# Using Subwoofers in Free Air when they are not designed for it



## AMG55E (Jul 29, 2018)

I want to upgrade the 2 rear deck speakers in my car. The speakers are 6.5 inches. I could only find one decent subwoofer that was 6.5 inches. It's a JL audio 6w3v3-4. I plan on buying two of them and running them in parallel. I will be powering them with a JL audio XD300/1v2. 

These speakers are designed for a sealed or ported enclosure. But I want to use them free air. I want a factory look. I don't want the box in the trunk and I'm not even sure that having a box in the trunk will sound the best anyway, because there is a lot between the trunk and the cabin (back seat, gas tank, insulation from trunk, and insulation between rear deck and deck liner). 

Car audio shops are very hesitant to install the subs for me because they say it will sound terrible. I know it's not ideal but I don't expect to win any competitions and I don't expect you to hear me coming down the street. I just want something that sounds better than the factory speakers. 

What should I do? Will those subs sound that bad in free air? Have any of you, used subs in free air that weren't designed for it?


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## miniSQ (Aug 4, 2009)

Think you could fit this in?

https://www.parts-express.com/tang-...source=google&utm_medium=cpc&utm_campaign=pla


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## EFMax (Jun 25, 2018)

Back in the day, long before boxes were built into cars for bass, we use to always run our speakers on the back shelf (free air) back then they sounded good. These days, speakers that are okay in free air are nearly always speakers that would work well in big boxes and often had quite stiff suspensions - the chances are that your speakers are nothing like this but if you do try them with no correct box underneath them, then don't go all crazy on them, at least be gentle and see how things go.. and be honest about what you hear.


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## Justin Zazzi (May 28, 2012)

Remember infinite baffle is just a really large sealed box. That JL 6W3v3 has a Qts near 0.5 and an Fs near 40hz and a really long Xmax for what it is, all ideal for infinite baffle in my eyes. You can add a little bass boost to the lowest octave (like a Linkwitz transform) and get whatever bass you want out of it, so long as you don't listen super loud. A pair of these running in parallel off the amplifier you chose shouldn't be a bad combination if you're not completely clueless with the volume knob.


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## AMG55E (Jul 29, 2018)

miniSQ said:


> Think you could fit this in?
> 
> https://www.parts-express.com/tang-...source=google&utm_medium=cpc&utm_campaign=pla


It would not work. I'm very limited in the space that's available and the oval shape just won't fit.


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## AMG55E (Jul 29, 2018)

EFMax said:


> Back in the day, long before boxes were built into cars for bass, we use to always run our speakers on the back shelf (free air) back then they sounded good. These days, speakers that are okay in free air are nearly always speakers that would work well in big boxes and often had quite stiff suspensions - the chances are that your speakers are nothing like this but if you do try them with no correct box underneath them, then don't go all crazy on them, at least be gentle and see how things go.. and be honest about what you hear.


Will do. Thanks


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## AMG55E (Jul 29, 2018)

Justin Zazzi said:


> Remember infinite baffle is just a really large sealed box. That JL 6W3v3 has a Qts near 0.5 and an Fs near 40hz and a really long Xmax for what it is, all ideal for infinite baffle in my eyes. You can add a little bass boost to the lowest octave (like a Linkwitz transform) and get whatever bass you want out of it, so long as you don't listen super loud. A pair of these running in parallel off the amplifier you chose shouldn't be a bad combination if you're not completely clueless with the volume knob.


Thanks for the info. If I did get crazy with the volume for whatever reason, do you think the subs would be able to handle it once or twice, or is there a chance of sudden failure? I'm assuming if it didn't fail right away, it would still shorten the life of the subwoofer, correct?


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## miniSQ (Aug 4, 2009)

AMG55E said:


> Thanks for the info. If I did get crazy with the volume for whatever reason, do you think the subs would be able to handle it once or twice, or is there a chance of sudden failure? I'm assuming if it didn't fail right away, it would still shorten the life of the subwoofer, correct?


just set your gains low, and maybe chose an amp that has a subsonic filter instead of the JL?


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## Justin Zazzi (May 28, 2012)

miniSQ said:


> just set your gains low, and maybe chose an amp that has a subsonic filter instead of the JL?


This is a very good answer to your question!


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## JCsAudio (Jun 16, 2014)

Yup, power handling goes down significantly when subwoofers are run free air or infinite baffle.


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## gijoe (Mar 25, 2008)

Most importantly, build a baffle for them.

Infinite baffle works very well in a car, but infinite baffle only works when you separate the front and rear waves of the speaker. The sub produces the same wave in the front of the speaker as it does the back of the speaker, only they are 180 degrees out of phase from each other. Either the front, or back wave will sound really good in a car, but not both. If both the front and rear start to interact with each other, they will cancel each other out and you'll lose output, as well as wreck the frequency response. 

Infinite baffle setups require a baffle that separates the front and back wave, preventing them from interacting. If you want those subs to sound good you need to prevent the front and back waves from interacting by making a baffle on the rear deck, and behind the rear seats. If you can prevent the rear wave (from the bottom of the speaker) from getting into the cabin area, you'll have really nice bass. If you just screw the speakers into the sheet metal and call it good, you'll have sloppy, quiet bass.


