Need help building a subwoofer box.

[AB_Razer]

Hey! I am planning to build a new enclosure for the subwoofer from my 2.1 speaker system. Its a 4 inch driver. The factory made box is a bandpass enclosure with one port. I want to build a ported box to make the bass sound more natural. These are the dimensions that I figured out would be good... Length x Width x Height - 4.5 x 11 x 9... this equals to around 0.25 ft^3 box volume. I will mount the sub in the centre of the 11 inch mdf panel. Now one thing I have not been able to calculate is the port size/length/diameter. The amplifier's bass output is rated at 20w RMS and the subwoofer is audible at 40hz after which it hardly produces any good bass.

With the new box I want the bass to sound slightly boomy, warm and as accurate as it can be in a ported box.

Please help me calculate the port dimensions. Also I would like to know if the box dimensions are suitable for the sub driver.

 

[TLS Guy]

Hey! I am planning to build a new enclosure for the subwoofer from my 2.1 speaker system. Its a 4 inch driver. The factory made box is a bandpass enclosure with one port. I want to build a ported box to make the bass sound more natural. These are the dimensions that I figured out would be good... Length x Width x Height - 4.5 x 11 x 9... this equals to around 0.25 ft^3 box volume. I will mount the sub in the centre of the 11 inch mdf panel. Now one thing I have not been able to calculate is the port size/length/diameter. The amplifier's bass output is rated at 20w RMS and the subwoofer is audible at 40hz after which it hardly produces any good bass.

With the new box I want the bass to sound slightly boomy, warm and as accurate as it can be in a ported box.

Please help me calculate the port dimensions. Also I would like to know if the box dimensions are suitable for the sub driver.

First of all you won't get much bass out of a 4" driver.

Next I can't design a box for you without knowing the Thiel/Small parameters of the driver. You need to either get those from the manufacturer, or purchase the equipment to measure the T/S parameters.

Bottom line, for an unknown 4" driver you are wasting your time.

 

[AB_Razer]

Can someone atleast point me to a guide that could help?

 

[AB_Razer]

First of all you won't get much bass out of a 4" driver.

Next I can't design a box for you without knowing the Thiel/Small parameters of the driver. You need to either get those from the manufacturer, or purchase the equipment to measure the T/S parameters.

Bottom line, for an unknown 4" driver you are wasting your time.

I don't have the Theil/Small specs of the sub driver. And I don't think its worth it to get the measuring equipment for just this project.

So now what I want to know is whether a sealed box can be built without knowing the theil/small specs... because it seems like a sealed box is much simpler to built.

I know that a 4" driver is not as powerful as some larger subs out there but still it does pump out some decent bass and I want to make it better.

 

[TLS Guy]

Can someone atleast point me to a guide that could help?

There is no help beyond what I have just told you.

Any speaker enclosure has to be designed specifically to the driver on question. You can not calculate box dimensions and porting without the all important T/S parameters of the driver.

This is how you measure them.

You need to educate yourself on how to design and speaker first. You will learn pretty fast you can not make a sub with a 4" speaker. Getting to 40 Hz is very good for a 4" speaker. You will not get to sub range with a 4" driver.

If you are interested in building a sub, you need to educate yourself and then purchase a driver worthy of your efforts.

Bottom line: - trying to build a sub with a 4" driver is idiotic and not possible.

 

[TLS Guy]

I don't have the Theil/Small specs of the sub driver. And I don't think its worth it to get the measuring equipment for just this project.

So now what I want to know is whether a sealed box can be built without knowing the theil/small specs... because it seems like a sealed box is much simpler to built.

I know that a 4" driver is not as powerful as some larger subs out there but still it does pump out some decent bass and I want to make it better.

If you put a 4" driver in a sealed box it won't go below 100 Hz. The Fs of a driver basically sets the lower frequency limit, in fact it will be a little above for a ported enclosure, and for a sealed enclosure two to three times Fs. Sealed subs even with large drivers need Eq. In fact sealed subs are more difficult to design and need expensive robust drivers that can handle a lot of power.

Your problem is you don't know what you don't know.

To design any speaker some basic knowledge of physics is essential.

Unfortunately trying to assist someone to design a speaker who is not conversant with the very basis of what is involved is beyond the scope of this forum

You are welcome to come back when you have completed the required body of study. Right now we can not help you.

