In this tutorial, I'll be giving the very basics of what you need to build a subwoofer, but in enough detail to understand how to make decisions based on need.
Unfortunately i can't explain everything or this would be too long, so if you don't understand something google it, if you don't come right ask me, if it needs to be added to the tutorial I'll add it in
I also wont be able to cover everything, and might leave out some things. This isn't really a Sealed vs Vented which is better thing, cause it all depends on application This is just a tutorial to show how one can go about comparing and playing around.
I'm sure you went to google and searched: "subwoofer build" or "subwoofer DIY" and you know you need a Driver, Box and Amplifier.
However what you need to understand is your own requirement first.
Eg.
I want to build this subwoofer for:
This is your most basic requirement, and most likely the reason you said, "hey I want to build a subwoofer" (right after you said "damn these commercial subs are pricey, there must be another way").
Now that we know what we are aiming to build for, we need to estimate what we can use to achieve our goal.
We need to have the following information:
Lets take only these for our starting criteria.
1) I want to build subwoofers for HomeTheater, I do listen to music, but usually not critical listening.
If I was to estimate probably around 95% HT, 5% music. So for me the HT element is most important.
2) I can fit one in a corner and one will be in the left side of my room, but not in the corner.
3) So my aim will be two subwoofers.
4) Measuring the areas, I'd be able to get 600x600x700mm(LxWxH) for both subs.
5) Current system plays down to 40-50hz.
6) Lets just make it an even 10k(two subs). Will go into this in more depth later.
From our requirement we see that we need to produce a lot of low frequency at high enough volumes (SPL) to be able to satisfy our need.
Here we get an important factor, volume. 252 Liters external volume. If we use 16mm MDF we'll have 216 liters, if we use 32mm 183liters of internal volume. This volume will become less when adding bracing and if vented, the port will take up some volume too.
This is important because when we select our driver, we must be able to fit it in the space accordingly to achieve our goal.
So now comes the question of what Driver will we use? Well our budget allows for 2k per driver, which doesn't allow us for much in terms of importing, so as most people in SA have to do
we look at local subs, car subwoofers or the classifieds for a bargain.
When looking at drivers, there is a magnitude of things too look at, but I'll leave that for another post.
For now we'll play around with 1 driver, of which I do have parameters.
Many manufacturers give parameter sheets with their drivers, just be wary of if they tested it in a box or free air.
I strongly suggest getting WinISD, it's free to download: http://www.linearteam.dk/default.aspx?pageid=winisd
This manufacturer provides a 10", 12" and 15" model, but for now we'll just go with 15" model.
Here is a comparison of the frequency response graph, for "optimal" tuning per driver, sealed and vented.
Vented: Red(15"), Sealed: Green(15")
Here we can clearly see that there is significant difference in each instance.
This 15" has a FS of 29Hz and costs ~R1000
Typically for hometheater you want to get drivers with an FS lower than 25Hz. (However in this scenario lets say we only have these available)
We do see however that this driver fits our budget very well and we'd actually be able to buy 4 of them.
A comparison of 1 (Green) vs 2 (Blue) vs 4 (Red) drivers, yellow is the sealed version of the same number of drivers:
This graph shows the Maximum SPL for the combination of drivers.
So as you can see one driver requires 169.6 liters of air, 4 requires 4 times that so ~678 liters for the Vented enclosure and,
77 liters for a sealed box, but we could actually get 2 drivers in one box, with the amount of air available.
So this will be a shootout between the 2 x 1 x 15" vented enclosures, and 2 x 2 x 15" sealed enclosures.
Calculating in the Vent the graphs look like this:
We need to get low bass out of these, so playing around with the tuning frequency and box size we can see the following on the max SPL:
For the sealed enclosure there's nothing more we can do. The vented however we could decrease the volume a little more, and decrease the port tuning even lower.
We now have clear 4db gain over the sealed box down to 15hz from 13-14hz down, the sealed takes the lead.
The vented enclosure is now down -7db at 17hz, and the sealed -16db down.
We can however trim the high frequencies for the sealed enclosure a bit, to bring the sealed to around 8-9db down at 17hz.
So you say the vented enclosure for this HomeTheater build is the clear winner right? We've hit our goal which is low frequency response, we've made our box accommodate the port, bracing will be ignored for now, with 20 liters bracing the effects on the subs are very little.
Even though we've hit our target with the vented enclosure, the sealed is actually also meeting our requirement, if were were to factor in that one subwoofer is in the corner, which will give us a couple of free dbs including the normal room gain even if minimal, we'll still be seeing around 118db(+3db) at 15hz.
All good and well, but the vented enclosure will also be getting the gains, and you will once again have a more capable vented subwoofer.
Now we need to factor in that these numbers are for the MAX SPL. This will be the hardest the driver can be pushed before failure.
So lets back down a bit from MAX SPL and just feed these two subs 500w rms.
So now suddenly we are seeing a very different picture, the vented enclosure is by far surpassing the sealed enclosure due to the port giving us that additional dBs at the tuning frequency.
In this design we see that power will be the eliminating factor, because we are using car subs that chomp down on the watts, our amplification will be too costly to build this as a sealed unit.
Also the gain at tuning frequency will give us a much better HomeTheater experience.
So all in all we have designed two subwoofers, very capable of representing themselves in a hometheater.
In the end:
Vented costs:
2 x 15" = R2000
1 x ~2kw Amp = R3500
2 x MDF = ~R1000
Sealed costs
2 x 15" = R4000
1 x ~2kw Amp = R3500
2 x MDF = ~R1000
With some moola left for finishing
Unfortunately i can't explain everything or this would be too long, so if you don't understand something google it, if you don't come right ask me, if it needs to be added to the tutorial I'll add it in
I also wont be able to cover everything, and might leave out some things. This isn't really a Sealed vs Vented which is better thing, cause it all depends on application This is just a tutorial to show how one can go about comparing and playing around.I'm sure you went to google and searched: "subwoofer build" or "subwoofer DIY" and you know you need a Driver, Box and Amplifier.
