teamSPB Corsa build - 2 AA Arsenal 10's, 4th order bandpass, AudioSystems front end

[loganberry]

Looking great! Im gonna build my first bandpass here in the next few weeks...are you not glueing down the front so you can still get to the subs on the inside if you need to? Thats the part im having the hardest time with, what part to leave accesable on mine

[6berry]

awesome! cant wait to hear how these sound

[teamSPB]

Some artsy shots

The top panel is just on with some screws and some gaffa tape....

Tomorrows installment....testing time!

teamSPB

[6berry]

i like that port. cant wait to see a video of these

[teamSPB]

4th Order bandpass boxes

As you can see, we have decided to go down the 4th order bandpass box route in our recent Project in the Corsa. Alot of people don’t understand this type of box and I have got alot of questions in regards to what they are, how they sound, how do you spec one etc. So I thought I would put this little bit of information together for you.

So what makes a 4th order bandpass different to a typical box? Well, lets start with what a 4th order band pass actually consists of. There are 2 parts of a 4th order box. Most boxes that you would have seen would have been regular sealed or ported boxes. A 4th order band pass box is special in the sense it combines both sealed and ported sections.

Both sealed and ported boxes have both merits and drawbacks in their own right. A sealed box will give you a very tight, precise and accurate type of bass. Hard hitting in most cases. Their sound quality is second to none and are able to provide, arguably, the best sound quality possible from a subwoofer. The fall back being they don’t tend to like producing very low frequencies with much authority. Also their output can be questioned especially when compared to the likes of ported boxes.

Ported boxes give you a tremendous amount of output, on average equating to +3db in comparison to a sealed box. They can also be tailored to suit your musical needs, in the sense, they can be ‘tuned’ to a certain frequency in which they will excel and perform best around. For example, if you like extended low frequency bass, you may want to tune the box to 30hz or below. If you like hard hitting bass, you may want to tune to around 35-40hz. Around these tuned frequencies, audio levels excel greatly above those of a sealed box, meaning these are often the preferred boxes of the streetbass and SPL guys. Having all the output does not come without its downsides; delayed response (time delay), port noise (possibly) and the size of the box. Due to the size of the box, coupled with the physics behind the port, there will be a slight delay with the bass. Port noise becomes an issue when ports are too small. The size of the box is generally twice the size of a normal sealed box.

Now, a 4th order couples these two types of boxes together. Yes, thats right, there are BOTH sealed and ported sections within this ‘one’ box. You are coupling the tight, precise and accurate bass of a sealed box, coupled with a high output ported section. There is another slight twist with these boxes, where the bottom end of the frequency range is not dictated entirely by the tuning of the port. What dictates the bottom end of the frequency range, is mainly dictated by the size of the sealed chamber/s. The bigger these chambers, the more extended the frequency will be. However, the downside will always be, the bigger you go, the more efficient the box will be, hence the lower the power handling of the subwoofer/s will be. With using a smaller sealed chamber, even though the downside will be a slight lack of bottom end extension, using more power into the driver, will mean the bottom end can be restored with no other alterations.

So how big do you make the sealed chamber/s? Thats a good question, however, there is no set answer. This is generally dictated by trial and error. You can make an educated guess depending on power available, the bandwidth you want the subs to play and what subwoofers are being used.

As a rough guide, a good starting point is generally basing the sealed chambers on how big the speaker manufacturer recommends them to be, which will vary from subwoofer to subwoofer. However, as a general rule, I tend to use the following;

8inch sub : 0.2-0.5cuft

10inch sub : 0.3-0.6cuft

12inch sub : 0.5-1.5cuft

15inch sub : 1.5-3cuft

I tend to lean towards the smaller sizes when I can counteract the size with power. However, if bottom end extension is what the aim goal is, then I aim for either the middle or the bigger end of the scale. The choice of driver will generally dictate howmuch power we can drive into the speaker.

The ported section of the box is generally decided upon on based on a ratio of the sealed section. The box going into the Corsa is based on a 2:1 ratio. The sealed sections combined give a total of 0.8cuft, and the sealed section is 2.4cuft after displacements.

Generally, greater the ratio, the smaller the bandwidth (we will cover bandwidth later) but greater the output, the smaller the ratio, the greater the bandwidth but at the expense of reduced output. For example, a box of a 5:1 ratio will play with great output and with great efficiency but the bandwidth will be small. A box of a 1:1 ratio, will play just like a regular sealed box and will not have very many benefits over a regular sealed box.

