DIY Sealed Subwoofer

[Decadent_Spectre]

You should identify bandwidth and spl requirements first. As an aside while it is not conventional wisdom for a sealed box for fast/tight bass I recommend using driver with qts less than 0.25 and as low mms as possible. If using bookshelves dont be afraid to use it upto 200Hz. Also Ive found 12s to work best.

 

[Vineethkumar01]

The bracing does not need to be as elaborate. Bracing like this is less complex, uses less material and is as effective. And all strips can be separate ones just as long as they are glued to each other at the points they intersect.
View attachment 71823

Are these wooden strips glued together in this pattern? and at what place in the cabinet do they need to be fixed. In the middle?
With the other elaborate bracing scheme, the the panel on each side is effectively divided into approx 4 sub panels with each sub panel now having a higher frequency at which they will tend to exhibit panel resonances. With this new scheme, will we get the same benefits?

You should identify bandwidth and spl requirements first. As an aside while it is not conventional wisdom for a sealed box for fast/tight bass I recommend using driver with qts less than 0.25 and as low mms as possible. If using bookshelves dont be afraid to use it upto 200Hz. Also Ive found 12s to work best.

In the initial posts, he has told that he doesn't want much high SPLs. So I have described a bass alignment which is decent but not the best in terms of utilising the power handling capabilities of the driver.

Also, can you tell a bit more about what is the speciality with Qts less than 0.25 and light diaphragm driver for a subwoofer application ?

Thanks
Vineeth
@aeroash : Few questions
1) With what speakers are you planning yo use a sealed subwoofer like this?

2) What is your room size and typical listening distance under consideration here?

 

[ssf]

@aeroash : Few questions
1) With what speakers are you planning yo use a sealed subwoofer like this?

2) What is your room size and typical listening distance under consideration here?

https://www.hifivision.com/threads/speaker-suggestions.90307/page-4

 

[Decadent_Spectre]

In the initial posts, he has told that he doesn't want much high SPLs. So I have described a bass alignment which is decent but not the best in terms of utilising the power handling capabilities of the driver.

Also, can you tell a bit more about what is the speciality with Qts less than 0.25 and light diaphragm driver for a subwoofer application ?

Thanks
Vineeth

I did read that but he did not define a number, high or low SPL is relative and subjective. You are well aware of the roll off of a sealed system, particularly noteworthy for subs and the bandwidth you wish to cover, desired response curve and available equalisation.

Listening tests I have done show the difference in subjective speed here with low qts and light mass drivers. While I can't quantify it anymore than the obvious that low qts means more control of the driver and low mms helps with high frequency response, subjectively they provide fastr/tighter bass. As before I am less inclined to side with conventional audio "science" and more with my own experiences.

 

[Vineethkumar01]

I did read that but he did not define a number, high or low SPL is relative and subjective. You are well aware of the roll off of a sealed system, particularly noteworthy for subs and the bandwidth you wish to cover, desired response curve and available equalisation.

Listening tests I have done show the difference in subjective speed here with low qts and light mass drivers. While I can't quantify it anymore than the obvious that low qts means more control of the driver and low mms helps with high frequency response, subjectively they provide fastr/tighter bass. As before I am less inclined to side with conventional audio "science" and more with my own experiences.

Thanks..
Can you please suggest any drivers?
Something with low Qts and a low Fs.
Faital pro 15FH510 seems to have a Qts of 0.26 and fs of around 35Hx per their specs and quite a bit of power handling to take EQ well but what is a low mms target here?

 

[keith_correa]

Are these wooden strips glued together in this pattern?

Yes.

and at what place in the cabinet do they need to be fixed. In the middle?

At the same place the window braces need to be placed.

With the other elaborate bracing scheme, the the panel on each side is effectively divided into approx 4 sub panels with each sub panel now having a higher frequency at which they will tend to exhibit panel resonances. With this new scheme, will we get the same benefits?

If you look at the elaborate bracing scheme, you will see that the scheme "braces" it at unnecessary (ineffective) places, IMO.
Now, to address the division part. Is it really dividing it? To really divide it, the brace needs to be a "holey" brace.

 

[aeroash]

@aeroash : Few questions
1) With what speakers are you planning yo use a sealed subwoofer like this?

Sonus Faber Lumina 1

2) What is your room size and typical listening distance under consideration here?

Room Size: 11'x11'
The listening distance is 7'
@Vineethkumar01 this is the draft. I will incorporate @keith_correa simpler bracing scheme or a version of it.
View attachment SB Sub.jpg

Posting some basic information about impact of damping materials

Data-Bass: Subwoofer Measurements

data-bass.com

That's good insight. I have the Rockwool SIlent Pro 350 (Density 60kg/m³) in 50mm Thickness. Reading the article I hazard that this would perhaps be an "overkill". What else could I use? @keith_correa any suggestions?

