building a new bass cab

MATAMOUROS · #1 07-21-2010, 09:40 AM

Hi folks. I decided to build a 2 12 bass cab,and got all the wood cut up for it.Im going to order a 15 lfa 500 watts rms eminence,and a 12 lfa 500 watts rms,also eminence.The total load will be 4 ohs. I also want to instal a motorola cts powerline tweeter,and a L pad to control the tweeter.My question is this. I have an old passive crossover made by carvin,that i pulled from an old monitor.Can i instal it on this cab? Will it affect the output of the woofers in anny way.or it controls just the tweeter? The crossover is rated at 8 ohs,and both woofers will be 8 ohs,but ill wire them in parallel to get the load to 4 ohs,and thus augmenting the power of the amp signal.Anny ideas will be appreciated.Thanks in advance.

NoGraveConcern · #2 07-22-2010, 05:48 AM

Installing a random crossover will give you a random result. With a comp driver you would be better off just putting a 4 uf cap on the tweeter and calling it good. With that peizo you have more issues than just picking out an x-over.

Are you building a 2x12 or a 1x15 & 1x12 in the same box? Why the LFA's? Those are going to give you a nice hole in response unless you use a tweeter that can do sub 3khz.

billfitzmaurice · #3 07-22-2010, 06:24 AM

Quote:

Originally Posted by NoGraveConcern

Why the LFA's? Those are going to give you a nice hole in response unless you use a tweeter that can do sub 3khz.

You'll have an off-axis response hole crossing over anywhere above 1.5kHz. As for the 12LF, it's an obsolete driver, as is the 15LF. And there's absolutely no reason to use a 15LF and 12LF together.
The OPs questions are typical of those posed by speaker building newbies who shouldn't even be thinking about designing their own cabs, especially when good designs like the fEarful are available.

lbwdog · #4 07-22-2010, 06:25 AM

You would be much better off following the plans for one of the fEarful designs. The heavy lifting (research) has already been done and proven. Based on your question and component choices, I can tell there's not a lot of science in your design (no offense). That will guarantee a result of dubious quality.

IMO, the fEarful designs are the pinnacle of multi-way DIY bass cab building. Greenboy based it around the best new drivers available, as well as much thought into tuning, placement, etc.
A 15+6 would be plenty for most cases but if you must have two woofers, there's a 212+6 and dual 15 plans too. All these incorporate a 6.5" mid driver, and you can put in a tweeter if really necessary. Personally, I don't feel the need for a tweeter with the quality 6 inchers available. They reproduce above my hearing range anyway.

To answer your question, an 8 ohm crossover would only work properly with an 8 ohm woofer load.

MATAMOUROS · #5 07-24-2010, 11:12 PM

Oooops,i posted my thread without double checking it,and now i can see that i begun with building a 212 bass cab.No what im doing is building a 15/12,plus a tweeter.The box will be a little over 10 cubic feet,will have a 2/12 by 21 inches port(slot) on the bottom,and im going to instal a motorola ksn-1165a,and a l pad.Forget about the passive crossover.After i posted my thread ,i found out that with an electronic tweeter ,it is not needed.Inside im also going to build a horn like division.It should be ok,if not, ill just burn the box,and start over.Its by doing and experimenting,that we learn about things,and someone sugested that the 15 and 12 lfa woofers are outdated.I dont care if the box is to heavy or not,and according to the eminence website,those two woofers are on the same wavelenght(92db),and hold the same ammount of watts(500)After im finished with it ill comment about it here,and ill be honest about it.Regards,and thanks for the replays

billfitzmaurice · #6 07-25-2010, 06:49 AM

Quote:

Originally Posted by MATAMOUROS

Its by doing and experimenting,that we learn about things

There's certainly nothing wrong with experimentation under the right circumstances. But this isn't one of them. Experimentation is what one does when someone else hasn't already done it, and written down the results so that others need not trod the same ground over again. If there was a single aspect of what you're doing that made sense I'd offer some encouragement, but the fact of the matter is that you're not doing a single thing right, from the choice of drivers to the size of the box. I'd stop right now, put the project on hold, and learn something about speaker design before cutting any wood.

