PDA

View Full Version : To bridge or not to bridge



louisiana21v
05-27-2012, 11:29 PM
I just installed a pair of Polk MM651UM speakers in my tower cans, and will be running them with a kicker 350.4. Should I just run them off 2 of the channels and save the other channels, or should I bridge it down to 2 channels. The speakers are labeled 3ohm on the back but the paperwork that came with them says they are 4ohm. If 3ohms is correct will that be too much on the bridged amp.

501
05-28-2012, 01:51 AM
I'd bridge it. It will be much louder. Just make sure to turn the HP Filter on to keep the low bass out of the speakers.

jmvotto
05-28-2012, 09:03 AM
Agreed Polk site states 4 ohms. That's strange that's it stamped 3 ohm on the speaker. Email Polk tech service and get the straight skinny.

moombahighrider
05-28-2012, 12:17 PM
Do you have a multimeter? Just test the ohms on the speaker terminals to verify. You should see 3.7 ohms or so and that would be appropriate for a 4ohm speaker.

louisiana21v
05-28-2012, 10:13 PM
Thanks for the multi meter suggestion, guess I should have thought of that. The Polks measure 3.3ohms and an old speaker I had just laying around measured 3.8. I guess they are a lower ohm speaker.

So I think the Kicker 350.4 bridged 2 channel puts out like 175 at 2ohms but may be closer to 200 with these speakers.

Thats right at the peak rating of the Polks, is that too much? Any one running a similar setup?

I hear its better to over power than under power but there's a limit to that right?

501
05-29-2012, 02:42 AM
It will sounds great. You are right, better to over then under power them. I have hit the Polk DB Speakers with lots of clean power and they did fine. For tower speakers you will want the eaxtra power and just make sure the HP filter is on because you don't need low bass going to them. And because they are full range I wouldn't worry too much about overloading your amp, it will be fine.

bergermaister
05-29-2012, 02:18 PM
Kicker amps are notorious for putting out more power and delivering more than they advertise too! ;)

jmvotto
05-29-2012, 08:22 PM
Fwiw I thinks the Polk um are in the new surpas '12 and are certainly running 2 ohm in the cockpits .

501
05-29-2012, 09:30 PM
JMvotto is correct. They sure are. My Buddy just got his new Mojo yesterday and it's running at 2 ohms for the rear cockpit speakers.

cab13367
05-29-2012, 09:58 PM
Thanks for the multi meter suggestion, guess I should have thought of that. The Polks measure 3.3ohms and an old speaker I had just laying around measured 3.8. I guess they are a lower ohm speaker.

So I think the Kicker 350.4 bridged 2 channel puts out like 175 at 2ohms but may be closer to 200 with these speakers.

Thats right at the peak rating of the Polks, is that too much? Any one running a similar setup?

I hear its better to over power than under power but there's a limit to that right?

The 350.4 bridged is stable only down to 4 ohms. I think you're asking for trouble running it bridged with a 3.3 ohm load. I guess you can try it and if the amp can't handle it, it will go into protect.

louisiana21v
05-30-2012, 12:14 AM
That's one thing I was worried about. My buddies new (2010) Centurion Enzo is running three of these amps and I was impressed with them, so I ordered one to run my new tower speakers. Mabey I jumped the gun a little. I usually over analyze everything.

So if I just run them of 2 of the 4 channels would that be under powered?

wolfeman131
05-30-2012, 12:25 AM
JMvotto is correct. They sure are. My Buddy just got his new Mojo yesterday and it's running at 2 ohms for the rear cockpit speakers.

What? Gisepi doesn't own a camera or did I miss the pics?

WaterBullDawg1980
05-30-2012, 03:02 PM
What? Gisepi doesn't own a camera or did I miss the pics?

I think our kumputers are broken. I don't see no piks eeether.