 

[Vineethkumar01]

@Vineethkumar01 this is the draft. I will incorporate @keith_correa simpler bracing scheme or a version of it.
View attachment 71833

Now that changes the sealed box bass alignment a tiny bit. This is because a 15inch driver will take up about approx. 5litre of space and your bracing too will take up a bit of space (I have assumed that it too takes up 5L of space) This is going to give you about 95L internal volume effectively. A bass alignment like this can give the following frequency response (solid blue line) compared to this driver in a cabinet with 105L effective internal volume (dot-dash line). This is not bad. It may even be a little better in terms of power handling (you will be able to put in a little bit more power in the 95L cabinet compared to a 105L cabinet)

First thing that is new here is that now I have added the effect of rising inductance at higher frequencies caused by the driver's motor system (due to the lack of shorting rings in the motor). This is causing the droop down in response after 150Hz. However one will still be able to hit reasonably high SPLs as shown in the figure from 30Hz to greater than 200Hz with some EQing (if at all needed). So it is ok.

Here are some frequency response decay numbers (frequencies at which SPL is 3dB down from the max value (f3) , 6dB down from max value(f6) , and 10dB down from max value (f10))

Values for the105L cabinet
f3 48.3 Hz
f6 35.6 Hz
f10 26.3 Hz

Values for the 95L cabinet
f3 49 Hz
f6 36.2 Hz
f10 27.1 Hz

Notice the teeny tiny bit of loss in low frequency extension with 95L cabinet compared to 105L cabinet. This is typical. The advantage with 95L cabinet is that you may be able to put in about 20-30W more power into the system (this will help with frequency response shaping using EQ)

Here are more detailed results for the simulation above for those interested.

Now here is the impact on box resonance mode distribution for your cabinet dimensions as per the drawings

Notice how the green and red box modes have now collapsed into one single peak close to 400Hz compared to two more separated out modes in my previous posts. This will mean that there will be relatively strong box mode and impedance bump somewhere above 350Hz. The audibility of it will depend on the SPL levels, damping used inside the box and the upper frequency cut off used for the sub. If you intend to roll of the subwoofer around 120Hz or so or even lower, This may not be an issue. Still a thing to keep in mind.. Please do estimate the volume with bracing added. The lower the box internal volume is going to be, the more it will start to move into the "booming" regime. Ideally, with this sub you may not want to reduce the internal volume of the cabinet much further.

Cabinet construction detail-wise, do keep in mind that the driver has an outer diameter of about 420mm. Double thick baffle as you have drawn is a good idea. I prefer to have bracing interconnecting all panels of the box together. Especially the baffle to the back of the box, as the baffle is where most of the forces are going to be exerted. This is why I liked the initial bracing scheme. If you are going for a simplified bracing and going to put bracing only in the middle, please do take this aspect also into consideration. The forces exerted by a driver of this size on the baffle is not trivial and is better considered in the design stage itself in my opinion.

If you look at the elaborate bracing scheme, you will see that the scheme "braces" it at unnecessary (ineffective) places, IMO.

You mean the middle of the panel is where the forces/velocity modes are at their minimum and having the brace connecting all the middles of the panels may not be as effective as it looks like?

Now, to address the division part. Is it really dividing it? To really divide it, the brace needs to be a "holey" brace.

Ok. Would this kind of bracing be good?
similar to the simplified bracing shown above but located offset from the middle inside thr box. Also having something connecting the fromt baffle and back of the box

 

[Decadent_Spectre]

Thanks..
Can you please suggest any drivers?
Something with low Qts and a low Fs.
Faital pro 15FH510 seems to have a Qts of 0.26 and fs of around 35Hx per their specs and quite a bit of power handling to take EQ well but what is a low mms target here?

Don't have suggestions off hand, I've been out of DIY for a while. I suggest GPA if he has the budget, or AE or Faital, RCF, PD, Celestion. For more easily available there is 18sound and Eminence. Mysuggestion is to stay away from B&C and JBL. For home audio dont know. For mms it's been a while but I guess less than 100 grms for a 15, I used to look for 80 IIRC, again don't remember too well it's been a while.

 

[ravindrads]

So I made an enclosure calculation based on dimensions shown in below pic to get the volume of 105 Litres. I have roughly allocated some 2 litres for volume taken up by driver and 8 litres for volume taken up by bracing. Depending upon the bracing scheme, these numbers vary a little


I have assumed a double baffle of 36cm thickness and put only 18cm thick walls everywhere else. These numbers cam be read out from below pic.

A key aspect of woofer/subwoofer cabinet is to brace it well.. Now we want some one to draw a box with these kind of dimensions and decide the bracing scheme etc..

