Divider

they are not really needed..but do you have adequate bracing between the woofer cutouts??

 

If it were me, I would have them divided....I really am not sure if it is absolutley needed, but I look at it this way.....

If each driver required 1 cu. ft. of enclosure and you had three of them in a 3 cu. ft. box, I am not sure if that is the same thing.....Each driver in the sealed box will perform with the cu. ft. that is required...that means that the sound wave coming off of the back is contained. How the driver reacts and it's control, depends highly on that air space. The wave comes off and interacts with the boundries of the box. When you use polyfill, you slow that wave down, so the wave travels from the driver and bounces of the enclosure, it comes back as sort of a back pressure against the cone. The polyfill slows down this wave so the wave does not come back to put back pressure on as soon (just like if the box was bigger, it would take longer)...That usually translates into deeper (lower freq response) bass....Now if the box was supposed to be between 1.0 cu. ft and 1.5 cu. ft and you put it in a box that was 2 cu. ft. You are not controlling the driver as rigidly and that can translate into flutter and loose (bad) low freq. response.....

In a sealed box, when the driver moves out, it creates a vacuum in the box. That controls the excursion of the driver. When the driver comes back and then moves inward, you are pressurizing the air in the box...The driver will move inward and compress the air...This vacuum and pressure do a great job to control the driver and that controls the bass response....In a ported box, you have no pressure or vacuum...You basically enclose the back of the speaker (usually) and that keeps the sound waves from the back of the driver from crashing into (and cancelling) th wave from the front....You build the enclosure and vent so you tune the frequencies that are allowed to escape....it is important that these are matched to the speaker to make the speaker perform as best as it is designed to...That is why the wrong box can make even the best driver sound like a s s.......


Willy

 

yeah that is a big problem...I'd replace that board or rebuild a box and use bracing between the woofer cut outs if you don't divide them.

It will sound A LOT better and the box will not vibrate apart

 

I'm gonna agree with Azn. The 3-10's do not need to be seperated and I would not seperate them.

 

I would like to make a correction. There is an extreme amount of pressure in a ported box. At low frequencies, the port or vent contributes substantially to the sound output. It does so by increasing the acoustic load at the rear of the driver. This reduces the excursion of the driver. In Fact, the pressure behind the driver at tuning frequency is so great that the woofer is barely moving. You see, at tuning frequency the port makes almost all the sound because the pressure behind the woofer is so great it almost prevents it from moving. Now the pressure behind the woofer decreases substantially as we go below tuning frequency but at tuning frequency or above tuning frequency there is more pressure in a ported box than in a sealed box.

One other thing, we don't let a certain frequency escape. We tune to a specific frequency in order to take advantage of the resonance of the enclosure.

While the pressure/vaccuum analogy is a good one, it is wrong. Acoustic load is what provides control not pressure or vaccuum. Typically, boxes are 2 to three times larger in volume than the compliance of the drivers suspension (I hope I worded that right) which means that while pressure/vaccuum might help in the control it is not the primary source of control.

(I know The Viking is going to add his 25-cents worth here)

 

Ranger I was gonna correct him on that but did not know the words to put it on...nice one though.

Now we wait for Viking and his flux capacitor

 

Good job Ranger!


Working nights till 2;30 in the dammed AM throws me off !!!!!!


My fluxually enhanced capacitor is sitting right here waiting for your presence Azn!!!!

 

well you can take it and shove it up your chicken

 

Hey Willy D, please continue to use the Pressure/ Vaccuum analogy as most people would not understand what is actually going on. But remember it is an analogy not an accurate discription of what is actually going on.

I use the same analogy for my customers, because its something they will understand. But it makes understanding ported boxes much harder, so we are going to use another comparision. There are two things in a box, air and sound waves. Lets pretend we are at a sunny beach front in Miami with lots of bikini clad girls. Blond girls with large...........back to the beach.

The waves coming up on the shore are the sound waves. Put a stick on the water, it represents the air. Eventually the waves will push the stick to shore. But the stick is moving much slower than the waves. Wave after wave comes on shore and the stick is barely moving toward the shore.

Something very similar is happening in the enclosure. The pressure from the sound waves is what is providing control. The pressure from the air itself is moving much to slow.

Hope this helps and yes I use the Presuure / Vaccuum explination all the time

 

Doesn't a transmission line enclosure have no back pressure...just sound waves

Ranger I like the box you designed me...there is virtually no air coming out of the port...just 100% sound waves.

