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-   -   How do I determine the impedance of a cabinet? (http://www.talkbass.com/forum/f15/how-do-i-determine-impedance-cabinet-1025177/)

 Invisible_Kid 10-24-2013 06:26 PM

How do I determine the impedance of a cabinet?

Might be a stupid question, but I got an 8x10 today with Trace Elliot speakers. The guy said he had bought it from someone who had assembled it himself, so he doesn't know the impedance (or wattage, for that matter). Also, the tweeters are not hooked up. I'm guessing it's a stereo cab, based on the back panel. How would I find the impedance of these inputs? I read that one might be able to use an ohmmeter or multimeter to measure the resistance, but I also read that since that is a statistic that uses DC power rather than AC, it may not provide an accurate result. In any case, I have no clue where to go from here. Please help!
Pictures:

 ArtechnikA 10-24-2013 06:40 PM

two connectors -typically- mean the cabinet is designed to allow daisy-chaining.
I expect you'll find both those connectors are wired exactly the same - i.e. they are parallel connections. One in (pick one) one out.

DC resistance is usually -somewhat- lower than true impedance.
Driver impedances 'usually' come in a nice multiple-of-4 number so if, for instance, you measure the DC resistance at 6 Ohms, you're probably looking at an 8-Ohm cabinet.

The only way to be really sure is open it, read the impedances off the drivers, and check out the connections. You'll need to open it to connect the tweets anyway, yes ?

 Downunderwonder 10-24-2013 06:46 PM

Take the connector panel off and see what's what. More likely the inputs are mono parallel but could be stereo too. Whatever you do, don't connect two amps to it until you know for sure if it's stereo or you could kill two amps instantly.

While you got the panel off rig a 9v battery to + and -, all the cones should jump outwards together when voltage is applied.

The DC resistance is a pretty handy guide to nominal cab impedance. DCR is around 75%.

 wcriley 10-24-2013 07:35 PM

Might also want to plug those holes (between the jacks) to keep them from whistling.

 Invisible_Kid 10-24-2013 11:03 PM

Quote:
 Originally Posted by ArtechnikA (Post 15033998) Driver impedances 'usually' come in a nice multiple-of-4 number so if, for instance, you measure the DC resistance at 6 Ohms, you're probably looking at an 8-Ohm cabinet. The only way to be really sure is open it, read the impedances off the drivers, and check out the connections. You'll need to open it to connect the tweets anyway, yes ?
I'll borrow my guitarist's ohmmeter and take a reading. What do I touch the leads to, though? I have two speaker cables, both 2 pole SpeakON to 1/4". Do I put one of the leads on the tip and the other on the sleeve?

The problem with opening it is that there don't seem to be any screws on the back of the cab except the ones to remove the panel with the inputs and dial (whose function I am not sure of). All I can remove from the front is the grill.

Quote:
 Originally Posted by Downunderwonder (Post 15034013) Take the connector panel off and see what's what. While you got the panel off rig a 9v battery to + and -, all the cones should jump outwards together when voltage is applied.
How can I tell what's what by looking at the back of the panel? I have no experience with wiring. Are there some good diagrams I can look off?

What do I connect the 9V too? Would the jump from the voltage harm the cones?

Quote:
 Originally Posted by wcriley (Post 15034171) Might also want to plug those holes (between the jacks) to keep them from whistling.
What should I use for that?

Sorry for all the questions, guys. I'm kinda new to this and I want to make sure I'm doing everything right.

 GLEN18INCHSPICA 10-24-2013 11:19 PM

Unscrew the front grill & unscrew a speaker from the cabinet. See how its wired parallel or series look for diagrams readily available on the web as well as ohms law. The back of the speaker should tell you what its ohmage is on a sticker usually. Its most likely 4 ohms but, still you should make sure .

 Downunderwonder 10-24-2013 11:29 PM

Dude, unscrew the screws holding the jack panel into the cab, the whole thing will come away on the wiring. Take a photo or ten.

What you're looking for is wires jumping from one speakon to the other, parallel wiring. If each has its own wires disappearing into the cab then it's probably stereo.

Probing speakons from the outside is a non starter but hopefully there's enough slack in the wires to get to the inside wiring terminals.

Easier might be to pull one of the drivers and apply battery there. If half the drivers pop you got stereo, or mono and four blown drivers, check the other set similarly.

On and off 9v Dc isn't harmful. If you left it on it might cook the battery before the coils.

 Vince Klortho 10-25-2013 12:07 AM

This page shows a Trace Elliot cabinet with eight 10s in it but it doesn't appear to have three horns. That one has an impedance of 4 ohms and it can be run in stereo with two 8 ohm channels. It uses either 8 or 32 ohm speakers, I would guess the 32-ohm ones. Yours is not exactly that cabinet but I expect that it shares some of the same features.

