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Building a low cost subwoofer for the home

TheBatsEar

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My very old Magnat subwoofer stopped working recently, time to get something new. Butget should be under 500€, i made it in 280€.

Woofer:
Looking at different woofers and their prices, i found the Alpine SWG-1244, 4 ohm (80€). It's a 12" car subwoofer that seems to be happy in a small, closed enclosure.
woofer2.jpgwoofer1.jpg



Enclosure:
The enclosure is made from 26mm thick MDF, the box will be exactly 380x380x380mm. The material is solidly colored black, so there is no painting needed. The MDF was sent to me by an online service and the cost was 54€. I only have to make one cut for the speaker itself, and one for the terminal, with a jigsaw. I guess this can be done on the balcony. To connect the parts, i'll use wood plugs and glue.
MDF.jpgconnections.jpg

Amplifier:
I'll use a Monacor SAM-300D plate amp. 300W into 4 ohm, class D, 140€, the usual active subwoofer knobs and connections. The amp will have a separate enclosure.
sam-300d.jpg


I don't have a speaker cable terminal yet, i guess i'll just drill a hole and stick some cable through for now.

Anything i didn't consider?
 

DVDdoug

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Did you buy this stuff already? If not, do you have the Theile-Small parameters for the woofer?

If you have the parameters you can use WinISD or similar software to predict performance in a particular sealed or ported box or to optimize box design.

I don't have a speaker cable terminal yet, i guess i'll just drill a hole and stick some cable through for now.
That'll work but the plate amplifier is designed to be installed in the box and there will be connections of some kind on the back/inside of the plate amp for the speaker connections.
 
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TheBatsEar

TheBatsEar

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Did you buy this stuff already?
Yep.

If you have the parameters you can use WinISD or similar software to predict performance in a particular sealed or ported box or to optimize box design.
I have the parameters and constructed the the box with this:
1647134242721.png1647134277494.png

They have the speaker and it's parameters in their database. Their predicted FR looks like this, but i'll bend it to my will with DSP:
1647134488721.png


This is what they predict max SPL would be at 300W input. Which is not possible in my apartment. Plenty of room to DSP to taste:
1647134534559.png


Cone travel in mm at 300W has some reserves as well:
1647135056254.png



That'll work but the plate amplifier is designed to be installed in the box and there will be connections of some kind on the back/inside of the plate amp for the speaker connections.
Right, but i want the plate amp to have it's own enclosure and speaker terminals. Makes it easier to experiment i think.
 
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TheBatsEar

TheBatsEar

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I may have forgotten wood glue.:facepalm:
 

alex-z

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It looks like your -3dB point is 54Hz, which is really high even for a 12" sealed sub. That particular driver is built for high SPL car applications, rather than deep bass you want in a home audio setup.

If you want to avoid purchasing a different driver, adding 50 grams of mass to the cone would drop the FS, allowing -3dB at 41Hz in a 1.7ft cabinet.

You should also consider using a pair of drivers per cabinet, firing in opposite orientations. This removes almost all cabinet vibrations, allowing for the use of thinner MDF. Bracing should still be used of course.
 

digitalfrost

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I may have forgotten wood glue.:facepalm:
Sorry to the english speakers, just some wood glue advice that I cannot translate.

I würde Fugenleim empfehlen, den kannst du ohne Schraubzwingen verarbeiten und er zieht sehr schnell an. Das Loch fürs Kabel kannst du mit Heisskleber gut abdichten, der lässt sich später auch wieder entfernen.
 
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TheBatsEar

TheBatsEar

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It looks like your -3dB point is 54Hz, which is really high even for a 12" sealed sub. That particular driver is built for high SPL car applications, rather than deep bass you want in a home audio setup.

If you want to avoid purchasing a different driver, adding 50 grams of mass to the cone would drop the FS, allowing -3dB at 41Hz in a 1.7ft cabinet.
That probably means i still have apartment level SPL left, once i cut something off the top using DSP. I was hoping to get the blue FR in the end:
cut.png
I could get more SPL by using higher amplification, there is some cone travel left. Seems easier than modifying the driver.

You should also consider using a pair of drivers per cabinet, firing in opposite orientations. This removes almost all cabinet vibrations, allowing for the use of thinner MDF. Bracing should still be used of course.
Hmm, let me think, two drivers means i would twice the cabinet volume, right? Also, 80€ more cost. Is it really worth it, given that the MDF is really heavy and thick already and i'll probably never use max SPL? Also, two drivers means either in series (8 ohms, amp is down to 150W) or parallel (2 ohms, not sure the amp can do that).