The other consideration on the ported section is the tuning of the port. For example, if you tune a box to 30hz, the subwoofer will generally ‘unload’ around 25hz or thereabouts (obviously subwoofer dependant). With a 4th order band pass box, the port tuning frequency will dictate the low pass filter. What this means is say you tune to 65hz, the box will not play bass ABOVE 65hz and will generally unload. Again, I did say there is a twist with 4th order band pass boxes!

The box in the Corsa has been specc’d as below;

0.4cuft per sealed chamber

2.4cuft tuned to 65hz on the ported chamber

The last consideration on the ported section will be port area. With band pass boxes, you want as much port area as you can get and try to get the port as short as you can. Luckily, with the port tuning being so high, generally the port lengths are short, and the shorter the better! The Corsa has been built with 49sqin of port area, with equates to approx 20sqin of port area per cuft. You want to be around this general area per cuft on the external port. You can go even bigger which will aid output. Just make sure you don’t go smaller than around 15sqin per cuft otherwise you will choke the output.

The final thing I guess to cover is how the 4th order band pass boxes sound...well, its safe to say you DO get the benefits of both the sealed and ported boxes. You get the tightness and response of the sealed section, and you get the awesome output of the ported section. You also get the roll off of a sealed box which is believe to be around a 12db slope compared to a 24db slope for a ported box. This means rather than the subwoofer unloading itself pretty quickly below the tuning frequency as it would in a ported box, it will continue to remain loaded for even lower frequencies.

Compare the graphs below, there is one for a sealed box, a ported box, and a 4th order band pass box. The frequencies are shown at the bottom and the left hand side shows the slope (rate) of how quick or slow the bass will role off at the higher or lower frequencies and where the boxes will peak etc.

Looking at the sealed box, it will remain at 0db until the box hits a relatively high frequency (generally around the 50-60hz mark), before it starts to roll off at a 12db slope. Due to this relatively shallow slope, the subwoofer will still be able to play the lower frequencies (~30hz), albeit, at a lower volume than say what a ported box tuned to 30hz will do.

Sealed box

Ported box

4th Order band pass

Looking at the ported box, it will remain at 0db until the box hits its tuning frequency where it will raise to + xdb, however, around 5hz below this frequency, the roll off will be pretty sharp at 24db which will be like falling off a cliff!

Now, going back to what I said earlier about the ported section acting as a low pass filter, whatever you tune the ported section to, will have a sharp roll off ABOVE this frequency.

What does this mean? Look at the 4th order band pass graph, you get the 12db roll off on the bottom end of a sealed box, and you get the 24db roll off on the top end of a ported box. These frequencies between the -3db points on the lower and upper frequencies, is called the band pass frequency. These are the frequencies that will play in harmony through the band pass box.

One thing worth noting, it is easy enough to put something on paper, but building a band pass box will require ALOT of precision building AND ALOT of testing testing and more testing. You have to ensure everything is built with mm precision and then be able to change certain parts of the box to fine tune it so you can tailor the sound the box produces.

If your going to try building one....test test test! One final thing....GOOD LUCK!

teamSPB

[Guest grim83]

any new updates?

[Guest grim83]

updates???

[teamSPB]

Yes mate, things have been slowly progressing...

The headunit has been sold

The subs have been sold

And the amps and components look like they also may have been sold!

Before the move to sell everything, we made a few adjustments to the box as I wasnt happy with the way it was playing...

The central chamber tuning was dropped to approx 45hz by reducing port area to around 33sqin from memory

This increase the bottom end of the music dramatically and also increased SPL in a big way...all at the trade-off of bandwidth ability...not too much of a biggy I suppose, however, it would be nice to have a little more impact on the top end...

All the above parts are now making way for;

AudioSystems/Gladen Audio XION 165 components in the front

2 Chaos 10" subs

Amps are still to be chosen

Headunit is currently a Pioneer 77MP which may be replaced by an Alpine IDA X305 depending on what the other half prefers!

Box wise, I will try the chaos' in this box and see how we get on...if I still think we can eek more out of them, then I may possibly try a 6th order bandpass or a conventional ported box...we will have the power to drive the subs hard no matter which direction we choose to go in

teamSPB

[teamSPB]

Small update today...

As the Rockford components have now been sold, we have finally got round to wiring up the new components...

The Rockfords have made way for a pair of Gladen Audio (Formally AudioSystems) XION 165's

I didnt take any pics of the components but they are the same as the ones I used on the cheap Corsa build...

The subs are now also here

2 x Ascendant Audio Chaos 10's....2012 versions....they are MEGA!!!!! Cheap for what they are! Just some quick pics off my phone;

teamSPB

[qu1cks1lver56]

Think that 4th order would work on a pair of Assassin 10's on about 500rms?

My buddy has a pair we need to come up with a box for and that looks like it'd do pretty well in a hatchback car.