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Slightly increased sensitivity. You get around +1dB free on the drivers I use with other drivers it might be less but generally you will see a slightly increased sensitivity because of the magnets of each driver working as a bucking magnet for the other driver. (Saturnus)
- However, in June 2014 (Saturnus) notes that: P.audio changed the magnet on the HP10W to a smaller and lighter but equally powerful one since the first version so now it's 6mm less deep overall. That means you glue them to the center brace instead. It also means that the small efficiency increase potential there was by gluing them together due to the former version having a poorer magnet design has gone so there's no need to do it anymore. The benefits are now purely mechanical in nature.
- Automatic magnetic shielding. Since the magnet of driver works as a bucking magnet for the other magnet, you get the same benefit as a regular bucking magnet which is to severely reduce stray magnetic fields. This will have some influence when used near other electronic devices. (Saturnus)
- Structural strength. With the drivers connected internally and each driver connected to each front baffle, the drivers themselves work as an extremely efficient brace on the baffles. With a center brace running down the middle and connected to the drivers to support the top/bottom and ends, what you end up with is a structure that by design is extremely rigid. In effect this design is as strong and resistant to vibration as a cabinet made of at least 50% thicker wood. (Saturnus)
- Bipolar design. By very nature a bipolar design has many advantages in outdoors speakers. First one is baffle step; it's gone, it doesn't exist in bipolar speakers. Second one is automatic bass compensation; try placing a normal speaker outside on a grass field and play something, now as you walk around it you will find that on the opposite side of where the speakers are facing treble and midrange will be lower than directly in front of it, this is because the air works as a gentle acoustic filter of higher frequencies but letting lower frequencies pass. Now in a bipolar design you add the response of the front facing driver with acoustically filter back facing drivers and thereby get a completely free bass boost. (Saturnus)
- There's tension on the baffles, not on the magnets per say, when you stack two drivers like this it takes considerable force to pry them apart again. (Saturnus)
- In principle you could use the center brace to divide the cabinet into two separate chambers, each with it's own reflex port and have a Boominator Mini of half the originals size plus a little for electronics. Just with each side playing the left and right signals instead of the same signal. (Saturnus)
- The cabinet is tuned to 0 dB at 82 Hz which results in a free field -3 dB at 91 Hz, so roughly 90 Hz after which it rolls off 36 dB/octave due to both acoustic and electronic filtering. (Saturnus)
- It's optimized for optimum response in actual typical listening positions, which is a very wide area, 2-3m from the speaker, 1-2m above on-axis, and up to 60 degree angle off-center. Original measurements included 16 different FR plots in those listening positions. The Boominator will practically never be listened to on-axis, unless you're lying flat on the ground in front of it (in which case your ears won't be on-axis anyways). (Saturnus)
The recommended material type for the enclosure is 12mm 9 ply filmed birch plywood (Saturnus).
It's not because of the filmed surface that I recommend this type of plywood. It's because of the used resin to glue it which is different from other plywoods and makes it up to 22% stiffer and 5% lighter than regular plywood. (Saturnus)
Stiffness being the principal quality as we want the cabinet to be exceptionally rigid to low frequency vibrations. (Saturnus)
In effect using the correct 12mm plywood is in terms of cabinet properties the same as if a 15mm regular plywood had been used. (Saturnus)
I should note that it might not be all types of filmed plywood that are the same but it was during a visit to a WISA plant in Finland I was introduced to WISAFORM which is WISA's version. Also available is the ever higher strength WISAFORM BURCH MAXI and SUPER MAXI. I have used this type of plywood for all cabinets intended for bass output since. (Saturnus)
It's not only the type of resin that is different, it's also the application and manufacturing technique. Standard plywood is typically applied resin/glue in strips and then smoothened with rollers before the next layer is applied, getting roller pressed, sanded and dried. Filmed types are generally spray coated with resin to a uniform layer which makes the time before the next layer is applied lower. And instead of being roller pressed, it is form pressed with ultrasound which generates heat in the resin and almost instantly hardens it. This is then sanded and applied with a thin resin soaked paper/cloth/glass-matte which in turn is either roller pressed with structures or goes directly to hot air drying. (Saturnus)
These boards are then packed on pallets, baked and stored until optimum humidity is achieved like normal. (Saturnus)
As an alternative MDF would be better if it's not possible to find birch ply. I wouldn't use 3 ply if it can be avoided. With MDF, remember to pre-drill all screw holes and to prime all surfaces, even the internal ones (Saturnus).
Make very sure to seal every single surface internally, so that the chipboard doesn't pick up too much moisture. Otherwise it'll become very heavy and fall apart very fast. The internal forces put on the wood is quite extreme. (Saturnus)
- For mounting Goldwood GW-1058, cut out a piece of plywood to put on either side of the center brace, 12mm (0.5") so that the magnet is in direct contact with center brace. This can be done from the speaker cut-outs you have left from the sides (Saturnus).
- The bond between the driver and the center brace is what holds the driver in place. The screws on the front are not necessary, just the sealant. The screws can help to hold it in place while it's being mounted. (Saturnus)
- Mounting woofers in such way linearizes the frequency response in the 3khz-3.5khz region. If you do not mount them correctly, it will have an audible dip in the frequency response due to diffraction (Saturnus).
- The 9mm 45 degree chamfer or full 12mm round over is correct on the Boominator with HP10W (or GW-1058). It serves to correct the slight dip between 600hz and 1khz (Saturnus).