Let's build a custom Subwoofer for Carlman's basement theater

[richidoo]

I'll check it with CAD once I start on the design. It's OK to tilt back farther. We can point it down. I went to borg (Big Orange) today to get baffle screws and router bit.  I will assemble it with glue and 1.25" staples. I will laminate the MDF walls together with glue and staples while standing on it. If the're room I'll make the baffle 3 layers thick, two layers for the rest. With supports inside. Weather should be nicer later this week. So I will try to get the design done by then.

[Carlman]

Thanks!  This week is all rain..   If you get the design done this week, I can come over for a full day next week to put it together.
-C

[richidoo]

The client who shall remain anonymous (eh-HEM!) wired the voice coils in parallel, giving my poor little AudioSource amp a punishing .35Ohm load. It is remarkable that the amp played at all, and it played pretty damn loud. I had the volume up to 75% on the Sonos and it ran that way for 10 minutes, but it did get very hot. I turned up the volume to 90 and it blew the thermal protection after a couple seconds, no harm. Shane helped me figure it out. Rewired in series for 5.6ohm impedance, the excursion at same volume level doubled and no heat from the amp. I played a godallmighty house shaking organ track through it at same volume setting I would use in my system and the driver cone only moved about 1/2"p>p. Running the torture test track on it at same volume setting makes it move >1". Turning up the volume it will go farther and farther with no bottoming. This thing is SICK! I better use some extra staples.
Shane thinks a few hours of play will be enough to loosen it up enough. I should be able to do that tomorrow.

[Carlman]

   I'm the dumb client.. 

I blame the manufacturer for making me think.

[bpape]

Wow - 20Hz on an amp into 0.35 ohms!  That's amazing that it played at all.

Bryan

[richidoo]

I should listen to it again now after that serious "burn in". You know it's done when you can smell the resistors.    It's a good little amp. It's my emergency spare when all else fails.  "bluisana" (AN) recommended it to me.

[richidoo]

You are right Carl, this driver is just too damn big. Here are some options to mount it.

If you can do a 4" bump up for total height 16" at the baffle then we can mount it vertical with no tilt. The bump can be a foot wide and 2 feet long. If your couch will have 4" clearance under it than that will be the easiest. Tilting the driver 25 degrees lowers the max height to 15", but adds build complexity. Removing the driver for maintenance or tuning the volume will be easier with vertical mount than diagonal.

You could also mount it facing up into the couch above. The whole driver including the roll surround would be recessed below the top surface so you could cover it with steel grid, cloth, etc. But the platform needs to be decoupled from the driver baffle (imo) and the driver needs to be protected from debris and stepping from above, it is more vulnerable facing up.

Any opinions on which is better?

[_Scotty_]

richidoo,your experiences loosening up the suspension on Carl's subwoofer reminded me of what happened when I first took delivery of my loudspeakers. They have two Dayton Titanic MKII subwoofer drivers per speaker and the efficiency is 96dB1w/m.. The fallout from the combination of high efficiency
and two 350w rms subwoofer drivers per side was that for 3 months I looked at the speakers and wondered where the bass was. I finally got a brainstorm and realized that I was not breaking in the speakers with maybe 10
watts on crescendos when I played the system loudly.  I did something similar to break in my speakers, I hit them with 20Hz sinewaves at -20dB and hit about 110dB continous for a half an hour. It took three "treatments" to loosen up the drivers and get the output below 70Hz. to match up with the rest of the spectrum. This being a vented system, the port was doing most of the work below 30Hz which didn't help it break in,the drivers were still only moving about a half inch at 110dB. That insane sub you guys are building will certainly work better from the get go with the driver already loosened up. You won't risk damage to your foundation trying to break in in after it is assembled. It looks like there is no good reason that the sub shouldn't work as well for music as it would for home theater,that is one incredible looking driver.
Scotty

[Carlman]

I measured the couch and I only have 3.5" of clearance there.. I took some photos of the platform yesterday but I got sidetracked (as always) and now can't find the camera. 

I was thinking of putting the platform on gliders to adjust the seating anyway.. I could just leave those gliders in long-term.  Just a thought.  That would add at least .5" to the whole platform.

-C

[richidoo]

Thank Scotty. It is kinda scary to see that 15" cone moving in and out that far, that fast. I showed my 8yo, told him if there was a box around it, it would sound like a giant bomb exploding. Oooooo   

Carl,  After talking with you yesterday I think we have decided to build the sub box with driver vertical, with tall baffle sloping down to meet box. The couch may have to be a few inches away from the rear edge of the platform. If you can specify how many inches the bottom edge of the couch can be moved forward of the rear edge of the platform would help me design the top angle of the sub box. You suggested 6 inches yesterday, that is enough to accomodate your 3.5" couch height if the couch is moved in 6". I will try to minimize how far in it must be moved. The thickness of the MDF is the limiting factor there.

[Carlman]

I'd like the couch to be on the back edge.. so, I'll raise the couch a half-inch, no big whoop.   BTW, that's a scrap of wood across the back for structural rigidity whilst moving it around.
Here are some photos:


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[richidoo]

What is that smaller hole photo #004?

I'll get the top surface of the box down as quick as possible, then you can fiddle the box/couch/platform together.


Q test results:
Re      5.090 ohms       
Fs     24.666 Hz       
Qes    0.4135 
Qms    7.0802 
Qts    0.3907 
Le      5.049 mH @1k

Still to do Vas test.

[Carlman]

Looks great, thank for doing the testing, Rich.  I'm not sure how to repay you for the work you're doing but let me know what works for you..

The other cutout is for the plate amp.  There is a little tiny hole on the step for the power and signal cables.

-C

[richidoo]

Cool, that amp is big too!

The Vas test is not working well. It runs and runs for hours not making headway.  I have anice 60g stack of coins in the cone, but the tester seems stuck. It keeps flashing "Vas: Fiding Zmax::Search", and then  never rises above 1Hz. Drive is 100%, voice coils in series. Any ideas to try?
Thanks

[richidoo]

Please comment on this design. This is about as compact as I can make it. Air can move behind the cone into the volume easily when driver is rotated 45 degees. One 2x4 brace vertical in the center.



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