PP Slot Loaded Sub with Alpine SWR 12D2

[xrk971]

Edit Nov 25: build started.

I received a request from a member to design a push pull slot loaded sub using the Alpine SWR 12D2 drivers. His goal was to achieve a 37Hz -3dB and to fit in a space constraint of 34in x 15in x 25in, with lots of output from 40Hz to 60Hz.

The design I came up with is shown in the sketch below. Each chamber is 40 liters (13.5in tall x 15.25in deep x 12.0in long) with a central slot with dimensions of 7.0in wide x 16.25in deep (not including vents) x 13.5in high, and each chamber having a 0.90in wide x 13.5in tall x 24in long vent from the chamber to the slot. The vents will have two 3/4in braces. It is assumed that 3/4in ply will be used throughout except the vents which can be 1/2in ply. The Alpine SWR 12D2 drivers are dual voice coil deals. Assume the drivers VC's are wired in series for 4ohm nominal, then wire the two drivers in parallel for 2ohms nominal load for the amp. This is a car application so I am assuming 2ohm load is not an issue. Or each side can be driven at 4ohms with stereo amps.

Sketch (note that drawing shows 1.0in wide vents, but should be 0.90in wide to match sims below):

Predicted response at 2.83v and 1m, in 2pi space with no filters:

Predicted cone displacement at 67volts and 24Hz -24dB/oct HPF to reach 2kW max thermal rating (RMS) and xmax of 20mm:

Predicted max SPL at 67volts with above LPF and -24dB/oct HPF at 125Hz is 133dB at 1m:

Predicted electrical power input to both drivers (2kW max):

Predicted vent velocities and slot velocity at 67volts (a bit high - so there may be some port compression - the ports are internal and have a slot to reduce turbulence noise if it becomes a problem). A larger vent could be used but that would require a longer than 24in vent which may have other problems like resonances:

In summary, I think that this design should provide plenty of bass down to the requested 37Hz, and with cabin/room gain, probably much deeper.


Update Nov 14, 2014 - here is predicted performance with a 12in long x 7in x 8in extension duct at the output slot to bring the bass through a small flip down "ski door" in the back seat of a car.
It achieves 105dB sensitivity at 2.83v and 1m with 32.3Hz (03dB) bass extension:

Update Nov 18, 2014: Tb46 was kind enough to provide a drawing of a modified angled waveguide output version below:

Here is predicted output at 68 volts (with 26in long x 1.0in wide vents) driven to xmax here:

Update Dec 19, 2014: Another variant of the PP SL bandpass with MCM 55-2421, courtesy Tb46 and lawbiding:

Here is what I call the "Offset SV" Thanks to Tb46 for the great drawings as usual:
http://www.diyaudio.com/forums/attachments/subwoofers/451740d1417487191-pp-slot-loaded-sub-alpine-swr-12d2-mcm_55_2421_ppsl_sv.pdf

Here is the completed sub by lawbiding:

 

[xrk971]

Extension Duct for placement in car trunk

I received a request to add an extension duct in order to place the main sub box in the trunk of the car and have the PPSL duct extend through the small flip down hole located in the rear seats normally used as a pass-thru hole for skis and the like. I am assuming that the same 7.0in wide x 13.5in high CSA of the duct can be maintained with an additional 16in of length added. This results in additional bass extension with a -3dB point of 34.5Hz, a the max drive voltage is now 65volts with a -24dB/oct HPF at 23.3Hz and the upper extension is reduced quite a bit and a 90Hz -48dB/oct LPF filter is needed.

Here is the predicted max SPL with the extension for the seat back duct:

 

[Zero D]

Nice That should blow his socks off, maybe some car parts too

 

[lawbiding]

Hi xrk971 thanks for your help with this design.let know if you need anymore information

 

[lawbiding]

I am assuming that the same 7.0in wide x 13.5in high CSA of the duct can be maintained with an additional 16in of length added. This results in additional bass extension with a -3dB point of 34.5Hz, a the max drive voltage is now 65volts with a -24dB/oct HPF at 23.3Hz and the upper extension is reduced quite a bit and a 90Hz -48dB/oct LPF filter is needed.

Here is the predicted max SPL with the extension for the seat back duct:

Xrk971 if you rise the f3 from 34.5hz will that give me more spl in the 40-60hz area

 

[xrk971]

Yes, that can be done. The simple addition of the extender duct brought the tuning frequency lower. 133dB SPL not high enough for you? I think 34.5Hz is nicer than 37Hz I you can still hit your max SPL goal.

