sure you wear cloves and a mask when working with that mineral wool. It is wicked stuff.

 

[lsiberian]

Yes, you have it. Just cover 50% like you stated. Make sure you wear cloves and a mask when working with that mineral wool. It is wicked stuff.

Not as bad as fiber thankfully, but make sure you cover it in cloth. I suggest 4" on the back 2" on the other sides.

If your gonna skimp don't skimp on the back

Another option is to put a brace in the box and put the 4" rockwool a few inches behind the driver.

http://forums.audioholics.com/forums/attachment.php?attachmentid=6883&d=1234388792

This is how it's done for the Kappa build. Which is a high quality design. I suggest using that as a model for your build. I plan to use it for the model for my sub

 

[s162216]

Do I include the volume of the mineral wool in my calculations for the total box volume or does it not matter?

 

[TLS Guy]

Do I include the volume of the mineral wool in my calculations for the total box volume or does it not matter?

Mineral wool is very cellular, fibrous and porous. It holds large amounts of water and is used in hydroponic plant culture. The volume of the fibers is impossible to know. I would ignore the wool volume and just be a little generous with the brace volumes.

 

[lsiberian]

Do I include the volume of the mineral wool in my calculations for the total box volume or does it not matter?

I usually subtract it from the volume. Maybe that's wrong of me. But in a large volume the variances of small areas aren't huge in the sound produced.

It takes a huge change to make a noticeabel difference.

 

[s162216]

Just checked out that PDF you posted about this sub, noticed this:

--Box Parameters--
Vb = 2.415 cu.ft
V(total) = 2.744 cu.ft

Which one is the actual one I should use? Vb or total?

 

[lsiberian]

Just checked out that PDF you posted about this sub, noticed this:

--Box Parameters--
Vb = 2.415 cu.ft
V(total) = 2.744 cu.ft

Which one is the actual one I should use? Vb or total?

The vb.

I use Box notes to design the dimensions of my box.