I want to build a sub for the LFE channel for movies. I have good main speakers but I'm lacking rumble. After much digging around, I was able to find drivers with decent Q and low Fs in the local market (Argentina). The rest of the available drivers in the market are "car audio" drivers for SPL competitions with Fs all >40Hz.
The available drivers are Alpine 12" with the following specs
I've simulated them in WinISD and got these curves:
Running environment:
The conclusions I arrived to were the following:
All 3 drivers in closed boxes will give a -3dB of 45Hz with pretty much the same curve. 20Hz will be at -16dB in all cases. I read about using room gain to take advantage of subwoofer rolloff. I'm all for using a small box but, is room gain predictable or reliable? Is it a curve or is it spikey depending on what's in the room and its layout, etc? I don't think it'll be very helpful if the room only gives me gains on a single frequency but the rest is the same.
I imagine it's always possible to tame down the excess bass with DSP, than trying to recreate it with DSP gain?
The available drivers are Alpine 12" with the following specs
| Series S | Series R2 | Series X | |
| Qes | .58 | .55 | .62 |
| Qms | 4.68 | 6.5 | 5.63 |
| Qts | .52 | .51 | .56 |
| Fs | 31 | 30 | 27 |
| Vas (L) | 46.4 | 32.8 | 56 |
| Xmax (mm) | 15 | 20 | 24 |
| Price | $ | $$ (2x series S) | $$$ (4x series S) |
| Chart color | GREEN | BLUE | RED |
| Enclosure volume (L) | 100 | 67 | 130 |
| Tuning freq | 24 | 24 | 20 |
| -3dB freq | 21.1 | 21.14 | 17.5 |
I've simulated them in WinISD and got these curves:
Running environment:
- The speakers will run in a 3x6 meter room where one of the corners is a bathroom, so the room is more L-shaped (I can provide a floorplan).
- I ordered a UMIK-1 so I'll run REW here to characterize the room as soon as I get it
- There will be DSP and EQ applied after characterization with REW.
The conclusions I arrived to were the following:
- Vented box will be required for low freq (of course)
- Series S will be the cheapest but requires a large box
- Series R will perform the same as an S in a much smaller box
- Series X will go much lower, in a box the same size as S
- What's the required SPL for "feeling" LFE channel? If I'm watching a movie and I want to feel the explosion on my chest, how many decibels is that?
- Do I want such a big-and-deep driver as the Series X which will go low , but will require a considerable box? Or will I get enough with a Series R that requires a fair bit smaller box and delivers very respectable -3dB of 21Hz in a 67L box?
- I suppose the answers to the second question is actuall the first: if the required SPL is enough for a R-series with more power I'm willing to sacrifice efficiency for space. I guess it's fine to run the driver at 100W instead of the larger and more expensive one at 50W to compensate, if the required SPL dB is reached?
All 3 drivers in closed boxes will give a -3dB of 45Hz with pretty much the same curve. 20Hz will be at -16dB in all cases. I read about using room gain to take advantage of subwoofer rolloff. I'm all for using a small box but, is room gain predictable or reliable? Is it a curve or is it spikey depending on what's in the room and its layout, etc? I don't think it'll be very helpful if the room only gives me gains on a single frequency but the rest is the same.
I imagine it's always possible to tame down the excess bass with DSP, than trying to recreate it with DSP gain?
Can't answer your questions without knowing what SPL you like to listen at. Our hearing is much less sensitive to extreme low frequencies than vocal range frequencies so LF sound levels need to be quite a bit higher to "sound" balanced... see the Fletcher-Munson curve. Room gain can mitigate some of that but there is no escaping room nodes indoors so you won't get the same LF SPL at all listening positions... you will have booming bass at one spot and nothing at all 3ft away.
Make sure you include the effect of driver inductance on the sim.
For a vented alignment, tuning below Fs could end up producing audible transient response issues, particularly with high Q drivers
Of those drivers, I'd probably look at using two of the Series S, using a sealed alignment (or a passively-assisted sealed alignment), and use a bit of EQ below the F3 point to extend the response.
For a vented alignment, tuning below Fs could end up producing audible transient response issues, particularly with high Q drivers
Of those drivers, I'd probably look at using two of the Series S, using a sealed alignment (or a passively-assisted sealed alignment), and use a bit of EQ below the F3 point to extend the response.