will33 · #7 07-25-2010, 10:26 AM

Quote:

Originally Posted by MATAMOUROS

Oooops,i posted my thread without double checking it,and now i can see that i begun with building a 212 bass cab.No what im doing is building a 15/12,plus a tweeter.The box will be a little over 10 cubic feet,will have a 2/12 by 21 inches port(slot) on the bottom,and im going to instal a motorola ksn-1165a,and a l pad.Forget about the passive crossover.After i posted my thread ,i found out that with an electronic tweeter ,it is not needed.Inside im also going to build a horn like division.It should be ok,if not, ill just burn the box,and start over.Its by doing and experimenting,that we learn about things,and someone sugested that the 15 and 12 lfa woofers are outdated.I dont care if the box is to heavy or not,and according to the eminence website,those two woofers are on the same wavelenght(92db),and hold the same ammount of watts(500)After im finished with it ill comment about it here,and ill be honest about it.Regards,and thanks for the replays

None of this makes any sense at all. I'd be listening to Bill here or you're going to be out money, time etc. and end up with a useless product. You have a lot of reading to do before you cut anything. Either that or build an existing/proven design and just worry about getting the carpentry and soldering part of it right.

MATAMOUROS · #8 07-25-2010, 09:31 PM

This is a replay to Mr.billfitzmaurice.Hi Bill.Thanks for the replay.Youre not the first person that says that i dont make sense.I know you mean good and are just trying to help me.The reason why i wanted to make it a 15 and 12 cab, is that i play mainly 5 string basses,and the 15 would reproduce the sound from the low B better.The birch playwood pieces are already cut.I was going to start to put it together! So you say i should learn a little more about cab design,but where do i get the information? About the work,i can probably do a better job ,or as good as the professional builders.I do precision work for a living,and everything i do is expected to be right everytime,so im not affraid,so if you dont mind give me the right dimensions for the cab.Please? Thanks again.

rbonner · #9 07-25-2010, 09:40 PM

Ya know, there's been a lot of bass cabs built across history that worked, maybe not as good as they'd work today with all the software for cab design out there, but they worked. Some didn't work so well. I've built some of both. The good news for me was I was like 15 and 16YO and plywood was under $8 bucks a sheet back then. So blast away and make sawdust. All my cabs looked great and there ended up being new happy owners when I was done with them, HA

But if you are asking for some cab dimensions now, after the wood was cut, I think Godzilla has already busted out of the cage. I think its time to glue and screw and see how they sound.

I built a bunch of cabs in 1970 2'X3'X1' deep and stuffed a pair of 15" in there they worked great. Give that a try with your speakers.

BOB

::::BASSIST:::: · #10 07-26-2010, 02:19 AM

Quote:

Originally Posted by MATAMOUROS

This is a replay to Mr.billfitzmaurice.Hi Bill.Thanks for the replay.Youre not the first person that says that i dont make sense.I know you mean good and are just trying to help me.The reason why i wanted to make it a 15 and 12 cab, is that i play mainly 5 string basses,and the 15 would reproduce the sound from the low B better.The birch playwood pieces are already cut.I was going to start to put it together! So you say i should learn a little more about cab design,but where do i get the information? About the work,i can probably do a better job ,or as good as the professional builders.I do precision work for a living,and everything i do is expected to be right everytime,so im not affraid,so if you dont mind give me the right dimensions for the cab.Please? Thanks again.

fEarful 15/6 = all your problems solved.

There is full details of how to build one in the fEarful wiki on Talkbass.

If you get frustrated with your experiments, give the fEarful stuff a try.

With all due respect I'd bet heavy that it will be better in every way than what you try on your own. The fEarfuls have been R&D for hundreds perhaps thousands of hours.

Read about them here on TB, all those people cant be wrong. I continue to be amazed with mine.

good luck!

Mr. Foxen · #11 07-26-2010, 06:34 AM

Quote:

Originally Posted by MATAMOUROS

the 15 would reproduce the sound from the low B better.

