Understanding Subwoofer volume requirements

[Xplode69]

Good day everyone,

I currently have a Fi 3.9 Neo Dual 1.4 ohm subwoofer, which is recommended to run in an enclosure between 1.8–2.5 cu ft. The amplifier I have available is a 8k. Taking impedance rise into account, I expect to see roughly 4000W RMS in actual output. I’m trying to determine the most suitable enclosure volume for my setup. I don’t plan on playing rebassed music, my listening is mainly hip hop, techno, pop, reggae, etc. and I’m aiming for a tuning frequency of around 36 Hz.

I understand that with the power level I’m working with, the port will need to be quite large to avoid chuffing around 27 per cube, but I’d really appreciate guidance on what enclosure volume within the recommended range would give the best overall performance for my use case.

 

Thanks in advance for any advice!

Edited March 19 by Xplode69

[Joe X]

The ideal box will let your sub fully reach Xmax on the power available, Xmax is the maximum distance the cone move from its resting position while sounding good and avoiding damage to the sub.

 

Box size has to do with how efficiently power will be used and what type of sound you will get, larger box results in higher efficiency and lower notes being playing louder, smaller box is for higher sound quality but less efficiency and lower notes being played less loudly.

 

If your amp has little power compared to what the sub can take you will want a larger box so you get louder on the power you have.

 

To decide your box size, tuning and port area you use modeling software like WinISD, hornresp and others to give you an idea on what needs to be done, there is a thread right next to yours by the name  "Need Box/WinISD Advice " where you can see how they work.

 

Also one needs to bear in mind the vehicle you use, among many factors the cabin size will determine how loud lower bass will sound, the smaller the cabin the louder lower bass will sound.

 

I can give you some magic numbers but best is that you better understand what you are doing.

 

Edited March 18 by Joe X

[Xplode69]

5 hours ago, Joe X said:

The ideal box will let your sub fully reach Xmax on the power available, Xmax is the maximum distance the cone move from its resting position while sounding good and avoiding damage to the sub.

 

Box size has to do with how efficiently power will be used and what type of sound you will get, larger box results in higher efficiency and lower notes being playing louder, smaller box is for higher sound quality but less efficiency and lower notes being played less loudly.

 

If your amp has little power compared to what the sub can take you will want a larger box so you get louder on the power you have.

 

To decide your box size, tuning and port area you use modeling software like WinISD, hornresp and others to give you an idea on what needs to be done, there is a thread right next to yours by the name  "Need Box/WinISD Advice " where you can see how they work.

 

Also one needs to bear in mind the vehicle you use, among many factors the cabin size will determine how loud lower bass will sound, the smaller the cabin the louder lower bass will sound.

 

I can give you some magic numbers but best is that you better understand what you are doing.

 

Thanks for the response. I downloaded BassBox Pro and ran some simulations based on my design.

I’ve modeled an enclosure with a net internal volume of approximately 1.97 ft³ and a port area of 49 in². At 8000 W RMS input, the model shows a peak port air velocity of about 33 m/s. Since I won’t be operating the subwoofer at that power continuously, I also simulated at 4000 W RMS, which results in a more reasonable port velocity of approximately 24.3 m/s.

The port dimensions are 14" × 3.5", giving a slot port configuration tuned to ~37 Hz. My listening preferences do not include rebassed content; I primarily listen to hip hop, techno, rock, EDM, and reggae.

So overall, the enclosure specifications are:

• Net volume: 1.97 ft³

• Port: 14" × 3.5" (49 in²)

• Tuning frequency: ~36 Hz

The enclosure will be installed in an extended cab truck. I’m currently evaluating optimal orientation, options include:

• Sub up / port up

• Sub up / port firing toward the passenger door

• Sub forward / port forward

I understand the differences may be subtle, but I suspect boundary loading could vary depending on whether the port fires toward a solid surface (door) versus a softer boundary (seat). I’d appreciate any insight on how much this might affect performance. The vehicle is an extended truck with 2 out of the 3 seats removed.

 

 

Edited March 18 by Xplode69

[pnutz37]

I also recommend pulling the TS parameters of the sub. This will get you a more accurate graph on frequency response etc. I have a Fi Neo 4.11 18" and the parameters are way off.....

[Xplode69]

16 minutes ago, pnutz37 said:

I also recommend pulling the TS parameters of the sub. This will get you a more accurate graph on frequency response etc. I have a Fi Neo 4.11 18" and the parameters are way off.....

Yep, parameters were pulled using DATS V2 then inputted into Bassbox Pro.

[Joe X]

7 hours ago, Xplode69 said:

Thanks for the response. I downloaded BassBox Pro and ran some simulations based on my design.