Sent from my bag phone using Tapatalk Dos

louisiana21v
05-31-2012, 01:58 AM
So the Kicker 350.4 was waiting at my door when I got home from work. The certificate said 425 watts total. I hooked it up straight not bridged and measured the ohms at the amp while running, it read 3.0 exactly. Considering the actual output and the 3ohm load I figure its close to 100 watts per channel this way (or is this wishful thinking), that's about double what my old amp was pushing. It was too late for a good test, but considering I have less than $400 in this upgrade I think this is gonna be a good bang for the buck deal.

501
05-31-2012, 02:36 AM
I would definitley try bridging it. If it goes into protect, then wire back. only takes a few minutes to try.

newty
05-31-2012, 02:39 AM
Maybe I'm missing something but if you bridge a 4ch amp two channels with 1 speaker to each channel, you get a 2 ohm output from each of the 2 channels (roughly doubling the amp output). You add a second speaker to each channel now you've doubled the output again and dropped the impedence load to a 1 ohm which will likely send the amp into protect and/or cause the amp to overheat. Assuming the amp is not 1 ohm stable, it will not last long.

Be sure to check the owners manual on the amp to insure the amp is up to the task.

There is a learning curve to this stuff and I encourouge folks to research this stuff before commiting. It will cost you more in the long run if you dont.

louisiana21v
05-31-2012, 09:42 AM
That's what I always though too, bridged equals 2ohms, but that is based on using 4ohm speakers right? The manual states bridged power is 175 watts at 4ohms not 2ohms, that confused me. I think they mean 4ohm speaker load. These speakers are 3ohm which would present a 1.5ohm load. Correct??

cab13367
05-31-2012, 12:52 PM
Maybe I'm missing something but if you bridge a 4ch amp two channels with 1 speaker to each channel, you get a 2 ohm output from each of the 2 channels (roughly doubling the amp output). You add a second speaker to each channel now you've doubled the output again and dropped the impedence load to a 1 ohm which will likely send the amp into protect and/or cause the amp to overheat. Assuming the amp is not 1 ohm stable, it will not last long.

Be sure to check the owners manual on the amp to insure the amp is up to the task.

There is a learning curve to this stuff and I encourouge folks to research this stuff before commiting. It will cost you more in the long run if you dont.


That's what I always though too, bridged equals 2ohms, but that is based on using 4ohm speakers right? The manual states bridged power is 175 watts at 4ohms not 2ohms, that confused me. I think they mean 4ohm speaker load. These speakers are 3ohm which would present a 1.5ohm load. Correct??

Guys, this is not the way it works. I think you guys are confusing wiring speakers in parallel with bridging an amp. Wiring two speakers in parallel does reduce the total load that the amp sees (for example, if you wire two 4 ohm speakers in parallel, the amp sees a 2ohm load).

But the load that the amp sees (measured in ohms) depends on the speakers being used, NOT on whether or not the amp is wired bridged or standard. Most amps I know of are stable down to a 2 ohm load when wired one channel per speaker, and down to a 4 ohm load when wired bridged (two channels per speaker). I am not an electronics engineer so I don’t know why that is. But I know for sure that if you wire your 350.4 bridged to drive your pair of 3 ohm speakers, your amp will see a 3 ohm load per side which it is not designed for.

So if I were the OP, with two tower speakers rated 100W continuous, I would return the 350.4 and look for a 2 channel amp that is rated at least 125W RMS per channel. This will give you a bit of headroom on the amp so that you are not running it full tilt when you want to crank it up.

Also, if your goal is to hear your music while wakeboarding, be forewarned that you WILL be cranking it up and you still will not be able to hear it that well over the wind and engine noise.

BTW, the 350.4 is rated 60W @ 4 ohms, and 90W @ 2 ohms, so with your 3 ohm speakers, you are probably getting somewhere around 75W rms out of your amp to each speaker if you wire it one channel per speaker (this assumes an inverse linear relationship between resistance and power, which I am not sure is correct). But for sure, it will be somewhere between 60W and 90W.