 

[AB_Razer]

There is no help beyond what I have just told you.

Any speaker enclosure has to be designed specifically to the driver on question. You can not calculate box dimensions and porting without the all important T/S parameters of the driver.

This is how you measure them.

You need to educate yourself on how to design and speaker first. You will learn pretty fast you can not make a sub with a 4" speaker. Getting to 40 Hz is very good for a 4" speaker. You will not get to sub range with a 4" driver.

If you are interested in building a sub, you need to educate yourself and then purchase a driver worthy of your efforts.

Bottom line: - trying to build a sub with a 4" driver is idiotic and not possible.

If building a subwoofer with a 4" driver doesn't make any sense then whats up with PC speaker manufacturers like Logitech building 2.1 systems with 4" subs?

Thanks for the guide links. I will go through them and post if I need any help!

 

[ARES24]

They make them because people will buy them. The 4" 'sub' does do lower frequencies then the satellites, they are just not frequencies that anyone on this forum would consider bass.

 

[BoredSysAdmin]

Nothing's wrong with desire to build something to learn in the process, but if you rather want to achieve great results and not waste time and money for end product which none of us would call subwoofer without double quotes around it.

Here's a relatively cheap and solid DIY sub which if not hard to build and you will get great bass for your money:
http://forums.audioholics.com/forums/threads/musical-sub-with-12-infinity-1260w.81671/
http://forums.audioholics.com/forums/threads/modeled-the-infinty-reference-1260w.78575/

Jin says the build should cost about $220 in materials and based on results I would easily put in on par with many $600 commercial subs any day.

 

[Gary147852]

Hey! I am planning to build a new enclosure for the subwoofer from my 2.1 speaker system. Its a 4 inch driver. The factory made box is a bandpass enclosure with one port. I want to build a ported box to make the bass sound more natural. These are the dimensions that I figured out would be good... Length x Width x Height - 4.5 x 11 x 9... this equals to around 0.25 ft^3 box volume. I will mount the sub in the centre of the 11 inch mdf panel. Now one thing I have not been able to calculate is the port size/length/diameter. The amplifier's bass output is rated at 20w RMS and the subwoofer is audible at 40hz after which it hardly produces any good bass.

With the new box I want the bass to sound slightly boomy, warm and as accurate as it can be in a ported box.

Please help me calculate the port dimensions. Also I would like to know if the box dimensions are suitable for the sub driver.

I can design you an enclosure. Pm me.

 

[TLS Guy]

I can design you an enclosure. Pm me.

Please explain how, without knowing the T/S parameters.

 

[Gary147852]

You can design based off of the lowest frequency available(usually also fs, or resonant frequency) for a driver this small any changes made to the enclosure and or tuning will be nominal. I think 0.25 ft3 will be sufficient but a slightly larger box will allow you a slightly flatter response and allow you to tune lower. Cone size and excursion are limited so port velocity should not be a problem with reasonable port diameter. Although a slot port will be better. You will get a slight boost in spl around the tuning point.

 

[TLS Guy]

You can design based off of the lowest frequency available(usually also fs, or resonant frequency) for a driver this small any changes made to the enclosure and or tuning will be nominal. I think 0.25 ft3 will be sufficient but a slightly larger box will allow you a slightly flatter response and allow you to tune lower. Cone size and excursion are limited so port velocity should not be a problem with reasonable port diameter. Although a slot port will be better. You will get a slight boost in spl around the tuning point.

I'm glad you don't design my speakers! You have no idea of the suspension characteristics. With small drivers and ported boxes, the tolerances are even tighter, with less room for guessing.

 

[Gary147852]

Well if your so good then why do you just design it?

 

[Gary147852]

I'm glad you don't design my speakers! You have no idea of the suspension characteristics. With small drivers and ported boxes, the tolerances are even tighter, with less room for guessing.

Btw. You can probably borrow some ts params from some cheap oem 4" drivers.

Have fun.

 

[Gary147852]

Perhaps you can build an anarchy horn and call it a day.

 

[TLS Guy]

Btw. You can probably borrow some ts params from some cheap oem 4" drivers.

Have fun.

How do you borrow T/S parameters? That is like borrowing finger prints.

The fact is you can't design a box without measuring the T/S parameters of that driver or having reliable data from the manufacturer.

 

[Gary147852]

How do you borrow T/S parameters? That is like borrowing finger prints.

