Dual 10" Sub Design For Your Review

[theater_lover]

Here is where I am currently with my design and I feel fairly comfortable with the numbers. This was calculated with WinISD.

SPEC:
Dual ACI SV10s
Passive Vented Design, with front/back opposed drivers, port also on back.
Enclosure of 2.85 cubic feet.
I will likely be using polyfill to get an effective 25% size increase.
Port will be 4" Diameter at 41.5" long.
Drivers, bracing and port are roughly .45 cubic feet.
This should result in a 3.0 cubic foot enclosure tuned between 16-18Hz.
I will have two of these.
This will ultimately be EQ'd.

At MAX POWER for the drivers (500 Watts for two), I get...

SPL:
94 dB at 10 Hz
106.6 at 20 Hz
111 at 30 Hz
112.6 at 40 Hz
113 at 50 Hz (with 1 dB up from there)

GROUP DELAY:
15.2 ms at 20 Hz
9.8 ms at 30 Hz
6 ms at 40 Hz
4 ms @ 50 Hz (drop from there)

PORT AIR SPEED: (I will have large flares on the ports)
19.6 m/s at 20 Hz
9.7 m/s at 30 Hz (continues to drop)

DRIVER EXCURSION:
XMax + 10%

Any thoughts/improvements on the design are welcome, but I think this should give a great result in not much space. Hopefully when combined with room gain and the equalizer, it will give quite the quality bang for the buck.

Agree? Disagree?

Thanks!

[ThomasW]

Using damping in an attempt to get the box to appear 125% larger is basically impossible. The normal rule is 30%

A 41.5" port is a bad idea since there will be problematic port resonances. It's a good idea to keep ports 32" or less.

Tuning low excursion drivers as low as 16-18Hz isn't the best idea. Those drivers are designed for car use and are typically tuned 25-30Hz

[theater_lover]

Using damping in an attempt to get the box to appear 125% larger is basically impossible. The normal rule is 30%

A 41.5" port is a bad idea since there will be problematic port resonances. It's a good idea to keep ports 32" or less.

Tuning low excursion drivers as low as 16-18Hz isn't the best idea. Those drivers are designed for car use and are typically tuned 25-30Hz

Typo on my part. That should have read 25% , not 125. Fixed it.

My only other option if I can't do a port of that length is a passive radiator.
No way to do something that long? Slot port?

It is a fairly high excursion driver. 16mm isn't bad for a 10" driver. I'm not sure these were designed for car use either - ACI used them in their home theater subs.

[theater_lover]

I just calculated that the first order resonance of a port that long is 163 Hz.
Since I will be crossing at 100Hz, I should be fine, correct?

[PhilDSP]

The SV10's are related at 4 ohm nominal impedance, aren't they? To get your SPL figures you'll need to run them in parallel which will drop the impedance below 2 ohms. Can your power amp handle that comfortably? You could run 4 of them in a serial-parallel combination at 4 ohms. The excursion for a specific SPL would be a quarter of the excursion of a single driver in that case.

The SV10's I've used in a ported cabinet overran Xmax at about 108 dB and what you heard at that point was a garbled but not obnoxious response.

I'd probably increase the port diameter to at least 6". Anything smaller tends to have severe non-linearities near the resonance point (severe distortion and honkiness). (oh yeah, now I see Thomas said something similar)

I don't think the group delay figures you found are accurate unfortunately. With a ported configuration even with an F3 of around 25 Hz to 30 Hz you should expect about 20 ms at best, more likely closer to 40 ms in the lower frequencies unless there is so much damping that the SPL is significantly lowered.

But regardless you'll probably like the response of that driver in a suitable cabinet.

[theater_lover]

Thanks for the info. Yes, my amp can handle 2 Ohms per channel.

After hearing from several people, I am little wary to pursue a ported design.

My current thinking is to either go sealed, or go with a passive radiator design.

The upside of the sealed is that I think the drivers will handle better, there is a little more room for EQing them, and I don't have to worry about port/PR tuning. Down side is limited SPL and no real deep end.

The upside of the sealed is that I get nearly the same performance of the vented, but with less problems, and I can tune it after the build. Down side is cost, complexity, size, and less EQ wiggle room.

Which way would you suggest?

[PhilDSP]

I did some quick modeling this weekend using a couple of different tools. The response looks surprisingly good with 2 SV10's, a volume of about 120 liters and a 6" pipe 27" long. F3 (or Fb) would be 22.9 Hz and group delay would max out at around 22 ms around 22 Hz.

The group delay looked very nice below that being less than 8 ms for a frequency greater than 40 Hz (where you're actually likely to hear it). That assumes you are using a moderate amount of damping. The FR was very, very flat. You can also substitute 2 4" pipes for the single 6" one or lengthen the 6" pipe to around 33" if you can fit that inside the cabinet to shift the group delay curve even lower in frequency.

No problem from the looks of things with cone excursion when less than 200 watts is actually applied to the subwoofer (probably about 1000 watts total amplifier output).

[fbov]

...
The upside of the sealed is that I think the drivers will handle better, there is a little more room for EQing them, and I don't have to worry about port/PR tuning. Down side is limited SPL and no real deep end....

Don't forget room gain. It'll increase achieved SPL and extent your low end. One advantage of smaller sealed subs is flexibility in room placement, and if I were considering a dual-driver design, I'd do separate boxes, placed in different locations to improve uniformity in the room.

That said, I have a single big sub, with plans for a second one once my kids are out of college. The only part I can speak to from personal experience is the room gain; I'm flat to almost 10Hz with the sub on...

Frank