Hope that helps.

louisiana21v
05-31-2012, 01:04 PM
That makes sense. Thanks man. I may have another use for this amp, but I'll have to run it for now. Definitely don't think I'm gonna bridge it.

501
05-31-2012, 02:48 PM
Well although the speakers aren't "exactly" 4 ohms, they aren't a 2 ohm speaker and are just 6.5" Co-axials not 15" Subs. I would bridge it myself. You won't "break" the amp. The worst thing that it could do it go into protect mode and I'd bet it wouldn't even do that. I have bridged amps to a 2ohm load many times without issue even if it doesn't spec it. In this case since it's driving small full range speakers I would bet it would be fine. Its double the power from the same amp for your tower speakers.

newty
05-31-2012, 04:25 PM
You bridge an amp you drop the ohm load. You add speakers you drop the ohm load. You do both and essentially drops the load twice, hence the 1ohm.
If he has speakers that are 3.5 it will be even lower.

We can all agree he needs a 2ch amp or a much bigger 4ch to run the whole boat.

Sent from my duhroid

cab13367
05-31-2012, 07:07 PM
You bridge an amp you drop the ohm load.

Newty, I don't want to get into a pissing match but this is simply not true.

Please see this link http://www.caraudioforum.com/showthread.php?t=97288 and in particular, this part:

3.5.4 Does bridging an amp halve the impedance of the speakers?
Impedance is a characteristic of the speakers. The speakers don't give a flip how the amp is configured: they have a given impedance curve, and that's that. It should be clear that when you bridge an amp, you are changing *the amp*. The speaker's impedance is *not* a function of the amp, but the amp's tolerance to a given impedance depends completely on the way the amp is configured. If you'll remember from section 4, an amp bridged into a given impedance draws twice as much current as it would if it were driving two separate channels, each at that impedance. So, a four ohm speaker stays a four ohm speaker, if it's hooked to one channel, a bridged channel, a toaster, or the wall socket.

501
05-31-2012, 09:18 PM
Bridging an AMP does not DROP the OHM, load, it increases (usually doubles) it power when bridged just like if the amp had 4 speakers running in stereo (at 2ohms) which is why is an amp is 2 OHm stable, it's only stable to 4ohm when bridged.

I still don't care what people say, its a decent amp and bridging that amp to run 2 X 6.5" co-axial speakers will be fine. I would at least try it out. Tower speakers without a lot of power just kinda blow. You can never hear them.

Also many '4 Ohm" speakers don't measure exactly 4 ohms.

newty
06-01-2012, 01:11 AM
Newty, I don't want to get into a pissing match but this is simply not true.

Please see this link http://www.caraudioforum.com/showthread.php?t=97288 and in particular, this part:

3.5.4 Does bridging an amp halve the impedance of the speakers?
Impedance is a characteristic of the speakers. The speakers don't give a flip how the amp is configured: they have a given impedance curve, and that's that. It should be clear that when you bridge an amp, you are changing *the amp*. The speaker's impedance is *not* a function of the amp, but the amp's tolerance to a given impedance depends completely on the way the amp is configured. If you'll remember from section 4, an amp bridged into a given impedance draws twice as much current as it would if it were driving two separate channels, each at that impedance. So, a four ohm speaker stays a four ohm speaker, if it's hooked to one channel, a bridged channel, a toaster, or the wall socket.

I've never been able to piss very far anyway. Lol
Thats the way I've always understood it. I've been through a lot of trials and tribullations with DVC woofers and 2ch stereo amps.
Maybe we're not considering the stereo vs mono watts here. Hopefully Brian will chime in here and clear things up.

newty
06-01-2012, 01:17 AM
Take a look at this. This is how I've always understood it to work.
http://www.zedaudiocorp.com/index.php/tech-talk/bridging-amplifiers/item/bridging-amplifiers.html

Brianinpdx
06-01-2012, 01:48 AM
Hey guys - so I'm laying here "summer sick" and I get a call from one of my local to me moomba owners asking me about this thread. Let me lay it out for ya'll in really simple terms... I skimmed thru the info here and Al is on track and to a degree so is Newty...but it really comes down to a couple of things....

