Frequency limiter for sub

[yonyz]

Hi,

My subwoofer "farts" sometimes, I think when it's trying to produce frequencies that are outside its capabilities.

The receiver gives it an upper limit of 80hz via the crossover feature, but nothing prevents it from trying to produce 10hz sounds and such.

I know that a device such as a miniDSP can do this, however it's expensive for this purpose.

The only source of audio for my system is my PC, and I use JRiver as the media player.
Does anyone know a good software solution, or a device much cheaper than a miniDSP?

Thanks

 

[lovinthehd]

Doesn't jriver have sufficient dsp built-in? Think I've read that it has the necessary filters (a high pass filter that can be set at a sufficient frequency, like the minidsp would, to do what you want) but not a user so not sure.

 

[shadyJ]

Hi,

My subwoofer "farts" sometimes, I think when it's trying to produce frequencies that are outside its capabilities.

The receiver gives it an upper limit of 80hz via the crossover feature, but nothing prevents it from trying to produce 10hz sounds and such.

I know that a device such as a miniDSP can do this, however it's expensive for this purpose.

The only source of audio for my system is my PC, and I use JRiver as the media player.
Does anyone know a good software solution, or a device much cheaper than a miniDSP?

Thanks

Hsu has some very simple high-pass filters available that can alternate between two frequencies with a 12dB/octave slope. But Jriver looks to have a high-pass filter capability in its parametric EQ, you can read about it here, that should do the trick.

 

[yonyz]

OK, the JRiver limiter does work but it doesn't solve the problem.
It's only when I put the high pass filter at 100hz (12db octave) that the subwoofer stops making that noise. And the volume is very low... I think it might be damaged.

 

[TheWarrior]

OK, the JRiver limiter does work but it doesn't solve the problem.
It's only when I put the high pass filter at 100hz (12db octave) that the subwoofer stops making that noise. And the volume is very low... I think it might be damaged.

What subwoofer is this?

Port chuffing - turbulence from the port can happen for a couple reasons, but a fart noise does suggest a damaged driver.

 

[lovinthehd]

Of course there are farts and then there are farts.

 

[TheWarrior]

Of course there are farts and then there are farts.

I usually find the louder ones to be less deadly.....

Wait, what are we talking about, again?

 

[yonyz]

It's a diy sub with an Infinity 1260W driver. Never let it play at extreme volumes (it's in a small room).
It's definitely not port chuffing, because I've had it for a year and a half or so and it's a new problem.

 

[lovinthehd]

What amp? You were running a ported sub without the protective dsp?

 

[yonyz]

BASH 300s. Protective DSP? Afaik, the BASH has a high pass filter set at 17hz or so, but I'm not really sure about that.

 

[lovinthehd]

BASH 300s. Protective DSP? Afaik, the BASH has a high pass filter set at 17hz or so, but I'm not really sure about that.

Sounds right but might depend on model. Check the manual?

 

[TheWarrior]

It's a diy sub with an Infinity 1260W driver. Never let it play at extreme volumes (it's in a small room).
It's definitely not port chuffing, because I've had it for a year and a half or so and it's a new problem.

How was the cabinet size and port length/diameter chosen?

 

[yonyz]

These are the default values for the BASH 300s:

I used a simulation program to choose cabinet size and other parameters. IIRC the port was tuned to 20hz.
I can find all the data in my Google Drive if you think it's important.

 

[rojo]

@TheWarrior See yonyz's sub build plans and photos and discussion thread. The vent is a slot port tuned to the published Fs of the driver, around 23.5 Hz. Since the symptoms are recent, I don't think it's a design problem.

@yonyz welcome back! I've been wondering how you've been getting along with your sub. Do you still have EqualizerAPO installed? Have you tried setting a high pass filter there? Try this in your config file:

ON    HPQ    Fc 25.0 Hz    Q 0.500

You might also pull out the driver and inspect the cabinet seams, maybe give them another coat of caulking, and make sure the wire between amp and driver isn't touching the back of the cone.

And if you gently press on the driver cone, does the travel feel smooth or scrapey? The surround has no holes or other damage?

The farting noise isn't coming from somewhere else in your room, like a picture rattling against the wall or a loose bolt on your chair?

Have you tried playing simple test tones to see at what frequency the farting occurs? If you could narrow it down, maybe you could attenuate just that range.

 

[TheWarrior]

@rojo Thanks for the details!

The instructions show a double walled baffle - the pics of the actual do not reflect that.

I still am questioning the actual build as it is also unusual for a slotted vent to fart - that is a distinct sound that I wouldn't confuse with rattling.

@yonyz It is entirely possible that your internal volume is larger than it should be, and just over the period of regular use the driver has damaged itself. As rojo said, you need to pull the driver and examine it. Double check your actual cabinet measurements and compare to the plan.

 

[yonyz]

The vent is actually tuned to 20hz, which is below the Fs of the driver.
The cabinet does have a double-walled baffle.

With the existing cabinet design, the risk was always that of too much cone excursion (and increased group delay). Looking at the WinISD file for this build, cone excursion reaches the maximum of 13mm at 16.45Hz, so theoretically the BASH amp should do the trick of avoiding over-excursion.

It's actually hard to replicate the farting sound with a frequency generator, maybe because these tools generate just one frequency. Anyhow, it sounds odd at around 27-35hz. I honestly am no longer sure of what it's actually supposed to sound like, though.

 

[highfigh]

It's a diy sub with an Infinity 1260W driver. Never let it play at extreme volumes (it's in a small room).
It's definitely not port chuffing, because I've had it for a year and a half or so and it's a new problem.

I would remove the woofer and inspect it. Make sure the dust cap isn't loose.

 

[TheWarrior]

The vent is actually tuned to 20hz, which is below the Fs of the driver.
The cabinet does have a double-walled baffle.

With the existing cabinet design, the risk was always that of too much cone excursion (and increased group delay). Looking at the WinISD file for this build, cone excursion reaches the maximum of 13mm at 16.45Hz, so theoretically the BASH amp should do the trick of avoiding over-excursion.

It's actually hard to replicate the farting sound with a frequency generator, maybe because these tools generate just one frequency. Anyhow, it sounds odd at around 27-35hz. I honestly am no longer sure of what it's actually supposed to sound like, though.

Was this your decision, or part of the design?

The cone needs to have a correctly proportioned pillow of air to push back on.

If you changed the internal cabinet volume by modifying the cabinet design and/or the port tuning selectively, we have found the issue.

 

[yonyz]

Was this your decision, or part of the design?

The cone needs to have a correctly proportioned pillow of air to push back on.

If you changed the internal cabinet volume by modifying the cabinet design and/or the port tuning selectively, we have found the issue.

I was suggested a certain design by rojo and decided to modify it. The cabinet size is correct for the port tuning.

 

[TheWarrior]

I was suggested a certain design by rojo and decided to modify it. The cabinet size is correct for the port tuning.

You size the cabinet for the driver, and you ideally tune the port for the driver too - which is usually the resonance frequency of the driver.

(Vas) is the Thiele-Small parameter that represents the volume of air, that when compressed, exerts the same force as the compliance of the suspension (Cms). Those metrics, combined with a formula, allows you to calculate the internal volume of a cabinet for a specific driver. That would be the 'pillow of air' I referenced earlier.

I'm sorry to say but I think you took too many liberties in your design and construction. This is what makes science, repeatable!