So what did I do wrong while building these cabs?

[Rick James]

Could it just be the cheap speakers you used?

They're actually pretty good spec wise.

I have this feeling the cab is too big.

For best results it's too small. Modeled in WinISD Pro those speakers work best in 4 cubic feet each, with the cab tuned at 35 hz.

Lack of projection can also be speaker unloading due to incorrect port tuning. Unloaded will move lots of air up close but not at the audible frequency,

+1. The main problem is that he didn't duct the ports. With 8 inch tubes it would probably work OK.

My advice would have been to get some plans from someone like greenboy or BFM and save yourself the anguish of trial and error.

+1. You can build a much better cab than you can buy, it's the 20 years or more of experience that you need to know how to do it that's the problem.

 

[bassmeknik]

It's true though, and I wonder why they make them that way.

To keep the form factor small. Most would not buy a cab that was tall and skinny. While this is pure aesthetics for some, many simply won't buy a tall skinny cab even if it was the best arrangement because it doesn't look good to them.

 

[vaesto]

Hi,
Is it correct???:

They're 3.25" in diameter but otherwise they're just holes cut in the front baffle

Ports are just holes? If it is true - then you got not a ported cab but rather closed box with terrible air leak.

Port shouldn't be a hole. It should be a tube. Although, it is not clear at all how it's length (Lv) could be 0.75 inch in BB design. maybe driver details are incorrect. Or they are not meant to be in a ported cab.

You may "simulate" the tuning of the port by putting a cardboard tubes of various length to the hole outside the box. For convenience you may make a telescopic tube out of two tubes.

 

[xk49w]

Hi,
Ports are just holes? If it is true - then you got not a ported cab but rather closed box with terrible air leak.

Port shouldn't be a hole. It should be a tube. Although, it is not clear at all how it's length (Lv) could be 0.75 inch in BB design. maybe driver details are incorrect. Or they are not meant to be in a ported cab.

Not really. BFM's new cab designs (forget the model) have only holes in the front baffle IIRC. A simple port will still resonate the chamber and it makes a simpler build I suppose, but there will be no tuning the volume other than by changing port size. The ability to somewhat easily tune is one advantage of the tube style port.

Edit: corrected.

 

[giglawyer]

I love experimenting, and DIY. That said, there really is a lot of science behind cab design, to the point where many designs only work (as intended) with certain speakers, etc. I commend your efforts, but I recommend you look into Greenboy's designs, or check out Bill Fitzmaurice's page.

Or, by all means - keep experimenting - you may come up with something unique and awesome.

 

[wcriley]

Codger,
If you are referring to BFM's Simplexx line, you do not remember correctly. They are ducted.

 

[giglawyer]

It's true though, and I wonder why they make them that way.

Saves money.

 

[WarriorJoe7]

which port tubes are the best for metal?

 

[xk49w]

Codger,
If you are referring to BFM's Simplexx line, you do not remember correctly. They are ducted.

Corrected, thanks.

 

[paparoof]

so if ports *must* have ducts, what's the science behind the "vent" in my 40 year old Ampeg B25 cab? It's just a hole in the baffle.

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[astack]

By building a few properly-designed cabs you would surely gain insight in which paths not to go down.

That is all.

Hmm, I'm thinking of the quote about leaning more from failures than successes. The only thing you learn building a just-add-water Betty Crocker cab is how those guys do it, but not why. If you're building just to build, then yes, use their plans. But if you want to learn something new, you have to make mistakes. Or try things the "wrong" way and see what happens (there's a thread from a couple years ago from Bogey that did this -- it's a good read).

 

[FatBoutedGirls]

Hmm, I'm thinking of the quote about leaning more from failures than successes. The only thing you learn building a just-add-water Betty Crocker cab is how those guys do it, but not why. If you're building just to build, then yes, use their plans. But if you want to learn something new, you have to make mistakes. Or try things the "wrong" way and see what happens (there's a thread from a couple years ago from Bogey that did this -- it's a good read).

Agreed. The best way I learned what not to do is to have done it and failed.

I think the OP had the right idea, take some cheap speakers, build a box, find out what went wrong. As long as he is willing/can afford to fail it's a fantastic learning exercise.

 

[INTP]

The wiring diagram shows the drivers wired in series. Two 8 ohm drivers in series will be 16 ohms. Probably not getting the power out of your amp that you think you are. Also, the spec says 96dB @1W/1m, but that's probably overstated for bass frequencies. Try running them wired parallel instead and of course, observe polarity.

 

[Handyman]

so if ports *must* have ducts, what's the science behind the "vent" in my 40 year old Ampeg B25 cab? It's just a hole in the baffle.

Your flaw here is mixing the concepts of "science" and "Ampeg cabs".

 

[BassmanPaul]

so if ports *must* have ducts, what's the science behind the "vent" in my 40 year old Ampeg B25 cab? It's just a hole in the baffle.

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They are ports. Area of the hole by the depth of the baffle.

 

[Passinwind]

Hmm, I'm thinking of the quote about leaning more from failures than successes. The only thing you learn building a just-add-water Betty Crocker cab is how those guys do it, but not why.

Not necessarily, if you ask enough questions and read all the available discussion. You can also plug their designs into modeling tools and do a zillion what-if simulations without ever building anything at all. Also, having a known good reference on hand is the best reality check I can think of for DIY'ers. But with all that said, I'm a big fan of making smoke and sawdust and seeing what happens too...Link Removed

 

[BassmanPaul]

Be sure to tell most cabinet manufacturers about this theory. I think they missed the memo.

Please do not confuse what a manufacturer does for correctly implemented science. Very often the design is more about what Marketing believes will sell rather than audio engineering. Sad but true!

 

[B-string]

Just a hole in the baffle? Well I guess full and 3/4 bass reflex has been forgotten. They existed before duct porting. Duct porting allowed smaller cabinet volumes.

 

[BurningSkies]

I love experimenting, and DIY. That said, there really is a lot of science behind cab design, to the point where many designs only work (as intended) with certain speakers, etc. I commend your efforts, but I recommend you look into Greenboy's designs, or check out Bill Fitzmaurice's page.

Or, by all means - keep experimenting - you may come up with something unique and awesome.

This. And this is why I'm still after 20 years working on my crossbreeding of a platypus and leopard. I'm totally sure that I can make a brand new awesome and unique animal, even though geneticists keep telling me that's not how it works.

And I like to watch the platypus and leopard 'interface'. Endlessly entertaining.

 

[BurningSkies]

Hmm, I'm thinking of the quote about leaning more from failures than successes. The only thing you learn building a just-add-water Betty Crocker cab is how those guys do it, but not why. If you're building just to build, then yes, use their plans. But if you want to learn something new, you have to make mistakes. Or try things the "wrong" way and see what happens (there's a thread from a couple years ago from Bogey that did this -- it's a good read).

I guess it depends. Is the goal specifically and purely academic: To learn about what not to do or what to do when building.

Or is the goal to build a cabinet that works well, is loud and sounds good on the first try.

The first one is awesome, although probably expensive and not that efficient. The second one is for people who want to play music.