SP4 box for back seat. am i designing this right?

[swift 501]

no way i would want that much port. you want this musical right? 

[swift 501]

I would do 7.5cu with 100sqin of port, sub forward port up

Edited May 15, 2013 by swift

[ncc74656 2]

from what ive read i want some where from 81 to 152 sq inches. the more port i have the slower the air but i dont really know how that effects the 'musical' side of things. do i want faster air for better notes or do i want it in the middle? im trying to understand the correlation to port air velocity and the frequency response/quality of the notes.

[swift 501]

Just over thinking it. Too much port the low notes will sound like ass, especially in a forward port where no loading will take place. From my experience with SP4's I will stand by my suggestions.

[ncc74656 2]

ok, ive had some suggestions on the 80-90 mark and you with 100 so it seems that the consensus is less than 150 for sure. id still like to have a more narrow window than 80-100.

what happens if the port is to small?

[kirill007 52]

 

 my thought behind this was that a larger box would aid in the low notes and a higher tune would help keep the higher frequencies.

Nope. Box tuning is a world of trade-offs. No secret magic that can make you hit those 45-50hz like your old box and also destroy the 30-38hz range. 

> 

 

 i have had some input however that tells me i am incorrect about this assumption and i should tune at around 32-33hz and a larger box would only reduce the amount of power the sub can hold.

 

This statement is correct. Except you should tune at wherever you want. But a larger box makes the speaker reach it's mechanical limits with less power than a smaller box. 

 

 wich direction should i go?

 

Wherever you want to go. If it was me I would go for 33hz. But that's just my preference. 

 

i want to be able to kill the lows while still destroying hte highs. i seriously do not want any dead spots.

But no matter what, this isn't going to happen. It just isn't. It's the equivalent of saying "I want a car as fast as a Ferrari that I can also use as a moving van that triples as a vehicle to tow my motor home with."

 

If you can't build a box that plays flat to the ear from 30-50 hertz, you are doing something wrong.

A bandwith of only 20hz is easy to achieve, the only "trade-off" is that it won't be as peaky which results in a lower peak volume.

 

@ncc74656.

Since you seem to like to listen to normal music, and no slowed music, 33hz will be a little low.

Eventhough you probably will barely hear any difference with the box tuned to 37hz, I suggest tuning to 37-38Hz. (you get quite a bit of cabin gain on the low end if you are in a car)

100sq inches of port area as swift suggested, is a good one.

Since you have a 2.5kW amp, making the box about 6.5cubes big should give you good results.

 

If you can't input the T/S parameters of the SP4, that means you are doing something wrong. (read the manual on how to enter a new driver)

Edited May 15, 2013 by kirill007

[ncc74656 2]

ill give winISD another go. what is an example of slowed music?  i was originally thinking of tuning to around the 35hz mark to try and get a bit more high end. tuning however is less of an issue than the port area as i intend to build the box with a series of ports to test it from 32-36 hz.   a 6.5  cubic box i think is to small, not from a acoustic stand point but for the space in my truck. the box needs to be a minimum of dimensions for my plans back there.   am i going to negatively impact my audio quality by building a larger box?   if so is it because my amp is only a 2.5?

[ncc74656 2]

this is what i get when i use winisd. the graphs are always way off the scales and nothing like what i see others post on here.  the specs of hte SP4 do not enter exactly but the tutorials say to just allow the program to fill in the blanks that it can and run with it so thats what i did. the spec that is the most off is BL: listed on Fi website as 13.7 and computed by winISD at 9.6.

 

[ncc74656 2]

these are the values Win ISD calculates for the SP4. they are crazy far off from Fi's website. do the small parameters matter?  

[BsEMS 1]

Me personally, I only used two charts to design my box. Rear port velocity, to show what the speed of air would be exiting the port at each frequency, and the graph that displays the output bandwidth. The others I didnt find usefull, or I just didnt understand quite well enough.

With those two you can play with your tuning and see how it effects the output bandwidth of the design, and how much stronger/weaker the port velocity is at your desired range of frequency.

[ncc74656 2]

what is a speed of air that is going to make port noise? ive heard that you want to keep a 9:1 ratio or below on hight X width of port. is that a hard set guide for port noise?   will 25m/s air flow give me any different volume or sound quality than 20m/s assuming port noise is equal between the two?   how does rounding off the port edges effect things? how much faster can the air flow with a rounded port than a blocked one before port noise will occur?

[ncc74656 2]

in torres i have a box of 26HX30WX26D  port of 28.5W x 3.5H. when i input 21.75 as port length it tells me the physical port is 20.25", i do not understand this.  the port from front of box to rear of box (leaving port height to rear of box) is 21.75" so why then does it say the physical piece of wood is 20.25" long? does some of the physical port get subtracted in some kind of equation? 

 

if i then change from 21.75 length to 22.75 the stats change to 17.75" physical port length? how can i add wood and yet have a shorter piece of wood? 

Edited May 15, 2013 by ncc74656

[ncc74656 2]

here is my latest build. i believe i have the correct port area, cubic footage, and port size. is anything wrong or incorrect in my box? do i need more bracing? as it stands i will not need to bend my port.

 

http://imgur.com/a/P6goi   <---- 3d model

 

Edited May 15, 2013 by ncc74656

[ncc74656 2]

is that enough bracing or should i add more? if i need more what kind should i use?