My latest subwoofer project

[sidd_raj2002]

I am an amatuer to diy of course i have built some subs before but they are all like quci k and dirty and unscientific.

my latest project is a bipolar sealed sub which uses 2 6inch local drivers. and a sony amplifier. i have no testing equipment so i dont know the freq. response of the sub.

it is a 14" cube made with 18mm mdf and some braceing. i used some scrap foam as a stuffing which actually made a lot of deifference in the depth of the bass.

i have heard to a lot of ht subs by now and i can proudly say that this baby will beat any of the entry level ht subs from sony or yamaha or philips (which cost around 150$)
the total cost including drivers 4 this project was 30$ (excluding the amp. cuz i am using a sony hifi systam amp )
i made this sub with lot of help from a friend ( whose name remains a mystry)

[BAM]

Looks like you found something that will work well for you. Adding stuffing increases the apparent volume of the box, so the woofers have a more squishy air spring to compress when the cones go inside the box. That increases the depth of the bass, but the woofers can bottom out more easily at high excursion. So if you bottom out your woofers (they make a pop sound when they reach the inward end of their travel), you should remove stuffing from the box. But since it works well for you, then it's probably best not to mess with it any more. Try putting it in a corner of the room.

[paulspencer]

I am an amatuer to diy of course i have built some subs before but they are all like quci k and dirty and unscientific.

My subs are almost as quick and dirty as you can get right now! Yours looks pretty in comparison. Quick and dirty is a good place to start when you want to try something out.

my latest project is a bipolar sealed sub

Bipolar is a more appropriate term for fullrange speakers. It's really a monopole since bass is omnidirectional. Someone more knowledgeable on this may correct me here ...

[BAM]

Paul is correct in saying it is still considered monopole. Radiation patterns really only make a difference above 200 Hz. However, VMPS uses side-firing woofers on some models as a way to beat room modes.

[sidd_raj2002]

i can see u guys look interested in my project. im only 17 u know this is my 3rd project if u count but its my 1st sub i made a bit scientifically by measuring the valume and all and using 3/4" mdf.

i think its a biploar cuz like in the picture u can only see one side there is another identical driver exactly opposite the one shown in in the picture.
it is sealed and sounds too good 4 the price and casual construction. it can easily out perform any entry level subs from jbl yamaha sony. maybe it wont go too deep like 25hz or 20hz but it is certainly sounding pretty good in my room(which is very big and in which most of the other branded subs dont seem to punch the bass)

[paulspencer]

Sidd, the fact that there is a driver pointing out the back doesn't make it bipolar. In fact I don't think bipolar can refer to a subwoofer at all. Dipole yes, bipolar no.

A fullrange bipole has a different polar response due to the two poles radiating in opposite directions. However, in the bass range, radiation is omnidirectional, hence monopole is the appropriate term.

I believe this is usually defined by the polar response, not the location of the drivers. Otherwise a bass reflex with a rear port, or a passive radiator sub would both be considered bipolar.

At 17 ... that's an early start! I was first interested in audio when I was 16, but it wasn't until I was 18 that I made my first attempt at speaker building as part of a high school project. If they knew anything about audio, I would have gotten a bad mark! Fortunately they knew nothing about speaker measurements and design, so I got an "A" .... *grin*

[m4dm4n]

The positive effect when putting drivers like that is the minimized box vibrations, in the same way when using PR that got very high cone weight.

The sunfire only got 1 PR, that make the box "dancing". If it had been 1 PR on the opposite side it would have been standing still.

[sidd_raj2002]

hey i guess ur totally right abt the bipolar thing. its like i dunno these terms and some guy once told me that this sort of design is called bipolar.(i guess he was wrong )

so can u guys tell me how can i measure the frequency response of the sub? i mean the frequency responce that i'll get when its actually firing in the box.

and u r also right abt the vibrations man, this subwoofer has got really low vibration 1st i wasnt able to understand why this sub is so vibration free cuz all my other subs and many of the subs i have seen seem to get pushed by their own power.

[richie00boy]

sidd,

Glad to see that you are still enjoying your sub

I called this sub a bipolar design as I was using the term to describe the physical layout rather than the response. The others are correct in their descriptions of what bipolar means acoustically.

Their are two approaches you can take to work out the frequency response of your sub.

The first and simplest is to look on the diy subwoofers site I pointed you to when we were going through the design and see how to measure Fc and Qtc. From these you can predict what the response will be.

The second method is to actually run a frequency sweep and measure it. However, this can be troublesome as room interactions can dominate and you need decent quality mic etc.

[sidd_raj2002]

richi i am not able to find the qtc and fc page on the diysubwoofers site. can u post a direct link to such a page.
and wut should i call this enclosure as? sealed?