Moving to 2-sub; What should I do? - AVS Forum
DIY Speakers and Subs > Moving to 2-sub; What should I do?
djkest's Avatar djkest 08:40 AM 12-05-2012
Currently have:
RSS315HF-4 with O-audio 500W BASH amp in 68L sealed enclosure. F3 is ~36 although with the bass boost of the O Audio, it's probably a little lower.
Not ideal, I have to set the HPF at 25 Hz to avoid hitting Xmech. It's too much power. Can be pretty loud at 40Hz (which I guess is most subs)

Looking to move to a 2 sub setup so I have to decide what way to go. I want deep but not necessarily need 120+ dB at 80 Hz. I would like the ability to have deep bass, as well as eliminate any worries of hitting XMECH when I crank my system to extreme levels.

I can sell everything, but selling the subwoofer driver is not ideal as it is heavy and expensive to ship. Also, it seems that the last sub enclosure I made turned out pretty well, but it was more work than building a simple box seems to be.

Option 1:
Build a 2nd sealed RSS315HF-4 to match, sell O Audio, buy iNuke 1000 DSP or other amp to power both with ~ 300W (Total cost ~$300)

Option 2:
Buy RSS460HO-4, use O-audio amp on that. Buy 300W amp for the 315HF. Run an 18" and 12" sub. (Total cost: ~$400)

Option 3:
Blow it up, sell it all and get something different. This could include 2 Alpine SWR-1243Ds in sealed boxes, 2 FiCar x12 or x15, powered by some amp. (Total cost: $100-$500)

Wife seems to be allergic to bass, but I love bass and want to improve the quality and room-filling balance with a 2-sub setup. Oh yeah, and smaller enclosures, under 100 L are preferred. What would you do?
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Jay1's Avatar Jay1 07:44 PM 12-05-2012
Sounds like you have a nasty room mode. You really need to measure and use the PEQ to knock it down, any sub you run is going to have this same problem, but multiples can help. You should also try the 20hz filter, it will not push you over Xmax anymore then the 25hz filter already is, but it will extend you deeper while slightly flattening your response.

This image shows your sub with the 25hz filter (orange) and the 20hz filter (blue). Below 25hz your output increases by +4db

You have two problems with expanding your system. Oaudio is out of stock, with no estimated date of stock. If you go with a DSP based amp, you will definitely need to measure to achieve a flat response.

Personally I would take your current components and build a 5ft3 ported box, that makes use of the Oaudio's unique filters for SVS like bass response. I know you want something smaller though... By the time you're done with the build you might be able to get your hands on a second Oaudio, whether used or new for a second sub. Anyways here's what I propose

The green shows a single 4" x 28" port, with the Oaudios 20hz filter engaged. You get flat response, with an F3 under 16hz, and an air velocity around 25 M/S. Xmax would be exceeded by about 2.5mm, which is less then your sealed setup, and well away from Xmech.
djkest's Avatar djkest 08:19 AM 12-06-2012
Hello, thanks for your reply. Currently it's in a large open room, but I hope to move it downstairs into a smaller area in the next 6 months. I should do some measuring to look at different things.

About the filter- with the 20 Hz filter engaged, I hit Xmax with 50% gain watching blu-ray movies with very low bass. One in particular is "Tron: Legacy". When listening to music, I can use the 20 Hz filter without issue.

Do your Win ISD simulations take into account the bass boost the Oaudio amp has? I had been looking at possibly modifying my amp to reduce the boost, I got the information from Oaudio to do that if I need to. They have charts so you can set the boost from 1-5 dB of boost and the Fc from 22-38 Hz.

Switch Setting - 16 Hz C1, C2 = 1.00 uF
Filter Fc = 12.98 Hz
Filter Q = 2.41
Fc dB = 7.62 dB
dB Boost = ~10 dB

Switch Setting - 20 Hz; C1, C2 = 1.00 uF
Filter Fc = 17.33 Hz
Filter Q = 1.72
Fc dB = 4.71 dB
dB Boost = ~6 dB

Switch Setting - 25 Hz; C1, C2 = 1.00 uF
Filter Fc = 23.06 Hz
Filter Q = 1.42
Fc dB = 3.05 dB
dB Boost = ~4 dB

When I first built my sub, a lot of people suggested that I build it ported (after I had the box 80% complete). But they also suggested with more than 1 sub, sealed starts to get better. Probably because sealed enclosures don't have the excursion issues below tuning frequency that ported designs have. For the record my wife thinks my current 68L sub is "big". tongue.gif

My current thoughts are leaning toward building a 2nd sealed and going with the iNuke 1000 DSP; would be 300W per channel roughly. But of course I am open to other suggestions.
Jay1's Avatar Jay1 11:56 AM 12-06-2012
Yes, all of those sims are with the filter's boost included. 300 watts is all this driver can handle in a 68l enclosure to stay under xmax, but 450 watts will not bottom the driver (the Oaudio was measured to do 450 watts). If you're getting some bad noises you're possibly clipping the amp. You said with the gain at 50%, that makes it sound like you're using the gain as a volume control. The gain should not be touched once your system is calibrated, and levels should only be adjusted from the avr.

