Newbie - Basic Questions

[Spadez]

Hi,

I have no idea what im doing at this stage. Ive only just been introduced to the idea of building my own sub, but it is a route I would like to go down, so Ive got to do my research. I would appreciate it if someone can answer my basic questions to help me on my way:

1. When building a sub, is it possible to use subs designed for cars? I remember when I tried to hook up a car sub to my amp and it didnt work because of the difference in impeedence.

2. Is it a problem to design a sub so that it points up to the sky? Would it be better to have it point down at the floor or sideways.

3. Is a strong wood the best material for a sub housing?

4. Is a 15" sub a strong choice if I can afford it? Ive heard they sound great, especially the low tones.

5. Ive seen people putting additional electronics in their sub box. Is this an additional amplifier?

Im sorry for all the questions, im quite excited by the project so im trying to find out all I can so I can get stuck in!

[StereoClarity]

Spadez wrote:

Hi,

I have no idea what im doing at this stage. Ive only just been introduced to the idea of building my own sub, but it is a route I would like to go down, so Ive got to do my research. I would appreciate it if someone can answer my basic questions to help me on my way:

1. When building a sub, is it possible to use subs designed for cars? I remember when I tried to hook up a car sub to my amp and it didnt work because of the difference in impeedence.

2. Is it a problem to design a sub so that it points up to the sky? Would it be better to have it point down at the floor or sideways.

3. Is a strong wood the best material for a sub housing?

4. Is a 15" sub a strong choice if I can afford it? Ive heard they sound great, especially the low tones.

5. Ive seen people putting additional electronics in their sub box. Is this an additional amplifier?

Im sorry for all the questions, im quite excited by the project so im trying to find out all I can so I can get stuck in!

1)Yes, you can use a car audio sub as long as it meets your specific design requirements. Many home audio subwoofer amplifiers are stable at 4 ohms so you should be able to use one of those. 2ohms is a bit less common to find an amp that will work with that.

2) Firing a sub straight up is not a problem but some people worry about a certain amount of "sag" that the driver will experience due to gravity over time. In my opinion it's not really an issue and most suspensions are sturdy enough that it's not something I ever worry about.

3) Wood is probably the most ideal material you could use. It's strong, light (comparatively), easy to work with, and is readily available.

4) A 15" sub will move a good amount of air and is great for HT use.

5) Not sure what you've seen but most will mount a plate amplifier on/in the sub. This amplifier takes an LFE (low frequency extension) signal from your receiver and amplifies it. Some people have a rack mount or a free standing amplifier which means that no plate amp is needed.

[Moonfly]

I'm doing the exact same thing right now,and loving it. Its driving me mad waiting for my drivers to be delivered. Theres plenty to read up on though, and plenty to think about. Where would yuo like to start

[Spadez]

Moonfly wrote:

I'm doing the exact same thing right now,and loving it. Its driving me mad waiting for my drivers to be delivered. Theres plenty to read up on though, and plenty to think about. Where would yuo like to start

Thank you both for the reply. My idea so far is to use a single JL 15" driver in a cherry wood container.

In an ideal world, I would like the biggest driver in the smallest container but something tells me this won't give me great results. Is it ok just to stick a sub in the side of a box or does it need special ducting? Is there any benefit to the box size when you mount it this way?
Posted via Mobile Device

[Mike P.]

My idea so far is to use a single JL 15" driver

Do you already have the sub? Can you post the T/S parameters or a link to them? Modeling will show what the sub is capable of and the best size box for it.

