# Subsonic Filter question



## mattldm (Apr 27, 2006)

How important is a subsonic filter for a mono sub amp?

Is this a feature that a must have, or is this an audiophile tweaky type accessory?

Is having a subsonic filter more or less important or useful when using a ported box?

What would I expect to notice using an amp with a subsonic filter to power my ED 11Kv.2 in a ported box as opposed to an amp without a subsonic filter?


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## AudioBob (May 21, 2007)

The use of a subsonic filter becomes much more important when using a ported enclosure. When you are giving a woofer a lot of power it is easy to drive the woofer too hard when trying to play music that has content below the tuning frequency of the enclosure. This kills many woofers because it drives the woofer to mechanical failure due to overexcursion.

On a sealed enclosure it is less important, but can still be beneficial.


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## Oliver (Jun 25, 2007)

Imagine if you will bench pressing a heavy weight and half way up the weights fall off the bar [ unloading], you throw the bar straight up and your shoulders out, OUCH !

When a subwoofer plays below the tuned frequency [it unloads] OUCH !!

How can a signal be stopped from getting to the sub, infrasonic filter !

No input, no problem.


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## mattldm (Apr 27, 2006)

a$$hole said:


> Imagine if you will bench pressing a heavy weight and half way up the weights fall off the bar [ unloading], you throw the bar straight up and your shoulders out, OUCH !
> 
> When a subwoofer plays below the tuned frequency [it unloads] OUCH !!
> 
> ...


So the subsonic filter should be set to roll off frequencies at or below the tuning frequency of the box? 

My box is tuned to 30Hz so I would want to set a subsonic filter to around 30Hz correct?


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## 60ndown (Feb 8, 2007)

mattldm said:


> So the subsonic filter should be set to roll off frequencies at or below the tuning frequency of the box?
> 
> My box is tuned to 30Hz so I would want to set a subsonic filter to around 30Hz correct?


yup..


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## chad (Jun 30, 2005)

mattldm said:


> So the subsonic filter should be set to roll off frequencies at or below the tuning frequency of the box?
> 
> My box is tuned to 30Hz so I would want to set a subsonic filter to around 30Hz correct?


Just a bit lower is fine.


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## 14642 (May 19, 2008)

If your box is tuned to 30Hz, a subsonic (actually infrasonic) filter isn't necessary. There isn't much content below that and the excursion of the driver is minimized at the tuning frequency, but not only the uning frequency. You're probably nowhere close to linear Xmax at 20Hz. If the box was tuned to 45 or 50Hz, that would be a different story...


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## mattldm (Apr 27, 2006)

Andy Wehmeyer said:


> If your box is tuned to 30Hz, a subsonic (actually infrasonic) filter isn't necessary. There isn't much content below that and the excursion of the driver is minimized at the tuning frequency, but not only the uning frequency. You're probably nowhere close to linear Xmax at 20Hz. If the box was tuned to 45 or 50Hz, that would be a different story...


So are you saying that the infrasonic filter is not really necessary??


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## GlasSman (Nov 14, 2006)

He's saying it isn't necesary for *MOST* program material.

But is some pinhead puts in a BAss Mechanic CD with 16 HZ sine waves you could be wishing you had that extra measure of protection.


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## MuTT (Apr 4, 2007)

so whats the tuning frequency for an IB setup??? (sorry for the threadjack


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## 60ndown (Feb 8, 2007)

MuTT said:


> so whats the tuning frequency for an IB setup??? (sorry for the threadjack


-4hz 

wiked bass.


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## 14642 (May 19, 2008)

Hmmm...Full power at 16Hz might reach Xmax.


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## MuTT (Apr 4, 2007)

60ndown said:


> -4hz
> 
> wiked bass.


very low, in fact I'm still picking up my intestines that spewed out because of it.


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## yermolovd (Oct 10, 2005)

MuTT said:


> so whats the tuning frequency for an IB setup??? (sorry for the threadjack


whatchu talking about?


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## mvw2 (Oct 2, 2005)

There isn't one.

As far as the subsonic filter, it's just a high pass filter for the sub and does the same task as the high pass filters for mid and tweeter. It's both an excursion and frequency controling device.

What to set the subsonic filter to? That depends on the sub + box setup as well as power use and the crossover slope of the subsonic filter. For the most part, the filter will be around the 20Hz to 30Hz range. The correct point becomes much more obvious if you model up the sub + box and look at excursion use. Some software or spreadsheets show excursion use and may also incorporate the ability to add a high pass filter in the subsonic range and show the effects of this filter on frequency response and excursion use.


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## MuTT (Apr 4, 2007)

yermolovd said:


> whatchu talking about?


trying not to blow up my sub you know  I kinda like it.


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## chad (Jun 30, 2005)

Even if you don'thave a vented box there's no harm in running a HPF on the sub to get rid of some of the wicked low end rise that's not needed and keep the excursion down, you may find that it really tightens things up


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## yermolovd (Oct 10, 2005)

MuTT said:


> trying not to blow up my sub you know  I kinda like it.





chad said:


> Even if you don'thave a vented box there's no harm in running a HPF on the sub to get rid of some of the wicked low end rise that's not needed and keep the excursion down, you may find that it really tightens things up


remember, just an hour ago you asked about subsonic on my subs 
i think its a done deal now.
we should do a session with your monster and try cut it up from the bottom a bit.
but just tell us the truth and say that you indeed like over exaggerated low end .


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