# Ported enclosures need infrasonic filters



## FG79 (Jun 30, 2008)

My good friend who is excellent at tuning sound systems (home & car) tells me that the typical ported enclosure volumes for car audio are almost always too small to be ideal, in the SQ sense. 

By making the enclosure quite large, you gain the efficiency needed to handle the very deep bass frequencies without a filter. Naturally you will have to tune the port properly, but its doable and he said he's never had any problems.

When I say large enclosures, I mean they are quite large. For a 10" sub, in the 3-4 cubic foot range, 12" 4-6 cubic feet. I won't even get into 15" but wouldn't be surprised if 10 cubic feet! 

With these sizes you get the benefits of a low QTC box with greater efficiency, and no need for a filter. 

Naturally you cannot recommend these sizes to most people since it would be a massive turnoff. In home audio you do not have this problem because you have for the most part unlimited space. At least nowadays.....the JL Audio specs for their vintage 10W1 calls for 2.5 cubic foot ported. Morel for their 10" SW10 Elate woofer, calls for 2.8 cubic foot. 

When I look carefully at the enclosure sizes for home audio speakers and subs, they tend to reflect these larger sizes. A floor standing full range speaker with a 6.5" woofer probably is in the 2-3 cubic foot range, vented. And nobody uses infrasonic filters in high end home audio. 

Anyone build a large ported enclosure around the ranges I specified above?

I want to go out and do this myself but do not have the proper vehicle at the moment.


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## jp88 (Jun 25, 2007)

The need for a infrasonic filter on a ported enclosure has to do with the tuning frequency not the enclosure volume. Below the tuning frequency a ported enclosure no longer provides mechanical dampening for the driver


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## Ray21 (Oct 19, 2009)

Home audio subs are typically tuned much lower than car audio applications, especially the very large enclosures you're talking about - LLT setups are typically tuned in the teens. No need for an infrasonic filter.


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## 07azhhr (Dec 28, 2011)

These large size boxes provide a very very low tune down below the 20's typically. With the much less musical content at these frequencies it is said that the need for a subsonic filter is reduced if not removed.


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## Oliver (Jun 25, 2007)

Unloading is what we are talking about.

When the subwoofer plays sounds at full volume ( as opposed to 1/2 or 1/4 or 1/8 - filtered ), with no control from the enclosure ( lack of air spring ), think Over-excursion or Xmaximum and Xmechanical ( being surpassed with violent force = voice coil damage from hitting back plate.


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## Hanatsu (Nov 9, 2010)

Probably necessary if you tune above 40Hz. Set it 10Hz below Fb (or so)...

I never use a HPF with vented boxes if they are tuned in the low 30's or below. Small risk of unloading, well unless you're listening to music with lots of content in the low 20's... 

Answer to the OPs question: It depends...


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## Hanatsu (Nov 9, 2010)

FG79 said:


> My good friend who is excellent at tuning sound systems (home & car) tells me that the typical ported enclosure volumes for car audio are almost always too small to be ideal, in the SQ sense.
> 
> By making the enclosure quite large, you gain the efficiency needed to handle the very deep bass frequencies without a filter. Naturally you will have to tune the port properly, but its doable and he said he's never had any problems.
> 
> ...


"Too small enclosures" Hm... Car audio subs are often made for reproducing deep bass in small enclosures, unfortunately sensitivity will be low for such driver. Efficiency however is at a maximum point where Fs/Fsc ends up (if we're talking about sealed enclosures or IB), where Fsc ends up is a function of the drivers T/S parameters combined with a given enclosure size. We can't generalize what's a small or big enclosure for a speaker just because it's a 10" driver. 

Small ported enclosures with low tuning tend to sound best without processing in the car imo. If you got EQ, build a large enclosure (relative to the driver's T/S parameters ofc) and then you bring down the peak created and gain efficiency that way. Fyi, I use a home audio driver in a relatively large vented enclosure with low tuning (25-26Hz or so), no HPF applied.


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## minbari (Mar 3, 2011)

jp88 said:


> The need for a infrasonic filter on a ported enclosure has to do with the tuning frequency not the enclosure volume. Below the tuning frequency a ported enclosure no longer provides mechanical dampening for the driver


this is the reason behind it. most people tune a ported box to 30-35hz or so. so under those freqs you will unload the sub. tune for 25hz and the likely hood that you will unload it is low since there is very little content down there, so you might get away without an SSF.


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## syc0path (Jan 23, 2013)

Your friend is right, but just becuz u can, it doesn't mean u should. Boxes that big are impractical for the automotive environment. But u will also lose response in the higher bass freqs w/ a box that large. Again, that's something that's ezr to address in a home setup than in a car.


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