 T-Bird 10-25-2013 01:12 AM

Hi.

Quote:
 Originally Posted by GLEN18INCHSPICA (Post 15034718) Unscrew the front grill & unscrew a speaker from the cabinet. See how its wired parallel or series look for diagrams readily available on the web as well as ohms law.
^This.

IME/IMO only that as well.

With eight (4+4) speakers plus 3 horns, and possibly two 4pole Speakon jacks, the possibilities of how it's wired are endless really.

The four bottom ones look like Eminence Gammas, the top ones look weird, but probably only because the circles on the dust caps.

I wouldn't even try to plug something like that in (again anyway ;)) before finding out exactly how it's wired.

If You don't want anything fancy, a couple of flat washers, nuts and bolts will cover those extra holes.

Regards
Sam

 Downunderwonder 10-25-2013 03:28 AM

Good points. ^

I still reckon you could get some good hints from opening up the jack panel. If indeed it turns out to be be 4 pole speakons you want to verify that.

My Trace cab has a sealed box inside behind the jack panel.

If you got a birdsnest of wires coming off the jacks to the drivers it's going to spin you out. A single pair guarantees some series / parallel mono arrangement. Much easier to make sense of the driver wiring birdsnest in that case.

Good luck.

Hopefully the replacement drivers are all the same impedance as the original trace ones and it's all series parallel 4ohm total, nice and simple.

 ArtechnikA 10-25-2013 05:07 AM

Lots of good replies - read all of them.

Quote:
 Originally Posted by Invisible_Kid (Post 15034691) I'll borrow my guitarist's ohmmeter and take a reading.
OK for now, but you should own one. For our purposes the <\$20 Harbor Freight digital is more than adequate.

Quote:
 I have two speaker cables, both 2 pole SpeakON to 1/4". Do I put one of the leads on the tip and the other on the sleeve?
Yes. You are looking for everything that moves to move in the same direction. If half the cones move, attach to the other connector and see if the other half do. If so - stereo! Probably everything moves together...

Bass cabs work with ~60V at full chat - 9V is just a tickle...

Quote:
 All I can remove from the front is the grill.How can I tell what's what by looking at the back of the panel?
Because -no one- knows the provenance of this cab and there are way too many possibilities for connecting it correctly, which you cannot know, and even more ways of doing it wrong - you're going to have to assume nothing and inspect everything. You will need to see the wiring of every part.

Quote:
 I'm kinda new to this and I want to make sure I'm doing everything right.
Better to ask these questions now than post 'Flames from my cab - now what?' later... To be sure, you must verify everything. It will be tedious and frustrating - just think back on the good deal and forward to the sounds...

We can't make much in the way of specific suggestions on stuff like how to plug the holes because we don't know what country you're in or what you have access to. In North America, I'd suggest some place like McMaster-Carr which has all manner of industrial goodies.

"Typically" panels like that have 1/4" jacks mounted as an alternative to the Speakons. Since you already have those, I wouldn't go the jack method. -But- another possibility that the original designer had in mind is a bi-amp cab, where another completely separate amp was to power the horns. Without knowing how (or if) they're wired it's impossible to speculate. It may be something to consider, but it's probably unnecessary complexity at this point.

 Downunderwonder 10-25-2013 06:35 AM

Take one lead and plug it into cab, apply the plus terminal to tip and - to the sleeve, cones will jump out with a bit of a fright but don't worry, just remove the battery. Verify what cones jump which way. If all jump out you're nearly golden, measure DC resistance.

Still it would be prudent to check on the speaker wiring to make sure it isn't fubar.

If half jump, try the other jack plug, then the other half should jump out while the others stay. Stereo.

 Invisible_Kid 10-25-2013 09:00 PM

Update

Quote:
 Originally Posted by Downunderwonder (Post 15034732) Dude, unscrew the screws holding the jack panel into the cab, the whole thing will come away on the wiring. Take a photo or ten.
Here we go!

The potentiometer-looking thing is connected to the hot glued yellow cylinder thing and I have no clue what either of them do. More pictures for the curious: 1 2 3

Quote:
 Originally Posted by Downunderwonder (Post 15034732) What you're looking for is wires jumping from one speakon to the other, parallel wiring. If each has its own wires disappearing into the cab then it's probably stereo.
Based on that information, it looks like it's parallel wiring.

Quote:
 Originally Posted by T-Bird (Post 15034917) The four bottom ones look like Eminence Gammas, the top ones look weird, but probably only because the circles on the dust caps.
Those circles say "Trace Elliot!" Lo and behold, indeed they are.

Some light Googling suggests that these are 32-ohm speakers.

