Free air

Replies (22)

asplundher on 08/12/2004 20:44:25
Any one know of some decent budget free air subs? I've checked a few products at sounddomain but Im not sure if they are designed for that use. They claim in their site that quite a bit of them are but the manufacterers specs call for small sealed so you know how that goes. I rather go by someones experience. Anyway I plan to run them in my girls corsica with about 100 to 150 watts each. Either tens or twelves I prefer.

Bigeazy4387 on 08/12/2004 22:18:01
pioneer makes some good free air subs that are made just for free air

asplundher on 08/12/2004 23:19:39
They have been discontinued and you would be lucky to find a good pair at a fair price. I have installed a pair of the older paper composite models and they performed very good despite the low rms handling. I'm looking for a similiar type sub though that type of setup has diminished from the market quite a bit.

Thanks for the input though!

uochronos on 08/13/2004 02:33:03
look at partsexpress.com i belive when i was kicking around there the other day i saw some free air 10" subs that where 100watts rms... i cant remember model or brand but i distinctly remember thinking about them because someone here asked one before.

at least taht gives you a starting place to look

asplundher on 08/13/2004 07:45:29
They have a lot subs that could be "potential" free air material:

Qts above .61
Fs/Qes ratio still of a sealed nature
relatively low fs
high sensitvity rating

However, there must be some other spec that helps determine for there are other brands (like blaupunkt for one) that says their subs or okay for that type setup. Yet when you look at the specs , they are nowhere close.

One thing also to take into consideration is that power handling will be down by a large margin around 50-65%, so one that has a fairly strong motor structure may also be needed to be able to handle enough power to perform in free-air. This is due to the fact the motor structure will be mainly responsible for the cone dampening.

This also makes finding and choosing one difficult

asplundher on 08/13/2004 10:05:10
I just received a email from Mitek (mtx) about the road thunder series in that the ones with the higher Qts are able to run in that type setup.

It is weird how many subs are claimed to possibly be able to run that way but are not being advertised as so. I also ran a search at crutchfield for free air and you would be surpised what woofers can. However there are other sites that claim the same for other subs that some sites don't mention like sounddomain. Could this be due to some are not doing their homework or are some beefing the product to sell? I don't know but that makes it hard to trust any of them at times.

asplundher on 08/13/2004 12:53:58
Heres a perfect example of what I'm talking about:

MTX Audio Thunder5500 T5510-04- both crutchfield and sounddomain sell this sub. Yet sounddomain states it good for free air usage and crutchfield says it is not. Look at the specs and you'd think with a high Qts of .67 (I believe) that it would be suitable for it.

Could crutchfield be wrong? Being around all this time you would think they do their homework and totally research a product they sell.

Could sounddomain be recommending a usage that could possibly damage the product and worse maybe void the warranty?

Note that both companies are authorized by MTX! So surely MTX wouldn't let an authorized company mislead others about their product, right? So, who is right? I believe these are the kind things (mis-information) that stump a lot of newbies into giving up on installing their own equipment or even purchasing the wrong stuff in the first place.

Remember I contacted MTX earlier and they did agree on the high Qts thing even though the question was toward a different model.

So..... what do you guys think?!!!

swez on 08/13/2004 18:25:05
Can I change you mind about using free air subs? The power handling and bass quality are very inferior to sealed or ported subs. The box is a key element to great sounding bass... even at low power.

Even with minimal effort, you can make a wall, install the subs and seal off the rear baskets with a small to medium sized (rigid) bucket, packed with poly fill or such and sealed with silicone. This will work nicely for low powered subs and add very little weight or size to the overall install.

Swez

uochronos on 08/13/2004 22:23:35
they make the foam baffles up to 15 inches in diameter and i belive 7 inches deep. for a free air sub one of these could help with bass as well

asplundher on 08/14/2004 07:10:25
Don't take it personal but, I consider your suggestions as a means of failure. To me giving up means admittance that it is impossible yet I know it is not. In my past experiences with free air, the results were very pleasing. Enough to try it again. The advantages of a well designed system, in my case, will out-weigh building boxes or other contraptions to manipulate frequency response.

I appreciate your suggestions but, I will continue my pursuit on this project. I have contacted an old colleague of mine who happens to be a certified bench technician/ installer about this subject. He has really shed some light on this subject and the info that is misleading. I have found the missing link that I was looking for and it should help me on this one.

