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Subwoofer enclosure for two 12" subs 4th order with the port in an isobaric load?

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I'm not sure if I'm wording this correctly... I'm building a box for my manager for his two ds18 exl 12inch 2500watt subs... I've tried googling it, but I can't find any info for using a port in between two subwoofers in a 'parallel isobaric load'? If thats the correct technical definition? I'm not sure. I'm probably over thinking it, but I wanted to be absolutely sure. I'll post a picture of my chicken scratch blueprints...
 
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This is my chicken scratch blueprints... Don't judge.. this is how my brain actually operates, sadly, and I suck at drawing, so I don't have much control over the appearance lmao.
 

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DVDdoug

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Try WinISD (free speaker design software). There is an isobaric option and there is something they call "ABC" with two external ports and port in and internal baffle. ...But it doesn't show where the drivers are mounted. (They do have "standard" 4th & 6th order designs.)

And I wouldn't build anything 'permanent" that you can't model in software first...
 
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There is absolutely no need for anyone in 2022 to do isobaric, if you want to add extension without adding volume just use DSP.
I honestly just drew the initial plan on the fly at work without much though... I've only built a few boxes before but I have a tendency to be experimental... I'm thinking I'm definitely going to have to make some changes to the design... He just wants it to be better than the Q bomb box he has them in, which shouldn't be hard to do... I'm not familiar with DSP though... What do you mean?
 
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Try WinISD (free speaker design software). There is an isobaric option and there is something they call "ABC" with two external ports and port in and internal baffle. ...But it doesn't show where the drivers are mounted. (They do have "standard" 4th & 6th order designs.)

And I wouldn't build anything 'permanent" that you can't model in software first...
Thank you. I'll have to check that out. I tried finding an app for box design but really i don't know what I need my box volume to be.. the only numbers I have to work with are the dimensions of his trunk and the cutout size to mount the subs.. I'm still new to port tuning.. the boxes I've made before always include a spiraling sort of T-line port, but I've never really had an actual plan when building, much less actual measurements.. i just eyeball everything, throw it together and get surprising results each time, lmao.
 

abdo123

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I honestly just drew the initial plan on the fly at work without much though... I've only built a few boxes before but I have a tendency to be experimental... I'm thinking I'm definitely going to have to make some changes to the design... He just wants it to be better than the Q bomb box he has them in, which shouldn't be hard to do... I'm not familiar with DSP though... What do you mean?
You can always equalize the response to flat as long as you have enough excursion. Two 12 inch drivers should have plenty.
 
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You can always equalize the response to flat as long as you have enough excursion. Two 12 inch drivers should have plenty.
how would I do that? I'm sorry I'm still new to the actual physics and terminology...
 

Chrise36

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These are too big drivers for a complicated box that you want. You need very good bracing for a 2500 watt driver. Two normal boxes and eq is more practical for these.
 
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These are too big drivers for a complicated box that you want. You need very good bracing for a 2500 watt driver. Two normal boxes and eq is more practical for these.
Could I do one ported and one sealed to get better dynamic range? Or would I run into problems with sound waves cancelling each other out?
 

Chrise36

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Could I do one ported and one sealed to get better dynamic range? Or would I run into problems with sound waves cancelling each other out?
Do what the manufacturer advises or what the simulation shows to work. If you dont mind the sub to look like a table there are horn type boxes for two subs with big gains but two subs in different places actually helps with the frequency response.
 
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Do what the manufacturer advises or what the simulation shows to work. If you dont mind the sub to look like a table there are horn type boxes for two subs with big gains but two subs in different places actually helps with the frequency response.
Ahh thank you so much.... The manufacturer doesn't have any info for the subs box dimensions... They have a section on their website that says box specs or something like that, but its empty.. and my manager isn't too worried about what it looks like as long as it isn't trashy... His trunk is 4 ft wide, 3 ft long, and 3 ft tall, so there's a good bit of space to work with there, but I'm wondering what you mean by different places? Like one closer and one further back? Or the same distance but one on each side? And which way should they face? It's a hatchback SUV btw..
 

Chrise36

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Ahh thank you so much.... The manufacturer doesn't have any info for the subs box dimensions... They have a section on their website that says box specs or something like that, but its empty.. and my manager isn't too worried about what it looks like as long as it isn't trashy... His trunk is 4 ft wide, 3 ft long, and 3 ft tall, so there's a good bit of space to work with there, but I'm wondering what you mean by different places? Like one closer and one further back? Or the same distance but one on each side? And which way should they face? It's a hatchback SUV btw..
One on each side.The more direct to the ear the better for spl
 

Don Hills

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Are they these drivers?
If so, that page lists all the relevant info (driver TS specs, suggested enclosure sizes). I strongly recommend you posting in the subwoofer forum on diyaudio.com, or on diymobileaudio.com. The folks there are familiar with modelling tools such as ABEC and can suggest a design to get the most out of the drivers.
 

alex-z

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Could I do one ported and one sealed to get better dynamic range? Or would I run into problems with sound waves cancelling each other out?

That isn't how dynamic range works. Dynamic range is the difference between the minimum and maximum output levels offered by the subwoofer.

How you design a subwoofer is take the T/S parameters of the woofer (measure them yourself, manufacturer tolerance makes their numbers unreliable), then model a cabinet with software like WinISD or VituixCAD. If you are a perfectionist, heat the voice coil by playing pink noise at 25% of the RMS power for a few minutes, then measure the T/S parameters again. This gives you data similar to when the subwoofer is actually in use, without having to measure the large signal parameters using Klippel gear.

For measuring T/S parameters, you can either use hardware like a DATS v3, or DIY it with a PC soundcard + pair of resistors (the DATS is basically a PC soundcard with software attached).



You should not mix ported and sealed subs in the same system, unless you are knowledgable about using DSP to smoothly blend the subs. Ideally, all subs in a system are identical.

When you spread subwoofers throughout the room, it results in a smoother frequency response, because of reduced room mode influence.


On the topic of using 2 drivers per subwoofer, this is possible, but isobaric is generally the wrong answer. Isobaric loading halves the air volume required, so you can build a smaller box, but you are paying the cost of 2 drivers, for the same SPL output (because efficiency is halved, and power handling doubles), which means you also need twice the amplifier power.

The better choice is placing the drivers on opposing faces, so that cabinet vibrations are minimized. This can reduce distortion, particularly if your cabinet is not structurally robust.
 

sarumbear

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This is my chicken scratch blueprints... Don't judge.. this is how my brain actually operates, sadly, and I suck at drawing, so I don't have much control over the appearance lmao.
That is not isobarik. It is a variation of a vented box. Isobarik has no vent. The volume between the drivers stays at the same pressure, hence the use of the term iso.
 

thulle

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The better choice is placing the drivers on opposing faces, so that cabinet vibrations are minimized. This can reduce distortion, particularly if your cabinet is not structurally robust.

Another choice is to place two drivers on the same surface with a C-C distance of less than a quarter wavelength and mounting one driver inside out with reversed polarity, this cancels out unlinearities in suspension and engine, and lowers 2nd harmonic distortion.
 
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