 

Transmission line is an example of a NON-Resonent enclosure. The length of the port (correct term is line not port) Corresponds to the length of the wave. This way the line is actually reinforcing the low frequency that has the same length as the wave (1/4 or 1/2 octave lengths would still correspond to the frequency we are trying to reinforce).

But because it is a NON-Resonant enclosure, I wounder if you might be right.
I will have to look into that.

One really big fallacy is the fact that air moving in and out of a port is important. IT IS NOT. As you have seen. Remember, at tuning frequency the port makes all the sound, so we make the port as big as possible (never larger than the Sd of the woofer, except for competition systems) in order to reduce air velocity. As we reduce the air velocity, the tubulance that the sound waves must pass through decreases. "More Sound"

 

Is it bad to have more port than woofer area???

 

No it is not, but as port size increases past Sd then so does the power needed to make it work at its best. Your box is an example of me not getting carried away. Your woofer Sd should be around 131 sq. in. while your port cross sectional area should be 110-115 sq. in. which means that your port is 85% of your woofer Sd. (I'm rounding because my TI-89 is in the other room).

Your box has super good control of the woofer so you really need to throw a lot more power at it. Lets get to the 700 - 800 watt RMS range.

Watch and hear how much more intense it becomes. As you get past Sd, (like in my van port size is 2.5 times Sd) power needs to go way up. And even with a port this size and 5000-watts per woofer, the woofers barely move at full volume. There is almost no noticable excursion at all.

You have no even begun to see the full potential of your box

 

LoL...wow this makes me excited.

BUT...the 15W4 has died. I bought it for really cheap because the tinsel leads were cut...but I re soldered it. In my box that you design it worked very well but I had it in a 2.5 cu ft sealed box and the excursion was a lot more and it snapped right at where it enters the cone...not even at where I fixed it...But I do very clearly remember when playing the sub full tilt with 500 watts the woofer had very good control and was barely even moving

Before spring break I am ordering an ED 9.1 amp...so I will have and underrated 1200 watts to throw into my box.

Just need a new candidate for the box...any suggestions for a 15 that can handle some power for my box that is under 200 dollars??

 

In a transmission line, there is "back pressure" on the driver. This is due to the fact that the wavelenght on the back side of the driver sees an enclosure down to the point of where the frequency of where the line terminates in supporting the lowest frequency. Did that make sense?????? Also, there most certainly MUST be supporting air mass behind the driver or its dicsplacement limited power handling would be very poor.

 

I stand corrected.....

Actually what you say makes very good sense to me....The sound wave is actually moving in the air, not just the driver pushing air....The driver is pushing a wave of sound that pushes the air.....

I understood the port incorrectly too....I cannot remember where I read that, but it was quite a few years ago.....

Is it true that the sound waves that escape the enclosure via a port are usually of a higher frequency? Ones that are unusable for a sub, so if they cancel each other (front and rear of driver waves) it will be inaudible or basically not important??

Willy

 

3 subs in a sealed enclosure?

I would definitely suggest dividers because those subs may be exactly the same, but they are NOT exactly the same.

when anything is manufactured, there are minor flaws and discrepancies from the original design. You can make 100 things from the same mold and you will invariably have several different versions. may be weight, may be frequency response, may be rigidity.

What I'm saying is that even on a minor level, these three subs will not all respond the same to the exact same stimuli (power and signal). Dividing these subs will ensure that the strengths of one do not become the weakness of the others, and vice versa. Not to mention the integrity of the enclosure as a unit. Use baffled dividers in a ported enclosure, but always use solid dividers in a sealed multi-sub enclosure.

 

We can tune the port at any frequency we want to. Tune too high and the woofer will go out of control at extreme low frequenies. Tune too low and we do not get the desired gain that we might want.

(The Viking is going to yell at me again) I have only built around 500 to 600 boxes so I do not have a lot of experience, but here is what I've learned. Tuning low does not generally mean a lower hit but it does mean that we do not get any relative gain. Tuning high does not mean that we get a high hit, but it does mean that we have a lot of gain. For most cars I like to tune between 35 to 45 Hz. Most of my boxes are tuned between 40-45 Hz. I have never had a customer complain.

There is no cancellation of sound, at tuning frequency the port is making nearly all of the sound. Not the speaker, nothing to cancel.

Do you have access to a graphing calculator? Graph the function F(x)=sin(x) and the function F(x)=-sin(x). Look at the graphs, the are exact opposites and if this was a sound wave there would be cancellation.

Now graph the functions F(x)=sin(x) and F(x)=cos(x). Look at the graphs. The two functions are out of phase by 90-degrees. While there would be cancellation the overall effect would be much less.

Ports are not linear. Normal sized ports will not have any cancelling effect