Say for instance you use 3/4" MDF and build a box with internal dimensions of 10x1x1. Obviously you don't need any bracing with this box. Say then you step up to 10x2x2...gonna guess no on the bracing.
I know that was a stupid example, but seriously, when do you need to start adding braces inside your speakers?
Reason I ask is because I'm designing a set of line arrays that will have these rough internal dimensions:
68h x 5.5w x 8d
Seeing the internal width and depth are only 5.5 inches wide and 8 inches deep and this box will be ported, does this constitute needing to use internal bracing? I will probably do it just for the sake of argument but I was curious what some of you may think.
Thanks!
I know that was a stupid example, but seriously, when do you need to start adding braces inside your speakers?
Reason I ask is because I'm designing a set of line arrays that will have these rough internal dimensions:
68h x 5.5w x 8d
Seeing the internal width and depth are only 5.5 inches wide and 8 inches deep and this box will be ported, does this constitute needing to use internal bracing? I will probably do it just for the sake of argument but I was curious what some of you may think.
Thanks!
My guess would be no, however...
I expect many people will say 'couldn't hurt!'.
Not having worked with MDF, I can only speak to particleboard and plywood. However, 3/4" of either of those materials that's only 5.5" or 8" wide is going to be extremely stiff in that dimension. Sure, you can bend it like crazy in the 68" dimension, but that is eliminated when you glue/screw all the sides together. Given the size, I think we can safely assume that it won't have any super woofers inside and low end extension won't be extreme, so I don't think you'll be dealing with high internal pressures. I'd be surprised if you were able to hear a difference with and without bracing.
Aaron Gilbert
I expect many people will say 'couldn't hurt!'.
Not having worked with MDF, I can only speak to particleboard and plywood. However, 3/4" of either of those materials that's only 5.5" or 8" wide is going to be extremely stiff in that dimension. Sure, you can bend it like crazy in the 68" dimension, but that is eliminated when you glue/screw all the sides together. Given the size, I think we can safely assume that it won't have any super woofers inside and low end extension won't be extreme, so I don't think you'll be dealing with high internal pressures. I'd be surprised if you were able to hear a difference with and without bracing.Aaron Gilbert
Like most things in audio, it depends. High aspect ratio cabs only need to worry about bracing the pipe's cross sectional area (CSA), with the material's MOE and the max acoustic pressure likely to be generated determining the point where the pipe will begin to 'breathe'.
In general, I've found 0.75ft^2 CSA for 5/8" and 1.0ft^2 for 3/4" void free plywood to be the point where bracing around the driver is required, and I don't bother with the rest of the pipe until it gets large enough to develop standing waves (eigenmodes) in its BW.
Don't have a clue about MDF since I avoid it like the plague due to it having to be so thick/heavy to compete with the plywood's stiffness, but with <1/3 the plywood's MOE, I imagine that bracing anything bigger than a small FR driver's pipe would be a 'good plan'.
GM
In general, I've found 0.75ft^2 CSA for 5/8" and 1.0ft^2 for 3/4" void free plywood to be the point where bracing around the driver is required, and I don't bother with the rest of the pipe until it gets large enough to develop standing waves (eigenmodes) in its BW.
Don't have a clue about MDF since I avoid it like the plague due to it having to be so thick/heavy to compete with the plywood's stiffness, but with <1/3 the plywood's MOE, I imagine that bracing anything bigger than a small FR driver's pipe would be a 'good plan'.
GM
No bracing required with those drivers, too high an fb. I'd reconsider the single ribbon. At the crossover frequency in an average size room the midbasses will be operating in the nearfield, and a single tweeter (unless it's a 36 in ribbon) will be in the farfield, and the two won't integrate well. I'd also question the box height, as frame to frame even twelve 4.5s only comes to 54 inches, unless you've got a bit of leftover down below the drivers if it's a floorstander.
An interesting tweeter for LA is the Hi-Vi BS 1, they'll mount really tight. cost only $6 in quantity. and the 3 watt power handling is of no concern when using 18 to 24 of them. Also worth looking at the Dayton NTD20s, also able to pack tight and low priced.
An interesting tweeter for LA is the Hi-Vi BS 1, they'll mount really tight. cost only $6 in quantity. and the 3 watt power handling is of no concern when using 18 to 24 of them. Also worth looking at the Dayton NTD20s, also able to pack tight and low priced.