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## sqshoestring (Jun 19, 2007)

If it were my car I would find a cheaper set of 10" subs with a high qts/low Fs and hang them under the deck blowing into the 6.5 holes. They should outdo any 6.5 easily, have a lower Fs/more power handling/more efficiency to start with, and long as you have a little room under there cheaper subs are usually not that deep maybe less than 3" or so not much more than 6x9. You need a baffle under there large enough to fit the cone at xmax though, or at least a ring above it, but a baffle makes it easier to attache everything. Keep your grilles on top. In my experience you can blow through a hole like this that is half the size of a sub easily. I don't know if that is true with a big xmax sub, but a typical old sub it is. Or use 8s if 10s don't fit, its better than 6.5 either way but the cheaper 10s are a great way to go in this case and get you some real bass. Long time ago I ran paper pyramid tens like this on 50-75w/ch and they did way more than I expected lol, so I put 4 in the deck and it was even better. If you can't fit them, well then you are stuck with 6.5. This assuming you want subs back there, not speakers, or I would say do the same with 6x9/7x10/coax 8s/etc.

When I did this I usually made a baffle out of cardboard, when it was right I cut it out of 3/4 ply, spray canned it flat black, and mounted it in there with weatherstrip foam in top to seal it. Premount the subs on the baffle to make it easy to get them in if you do them last.


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## Iamsecond (Jan 3, 2017)

There is a reason car audio shops are hesitant. Unsatisfied customer can cause issues. Lol. Basically it will not stop the upgrade sickness, it will start it. To get a lot from ib install you need to build a baffle on the back deck and probably another one behind the seats to seal off the trunk from the cabin. And then the term “ no replacement for displacement” comes into play. A good pair of 10s or 12’s minimum will give a super sweet low end but larger subs are better in ib installs. The jl is a good speaker but will not give much as far as low end. I love ib installs and have done a lot of them. As a matter of fact my home theater has 2 ib subs in the attic. Best bass there is IMO.


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## sqshoestring (Jun 19, 2007)

Back in the old ancient days we put in IB 8s and 10s all the time with no baffle, just a small one on the rear deck for mounting and the seat was not touched. Often that was closed off but just a thin panel to cover up the seat parts. But that was low power with maybe a 300w old school amp at max. It worked fine. When you start shaking the car, you have to do a lot more. My 15s have solid 3/4 ply or doubled ply over the entire baffle. Starting nearly at the bottom of the glass, under the deck to the crossbeam, around the beam, down to the floor and the center is doubled. It is screwed into the floor, the opening sides, and the deck. All of it is mounted on foam and screwed tight to it, and the deck to crossbeam is glued also. And these are cheap 15s, I only run 500rms on them. Yes ply is lighter and way easier to work with in this case, and likes screws better lol. Anyway it seems to work fine for what it does, which starts right at about 25hz.

He is right, if you could mount a single 15 in the center of your rear deck you would fall out of the car in disbelief of how much bottom it made. Larger cone is a lower Fs, more efficient, its just better if you can fit it.


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## AMG55E (Jul 29, 2018)

Just an update for everyone... I put the subs in the rear deck and it sounded pretty good. Better than the factory speakers. But there was one problem. 

The subs were rattling the deck so much that it was killing the sound. The rattling was so bad I had to turn the bass down and just keep the head unit at a very low volume because I couldn't take it. It was that bad. 

I was so worried about the performance and sound quality of the subs in a free air setup, that I completely forgot these subs are a lot stronger than the factory speakers. I overlooked this one obstacle. I ended up having the JL subs and amp taken out and I had the factory speakers put back in. I will just return the amp and subs.

You're probably wondering why I don't go ahead and just add a box to the trunk. I won't do this right now because who's to say that the trunk won't start rattling or the quarter panel of the car. I just want to enjoy the radio right now without having the worry about getting the audio system to sound perfect. Right now it's good, not great but it's good and I can enjoy it. Most likely I will add a box eventually. And at that point I will be prepared to also deal with any rattling that might occur.


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## Bayboy (Dec 29, 2010)

Years ago when trunk baffles first became popular, there were plenty of subs "designed" for it in various sizes. Now people have built up in their minds that if you don't have a certain size, it won't perform. Not sure how that has ever made sense. I've never believed in that and still use a set of 8" in the rear deck to this day with much satisfaction. It's just a matter of finding suitable subs since labeling & marketing can obscure viable options.


As far as rear deck rattles, that's almost a guarantee, but there's a workaround. You may not want to build anything extra, but a manifold, in this case, has its purpose and is very simple to build. For one, a dual opposed manifold will heavily reduce vibrations and allow a much higher output. Secondly, the design naturally allows for more cone area which is always a good thing even if you aren't looking for a lot of output. I use a pair of 8" in a dual opposed firing through a single hole made for one 8". The difference between one sub flushed in the deck vs the manifold is night & day. Like you, I couldn't turn the single up much before rattling like hell. Now, the pair can get a little boogie level to them without issue and almost no deadening done. No way in hell I would return to standard mounting after experiencing that. 


You could manifold the set you have into one hole while closing off the other, or you could spring for another set and run another manifold on the other side as well. I highly doubt anyone would be less than impressed after hearing it in action unless just being cynical.


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