Design GIGAAMP SubWoofer.

[myanmar]

Hello Friend,

I already designed 5.1 amplifier, satellite spk & sub woofer.
6" 8ohm woofer spk.
You can see in http://gigaamp.com

But i didn't satisfy that.
Woofer amp power is small.
So, I designed bridge/parallel amp with tda2030.( from national )
( Old one is designed in bridge. )

And then I put another 6" 8ohm woofer spk.
Two spk join in out of phase in parallel.

I screwed two spk front to front.
But woofer sound is no good at all.( more disappoint ).
I reduce or increase the pipe of the port ( try-and-error ).
One spk is better than two spk.

Pls, help me for subwoofer design.
sorry for my poor english.

How can I calculate my design?
How can I design my subwoofer?

[nunayafb]

what you did is called an isobarik configuration. When you mount to woofers together like this (front to front) the Vas is reduced by one half, and the box needs to be half the size and the port needs to be more than twice the length, or maybe a smaller port.
If you have the T/S parameters of the woofers then I could give you an idea of what port to use, the box needs to be half size though.
Using the same port or shorter will raise the tuning resulting in a huge resonant peak, making it sound like the sub only produces one bass note instead of the whole bass spectrum.

Hope this helps a little
BTW winisd is free to download and will help you in designing woofer enclosures.

[myanmar]

Hello Friend,

Thanks for the softare.
I will try & test with that software.

How can I get Fs,Qes,Qms,.......?
In our country cannot get that data.
Ohm & watts are not the same which is type on the spk.( made in china or thailand ).

So, How can I calculate & test to get that data of my spk?
Can you give me general calculation for speaker?

Pls, continue help me.

[DigitalJunkie]

Also,be sure to reverse the phase to one woofer (the "front/top" one) so that they move in the same direction. You want them to work together as one,not against each other.

[nunayafb]

How can I get Fs,Qes,Qms,.......?

Ok, now it gets difficult. If you can download Speaker Workshop from the website, and from searching the diyaudio forums you can get a link to the "unofficial speaker workshop manual 2.0" it will help you through the program. you will also need the wallin jig or equivalent, the manual will help you with that, or search here for more info.

I have to warn you the program is hard to learn, especially if you have trouble understanding english. You have two other options:
1. bring the speakers to someone in you area and have them test them.

2. Just buy two woofers (or one good one) from a website like partsexpress or wherever, that includes the necesary parameters, Fs,Qes,Qts,Qms,Vas.

Good luck

Actually, there is a number three option:
3. I randomly selected 5 woofers from the winisd databse, and modeled them as single woofer and isobarik, each time the box size was reduced by one half and the port lenth was increased by a factor of (average) 2.10, the lowest factor was 2.05 and the largest was 2.126, so I would recommend buying an adjustable length port and initially setting it to 2.1 times the length of the one you have and tuning by ear or with a spl meter and a sine sweep function, I think you should be able to get a close enough tune that way.
You can also try this experiment with winisd if you want.

[myanmar]

Hi nunayafb,

You said box size reduce 1/2 & pipe length increase 2.1 times.

Box size reduce when pipe length increase. ( in my woofer ).
Is that right?
Need to calculate pipe volume in the woofer?
Box size will not reduce 1/2 if pipe volume need to calculate.
Box size will reduce under 1/2.


In my subwoofer,
Can I need to calculate bottom of the box volume (between spk & ground)?


Pls, reply me.
Thanks.

[nunayafb]

I am pretty sure you do not need to worry about the volume of the port, I have never heard anyone mention that before. No time right now but tonight I'll check my book and make sure.

I just noticed in the photo that the woofer fires down, are you going to have enough room for isobarik, or are you going to raise the box up?

[JRace]

You must calculate the port volume and subtract that from the final internal volume.

For example, if you need 1cubic ft internal volume and your port takes up .25cubic ft then you must make the internal volume 1.25cubic ft.

[simon5]

Originally posted by myanmar
Hi nunayafb,

You said box size reduce 1/2 & pipe length increase 2.1 times.

Box size reduce when pipe length increase. ( in my woofer ).
Is that right?
Need to calculate pipe volume in the woofer?
Box size will not reduce 1/2 if pipe volume need to calculate.
Box size will reduce under 1/2.


In my subwoofer,
Can I need to calculate bottom of the box volume (between spk & ground)?


Pls, reply me.
Thanks.

If you have a box of 1/2 the size, the port need to be 2 times longer. Smaller box = longer port.

You don't calculate the volume under the box.

[myanmar]

I just noticed in the photo that the woofer fires down, are you going to have enough room for isobarik, or are you going to raise the box up?

1.5cm left between spk back & ground.

If you have a box of 1/2 the size, the port need to be 2 times longer. Smaller box = longer port.

Same thaught.
Will it be OK, if i only increase the lenght of my pipe?
Not reduce of my box.

Is air flow in pipe effected when the pipe is bent?
Because my pipe is nearly Long to the spk height.