# Does having a sub fireing down at the floor vs upwards make a difference?



## Bupalooga (Mar 15, 2014)

Planning to have 2 IDQ 10" in a sealed enclosure behind the drivers seat in a space cab.
Will having them firing towards the Carpeted floor with the box raised up 1-2 inches effect the sound compared to having them firing upwards towards the roof?

Due to the seat inclination, having the wider cones at the bottom will give me more room to work with as I taper the box off towards the top. They will also be safer incase gear lands on the cone if they face upwards.


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## MacLeod (Aug 16, 2009)

Yeah down firing the sub will increase the output a good bit. It'll be a little sloppier but it'll be louder.


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## qwertydude (Dec 22, 2008)

Downfiring doesn't increase output. All it does is tend to muffle some of the higher frequencies the subwoofer creates, which should be removed by the crossover anyways.

I suppose if the box was very long and the downfiring controlled by a baffle you'd have a quasi bandpass arrangement but then that becomes unpredictable in terms of output.

Downfiring is mostly done to protect speakers without needing to use a grill.


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## cubdenno (Nov 10, 2007)

Boundary loading can increase perceived output. Try it.


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## qwertydude (Dec 22, 2008)

cubdenno said:


> Boundary loading can increase perceived output. Try it.


Boundary loading only works when the sound would actually dissipate due to the sound waves filling a large volume ie a large living room.

When you have a small cabin or trunk volume, the wavelength of the bass sound waves is longer than any actual individual measurement. This means every sound wave pressurizes the volume essentially equally.

This is what constitutes cabin gain and would pretty much eliminate boundary loading because the waves don't dissipate trying to fill a large volume.


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## cubdenno (Nov 10, 2007)

I get what you are saying, but have seen it work in a vehicle. Heck, it's what sold a million bazooka tube subs. Plus there are numerous trials done measuring the output of subs and their various locations in a vehicle. I am not saying it's going to work every time, but it won't hurt the OP. And it may help.


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## qwertydude (Dec 22, 2008)

Boundary loading is not what sold Bazooka subs, they were sold with marketing, part of that was marketing the exaggerated effect boundary loading has with them. But in my experience you're more likely to not get anything with downfiring than to actually get audible gains. Use it to protect your speakers.

In a trunk in a car I've always had more success either firing into the seats to more directly couple the sound into the cabin through the seats or firing up through the rear shelf again giving the sound the shortest possible path into the cabin.

In a hatchback, SUV, or wagon subwoofer placement has almost no effect on the perceived loudness.


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## hurrication (Dec 19, 2011)

qwertydude said:


> In a hatchback, SUV, or wagon subwoofer placement has almost no effect on the perceived loudness.


Sure it does, what makes you think it doesn't?


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## diy.phil (May 23, 2011)

^because when we sit in the vehicle we are actually sitting inside the speaker box (different from home speakers arrangement).


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## qwertydude (Dec 22, 2008)

hurrication said:


> Sure it does, what makes you think it doesn't?


The fact that I've had several SUV's, hatchbacks and wagons because I like their practicality and have tested output with a meter and placement had less than a 1 db difference in output. And when placing the subwoofer closely facing a wall I've had more than a 1 db drop in output when I should theoretically be getting more due to "boundary loading".


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## hurrication (Dec 19, 2011)

I've experienced the exact opposite in a SUV. Rear firing on the passenger side as close to the rear hatch as possible being the loudest, and sitting in the passenger seat firing up being substantially quieter.


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## qwertydude (Dec 22, 2008)

If it's substantially louder when putting the subwoofer further away from you I'd say it's less boundary loading against the rear wall than getting null spots.

Does it change significantly if you have the subwoofer in the same spot and simply face it up vs facing the wall?

Because in every application I've tried, between facing the wall and facing up, had less effect than physically moving the subwoofer around getting closer or further from the listener.


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## Bupalooga (Mar 15, 2014)

Ok, so, hmm, lots of complicated specific situational answers.