I’ve modeled an enclosure with a net internal volume of approximately 1.97 ft³ and a port area of 49 in². At 8000 W RMS input, the model shows a peak port air velocity of about 33 m/s. Since I won’t be operating the subwoofer at that power continuously, I also simulated at 4000 W RMS, which results in a more reasonable port velocity of approximately 24.3 m/s.

The port dimensions are 14" × 3.5", giving a slot port configuration tuned to ~37 Hz. My listening preferences do not include rebassed content; I primarily listen to hip hop, techno, rock, EDM, and reggae.

So overall, the enclosure specifications are:

• Net volume: 1.97 ft³

• Port: 14" × 3.5" (49 in²)

• Tuning frequency: ~36 Hz

The enclosure will be installed in an extended cab truck. I’m currently evaluating optimal orientation, options include:

• Sub up / port up

• Sub up / port firing toward the passenger door

• Sub forward / port forward

I understand the differences may be subtle, but I suspect boundary loading could vary depending on whether the port fires toward a solid surface (door) versus a softer boundary (seat). I’d appreciate any insight on how much this might affect performance. The vehicle is an extended truck with 2 out of the 3 seats removed.

 

 

To answer your question, if firing against a close surface it best that is a stable (no flexing or rattling) and non absorbent (like the seats) surface, typically in a daily setup you will fire the port to the passenger side and sub up or forward, experimentation is most important as well a doing some research on what works for a particular vehicle, there is no general rule as personal preference is also a factor.

 

To better model with bass box pro activate cabin gain setting and setup to 60Hz, the way you have it output drops fast below tuning which is not the case inside a car cabin, also since rises very fast below tuning, you need to setup your subsonic filter to protect your sub.

[Joe X]

BTW the DATS or similar device are used on a well broken in driver, if you use it in a new sub it is going to give you bad parameters, quite frankly Fi provides reliable parameters, DATS is necessary on reconed/modified subs or those chinese subs where the manufacturer gives fake parameters to boost sales.

[Xplode69]

46 minutes ago, Joe X said:

 

To answer your question, if firing against a close surface it best that is a stable (no flexing or rattling) and non absorbent (like the seats) surface, typically in a daily setup you will fire the port to the passenger side and sub up or forward, experimentation is most important as well a doing some research on what works for a particular vehicle, there is no general rule as personal preference is also a factor.

 

To better model with bass box pro activate cabin gain setting and setup to 60Hz, the way you have it output drops fast below tuning which is not the case inside a car cabin, also since rises very fast below tuning, you need to setup your subsonic filter to protect your sub.

Thanks for pointing out the cabin gain factor, I applied it, and the bandwidth ended up being very narrow, roughly 33–43 Hz at -3 dB on either side of the peak. I’m not sure if that’s the best I can achieve...

Using the DATS, I’m seeing an Fs of around 33 Hz when I test the sub in free air. The sub has about a year of use on it, so it’s well broken in. From what I can tell, this design looks quite peaky within that range.

Do you have any suggestions on how I could flatten the response a bit? This setup is mainly for music, not competition.

[Joe X]

Your sub has an incredibly stiff suspension and a brutal motor so is not surprising that it does that, actually is meant to do that, to fix that behavior without losing a lot of output I came up with a "compact" parallel 6th order box:

 

 

It's about 4 cubic feet net (which defeats the purpose of getting a 12" sub) but you get 28-55 relatively flat.

 

That sub is so SPL oriented that it has dual 1.4 ohm coils clearly aimed at wiring in parallel to 0.7 ohm to suck all the power it possibly can from most amps.

Edited March 19 by Joe X

[Xplode69]

6 hours ago, Joe X said:

Your sub has an incredibly stiff suspension and a brutal motor so is not surprising that it does that, actually is meant to do that, to fix that behavior without losing a lot of output I came up with a "compact" parallel 6th order box:

 

 

It's about 4 cubic feet net (which defeats the purpose of getting a 12" sub) but you get 28-55 relatively flat.

 

That sub is so SPL oriented that it has dual 1.4 ohm coils clearly aimed at wiring in parallel to 0.7 ohm to suck all the power it possibly can from most amps.

 

Thanks a lot for the help. That makes sense about the sub. When it was brand new it was super stiff like you said, but now after some use it’s actually really easy to push in by hand, so it definitely loosened up a lot.

That 6th order design looks solid, especially the 28–55 Hz range, but I just can’t make a 4 cubic foot box work in my space at all. The max space I got available is 30" wide 16" depth 20" height.  Unless I can get the 6th to fit within these specs then I guess I’ll have to try the current enclosure plan, even though it’s a bit peaky.

Really appreciate the insight though, it helped me understand what’s going on a lot better 👍

Edited March 19 by Xplode69