I'm in the design process of making an ultimate, compact all in one home super system, using the subwoofer box to house and mount the majority of the components.
The issue of subwoofer mounting is what I'm pondering about, depending on the woofer chosen...........
BOX IS 1.25 CU FT SEALED (I like sealed box for clean, low bass, even if it's not as loud)
The Amp/Heatsinks/PCB will be mounted on the back of the box. (DIY AMP)
The power supply will be a 1200VA Toroid 26-0-26V with 2X 70,000uf 40V caps, and bridge rectifiers placed inside the box.
A small seperated wood box mounted on top will hold the car stereo headunit/misc electronics for the system.
Now everything is mounted outside the box to not use internal box volume, except the toroid and caps. They don't take much room so the volume loss may be negligible, however, I believe if the subwoofer is mounted magnet-out that it will make up for the volume loss, and it looks cool if you have a big magnet.
I'm wondering if the woofer being mounted magnet-out will sound better being the internal volume is bigger, or might sound worse because of the basket and magnet?
Also, considering these woofers : Lanzar Optidrive 1232D Lanzar OPTI1232D 12" Subwoofer Dual 2 Ohm VC Big VC, High RMS, Low VAS and QTS for small sealed box.
And This One: Sony Xplod 12" - Walmart.com: Sony Xplod XS-GTX120LW 12" Car Subwoofer: Auto Electronics similar to my old Sony woofer, sounded GREAT before when this box was empty (no PSU inside) Also Low VAS and QTS for sealed box
The issue of subwoofer mounting is what I'm pondering about, depending on the woofer chosen...........
BOX IS 1.25 CU FT SEALED (I like sealed box for clean, low bass, even if it's not as loud)
The Amp/Heatsinks/PCB will be mounted on the back of the box. (DIY AMP)
The power supply will be a 1200VA Toroid 26-0-26V with 2X 70,000uf 40V caps, and bridge rectifiers placed inside the box.
A small seperated wood box mounted on top will hold the car stereo headunit/misc electronics for the system.
Now everything is mounted outside the box to not use internal box volume, except the toroid and caps. They don't take much room so the volume loss may be negligible, however, I believe if the subwoofer is mounted magnet-out that it will make up for the volume loss, and it looks cool if you have a big magnet.
I'm wondering if the woofer being mounted magnet-out will sound better being the internal volume is bigger, or might sound worse because of the basket and magnet?
Also, considering these woofers : Lanzar Optidrive 1232D Lanzar OPTI1232D 12" Subwoofer Dual 2 Ohm VC Big VC, High RMS, Low VAS and QTS for small sealed box.
And This One: Sony Xplod 12" - Walmart.com: Sony Xplod XS-GTX120LW 12" Car Subwoofer: Auto Electronics similar to my old Sony woofer, sounded GREAT before when this box was empty (no PSU inside) Also Low VAS and QTS for sealed box
Some woofers have lots of vent noise which can be heard if they are mounted magnet out. The noise can be from the spider area as well as vent holes in the back plate.
I recently did a PP comparison using front loaded Lab 12s in "normal" and PP (push pull, the reversed "magnet out" cone polarity reversed) and the vent noise from the reversed cone was very objectionable.
http://www.diyaudio.com/forums/subwoofers/191833-push-pull-vs-normal-distortion-compared.html
Unfortunately "vent noise" is not a TS parameter, you have to check the speaker out to see how bad the noise is at the level you will use the speaker at.
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"Some drivers may buzz due to marginal attachment of the magnet assembly to the basket. This is difficult to determine before the dipole woofer is completed. To avoid this, apply a heavy bead of Silicone II Sealer & Glue to the gap between magnet and basket. "
"There is an added benefit to the chosen driver arrangement. The direction of cone movement is such that mechanical forces cancel and only a minimum of vibration is transferred to the cabinet's outside surfaces for possible re-radiation. "
"A driver with Xmax = 12 mm will generate quite a bit of aerodynamic noise, i.e. distortion, at such high excursions. The space behind the spider needs to be open to the outside to minimize noise. The pole piece should have a large vent, or the cone should have no dust cap, so that air trapped behind the dust cap does not contribute noise.
For a qualitative evaluation of a new woofer perform a simple test. Put a dot of white paint on the cone or dust cap to monitor excursion. Connect the driver to a power amplifier and drive it from a signal generator set to 35 Hz. Hold the unbaffled driver in your hands. Increase the generator output and observe how quiet the driver remains and how much excursion it can handle before sounding obnoxious. Remember that an open baffle cabinet will not attenuate this noise. Lower the frequency and repeat the test. Be careful not to overheat the voice coil or to destroy the driver mechanically!! "
"The major problem with increased excursion is the disproportionate increase in aero-dynamic noise. It is generated by the turbulent flow of air in and out of the magnet vent and by the air trapped behind the spider if it is not completely vented. The typical, low cost stamped basket design is not suited for venting the spider. "
"In effect, the turbulence noise limits the useable excursion."
"the Peerless XLS series model 830500, a 12" (Sd = 466 cm2) unit with Xmax = 12.5 mm peak excursion. While other units on the market claim similar excursion capability, they usually suffer from excessive air turbulence and other noise at large displacements"
I have removed solid dustcaps and replaced with felt type, and then covered rear cooling vents on some woofers to get them quiet. PA is less critical of this than home hi-fi. Mounted in the plenum with some damping material quiets them down quite a bit from co-planar mounting (used by EAW, TAD, others).
