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Old 1st May 2013, 03:23 AM   #1711
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For vented, maybe so. However, for any TL speaker, a higher Q is desireable.

From MJK spreadsheets via Bjorn Johanssen
Qts -- I use a Qts value of 0.35 to distinguish between high and low Qts. You might have another definition. Drivers with a high Qts perform better than driver with low Qts in a quarter wave design. On the other hand, the lower Qts driver seems to require less volume, thereby resulting in a smaller enclosure. Low Qts drivers have a roll off that starts earlier than high Qts drivers, and drivers with a moderate or high Qts will often result in the best low end performance. But this is also a matter of taste and preferences. "Good sound" is defined by you only. The output from the opening is broader with high Qts drivers, compared to low Qts drivers that have a narrower output from the opening. Drivers with a Qts lower than 0.30 seem to be difficult to control in a TL.
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Old 1st May 2013, 04:31 AM   #1712
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by motrctyman View Post
You are going to laugh.....but I was looking at this Goldwood.

High sensitivity, decent FS, and under $30.
The Qts is not too big for a MLTL, it will let you reach a frequency lower than the fs of the driver which is already low. The recommended vol is 12.4 cu ft for vented enclosure. If you make a 96 in tall box that is 14 in wide x 8 in deep x with a single fold (total depth of 16 in) for a TL of 192 inches, that should give a pretty low fb of 17.5 Hz. Now calculate the vent using WinISD based on the diameters you have on hand with recommended tuning freq, and it will drive actual MLTL tuning freq down into 12 to 15 Hz range. Be careful with driver excursion. You can also just make a shelf vent and save your flared tubes. You will have a theater style sub that can reach 12 Hz at 101 dB with 4 watts of power! What does a sub at 12 Hz sound like? Whamp whamp whamp whamp whamp like a helicopter.

If 12 Hz is too low for your taste, don't fold and you have a nice 20 Hz capable sub.

Last edited by xrk971; 1st May 2013 at 04:37 AM.
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Old 1st May 2013, 02:48 PM   #1713
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That looks like it might be an awesome little project!! Would be very cool to run it off of a small chip-amp I have (I think it is 14W). That would just blow some neighbors minds...and probably make my wife very happy...heh...

I am on my way to The Depot to check and see how much this styrofoam is and hope I can fit full sheets in my Suburban.
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Old 1st May 2013, 03:09 PM   #1714
xrk971 is offline xrk971  United States
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Motownman,
Very cool, glad to see you are excited. I will calculate vent and box dimensions. Are you interested in the 10 Hz or 20 Hz version? I may give this a go with AkAbak and do a real MLTL sim rather than just a AMLTL estimate. It will be something if this thing can indeed pump out 101 dB at 10 or 20 Hz with little more than a flea amp. A suburban can hold full size 4x8 ft sheets of ply or foam no problem. You need to fold/remove rear seats?
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Old 1st May 2013, 03:30 PM   #1715
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Originally Posted by motrctyman View Post
TL speaker
I misunderstood your intentions.
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Old 1st May 2013, 03:52 PM   #1716
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X,

The problem is I have my three kids with me (three car seats). I just measured and if it were not for my four year old, it would fit....ugh... She would not be cool with having a sheet of styrofoam over her head and I don't think I could listen to it all the way home. Might be able to pick it up next week (weekend won't work because it is Lone Star Audio Fest!!!)

I think I would rather try the 20Hz version, because it will still have some gain for the lower frequencies....but don't know what xmax will be there. Regardless, I don't think I have any FLAC's that have infrasonic information to them. I am betting that the 25-35Hz info will be rather impressive though...and it will have to be corner-loaded too (the only place I can put it in my garage). With it there, it will be between two racks of industrial type shelving, so it will be hidden. My neighbors know I have been working on these Radio Shack speakers, so I will just wait until I get this sub built and then invite them over to listen to the Radio Shacks. I bet I can make them shart themselves...
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Old 1st May 2013, 03:59 PM   #1717
xrk971 is offline xrk971  United States
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Default Goldwood GW-412D Monster FC Sub MLTL

I just ran an AkAbak sim for the Goldwood monster foam core sub as a MLTL.

Design: 14 in wide baffle x 16 in deep cabinet x 96 in tall, with a 14 in wide x 4 in tall x 11 in deep "shelf vent" at the bottom. Use COPIOUS bracing with additional foam strips in both directions to reduce foam wall flex. In AkAbak, I optimized the driver location which appeared to give the best response with good efficiency when driver is mounted at 53 inches from the top (3.58 ft from floor - about seated ear level). The simulation doesn't yet account for stuffing so there are peaks that really shouldn't be there with proper damping. I would recommend starting with using stuffing at about 0.5 lb/ft^3 of pillow stuffing or polyfill in the top 64 inches of the speaker cabinet. Adjust to taste. I have also calculated speaker cone displacement at 4 watts - you will not want to exceed 4 watts if you have musical content below 20 Hz. Most amps crap out below 20 Hz anyway and you have a built in high pass based on low-end of amp. But the speaker max displacement is 3.5 mm so you should be under this if you stay below 4 watts at 20 Hz. Above 20 Hz, you can put more juice to it.

The frequency response chart is attached below and shows indeed 96 dB of SPL at 20 Hz driven by 1 watt at 1 meter with speaker back placed against the wall to minimize baffle step losses. And at 4 watts (5.66 volts) the speaker should produce 103 dB at 1 meter! Whamp, whamp, whamp, whamp, whamp !!!

Let me know if this design sounds OK, and if you need more info.

Sounds like a boat load of FC fun!
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Attached Images
File Type: png GW-412D-MLTL.png (21.3 KB, 228 views)
File Type: png GW-412D-MLTL-displ.png (20.0 KB, 226 views)

Last edited by xrk971; 1st May 2013 at 04:04 PM.
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Old 1st May 2013, 04:10 PM   #1718
xrk971 is offline xrk971  United States
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The calculation above is for one of the voice coils in the DVC driver. With both coils firing and driven by a stereo amp, add 3 dB to the calcs above! 106 dB at 20 Hz with 4 watts per channel!!!! Yahhh baby!

Edit: you may be able to get away with tossing entire pillows with their factory covers still on inside the cabinet rather than remove the sacks with bare stuffing. Go to Bed Bath and Beyond and buy four of the 4 ft long "body" pillows at $5 ea. Throw them in en masse... Although you will have to work them around the bracing somehow... may require gutting pillows after all ?

Last edited by xrk971; 1st May 2013 at 04:19 PM.
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Old 1st May 2013, 08:21 PM   #1719
ryani is offline ryani  United States
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Now building a total foamcore system sounds fun! Not sure where I can hide 8' pink tower, but it's a worth a shot.
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Old 1st May 2013, 08:48 PM   #1720
xrk971 is offline xrk971  United States
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Do you have left over flat latex wall paint and a big roller brush? It will blend right in with the Mrs barely noticing.
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