However what you need to understand is your own requirement first.
Eg.
I want to build this subwoofer for:
- HomeTheater
- Music
- HomeTheater and Music
- Massive amounts of noise at one frequency
- To Fill a gap, or handle a certain range
- etc
This is your most basic requirement, and most likely the reason you said, "hey I want to build a subwoofer" (right after you said "damn these commercial subs are pricey, there must be another way").
Now that we know what we are aiming to build for, we need to estimate what we can use to achieve our goal.
We need to have the following information:
- Where will this subwoofer(s) stand?
- How many subwoofers can be accommodated?
- How much space is available, measure for maximum Length Width height
- What is the current capability of the system?
- budget for the project?
Lets take only these for our starting criteria.
1) I want to build subwoofers for HomeTheater, I do listen to music, but usually not critical listening.
If I was to estimate probably around 95% HT, 5% music. So for me the HT element is most important.
2) I can fit one in a corner and one will be in the left side of my room, but not in the corner.
3) So my aim will be two subwoofers.
4) Measuring the areas, I'd be able to get 600x600x700mm(LxWxH) for both subs.
5) Current system plays down to 40-50hz.
6) Lets just make it an even 10k(two subs). Will go into this in more depth later.
From our requirement we see that we need to produce a lot of low frequency at high enough volumes (SPL) to be able to satisfy our need.
Here we get an important factor, volume. 252 Liters external volume. If we use 16mm MDF we'll have 216 liters, if we use 32mm 183liters of internal volume. This volume will become less when adding bracing and if vented, the port will take up some volume too.
This is important because when we select our driver, we must be able to fit it in the space accordingly to achieve our goal.
So now comes the question of what Driver will we use? Well our budget allows for 2k per driver, which doesn't allow us for much in terms of importing, so as most people in SA have to do
we look at local subs, car subwoofers or the classifieds for a bargain.
When looking at drivers, there is a magnitude of things too look at, but I'll leave that for another post.
For now we'll play around with 1 driver, of which I do have parameters.
Many manufacturers give parameter sheets with their drivers, just be wary of if they tested it in a box or free air.
I strongly suggest getting WinISD, it's free to download: http://www.linearteam.dk/default.aspx?pageid=winisd
This manufacturer provides a 10", 12" and 15" model, but for now we'll just go with 15" model.
Here is a comparison of the frequency response graph, for "optimal" tuning per driver, sealed and vented.
Vented: Red(15"), Sealed: Green(15")
Here we can clearly see that there is significant difference in each instance.
This 15" has a FS of 29Hz and costs ~R1000
Typically for hometheater you want to get drivers with an FS lower than 25Hz. (However in this scenario lets say we only have these available)
We do see however that this driver fits our budget very well and we'd actually be able to buy 4 of them.
A comparison of 1 (Green) vs 2 (Blue) vs 4 (Red) drivers, yellow is the sealed version of the same number of drivers:
This graph shows the Maximum SPL for the combination of drivers.
So as you can see one driver requires 169.6 liters of air, 4 requires 4 times that so ~678 liters for the Vented enclosure and,
77 liters for a sealed box, but we could actually get 2 drivers in one box, with the amount of air available.
So this will be a shootout between the 2 x 1 x 15" vented enclosures, and 2 x 2 x 15" sealed enclosures.
Calculating in the Vent the graphs look like this:
We need to get low bass out of these, so playing around with the tuning frequency and box size we can see the following on the max SPL:
For the sealed enclosure there's nothing more we can do. The vented however we could decrease the volume a little more, and decrease the port tuning even lower.
We now have clear 4db gain over the sealed box down to 15hz from 13-14hz down, the sealed takes the lead.
The vented enclosure is now down -7db at 17hz, and the sealed -16db down.
We can however trim the high frequencies for the sealed enclosure a bit, to bring the sealed to around 8-9db down at 17hz.
So you say the vented enclosure for this HomeTheater build is the clear winner right? We've hit our goal which is low frequency response, we've made our box accommodate the port, bracing will be ignored for now, with 20 liters bracing the effects on the subs are very little.
Even though we've hit our target with the vented enclosure, the sealed is actually also meeting our requirement, if were were to factor in that one subwoofer is in the corner, which will give us a couple of free dbs including the normal room gain even if minimal, we'll still be seeing around 118db(+3db) at 15hz.
All good and well, but the vented enclosure will also be getting the gains, and you will once again have a more capable vented subwoofer.
Now we need to factor in that these numbers are for the MAX SPL. This will be the hardest the driver can be pushed before failure.
So lets back down a bit from MAX SPL and just feed these two subs 500w rms.
So now suddenly we are seeing a very different picture, the vented enclosure is by far surpassing the sealed enclosure due to the port giving us that additional dBs at the tuning frequency.
In this design we see that power will be the eliminating factor, because we are using car subs that chomp down on the watts, our amplification will be too costly to build this as a sealed unit.
Also the gain at tuning frequency will give us a much better HomeTheater experience.
So all in all we have designed two subwoofers, very capable of representing themselves in a hometheater.
In the end:
Vented costs:
2 x 15" = R2000
1 x ~2kw Amp = R3500
2 x MDF = ~R1000
Sealed costs
2 x 15" = R4000
1 x ~2kw Amp = R3500
2 x MDF = ~R1000
With some moola left for finishing