First the AMP - amplifiers are designed to produce various power into various load conditions which are dictated in terms of impedance (ohms). at 4 ohms x4 ch it does xx, or 2 ohms it does xx. This is all fancy talk for the condition the power supply of the amplifier operates at. You can use a very simple rule here to cut to the chase ::::::

4 ohm BRIDGED power is the same output condition as
2 ohm STEREO power

2 ohm BRIDGED power is the same output condition as
1 ohm STEREO power.

The part that is messing with everyones minds is the fact that this is a 4 ch amp. Bridged does mean summed and yes the output impedance condition rises.. pretty much across the board amplifier wise you do not want to run 1 ohm stereo loads (or 2 ohm bridged loads) on multi channel amplifiers. To do so creates a lot of heat, or worse yet, BOOM in the power supply. When bridging 4 ch amplifiers, you create a bigger 2 ch amplifier with bigger 4 ohm power capability. <---read that again 4 ohm power capability.....

PART II - this is the area that Al was speaking about. All that condition crap is just fine and dandy but what happens when we hang different speakers off the terminals of the amp. series vers parallel. Typical speakers DCR is 4 ohm nominal impedance. I use that word nominal on purpose because in certain frequency range that "nominal impedance" can dip down some (or up).

In the typical case 2 pair of 4 ohm speakers is a 2 ohm bridged load / 1 ohm stereo load. And this is not a good idea for a multi ch amplifier. PERIOD.

PART III - why do speakers come in different nominal imp ratings. This is an age old sales versus engineering trick that companies engage in to sound better on a display board. Think about it with me for a moment. If we have a display board full of 6.5 speakers and 10 pair of them are all 4 ohm speakers but 1 pair is 3.3 ohm, when you listen to them the 3.3 ohm pair sound... "my oh my, a little brighter, a little louder than those others." So they must be better right? Nope not really. Just smoke and mirror game because its just telling the amplifier to work a bit harder and deliver a little more power.

In fact, that little sales trick gets people into trouble when they start to double up on the speakers as is the case being asked here. notice on display boards they don't do that. Reason is? It shuts down their switching system within the board--- i.e. to low of impedance.

In summary - lets take it to the real world. We put these 2 pair of 3.3 ohm speakers wired in parrelell on the amp in bridged mode, and now we effectively have a 1.5ohm ('Nominal') load with dips down as far as 1 ohm. Under hard power real world use, this amplifier is either going to gag on itself and try to protect itself by turning off.. or it will cook and blow the power supply.

Is it a good idea? no!
Will it sound louder? yup.
Will it burn for sure? Depends how hard you run it. and how long.

Bottom line is: run your multi ch amp in 4x mode with these 3.3ohm speakers and your gear will live longer.

Hope that makes sense to everyone. I tried to keep it simple and not techie.

-Brian
Exile Audio

501
06-01-2012, 02:43 AM
I believe the OP is only planning to run 2 speakers total on the 4 channel amp, so 1 X 6.5" speaker to each bridged pair of channels. Personally I think a single 4 ohm 6.5" will be fine to a bridged amp, but 2 would definitley be pushing it by dropping the impedence and is a different story.

cab13367
06-01-2012, 02:52 AM
Wow Brian, thanks for the thorough reply. However, the OP has just one pair of these speakers. All I'm sayin is, whether he wires them bridged or regular, the amp sees the same 3 ohm load. So will the amp safely drive a 3 ohm load bridged or not?

cab13367
06-01-2012, 02:56 AM
I believe the OP is only planning to run 2 speakers total on the 4 channel amp, so 1 X 6.5" speaker to each bridged pair of channels. Personally I think a single 4 ohm 6.5" will be fine to a bridged amp, but 2 would definitley be pushing it by dropping the impedence and is a different story.