As for the bottom ones? Surprisingly, also Trace Elliot!

I couldn't find the model number on Google, but the impedance is right there: 8 ohms.

Quote:
 Originally Posted by ArtechnikA (Post 15035102) OK for now, but you should own one.
Some digging around the garage managed to reveal an old multimeter! However, when I tried measuring the resistance, it got pretty weird... see for yourself.

For those of you who can't view that video, I touched the leads of the meter to the tip and to the sleeve, and the display showed wildly differing numbers, between -102 ohms and 168 ohms. I don't know what the issue is here; I tested the voltage of a 9-volt battery using that multimeter and it came out to 8.89V, so I wouldn't be too quick to assume that the meter itself is faulty, although it is a different kind of measurement.

Quote:
 Originally Posted by Downunderwonder (Post 15035039) If indeed it turns out to be be 4 pole speakons you want to verify that.
How do I go about verifying this? Luckily, I still haven't used one of the cables, so if need be, I can go return it for a 4-pole speakON to 1/4". I checked the model number of the chassis (seen in the first post) on Google, but came up with nothing. However, the model name does have the number 4 in it, and in checking Neutrik's websites for all their chassis, I found that all the 2-pole chassis had the number 2 in their model name, while all the 4-pole chassis had the number 4 in their model name. Based on this, I would assume that it is a 4-pole chassis, but is there a way to be sure? After all, I can't find the model of the chassis anywhere.

Thank all of you for your help so far!

 B-string 10-25-2013 09:21 PM

Wow that's a mess. The top four speakers should be wired in parallel, BUT, the bottom being 8 ohm each should be wired as two pairs in series and the two series pairs in parallel. The top four and bottom groups then wired in parallel. Net 4 ohms.
The yellow thing is a crossover cap for the horns but that does not look like a proper L-Pad or at the very least not wired correctly. Looks like a 2.2K ohm pot???

BTW always short your meter leads together first before hooking up to what you want to test. This will test your meter leads and also verify the minimum resistance (error) of your meter and leads. Then hookup to what you want to test (leads unshorted of course).

Lastly those speakon jacks are indeed 4 pole.

 Invisible_Kid 10-25-2013 09:36 PM

Quote:
 Originally Posted by B-string (Post 15038641) Wow that's a mess. The top four speakers should be wired in parallel, BUT, the bottom being 8 ohm each should be wired as two pairs in series and the two series pairs in parallel. The top four and bottom groups then wired in parallel. Net 4 ohms.
I sure hope so!

Quote:
 Originally Posted by B-string (Post 15038641) The yellow thing is a crossover cap for the horns but that does not look like a proper L-Pad or at the very least not wired correctly. Looks like a 2.2K ohm pot???
How do I test to see if it's wired correctly? I do want to hook those tweeters up eventually.

Quote:
 Originally Posted by B-string (Post 15038641) BTW always short your meter leads together first before hooking up to what you want to test. This will test your meter leads and also verify the minimum resistance (error) of your meter and leads. Then hookup to what you want to test (leads unshorted of course).
Interesting: when the circuit is open, the screen reads at 1 Ohm. But when I touch the two leads together, I get the same wild fluctuations as seen in the video, except with no negative voltages. Does this mean the ohmmeter is broken? Thank you!

 gumtownbassman 10-25-2013 09:40 PM

That's a super fugley setup there,
you idealy want all the speakers to be matching in impedance, but could work with what you have.
(as posted above)
Looks like the potentiometer for the horns is not finished being wired.

 Invisible_Kid 10-25-2013 09:47 PM

Quote:
 Originally Posted by B-string (Post 15038641) Lastly those speakon jacks are indeed 4 pole.
Well, time to stop by the music shop again...

Quote:
 Originally Posted by gumtownbassman (Post 15038691) Looks like the potentiometer for the horns is not finished being wired.

 B-string 10-25-2013 09:51 PM

Yes your meter is malfunctioning! With the leads not touching the display should flash with most meters displaying "OL" (over limit). It is possible for the meter to have a flashing "1" but whenever you measure something the display should be on steady.

 Invisible_Kid 10-25-2013 10:02 PM

Quote:
 Originally Posted by B-string (Post 15038714) Yes your meter is malfunctioning! With the leads not touching the display should flash with most meters displaying "OL" (over limit). It is possible for the meter to have a flashing "1" but whenever you measure something the display should be on steady. This page shows a 100 watt L-Pad and how to wire it. The L-Pad is usually 8 ohms.http://www.parts-express.com/pe/show...m_campaign=pla
Alright, I'll give my guitarist's ohmmeter a try.
Oh, and thank you for the information on the L-Pad!

 B-string 10-25-2013 10:10 PM

No trouble life is a learning and sharing game ;)

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