Hey guys ! Quick question here to the experts of audio . I have a UNIQUE project about doing a SEALED subwoofer build to hit infrasonic.. Precisely a big number at 10hz- 19hz seeing that no one has achieved a high 140db+ in that region .. I plan on doing this in a 4 door Tahoe . Doing an b pillar wall completely sealed off and planning to achieve a lot of the 10hz output from cabin gain ... What I had in mind was 8-10 re xxx 18s or LMS ULTRAS with a parametric EQUIPMENT of some sort to flatten it out . Bracing in the vehicle would be provided by a chassis shop .. Enclosure would be done by my friend who builds systems daily ., so what do you guys think ?? Please don't criticize me saying stuff like "WHATS THE POINT OF THAT"?? Etc ... It's a goal that rarely anyone has accomplished and I wanna do something different . Practical advice is always welcome . Thx
Hi Infrasound,
Question... How much 'Surface area' (in cu inches) and Wattage are you willing to invest into this experiment to reach your goal(?) just curious. I'm guessing that you'll be playing mostly 'Generated signal tones' since most musical program doesn't go anywhere near 10hz as it's not very musical! Below is a shot of my very last set-up... P.S. 'two 15's have since been removed due to the space restrictions and inconvenience', "See below":
4-15 inch Alpine 'R series' subs driven by TWO JL Audio "HD-750/1's"
I don't doubt that 10hz is reachable, but the decibel level that you're aspiring to may be difficult at best; ten cycles per second is really slow and the air moving barely makes a (humanly perceptible) sound at that speed. My system doesn't go down to 10hz, but rather, a more musical and easilier achieved f3 of 35 to 40hz and possibly 125db. Here's a 'YouTube' video featuring a system that is claimed to go to 10hz using a "continuous sign-wave" track, check it out... https://www.youtube.com/watch?v=GKd9_kNv5B8 ..."Hope you can do it, please let us know how it was achieved! Rgds!
Question... How much 'Surface area' (in cu inches) and Wattage are you willing to invest into this experiment to reach your goal(?) just curious. I'm guessing that you'll be playing mostly 'Generated signal tones' since most musical program doesn't go anywhere near 10hz as it's not very musical! Below is a shot of my very last set-up... P.S. 'two 15's have since been removed due to the space restrictions and inconvenience', "See below":
4-15 inch Alpine 'R series' subs driven by TWO JL Audio "HD-750/1's"
I don't doubt that 10hz is reachable, but the decibel level that you're aspiring to may be difficult at best; ten cycles per second is really slow and the air moving barely makes a (humanly perceptible) sound at that speed. My system doesn't go down to 10hz, but rather, a more musical and easilier achieved f3 of 35 to 40hz and possibly 125db. Here's a 'YouTube' video featuring a system that is claimed to go to 10hz using a "continuous sign-wave" track, check it out... https://www.youtube.com/watch?v=GKd9_kNv5B8 ..."Hope you can do it, please let us know how it was achieved! Rgds!
Why sealed? With a port tuned between 10 and 20hz you can cut your driver requirements in half. Check out notnyts HT build (8xlmsu 5400). That will give you a good idea of how much space you need.
Hi sine'
For his application (max output/@lowest octave), definitely needs to be Ported... not too sure if a Tapped Horn alignment would apply here...
You'd be looking at LMS 5400 drivers for sure for the excursion and power handling.
A ported box might not be big enough to allow a reasonably-sized vent, but if it is possible then it would certainly be better than going sealed.
A ported box might not be big enough to allow a reasonably-sized vent, but if it is possible then it would certainly be better than going sealed.
Did a quick vented box calculation based on roughly 220 cubic feet available in the back end of the Tahoe.
Box volume: 220 cubic feet
Port: 10 Hz tuning - you need one hell of a slot port to reduce chuffing to acceptable levels
Driver: TC Sounds LMS 5400
If each driver is limited to 4000 W, you would need 18 drivers and about 80 kW to make 140 dB at 10 Hz, not accounting for the effects of power compression, which would be considerable.
Box volume: 220 cubic feet
Port: 10 Hz tuning - you need one hell of a slot port to reduce chuffing to acceptable levels
Driver: TC Sounds LMS 5400
If each driver is limited to 4000 W, you would need 18 drivers and about 80 kW to make 140 dB at 10 Hz, not accounting for the effects of power compression, which would be considerable.
A 'Passive Radiator' (Drone) may be a considerable alternative for a box that's too small for a properly sized tube/port, and can be tuned w/o enclosure disassembley/modification.
