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1BadAction
09-15-2005, 01:33 PM
Read here... http://www.elitecaraudio.com/article.php?sid=18&mode=&order=&thold=&pagenum=2&totalcutoff=3086

sounds very interesting. cut down on weight AND have good SQ. I need to do the subs in my GTO decklid (free air, they blew), this is looking like a good way. Im more into the sound quality and not having it sound like a retard car, seems like to me that these deliver that.

anyone have experience with this style enclosure?

dma251
10-07-2005, 03:53 AM
Sounds cool, but I think anyone that is willing to sacrifice windows that roll all the way down so they can stuff a 12" subwoofer in their door should reassess their priorities. Is it really that important?

But what do I know.... It's all about what's important to you. Some things you look back on later in life, though, and laugh about it. I think this falls into that catagory...

Seriously, I think it would sound awesome.

sho305
11-21-2005, 11:52 AM
I did that a long time ago, but never with subs. In general you are creating a 'half box' for the speaker to tighten it up part way. It does not work that well from a performance standpoint like he points out. It would be good for jazz and classical because you would have a flat responce. However that is no good for what most loud system listeners want...they want more, more, more! I used that trick on 6.5" and smaller speakers usually in the front of a vehicle. They needed to make some mid-bass for me but had no box; this way they could make some without distorting...it just gave them some dampening and control. I used the foam protectors then made tiny holes in them to free it up to what I wanted.

Really a large box or free air (infinite baffle) would perform better as it still has a pretty flat curve. Problem today is that it is hard to find a good free air speaker. You are only going to be able to go so far for power depending on the speaker, but it will sound nice. I could rattle my head pretty hard that way so I never saw the point of the small box/high power/poor sound combo most prefer today. It is nice if you don't have room for anything else, but then again I was near run off of here for supporting the "OLD WAY" of making good thump. Yes you could hear me a mile down the road, could not see the point of more than that. Four 10"s is my favorite setup.

The reason you want a box or better yet a ported box is because you get a lot more sound for your power...it actually increases the responce of the woofer to more than it would normally have been. Free sound, what could be better? I've played with the 5th orders but still am not that impressed with them. They are not bad when you have no crossover, like home use. Crunch used to make a good free air, the magnet was near the size of the cone in the 10", very heavy.

One problem most do not consider is how the item affects the system. You might use one amp/sub/tweeter and it works like so, then try another and it is complelety different. Sure you can adjust box sizes, crank crossovers around, and turn amps up/down but the components still make a huge difference in how it works. I know, who can afford to buy three of everything to see what works for them? Well you can't. That is especially true with free air woofers because you can't change a thing; got no box to tune. Like I said before, I used the cheapest subs I could find and with the right amps they worked great...better to spend the money elsewhere unless subs are your whole system.

Spalmer
11-29-2005, 09:43 PM
This setup can work rather well, but I would definately recommend having it done professionaly. Unless you have a VERY HIGH degree of experience in this area, this is a very complicated enclosure to build. Also, you may want to build the entire enclosure out of fiberglass if you are trying to save weight.

The most difficult part of this type of enclosure is "tuning" it. Unless it is done perfectly, it will not have the sound quality you are expecting. The other part to this is to make certian that you soundproof the entire rear deck with a few layers of dynamat, brown bread, or other type of acoustical treatment. otherwise the rattles will make it terrible also.

I have been installing professionally for many years now, and I can tell you that the first time you build one of these enclosures will not be very nice or pretty. It will take a few tries to get one that fits well, sounds good, and is solid. Let me know if you have any other questions about this install, I will do my best to give you some assistance.

Steve

1BadAction
11-29-2005, 09:58 PM
thanks for the insight steve. Is it possible to build and "tune" a box with the speaker outside of the car, or is it a MUST that its tuned in the car, in the spot it will sit? I'm not really fond of having most of the interior out of my car taking up space in my house when I'm working on this.

funny, I posted this question on several "audio" forums and most answers were like "an A-what?" LOL

Spalmer
11-29-2005, 10:11 PM
The woofer needs to be tuned to the enclosure, and the enclosure needs to be tuned to the trunk size.

The point to the enclosure is for the membrane to allow enough pressure to pass to make the woofer "feel" as if it is in a larger enclosure, without letting too much through and allowing the woofers cone to "unload" and get out of control (and sound like crap)

So, to tune the enclosure you need to calculate how much area (LxW) the membrane is, what material you use for the membrane, how thick the material is, and what you sandwich it between. There are MANY schools of thought on how to do this. I would recommend using the pink fiberglass insulation, and try a few different thicknesses before deciding on one. For the outer two sides, you need some type of metal grating to sandwich the insulation in. It needs to be strong (cannot flex) but will allow sufficient air to pass through the membrane. The less space the grating has for air to pass, the bigger the membrane will be, and the thinner the insulation.

There are MANY variables to this, keep me posted!!

Steve

sho305
12-01-2005, 12:19 AM
The sub will drop off in low frequency with no enclosure, and drop off more if there is a poor baffle between the front and rear. You will have some bass, better response at higher frequency like say 200hz not 50 where you want. But you will have low bass, just not that much. As you tighten it up you will get more bass, but the curve will get higher and then you get little super low bass, good bass at 50 and up, little more at 200 (the sealed curve in below link). Even tighter and you get no 50hz and tons of 200hz (the small box). You never hear that much of this because you typically have a crossover killing 150 and up. What also happens at the same time is the speaker starts out loose with no dampening from the air...that helps make 30hz sound but can't handle any power or the cone gets out of control. The tighter it is the more it can handle, but the more your bass hit moves up to a higher frequency. It is very hard to hear the sound response doing it by ear but possible.

