Port Help for My HDC3 18"

[ObTechAudio 0]

Hey guys,

 

I am needing some direction or reassurance in what I'm doing with my port. This is my first time working with an 18" sub and with SoundQubed equipment. According to soundqubed.com, the HDC3 18" wants a box anywhere from 5-6 cubes with a vent of 96sq" x 18" long. To me, that port seems odd.

 

So I just got done designing my box. External dimensions are 25" x 25" x 26" but I'm using double sheets of .75 MDF, so each measurement take off 3". I calculate internal space at 22" x 22" x 23" = 11,132 inches = 6.44 cubes. Rough internal space after ONLY sub displacements is 6.4ish cubes. My desired tuning frequency is 31-32hz, because the fs of this sub is 31hz. So, I designed my port on both WinISD and CarStereo.com at 3" x 16" and 15.5" long. 

 

Both WinISD and CarStereo said with that size of box (6.3 cubes internal), port size (3 x 16 x 15.5), and tuning frequency (31-32hz), I should have zero problem. After all displacements, I'll roughly have an internal space of 5.95 cubes, which is EXACTLY what I wanted. I'm asking you guys, because it's not what soundqubed suggests and that's what worries me. I want you guys to check out what I'm doing and see if it all looks good to go. I appreciate any insight or feedback.

[///M5 2,833]

Port area depends on power. No such thing as rec'd without.

[Lee Carter 150]

I would venture to say that on moderate power those specs makes sense.  Not actually running the #'s since you already used the same methods I would.  but as M said- power plays a factor...

 

Also want to add that all the SQ recommended boxes use the 16 sq in of port area/cubic foot rule...and a 18" port.  seems strange to me too.

Edited June 10, 2014 by Leedogg

[///M5 2,833]

Also want to add that all the SQ recommended boxes use the 16 sq in of port area/cubic foot rule...and a 18" port.  seems strange to me too.

No such rule, that is dumb

[ObTechAudio 0]

I would venture to say that on moderate power those specs makes sense.  Not actually running the #'s since you already used the same methods I would.  but as M said- power plays a factor...

 

Also want to add that all the SQ recommended boxes use the 16 sq in of port area/cubic foot rule...and a 18" port.  seems strange to me too.

That just seems strange when I first saw it. For power, I'll be running a Soundqubed Q1-2200 at .5 ohm. Got plenty of electrical/power to give it what it needs to run .5 daily.

[ssh 924]

3" x 16" = 48in^2, 2000watts, 32hz, vent mach: 36 m/s or 0.10 (36/340).

 

96in^2, 2000watts, 32hz, vent mach: 18 m/s 0.05 (18/340).

 

I don't see why their recommendation strikes you as being odd.

[///M5 2,833]

In a car you fine with 36 if chuffing is your concern.

[ObTechAudio 0]

3" x 16" = 48in^2, 2000watts, 32hz, vent mach: 36 m/s or 0.10 (36/340).

 

96in^2, 2000watts, 32hz, vent mach: 18 m/s 0.05 (18/340).

 

I don't see why their recommendation strikes you as being odd.

Ya I get what you're saying. It's my understanding that 0.10 isn't the worst. Obviously people aim for the .04-.05 range. In your opinion, did I totally screw up my box? Is 0.10 going to screw up the entire build?

 

I just had a hard time wrapping my head around a port at 96sq" x 18" is necessary for a singe 18", but now looking at mach, I get it. 

[ObTechAudio 0]

In a car you fine with 36 if chuffing is your concern.

Do you mind rewriting that for me? I didn't exactly get what you were trying to say.

[ssh 924]

 

In a car you fine with 36 if chuffing is your concern.

Do you mind rewriting that for me? I didn't exactly get what you were trying to say.

 

He's saying you shouldn't be concerned about port noise that's in a vehicle if the port speed is 36 m/s.

[ssh 924]

 

3" x 16" = 48in^2, 2000watts, 32hz, vent mach: 36 m/s or 0.10 (36/340).

 

96in^2, 2000watts, 32hz, vent mach: 18 m/s 0.05 (18/340).

 

I don't see why their recommendation strikes you as being odd.

Ya I get what you're saying. It's my understanding that 0.10 isn't the worst. Obviously people aim for the .04-.05 range. In your opinion, did I totally screw up my box? Is 0.10 going to screw up the entire build?

 

I just had a hard time wrapping my head around a port at 96sq" x 18" is necessary for a singe 18", but now looking at mach, I get it. 

 

I have no idea. I haven't checked your net volume or port length to see if they're correct, and I honestly can't suggest what maximal port speed is acceptable. All I know is my last setup was 25 m/s and I didn't run into any issues--that's not to say I couldn't have gotten away with higher port speed / less port area.

[ObTechAudio 0]

 

 

In a car you fine with 36 if chuffing is your concern.

Do you mind rewriting that for me? I didn't exactly get what you were trying to say.

 

He's saying you shouldn't be concerned about port noise that's in a vehicle if the port speed is 36 m/s.

 

Ahhhh got it. I'm not super concerned because I'm not an SPL competitor, but I definitely want a setup that's going to get down.

[ObTechAudio 0]

 

 

3" x 16" = 48in^2, 2000watts, 32hz, vent mach: 36 m/s or 0.10 (36/340).

 

96in^2, 2000watts, 32hz, vent mach: 18 m/s 0.05 (18/340).

 

I don't see why their recommendation strikes you as being odd.

Ya I get what you're saying. It's my understanding that 0.10 isn't the worst. Obviously people aim for the .04-.05 range. In your opinion, did I totally screw up my box? Is 0.10 going to screw up the entire build?

 

I just had a hard time wrapping my head around a port at 96sq" x 18" is necessary for a singe 18", but now looking at mach, I get it. 

 

I have no idea. I haven't checked your net volume or port length to see if they're correct, and I honestly can't suggest what maximal port speed is acceptable. All I know is my last setup was 25 m/s and I didn't run into any issues--that's not to say I couldn't have gotten away with higher port speed / less port area.

 

Before ALL displacements I'm at 6.44 cubes. With the port at 3 x 16 x 15.5 and sub displacement I'm at roughly 5.95 cubes

[Lee Carter 150]

Your right M5- I should've said ideology...LOL

 

My box I am putting in the Avalanche has only 10" of port per foot...recommended by my sub builder...so I don't buy into the whole 'you have to have a huge port' idea.  This may be totoally wrong when searching for ultimate SPL though.  I just want a loud but good sounding box for mine though. Loud being relative.

 

If you are that worried- just build it to their specs and be done with it....

[ssh 924]

Your right M5- I should've said ideology...LOL

 

My box I am putting in the Avalanche has only 10" of port per foot...recommended by my sub builder...so I don't buy into the whole 'you have to have a huge port' idea.  This may be totoally wrong when searching for ultimate SPL though.  I just want a loud but good sounding box for mine though. Loud being relative.

 

If you are that worried- just build it to their specs and be done with it....

I think you might be misunderstanding. There is no relationship between enclosure volume and port area, so saying 10in^2 per ft^3 or 16-18in^2 per ft^3 are both equally meaningless.

 

You can't gauge how "big a port" (or rather the port speed) is relative to the enclosure volume--it's the same thing as saying "That car is fast because it is red."

 

When you design an enclosure with a port you design for an acceptable port speed and the resultant is some quantity of port area. Thus, port speed is a function of the number of drivers, power, Fs, Vas, Qes, tuning frequency, and port area.

Edited June 10, 2014 by ssh

[Lee Carter 150]

you are correct sir.