Theorization in progress; Mindblowing Minisculities and Goosebump PR-Bandpass...

[Wolf]

Well-
I had some 0.72mH 18AWG with steel cores I wound myself. That should be close enough. I bet even some steel-rod-cored 20AWG coils would likely do.
I had some 50uF NPE caps, and some 4.7uF Daytons, and measured comes out to just shy of 55uF in parallel.
I had some 10W Dayton 3.3 ohm (measured 3.4 ohms) resistors.

I'm glad I chose to place these inside or adjacent the sub. Here's why:



And these are CHEAP and SMALL parts! No way would that have fit inside...

Later,
Wolf

[Wolf]

For fun, a re-post of my poem...

Ode to a small speaker...

When the wires pull the speaker off the stand,
Or when they barely fit the palm of your hand,
Or internally they don't go as planned,
Then it's a small design.

When the bass makes them dance and oscillate,
and also you hyperventilate,
and you question the project's thermal state,
Then it's a small design.

When nothing else will fit inside,
then bending rules you past abide',
But all your logic's justified,
Then it's a small design.

If empty cabs weigh less than parts,
and going outside the box is art,
Then you'll know right from the start,
That it's a small design.

[Wolf]

Had to use packing tape to hold them down on the entertainment center and keep the wires at bay.

Wolf

[djg]

Sticky back velcro, or suction cups.

[Wolf]

Okay- fitment details for the woofer:
Woofer goes in 3" hole.
PR has a 3.75" through-hole, which is big enough to install woofer through.

I'll update the graphic with this and fix the driver name error in the near future,
Wolf

[zx82net]

Nice, now that's what I call a satellite!

What's your main motivation for the bandpass sub rather than a single 1.2l chamber with PR? Is it just the "free" low pass it gives you?

Luke

[Wolf]

With the bandpass alignment, you get the sealed box air-spring for the highpass of the bandwidth, whereas you would not have that in a vented or PR box of approximately 2 ltrs. This keeps the driver in check and (to be tested) hopefully not require the passive highpass or active highpass components to keep it from over excursion. In a vented/PR design, you really do have to have the highpass in place with this driver at about 40Hz or thereabouts so it does not simply destroy itself. Of course the mechanical lowpass is also favorable so it 'gets out of the way' faster, and much below the 150Hz inherent LP in the amp. My guess is harmonics might still be present up to the 150Hz point, and then blend okay with the 2" Omnis without too much trouble. Since the initial rolloff is an octave below there, the 'localization' or identifying the position of the woofers becomes less of an issue as well. While the alignment of the bandpass shows basically a null increase of sensitivity, changing the PR volume to a larger cavity can also increase the output. It is a pretty flexible box design, and fits great in the purchased boxes I attained. I've actually had a bandpass alignment for this driver with a port 'at the ready' for quite a while now, nut this PR-BP entices me more.

If the added capacitor is required on the woofers to keep xmax in check, I plan on aligning it with the rolloff to boost the knee a smidge before the rolloff now becomes a 3rd order highpass. This could yield a slightly lower F3 than the 55Hz modeled.

Later,
Wolf

[zx82net]

With the bandpass alignment, you get the sealed box air-spring for the highpass of the bandwidth, whereas you would not have that in a vented or PR box of approximately 2 ltrs. This keeps the driver in check and (to be tested) hopefully not require the passive highpass or active highpass components to keep it from over excursion. In a vented/PR design, you really do have to have the highpass in place with this driver at about 40Hz or thereabouts so it does not simply destroy itself. Of course the mechanical lowpass is also favorable so it 'gets out of the way' faster, and much below the 150Hz inherent LP in the amp. My guess is harmonics might still be present up to the 150Hz point, and then blend okay with the 2" Omnis without too much trouble. Since the initial rolloff is an octave below there, the 'localization' or identifying the position of the woofers becomes less of an issue as well. While the alignment of the bandpass shows basically a null increase of sensitivity, changing the PR volume to a larger cavity can also increase the output. It is a pretty flexible box design, and fits great in the purchased boxes I attained. I've actually had a bandpass alignment for this driver with a port 'at the ready' for quite a while now, nut this PR-BP entices me more.