[JCD]

some random answers

1. Car audio can be used, and some do so with decent results, but I'd stick to a home audio sub
2. Firing the driver in any direction should be fine. I wouldn't want it on top since it's more likely to be damaged that way. If it's firing down, you need to make sure there is enough room between it and the floor (I'm not sure what that spacing should be)
3. 3/4" MDF is my preferred material. Baltic birch is also a common wood. Solid wood is usually not as good acoustically and is a LOT more expensive. If you want it to look like solid wood, I'd build it with MDF and then veneer it with whatever looks good to you.
4. When trying to reproduce bass frequencies, size matters. That doesn't mean a 15" driver is always better than a smaller driver. Depending on the size of the room, a 12" driver may work just fine.
5. I think someone already referred to them, but you seem to be talking about a plate amp. For most applications, it acts as the amp for the driver as well as performing some phase shifting.
6. Generally speaking, the bigger the driver, the bigger the box. You should prepare yourself for a big box.
7. If you don't want to worry about the design issues of a subwoofer, there are numerous designs out there already. If you lived on this side of the pond, Parts Express, Madisound, Solen, Zalytron, etc. all offer drivers that can be used to build a sub as well as kits that just require you to cut and assemble the wood.

[Mike P.]

HT Subs and can be found at CSS, Exodus Audio, Fi, and SoundSplinter (when they are back in stock) Subwoofer kits can be found at CSS.

[Spadez]

Thank you again for your replies. Ive looked into it and Ive found some subs that I like but I think I still have some more questions to decide on what I want. So I know im after a 15" sub, I want to make my own container and use laminated MDF. I want to keep the box size as small as I can. Its to fit under my bed at uni and I dont have a lot of extra space in my room that I could put the sub. The height under the bed is only about 18CM so im going to mount the speaker facing down at the floor with small feet.

Can you tell me if there are different styles of speakers that will allow me to have a smaller box design to put it in.

The sub im currently looking at is this one (but im open to suggestions)
http://www.diycable.com/main/product...roducts_id=684

[Spadez]

Also a side note. Im not actually that 15" is the best option for me. I dont really know much about it, but people have told me about the "magic" of a 15" that just sounds significantly better than a 12". Is this true, or bull?

My way of thinking is that the 15" dont seem to cost a lot more than the 12" and bigger is probably better, but then again what do I know?!

[Moonfly]

Thats an IB driver. Its not suitable for use in a normal box woofer. If you look down the list of parameters at the bottom, you will see one labelled VAS. This figure is the size of cabinet required for that driver. You can mess with this figure a bit, but ideally you want to follow this. IB drivers are no good as they are designed to use an entire room as the cabinet, much to large. Also, the Vas figure on IB works slightly differently, so just ignore IB drivers.

I'm using these drivers myself:

http://aespeakers.com/shop/catalog/p...products_id=68

[Spadez]

Thank you for the reply. Your driver looks very cool, im assuming its a 15" by its product number?

How does it compare to this driver:

http://www.creativesound.ca/details.php?model=SDX15

Also the site listed above has designs for enclosures which will probably be a big help to me.

[Moonfly]

Box designs arent a problem, its building your first one thats the tricky learning curve bit. That driver is supposed to be very good. Comparing to the 15" AE driver I chose, Ive seen it said mine has better SQ, but yours might just have a db or 2 more when going very deep.

Are you thinking of a sealed, or ported design?

[Spadez]

Im going for a sealed design. Its seems to be better suited to me and also helps keep the size down. They seem quite matched then, yours looks better though . Im sorry to ask, but what is SQ? Are these subs all generally 4ohm or is it more specialist?

Id quite like to make the box out of aluminium, is that a bad material to use, and i better off with MDF?

What determins the size of the box? If im using a sealed box rather than ported will it really make a lot of difference?

[Moonfly]

SQ = Sound Quality. A sealed box is smaller and easier to design. It will also generally integrate better within a room due to its simpler design. They are less efficient than ported subs though so need more power generally speaking. Power is quite cheap these days though so that not an issue depending on exactly how you want to drive the sub (some people prefer the cheaper, simpler but more powerful separate rack amps). Ported subs will go deeper easier, but with a 15" driver I cant see depth being an issue for you anyway, especially if your placing it under your bed etc.

A lot of subs are 4 ohms, and thats a fairly common figure, but some are 8, or use 2 x 2ohm voice coils etc. Some manufacturers will build the voice coil to your desired impedance (Fi are an example I believe). Sticking with 4 oms will be fine, and most amps are happy with that.

