bass cabinet porting

I am in the middle of a bass guitar cabinet project. I've gotten most all of the components and am ready to start but I have one small prob. What size to make the port in the cabinet. I talked to the guitar and combo salesman at my local music store and he said there is some sort of formula or equation you use to get it but he couldn't remember what it was and he refered me to the internet. Not much luck there either. So if anyone would happen to know what this formula is or have any info that would be usefull to me it would be greatly appreciated.

The size of the port doesn't have much to do with the eventual sound you'll end up with. It's the length of the path the sound will travel within the cabinet, and then go out of the port, that will determine the effect created by the port.
Generally, I think the length of the path which the sound follows in the cab, to eventually exit through the port should be the same as the wavelength of the frequency(plus it's harmonics) you want to emphasize. You can influence the path length the sound has to travel within the cab by adjusting the cab's depth and/or building kind of a labyrinth inside.

eg: you want a boost at 300Hz

wavelength = 340m/s (speed of sound) / 300Hz = 1,1333m

Now build the cab with a depth of about: 1,1333 / 2 = 0,66m

Acoustics nerds, feel free to correct me. ;)

OK, in typically James fashion I slapped together a cheapo Cab earlier this year. It has 2by10" speakers with a range of 60 to about 4000hz. As it cost me about £40/$65 to make i can currently put up with it's frequency range.

Any general suggestions for boosting the high mids somewhat?

- bearing in mind that i usually experience 2by4s as disabled SUV/landrovers. ;)

The question is a bit academic at the moment as i'm waiting for someone to send me high wattage resitors so i can rewire it to a nominal 8 ohms and run the Vox through it.

I hear stuffing it with glass wool ??(trial and error) can be one way to go, or is it better to try and calculate a "Maze" type affair of baffle boards,ports etc ?.

I realise that this can be a very scientific and precise topic,but i'd like to keep it simple if possible.

You might want to look here,

http://www.celestion.com/pro/pro.htm

I've heard that these folks know a thing or two about this kind of stuff,

This is a good place too, and has some info for jesse and James
http://www.webervst.com/sptalk.html

it might take a while to find what you need, but you can also ask questions there, and who knows, you may even get an answer......... Good Luck

Thanks pstring,

'll have a look around over the next few weeks ..as thats the timescale i expect them to deliver over..long story..

Any news on amps or projects?

cheers.

thanks for the advice guys

I hope those links are of some help, I'm in between projects right now, which means I'm scheming for the next one, I'm trying to gather some info and some parts for an amp, tell me about your 2x10 cab, what kind of speakers are you using? it seems I'm building a cache of 10's, and I'm thinking of building a 2x10 myself, have you ever seen anything on "tone rings", I know there is mention of them on the Weber site, I read a little about them in an interveiw with Dr.Z on
http://www.tonequest.com

I haven't seen much else about them, talk at you later

Hi pstring,


You -asking MY Advice on amplification!? i know little more than zip I'm afraid and the cab was a hasty stopgap measure.

I don't think you want to go the way i did as the speakers are mundo cheapola and will not rock your socks off. I hear
jensen and weber are about the best sort of little puppies for 10"s.

The webervst.com forum you mentioned seem very knowledgable (spl) and answered my questions promptly I gave 'em the specs and the sussed that i'd used cheap nasty speakers..

So guess what i'm gonna change..eventually..Overall i'm happy with it for 40 quid, and it improves the low end of my 10 watt Marshall which is what it was designed for - when the Paul worked it made the Marshall's speaker ..shimmy... The cab does make shettty amps sound better as i ran my 15 quid s'queer 15w into it and it made my small room vibrate..loudly.



For the box i used (Laughing Out Loud ..commence) ..a pine storage/blanket "kit" from a Large DiY chain here (15 quid) and it's approx the right volume,put hinges on the back so it can be open or closed to any degree.

For the record a marshall 1936 2x12 cab has dimensions 750mmX310mmX600mm (this is what mine's "based" on)..you can get more specs off their site.

If you search in this section the Lord recently mentioned a thread in which he goes into Cab design. I'll have to dig that out too.

i'll check out tonequest when i can...cheers.

I know less than nothing about tone rings..Tone knobs ..yes ;) Take it easy.

Right, I've just gotta jump in here!

I'd rather not repeat myself (too often) so take a look at this thread and the link in one of my posts there.

Thanks(again) Lord, hadn't quite got there yet.

I'll read and reread that/those one[s]...and cook up something slowly and hopefully more... tastefully.

Cheers.

Bass Cab Porting, L's favorite topic!

Originally posted by pstring
Bass Cab Porting, L's favorite topic!

LOL... I don't really rant until I start talking about TUBES! :D