What is the internal volume of this cabinet"
Also, what are the diameter & length of the ports?
DIY Altec 2 Way Build ala JELabs - 802/32/414
- Thread starter marantzfan
- Start date
Do It Yourself
Also, what are the diameter & length of the ports?
FalseMetal666
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The original 614 dimensions:
Internal volume is around 3.5cf, not exactly sure what precise volume is once driver displacement and the bolt-in "sub baffle" are accounted for.
Ports are two 3" diameter PVC tubes, 6" in length.
@Jeb
If the online T/S specs I found for the 414A are correct, the woofer will have a response as below in a 3 cubic foot enclosure tuned to 39Hz.
Based on the external dimensions: 24 3/4" x 18 3/4" x 14 1/4" = 3.375 cu ft internal.
Tuning to a higher frequency will give you a better damping & response and lower F3.
39Hz Tuning
53Hz Tuning
59Hz: Two 3" ports, 2.31" long
Based on the external dimensions: 24 3/4" x 18 3/4" x 14 1/4" = 3.375 cu ft internal.
Tuning to a higher frequency will give you a better damping & response and lower F3.
39Hz Tuning
53Hz Tuning
59Hz: Two 3" ports, 2.31" long
Thank you both — this is exactly the kind of information I was hoping for, and your WinISD simulation seems to confirm that two 3-inch ports approximately 6 inches long would tune a cabinet of around 3 cubic feet close to 39 Hz.
I may be interpreting the cabinet dimensions incorrectly, but multiplying the stated external dimensions gives me approximately 3.83 cubic feet externally. Assuming ¾-inch panels, the internal geometric volume seems to be close to 3 cubic feet before subtracting the woofer, additional sub-baffle, ports and any bracing. I suppose the final usable volume could therefore end up somewhat below 3 cubic feet.
As a rough working estimate, I averaged measurement data from four different 414A woofers, which gave approximately Fs 26.6 Hz, Qts 0.226 and Vas 150 litres. I realise that this is not the same as measuring my own pair, so I would also be interested to know which online T/S figures you used for the simulation.
The comparison with 53 Hz tuning is particularly interesting. As far as I understand the graphs, the higher tuning gives a flatter response and a lower formal F3 by adding more output through roughly the 50–70 Hz region, rather than by extending the response farther below 40 Hz. Please correct me if I am reading that incorrectly — I am still learning how to interpret these alignments.
In any case, the 39 Hz result makes Bobland’s two 3-inch by approximately 6-inch ports look like a very sensible starting point for the 414A. The quick-swappable arrangement is especially attractive, since it would make it possible to try slightly different port lengths and then confirm the result with an impedance sweep and listening.
I may be interpreting the cabinet dimensions incorrectly, but multiplying the stated external dimensions gives me approximately 3.83 cubic feet externally. Assuming ¾-inch panels, the internal geometric volume seems to be close to 3 cubic feet before subtracting the woofer, additional sub-baffle, ports and any bracing. I suppose the final usable volume could therefore end up somewhat below 3 cubic feet.
As a rough working estimate, I averaged measurement data from four different 414A woofers, which gave approximately Fs 26.6 Hz, Qts 0.226 and Vas 150 litres. I realise that this is not the same as measuring my own pair, so I would also be interested to know which online T/S figures you used for the simulation.
The comparison with 53 Hz tuning is particularly interesting. As far as I understand the graphs, the higher tuning gives a flatter response and a lower formal F3 by adding more output through roughly the 50–70 Hz region, rather than by extending the response farther below 40 Hz. Please correct me if I am reading that incorrectly — I am still learning how to interpret these alignments.
In any case, the 39 Hz result makes Bobland’s two 3-inch by approximately 6-inch ports look like a very sensible starting point for the 414A. The quick-swappable arrangement is especially attractive, since it would make it possible to try slightly different port lengths and then confirm the result with an impedance sweep and listening.