Actually, the OP posted that he measured the impedance with a multi-meter and it's 3.0 ohms.

cab13367
06-01-2012, 03:22 AM
Take a look at this. This is how I've always understood it to work.
http://www.zedaudiocorp.com/index.php/tech-talk/bridging-amplifiers/item/bridging-amplifiers.html

Newty, I read the info in the link. It says that when an amp is bridged, each channel drives half the load. This is not the same as saying that the load is cut in half. So in the OP's case, if he wires it bridged, two channels will be driving each side and each channel will drive half the load. So the load is still 3 ohms and each channel will drive 1.5 ohms. So again, the load being driven is still 3 ohms because that's the impedance of the speaker.

Maybe think about it like this. You have a 500 trailer with a rope attached. If you have one guy pulling the trailer, he is pulling a 500 lb load. If you have two identical guys pulling the trailer, each guy is pulling half the load but the total load being pulled is still 500 lbs.

I hope that makes sense.

MLA
06-01-2012, 07:22 AM
Newty, I read the info in the link. It says that when an amp is bridged, each channel drives half the load. This is not the same as saying that the load is cut in half. So in the OP's case, if he wires it bridged, two channels will be driving each side and each channel will drive half the load. So the load is still 3 ohms and each channel will drive 1.5 ohms. So again, the load being driven is still 3 ohms because that's the impedance of the speaker.

Maybe think about it like this. You have a 500 trailer with a rope attached. If you have one guy pulling the trailer, he is pulling a 500 lb load. If you have two identical guys pulling the trailer, each guy is pulling half the load but the total load being pulled is still 500 lbs.

I hope that makes sense.

You have answered your own question so to speak. When an amp is bridged with a given load, or speaker impedance if you will, each channel "sees" half the applied load. Example: Bridge a 4 Ohm speaker and each chnl "sees" a 2 ohm load and the amps output to the speaker is generally the rated 2 ohm wattage p/chnl x 2. So if an amp had a 2 ohm output of 200W rms, then the 4 ohm bridged output would be 400W rms.

In the case here with the 3.0 ohm Polk and the Kicker zx350.4: Bridging a 3 ohm load would equal a 1.5 ohm load to each chnl. This puts the impedance below the amp's 2 ohm stability threshold. The amp will more then likely go into protect mode if driven past half volume. So, the gain in wattage RMS by bridging, is lost to having to govern the volume due to instability in this case.

louisiana21v
06-01-2012, 09:58 AM
Thanks for the input Brian. You confirmed my decision to just run on 2 of the 4 channels. Like I said before, I usually over analyze things ahead of time so I don't have these problems. This time I bought something on a whim and now its not really what I need. No big deal I can sell this one and get something else later. Thanks for all the input guys!

louisiana21v
06-01-2012, 10:18 AM
Ok, just for conversation. I bought this amp because my buddy's new (2010) enzo runs 3 of these amps and they scream. This is the factory system, all skylon speakers. 6 in boat coax 6.5's on one amp. 4 hlcd tower speakers on another. Sub on third. We had to turn the gains down from half to quarter just to turn the HU up past 12. 8 was too quiet 10 was loud 12 was crazy loud. That's why I was impressed. Guess his MB Quart HU puts out more preempt signal than my Kenwood.

louisiana21v
06-01-2012, 10:42 AM
Pre Amp signal. Stupid auto correct text.

Brianinpdx
06-01-2012, 12:22 PM
Whoops on the 1 pair versus 2. Sorry bout that. Even if thats the case, I'd still agree with MLA's take on it being below the rating. Especially when you consider the impedance dips that will happen with music.

21V - Nothing wrong with analyzing all this. Hopefully it will give people out there in your same position some pause and not head down the wrong path so to speak.