I suppose it's an option too. The room is small and the drivers can handle 500W. I guess i could drive VLF at very high power (strictly speaking, it won't be a continuous 20Hz tone so the speakers should be able to handle the power very easily)... as long as they're within xmax.
I noticed the sensitivity of the R is 2dB lower than the S, and in the SPL chart, the S comes out ahead, even though in the magnitude chart, R is the winner.
As far as SPL goes, at 100 watts, both seem to hang around 93dB @20hz (105dB @100Hz), which would mean around 100dB when driven to 500W. I'm not sure if that's a lot or too little for 20Hz. I'd like to feel "rumble effects" with movies as well.
Series S wants a 52L box for a Qtc of 0.707
Series S will be pretty nice.
I have a average to small front room.
Single 8" sub in the corner facing up.
Not much more than 60 to 80 watts.
For more pounding bass
My old setup
would be similar to what your doing. A 12" with a common
250 watt amp. Actual used Power around 100 to 140 watts.
Way before I start thinking about larger amps
I would just double the speakers
Small room just 1x12" all that is needed
To go deep I use the corner.
with a actual sub not really needed.
What a have now is borderline " woofer"
So I cheat a bit in the corner.
Mainly for music sound. Movie effects
are easy not much detail. More of a slam.
50 Hz boost will make the slam more noticed.
Really not needed with a actual Sub
I have a average to small front room.
Single 8" sub in the corner facing up.
Not much more than 60 to 80 watts.
For more pounding bass
My old setup
would be similar to what your doing. A 12" with a common
250 watt amp. Actual used Power around 100 to 140 watts.
Way before I start thinking about larger amps
I would just double the speakers
Small room just 1x12" all that is needed
To go deep I use the corner.
with a actual sub not really needed.
What a have now is borderline " woofer"
So I cheat a bit in the corner.
Mainly for music sound. Movie effects
are easy not much detail. More of a slam.
50 Hz boost will make the slam more noticed.
Really not needed with a actual Sub
I have a single 12" powered sub in my basement HT setup that produces audible movie rumble, it is only rated at 120w or something but it does a pretty good job in my opinion. The difference between rumble you can hear and rumble you can feel is quite large, the latter requires enough air displacement to pressurize the room, so while a single 12 might accomplish that in a car it could take a couple 18's to even begin to do it in a listening room.
in my defense, my previous 10" sub did shake things around in the room
as in, things falling off shelves, drywall roof cracking along the edges, etc
but the response was just bad and i never got it to work like i really wanted. and it was too big of a box to keep around.
if i can accomplish something similar with a12" sub in a 50-ish L box, that would be ideal.
In a very generalized or generic approach.
Yes about 50 to 55 liters for a decent 12"
Ports/bracing etc etc
55 to 65 liters is realistic.
I dont try to minimize size like some do
and add a bunch EQ
Whatever the standard Alignment is.
That is what gets built.
Usually with subs SC4/ QB3 almost the same.
likely use the lower tuning. Depends
Some instances go for BB4
People play around with sims too much.
If it doesn't knock as hard as you like.
Double the cone area and use a 2nd sub.
Same driver same box etc etc
What WinIsd shows for s series looks more than
good. Im happy if the reflex is actually tuned 25 Hz or lower.
No high tuners
Yes about 50 to 55 liters for a decent 12"
Ports/bracing etc etc
55 to 65 liters is realistic.
I dont try to minimize size like some do
and add a bunch EQ
Whatever the standard Alignment is.
That is what gets built.
Usually with subs SC4/ QB3 almost the same.
likely use the lower tuning. Depends
Some instances go for BB4
People play around with sims too much.
If it doesn't knock as hard as you like.
Double the cone area and use a 2nd sub.
Same driver same box etc etc
What WinIsd shows for s series looks more than
good. Im happy if the reflex is actually tuned 25 Hz or lower.
No high tuners
I have a pair of Alpine 12" R 2x2ohm and my T/S parameters are very close but not identical to the ones you posted. Mine are in 85l each tuned to 22hz. In room response is in the high teens (amp has hipass at 18hz I think). I have a 1000 watt dayton powering each and these will take a beating. I don't think the x type is worth the extra money. Have fun!
THX reference is 85 dB @ the listening position (LP)/channel so for (5) channels (math here) we add 10log(5) = +7 dB = 92 dB with +20 dB dynamic headroom = up to 112 dB peaks, so quite loud. The LFE reference is 95 dB/115 dB, so in a super wide BW scene such as an explosion this totals 10log(10^11.2 + 10^11.5) = ~117 dB, very loud for folks used to watching a TV movie in the 60-65 dB range!
