Sp4 V2+ design help

[Triticum Agricolam]

11 hours ago, Joshdashef said:

Thank you! I was just wondering in my head if that’d be okay.

no end grain gotcha, so just put the double baffle the entire length and height of the box and the sides, top, and bottom behind that right ?

 

Just one question @Triticum Agricolam

I’ve been using your port area calc and wanted to see if you had any input. 

With a box that has 3.5 or 4 cubic feet net after displacements should I shoot for the optimal port area ? Or is 70ish square inches okay ? I’ll end up with a port 14.5 high with variable length / width that’s why I’m asking. 

If you really want the most strength, what you could do is put your inner baffle inside the top, bottom, and side panels, and then your outer baffle so that it overlaps the top, bottom, and sides.  Its more work and your baffle panels will be two different sizes, but its gives you more surface area for glue.  

As far as your port area goes, you are at that magic 1000 watts per cube spot where getting enough port area becomes very difficult.  Understand that both the "optimal" and "minimum" port area numbers are both going to lose some output to port compression, the difference is how much and how prevalent port noise may be.  At the "optimal" amount you are still going to lose 1-2 dB of output when playing at peak volume and right at the tuning frequency.  At the "minimum" port area you are likely going to lose 3 dB or more of output and noticeable port noise is going to be pretty likely.  Getting enough port area to get to the "optimal" number may require a port that is unreasonably long,  or may take more space than you have available.  In the end you are going to have to decide what design compromises you are willing to make.  Hopefully my calculator can at least give you an idea of where you want your port area to be and can help you make a more informed decision.  When I design boxes I try to get as close to that optimal port area number as I can, but every situation is different.  

[Joshdashef]

17 hours ago, Triticum Agricolam said:

If you really want the most strength, what you could do is put your inner baffle inside the top, bottom, and side panels, and then your outer baffle so that it overlaps the top, bottom, and sides.  Its more work and your baffle panels will be two different sizes, but its gives you more surface area for glue.  

As far as your port area goes, you are at that magic 1000 watts per cube spot where getting enough port area becomes very difficult.  Understand that both the "optimal" and "minimum" port area numbers are both going to lose some output to port compression, the difference is how much and how prevalent port noise may be.  At the "optimal" amount you are still going to lose 1-2 dB of output when playing at peak volume and right at the tuning frequency.  At the "minimum" port area you are likely going to lose 3 dB or more of output and noticeable port noise is going to be pretty likely.  Getting enough port area to get to the "optimal" number may require a port that is unreasonably long,  or may take more space than you have available.  In the end you are going to have to decide what design compromises you are willing to make.  Hopefully my calculator can at least give you an idea of where you want your port area to be and can help you make a more informed decision.  When I design boxes I try to get as close to that optimal port area number as I can, but every situation is different.  

Thank you for the input man I appreciate it. 

I think I will go for your idea of two different size baffles to get a sturdier box. 

Im going to do some work in win isd and your port calc and see what I come up with. 

Hopefully I can fit close to optimal port area. Would there be any harm in going over optimal? You mentioned lose of output going down as port area went up, so I’m just curious. 

 

[Triticum Agricolam]

22 hours ago, Joshdashef said:

...Would there be any harm in going over optimal? You mentioned lose of output going down as port area went up, so I’m just curious. 

 

Port compression scales in a fairly linear fashion with port velocity.  You lose about 1 dB of output per 10 m/sec of port velocity...to a point.  Once you get much over 30 m/sec the airflow through the port can become turbulent and then your port compression increases at a much higher rate.  The exact point at which this happens depends on the layout and orientation of the port along with other factors.  

You certainly can have more port area than the "optimal" amount.  More port area doesn't hurt anything and is usually beneficial to output.  Where you get into trouble is some of the things that going along with more port area.  All else being equal, a port with more area is going to have to be longer to keep tuning the same.  Having a port get too long can definitely cause problems (such as pipe resonance issues).  Not to mention it takes up more space.  I try to keep ports under 44" of total length.