Building a sub in a stereo cabinet

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I have a Philco cabinet that had a blown amp (disconnected speaker with tube amp) that I’ve been re-purposing as a cabinet for my tube amps, turntable, preamp, etc. Ultimately I am working towards a surround system using a 25W/channel tube amp (PP 6L6s) driving a pair of Klipsch Heresy (H-700) speakers in front, and an 8W/channel SE amp driving a pair of FE103En speakers in the rear.

This leaves me with the subwoofer as a project. I have a Hafler DH-200 that I am considering for the sub amp. It is rated at 100W/Channel into 8 ohms. And it should be possible to bridge to channels to get 200W if necessary.

I got thinking today that it might be possible to seal off the bottom of the cabinet and convert it into a sub. The dimensions of the bottom section are 13” X 30” X 10” which yields a 2.67cu-ft volume.

In this configuration, the Sub could not be used when playing records, or feedback could be an issue.

The entertainment area is 12’ wide 8’ high and 14’ deep. One side is brick with a fireplace. One side is covered with drapes, the floor is wall-to-wall carpet the rear wall is paneling as is the front wall, except it has a large window as well. The stereo and TV currently are under the window. One couch and one recliner are all else in the room.

This is a moderately small room and should not require a lot of power as listening is normally at low to moderate levels (Measured level while watching “Jeremiah Johnson” is 62dB, fast response, C weighted). Musical taste varies from Jazz, rock, country, Hip-Hop, Blues, etc.

I don’t listen at concert levels, but do watch Action, Military, Sci-Fi, Western, movies etc.

Does this sound feasible to use the bottom to build a sub enclosure? I’ve not seen many 9” subwoofer drivers, other than ebay and 10” drivers won’t fit. I was thinking about possibly using a Super 8 from Apex Jr. but am concerned that the Re=2.65 ohms might be an issue.
 

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That, or a pair of W8Q-1071F in a PPSL as they have a Re of 3.2 which would be more friendly to the amp I have. Fs of 27, and Xmax of 12mm look good as well.

I'm reading the thread on the PPSL as this sounds promising.

Otherwise I guess I'll give up on putting the sub in the bottom of the cabinet and look at making the sub to fit under the left speaker, which would have the added advantage of raising it to the same level as the right speaker.
 
Wiring the drivers in series is what I had in mind. However the TB won't fit if I'm limited to 13" depth and still have a reasonable plenum.

Dayton Audio DCS205-4 would fit, and might allow a 4" plenum depending on wood thickness, etc. With a depth of 4.25" it allows the speakers to be located closer together than the TB, thereby increasing available internal volume.

Am I correct that the lower Vas of the DCS205-4 (1.35cu-ft) compared to the W8Q-1071F (70.2L~=2.98cu-ft) would allow for a smaller enclosure for the same lower frequency cutoff?
 
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Hi,

The DCS205-5 would have a similar response to the ApexJr Super 8, and twice the Xmax. App. same enclosure size. Nice find.

As to the construction, one way would be to integrate the front baffle and the plenum, and make both removable from the front. That might make mounting the drivers easier. You could also attach the ducts to the front baffle, that may make it easier to get to them for length tuning.

Just thoughts,

Regards,
 

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One thought I had was to mount the grill cover on a new front-board mounted from the rear as it originally was, and insert the speaker assembly from the rear independent of the cabinet so it would be removable for tuning. (no fancy finish required.)

I had planned on one shelf inside for the amps, and intended to place the turntable (SL-1200 MKII) on top to keep it as far from the sub as possible.

Actually, it would be possible to raise the shelf to leave more room for the sub, but I'd have to do a bit more work on a false front below the shelf.
 

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For the last couple of days I've been playing with Hornresponse, but I'm missing something.

Specifications for DCS205-4 8: • Power handling: 150 watts RMS/300 watts max • VCdia: 1.5" • Le: 1.76 mH • Impedance: 4 ohms • Re: 3.53 ohms • Frequency range: 30-200 Hz • Fs: 30 Hz • SPL: 87 dB 2.83V/1m • Vas: 1.19 cu. ft. • Qms: 5.86 • Qes: 0.35 • Qts: 0.33 • Xmax: 8.8 mm • Dimensions: Overall diameter 8-1/4", Cutout diameter 7-1/4", Depth 4-1/4".
 

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Hi,

When in the SPL window hit Tools>Combined Response.

Also L12 and L23 should be kept about as short as possible, S1 can be reduced (use fill in the back corners). djk says that the big peak past the passband does not happen; Hornresp cannot easily take the reduction in the plenum @ S2 because of the reversed driver into account.

