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Old 16th January 2011, 08:42 PM   #71
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by jwmbro View Post
..On the other hand, compared to some ..., bass isn't that much more impressive...
No doubt, I simulated your 'tapped pipe' design: See the complying results in the first column/ picture:

Quote:
..I've done some simulations, and I'm rather surprised at how close at 20Hz a dual driver vented box is to the horn (all the while being half the volume)..
Click the image to open in full size.
If two bad designs are compared, one will always be a winner.

Quote:
It gives up about 2dB at 20Hz (both designs xmax limited, and both requiring a 20Hz highpass), and is surprisingly lower in group delay (one of the reasons I had originally discarded vented boxes was the high group delay)...
What BW are you targeting?Looks you have targeted ~60 Hz for an upper boundary.

Quote:
..And, the response of the vented box is flat for 4 octaves, which is more than any TH I've ever seen can achieve...
No way, See the submitted MJK simulations where only the heavily stuffed box and port design would be considered to incorporate a flat response up to ~50 Hz where f-3dB is in the vicinity too.

Quote:
...Oh, and by the way, even with the small (3" diameter) reflex pipe, my calculations reveal max vent speed of 15 m/s at 20Hz (would be 20 m/s without the highpass), which should mean no chuffing at all.
I disagree again, See the simulations showing if exceeding 7W (if the box is stuffed): the port air velocity would be more than 30 m/S.

b
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Old 17th January 2011, 06:38 AM   #72
jwmbro is offline jwmbro  United States
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Morning bjorno!

Wow, long reply, thanks very much for all the feedback. I'll try to reply to each of points you address individually.

Quote:
Originally Posted by bjorno View Post
No doubt, I simulated your 'tapped pipe' design: See the complying results in the first column/ picture:
I'm a bit curious how come you used a different Cms (thus also different Vas) figure than me.... due to this difference your simulation comes out even peakier than mine. EDIT: Never mind, I think I've figured this one out, you're using a higher Fs.

Perhaps we may both be wrong - I really should make my next investment a woofer-tester so I can measure the params.


Quote:
Originally Posted by bjorno View Post
If two bad designs are compared, one will always be a winner.
No doubt, I'm only a beginner at this, and while there are surely better designs to be made, so far this is the best I can come up with at this stage. But as long as I learn from my actions and mistakes, I'm happy.

Quote:
Originally Posted by bjorno View Post
What BW are you targeting?Looks you have targeted ~60 Hz for an upper boundary.
Ideally I would like to have a flat 20Hz-80Hz range of 100dB SPL.

If I had to make sacrifices, I'd rather lose the top octave than the bottom octave. So I'd prefer 20Hz-40Hz if that was all I can get, rather than give up bottom end extension.

Perhaps I should mention, I have DSP at my disposal for this project, and also it will mainly be used for movies. For relaxed music listening this often won't even be in use. So SPL and depth are a higher priority than musicality.

To be quite honest, the main thing I was looking for when making my design was not the flatness of the curve, but rather this:

Click the image to open in full size.

Max SPL is >100dB all the way from 20Hz to 80Hz.... DSP can handle the rest.

Quote:
Originally Posted by bjorno View Post
No way, See the submitted MJK simulations where only the heavily stuffed box and port design would be considered to incorporate a flat response up to ~50 Hz where f-3dB is in the vicinity too.



I disagree again, See the simulations showing if exceeding 7W (if the box is stuffed): the port air velocity would be more than 30 m/S.

b
Wow, interesting how extremely 3 simulations of the same thing in 3 different programs can differ. Sometimes WinISD and HornResp show the exact same thing, and sometimes they differ wildly by >10dB. It's interesting.

Also, your post has finally prompted me to spend my first ever cash on audio software (I'm a very reluctant person to ever spend cash on any type of software). I just sent €19.20 in the way of Martin J King's paypal account! Looking forward to learning to use the spreadsheets.

So, getting back to the very first reply in this thread:

Quote:
Originally Posted by tinitus View Post
One advantage with a "stand alone" is that its practical to use just one amp with two subs, but its also good value with very nice funtions, and made in Germany
Well, some two years after receiving this advice, here's me following it:

standalone 4-channel class-d subwoofer amp with integrated DSP. 'Tis currently a work in progress, will share some more pictures when I'm finished. This is what will power all my subwooferage:

Click the image to open in full size.
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Old 5th November 2011, 09:33 PM   #73
jwmbro is offline jwmbro  United States
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So, long time no reports here. After some time I spent occupied with other things, I finished up the bulk of the work of this project.

Many thanks go out, in no particular order, to:
- Duke LeJeune of AudioKinesis for his advice on multisub setups and small vented boxes
- Earl Geddes for his Multisub approach detailed in this thread
- Markus Mehlau, despite his occasional bickering, who has contributed much useful information on multisub setups, particularly this very helpful summary
- Dave Dlugos for all his designs, particularly this push-push concept with its reduced cabinet vibrations
- and of course everybody who has contributed to this thread

Building the subs

Before building, I made a model in Sketchup:

Click the image to open in full size.

Here are the Basic ingredients:

Click the image to open in full size.

The braces, which are made of 12mm (1/2") birch ply, after getting the air holes routed in, get a quick roundover routed, because I'm too lazy to sand down all the edges:

Click the image to open in full size.

The baffles consist of 18mm (3/4") birch ply as a structural component, with 10mm (3/8") MDF glued on, which serves the purpose of recessing the woofers without losing stability by routing away plywood. Due to the thickness of the wood, it is chamfered around the back, to allow airflow, and T-nuts are put in.

Click the image to open in full size.

The body of the sub is also made of 18mm (3/4") birch ply. The braces are glued slighly asymetrically, as not to create equal resonances.

Click the image to open in full size.

The rest of the body gets glued up, and the edges of the top and bottom (which are slightly wider then they need to be) are trimmed with my absolute favorite woodworking tool - the flush router bit.

Click the image to open in full size.

Then the baffles are glued on, once again trimmed down with my favorite flush router bit, and the edges of the sub are chamfered.

Click the image to open in full size.

After chamfering the edges, some leftover bits of birch veneer I had from my last project were applied to cover up the open edges of the plywood. Also the baffle edges are rounded over. Not that it would be acoustically necessary with with the large wavelengths involved, but the idea is to match the appearance of my speakers.

Click the image to open in full size.

After this, I drilled holes for and inserted the Speakon plug.

Click the image to open in full size.

Multiply the process times 3, and you get the following stack:

Click the image to open in full size.

And here's a picture of one of the subwoofers setup under my computer desk.

Click the image to open in full size.

The sub isn't completely finished, but it's unfortunately already too cold to properly spraypaint outside, so painting the baffles black will need to wait until the springtime.

Each sub has a volume of approximately 15 liters, perhaps more considering the stuffing (Sonofil), but as you can see from this sketchup result, the enclosures are too small to produce proper bass naturally:

Click the image to open in full size.

However my amplifier has a a built-in DSP, and I use Linkwitz transform to flatten the subs out to a -3dB point of about 40Hz.

As such they are excursion limited to reach about 100dB each.

In addition to the 3 closed subs, I still have the OSB horn shown the post above hidden underneath my bed, for the real low frequency ranges, below the room nodes, and below most musical content. It really comes into play for movies. The 3 closed subs alone are enough for music mostly.

Long enough post for today, I'll contribute measurements soon.

Thanks everybody for your help, and it's amazing to listen to music wiht such a full spectrum.
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