 

[xrk971]

Hi xrk971 thanks for your help with this design.let know if you need anymore information

You are welcome. Yes, what is the dimension of the flip down opening from the trunk to the main cabin? I need the actual hole dimensions so I can subtract the wood wall thickness to get actual flow area. Is 16in long enough to go from the box to the cabin?

 

[lawbiding]

Yes, that can be done. The simple addition of the extender duct brought the tuning frequency lower. 133dB SPL not high enough for you? I think 34.5Hz is nicer than 37Hz I you can still hit your max SPL goal.

I read that there is not a lot of music that goes Down to 34hz. I listen to a lot of r&b, hip-hop and reggae.
I love the deep bass that old school reggae have.

 

[Brian Steele]

The Alpine SWR 12D2 can produce an incredible amount of bass in-car in simple sealed cabinets (I know - I use two of them in my Hyundai Tucson). The key is to give them enough clean power. I run both of mine in parallel off a 1.2kW amp.

Running them vented should produce a huge peak at those low frequencies because of the car's transfer function.

My concern with your design is the aspect ratio of the vents you propose to use. It seems a bit high.

 

[lawbiding]

You are welcome. Yes, what is the dimension of the flip down opening from the trunk to the main cabin? I need the actual hole dimensions so I can subtract the wood wall thickness to get actual flow area. Is 16in long enough to go from the box to the cabin?

8 1/2'' wide by 9'' height is the port hole
The port length can be 16'' to 20'' long

 

[MemX]

I read that there is not a lot of music that goes Down to 34hz. I listen to a lot of r&b, hip-hop and reggae.
I love the deep bass that old school reggae have.

FWIW I saw some 28Hz peaks in a Tyga track the other day when running it through REW RTA.

 

[xrk971]

8 1/2'' wide by 9'' height is the port hole
The port length can be 16'' to 20'' long

With the seatback duct set at 7.0in wide x 8.0in tall (internal dims), the sub works quite well with 132dB output at 1m and 65volts, and the -3dB point is now is 31Hz. That is peak output and I don't think you ever want to operate that point as it will burst your eardrums and possibly break windows in an enclosed car. At a more modest 35volts, you will reach 127dB, still above the threshold of pain, and the velocity of the seatback vent is below 15m/s which is suitable for keeping port noise low. I have increased the vent channel width up to 1.00in (from 0.90in), and just attached a 7.0in wide x 8.0in tall x 16in long duct (reducer step-down from slot dims) and put that through the seat. The step down actually provides some mass loading which pushed the bass extension lower.

Here is max SPL at 65volts:

Here is the predicted SPL at 35volts:

Here is the cone excursion at 35volts with the 24dB/oct HPF @23.2Hz and 48dB/oct LPF @90Hz:

Here is the impedance:

Here is the vent and slot and duct velocities:

Here is the Impulse Response:

Here is the Group Delay:

Electrical power input at 35volts:

I think this looks like a great performer, and should be more than enough in a car - you will need EQ cuts in the lower frequencies due to cabin gain. Looks like great performance outside of a car too.

Hope you build it. Good luck!
Regards,
X

 

[lawbiding]

Thanks for the plan. I have some questions about the drawings, that I want to ask you.

 

[chris661]

Hi x,

What conditions are these sims? 1/4 space? 1/8th?

Looks like a rather good PA sub to me...

Chris

 

[xrk971]

2pi or half space sitting on ground. Yes, I was surprised by how loud this gets too. For PA use I would recommend a bigger cabinet to accommodate larger CSA vents to keep velocities down. Larger vents mean longer vents - volume of vent will be approaching half the cabinet volume. However will allow max 133dB to be reached at 65volts without crazy high velocities in the vents. Cooling of voice coils may be an issue for sustained use. These are not pro drivers but car audio drivers so keep that in mind.

 

[lawbiding]

Xrk971 any ideas on how to do the reducer step down slot dim

 

[xrk971]

Xrk971 any ideas on how to do the reducer step down slot dim

Just make a rectangular flange board with a 7x8in cutout hole in it. This board has a rectangular 7x8in (inside dims) duct attached to it. The duct is 16in long and should fit through the access door for the back seat. The duct flange can be attached to main speaker with wood screws or machine screws and t-nuts mounted in main box. Use some foam gasket material to seal flange to main box. 1/2in thick ply should work for duct and add some reinforcing metal bands on the outside to strengthen it.

 

[lawbiding]

questions

xrk971 what will happen if the duct/port is cut to 12''.

Can you explain the bracing in the box a little clearer.

Can you give me the measurements for the line in the attach picture.




Thanks

 

[lawbiding]

Flange

xrk971 which one of the flange should i used.

 

[xrk971]

Use the flat one.