just a question about inverting subs, do you have to buy free air subs to be able to invert them? by inverting i mean mounting them with the basket pointing up, and the sub firing into the box.

 

I'm not one of them... but NO.

AJ

 

ok a guy i work with used to work at a car stereo place, and is getting me 3 phoenix gold qx 12's for $150 brand new, I wanted to build a fiberglass box and mount them inverted or something like that.

BTW is fiberglass strong enough to use for a sealed box?

 

Yes. I would recommend using a woven mat as opposed to a stranded mat. A good woven mat is Knytex from US Composites.

When building a fiberglass box make sure to BRACE!! A well braced fiberglass box can be EXTREMELY strong.

 

Most subs play as good inverted as they do normally mounted.But there are a few that will have degraded sound when inverted.All depends on the magnet structure design and basket. Some subs(MTX 8000 series for example) will make a whistling sound due to turbulence from the vented basket on the back side of the spider.
And yes,fiberglass can be used to build a sub enclosure,IF it is done right.I built a sub box for eight Earthquake 12" DBX subs for my Expedition out of fiberglass and bondo.The box weighs close to 100 lbs without the subs,a lot of the weight coming from bracing.

 

I agree. You don't have as clean an interaction between the woofer cone and the air when you have your sub inverted, due to the basket and magnet structure.

 

I've never had a sub whistle. That's not to say that it isn't possible, but it certainly isn't common. I've inverted a ton of different subs, and so far I haven't had any problems. There's more than enough room for the air to escape around the basket. The only point of concern that I'd have is the vented pole piece making noise.

 

While I like the idea of inverted woofers, mainly for cosmetic reasons if the woofer is chrome, IMHO, cone out sounds better.

 

Well,actually the MTX 8000 series and one other sub(I can't remember which,been a while) were the only two I have had "whistle" on me in the inverted position. Sure,most subs will sound okay inverted and not make a difference in a non competition vehicle,but in competition,you may lose a db or two,depending on the basket design and number of subs.

 

you won't lose any SPL nor will you sacrifice sound quality unless you get one of these whistling subs. The SPL is dictated by the excursion of the cone, and the cone is moving the same amount no matter what side the box is on. Sound is created by the driver compressing and rarefracting the air around it, which is a result of the sub's motion. The motion is oscillatory and only controlled by the physical restrictions on the sub (spider and surround), electrical restrictions on the sub (current through the voice coil) and the pressure from the box. That's it. The direction of the sub won't do anything. There's ample space around the basket to eliminate any and all pressure differential around the cone.

As for sound quality... that's not effected either. Subwoofers have a very limited, and very low frequency bandwidth. The highest frequencies that any sub usually reproduces is around 80 to 100hz. I'm not whipping out the calculator for an exact size, but at that frequency the sound waves are still many times larger than the sub itself, so having a basket in the way is like having a fly on your tv speaker... it's too small to matter.

 

JIM,that is good.Everything you said is absolutely correct,in theory. I know you know what you are talking about,so I hope you don't take offense that I am contradicting you.
I have believed that same thing for a long time until I met CEO of Earthquake. This same topic came up while he was at our shop and he gave me a demonstration using another employee's car at the shop. Our regional rep,Sal, used an RTA to measure the spl of two 12" subs in an '01 Honda Accord that were being pushed by a true nominal 1100 watts. With the subs mounted in normal position and facing the rear of the car inside the trunk,the highest recorded measurement out of the first two runs was 147.9db. We inverted both subs for the next test and recorded a high of 147.1db. While this may not seem much of a difference to alot of people, and certainly not a difference on an audible level,8 tenths of a db can mean the difference between winning and losing in the same class with 30 other people. Though the subs being tested did have a huge basket and magnet structure,it was not out of the ordinary for competition or high powered subs.

And I should have clarified myself when I stated the subs will have degraded sound quality when inverted.What I meant was that,while the octaves and harmonics produced by the sub will not be affected, the additional turbulence and so called "whistling"(in certain few subs) can be heard if the subs are in the same listening compartment(i.e. in a truck cab,not in trunk of car.)
All this is from personal experience of 11 years of mobile electronics. If I had not of experienced these myself,I would still believe the same thing you explained to everyone else.
Like I said, the difference is certainly not something to worry about.It is a very miniscule difference to everyday systems.But in spl competition,they go by numbers,and .8 dbspl is alot.

 

i was always informed the only real reason to invert subs was if you have a too small an inclosure, to move the basket and mag outside to box to free up a little space..

-scoob8000

 

That is true in that an inverted sub will free up the internal volume of the enclosure. But one reason why more and more inverted subs are showing up at shows is more of a fad. Manufacturers are designing and building subs with fancy basket designs and lots of chrome. Audiobahn,for example, have chrome baskets in the shape of flames.JL Audio's new W7 has a nice and beefy looking magnet structure that would look nice inverted. It's just another way to help the manufacturer's sell more subs. The only way I would invert a sub is if,like you said,the box needed just a bit more volume(if the box couldn't be built any bigger),or if it was a really nice looking sub.

 

I suspect that the difference in enclosure volume was the primary reason for the change in SPL. If 2 separate boxes were used to ensure the same volume for both tests, I'll bet your results would have been different.

With the sub inverted, you have the equivalent of a larger box. When you're dealing with those enormous magnet structures, it's not a small difference either. The larger box will raise the system Q, which will produce a less peaky response, which will lower SPL.

 

Good point Jim.

 

My mistake.

The larger enclosure will LOWER the system Q, giving a smoother response over a wider range instead of a peaky response within a narrow range like a box with a higher Q would provide.