Dumb idea?

[Greg B]

So I put a new 12w6 in a box I had sitting around. It's 2 cubes with 37.5" port area tuned to around 38. It actually sounds great but unloads on what seems to be lower frequencies. I know the right answer is to build a new one but I'd like to make this one work if possible. It's very well built and fits the space I have perfect.

I was thinking if I add another layer of MDF it would lower the port area to around 28" and drop the frequency some. If it's the tuning that's causing it to unload I could also lengthen it since I'm a good amount over the spec'd volume. Maybe both. Either way I'd appreciate any advice on what I should try.

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[CarAudio.com - Hal AI Bots]

So I put a new 12w6 in a box I had sitting around. It's 2 cubes with 37.5" port area tuned to around 38. It actually sounds great but unloads on what seems to be lower frequencies. I know the right answer is to build a new one but I'd like to make this one work if possible. It's very well built and fits the space I have perfect.

I was thinking if I add another layer of MDF it would lower the port area to around 28" and drop the frequency some. If it's the tuning that's causing it to unload I could also lengthen it since I'm a good amount over the spec'd volume. Maybe both. Either way I'd appreciate any advice on what I should try.

It sounds like you've done a great job getting your system to sound good overall with the 12w6, but as you've noticed, tuning and port area can greatly affect performance, especially in terms of unloading at lower frequencies. Here’s how you can approach the issue:

### Adjusting Port Area
1. Reduce Port Area: By adding MDF to effectively reduce the port area from 37.5 to 28 square inches, you can lower the tuning frequency of the box. But keep in mind that reducing the port area too much can lead to increased port noise or distortion, particularly if you start to approach the limits of the sub’s capability. Ensure that the new port area can still allow for good airflow during operation.

### Adjusting Port Length
2. Lengthen the Port: Since you're tuning your box to around 38 Hz, consider lengthening the port to help lower the tuning frequency further. You can utilize a calculator or software (like WinISD or BassBox) to determine how much longer you need to make the port for the desired tuning frequency.

### Combining Both Methods
3. Both Adjustments: Combining both approaches could be beneficial. By decreasing the port area and lengthening it, you’ll be able to effectively lower the tuning frequency without introducing too much turbulence and noise in the port. Make small incremental changes and test after each modification to see how the performance changes.

### Testing & Tuning
4. Test Iteratively: After making adjustments, do some listening tests to see if the unloading has improved at lower frequencies. Use varying types of music that challenge the lows and pay attention to how the sub reacts under load.

### Additional Considerations
5. Check Subwoofer Placement: Also, consider the placement of the subwoofer within the vehicle and how it interacts with the car's acoustics. Sometimes moving the sub or adjusting the angle may help with performance as well.

6. Damping and Isolation: Adding some acoustic damping materials inside the box may also improve sound quality and reduce any unwanted resonances.

Before proceeding, ensure you have the necessary tools and safety precautions in place while making these adjustments.

Feel free to update with any changes you try or if you need further clarification on any specific aspect. I encourage more members to assist or chime in with their recommendations or experiences!

 

[Greg B]

Bump

 

[Doxquzme Premium Member]

You don't mention if that box is 2 cu ft net or gross.

JL says that the subwoofer should be in a ported enclosure no larger than 1.3 cu ft. The displacement of the driver is roughly .105 cu ft, the port as they list it is around 593 cu ub (31.625x12.5x1.5 =593 cu in or roughly .34 cu ft), which puts the gross internal volume at around 1.75 cu ft.

If your box is tuned to 38, it's tuned too high, and if it's 2 cu ft, it's too large.

You're losing everything below 37Hz, likely creating a muddy response comparatively and reducing its power rating considerably.

I would actually shoot for around 29Hz tuning on that driver, its fs is quite low at 26.9hz so anything at or above would be great.

Something like this.

30x14x12.5
port opening (on baffle with woofer) roughly 21.875 square inches.
port would be 12.5x1.75x30
Tuning frequency would be roughly 31 hz.

This also assumes a single baffle. I'd actually consider doubling the baffle.

 

[Greg B]

You don't mention if that box is 2 cu ft net or gross.

JL says that the subwoofer should be in a ported enclosure no larger than 1.3 cu ft. The displacement of the driver is roughly .105 cu ft, the port as they list it is around 593 cu ub (31.625x12.5x1.5 =593 cu in or roughly .34 cu ft), which puts the gross internal volume at around 1.75 cu ft.

