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Discussion Starter #1
I am trying to figure out the most bang for the buck here. I have three choices I am modeling right now.

The first is the SDX 15. This was modeled using a Behringer EP2500 and probably a rekhorn b-1.

The second is the Mach 5 IXL 18.2.2, also using a Behringer and rekhorn.

Finally the RE SE 15. Not a lot known about this driver except for it's really big brother!! But, it models very nicely for me. This was modeled using an OAudio plate amp. (I can provide specs if needed.)

Clearly I need help with the rear port air speed. The CSX for example is the factory recommended setup but it is off the charts with regard to air speed. So, if you guys can help me out that would be appreciated as well as chimeing in with your thoughts on any of this.




Also, looks like I could use a little help on posting better images!:nerd:
 

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I guess my question is where do you feel uncomfortable with the models?

If you want lower port velocity, then the only option is to go with more mouth area on the port (which also means it will need to be longer). Don't forget to subtract the volume that the port takes up inside the cabinet. You will be able to make the cabinets much smaller if you go with passive radiators, but that's going to be more expensive than ports.
 

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Discussion Starter #5
I guess my question is where do you feel uncomfortable with the models?

If you want lower port velocity, then the only option is to go with more mouth area on the port (which also means it will need to be longer). Don't forget to subtract the volume that the port takes up inside the cabinet. You will be able to make the cabinets much smaller if you go with passive radiators, but that's going to be more expensive than ports.

My concern with the SDX model is that my port speed is so high that I can't believe that that would be the recommended enclusure by the manufacturor. I am thinking that I may have made a mistake on that particular model.
 

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I think I noticed the same thing when I modeled that speaker in their recommended enclosure. My only guess is they don't give a about port air velocity or don't take that into account because most people know squat about audio and probably wouldn't know port noise if they heard it, or in some cases may mistake it for bass instead of port noise.
 

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The SDX, along with quite a few other high excursion 15's are a bit problematic. They're usually designed so they work well in 9-13ft enclosures, but move so much air that a single 6" port leads to chuffing and compression. An 8" port is nearly too big because now you're looking at around 40" port lengths...which means low 1st port resonances.
A 7" port would be real nice!

*edit*
Lower excursion 18's, like the IXL, fall into that catagory too. High excursion 18's require at least an 8" port, though depending on the application, a 10" might be better.

Anyhow, you don't have to follow the manufactured suggested enclosure. If you want to build bigger/smaller, do it! For an SDX, 11-13ft tuned to 17-15hz works well. Especially if you have two of 'em.
 

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My concern with the SDX model is that my port speed is so high that I can't believe that that would be the recommended enclusure by the manufacturor. I am thinking that I may have made a mistake on that particular model.
Well the port speed is a function of the SPL being reproduced by the port (not the driver). At lower volumes (which most listening happens at), the port velocity is probably at a level low enough to not be noticeable.

Also, reducing port velocity isn't always a free lunch. As you move to the larger ports that have lower velocity, you're also lowering their natural resonance. You don't want this resonance to move into the passband of your driver because it doesn't take much to trigger it (and keep in mind that low pass filters aren't perfectly steep). However, too much air moving through the port will always trigger the port resonance, so keeping it outta the passband of the driver isn't a guarantee.

I have found with my own projects that controlling the port resonance is more important than controlling the port noise. That said, physics is physics and if you want more SPL from the port then you have to go larger. WinISD is pretty cool in that it lets you model the effects of a clipping port...it takes a bit of work to get the model accurate, but it's real easy to see the transfer function effects of a port that starts overloading from excessive velocity....so then the only question becomes at what SPL does it happen. But usually, you just want to make the ports as large as possible, so there's almost no point in learning what SPL it happens at. I suppose that's lazy engineering, but then it's DIY and for fun...

So all that to say, I wouldn't be surprised if the guys at SDX were thinking "oh , people are going to think this needs a huge enclosure...better make the recommendation smaller" knowing that most people probably won't notice the difference.
 
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