Okay! So... 80 KW (80,000 watts), divided by 12.5 VDC (the formula for converting watts to amps) = 6,666.6 amps that will be 'Required' from the truck's alternator "just to feed the subs alone", so I've added an extra 100 amps for the vehicle's 'normal accessories'. So that's 6,766.6 amps to supply ALL of the truck's electrical needs. I found a 300A 'High Output' alternator online; which seemed to be one of the largest ones available during my search, so 6,766.6A divided by 300 (amps per alternator) = 22.5; a total of 23 alternators needed. Using a 'Multi-alternator bracket' kit (complete w/slot adjuster, 2 tensioners, 2 idlers etc), an electrical power station grid can be built. Also, special copper cables; the ones used to feed residential street power demands would be available for amplifier power supply feeds..
In conclusion: After carefully considering all of the pros & cons of building a "Low frequency reproduction system" that can hit 10hz at 140db, I am very, very sorry to inform you that this project CANNOT be executed as planned because... "Where the heck you gonna get a fan belt that will fit it??"
Lol' rigtec
Rgds
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They make amplifiers that run from large banks of batteries in series. There are amps rated at 40kw into 1 ohm when powered by 300v DC. It may not do 40k but no matter the actual power output, the current draw is significantly less due to the higher voltage.
I think those calculations are a little bit off. Once you get that low in frequency, the SPL depends purely on the pressure difference in the cabin between "cone in" and "cone out". In theory, for a 220 cubic foot cabin, 4 of the TC Sounds drivers should be more than enough. This assumes an airtight concrete bunker...
How would you normally implement this? Use the cabin itself as the enclosure with the drivers facing open air? It would make sense based on the typical Helmholtz resonance (10 - 15 Hz) experienced by many when driving with a window open...
I think some of @454Casull's exploitation of the extremely 'LARGE NUMBERS' was intended purely in fun; as was my response! P.S. It's (12/24/2014) Christmas eve... "So now, I do hereby order each and everyone of you to ...HAVE FUNNNN!" 
...and please remember to "Drink responsibly" 
"HAPPY HOLIDAYS"
...and please remember to "Drink responsibly" "HAPPY HOLIDAYS"
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I could be wrong but I thought for each and every octave you go down 4 times the excursion is needed to produce the same output.
So in this case there would need to be 16 times the excursion at 10hz then at 40hz to equal the same output.
So in this case there would need to be 16 times the excursion at 10hz then at 40hz to equal the same output.
That is in free air only. Sound is air pressure differences. If you accelerate (push or "pull") a volume of air with a speaker cone you make a pressure difference. The pressure difference moves away at the speed of sound. (A "sound wave".) To make a sound louder you have to increase the frequency (higher acceleration) or amount of push/pull (greater excursion). As you lower the frequency you lower the acceleration, so the excursion has to increase to maintain the same acceleration (SPL). [1]
The situation changes if you enclose the space in front of the speaker, especially if the space is too small for any resonances to form. The pressure variations can't disappear into the distance at the speed of sound any more. All you have is an air pump attached to a container. The pressure in the container no longer depends on the acceleration of the cone, just on the excursion. [2]
This give rise to what is called "cabin gain". It's not really gain, it's just that because your speaker excursion increases as the frequency drops, the pressure increases. This is one reason why sub speakers for car use are typically designed with a falling free-air frequency response rather than a flat response. Properly designed, the falling response will be exactly compensated by the cabin.
All of this assumes a perfectly sealed and rigid "cabin". If there are air leaks, or the cabin walls flex, you lose some of the pressure. The top SPL cars have rigid, hermetically sealed "cabins". They also use frequencies high enough that the mass of the walls helps to reduce flexing. Careful design can also make a resonance peak form at the measuring mic position, increasing the measured level.
[1] You can see this in the bathtub or swimming pool. Move your hand back and forth an inch or so to make waves. The faster you move your hand, the higher the waves become. If you move your hand more slowly, you have to move it further to generate the same height of waves. Wave height = SPL.
[2] Now switch to a bucket. For ease of visualisation, instead of your hand, use a syringe. Squirting / sucking water raises and lowers the level of the water. It doesnt matter if you suck/squirt fast or slow, the level change is the same. Level change = SPL.
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Thanks for the advice guys ! I went over to AVS FORUMS and it seems the guys over there to hit single digit hz numbers and high spl are using lots of SEALED drivers ?? So I'm still a little confused as to which route to go with ?. I know cabin gain will help but won't CABIN GAIN be even higher if I do a sealed enclosure or will cabin gain be the same if I did ported ? Thx.. Ported is impractical because of port size .
The questions you are asking indicate that you have only limited experience with bass reproduction. I would kindly suggest that you start with something smaller and work your way up. It's much cheaper this way if you decide it's not for you, and also the mistakes you'll be making will be with fewer, smaller, cheaper stuff.
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