Dual 12" sealed subwoofer project with Linkwitz eq - diyAudio
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Old 16th July 2012, 09:23 AM   #1
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Default Dual 12" sealed subwoofer project with Linkwitz eq

Hi everyone, just thought I'd share with you my curent project. As per the title, it is indeed a dual 12" sealed sub utilising the Linkwitz transform eq.
The amplifier is a 350W rms plate amp, with front mounted volume/crossover controls and even a remote control haha. I bought the amp second hand for a good price, it is one of the amps that Jaycar used to sell.
The drivers are two of the 12" concave woofers also supplied by Jaycar. These too were purchased second hand (but unused and still in the box) for a very cheap price. So really, this sub came about from me deciding to make something cool out of stuff lying around.

I chose to make a big box, internal volume is around 110 L after the volume from the amp cavity and braces etc is taken into account. Both drivers are downwards facing, and one of them is mounted inverted to cancel out non-linearities in the suspension travel.

I discovered that the amp had a built in 6dB boost centred at 35 Hz, and if ignored this would cause a lump in response when using the Linkwitz eq. Thankfully, the Linkwitz eq that was calculated via the spreadsheet had the same gain at the same frequencies at 35 Hz and above, so what I did was altered the driver specs in the Linkwitz spreadsheet so that it only came into effect at 35 Hz and below. I made a speaker to line level converter to view the pink noise response on the computer to get the best response, to tune the eq with flat response down to 20 Hz. I made my own pcb for the eq from the schematics and attached to the back of the preamp pcb.
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Old 16th July 2012, 09:36 AM   #2
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After it was all assembled, it was given a thorough testing with lots of different styles of music and the performance is absolutely stunning! I honestly have not heard any other sub sound like this does, without costing an absolute fortune. Real deep, thick sounding low end but with excellent definition and attack. Very musical sounding, and it just sounds so effortless. So it sounds great with music, what about movies? Well, it is equally amazing. The room I had it set up in has a solid concrete floor, and during large explosions and car crashes etc you could still feel the low rumbling in the chairs and other furniture. So far I haven't run into any excursion related problems with the drivers, and I don't know its full capabilities, I pushed it to 112 dB listening to some fairly bass heavy music, how much more it had to go I don't know but it had already exceeded expectations by a large margin so I left it at that. All that's really left to do now is strip it all down and finish the cabinet. Then decide what to build next.

And if any of you are of thinking of making your own sub, I highly recommend the sealed Linkwitz method, provided the driver(s) and amp you plan to use can meet the requirements. It just sounds sooo good (well this one does at least )! The main and possibly only real pitfall to this sub is its large size, but once its behind the TV it's not really a problem anyway. It's currently set up at my mates house, and he told me he won't give it back until I make another one for him haha. Any comments and constructive criticism are welcome, I'd like to hear whatever thoughts anyone may have. The sole purpose of this design was first and foremost high fidelity, with maximum output only being secondary, but it delivers well on both fronts
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Old 16th July 2012, 02:13 PM   #3
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Take one of the drivers, place its magnet on the outside, and reverse the wires to the terminals.

Like the older m&k subwoofers, it will sound even better.

Norman
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Old 16th July 2012, 02:37 PM   #4
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One step ahead of you there, read the 2nd paragraph
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Old 16th July 2012, 02:43 PM   #5
tb46 is offline tb46  United States
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Hi flyingtele,

Post #1: "... made my own pcb for the eq from the schematics..."

Would you mind sharing your schematic and layout?

Great project, and a fine reuse of materials, well done. :-)

Regards,
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Old 17th July 2012, 08:00 AM   #6
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Would I mind sharing the pcb design? Not at all
IN a slight oversight some of the component spaces on the board are a bit tight, depending on the values required for its desired application, as different drivers or even simply different cabinet volumes will alter the calculated values. It will still fit though, if anyone wants I can alter the original design to give a bit more layout space. I have linked the original article that explains the circuit and its operation, as well as the schematics and a download link for the spreadsheet that is required. I altered the schematic slightly so I could use a standard dual opamp (4558, TL072, 4560 etc) as I have heaps lying around and I would have had to mail order a TL071 single opamp.
I have attached images of the layout and my own artwork, the artwork image is the top view, hence the lettering at the bottom being reversed, and the lettering helps with orientation so that you know its correct when looking at the copper side its readable normally. Pretty straightforward, though I'm happy to help with any questions etc.

In the below link you will find the information and schematics and the spreadsheet download. There are two schematics shown, first one is an input mixer and the second schematic is just the Linkwitz eq circuit itself. I made the pcb for the eq circuit only, as it was simply inserted between the preamp/crossover and power amp sections on a pre-assembled plate amp. If anyone here makes on of these or has done, I would like to trade notes on what was the same/different in terms of both what was done in construction and also performance, to get a better idea of how well the circuit works in other subs.

Linkwitz Transform Subwoofer Equaliser
Attached Images
File Type: jpg Screen shot 2012-07-14 at 10.27.27 PM.JPG (78.7 KB, 78 views)
File Type: png Linkwitz pcb.png (33.5 KB, 45 views)
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Old 17th July 2012, 02:35 PM   #7
tb46 is offline tb46  United States
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Hi flyingtele,

Thank you for the information.

Regards,
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