If your box is tuned to 38, it's tuned too high, and if it's 2 cu ft, it's too large.

You're losing everything below 37Hz, likely creating a muddy response comparatively and reducing its power rating considerably.

I would actually shoot for around 29Hz tuning on that driver, its fs is quite low at 26.9hz so anything at or above would be great.

Something like this.

30x14x12.5
port opening (on baffle with woofer) roughly 21.875 square inches.
port would be 12.5x1.75x30
Tuning frequency would be roughly 31 hz.

This also assumes a single baffle. I'd actually consider doubling the baffle.

Thanks for the reply. This is what I plan to do eventually but I don't have an indoor work area and it's been raining every day that I have spare time. I messed up my original calculation and it's actually 3x12.5 so 37.5 port area. I searched the forum before posting and saw the well reputed builders advise people to go with 2 cf for this sub. I'd like to go smaller though because I prefer even response over output.

What's the benefit of having the port on the front baffle? I've built both but they haven't been an apples to apples comparison

 

[Doxquzme Premium Member]

Okay, but what is the gross volume of the box itself, before the woofer and before the port displacement is accounted for?

Did someone indicate that 37Hz is the tuning frequency?

Without knowing the gross/net volume specifications, there is no way to calculate the tuning frequency based simply on the port displacement; all three specifications are interdependent.

What are the outer dimensions of the box, what thickness is the material used to construct it, and what is the length of the port?

Don't get too hung up on the port area since this is a temporary situation. Port area in correct proportion to the box volume is done to mitigate noisy ports, not whether they are tuned correctly.

Yes, port area and the length in a given size box determine the tuning frequency, but the size of the opening and the general applied rule of thumb for that size is strictly for preventing chuffing, wind noise, and turbulence.

As for the port and the driver exiting from the same size, it's not always possible, but the benefit is that the port, which is essentially an extension of the back wave of the driver, leaves the back of the driver, exits the port at about the same time, in sync with the front wave of the driver and combine to netting you that 3db extension of the bass output.

 

[Greg B]

Okay, but what is the gross volume of the box itself, before the woofer and before the port displacement is accounted for?

Did someone indicate that 37Hz is the tuning frequency?

Without knowing the gross/net volume specifications, there is no way to calculate the tuning frequency based simply on the port displacement; all three specifications are interdependent.

What are the outer dimensions of the box, what thickness is the material used to construct it, and what is the length of the port?

Don't get too hung up on the port area since this is a temporary situation. Port area in correct proportion to the box volume is done to mitigate noisy ports, not whether they are tuned correctly.

Yes, port area and the length in a given size box determine the tuning frequency, but the size of the opening and the general applied rule of thumb for that size is strictly for preventing chuffing, wind noise, and turbulence.

As for the port and the driver exiting from the same size, it's not always possible, but the benefit is that the port, which is essentially an extension of the back wave of the driver, leaves the back of the driver, exits the port at about the same time, in sync with the front wave of the driver and combine to netting you that 3db extension of the bass output.

I redid my calculations with the correct port volume and it's 3.18 gross and 2.4 net tuned to 35. 28.25x14 on the baffle side 18 deep 3/4 mdf and the port runs front to back then folds back the other way. Port is around 27. I messed around from there and lengthening could get me to 1.8cf and 32.5 which I'm comfortable with for now

 

[Doxquzme Premium Member]

If this is a 12W6 V2, that would be fine; if it's a newer driver, then the box is too big.

Too big gives you louder, lower bass but sloppier bass and reduces the acceptable wattage, in this case, by about 25%. I'd shy away from feeding any more than around 451 watts.

At the end of the day, if you like the sound the way it is currently, that's all that matters.

 

[Greg B]

If this is a 12W6 V2, that would be fine; if it's a newer driver, then the box is too big.

Too big gives you louder, lower bass but sloppier bass and reduces the acceptable wattage, in this case, by about 25%. I'd shy away from feeding any more than around 451 watts.

At the end of the day, if you like the sound the way it is currently, that's all that matters.

It is a v2. I'm not going going to be pushing it at all. Just looking for good sound

 

[Greg B]

Update: I was able to lengthen the port 19" which put it at 1.8 cf and roughly 33 hz. This fixed the unloading issue. It's also improved the peakiness and muddiness quite a bit. It's not perfect but good enough to live with until I have time to build one to spec.

For anyone who cares but didn't read the whole thread I put 4" for port width into the calculator instead of 3 so it originally was 2.4 which explains a lot.