Thanks anyway!

swez on 08/14/2004 17:48:35
Good luck and let us know how it all turns out OK?

Swez

asplundher on 08/17/2004 13:51:43
I have found the specs needed for choosing a sub, however there are not that many out there that fit into the criteria.

Even though you would need a Qts around .6 or higher the Vas cannot be greater than the available volume (of course), and the Qms needs to be a bit higher than most.

The high Qms is what allows some brands (Infinity,Blaupunkt,etc) with a low Qts to be ued in a infinite baffle. Yet, I'm assuming with that kind of combo, their performance is less than appealing than a optimized one.

If you look up the Dayton IB subs specs at Partsexpress and compare them to the Infinity or Blaupunkt specs you will get a perfect example of what I'm talking about.

There is no "black magic" to that kind of setup, just a limited amount of subs that are built with those specs. Some woofers are built with a higher Qms to help with dampening. Others are built with a higher Qes to help with dampening. For free air you will want the Qms. However I'm still willing to bet there are some (maybe not much) out there that will fit close to what I'm looking for.

As far as handling: I don't see the decreased power handling as a problem if you have enough sub surface area to move more air. Think about it: which moves more air? Two 8's or two 12's with the same power handling? So staying away from the smaller subs wil help with that one.

This was kind of a tutorial for those who don't fully understand what is involved with sub selection for "free-air". Hope this helps!

I'll keep you guys posted.

asplundher on 08/20/2004 11:29:22
After doing some extremely extensive research I think I have found at least one brand that is capable. Boss might be the only choice. Though they are not very liked by many, a few of their subs do meet the criteria. One model is very close but I fear I may not have the power to run them. The only advantage I may have is the fact that sensitivity is 95db, and in free air, power handling will be down to 50%. Which will put me within half of the rms. There are a few other Boss substhat are suitable, but I'm waiting to get the parameters for them before I proceed.

Wish me luck!

swez on 08/20/2004 11:32:04
Keep up the good work... we will all learn something from your efforts.

I must say... you are one determined fellow!

Swez

asplundher on 08/20/2004 11:58:56
I appreciate all your support!

Controlling the free air aspect is one that has always baffled me as well as others. Yet I think this is due in part that because building boxes and having high spl is so popular, that the market has strayed away from it. So, in that sense most do-it-yourselfers don't bother to learn that there is more to it than just settling for "sticking something back there and that's it". Afterall it is a form of a sealed enclosure which can be controlled to a point.

I don't expect a miracle, just pleasing results that are good enough to always consider in system planning.

When I'm done I plan on giving a small, but deep, tutorial on the subject since there really isn't one.

swez on 08/21/2004 09:45:57
Good idea. Yes, this is not an application for most SPL or SQL guys. But, OEM car audio is often just that... free air designs in doors and rear deck. The trunk becomes the chamber in free air applications.

However, one still has to figure out a way to block or channel rear bass waves from meeting front cone waves or cancellations and phase problems will become an issue. Greatly degraded SQ is the net result if we don't use a barrier or baffle of some kind. Can't just suspend the sub(s) in air and expect great results. Mids and tweets can work that way.. but not bass.

Keep us posted OK?

Swez

asplundher on 08/22/2004 20:40:05
Well, unfortunately Boss has failed to give me the parameters on the subs I was interested in as they said. That's the main area they lack in (customer support)

However, I have just acquired some Kicker F10A's off of ebay for only 64 bucks (used of course). But I don't mind as long as they operate properly and there's no damage. They did look fairly clean in the pic. Well I'll find out this week some time.

cplkittle on 08/22/2004 23:54:57
Are you atleast going to mount them in some sort of wall to seperate front from back waves? I have seen one vehicle with 2 audiobahn 15's mounted behind the back seat in a small chevrolet cavalier. they used the trunkspace as the box and sealed the back deck. As much as I hate audiobahn, i must admit this setup sounded pretty good.

asplundher on 08/23/2004 17:20:42
Of course Silly! LOL! (just kidding). The front and back wave must be totally separated to get the most out of any woofer in free air. This also applies to midbass.

The thing about free air which I will explain later is that a wide range of woofers can be used despite the misconceptions that we hear. The thing that you must keep in mind is the particular sound that you are trying to attain. Then there are different ways to approach that same goal.

I willing to bet the bad ones were miscalculated or poorly installed.