As for building. Aluminium will resonate like crazy and ruin the sound IMO. The box has to be sturdy and solid, and a bit of weight is required to to achieve this. MDF is common among DIY'ers and manufacturers alike. There is nothing to stop you putting an aluminium skin on this box though to acheive your desired finished though . Some people prefer to make the box out of thick ply wood, so that may be an option for you as well.

[Spadez]

Hi.

Thank you for the reply. Ive been thinking about it and I think I have an idea of where I want to go. I want to use the driver that you are using, since I think SQ is more important than DB.

Im going ot build it out of MDF and if the speaker works well, ill spend time improving the asthetics with a laminate.

Would I be able to get away with putting it in a 16"x16"x16" cube, which I think works out at 2.37 ft3. Should I model it in that program to really find out?

[Moonfly]

It works best in a 75litre enclosure (I'm in the UK). You can use the enclosure volume calculators on here to work out what size that is. A box of 16" cubed comes in at a little less than that size, and with bracing and driver displacement you'll lose a bit more volume, more still if you use a plate amp. You can however gain a little of that lost performance back by using fibrefill inside the and cabinet.

If you can make you box 17" wide and deep, then with 16" height you'll have the 75 litres before deductions for braces and driver etc. Again, you can gain that back with fibre fill to a degree. It'll be tight getting the 15" driver in a box with outer dims of 16" though.

[Spadez]

Hi moonfly, thanks for the reply.

Im in the UK too (Kent, England). How did you get the drivers from AE as they are US, do they have an outlet in the UK? Ill have a play about with the dimensions to get it to work.

As a last thing, can you please explain what effect fibre fill has? Does that allow me to have a smaller enclosure?

[Moonfly]

I had to order them direct from the manufacturers website. I did it with a couple friends to get a discount so didnt work out to bad for me, not sure for you mate, although as we are still waiting for them to arrive, I may be able to sort you something out as a one off. I'll PM you my number.

There is a good article on fibrefill here:

http://www.nousaine.com/pdfs/Box%20Stuffing.pdf

I guess the gist is that you can get away with a smaller box. But generally, I would rely on that 100 %. If you use win ISD to simulate your sub though, you can see the effect the smaller box will have on performance. Real world results with room gain, and adding stuffing, will likely be above what the simulation predicts. That should give you a good idea of what to expect.

There is a link to the file required to simulate this driver in a post here:

http://www.hometheatershack.com/foru...tml#post196196

Thanks to Mike P.

[Mike P.]

Regarding the comparison of the two subs, people who have heard both of them say the AV15-X is better in the mid bass region while the SDX15 has better low bass output.

Finding the right sub for your application will depend on what your goals are.

1. Is this for home theater, music, or both?

2. What is your budget for the sub and required amp to drive it?

3. What size is the room the sub will be in, is the room sealed off from other areas or is it open to other areas?

4. What is the biggest external box size that is acceptable?


Based on the answers to the above questions it ill help narrow down the options that are available to you.

[Spadez]

Hi Mike,

The biggest box I could go for is something like a 17"x17"x30" but Id rather keep it small if I can, as long as it doesnt heavily sacrifice performance.

Its mostly for music actually, but I will be using it for games and movies.

My budget for both is probably ~£500 but im a student so the less I spend on this the more food and beer I can buy :P. That said my current bose and yamaha amp setup probably cost more than that, and I want this to be significantly better to justify the money.

Attached is a picture of my uni room. This is where its going this year, but next year ill be taking it home to use there, which is probably 6mx6mx3m.

Regards,

James

[Mike P.]

Is your "Yamaha amp" a receiver that has has 5.1 capability?

[Spadez]

Unforntatly not, but im prepared to buy a new amp as I do want surround sound.

[Mike P.]

What country are you located in?

[Spadez]

England so ideally I would like a driver from the UK, however I do have a mate in the USA who could send it over to me.

[Mike P.]

Your box dimensions give a net volume of about 3.5 cu.ft if going ported. There's a website in England that stocks Dayton subs, I'm trying to locate it. We'll find a sub that will work in the given box volume.