This is one of those suppositions that is wrong. If you want the information, there is a vast amount on the internet, look for article that provide sources for their information. Read all of the Fearful threads, and the links within, as that will cover pretty much everything. HEre is a start for you on speaker size: http://barefacedbass.com/technical-i...y-response.htm

rpsands · #12 07-26-2010, 10:23 AM

People who hold this flawed pseudo-empiricist worldview need to be spending more time reading about the experimental method. The first thing anyone does when coming up with a hypothesis is research prior studies on the subject, and every research paper on an experiment is chock full of citations of previous studies.

BassmanPaul · #13 07-26-2010, 10:47 AM

Building a successful speaker system involves far more than sticking a couple of odd sized drivers into a box of an arbitrary size that you just pulled out of thin air. Your result could be wonderful but it is far more likely to sound like crap. If your drivers are far enough out of their comfort zone you could well damage them irreparably.

Build the Fearful - you won't regret it.

Paul

ptidwell · #14 07-26-2010, 12:06 PM

Matamouros,
There been great advice offered here. It would really be in your best interest to take it. The FearFul is probably your best option.
You should also checkout Vance Dickinson's Loudspeaker Design Cookbook to educate yourself. It's really not a book for a novice, and if it appears to be a bit over your head, then that may be a clear indication to slow the train down and learn before you burn.
Good Luck.

MATAMOUROS · #15 08-26-2010, 08:58 PM

Ok , ok, ok.You guys scared me,so my project is on hold for now.I do have now copies of all the fearful 15/6 cab,and will go for that,but first i want to find someone who will make the crossover for me.The same crossover that GB designed.Once i get the crossover,ill start the construction.I may make a castle for my cat with the wood i cut for my old project(money down the drain).If someone wants to build the crossover for me,please say so.Thanks

Execut1ve · #16 08-26-2010, 09:06 PM

^^^ now you're talking

be sure to post pics tracking your progress, folks around here love a good cab building thread!

::::BASSIST:::: · #17 08-26-2010, 10:13 PM

Quote:

Originally Posted by MATAMOUROS

Ok , ok, ok.You guys scared me,so my project is on hold for now.I do have now copies of all the fearful 15/6 cab,and will go for that,but first i want to find someone who will make the crossover for me.The same crossover that GB designed.Once i get the crossover,ill start the construction.I may make a castle for my cat with the wood i cut for my old project(money down the drain).If someone wants to build the crossover for me,please say so.Thanks

PM TBer 'Burning Skies". Its my understanding that he has built some crossovers for people.

rbonner · #18 08-26-2010, 10:18 PM

Chicken

MATAMOUROS · #19 09-01-2010, 05:25 AM

Quote:

Originally Posted by ::::BASSIST::::

PM TBer 'Burning Skies". Its my understanding that he has built some crossovers for people.

I asked burning skies to build me one,and he said he cant do it for now,because he is behind on some projects .Ill have to wait.Should i go with the peavey 3x crossover?

HookerRoad · #20 09-01-2010, 06:18 AM

I'm curious as to why the choice is one 15" and one 12" speaker. I'm assuming you are looking for something that will thump. Big speakers aren't necessarily the answer. What amp is going to drive these puppies? What kind of tone are you looking for? A 15 paired with 10's are a standard in most Pro-line rigs for a reason. 12's can move some air just like a 15 can. This makes me wonder if you aren't just creating a low frequency phase issue. Both the 12's and the 15's handle about the same low end frequency response... but the key word here is ABOUT. For instance, the 120hz frequency coming out of the 15 inch speaker is going to move more mass than the 12 inch speaker at that frequency. The vibration of the cab is going to resonate two sounds at that frequency.... well all the same frequencies in their response range. Makes me wonder what the audible result will be. I'm guessing a weird muffle at higher volumes.

It's like playing chords on your low strings on a bass guitar. Sounds like crap. The same chord in the higher strings sound good. Use identical speakers for your low end. 2x15 or 2x12... one of each just sounds goofy.