Internal volume is @ 3.375cu ft based on taking 3/4" off each external dimension. 24 x 18 x 13.5 = 5832"/1728" = 3.375 cu ft
1728 = 1cu ft in inches. Minus drivers, braces, etc; net internal volume is close to 3cu ft for simulation.
You are interpreting the simulation graphs correctly. The higher tuning should yield a better sounding response. With a bass reflex alignment, you typically want a flat passband with a sharp roll-off near cut-off not a drooping response unless it is intentionally for a specific design goal like adding EQ/PEQ to extend an alignment which would be considered a 6th order alignment versus a standard bass reflex alignment which is 4th order.
1728 = 1cu ft in inches. Minus drivers, braces, etc; net internal volume is close to 3cu ft for simulation.
You are interpreting the simulation graphs correctly. The higher tuning should yield a better sounding response. With a bass reflex alignment, you typically want a flat passband with a sharp roll-off near cut-off not a drooping response unless it is intentionally for a specific design goal like adding EQ/PEQ to extend an alignment which would be considered a 6th order alignment versus a standard bass reflex alignment which is 4th order.
FalseMetal666
Site Supporter
Awesome, will be great to try a couple shorter tubes on my 614 at some point. The 612 + 416-8B combo is currently in service, will need to run some simulations on that as well...
@THD+N
I can now see that the simulation is based on the measured CLIO data shown above: Fs 32.08 Hz, Qts 0.24 and Vas 268 litres. Those figures are quite different from the rough working values I had been using, particularly Fs and Vas, and that seems to explain why the higher tuning produces a much flatter alignment.
Your explanation of the response curves also makes sense to me. The 53 Hz tuning clearly gives the flatter fourth-order alignment and the lower formal F3, whereas the 39 Hz tuning retains somewhat more output below approximately 45 Hz but introduces a gradual downward slope through the upper-bass region.
This makes Bobland’s quick-swappable ports seem particularly useful. It should be possible to begin with the 6-inch tubes, compare them with slightly shorter alternatives, and then confirm the actual tuning with an impedance sweep and listening in the room.
I can now see that the simulation is based on the measured CLIO data shown above: Fs 32.08 Hz, Qts 0.24 and Vas 268 litres. Those figures are quite different from the rough working values I had been using, particularly Fs and Vas, and that seems to explain why the higher tuning produces a much flatter alignment.
Your explanation of the response curves also makes sense to me. The 53 Hz tuning clearly gives the flatter fourth-order alignment and the lower formal F3, whereas the 39 Hz tuning retains somewhat more output below approximately 45 Hz but introduces a gradual downward slope through the upper-bass region.
This makes Bobland’s quick-swappable ports seem particularly useful. It should be possible to begin with the 6-inch tubes, compare them with slightly shorter alternatives, and then confirm the actual tuning with an impedance sweep and listening in the room.
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FalseMetal666
Site Supporter
Mike414
Site Supporter
If the cabinet walls are 3/4" then you need to subtract 1 1/2" from each external dimension.
FalseMetal666
Site Supporter
Off topic: Might you consider running sims for a 612 enclosure + 416-8B combination?
612 SPEC
Volume: 6 cubic feet
Stock vent: 13" x 5.5" slot
Proposed vent: two 4" x 9.5" tubes
416-8B SPEC
| Model No: | Xmax (inch) | Re (ohms) | Vd - (cu. In.) | Fs (Hz) | Vas - (cu. ft.) | Ref (%) | Qts | Qms | Qes | Vid |
| 416-8B | 0.15 | 6.9 | 19.2 | 25.1 | 26.47 | 2.7 | 0.32 | 7.05 | 0.33 | 0.2 |
That comparison makes the point very clearly. With this particular driver and cabinet volume, the original short slot appears to tune much too high, while 30.75 Hz produces a noticeably falling response. The 42 Hz alignment looks like a very convincing middle ground. It is interesting how the most useful tuning is not necessarily either the historically original one or the lowest possible one.
