Is this true about ported subs in a car?

[mazeroth]

A guy on the Polk forum was asking if he should go ported or sealed for a car sub. I said the following and it got replied to with the following. Who is right, and why?

Originally Posted by Mazeroth
nesticle, go sealed. The cabin gain will make up for the sealed sub's response drop and give you a pretty flat response. A ported sub's tuning frequency will get overcompensated with the cabin gain and sound like poo poo.

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common misconception in car audio
-Cody


I thought I was right but I could be wrong.

Thanks!

[xstephanx]

well cabin gina in a car doesnt work out to 12db an oct perfectly cause there ARE losses, so id estimate 6dboct maybe 8. and with that if you tuned a ported sub low, it woudl be fine.

BUT IMO hes wrong, since if you model the average proted setup in a car you already end up with a peaky box(ive seen +5db at 35hz number times) in fact most car audio guys just tinker with box sizes, if you wanna go lwoer, go a bit bigger and abit lower tune.

so when it comes down to it most car applications are peaky anywy since alot of the drivers are high QTS and high FS.

BUT if i wanted a car setup, id prolly go big ported and peaky, blow your brains out with bass, thats all they reaally want, and as long as theyre not getting that much distortion, and reaches deep enough for most rap music(30hz maybe a bit lower) strongly, its sq.

THIS IS NOT TO OFFEND TRUE AUTOMOBILE SQ ENTHUSIASTS!!! i know youre out there, i know you exist and i know that your systems are impeccibly designed and probably sound fantastic, im just describing the average car audio guys idea of SQ. no offence.

[Eva]

Vented subs inside a car are only OK if some care is taken to equalise the otherwise peaky resulting response. Examples:

- Low (below 35Hz) tuning inside big lossy cabins, like vans with a lot of seats and weak wall and ceiling frames.
- Low tuning with high efficiency, low Qts and high Fs drivers (from PA, rarely seen on car-audio) mounted in undersized boxes, resulting in a smooth in-car frequency response.
- Active equalisation involving a little (-6dB or so) notch tuned slightly above the tuning frequency, usually at 45Hz.
-6th bandpass enclosures designed in such a way that the front chamber provides more boost at high bass frequencies that the rear chamber provides in the low end (inside the car).
-Vented boxes undersized and intentionally tuned to have a low Q (around 3). That's usually achieved just by placing a vent in a corner with relatively small cross-sectional area. Such a vent provides very little gain (1dB or so) and thus sealed-like frequency response, but it improves power handling dramatically as cone excursion is usually reduced by more than 50% across a quite wide frequency range (around port tuning).

Of course, the usual "brute-force" bass reflex tuning practices are not suitable for in-car use because they result in a sort of peaky bass quite frustrating.

[Volenti]

Originally posted by Eva


-6th bandpass enclosures designed in such a way that the front chamber provides more boost at high bass frequencies that the rear chamber provides in the low end (inside the car).

I do a similar thing with 4th order bandpass (rising response instead of a flat pass band), but not all drivers are suitable for this.

I have also had good success with short, heavily packed transmission lines.

[Puggie]

I've found cabin gain to usually be about 8-9dB/Oct starting around 60-90Hz depending on car, big cars start lower. because of this I find sealed boxes tend to work better generally but ported can work well if designed with this response in mind.

[paulspencer]

Sealed is easier, but you can't really generalise. For SQ you should match the cabin gain to the rolloff, and you can do this with either sealed or vented.

You can find measured examples of cabin gain at www.diysubwoofers.org

It's quite easy to get a vented subwoofer with a car sub driver to match cabin gain. There is the risk of unloading below tuning to consider where you have rare examples of music with VERY low high amplitude bass.

You would think that typical cabin gain of 12db/octave below 60-80 Hz to mean a sealed box. If your particular design involves a situation where output is xmax limited, you could have a peaky response and then eq out the peak to get flat again, then reduce excursion demands on the driver, or reduce distortion.

[Puggie]

I'm getting a dead link for the cabin gain examples on diysubwoofers site, anyone got another link or can point me in the right direction.

[paulspencer]

Ahhh, you're right, it's gone now. You could contact John and DB at AE speakers to see if it is located somewhere, or if they still have the info

[micb]

That top post is wrong! Ported enclosures in cars is fine if you know what you want from the response and design it with that in mind.

I measured in sealed enclosure car response with a mic and then designed a ported pox provide an almost completly flat resoponse in car, with tuning low like 26hz i was able you pull most of the group delay around fb to area where it is less noticable.

I managed to get a almost flat response between 22hz and 62hz.

It sounded very good, better than some top sealed installs I have heard.

[mandd]

i have a jl10w6 with 500 watts going to it the box i built sounds good but i was wondering if shortned the port if it would sound better