Regards,
 
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Thanks Oliver.

I am probably confused, but I thought :
S1 segment 1 throat - set to same as driver area.
S2 segment 1 mouth - set to driver area
S3 - plenum opening area

L12 is set to the depth of the internal box. I suspect this is wrong but don't see what else it could be.
L23 is set to the distance from the center of the driver to the mouth of the plenum.

If S12 is reduced by the use of fill in the back corners is there a general guideline for % reduction?
 
Hi,

For a quick try normally I would just model this as a bass-reflex enclosure, and forget about the plenum and all that, but it is probably good practice to try to model it correctly with a short horn, and an offset driver.

Si is the area at the back of the plenum, S2 is the plenum cross-section @ the center of the drivers, S3 is the mouth of the plenum. L12 is the distance from S1 to S2, L23 is the distance from S2 to S3. It probably does not matter in this case, but in front of the L12 window you can choose the taper (flare rate).

For the reduction of S1 use Hornresp as a guide.

There are some discrepancies in the T/S values, I'll attach a quick example:

Regards,
 

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I found another mistake, I had the set Rg (the amplifier output impedance) to 8 when I started out as I usually use tube amps. This will be driven with a SS amp so the output impedance will be much lower.

The inversion of the first peak looks weird in the impulse response. Like some kind of odd harmonic distortion?

I've noticed that most of the cabinets have very large ports relative to this design which uses two 1-1/2" dia pipe, each 20cm long.

Is the difference due to the large size of the cabinets allows for such a large duct in relative terms compared to this design? ie. The larger the enclosure the larger the port for the same tuning frequency.
 

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Hi TheGimp,

The impulse responses in Hornresp are calculated from the total frequency response, and do not reflect what you'll get once the passband is altered through the use of low-cut and high-cut filter; add to that, that it's not quite possible to simulate the PPSL in Hornresp.... I would not worry too much about it. The Tools>Impulse>Spectrogam (or: Ctrl H) gives you a much better idea of what you'll have left after filtering. You would probably be better of to just take the response from a bass-reflex enclosure for this project.

Naturally, you can go File>Export>AkAbak Script... that'll give you a start for getting into Akabak where you can build a simulation that closely reflects the enclosure and respective filters. Talk about a learning curve...

The ApexJr Super 8 goes a little lower, and looks a little flatter.

Regards,
 
Some of this is common ground for me, but some is totally foreign, like the Ang parameter. I presume it is related to the radiation pattern of the speaker, but can't interpret it yet.

I'll figure it out eventually.

For now I ordered a pair of the DCS205-4. I may pick up a pair of the Super 8 later for comparison.

I found enough scrap (mostly particle board) laying around to start a prototype. I'll use 1-1/2" PVC tube for the ports. 3/4 birch is available for $41 a sheet, but I'll wait till I'm confident I can make reasonable cuts before getting a sheet of it.
 
Some of this is common ground for me, but some is totally foreign, like the Ang parameter. I presume it is related to the radiation pattern of the speaker, but can't interpret it yet.

Hi TheGimp,

The Ang parameter specifies the solid angle into which the speaker radiates. This is not the same as the radiation pattern of the speaker.

Ang = 4.0 x Pi steradians - Speaker suspended in space at a large distance from any walls or boundaries (free space).

Ang = 2.0 x Pi steradians - Speaker placed on the floor in the centre of a room (half space).

Ang = 1.0 x Pi steradians - Speaker placed on the floor along a wall (quarter space).

Ang = 0.5 x Pi steradians - Speaker placed in the corner of a room (eighth space).

Kind regards,

David
 
Hi TheGimp,

Post #17: "Some of this is common ground for me, but some is totally foreign..."

Even with David McBean's constant effort to keep Hornresp simple and accessible, there is still a good size learning curve.

For a 36 L_net volume box I get:

2ea. 1.5" I.D. duct (AP=22.8cm^2) @ Lpt=10cm, and
2ea. 2.0" I.D. duct (AP=40.5cm^2) @ Lpt=16cm.

In Hornresp, if you go and click: Edit>Tools>Loudspeaker Wizard>change the left hand selection box from Schematic to Response, and change the right hand selection box from Default to Combined; then you can use the sliders on the right to modify the box volume, etc.. Also, on the lower right you can see the Helmholtz frequency.

Is that 4'x8'x3/4" birch veneer plywood for $41, and where?

Regards,
 
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