As a guideline, look to the hearing chart for SPL required and the instrument chart for the bandwidth (BW) of different sounds, so for chest thump we in theory want at least 117 dB in the 20-40 Hz BW; not many folks have the necessary room construction for such. That said, most folks are sufficiently thrilled with a cinema's 100 - 180 Hz 'boom/punch', which any decently constructed room can handle, though making it neighbor friendly tends to get expensive.
As noted, actual speaker design needs to account for room modes, boundary loading, etc., and not surprisingly, most folks set the reference levels lower and use EQ to boost certain frequencies for emphasis as an acceptable compromise.
That said, better to build in the ideal or as much as budget allows and tone it down if need be to keep distortion as low as practical for highest practical dialog intelligibility.
Room gain is typically a 'crap shoot' if not a concrete basement or a modern certified energy efficient construction, so in my case with a 1952 stick built, 'floating' floor construction atop a concrete block foundation, room gain is mostly MIA with only the living room's addition built to give me ~ +6 dB corner gain down low for my subs versus the theoretical +9 dB. In short best to measure the room.
Anyway, with the info provided you'll have to decide how much performance you can afford and help you answer your driver/cab alignment Qs.
I'm using a similar driver in 200litres sealed but I limit the amp to 100 watts approximately, but its a roadkill driver and cost me nothing but some time and skill to repair. It's loud enough and deep enough for my needs and it will produce a reasonable amount of deep bass with a touch of boost.
With bass drivers and sealed boxes bigger is usually better and doesn't add much to the box cost
With bass drivers and sealed boxes bigger is usually better and doesn't add much to the box cost
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Good insights @GM. On the "sealed" thread I mentioned a theoretical 102dB of SPL with 2 drivers at 500W (room gain not considered).
I'm not sure how much room gain i have (waiting on UMIK-1). The walls of the room are 30cm brick and the floor is a concrete slab. The celing, however, is drywall.
I have a few questions about your numbers though. As you said, the THX reference is @85dB. I think this may be a little loud, so we could knock it down 3 or maybe even 6 dB. But bass is bass, I'm a basshead, and I think, if you want chest thumps, you need to EQ UP the sub-bass to compensate for low volume. However, 117dB @20hz is a rather difficult goal. By my calculations, driving the speakers at their "peak" rating of 1600W could hit 107dB (something I wouldn't risk doing because, simply, they don't specify how long is tolerable for the "peak" - also clean 1600W of RMS to actually deliver that power can get expensive amp-wise).
Things change wildly with a vented box though. While at first glance a box could be tuned to be at -3dB @20hz, the group delay is a wild 45ms which seems completely useless, and also sounds like the excursion would throw the cone across the room. The reference Alpine vented box for this sub calls for 32Hz tuning, -3dB @28hz, but the 20Hz point drops -3dB lower than a closed box of similar size.
In short: I now know I won't be able to hit "THX reference levels" with this setup, however, considering group delay, available power, room size, available room space, I think two little 55L cubes could provide decent punch given enough power. I think I'll go for the closed box and see how it performs. In the end, MDF is cheap and I can always make a new box.
I'm not sure how much room gain i have (waiting on UMIK-1). The walls of the room are 30cm brick and the floor is a concrete slab. The celing, however, is drywall.
I have a few questions about your numbers though. As you said, the THX reference is @85dB. I think this may be a little loud, so we could knock it down 3 or maybe even 6 dB. But bass is bass, I'm a basshead, and I think, if you want chest thumps, you need to EQ UP the sub-bass to compensate for low volume. However, 117dB @20hz is a rather difficult goal. By my calculations, driving the speakers at their "peak" rating of 1600W could hit 107dB (something I wouldn't risk doing because, simply, they don't specify how long is tolerable for the "peak" - also clean 1600W of RMS to actually deliver that power can get expensive amp-wise).
Things change wildly with a vented box though. While at first glance a box could be tuned to be at -3dB @20hz, the group delay is a wild 45ms which seems completely useless, and also sounds like the excursion would throw the cone across the room. The reference Alpine vented box for this sub calls for 32Hz tuning, -3dB @28hz, but the 20Hz point drops -3dB lower than a closed box of similar size.
In short: I now know I won't be able to hit "THX reference levels" with this setup, however, considering group delay, available power, room size, available room space, I think two little 55L cubes could provide decent punch given enough power. I think I'll go for the closed box and see how it performs. In the end, MDF is cheap and I can always make a new box.