Multiple sealed can be great, but displacement is they key to going deep. 12" drivers arent really cut out for it. The ported RS12 above has more output at 20hz then two sealed RS12's. The Oaudio's filters remove the signal below the filter fc, so excursion issues below tune arent an issue if the sub is designed properly.

If you really dont like the ported idea, selling everything and starting fresh with a pro amp and a 15"-18" woofer might be your best solution.
djkest's Avatar djkest 11:45 AM 12-07-2012
Looks pretty good. I think you are right. The smartest thing to do would be to build this sub enclosure and try that out, and then if I don't like that I am only out about $50 in materials. Should be 6-8 dB more output from 30 Hz to 20 Hz. I'll have to run some of this through win ISD on my own just because I'm like that I guess.

I see your proposed build is 5 ft^3 (~141 L) and tuned to 15 Hz. How would you feel about 120 L tuned to 19 Hz? I would still use the 20 Hz filter as is, if possible. Looks like I would have a little stronger output between 20-30 Hz, still have SOME performance down to 15 Hz; it would be smaller and also have a little less excursion; at least according to Unibox. I'm guessing you are assuming "heavily stuffed" ? 4" would be 16" long.

The downside to this size/tuning is it looks like the port will be undersized, and may chuff near 23-19 Hz. Alternatively, 2 3" ports would only be about 19" long and would provide some relief. Of course that is all Unibox; without the filter; and most people prefer Win ISD I believe.
Jay1's Avatar Jay1 05:58 PM 12-07-2012
The 19hz tune gives you a 2db rise in response with the 20hz filter's boost, and has a lot of excursion below tune as the actual HPF is at 17hz, though that may or may not be an issue. Port velocity is also on the high side. I like how a 17hz tune looks a lot better, though you would have to squeeze a pair of 3" x 28.75" ports in the box (could use pvc 90 degree elbow joints). That cleans up pretty much all of the issues. It's hard to "heavily stuff" a ported box. I line the walls (fiberglass coated with spray adhesive) to not impeded air flow around the ports. The only real goal is to mute any internal sounds from escaping.
djkest's Avatar djkest 09:32 AM 12-09-2012
Cool, I am taking this project on for sure. I think I can get it done with 1 new piece of MDF, I have a TON of scrap I can use for bracing and whatnot. My plans right now are to make a 24" x 24" x 18" box, use PVC pipe for the ports, and do a double thick baffle. I also need to figure out a relatively easy way to put a speaker grill on it, and may make it a passive sub; relocating my plate amp to a separate box. Thinking about what internal braces I'll use. Not a huge fan of window braces since they are far from ideal. I have a router and some circle jigs but I don't currently have a jigsaw; might buy one. Also thinking about using the bracing to hold the ports in place. The opening for a 3" port internally needs to be at least 3" away from any side wall, right?

Probably start making this in January.
djkest's Avatar djkest 08:50 AM 12-12-2012
Did a bunch of simulations in winISD, and it's hard coming up with the exact design I want.

Questions relating to WIN ISD Alpha:

My air velocities seem high. I switched from a single 4" to a single 5" port. Looking around, it seems larger diameter ports can tolerate higher velocities before chuffing, so a 5" port is a huge advantage over the 4". I should be able to get 5" ABS or PVC from a local plumbing supply company, with at least 1 elbow.

The only problem with 5" is now the port is getting really long, which makes me want to go higher with the tuning. I think a 4.5 ft^3 box with 17 Hz tuning was wanting something like 37" of length, which I should be able to accomplish with 1 elbow.

1) What are the rules for internal port opening placement? I know you don't want the opening near the driver cone, but what about the side walls. I heard you don't want the rear wall within 1xD of the opening- right? But slot ports seem to "break the rules" by having the opening right up against the wall.
2) Should I assume that the driver will "roll off" below 20Hz and therefore the exursion peak around 14 Hz will be a little bit less than modeled? Depending on box size and tuning, I either get a big peak above or below tuning.
3) Even with a 5" ID port, I still have an air velocity of 40 m/s at around 14 Hz (not sure if it would be audible or otherwise noticeable). Is this OK?
4) Is the modeled excursion 1-way or peak to peak? If it's peak to peak, then my xmax limit is actually 28mm and not 14mm.

Was looking at the possibility of buying and RSS390HO-4 and building that instead, but the only real advantage that I see over my current plans is that it could potentially take more power should I change amps later. I could get the 390 for a mere $139.99 shipped today. Actually would like to buy an RSS460HO-4, but that's a lot of money and I'll always think it's underpowered with only 450W.
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