Here is a graph of a sealed box compared to a ported box to help show it. http://basszone.stryke.com/deonspace/pics/Difference%20in%20SPL%20between%20Ported%20and%20Sealed.gif The ported box is more 'loose', though it still has some of the control of the box enclosure...infact this one has more control below 9hz. Anyway note how the sealed curve is flat, trails off smoothly. The port curve has a bump at 20hz, right where you want it to work harder; that is why they are killer if you can use them. A tighter box will cause the curve to drop faster as frequency gets lower; but start dropping later. No box at all, it would start dropping sooner at high frequency but end higher than the box...because there is less dampening on the cone at very low frequency than with the box....and that graph is of a fairly large sub box to have that long of a drop off. A tight box hardly gets down to 100hz without dropping like a stone.

So not the same as a box, but your controlled vent will have sort of the same effect. With no insulation it will be weak and loose, too much it will be tight with no bass...you have to find the happy medium.

When I did rear decks in the old days:) I made a panel of ply that fit the whole thing to mount them in...but those old cars were easier to do that in back then. That got rid of lots of rattles. I still mounted them faced into the listening area. I often sealed the cracks with that butyl tape they used to put windshields in with before urethane.

Spalmer
12-01-2005, 12:41 AM
Sho,

The enclosure I am speaking of is ALMOST SEALED, and just big enough for the sub to fit.. It has a "membrane" (an air-permeable sheet which has frequency-dependent acoustical resistance properties) The membrane vents to the trunk-side of the enclosure, while the sub plays into the car side.

Physically, the aperiodic membrane isn't for every car. It requires sealing the trunk from the passenger compartment in an air-tight manner, as well as sealing the trunk from the outside for best results. The drivers are then mounted into the baffle between the passenger compartment and the trunk, as would be standard in an infinite-baffle/free-air set-up.

Not all woofers will work correctly in this enclosure. While several physical factors affect AP performance (lightweight stiff cone, good power handling, and SVC subs seem to work better), the single most important spec to look for is the Q factor of the sub. While Qes (electrical Q) and Qms (mechanical Q) can vary widely, it is the woofer's Qts (total system Q) that determines candidates for this type of enclosure. ANY WOOFER WITH A QTS OF .45 or LESS CAN WORK VERY WELL IN AN AP ENCLOSURE

You are correct that this type of enclosure can sound absolutely HORRID if it is done wrong. However, I have heard them sound FANTASTIC in a few systems. I think that if he places an 8" or 10" woofer (or even two!!) in the rear deck, this may be exactly what he is looking for.


Steve

sho305
12-02-2005, 10:03 AM
I read the article, that is what he wants to do right? I was trying to explain how the curve changes with tuning, maybe I did a poor job but that made it a lot easier for me to know what to listen for when using just the ear to tune. The graph is just an example.

IMHO I would search for different subs before I did this, though I don't know what ones blew out to start with. I liked 2 10" in the rear deck, and 4 was better yet. One would not do much that I ever saw and if you want real thunder 8"s can't handle it. One of the best systems I ran was 4 10s, and they were the cheapest $15 pyramid subs I could find. Used a 300w amp and they worked very nice all free air. Can't seem to find the heavy paper cone ones today though, the poly did not work as well. Two in deck and two in back of back seat. It had plenty of thunder for listening. Also amps make a difference, some have more dampening and can run free airs harder than others. I had a Blaupunkt 120 amp that ran them harder than a 300 pyramid or 300 coustic...in another setup (w/box) that amp didn't work as well. That car was an old T/A and had that small trunk that is ideal...that helped. I had better subs later but they didn't do any better.

It was a good writeup but I think most (and he warns about it) will not be happy with the results. We put foam sheets over the subs to give them more control. We tried this and that, but it just does not sound good; it does not give you anything like a box does. Sure you can put a 1000w amp on something today and force it to work, but what challenge is that? I was pounding with 60w/channel on a quality amp...though I blew 30 amp fuses on it. I just like the more efficient setups I guess. What you are doing, is making a filter that will slow down the air from the sub...and thus the sub will not travel as much. A good free air would have braking coils on it anyway....if you are trying to slow those down then you must require ear plugs in the car and are pretty serious...and you will have to go with a box.

By all means, don't take me as negative on this...build any crazy thing you want! I made all kinds of boxes, vents, and crazy stuff over the years and it was lots of fun actually. If you really need this baffle in your setup for X reason, do it to it and let us know how it works. I can't know exactly what you have over the PC.

As far as sealing the trunk for free air mountings, I don't believe most of that in my experience. IF the trunk is small enough to be a box for the subs maybe it matters....but likely not. You must seal holes near the speakers, the speakers must be sealed from the rear to the front of them for a distance away from the mounting areas. I could open my trunk and you could barely notice the difference in sound at wfo inside the car, with 4 free air 10s. I even had open 6x9s in the rear deck too that worked fine and didn't pump much. Later I covered them, but it didn't really matter. They were right next to the 10s, about 4" between at most.