The below pic also shows the location frequencies of box modes. In simple words, we domt have to see (hear) those peaks that we see in the below pic. Thier locations in frequency are decided by the enclosure dimensions. For this subwoofer box, they are not much of a problem since you will be crossing it over to other speakers well below 200Hz.

Also, it is to time to start thinking about power amplifier for this, crossover/low pass filter etc.. You need a minidsp and a separate amplifier or a plate amplifier with filter cut off frequency adjustment etc for all this.

Keeping all these in mind, coming up with an estimate of cost is also important..

View attachment 71820

Rythmik makes great sealed sub's.

 

[keith_correa]

This is a "holey" brace.
And no matter which bracing scheme is implemented, front to back bracing (along with side to side) is always effective typically, though with the 36 mm panel front suggested, not critical in this case.
What we can implement here, is tying up all box panels with solid panels but with many large/small holes in them so that bracing does not take up much volume but is also effective. Of course, if @aeroash can implement the initial bracing scheme without much effort, he should just go for that. I just think it's a bit fiddly to implement.

 

[aeroash]

Please do estimate the volume with bracing added. The lower the box internal volume is going to be, the more it will start to move into the "booming" regime. Ideally, with this sub you may not want to reduce the internal volume of the cabinet much further.

thanks, @Vineethkumar01 once I finalise the bracing scheme I'll take into consideration the internal volume and redraw if required to keep it between 95L and 105L.

@Vineethkumar01 @keith_correa I've no issues executing the original complex bracing. My concern is that I'm not able to calculate how much volume a bracing with 18mm ply will take up. My maths is worse than a toddler's. Can we hazard an estimate? I do not want to go under 95 litres with the box.

 

[Vineethkumar01]

@Vineethkumar01 @keith_correa I've no issues executing the original complex bracing. My concern is that I'm not able to calculate how much volume a bracing with 18mm ply will take up. My maths is worse than a toddler's. Can we hazard an estimate? I do not want to go under 95 litres with the box.

If you can give me a diagram (with dimensions) showing the bracing scheme for this box, I can calculate the volume for you or you just oversize the box for 5-8 litre more volume and build it

 

[aeroash]

If you can give me a diagram (with dimensions) showing the bracing scheme for this box, I can calculate the volume for you or you just oversize the box for 5-8 litre more volume and build it

How many millimetres would I need to add to the depth of the box for an extra 5 litres of volume?

 

[Vineethkumar01]

How many millimetres would I need to add to the depth of the box for an extra 5 litres of volume?

Based on some rough estimates that i could do with the initial elaborate bracing scheme, if you go with that kind of bracing, it will take up about 5-6 litres of volume roughly (or even less).

Now, if we had kept the volume occupied by the braces the same and oversized the box by extending the depth an inch more, That would increase the internal volume by 46.4cm (width) x 46cm (height) x 2.5cm (new extra depth) = 5.3 litres (approximately).

However note that this oversizing the depth of cabinet will also increase the dimensions of the two braces along the depth dimension by a small amount. Since such an increase is only marginal, we can safely assume that it will be occupying less than the 0.3litre (out of 5.3litres) margin we got based on extending depth by an inch.

 

[aeroash]

Based on some rough estimates that i could do with the initial elaborate bracing scheme, if you go with that kind of bracing, it will take up about 5-6 litres of volume roughly (or even less).

Now, if we had kept the volume occupied by the braces the same and oversized the box by extending the depth an inch more, That would increase the internal volume by 46.4cm (width) x 46cm (height) x 2.5cm (new extra depth) = 5.3 litres (approximately).

However note that this oversizing the depth of cabinet will also increase the dimensions of the two braces along the depth dimension by a small amount. Since such an increase is only marginal, we can safely assume that it will be occupying less than the 0.3litre (out of 5.3litres) margin we got based on extending depth by an inch.

Thanks @Vineethkumar01 point noted; driver’s on the way.
I found this for binding posts. Good enough? Any other options?

Sound Speaker Box Terminal Cups 2 Copper Binding Post Wire Cable Connector Acoustic Components https://amzn.eu/d/dFOkLZi

 

[DB1989]

Based on some rough estimates that i could do with the initial elaborate bracing scheme, if you go with that kind of bracing, it will take up about 5-6 litres of volume roughly (or even less).

Now, if we had kept the volume occupied by the braces the same and oversized the box by extending the depth an inch more, That would increase the internal volume by 46.4cm (width) x 46cm (height) x 2.5cm (new extra depth) = 5.3 litres (approximately).

However note that this oversizing the depth of cabinet will also increase the dimensions of the two braces along the depth dimension by a small amount. Since such an increase is only marginal, we can safely assume that it will be occupying less than the 0.3litre (out of 5.3litres) margin we got based on extending depth by an inch.