But basically it wont have any major negative effects, so ill have them down firing for the previously mentioned benefits! 

Thanks guys and gals


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## miniSQ (Aug 4, 2009)

Bupalooga said:


> Ok, so, hmm, lots of complicated specific situational answers.
> 
> But basically it wont have any major negative effects, so ill have them down firing for the previously mentioned benefits!
> 
> Thanks guys and gals


As cubanno said, it won't hurt ya and it may even help ya. I did it both ways in my Tundra and the sound was the same. I may have perceived that i was getting more tactile impact with the down firing...but that was probably all in my head.

Good luck with the subs!!


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## Jroo (May 24, 2006)

Ive never tried but have heard several pickup truck owners say downfire boxes were loudest in their trucks. I have read this from truck owners that had center console boxes and boxes that were under a rear seat. In both cases they said downfire seemed louder than previous setups.


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## cajunner (Apr 13, 2007)

down fire, traps the wave between the vehicle floor and the box baffle.

this slows down the wave, similar to a horn or bandpass, but it's closer to the horn.

the wave being slowed down from acoustic pressure, creates compression.

a mild compression can decrease distortion levels as well as exhibit mild gain.

2 other things happen:

a mild acoustic filter is applied, which not only helps decrease the amount of mid bass harmonics coming from the sub, it decreases the physical distortion of harmonics, which are audible and can add to the localization of the sub.

downfire, reduces localization, exhibits mild gain, decreases distortion and you have the added benefit of protection for the cones.

downside is the speakers can't have sag factors that eventually lead to blowing out the cones from suspension fatigue. Of course, up fire, is subject to the same limitation.


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## Golden Ear (Oct 14, 2012)

I had my sub facing down at the carpet in my F250 for about a year and output was good but staging was low. It was suggested to me that I face the sub upwards instead and I like the sound much better. This is in the front of my truck for sq so it depends on what your goals are.


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## cajunner (Apr 13, 2007)

Golden Ear said:


> I had my sub facing down at the carpet in my F250 for about a year and output was good but staging was low. It was suggested to me that I face the sub upwards instead and I like the sound much better. This is in the front of my truck for sq so it depends on what your goals are.


was staging higher because you had a midrange component bleeding through the harmonics of the sub frequencies, and the result was bolstering of the mid bass by another direct radiator?

or was it that the sub was vibrating the floor board, and the tactile sensation pulled your focus downward, and when you faced it up, no more tactile transfer?



it could be all about the front sub localization working for you, and not against you.


if the sub is right next to you in the console, or behind you, it makes a difference not to have harmonic distortion coming from the sub and having an acoustic filter help with that, is better overall than anything else you'd do electronically because harmonics from the sub are audible even if you have 72 db/oct filters, since they are a distortion that comes from the sub's physical characteristics, and not a part of the signal itself.


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## Golden Ear (Oct 14, 2012)

I believe it was tactile transfer. The sub is next to me in the center console. It was also bolted to the driver seat rail which was pulling focus down.


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## cajunner (Apr 13, 2007)

Golden Ear said:


> I believe it was tactile transfer. The sub is next to me in the center console. It was also bolted to the driver seat rail which was pulling focus down.


something unlooked for, but possible is that with a downfire you were putting way too much acoustic energy into the floor sheet metal, and the sheet metal itself becomes a secondary radiator that not only provides tactile transfer, but resonant tones that come right off the floor.

hardly anyone actually adds bracing and support to the large flat, thin, and highly resonant metal of the floor to reduce this effect.

You add a bit of dynamat and you lower the resonant frequency of the floor but it doesn't void it out, there's a definite radiator there being careless with your low tones.


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## UNBROKEN (Sep 25, 2009)

Don't forget the rule of thumb to keep the cone 1/4 of the driver diameter above the floor. So for a 10 I'd mount it 2.5-3" above the floor. It's been years since I read on the "why" but I played with it and it seemed to make a difference in output.


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