Hello out there,
During the past few months I have been working on a pair of 15" coaxial monitor speakers with which I am now mostly happy with the sound. The only place where they are still slightly lacing is in the sub 60 hz range, therefore I have decided to make subwoofers that can also double as speaker stands for the monitors. One sub for under each monitor.
The sub that comes quite close to my requirements is the 12" Deathbox from Steve Deckert, however it is designed to be placed in a car so not exactly sure how that translates to a big room. He also designed it with an adjustable inner compartment for tuning, but again that is probably more useful for in a car. The dimensions are pretty spot on for my use case though. Has anyone built or heard a Deckert Deathbox in a room?
https://www.decware.com/newsite/DBK212.html
My requirements (wishes) for this project are:
If anyone has any tips I would love to hear them! The subwoofer is a new frontier for me personally.
During the past few months I have been working on a pair of 15" coaxial monitor speakers with which I am now mostly happy with the sound. The only place where they are still slightly lacing is in the sub 60 hz range, therefore I have decided to make subwoofers that can also double as speaker stands for the monitors. One sub for under each monitor.
The sub that comes quite close to my requirements is the 12" Deathbox from Steve Deckert, however it is designed to be placed in a car so not exactly sure how that translates to a big room. He also designed it with an adjustable inner compartment for tuning, but again that is probably more useful for in a car. The dimensions are pretty spot on for my use case though. Has anyone built or heard a Deckert Deathbox in a room?
https://www.decware.com/newsite/DBK212.html
My requirements (wishes) for this project are:
- The sub / stand should be no taller then 90cm (35") and the width and depth should be +/- 40cm (16").
- I am looking for a design that hides the woofer within the cabinet, but I am fine with visible ports or vents.
- I am only interested in the 20 - 60 Hz region as the system will be used only for music and the monitors already sound good above 60 Hz.
- The system will very rarely be used above 90db so I value lower Hz vs high SPL.
- I plan to use a +/- 500w at 4ohm Class-D amp with DSP to drive each woofer. I am considering either the Crown XLS 2002 or if I'm feeling fancy a Hypex fa501 plate amp for each sub.
- The monitors + subs will mainly be used in am 8m (26ft) wide x 6m (20ft) long and 6m (20ft) tall space with the occasional stint in a larger space for parties.
If anyone has any tips I would love to hear them! The subwoofer is a new frontier for me personally.
The horizontal cone arrangement in the Deckert Deathbox will result in cone sag of the LAB12 over an extended period of time, not a good idea. It's horizontal slot port looks like it would be a fairly high tuning, well above the 20 Hz you want. "Speed and accuracy" are not good descriptors for a band-pass box of that type.
The driver could be mounted vertically in a slot if you don't want it visible.
For 20 Hz response, the cabinet tuning (Fb) must be 20Hz (or lower).
A bass reflex with an Fb that low requires a long, large port, which reduces the internal volume of the cabinet.
The volume of the Deckert Deathbox is only about 3.6 cubic feet exterior, 102 liters, getting closer to 125 liters net volume (cabinet interior not including driver, slot or port volume) would increase the 20Hz response considerably.
The driver could be mounted vertically in a slot if you don't want it visible.
For 20 Hz response, the cabinet tuning (Fb) must be 20Hz (or lower).
A bass reflex with an Fb that low requires a long, large port, which reduces the internal volume of the cabinet.
The volume of the Deckert Deathbox is only about 3.6 cubic feet exterior, 102 liters, getting closer to 125 liters net volume (cabinet interior not including driver, slot or port volume) would increase the 20Hz response considerably.
I need time to refine.
But, this is STEPPED negative flare tapped horn.
3 segments or chambers in the enclosure.
Chamber 1 = 33.5" high x 14.5" wide x 7" deep internal.
Chamber 2 = 33.5" high x 14.5" wide x 3" deep internal.
Chamber 3 = 33.5" high x 14.5" wide x 3" deep internal.
But, this is STEPPED negative flare tapped horn.
3 segments or chambers in the enclosure.
Chamber 1 = 33.5" high x 14.5" wide x 7" deep internal.
Chamber 2 = 33.5" high x 14.5" wide x 3" deep internal.
Chamber 3 = 33.5" high x 14.5" wide x 3" deep internal.
FYI/FWIW, etc.: Percentage of Sag = 24,849 / ( Xmax × Fs²) > 5 % acceptable
LAB 12C = 24,849 / ( 13 × 23²) = 3.613 %
LAB 12C = 24,849 / ( 13 × 23²) = 3.613 %
FYI/FWIW, etc.: a basic ~Vb = Vas, Fb = Fs T-TP results in a smaller cab than a comparably performing BR when limited to a sub's typically ~two octave BW due to the 'vent' being the entire sub box with a modest HR calc'd 1:1.48 CR @ >112 dB/m/2pi/500 W/> ~18 ms mouth/vent mach
Hmm, just realized from doing some other high Xmax/low Vas drivers that all including the LAB12c are physically too deep to fit, so will need to have a larger cross section, though still smaller than its BR ~equivalent. 