Why do you hate Audiobahn (out of curiosity)?

asplundher on 08/31/2004 18:23:10
Well, finally received the kicker f10a's but I'm kinda leary about the specs and what kind of sound they designed them for. The Qts is a little low for a true free air sub.

Here are the specs if anyone wants to check them out.

SPL 1W/1M 89.74dB

BL 8.69

Vas, CuFt. 2.88

Fs 32.4

Qms 5.395

Qes 0.440

Qts 0.407

Pmax, watts (Vented) 300

Pmax, watts (Freeair) 200

Xmax,mm 7.68

Freq. Response (Hz) 25-200

Magnet Weight (Oz.) 32

Voice Coil (Kapton) 2"

As you can see, the Qms is on track but, the Qts is quite low. I still will install them before I try to dismiss them. From my research, a subs Qtc will only get as low as it's Qts in free air. Which is supposedly why you should choose between .7 and up. Yet the trunk is still a somewhat confined space, so that might play a role in it's final sound. Afterall the combined Vas is around 5.6 cf. Normally free air should be a factor of 4 or more (opposite of sealed). However we'll see how that theory works once installed.

asplundher on 09/25/2004 18:48:44
Well, HELLO people! It's been a while since I have visited or wrote due to these @#$%&? hurricanes here in Florida. However I'm still alive&well though we had some close calls with over 6 major tornadoes in our area. Right now the weather here in Panama City is lovely and gave me enough time to finish the project.

Now finally it is over and done. And let me tell you guys a thing or two. Whoever doesn't believe that a free air setup is worth trying then I feel sad for you (lol).

Really though, I was impressed. Not just by the setup because I know they work for I have done one before, but from the way Kicker approached the sub design. Remember earlier about woofer Qts above .61 being ideal. Well unless the specs were wrong these .407 subs perform very good. After the install I played a few techno bass tracks, some southern hip hop, and Midnight Star's "No Parking On The Dance Floor" album. The subs handled all frequencies flatly with just a little more oomph in the 40 to 60 hz region. Could be the transfer function. With the Pioneer deck's parametric EQ decreasing 40hz by about 3-4 notches very bass-heavy techno tracks sounded quite natural. I have to even do that with sealed boxes at times so that is good. All other tracks played strongly, yet even, with the EQ set to Flat. With used Eq settings, total volume is loud enough to please while riding around town with windows down. However due to running the highs off the deck full volume cannot be attained.

Heres the setup:

Pioneer deck DEH-1500

Jbl 4" gto coaxial's in dash

Jbl 6x9 gto coaxial's in rear deck

2 Kicker F10a's

Boss AVA-600TR (My JBL 300.1 was used first to test power handling. Later I made the swap because I need the JBL for another vehicle. The Boss of course is not as strong yet it does power both subs with enough authority to be pleased with the matchup.

I equipped the 3/4" mdf baffle board with 3/4" thick 1" wide self adhesive sponge foam weather stripping on the front outer edges to minimize leakage and/or gaps.

Now for anyone that thinks that there is no interaction from the trunk. When the trunk is open the woofers tend to sound a little looser. When closed, the bass tightens up. So with that in mind the trunk does affect performance to a extent. How much can only be determined by your individual setup. It may be possible that Kicker has designed these woofers with a low Qts to insure a lower Qtc since a small trunk may increase the Qtc somewhat.
Remember, a infinte baffle exists when volume is at least a factor of 4. I don't know of any trunks that big, so theres the only connection of why. But what would happen if you used a sub with a already high (.8 and up) Qts and large Vas. It may be possible that with a small trunk closed that the Qtc could go above desired Q (usually around .7). This is assuming leakage losses are fairly low in the trunk. This also could be why you see some other subs (like Infinity, Blaupunkt, etc) also with a fairly low Qts but high Qms and Vas being okayed for free air use under lower power.

This is all theoritcal ,yet not hard to grasp if a little experimentation and research can be done.

Well I think I have written enough for now.

Later fellas! ASP!

swez on 09/26/2004 06:39:37
Interesting... care to summarize your findings and post them on the DIY part of the forum? If you do, try to include imperical as well as tested theories and a conclusion statement.

For those who do not have a good grasp of T/S parameters, may want to define each variable observed and a brief notation on what these parameters mean in layman's terms. (Ie: Qts, Qms, Vas and such)

Hey, good job! Seems that your persistance and excellent research on this design has paid off. Hats off to you there asplunder! CLAP

Swez