I würde Fugenleim empfehlen, den kannst du ohne Schraubzwingen verarbeiten und er zieht sehr schnell an. Das Loch fürs Kabel kannst du mit Heisskleber gut abdichten, der lässt sich später auch wieder entfernen.
Danke Mann, du bist ein Mentor und wahrer Freund. :cool: I'll get that stuff if i don't find my wood glue, which i thought i had.
fugenleim.jpg
 
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freemansteve

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A few years ago, coupled-cavity designs were popular - what happened to that as a design?
 

alex-z

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That probably means i still have apartment level SPL left, once i cut something off the top using DSP. I was hoping to get the blue FR in the end:
View attachment 192064
I could get more SPL by using higher amplification, there is some cone travel left. Seems easier than modifying the driver.


Hmm, let me think, two drivers means i would twice the cabinet volume, right? Also, 80€ more cost. Is it really worth it, given that the MDF is really heavy and thick already and i'll probably never use max SPL? Also, two drivers means either in series (8 ohms, amp is down to 150W) or parallel (2 ohms, not sure the amp can do that).
Make sure you actually have enough SPL left. How far away is the sub from your listening position, and how much DSP will you need to add for correcting room mode nulls?

Yes, 2 drivers takes more air space. But these drivers don't need much air space to start with, and 80 euro for significantly lower distortion is worthwhile.

Use 19mm MDF. 26mm is super overkill, better to add bracing than thickness.

That amp can handle 8 Ohm loads, and deliver half the power. Because you are doubling the surface area, the SPL will remain the same.
 
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TheBatsEar

TheBatsEar

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A few years ago, coupled-cavity designs were popular - what happened to that as a design?
I have looked at a lot of subwoofer designs, the added complexity isn't worth it for me.

Make sure you actually have enough SPL left. How far away is the sub from your listening position, and how much DSP will you need to add for correcting room mode nulls?
Maybe 2m, it's not far.
Not sure how much fixing room modes will cost, i haven't used proper bass integration yet. Didn't feel i need it, but it's on my agenda.

Yes, 2 drivers takes more air space. But these drivers don't need much air space to start with, and 80 euro for significantly lower distortion is worthwhile.
More air space means i need to order a new enclosure, that would come on top.

Use 19mm MDF. 26mm is super overkill, better to add bracing than thickness.
That's what i thought once i had the parts. :D
But the material looks nice in26mm. The color too, matte dark grey describes it best:
PXL_20220313_110618459.jpgPXL_20220313_111800253.jpg
 
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F1308

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What about forgetting wood and instead go using granite or marble ?
 
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TheBatsEar

TheBatsEar

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What about forgetting wood and instead go using granite or marble ?
Well, i guess price would be the first problem :)
 

alex-z

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I have looked at a lot of subwoofer designs, the added complexity isn't worth it for me.


Maybe 2m, it's not far.
Not sure how much fixing room modes will cost, i haven't used proper bass integration yet. Didn't feel i need it, but it's on my agenda.


More air space means i need to order a new enclosure, that would come on top.

Get a second identical enclosure, then you have two options.

1. Glue or bolt them together, forming one larger enclosure with the vibration cancellation I mentioned.

2. Put the second enclosure somewhere else in the room. Fewer room mode nulls, meaning less DSP needed. Amplifier can be shared between 2 subs still.
 
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TheBatsEar

TheBatsEar

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  1. Nah, thanks, i don't think i want a frankenwoofer in my living room. I don't think vibration will be such a big problem.
  2. Yes, i thought about this as well, as an option. That is the main reason why i want the plate amp to have it's own enclosure, it allows for easy experimentation. Adding a second subwoofer would cost about 140€.
 

Digby

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What is your time worth? Why not just buy a JBL LSR310S instead of DIY.
 
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TheBatsEar

TheBatsEar

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What is your time worth?
I don't understand. Are you telling me i should work for money this sunday, instead of building a subwoofer?
 

Digby

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It is an English phrase, it means what value does your time have (is it worth spending your time doing DIY, when you could get something similar for a bit more money, but requiring less of your time). Time has value.
 
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TheBatsEar

TheBatsEar

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It is an English phrase, it means what value doesn't your time have (is it worth spending your time doing DIY, when you could get something similar for a bit more money, but requiring less of your time).
What would i do with that free time?
 

Digby

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It is up to you, it is your life. I'm just suggesting that you can get reasonable subwoofers cheaply enough (for 500 euros), so I don't understand why build them. If you want to do it because you like it though, that is fine, of course.
 

FrantzM

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@TheBatsEar

It is always interesting to build something. You learn, you have a good time and ...
The thing is your current design is underwhelming in term of performance. No other way to put it, for the cash outlay. If that floats your boat, fine. You can get better performance and likely better reliability in a commercial subwoofer for the same cash outlay. We can't put value in the entrainment or satisfaction you would derive from designing and building your sub. Just pointing out those objective data points.

Peace.
 
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