Oh! Sorry to hear! I hope it was not a total waste of time.
Thank you for your feedback and the work. I will need some time to digest all the information you have shared but i really like the design that @BP1Fanatic suggests.
@GM can you (or someone else) translate your message below into layman terms. I am embarrassed to say but I don't know what you mean.
"FYI/FWIW, etc.: a basic ~Vb = Vas, Fb = Fs T-TP results in a smaller cab than a comparably performing BR when limited to a sub's typically ~two octave BW due to the 'vent' being the entire sub box with a modest HR calc'd 1:1.48 CR @ >112 dB/m/2pi/500 W/> ~18 ms mouth/vent mach"
Thank you for your feedback and the work. I will need some time to digest all the information you have shared but i really like the design that @BP1Fanatic suggests.
@GM can you (or someone else) translate your message below into layman terms. I am embarrassed to say but I don't know what you mean.
"FYI/FWIW, etc.: a basic ~Vb = Vas, Fb = Fs T-TP results in a smaller cab than a comparably performing BR when limited to a sub's typically ~two octave BW due to the 'vent' being the entire sub box with a modest HR calc'd 1:1.48 CR @ >112 dB/m/2pi/500 W/> ~18 ms mouth/vent mach"
There is also this nice looking, fairly compact MLTL design for the lab 12. Driver is not hidden though:
https://www.diyaudio.com/community/...l-tl-design-by-bj.216201/page-14#post-3731389
https://www.diyaudio.com/community/...l-tl-design-by-bj.216201/page-14#post-3731389
Thank you for the model! That is plenty of output down to 20Hz and within the size limitations. Super!
You suggest two options for the placement of the mouth, either on the front bottom horizontally or on the side vertically. Would it effect the output if I place a vertical mouth on the front baffle as in the drawing I posted?
You suggest two options for the placement of the mouth, either on the front bottom horizontally or on the side vertically. Would it effect the output if I place a vertical mouth on the front baffle as in the drawing I posted?
At 20Hz, a reduction of 5dB sounds around half as loud.
BP1Fanatic's 104L ST-TQWT is about -11dB down at 20Hz, about 1/4 as loud to your ears.
It is Xmaxed out at 101 dB, equal loudness to about 75dB SPL at 60Hz.
From my experience with different mouth exits on TH, I don't think a vertical exit compared to the horizontal would make much difference other than in the region of the 14dB peak around 100Hz. That peak won't actually be as sharp as the Hornresp sim shows, but may become a bit wider if the port is moved vertical.
As a comparison, I ran a Hornresp sim of a standard bass reflex of about the same exterior volume, (114L compared to 104L, but fewer panels required inside).
It produces 106dB at 20Hz, about twice as loud using the same 32 volt input level, 190 watts at Fb. As the excursion is only 5mm at the 20Hz Fb, the response could be EQed flat to around 112dB level while still well within the LAB12's peak thermal capacity.
The port exit would be 22.5 square inches, 36" long, "L" shaped to fit the cabinet height you want.
As mentioned in post #2, the driver could be slot mounted vertically, though the sim does not show the effects of the slot, an upper peak and dip in the response.
I'd probably put the driver at the top to minimize the distance between it and the co-ax, like this:
The cabinet the above composite photo was from did use a LAB 12, though a later iteration used a pair of slot loaded 10" .
In actual listening at Xmax or Fb, have not found the estimated port velocity of 18m/sec to be a problem with the port ends and "L" corner rounded over.
I also ran a 160liter cabinet, it is smoother and uses only 155 watts to do 107dB at 20Hz, though maxes out at about 108dB at 30Hz.
The smoother frequency and phase response through the crossover region with a BR will make alignment with the top cabinets easier than the TH. This is especially helpful when using a "loudness contour" response at low level listening, which effectively raises the acoustic crossover as much as an octave.
Art
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T-TP = tapped tapped pipe, IOW it's an offset driver pipe with a net volume = driver Vas (compliance) spec folded back on itself to load both sides of the driver with an acoustic pathlength = to the driver's Fs. CR = the compression ratio of the driver's pistonic radiating area (Sd) Vs baffle cutout area (the smaller of the two).
2pi = half space
Vent mach ms = the vent's air speed in meters/second, which if too high will audibly 'whistle' and at some higher point will basically begin backfiring like an exhaust system, which in turn will damage the driver and all the (potentially) bad things this implies if the designer and/or end user doesn't provide the necessary protection (limited by design in this case).
"I am looking for a design that hides the woofer within the cabinet, but I am fine with visible ports or vents."
Bandpass 4 life!
Probably not, but why alter the front panel with a vertical mouth when both enclosures have the same 16" wide by 16" deep dimensions?