Hello everyone 
I've been thinking about building a new subwoofer for my (bedroom) studio.
Being able to 3D print things I was wondering what the theoretically optimal subwoofer design would be.
I guess a flush mounted and sealed design dsp corrected up in to sub to be flat. (At least that my guess)
But even then, having a cube inside as a shape wouldn't be perfect right? Or doesn't it make a difference because the wavelengths are longer than the enclosure?
Apart from this, I can't flush mount. So what would be the best subwoofer possible? A sealed sphere? Or would a simple bass reflex / transmission line be better because it's (probably) flatter up to the rolloff point?
Is it even necessary to think about that?
LG
Johannes
I've been thinking about building a new subwoofer for my (bedroom) studio.
Being able to 3D print things I was wondering what the theoretically optimal subwoofer design would be.
I guess a flush mounted and sealed design dsp corrected up in to sub to be flat. (At least that my guess)
But even then, having a cube inside as a shape wouldn't be perfect right? Or doesn't it make a difference because the wavelengths are longer than the enclosure?
Apart from this, I can't flush mount. So what would be the best subwoofer possible? A sealed sphere? Or would a simple bass reflex / transmission line be better because it's (probably) flatter up to the rolloff point?
Is it even necessary to think about that?
LG
Johannes
Enclosure shape is irrelevant for a sub as the wavelengths are too long to be a problem. Sealed gives best step response, which I consider very important, but at the cost of low sensitivity. Most other enclosures will give you a higher output for your Watt but may require a much larger enclosures. The inevitable resonances will degrade step response. What size driver, expected output, and LF cutoff are you aiming for?
@MrKlinky thanks for your response
It's all very vague at the moment, I'd probably shoot for the new 10 inch purifi PTT10.0X08 if it makes sense.
LF cutoff as low as possible I'd say something like -3 at 30 or lower.
I guess output is a bit irrelevant because i wont be able to turn it up all the way anyways... i live in a tower with lots of neighbours.
It's all very vague at the moment, I'd probably shoot for the new 10 inch purifi PTT10.0X08 if it makes sense.
LF cutoff as low as possible I'd say something like -3 at 30 or lower.
I guess output is a bit irrelevant because i wont be able to turn it up all the way anyways... i live in a tower with lots of neighbours.
Given your home, I would suggest that a sealed Qts 0.5 sub would work very well. (My 18" sealed subs are only 55l). You will need lots of EQ and might need a large amplifier.
Unless you really have money to burn, you don't need to spend so much money on such an inefficient unit when there are so many other good speakers around. You would do well to look at a single PA driver, such as Beyma, BMS, and B&C.
Beyma 10NMFS 8 OH
Unless you really have money to burn, you don't need to spend so much money on such an inefficient unit when there are so many other good speakers around. You would do well to look at a single PA driver, such as Beyma, BMS, and B&C.
Beyma 10NMFS 8 OH
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IMO Dual opposed woofer in closed is the best you Can do. No need to turn one driver with magnet out.
No need to make magnet be very close to each other (you cant if driver has venting behind driver).
Benefit is canceling of forces = less vibrations.
You still need strong cabinet. If you Can get it, build from Birch ply of highest quality. MDF is bad.
10” with Long throw might do, but I would rather pick two 8” opposed in sealed. Or 2x10” or bigger.
No need to make magnet be very close to each other (you cant if driver has venting behind driver).
Benefit is canceling of forces = less vibrations.
You still need strong cabinet. If you Can get it, build from Birch ply of highest quality. MDF is bad.
10” with Long throw might do, but I would rather pick two 8” opposed in sealed. Or 2x10” or bigger.
jofero It depends on the room (I use four 18s in my PA system) but I have had to use a 28Hz high pass to avoid feedback on turntables. The EQ follows roughly a Linkwitz Transform but I am not aiming for infrasonic response; 10dB which you suggest is pretty close. The four 18s are powered by two bridged 3kW (peak) amplifiers. Power is so cheap these days that you could easily buy a good 1000W amp if you buy less expensive speakers!
Don't go any smaller than 10" (this is a midrange in my world!) as in my experience, nothing sounds worse than a tiny bass speaker moving many mm each way trying to move enough air - flapping around in the breeze as I call it! You want as much surface area as possible so that excursion is reduced - the reason I am building two more 18s and four 21" 130l sealed subs. An added benefit is that the impedance match of the speaker cone to the surrounding air is improved as its radiating area increases.
I coined an expression many years ago which some folks seem to now be latching on to:
Move a lot of air - GENTLY!
Don't go any smaller than 10" (this is a midrange in my world!) as in my experience, nothing sounds worse than a tiny bass speaker moving many mm each way trying to move enough air - flapping around in the breeze as I call it! You want as much surface area as possible so that excursion is reduced - the reason I am building two more 18s and four 21" 130l sealed subs. An added benefit is that the impedance match of the speaker cone to the surrounding air is improved as its radiating area increases.
I coined an expression many years ago which some folks seem to now be latching on to:
Move a lot of air - GENTLY!
This is what a typical Pro driver "optimised for ported" will do in a small (around 70 litres) sealed box... 112 dB at one meter at 30Hz.... A pair = 115dB and in room corners with around 4dB of boundary reinforcement will give around 118dB at 30Hz....OMG!
That is of course insanely (dangerously!) loud " and never needed in domestic homes.
This driver is AES rated for, 1,600 watts (!) continuous power and has 13mm Xmax!
In real world domestic all you need is a typical low cost Hypex/ICE power amplifier / plate amp of 250 watts into 8 Ohms max...
Here is what it does with just 200 watts (under 15% of max power) and never exceeding 4 mm cone movement (just 30% of Xmax) ... A single driver holds 105dB at 30Hz... A pair does 108dB and in room corners will exceed 112dB... Still waaaaay above most domestic requirements.
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Push-push sealed.
Only needed if you buy cheap woofers. Counterproductive otherwise.
2nd order, but increases third order. You want to keep the 2nd higher than the 3rd. You have to have fairly poor woofers to hit the 25% needed to start to become correlated with the sonics.
Good woofers magnet to magnet re better than having the noise from the back of the driver impinging.
Shape of the cabinet makes little difference given the typical size vrs wavelength, but it can play a role in terms of box rigidity. Why one sees bucket subs and those built into cyclindrical concrete forms.
But with push-push you are removing a huge amount of the energy dumped into the box itself making that last concern significantly smaller. Active reactive force cancelation is something you can get for next to free (ignoring the cost of 2 smaller woofers vrs one larger one).
Further in a sub you want topush any (potential) box resonances up high enuff that they will never get excited. ie No MDF.
dave
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