sundown sa8 single cab box ideas?

[x on 22s 10+ year member]

it is kinda ugly but it bangs!

 

[brown7348 10+ year member]

I have one built now, i used a 3in pvc port, its a short wedge, i have it tuned to 30hz, does anyone know if a 4in port would make a difference or even bringing the tuning up? It hits pretty hard down low, but not soo much on anything over around 45hz

 

[RangerDangerV2 5,000+ posts]

1.2 cu ft tuned to 28hz with a 2 inch aero was the loudest I could I get my single sa8.

 

[brown7348 10+ year member]

Yea, so i guess its doing its job the way it is, my box is right at 1 cu ft, and so far everyone thinks there is a pair of good tens or twelves behind the seat, had a guy looking for more subs in the truck last night lol, he was like no wayy..

 

[SilverSquared 10+ year member]

Hey Trav, you near BR?

 

[travicles 10+ year member]

Hey Trav, you near BR?

yeah, I see you're in nola

 

[brown7348 10+ year member]

The box i mentioned above seems to be getting pretty loud, i can put a plastic cd case over the port and it will nearly destroy it, im wondering if i should bump up to a 4in port?

 

[travicles 10+ year member]

Yes, a 4 inch port is what is recommended for the SA-8.

 

[Moble Enclosurs 10+ year member]

Yes, a 4 inch port is what is recommended for the SA-8.

As a minimum, yes. But port area is really power dependent, volume dependent, and cutoff dependent. So you can always use greater than a 4" if you have the room, and lower than a 4" if you don't have the room and want to minimize power levels. Its a tradeoff. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[brown7348 10+ year member]

I have yet to try a 4in port, been pretty busy, but have a couple questions about this 3in port, it gets decently loud in the cab, its actually flexing everything in the truck and really beating up my back but its not really all that loud for all the damage it seems like its doing, why would it move and shake everything so violently but not be very loud doing it?

 

[Moble Enclosurs 10+ year member]

I have yet to try a 4in port, been pretty busy, but have a couple questions about this 3in port, it gets decently loud in the cab, its actually flexing everything in the truck and really beating up my back but its not really all that loud for all the damage it seems like its doing, why would it move and shake everything so violently but not be very loud doing it?

Very good question actually. The reasoning is that pressure and intensity are based on two different physical variables. For instance, you can have a 10Hz sine wave move the sub quite well and produce a lot of pressure at the port, but it would likely have a more physical effect on the vehicle than acoustical if 10Hz is not an axial resonance in the vehicle and if it is out of phase. Most vehicles have axial resonances around the 16Hz range then output drops off there in most cases, but even then it may be an 1/8 harmonic or something that is less efficient where the acoustical output may be inferior to the physical movements that occur. Pressure is based on this form of movement where the air just compresses and expands without a sense of phase. That being the main reasoning of inaudible output, an out of phase response still has the same physical effects of pressure, maybe dropping only 1/3 of its pressure at 180 degrees for an average vehicle cabin. What that means is that if the port and driver are out of phase completely, you still get output. But though it may cause more pressure fluctuation based on lower frequencies, it may not couple well acoustically and be very faint. If you have ever seen the ROOM OF DOOM, look it up on youtube. This is a perfect example of pressure vs intensity. The 11-12Hz signal it produces can barely be heard, but can easily be felt. Intensity is what you feel when you put your hand in front of the cone and feel the oscillations occur. The more intense that is, the more output you will get, but if the frequencies that are most intense in output are not coupled to the vehicles nodes, then again you will get a lot of sound output, but no rattles, etc. This happens normally at higher frequencies into the mid bass region especially sense most designs work more efficiently in those ranges due to the limited volumes of compression we work with in car audio. Ever seen a response curve where it peaks above 100Hz higher than at tuning? This is due to efficiency and frequency relationship to that of the enclosures main compression volume tuning, not what it is actually tuned to at the port. There are two acoustical responses that occur in a box. one is inside the compression chamber, one is just outside the port. And if the port fights the compression tuning, you get out of phase responses.

So with pressure you have movement and compression. Pressure=compression/expansion with the added variable of timing. Intensity=power/pressure relationships. The two are measured differently, but share a common goal. To create output. In general, you can push a lot of air and not hear it well due to phase and coupling effects, or get hardly any mach out of the port, but the sound be very intense from correct coupling and phase. This is why pro audio drivers cost so much because they can conform to a more efficient/proper bass response curve than the lower sensitive drivers we use to gain power due to limited space.

You can make a horn that barely shakes a piece of paper at the opening, but makes your chest hurt. This is the timing effects of frequency oscillation. So again real quick. Pressure is more physical and intensity is more acoustical. This is also why a design that measures on a meter at 130dB can outperform that of a 140dB design in output by the ear.

Example: Blow air out of your mouth but don't make a vibration with your vocal chords. That is pressure from compression. Then hum only with your mouth open. That is intensity. If you hum, you get less air movement, but can get louder by ear, but vice versa you can blow a paper cup off a coffee table and not make a noise that audible. Make sense I hope?

I won't be able to reply back for a while. Ill be gone, but I hope that helps a bit. Sorry if it because a tad technical.

 

[brown7348 10+ year member]

Thanks, you guys are very helpful, and your right, with this 3in port it pushes out a ton of air, almost seems like it would have to be choking the sub its soo much air coming from the port, when i first built the box i guessed a bit on the port length and it was a tad too long i came out tuned to 27.xxx hz with the port 20in long, i cut it down to 16in and it brought me up to 30.xx hz. i know it gained some decibles but not much, im guessing ill have to find out if i have the room to go ahead and add a 4in port, it looks like it will have to be 35in or more to get to around 33hz, i think i have the room to do so as long as the port doesent come to close to the passenger wall. And another thing when i first built the box tuned that low the sub sounded like the cone was hitting the spider a lot, when i go the tuning up a bit it didnt do it unless it was a super low song, im hoping a 4in port will fix these problems and not make them worse...

 

[SilverSquared 10+ year member]

yeah, I see you're in nola

Been a long time since I lived in NOLA. I was in BR until 7/11/12. Now Im in Prairieville...like thats not BR, lmao.

 

[brown7348 10+ year member]

Ok so im about to build a new box for the sa8, have been sitting over the steering wheel for months now, i have a single cab chevy with the buckets and non moving console, the box i took out was a tad over a cube, with a 3in pvc port, sounded ok but sometimes heard the spider hitting the cone, so i guess im getting over excursion since the box is too big. Now to the new box, its gonna be 12''h 8''deep, and 24'' wide, this gives me 0.89ft3 before any displacement, couple questions on the port though, im using torres calculator and when i try to use the round port feature with a 4in port which most of will be external it tells me i need a really crazy length of port and the volume drops everytime i add a few inches of length almost as if it thinks the port is just snaking around inside the box. also need to know the displacement of the sub.. Any help here, this port stuff is killing me unless ill be fine using a 3in port again but dont want to build another box and still have over excursion issues..

 

[travicles 10+ year member]

Put it in .75 ft^3 tuned to ~35. You don't have to use an aero port; just do a slot port with 180 degree turns. If this isn't the V2, then just make the box 7 inches deep and you won't lose any leg room. Keep in mind that the port will be still be long, and it will take up over a third of the box. Another thing to remember is you're only dealing with an 8 inch subwoofer, and it is obviously a great sub but don't expect insane levels of output.