If the added capacitor is required on the woofers to keep xmax in check, I plan on aligning it with the rolloff to boost the knee a smidge before the rolloff now becomes a 3rd order highpass. This could yield a slightly lower F3 than the 55Hz modeled.

Later,
Wolf

Ah, cool. It basically avoids all the DSP cheats I need to use!

[Billet]

Mechanical filters are nice!

[Wolf]

I tested the mechanical air-spring filter today for the woofers alone. Ran some Usher- "Yeah!" with the Lepai amp and bass boost cranked. Up and even under duress the composure was maintained albeit a bit noisy. It just did not unload, and that's a benefit with these little loosey-goosey drivers. Let's face it, you can't get rid of ALL of the leaks, but I believe that is what I was hearing at pretty loud levels. With a pair as planned, the Xmax and Pe will be handled by both pretty easily.

I did not mount the woofers the conventional way this time. 6 screws will hold them well if you choose to though. What I did was use some 4" aluminum trim rings I've had for awhile, and with help of Aleene's tacky glue and a closed-cell foam rubber ring, I cranked down on the trim ring with the driver in a recess. The rings were not that pretty anyway, and I would have them out of sight. I used the socket-head #8 screws initially, and felt they did the job well- until I went to the second woofer. I could not get it as tight as the first. I swapped for the #8 deep-thread screws from here at PE and was amazed at the difference in torque. The air-spring is really tight on these, and I recommend these screws if you plate mount like I did.

Dry fit:






Driver plate mounted and rebate done:



I sealed the plate with RTV, and installed said mounting ring over driver. I stuffed the internals (not shown):



More in a few...
Wolf

[3rutu5]

Tiny projects that are fun ... You have my attention

[Wolf]

A little realization has set in...
Since I mounted the drivers with the trim rings, the trim ring will not fit through the PR's mounting hole. If you build this woofer and mount it conventionally, this will not be a problem.
I'll have to compound the thoughts for the PR mounting faces and see what I come up with.
I'm REALLY glad I did not just glue in the end-caps as I was thinking I would do.

Wolf

[Wolf]

Well, It's completed from a functional standpoint. I may have to add some things like PR grills /like/or a stood-off plate like the satellites have. I'll post pics later this afternoon....

Good news is- it rocks! :-)
Wolf

[Wolf]

Okay, here we go...

Being I decided to go dual-opposed to combat vibration, I gave myself a certain dimension between the 5" cubes to facilitate the electronics and connections. I'd say it's *about* 2". Without measuring, that's pretty close. Next step was to mock up positions for the stuff to go. I chose opposite corners for the contour networks to keep the coils further apart, and to place the L/R outs to the lower of the rear and the amp volume to the upper front:



Spacing:


I ended up purchasing a few minor parts for the assembly to finish it off. I bought a Switchcraft double 3.5mm bulkhead in a D-panel size. This meant I could find a short 3.5mm male to male cable to wire up the input to the 2.1 board. I found all but the 1' Slim-plug were out of stock as far as the short lengths go. I routed it under the amplifier and to the input jack to keep it away from the power and speaker lines.
(I bought the 10k log pot in the case of the sub/sat outputs being dissimilar enough that I wanted to be safe since Tom needed it on his Micro-B plate amp. I ended up not needing it, IMO.)
I bought the blue-LED round rocker switch for 12VDC applications as I wanted the little blue LED on the amplifier to match color wise.
I also bought a 2.1mm x 5.5mm wall-wart adapter-tip for the power input to the 2.1 amplfier. I didn't have much room to work with. I figured I'd just solder to the tip and heatshrink the connections. My initial trials on this worked well. When I went to first power it up after assembly was completed, I had power to everything BUT the amplifier. Voltage-probing led to the adapter plug itself. I used flush-cuts to remove plastic, and found the ground connection had severed. I wrapped a loop of 20AWG wire around the barrel and soldered it back into place, and added solder to the + connection for strength, and then reapplied the heatshrink for isolation. It now works solidly. I think I would still use this method of connection to avoid killing the warranty, and make an easy swap if the board goes bad.
Jungle supplied a 16VDC/4.5A floor-wart for power.

