Two separate boxes will still give you another 6dB over one, but open up placement options over a single sub. You can also place them pointing each other, which allows you to "tune" the bandpass effect. Or put them under your mains for better integration at the crossover point.
The internal volume will be the same for two drivers in separate enclosures as one.
I just layed my dB meter one meter from my sub which is EQd flat to 20 Hz, turned up the music fairly loud, and was swinging up around 100 dBC.
Turned it down to conversational level, (about 70 dBA, "A" scale reads about 20 dB down at 100 Hz) and then put on the loudness contour switch, with an Allison Krause song the sub was still swinging around 98 dBC. "C" scale reads about 3 dB low at 40 Hz, and -6dB at 20 Hz.
1" should be plenty thick if well braced.
That said, I found a 1.5" thick door made of MDF by a dumpster after a gig, had nice stainless steel hinges and handles on it, the door made up most of my home sub. A sub can never be made too heavy, till it comes time to move it.
The two separate subs also allows me to build only one right now and then build the other another time.
Here is a new dilemma. I was planning on using my Behringer A500 to power this sub. Unfortunately, it only offers a bridged-mono connection at 8ohms. The RSS315HF works at 4 ohms. That said, each stereo connection on the A500 outputs 230W at 4ohms. Will this be enough? Or should I just get a whole separate amp like the EP1500 (1400W at 4ohms) to power the sub?
Also, does Boxnotes account for filling? I'll probably use a fair amount of polyfill or something on the inside. Also, would it be good to use acoustic foam (Linky) I'm a bit new to the subwoofer thing so I'm not sure what to put on the inside, as I've seen different uses in both sealed and ported.
power... without the LT, that driver is rated for avg. 86 dB 1W/1m
The diference between 288w and 1152w is +6db theoretical (without power compression etc.)
that's ~
86db = 1w
89db = 2w
92db = 4w
95db = 8w
98db = 16w
101db = 36w
104db = 72w
107db = 144w
110db = 288w
113db = 576w
116db = 1152w
anyway that driver is 400w rms limited
The diference between 288w and 1152w is +6db theoretical (without power compression etc.)
that's ~
86db = 1w
89db = 2w
92db = 4w
95db = 8w
98db = 16w
101db = 36w
104db = 72w
107db = 144w
110db = 288w
113db = 576w
116db = 1152w
anyway that driver is 400w rms limited
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Inside a sealed sub fiberglass or pillow fluff (polyfill) will make the box seem larger to the driver, not by much, but a little. For a 2ft^3 box 3lb of fiberfill is optimal. fyi: Re: Fibre packing in sub enclosure why?
Boxnotes does not consider filler
acoustic foam = useless
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So what does this mean for Boxnotes? How do I account for the lack of volume? Is there a ratio that compares lb of fiberglass to volume in cubic feet?
Above link said:
So let's break down the math.
1.940ft^3 ideal total enclosure volume for Qtc of .707.
X=(1.94)/(1.3)
X=1.492ft^3 of volume without stuffing right?
(1.492)*(1.5)=2.238lbs of stuffing?
So, in Boxnotes, I need to calculate for an internal volume of 1.492ft^3, because the 2.238lbs of stuffing will account for a 30% increase, resulting in an effective 1.94ft^3 enclosure. Please correct me if I'm wrong, but this seems to be right. I'm just worried that I won't be able to measure out that precise of a weight of polyfill.
2.238lbs = 35.808oz. Should be easier to measure in ounces. Grams would be even better. Hmmm.....
It is extremely difficult to judge the volume of the stuffing. The air in he spaces between the fibers is not part of the stuffing. You have to literally compress all of the air out of it to measure it. The air including what's between the fibers acts as a spring obeying the ideal gas laws P1*V1=P2*V2. As the air in the box is compressed when the cone moves inward or rarified when it moves outward, the change in air pressure compared to the outside air pressure which remains constant creates a restoring force that is independent of frequency. This is one of an acoustic suspension speaker's advantages over other systems. The speaker is forced to work to squeeze air back and forth between the fibers which creates aerodynamic drag. This is the velocity related frictional force that controls the speaker's damping factor. Combined with the moving mass (the cone, voice coil, former etc.) thet form a classic mass-spring-dashpot configuration which can be seen in any college physics text or mechanics dynamic text. The equation that relates them is Newton's second law of motion as applied to forced oscillation. Thiel and Small's solution is a kind of cookbook shorthand for solving this equation. Parts Express has also solved it for you. They will tell you the optimal enclosure volume and amount of acoustic filling material they sell to get the lowest system F3 at a Q of .707. You can contact them on line, by phone or just buy the enclosure and stuffing as a kit.