-Brian

bzubke1
06-01-2012, 12:41 PM
The 3 ohm impedance on the polks really screwed me too. I got a jl audio 4 channel amp for the six interior polks and wired the 4 cabin speakers together on two channels thinking the speakers were 4 ohm like most. I wired them up and they sound great for about 20 minutes at max volume but then the amp gets hot and shuts off. Since then I disconnected two of the cabin speakers and the amp never overheats anymore. I wish I would have done my research on the speakers too instead of just assuming the speakers were 4 ohm.

louisiana21v
06-01-2012, 01:36 PM
Hey bzubke1 check out this sight on different wireing options. The third example combines series and parallel to keep lowering the 3ohm load. This might let you hook up that other pair of cabin speakers.

http://www.termpro.com/asp/pubs.asp?ID=124

MLA
06-01-2012, 01:45 PM
The 3 ohm impedance on the polks really screwed me too. I got a jl audio 4 channel amp for the six interior polks and wired the 4 cabin speakers together on two channels thinking the speakers were 4 ohm like most. I wired them up and they sound great for about 20 minutes at max volume but then the amp gets hot and shuts off. Since then I disconnected two of the cabin speakers and the amp never overheats anymore. I wish I would have done my research on the speakers too instead of just assuming the speakers were 4 ohm.

Just wire each pair in series on each of the two chnls. It may be slight reduction in amp wattage, but the amp will play along happily ever after.

Take the - from the amp to the - on cabin A, then take the cabin A + to the - on cabin B then the take cabin B's + to the amp chnl +.

bzubke1
06-01-2012, 02:08 PM
I'll give it a shot this afternoon and let you know how it goes. So if I wire them in series I will end up with each channel of the amp seeing a 6 ohm load is that correct? The amp does 90x4 at 2ohm, 70x4 at 4ohm. So each channel will see about 50watts and each speaker about 25watts. I wonder if I will get more volume out of two speakers powered at 80 watts or four at 25 watts?

louisiana21v
06-01-2012, 04:41 PM
According to the sight if you do the series parallel combo the amp will still see the 3ohm load which will allow the amp to push the same power its pushing now. It looks a little complicated but would give you more power.

cab13367
06-01-2012, 06:49 PM
According to the sight if you do the series parallel combo the amp will still see the 3ohm load which will allow the amp to push the same power its pushing now. It looks a little complicated but would give you more power.

I believe the wiring diagram you are referring to involves wiring four speakers to a single channel, whereas bzubke1 is looking at wiring two speakers to one channel.

cab13367
06-01-2012, 06:57 PM
I'll give it a shot this afternoon and let you know how it goes. So if I wire them in series I will end up with each channel of the amp seeing a 6 ohm load is that correct? The amp does 90x4 at 2ohm, 70x4 at 4ohm. So each channel will see about 50watts and each speaker about 25watts. I wonder if I will get more volume out of two speakers powered at 80 watts or four at 25 watts?

I'm thinking you're better off driving two speakers at 80 watts. 25 watts is not a lot of power. I think it's time to upgrade to a 6 channel :) I've got the JL M6600 driving my 6 in cabin Exile speakers and am really happy with it. Clean, full range sound and more volume that I ever need.

MLA
06-01-2012, 07:02 PM
According to the sight if you do the series parallel combo the amp will still see the 3ohm load which will allow the amp to push the same power its pushing now. It looks a little complicated but would give you more power.

With two speakers needing to share one channel, you can either wire them in series or parallel. In parallel = too low of an impedance and series puts it in a safe zone, but with a little loss of output.

If the output is not up to snuff, then add a small 2 chnl amp for the pair in the bow.

louisiana21v
06-01-2012, 08:56 PM
Your right about that being for 4 speakers on one channel, didn't notice that at first I guess. Work can be distracting sometimes!! These Polks sound good for the money but they are kind of a pain.