Think you have one too many doublings..
RJ,
As I recall, adding a driver in parallel gets you 6 dB more SPL (assuming the same drive voltage). With eight drivers, starting from one, you double once to get two, double again to get four, and a third time to get eight. So three doublings at 6 dB each is 18 dB, or 97 dB. Quite a jump, but needs an amp that's stable into one ohm! Note that 9 of these 18 dB are a result of the power increase due to halving the impedance with a fixed voltage.
Aaron Gilbert
RJ,
As I recall, adding a driver in parallel gets you 6 dB more SPL (assuming the same drive voltage). With eight drivers, starting from one, you double once to get two, double again to get four, and a third time to get eight. So three doublings at 6 dB each is 18 dB, or 97 dB. Quite a jump, but needs an amp that's stable into one ohm! Note that 9 of these 18 dB are a result of the power increase due to halving the impedance with a fixed voltage.
Aaron Gilbert
Here's why I asked. 4 of these would measure 5 3/4". They would have to match the woofer in a line array sensitivity wise. So 4 HI-Vi units would be 91 db. A string of 8 paralled units seriesed with four more strings would be 4 ohms. 32 units would be 46 inches.
It would make for a nice array. If they sounded as good as they're response graph.
32 x 3 watts would also be great. $192.00 per side is reasonable.
In the ballpark of 6 PT2 Planars. These Hi-Vi units crossing over at 1000 hz. would match more woofers than the PT2's at 2500 hz.
It would make for a nice array. If they sounded as good as they're response graph.
32 x 3 watts would also be great. $192.00 per side is reasonable.
In the ballpark of 6 PT2 Planars. These Hi-Vi units crossing over at 1000 hz. would match more woofers than the PT2's at 2500 hz.
When you use a whole bunch of drivers you have to go with series/parallel wiring to keep the impedance manageable. Wiring two drivers parallel picks up 6dB, but halves impedance. Add two more in a series/parallel arrangement, original impedance is restored. 8 drivers gets you another 6dB, 16 restores impedance, so 16 of these tweeters will have 91db/SPL with 8 ohm impedance, and will run down to a 1kHz crossover. Run 32 of them and you'll have 97dB/SPL at 4 ohms.
The Daytons are a lot better for SPL, with a base of 92dB/watt sixteen of them would get 104dB at 8 ohms, but with a 3.5kHz crossover. Obviously the tweeter choice is woofer determined; the Dayton's with 4.5s, the Hi-Vi with an array of 8's or larger.
This SPL boost is not linear, it's frequency limited by the height of the array, and has a finite cutoff of about 116 dB/watt irrespective of the number of drivers.
The Daytons are a lot better for SPL, with a base of 92dB/watt sixteen of them would get 104dB at 8 ohms, but with a 3.5kHz crossover. Obviously the tweeter choice is woofer determined; the Dayton's with 4.5s, the Hi-Vi with an array of 8's or larger.
This SPL boost is not linear, it's frequency limited by the height of the array, and has a finite cutoff of about 116 dB/watt irrespective of the number of drivers.
Not considering the extra cost and lots of extra construction work, the problem I have with tweeter arrays is that unless you use ribbons, you'll have problems with attentuated highs and comb filtering.
4 units in 5.75 inches is 1.43" center to center spacing, equal to the wavelength of 9500hz. While I don't believe that sound originates only from the center, I think some attentuation of the HF is likely. As a practical matter, I find it easier to use a single super tweeter of sufficient efficiency to exceed the array at the listening position and use an Lpad to adjust it for different listening situations.
Note that I haven't used this with woofers that only go up to 1-2khz, but it works very well with wider range drivers.
It also enables you to use more interesting shapes for the cabs instead of just tall rectangular boxes, because a narrower baffle is possible.
4 units in 5.75 inches is 1.43" center to center spacing, equal to the wavelength of 9500hz. While I don't believe that sound originates only from the center, I think some attentuation of the HF is likely. As a practical matter, I find it easier to use a single super tweeter of sufficient efficiency to exceed the array at the listening position and use an Lpad to adjust it for different listening situations.
Note that I haven't used this with woofers that only go up to 1-2khz, but it works very well with wider range drivers.
It also enables you to use more interesting shapes for the cabs instead of just tall rectangular boxes, because a narrower baffle is possible.
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