Well I'm glad I took AP Physics and Chemistry, else I'd be completely clueless as to what you just said.
What I'm wondering, though, is if it is even necessary to stuff this box? I'm fine with the dimensions that I got using Boxnotes w/o stuffing. From reading around on the forums, it seems that stuffing a subwoofer isn't exactly necessary and won't yield much of a difference. Since I don't need a smaller box, should I just skip stuffing altogether? Or does adding polyfill do more than just fool the driver into thinking it's in a larger enclosure?
The damping material in the ported sub box isn't mandatory, especially if the upper cutoff point is very low with high slope, the driver has low distortion, and the port velocity is low.
It helps with distortion and noise coming through the port in other cases. The driver you're looking at probably has fairly low noise from the spider and pole vents except maybe at very high drive.
It helps with distortion and noise coming through the port in other cases. The driver you're looking at probably has fairly low noise from the spider and pole vents except maybe at very high drive.
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You have to decide if you want a ported system or a sealed system. For a sealed system in a small enclosure the stuffing is required or you can expect a large FR peak. In a ported system it may not matter however the box will be considerably larger and the size of the port is critical. Ported systems obey the same laws as sealed systems of course but the resistance to the flow of air through the port is highly dependent on frequency. At resonance, air flows freely through it, half an octave away it's the opposite. When you get to integer multiples of the resonant frequency the flow becomes easy again. A ported system falls of at 24 db per octave below the system resonant point. that is its effective lower limit. It can't be extended with equalization the way an AS system can.
The difference in peak output between the A500 power at 4 ohm stereo and bridged mono is only 3 dB (usually "kinda" noticeable), and may be less if only one side is used, as the power supply may deliver a bit more juice to one side driven FTB (technical term, full tilt boogie) than both sides FTB.
If you add a second sub with the amp you have, you will gain another 6 dB output over one, which is quite noticeably louder.
Build one sub, if that is not enough, build the second, if that is not enough , get a real sub amp
.Then get evicted from your dorm...
Attachments
Its sealed. Optimal volume for Qtc of .707 is 1.94ft^3.
So will the math I posted earlier (30% increase in vol if 1.5lb per 1ft^3) work for this system? Or does it go off the final volume (3lb since I have a volume of ~2ft^3). I want the final actual volume to be equivalent to 1.94 soi get a Q of .707.
The best (reliable) figure I've heard is 20% gain in effective volume. These figures are still optimistic.
A large peak (Qtc >1.5) will not be removed by a 20% increase in cabinet volume.
A quick 8" test woofer in winISD showed Qtc = 1.5 when the cabinet is 2.5L. When increased by 20% to 3L, Qtc=1.4. The difference in SPL at the peak was 0.5dB.
Chris
You have a 2 cuft box, and want it to be 1.94cuft?
A temporary measure (once you have the driver) would be to try putting a 1.5L coke bottle in the enclosure. Probably best to fill it with sand.
If you can't tell the difference, just leave it at 2cuft and enjoy
I haven't built it yet. I'm still in the design phase. The volume which gives me all my measurements and performance (see graphs on previous pages) is 1.94ft^3. Im wondering if I should build it smaller since the stuffing will bring it to 1.94.You have a 2 cuft box, and want it to be 1.94cuft?
A temporary measure (once you have the driver) would be to try putting a 1.5L coke bottle in the enclosure. Probably best to fill it with sand.
If you can't tell the difference, just leave it at 2cuft and enjoy
very small box and 10Hz goes against all science.
The LMS5400 ($900+ driver) is the only driver built well enough to go in a 3cuft box and do serious SPL down low. Its a very special driver because of that!!
also why is there a discussion of 2 cuft vs 1.94 cuft....it won't be different not matter which volume you end up with. Splitting hairs over anything under even 5-7% volume difference isn't going to matter in terms of in room performance.
If you are building a small box I would not even model to worry about a Q of .7, just stuff it, EQ it in room after you build it. Its pretty basic stuff really just do not expect low, low frequency output. You require large displacement for the lowest octave output.
The LMS5400 ($900+ driver) is the only driver built well enough to go in a 3cuft box and do serious SPL down low. Its a very special driver because of that!!
also why is there a discussion of 2 cuft vs 1.94 cuft....it won't be different not matter which volume you end up with. Splitting hairs over anything under even 5-7% volume difference isn't going to matter in terms of in room performance.
If you are building a small box I would not even model to worry about a Q of .7, just stuff it, EQ it in room after you build it. Its pretty basic stuff really just do not expect low, low frequency output. You require large displacement for the lowest octave output.
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