Is it possible to increase cabinet height and create a tallboy subwoofer, something like the Perlisten D215S / Mission LX10?

That way, would it be possible to increase cabinet volume without increasing the length, breadth?

 

[Vineethkumar01]

Is it possible to increase cabinet height and create a tallboy subwoofer, something like the Perlisten D215S / Mission LX10?

That way, would it be possible to increase cabinet volume without increasing the length, breadth?

Yes. It is definitely possible to create a tallboy subwoofer.
In fact I personally prefer such subwoofers based on looks and some other factors.
Even acoustically, having different dimensions along length, breadth, depth is of some benefit in terms of box resonance mode distribution.
The cabinet shape usually doesn't matter much from a subwoofer point of view (less than 100Hz regime). The cabinet volume is more important.
Once we try to cross them over at higher frequencies, these things (cabinet shape, relative location compared to speakers etc) start to matter more and more.

 

[Vineethkumar01]

@Vineethkumar01 driver’s on the way.
I found this for binding posts. Good enough? Any other options?

Sound Speaker Box Terminal Cups 2 Copper Binding Post Wire Cable Connector Acoustic Components https://amzn.eu/d/dFOkLZi

I generally don't like the plasticky things around the binding posts..
How about this: https://diyaudiocart.com/diy-speaker/Speaker-Terminal/Dayton-Audio-BPA-38G-HD-Binding-Post-Pair-Gold
Requesting others also to chime in with suggestions.

Now, before buying anything else, I sincerely request you to write the requirements down in a piece of paper or a post here.
This is for planning the build and estimating the costs, efforts/manpower involved and to buy appropriate components (wood, driver(already bought),wires, binding posts, cables, damping material, glue, paint(?) even screws for the driver.. etc).
Then once we are confident with this list start buying things.

You should also add things in this list like:
1) where the speakers are located in listening space (on a desk, stands? how close to the walls will they be),
2) possible location of this subwoofer (in between the two speakers?)
3) Source that you will use to play music (AV receiver? How are you planning to simultaneously connect the subwoofer to the source along with the speakers. If AV receiver, will you be able to apply electronic delay to the signal to the subwoofer)
4) Location of the amplifier (specifically subwoofer amplifier) in the listening space, etc..
5) Do you have any DSP (minidsp) and any measurements equipment available with you currently (a measurement mic like minidsp UMIK-1 or anything else).

This is to clarify the whole purpose, process and make the build smoother to execute..

PS: At least regarding measurement equipment, you needn't worry. Based on how the build goes, we can arrange it at the appropriate time..

 

[aeroash]

I generally don't like the plasticky things around the binding posts..

Is this from an aesthetic point of view?

How about this: https://diyaudiocart.com/diy-speaker/Speaker-Terminal/Dayton-Audio-BPA-38G-HD-Binding-Post-Pair-Gold

I'll keep this as one of the options.

Now, before buying anything else, I sincerely request you to write the requirements down in a piece of paper or a post here.
This is for planning the build and estimating the costs, efforts/manpower involved and to buy appropriate components (wood, driver(already bought),wires, binding posts, cables, damping material, glue, paint(?) even screws for the driver.. etc).
Then once we are confident with this list start buying things.

I have all material at hand and executing this build myself, hence no labour costs.
All I need at this point are the binding posts and an external amp. My Crown XLS can be used for testing purposes, but I'll have to procure an additional amp for Sub duties.

You should also add things in this list like:
1) where the speakers are located in listening space (on a desk, stands? how close to the walls will they be),

On stands. 2 feet away from the front wall.

2) possible location of this subwoofer (in between the two speakers?)

This will depend on what REW shows me.

3) Source that you will use to play music (AV receiver? How are you planning to simultaneously connect the subwoofer to the source along with the speakers.

Sabaj A30a. It has a subwoofer out, as well as a crossover.

If AV receiver, will you be able to apply electronic delay to the signal to the subwoofer)

I have a miniDSP Flex, again, this can be used for testing purposes only. I have to return it to my main system. Depending on the location, if a delay is necessary then I'll have to think about managing the same.

4) Location of the amplifier (specifically subwoofer amplifier) in the listening space, etc..

Flexible.

5) Do you have any DSP (minidsp) and any measurements equipment available with you currently (a measurement mic like minidsp UMIK-1 or anything else).

Yes. Flex with UMIK 1.

This is to clarify the whole purpose, process and make the build smoother to execute..

I concur.

PS: At least regarding measurement equipment, you needn't worry. Based on how the build goes, we can arrange it at the appropriate time..

Thanks, I value your effort, guidance, and generosity, much appreciated.