I had these in house and used them as well:
large diameter Blue LED and dropping resistors
5x 1N4003 diodes for eliminating voltage reversal
circuit perfboard
DPST switch
Scrap plexiglass
binding posts without jam nuts
long cable for source connection
DC input jack from another piece of kit
knobs
wire, stranded 16AWG for output wiring and solid 18AWG for internal
techflex
9-tine probe style dual bananas
Speakon jack/plug for L/R output

Since i was using a removed DC input jack, I had to draw up a circuit to do what I wanted. The board is shown as 2 pieces for easy dissection. The voltage of the supply is just under 16VDC after the diodes are applied, so I had to derate the LED in the switch to add longevity. I applied the larger LED and resistors after the switch to light the interior as my wife suggested I should. Why, you ask? I used the piece of scrap plexiglass to bend over the front-top-back and conjoin the 2 woofer modules. I used my heat gun and a straight-edge to get it done. It's not perfect, but looks decent. I just glued the edge of the perfboard with the circuit attached to the edge of the input jack board.

Circuit:


And the electronics cavity within the wrap:


The DPST switch was used as a contour-network bypass-switch. While listening to music, the contour network brings everything into place. While listening to speech, sometimes intelligibility is a requirement. This will allow the vocal range to be at unaltered levels if preferred.

Wiring of series woofers:


More to come...
Wolf

[Wolf]

Another internal view or 2 (I have a bunch of 5W or higher resistors from an assortment that was given me awhile back, that's why I used more than one resistor in series):



Front layout:


Rear layout:


Majority assembled, and items labeled:


Now I had to address the mounting issue mentioned previously, as the mounting ring for the woofers will not fit through the PR holes the way I did it.

More in the next post,
Wolf

[Wolf]

I added a surface/outer baffle and screwed it to the inner one. This allowed me to seal it with weather stripping when mounting with screws to the inner panel. Since the outer panel is sealed to the main boxes, I did not glue these pieces together. Flush-trimmed the size to the box with tape on the surface to keep it looking nice.





I really wish I could get more of this stuff^^^. I found it at Menards about 10 years ago when I was building my Xenums project and used it in the xover bases. It's a dense polymer composite board. It's rough when purchased and very abrasive, but nothing sanding can't fix. It machines well, is fairly strong, and does not ring acoustically ie- it's very dead. It came in a smaller than 2' x 4' board, and is not quite 1/2" thick. I think it was an EPDM material, and I might have the label somewhere...

PR/baffles mounted, using PE coarse-thread screws:



This all resulted in a woofer module that can do quite well in my living room. I have not measured the tuning of the bandpass yet, but I feel I would not change it. There is no added mass on the PRs. A little batting is on the walls in front of the woofers, just a ring inside the front chamber.

The wiring I felt would be simple and hard to screw up if I used a Speakon. The single Amphenol unit from a grab-bag at MWAF suited well as I only had one, same for the jack. The dual bananas were used as that is also the simple kind on the MM satellites, and it will prevent shorting possibilities. I placed a red Sharpie dot on the tips for positive lead identification, and red heatshrink for the right channel as 'Right is always on Red', even in RCAs. No fiddling with bare wires, polarity, which is left or right, etc. Simple plug in and play.

Voila! The build where I finally beat the 2.1 Bose system in both size and performance! These really should not sound this good...



When I measure the BP tuning, I'll post the results.
All done in a module the size of a loaf of bread!

Later,
Wolf

[djg]

That is awesome.

[Wolf]

Thank you!
Glad you like it!
Wolf