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07-16-2010, 11:04 AM #11
With a full symmetrical crossover, half of the system has an imedance rising to infinity while the other half is lowering down to DCR on either side of the center frequency. So assuming the compression driver and the midrange driver are both 4-ohms, (as an example) and wired in parallel, the fully symmetrical crossover maintains a 4-ohm load at the amplifier. The Kicker KM6500.2 is designed this way, as it has a symmetrical crossover.
Without a low-pass curcuit on a two way system, the 4-ohm DCR of the midrange driver is in parallel with the compression driver, showing 4-ohms impedance well past the compression driver's crossover frequency where finally the natural inductance of the voice coil causes its impedance to rise. A voice coil is a natural inductor, since it is a coil of wire, around a ferrite core, just like a common iron-core crossover inductor. At crossover frequency, you have a 4-ohm, or slightly higher midrange impedance in parallel with what probably is a 6-ohm compression driver impedance. For those values, you are showing 2.4 ohms to the amp from a single midrange/horn coaxial unit, not 4-ohms.
Assuming the inductance of the midrange driver is already affecting the midrange driver at crossover, and maybe the midrange driver has an impedance of 6-ohms at the compression driver's crossover frequency. A 6-ohm midrange impedance in parallel with a 6-ohm compression driver impedance results in a 3-ohm impedance at crossover frequency.
So, as David points out, without a symmetrical low-pass crossover to complement the compression driver's high pass crossover you get impedance dips. This is whay you usually see me recommending a single 4-ohm speaker per amplifier channel for most full-range applications like with typical coaxial loudspeakers.
I am not sure that the folks who unwittingly or unknowingly wire to 1-ohm per channel are really getting away with anything. The inevitable is just around the corner, the thing either constantly goes into protection mode, or it simply blows up.
A little history:
The first round of amplifiers that were finally officially reported to be 2-ohm stable back in the day were stereo amplifers being put into subwoofer service. We did not have 1,000 watt, 1,500 watt or 2,500 watt amps back in the day, so to make bass, you moved jumpers around on the power supply transformers to allow you to run higher current, either by bridging a stereo amp into a single 4-ohm woofer, or using the same amp to drive four 4-ohm woofers. The original intent of bridging and 2-ohm operation was to drive subwoofers, where the load was inductive rather than capacitive. With a subwoofer, the impedance is always rising with frequency, so there are no impedance dips. I am not sure it was ever the intent of the industry for people to start bridging and parallel loading amps for full range applications.
These days, history is often lost, and too often people fail to deliver the full message, in part because it is complex, complicated, and makes lots of folk's heads spin, (like some of you reading this! )
4-ohm full range speakers are not 4-ohm, any more than 6-1/2 speakers are 6 and a half inches..... Both terms are generalities.... For the very reasons I point out above int eh crossover explanation, a coax spekare that measures 4-ohms DCR will have an impedance dip at crossover when actually played. Combine this with the fact that most "4-ohm" speakers have a 3.4 - 3.6 ohm DCR out of the box and you have a double-whammy at crossover.
Too many times, people complain that their amplifier shuts down with the 8 speakers they have wire to it. Too many times, I just have to laugh, and start thinking about how best to explain it, and to help. That is why I have my mantra:
IN GENERAL, and for most full-range applications, (in-boat coaxials, etc) the best practice is to wire one speaker to each amp channel.
There are multiple benefits for the boat audio enthusiast:
Current draw is minimized, resulting in cooler lasting amplifiers,
Minimal current draw meanas longer sitting with the motor off in party cove.
Clipping is minimized and headroom is maximized
No fires or explosions
For your original question, wiring the Krypts in parallel is likely going to make the amp shut down. Go ahead and try it, but do so making sure of the following:
high-pass crossover is turned ON
CROSSOVER FREQUENCY (HZ) is at 100Hz or even higher
BASS BOOT is turned totally off
GAIN is very subjective. Turn it up a little, then with a loud cd, (I like Nickleback for this) turn your radio up until you start to hear it distort, i.e. get crunchy and bad sounding. This is usually at around 75% of the radio’s max volume. Then turn the radio down a little, and turn the INPUT SENSITIVITY up until you hear the amp starting to make things sound bad, distorted, crunchy, etc, then turn INPUT SENSITIVITY down a little.
