Diy cab help

[dannyg3005]

Hey everyone
I need some advice, I am gonna build my own bass cabinet, I have a Ashdown blueline 15” 300w 8ohm speaker and the cabinet dimensions are 480x510x310, what port dimensions do I need? I would like to use round ports!
Many thanks in advance

 

[David Morison]

Really, you have 2 options. Assuming your cab is the same net internal volume as the original Ashdown from which your driver came, simply duplicating their ports should give reliable results.

Failing that you'd need to obtain the Theile Small parameters of the driver and model it in software to see what tuning frequency suits that driver. It's not all that likely that Ashdown would give you that info but it doesn't hurt to ask. They may even be willing to suggest port sizes that they already know to be suitable.

If that doesn't work, you're looking at measuring the TS parameters yourself, which can be done with software like Room EQ Wizard and a few quid's worth of components to make a measurement jig - there's a decent how-to guide in the REW online help. If you'd rather buy an off the shelf product to do the measurements Dayton's DATS is the most commonly used one.
HTH,
David.

 

[dannyg3005]

Thanks David, I’ll give Ashdown a try

 

[Redbrangus]

I hope it's obvious that in the absence of reliable T/S parameters, acquiring the equipment and necessary expertise to determine those isn't really practical for the purpose of building just one enclosure. The one parameter you ARE likely to have sufficient equipment to measure is Fs, the driver's resonant frequency -- do a search on the 'rice test' in this forum, or out in the Interwebs. There's nothing wrong with just tuning the cab to that frequency. Again, that's in the absence of the actual data, which I doubt you'll be able to source.

Alternatively, just as @David Morison suggests, you could essentially just copy the cab the driver is currently in. It can be any dimensions (within reason) as long as you retain the same internal volume. You need to duplicate the port in cross-sectional area, but it can round if you want. You also need to duplicate the length of the port -- the duct. That would be one way to 'design' a cab that works for your driver.

 

[dannyg3005]

Well Ashdown have kindly got back to me with the TS parameters, but no surprise they have blanked me when I asked for drawings of an ABM 115h cab, was worth a try!
Can’t find anything online either.
Think I’m gonna have to build it as close to the original as possible using outside dimensions and try the rice test to tune it.

 

[agedhorse]

Or do the math?

 

[dannyg3005]

I would if I knew how!

 

[agedhorse]

Ahhh, there may be a motivation for learning here?

 

[David Morison]

I would if I knew how!

Well, unless Ashdown specifically asked you to keep the TS data private, you could share it here and someone will be able to do some basic predictions for you easily enough.

 

[dannyg3005]

As luck has it, the chap from Ashdown has kindly told me what volume it should be and port lengths, so happy days.
I little bit of simple maths that I can understand to work out dimensions and I’m good to go, that’s my weekend occupied

 

[David Morison]

Brilliant, I wasn't surprised that they wouldn't share actual plans for their cabs, but giving you a target box size and port dimensions is great, good luck!

 

[agedhorse]

Hopefully you received the total port area too?

 

[M-Mittlesteadt]

Ahhh, there may be a motivation for learning here?

The best thing I ever did to expand my knowledge of all the factors in how we achieve the tone and volume from our rig, was learning how to design and build my own bass cabs.

Whether one continues to buy commercial cabs or keep building their own, understanding the how and why is really helpful.

I spent many years designing and building my own. After about 7 years on hiatus, coming back to playing bass again made selecting the right commercial amp/cab for me was so easy as I knew what to look/listen for.