The fact is you can't design a box without measuring the T/S parameters of that driver or having reliable data from the manufacturer.

A box with x volume tuned to x hz is still a box with x volume tuned to x hz even if some other parameters eg: motor strength are not equal. But you can accommodate for the wattage and ohm load specified by the manufacturer. obviously with changes in driver mounting depth and magnet size there will he some variation from driver to driver. But it is still only a 4 inch driver.
Rolloff will occur at 40hz but you can achieve a flatter response, by tuning it down lower than fs (40) by utilizing the fact that an spl increase around tuning point is inevitable.

You can still design a box that can fit his needs with regards to dimensions, internal volume and tuning.

But let's keep in mind that this is still only a 4" driver.

And no matter how ACCURATE you measure the drivers ts the difference in spl will change for a given volume/tuning and given displacement. Maybe Xmax could help. But it's still only a 4" driver and its still going to be limited(by the surround/spider and voice coil lenght as far as excursion goes) I'm sure just about all 4" woofers will be around the same ball park.

I'm not trying to argue with sound science but I still belive that an efficient enclosure can be crafted for the driver, even with limited information. And probably a fair amount better than the oem enclosure.

 

[jcparks]

Haha wow this thread is fun...
Firstly, Hi Gary and ABguy welcome to the forums.
Now he may have come off slighty harsh, but TLSguy has designed some of the most amazing subs built by others on this forum... and he is always quick to respond and offer his designs without question or asking for anything in return. However he is also very scientific about his craft his designs require the exact perimeters for the drivers he is designing for. Also he can be, well... blunt, if he thinks that you aren't working with a solid foundation he has no issue with letting you know it probably isn't worth your time. Don't be put off by this though as he is extremely skilled and is one of this most valuable assets in DIY on this forum.
ABguy I am assuming that you are dismantling a computer 2.1 sub... probably Logitech...
If you are doing it to experiment and have fun, by all means tear it up and get yours hands dirty, Gary seems to have a little experience in the matter and can possibly help you design something new. However if you are hoping to get a serious leap in audio fidelity... you may be a little disappointed when you complete your project.

 

[TLS Guy]

A box with x volume tuned to x hz is still a box with x volume tuned to x hz even if some other parameters eg: motor strength are not equal. But you can accommodate for the wattage and ohm load specified by the manufacturer. obviously with changes in driver mounting depth and magnet size there will he some variation from driver to driver. But it is still only a 4 inch driver.
Rolloff will occur at 40hz but you can achieve a flatter response, by tuning it down lower than fs (40) by utilizing the fact that an spl increase around tuning point is inevitable.

You can still design a box that can fit his needs with regards to dimensions, internal volume and tuning.

But let's keep in mind that this is still only a 4" driver.

And no matter how ACCURATE you measure the drivers ts the difference in spl will change for a given volume/tuning and given displacement. Maybe Xmax could help. But it's still only a 4" driver and its still going to be limited(by the surround/spider and voice coil lenght as far as excursion goes) I'm sure just about all 4" woofers will be around the same ball park.

I'm not trying to argue with sound science but I still belive that an efficient enclosure can be crafted for the driver, even with limited information. And probably a fair amount better than the oem enclosure.

What you are saying is erroneous. That is what we thought back in the fifties, until Thiel and Small's paper. The fruits if this were first employed by KEF,

The fact is that the box and drive parameters must match. The VAS (equivalent volume of the driver), that is the volume of air that has the same "springiness" as the driver. This depends very much on the mass of the moving parts of the driver and the compliance of the suspension. Even for 4" drivers there will be huge variation dependent on moving mass and compliance of the suspension.

I highly doubt a box would be better than the OEM one. Getting a 4" driver to output at 40 Hz is pretty good going. If you have a small driver a band pass enclosure is actually a good way to go, especially if one compartment is sealed and the other vented. This is the best way to control cone excursion and get decent output. It also gives you control of Q, although as you improve bass quality as you lower Q you reduce bandwidth.

The thing that trumps everything, is that the OEM designer had the vital data we don't. Taking a stab in the dark has almost zero chance of being an improvement.

You have committed a common fallacy to think you can tune an enclosure to any frequency you want and that will do the trick. It absolutely does not.

For every driver there is an optimal box, and anything over very minor deviations will not work.