At that point, you have max output from the amp, at the max output setting of the radio. From this point, if the towers are too loud, turn the INPUT SENSITIVITY down. You cannot turn the amp up past the setting you found without causing distortion and potential damage.
If after all of this you find that the amp shuts down, it is because you are dipping below 2-ohms. You have a couple of options:
Wire each side's pair in series, taking the impedance from 2-ohm nominal with dips to 1.5 or lower to 8-ohms nominal with dips approaching 6-ohms.
Buy an additional 850.2 and wire the 4 speakers up to the 4 amp channels.
Consider selling your 850.2 and trading into an 850.4 which delicers about perfect power for your 4 HLCD coaxes.
Let me know what you think, if you have any more questions, or if you wnat some more explanation. Sorry for writing the big book, but I thouhg I shuold tell th whole story! Sorry for being late to reply!!!
Last edited by philwsailz; 07-16-2010 at 11:18 AM.
07-16-2010, 12:10 PM #12Senior Member
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- Oct 2009
You obviously know far more than I ever will however I have a few stupid questions. I was under the assumption that when I wired 2 of the speakers (per channel) in series it was putting them @ 4 ohms, not 8? If it puts them @ 8 wouldnt this be only like 70 watts a speaker? If not what is the correct power figures to each speaker wire in series?
Also I like the idea of getting the 850.4 4 channel amp however wouldnt this require me to run 2 extra sets of wires thru the tower so each speaker gets its own channel? Running tower wire = sucks!!
07-16-2010, 12:42 PM #13
Many of my previous comments were directed at Brain's questions, not Brian. I keep repeating that mistake.
MM, Its extremely important to put a boat into storage with an empty bilge as this can really compound the issue. Just an addition to a good point.
To add to Phil's comments, a 2-inch multi-layer subwoofer voice coil for example may double its DCR by 100 hz and the impedance may take off above 150hz. But a smaller single-layer coil in a midrange may have an impedance that slowly rises and doesn't change significantly until maybe 8khz. And, you can't measure the true overall impedance or even the collective DCR with a basic multimeter, particularly since the highpass section is capacitor-coupled and won't pass DC. Knowing these and other less obvious details and the correct analysis of the individual components and how they truely interface can have a profound affect on the system's final performance.
07-16-2010, 12:49 PM #14
On an unregulated 4-channel amplifier the final output power and resuting stability should be equal for 4-channel 4-ohms or 2-channel bridged into 8-ohms. With a seriesed configuration at the top of the tower (just a simple jumper from one pod to the other) you can maintain a four total conductor tower harness without running new wires. However two HLCDs per side deserve 12-ga wire.
07-16-2010, 01:42 PM #15
With a 4-channel ZX850.4, wire each side pair of speakers in series to take the load to 8-ohms on a single speaker wire per side. Then run the 8-ohm load per side to a bridged half of the 850.4 amp. That will deliver the same power to each speaker as you would have with each speaker on it own amp channel. The impedance loading will be the same too, but you use half the wire runs.
I do agree with David too that you owe your spekaers 12ga wire if you go this route. Hopefully it is as easy as tying aome 12ga onto your esisting wire and pulling it through.
As for series wiring, when you wire two speakers together in series, you add the individual impedance values up to get the new load value. two 4-ohm loads add up to 8. A 4 and an 8 add up to 12, etc.
Parallel wiring is the tricky part. For similar loads, the impedance halves, but for non-matched loads, say a 4-ohm load in parallel with a 6-ohm load, you can find the value by taking the product, (4x6) and dividing it by the sum (4+6) resulting in 24/10 or 2.4 ohms.
07-16-2010, 02:34 PM #16
Wow, that's good stuff, but boy my head is just a spinning. takes me back to advanced physics in 12th grade.... LOLA Day at the Lake...Priceless
A Day in Powder...Endless
2012 Möbius XLV~ Loaded & Exiled
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