Can someone dirct me to a tutorial about designing a cabinet for a 15" bass driver?

pete1729

Member
2009-01-17 7:11 pm
Can someone dirct me to a tutorial about designing a cabinet for a 15" bass driver?

I have two 15" Utah woofers from a single Seeburg DDS1, I also have two Altec 811/804 horns. I'd like to build some fairly tall, relatively narrow cabinets for the bass drivers and mount the horns on top.

The original cabinets, one of which went underwater, held two 15's and were low and wide. The cabinets were also ported.

I have no T/S parameters for the Utahs, nor do I know their sensitivity. Am I just going to have to take a shot in the dark with cabinet sizes and port dimensions? Are there some simple rules of thumb that will get me some reasonable results?

I realize I will have to build crossovers with Lpads, I figure I will just copy an Altec design.
 
There is one rule of thumb: Guessing will build you a most horrid "boom box". Now if you wanted to build a SEALED box, you could guess and it would not be terribly bad. You won't have the bass you may be looking for though.

Copy the crossover for the altec may not be too bad, but you will need to adjust the levels.

If you have a computer, and as you are here on the forum I guess you do, you can put together what you need to actually measure the TS parameters. It is not that hard.

Sound card needs to do both in and out at the same time. Many old laptops don't.
Windows.
Download ARTA. The program you want in it is LIMP
Download WInISD This is the box stimulation you will use.
You need to DIY a set of measurement probes. Just a little work. 2 resistors and 2 zieners in each. ARTA FAQ's tell you about this. Also the Wallin jig.
You need a 10 Ohm 5W resistor.
It helps to have a digital volt meter to confirm the resistance of the voice coils.
A hand full of nickels for mass displacement method, or a sealed box smaller than is optimum. I am guessing a 16 inch cube would do. READ THE MANUALS.

That is all you really need. Have you looked at The Thiele-Small Loudspeaker Database for the driver data? That would save you all the measurement part.

I do have to say, you want to build speakers with no understanding of what you are up against. You will get sound out of them, no one will die; so go right ahead.

Speaker design is a very complex subject that takes years of mistakes to learn. It takes time, knowledge and equipment. There are hundred of considerations. Do you know what baffle step is? Diffraction? Cone breakup modes?
 

pete1729

Member
2009-01-17 7:11 pm
I have a clue as to what I'm up against, hence my inquiry, so spare me the condescention or else make it funny. "Most horrid boombox" is funny, "no one will die" is less so. I'm 51 years old. I've been in residential design and construction for 30 years. I have taught dozens of people different parts of my trade. I have never found it necessary or effective to talk down to anyone.

Thank you for your time. I'm sure your advice is sound.
 
Doing a bit of reading to understand the complexity involved will greatly improve your chance of a pleasing result. If you feel offended by my suggestion that total failure is really not important in the scheme of thing, my apologies. The suggestion that there would be a rule of thumb to build a ported box means you do not understand the physics yet.
 
The only "Rule of thumb" that I am aware of for ported boxes is that a driver with a Qts of 0.33 gives the smallest box size for a given performance, but that is a very broad generalisation, to say that above and below this figure boxes become larger is only a general indication.
I don't yet understand the physics so I rely on computer programs to do the designing for me.
When I don't know the parameters and cannot find them I simply look at the size of the magnet; if it looks small compered to the driver size a simply assume it is a high "Q" driver and meant for a sealed box and vice a versa but I have used high Q drivers in small sealed boxes.
If you don't know what the drivers parameters are; sealed is easier to do and lots of experimentation with bigger and smaller boxes.
Before the relationship between driver parameters and tuning was worked out I'm guessing most speaker boxes were built by trial and error
 

pete1729

Member
2009-01-17 7:11 pm
Here's my advice to my... self

I have a pair of Altec 811b horns with 804 drivers. The Altec model 19 is a proven design using that horn and a 15" woofer. The plans are available, why not build those cabinets and crossovers? Try the Utah woofers, they might sound OK set up like that. If they don't, which is likely, find a pair of Altec 416 woofers.
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
My 15s f3 at 70Hz, but then that's all I need them to do ;). I agree with the closed box option as it's hard to go wrong with at least basic information about the woofer and the only cost will be bass extension, which some of us address separately.