Question about DIY bass cabs

[netcastle]

I recently built a small bass rig consisting of a 4 by 6.5" cab and a 2 by 12" cab. I want to add more beef to my sandwich so I purchased a 15" driver to compliment the 2 by 12's. The problem is that I will be operating both the 15 and the 12's at the same frequencies (sub 150Hz). Being that one cab is sealed (2 by 12's) and the other will be vented (15), will I lose out to phase incoherence between them or is this generally not a problem?

BTW, the 6.5 drivers while uncommon aren't half bad in this application.

Tim

 

[adamasd]

I do not think there will be a problem. bass and guitar rigs seem to be pretty forgiving with this stuff. I know someone who runs a large JBL 15 ported PA speaker cab with a 2x12 for bass,they are both running full range there it sounds great. Although the marked speaker polarities between the 12s and 15 were reversed. why can't speaker manufactures have a standard for this.

adam

 

[CJ]

You can try to match things up by moving the big guy front or back of the 12's. I don't know, I may be talkin out the old wazoo. How many meters wavelength is a 100 hertz bass note?

Bass just kind of eminates the wood work. So once it leaves your ear, it's anybodys guess what the guy at the urinal is hearing. :razz:

 

[bcarso]

The standard is now cone moves out from the motor for + applied to +.

 

[CJ]

What about Jensen re-issues? Where they the guys that had it backwards during the fifties?

 

[bcarso]

One division of H*rman had it backwards, and this led to a crisis when that div. made some drivers for a computer OEM system. The same guy who stubbornly refused to change the convention, told Test to turn off the polarity checker on the line in an attempt to cover his tracks.

After years of believing this guy had the negatives of compromising photographic material on top execs (so reviled and dissed as he had been for years but apparently invulnerable) this incident finally brought him down.

 

[netcastle]

Good point (about the urinal). I'll let you all know how it goes.

Tim

 

[adamasd]

What about Jensen re-issues? Where they the guys that had it backwards during the fifties?

My 60s C12 is the same as my reissue C10s and my celestions, but my RCA branded P10 is backwards, but is the same as my 8" fisher and 15" oxford. I used to have a Jensen special design C12 and that one was backwards to my other C12, it was a slightly different C12 made for harmony. So maybe Jensen made all their custom speakers and speakers to be sold under other brand names reverse from the rest of their speakers. All these speakers with the exception of the reissue C10s and Celestions are from the 60s, so maybe they have gotten better since then.

Ted Webber has a story somewhere on his webpage about visiting a speaker manufactorer, and while looking about the factory he came accross two lines of machines that were makeing the same speaker, but at the end, each line was reversed for polarity.

I always check the speakers before soldering them, it is just so much easier in the long run.

adam

 

[CJ]

Good idea. 9 volt batt on the terminals, right?

 

[adamasd]

I just hook it up with a cable I made with push on terminals and give it a test with a second known cab along side it. Then solder it up.

adam

 

[pstamler]

For many years Gerbil woofers and mids were reverse-polarity (+ on red = cone moves inward). Why, I do not know, but they were. Made me paranoid about polarity.

Yes, a 9V battery works; I used to yank the battery out of the Makita cordless drill and use that, since it was always sitting on the bench.

Peace,
Paul

 

[Kev]

[quote author="pstamler"]Why, I do not know, but they were. Made me paranoid about polarity.
Yes, a 9V battery works; [/quote]

cos that was the standard and there was a reason ...
to do with mic polarity ... push mic diapram in speaker should come out ...
easier to explain when I can wave my arms

what came first
the mic
or the speaker ?

as usual it's all relative and about the position of the viewer
stand above the snare ... mic ... speaker moves in

JBL used to be the reverse also
I don't know what companies are doing these days But I agree for the most part + to + cone moves out


I DON'T use 9V ... I use 1.5 volt batts

 

[netcastle]

You know, I never thought about this and now I feel like I should be testing all my drivers with a battery before putting them in cabs. I just always took for granted that the red mark or the + on the terminal went to the red terminal on the amp and that this would be a standard. Anyway, good to know. I will check my cabs for this.

Truthfully though, I was more worried about the phase response of the driver than the polarity and how this could cause cancelation among the drivers in the two cabs. It's a mute (moot) point now because I am going to build the 15 inch speaker anyway and run it along side of the 2 12's and if there is cencelation...oh well.

Tim

 

[CJ]

The 9 volts don't have as much current behind them
1.5 D can supply amperes.

 

[Kev]

[quote author="netcastle"]You know, I never thought about this and now I feel like I should be testing all my drivers with a battery before putting them in cabs.

Truthfully though, I was more worried about the phase response of the driver than the polarity and how this could cause cancelation among the drivers in the two cabs. [/quote]

Single driver cabs is one thing but it is very important to know the polarity of all drivers in a multi driver cab aor larger system

Beware ... I have had some RCF's and JBL's ... incorrectly marked.
Use the Batt

Speakers with x-overs require you know about the order of the filter ... don't assume
check the schematic

[quote author="CJ"]1.5 D can supply amperes.[/quote]

yes .. correct
I should have said AA 1.5 v Batt


" phase response and cancellation "

yes a difficult subject
Band Pass or Double Venturi boxes are even more difficult as their phase response is continually changing from 20 to 120Hz with two resonant peaks on the imp plot

Having said that,
it is very typical to use a pair of 10s or 8s with a single 15

If it sounds good and you like it ... just go with it

 

[barefoot]

Here's a quick simulation of a generic ported response (blue) summed with a generic sealed response (green). The speakers have the same polarity and no distance separates them. The summed response (red) looks pretty straightforward. I tried a few different f3 combinations and they all look similar. As long as you keep the cabinets close together and don't cross them over at too high of a frequency you should be ok.

Thomas