"There is an added benefit to the chosen driver arrangement. The direction of cone movement is such that mechanical forces cancel and only a minimum of vibration is transferred to the cabinet's outside surfaces for possible re-radiation. "
"A driver with Xmax = 12 mm will generate quite a bit of aerodynamic noise, i.e. distortion, at such high excursions. The space behind the spider needs to be open to the outside to minimize noise. The pole piece should have a large vent, or the cone should have no dust cap, so that air trapped behind the dust cap does not contribute noise.
For a qualitative evaluation of a new woofer perform a simple test. Put a dot of white paint on the cone or dust cap to monitor excursion. Connect the driver to a power amplifier and drive it from a signal generator set to 35 Hz. Hold the unbaffled driver in your hands. Increase the generator output and observe how quiet the driver remains and how much excursion it can handle before sounding obnoxious. Remember that an open baffle cabinet will not attenuate this noise. Lower the frequency and repeat the test. Be careful not to overheat the voice coil or to destroy the driver mechanically!! "
"The major problem with increased excursion is the disproportionate increase in aero-dynamic noise. It is generated by the turbulent flow of air in and out of the magnet vent and by the air trapped behind the spider if it is not completely vented. The typical, low cost stamped basket design is not suited for venting the spider. "
"In effect, the turbulence noise limits the useable excursion."
"the Peerless XLS series model 830500, a 12" (Sd = 466 cm2) unit with Xmax = 12.5 mm peak excursion. While other units on the market claim similar excursion capability, they usually suffer from excessive air turbulence and other noise at large displacements"
I have removed solid dustcaps and replaced with felt type, and then covered rear cooling vents on some woofers to get them quiet. PA is less critical of this than home hi-fi. Mounted in the plenum with some damping material quiets them down quite a bit from co-planar mounting (used by EAW, TAD, others).
Well, it may NOT be noisy with the magnet out. You'll just have to try it.
But it seems funny to me you are obsessed* with the tiny sub box volume, and then will have all this magnet and such hanging out!
*OK, I'm kidding, but it's still funny.
The difference in internal box volume probably won't be huge.
Yes, you can change the apparent sealed box volume by stuffing. It also dampens internal reflections-the difference has sometimes been dramatic for me. Don't use polyester, it's not so effective. Fiberglass, or read Vance Dickason's Loudspeaker Cookbook for full tests of a variety of materials including foams.
But it seems funny to me you are obsessed* with the tiny sub box volume, and then will have all this magnet and such hanging out!
*OK, I'm kidding, but it's still funny.
The difference in internal box volume probably won't be huge.
Yes, you can change the apparent sealed box volume by stuffing. It also dampens internal reflections-the difference has sometimes been dramatic for me. Don't use polyester, it's not so effective. Fiberglass, or read Vance Dickason's Loudspeaker Cookbook for full tests of a variety of materials including foams.
The "push-pull" is also known as "isobaric". It linearizes the woofer to some extent and will reduce the effective VAS thereby making the box volume requirement lower.
The sound mentioned was mostly due to a vented pole piece pushing air through the hole... hard to eliminate if it is there...
Putting a felt or otherwise vented or removing the dustcap will change the T/S parameters in practice, since you have introduced a loss path, and no longer have a sealed box (or in the case of a ported box, QL is changed).
Bottom line is there is no substitute for a properly sized cabinet, made properly and with the driver installed properly.
Oh, if the magnet moves(!!!) silicone rubber is insufficient. You need a flowable and very strong epoxy or similar adhesive. Better still send the driver back to the mfr and complain...
_-_-bear
The sound mentioned was mostly due to a vented pole piece pushing air through the hole... hard to eliminate if it is there...
Putting a felt or otherwise vented or removing the dustcap will change the T/S parameters in practice, since you have introduced a loss path, and no longer have a sealed box (or in the case of a ported box, QL is changed).
Bottom line is there is no substitute for a properly sized cabinet, made properly and with the driver installed properly.
Oh, if the magnet moves(!!!) silicone rubber is insufficient. You need a flowable and very strong epoxy or similar adhesive. Better still send the driver back to the mfr and complain...
_-_-bear
Hi,
Push pull does is not necessarily isobaric, it is easy to do normally.
Simple fact here is a good driver will be somewhat assymetric to balance
the assymetry of the air in the box, so reverse mounting it is not good.
Personally I find the whole thing somewhat bizarre, make the box a little
bigger and internally mount everything, its a far cleaner form factor.
rgds, sreten.
Push pull does is not necessarily isobaric, it is easy to do normally.
Simple fact here is a good driver will be somewhat assymetric to balance
the assymetry of the air in the box, so reverse mounting it is not good.
Personally I find the whole thing somewhat bizarre, make the box a little
bigger and internally mount everything, its a far cleaner form factor.
rgds, sreten.
well not isobaric if they are mounted on opposite sides of the box... otherwise how would you define two closely coupled drivers, mounted together in series on the same box opening??
Or are you thinking of drivers in phase on opposite side of the box????
Trying to understand the definitions...
_-_-bear
Or are you thinking of drivers in phase on opposite side of the box????
Trying to understand the definitions...
_-_-bear
You've already got it.
Right - Standard push pull configuration.
Right - standard push pull in isobaric configuration. Done with a small chamber for the "exposed" woofer.
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