I don't see any Qs..........your room will certainly have more gain than mine .......yes, really need some form of (ML)TL or horn cabs for true sub bass at high SPL and use < 20 Hz tuning + high-pass filter for solid 20 Hz output, hence the ~14 Hz tuning of my dual 15", ~20 ft^3 corner loaded inverse tapered horns (MLTQWT in today's parlance)..........group delay only comes into play if it hasn't decayed enough by the time it's in our acute LF hearing BW, which IME is above ~35 Hz where the pioneers limited lower frequency output/tuning.
.......yes, really need some form of (ML)TL or horn cabs for true sub bass at high SPL and use < 20 Hz tuning + high-pass filter for solid 20 Hz output, hence the ~14 Hz tuning of my dual 15", ~20 ft^3 corner loaded inverse tapered horns (MLTQWT in today's parlance)..........group delay only comes into play if it hasn't decayed enough by the time it's in our acute LF hearing BW, which IME is above ~35 Hz where the pioneers limited lower frequency output/tuning.
Take this with somewhat of a grain of salt:
- The simulations going to zero and flat above that indicates to me that WinISD must model things as electric filters. That's fine, thank you Dick Small (and Thiele and Benson!) however it is a limited simulation. A more sophisticated model with frequency dependent impedance would show rolloff above sometimes even 80 Hz for big heavy drivers with massive coils.
- And "0 dB" will not be the same for all those. It would be surreal if sensitivity was the same for all those. And I don't mean the specification from Alpine or whoever, I mean plugging into the actual equation.* Then you'd have to offset each curve accordingly. The sensitivity spec is a MIDRANGE value which doesn't necessarily have anything to do with the bass sensitivity.
- Room gain can very above the lowest frequencies...at the lowest it depends on cubic volume of the room according to some formula I cannot remember for the life of me. That presumes though that the room walls and doors are all sealed and solid. I would want none of those responses-I'd want something that would "droop" more that is move down the tuning so the LF rolloff will begin higher but more slowly.
*like the one below "A version that is more easily calculated with typical published parameters is:" at
.............Thiele Small parameters equations – How each one affects the others
n0 and SPL rating – Efficiency
no is a percentage, showing how efficient the driver is at converting an electrical signal to an acoustical one. As a result, the bigger the number, the greater the reference sound pressure level.
n0 = (9.7822 * 10-10 * Vas * Fs3) / Qes
n0 and SPL rating – Efficiency
no is a percentage, showing how efficient the driver is at converting an electrical signal to an acoustical one. As a result, the bigger the number, the greater the reference sound pressure level.
n0 = (9.7822 * 10-10 * Vas * Fs3) / Qes
- n0 above is a ratio, not a percentage. To make it a percentage multiply by 100.
- Vas is in liters.
- Fs in Hz.
In Belgium THX rated is specified with 85dB + 20dB headroom at listening position. So your woofers should reach at least 105dB RMS at listening position if you want that. That is at least how it was explained to me when i assisted installing a private THX certified music/HT room about 10 years ago (as representive of the rich owner who was to busy).
Hmm, THX has several different tiers with the one I posted being the original for first run cinemas, but there's several different ones for consumers, so guessing yours is for small HT for TV movie playback levels. There's also one for computer setups and headphones also and maybe others by now as my knowledge is latest from 2003, though did check to confirm the one I posted is still in effect.
Or in fundamental terms n0 = k*[(BL)^2]*[Sd^2]/[Mms^2]*Re where constant k can be found at "2.1 Passband" at https://www.klippel.de/fileadmin/kl...rature/Papers/Green Speaker Design Part 2.pdf
So efficiency depends on the square of the magnet/coil force times the square of the area, divided by the square of the moving mass and the coil DC resistance. Hence why efficient drivers have big light cones with big magnets and coils, and why actual speaker impedances seem to be getting lower all the time.
BUT note these equations DO NOT APPLY TO LOW BASS AT ALL. They are "passband" = midrange calculations. In small boxes the trapped air makes a very stiff "spring" and just chokes off the response. Some modeling I did for 0.83 cubic feet showed very little difference (like 1 dB) in output below 70 Hz or something. from a cheapie woofer to a massive subwoofer. I'll have to publish those curves to
https://www.avsforum.com/threads/what-driver-for-a-0-83-cubic-foot-sub.3293881/