hey, I've got a question!

The 6.5" kevlar woofer is 4 ohms. The tweeter is I have NFI what ohmage. I ASSUME 4 ohms. Now, using the crossovers you get to use with this, I don't know how to wire it so I get a 4, or even an 8 ohm load. I don't see how you can wire it in series. You can parallel the tweeter with the driver, but that's a 2 ohm load, which lowers the quality, and puts the power usage through the roof! I've got a 4x130wrms amp which I run bridged. At 4 ohms this is something like 380wmrs a channel. It's not stable at 2 ohms, and would almost be a direct short if you DID run a 2 ohm load.

How the heck do I wire it up so it's not a 2 ohm load? Can anyone confirm that the tweeters are 4 ohms? And how do you wire the crossover in series. I don't think it can be. It's not a crossover like most splits come with. You just have to solder it into the main woofer line, which kinda only means you can parallel it.

Help! I don't want to fry my amp! :( Nor do I want to have 2 ohm speakers and unbridged channels! My 2x150wrms is 2 ohm stable, but I just don't want 2 ohm front stage.

obviously not a question you guys want to deal with..... but I'll try again.

I figured out how I can wire up the crossover in series. This is cool, but unless I'm missing something, this will now be an 8 ohm load.

Question: Does a passive crossover change the impedance of a speaker system?

Obviously it's going to have resistance, but does it have impedance. It's still flowing AC signal... thus must have some kind of average resistance thus impedance... but I don't know how to figure it in the case of this split.

I wish it was cleverly done so that it presents a 4 ohm load when connected in series. But it's Jaycar... so most likely not.


Tim? FHRX? Magnat? Please????

Your amp should see a NOMINAL 4 ohm load if you use the crossover correctly.

Most tweeters are higher than 4 ohms (normally 8ohms or over), and are higher still at the frequencies in which they are used.

Cheaper crossovers rely on the natural roll off (raising of impedance) that speakers have (being that they themselves are coils).

I assume that the crossover setup will be like this;

INPUT
+ -
| |
| |
| |
BASS SPEAKER
| |
| |
| |
| high
| pass
| filter
| |
| |
Tweeter

With the bass speaker wired in parrallel with the tweeter, and the tweeter having a high pass filter in series.

http://www.focalaustralia.com.au/2002%20Polyglass%20tech%20specs/130CV.pdf

Using this data sheet from focal (just for example) you can see that the bass speaker (top specs) has an inductance of 0.19mH. This means that at higher frequencies (eg above 5-8 Khz) the speaker impedance will appear to be very high (almost like an open circuit). The high pass filter should enable the tweeter to appear as almost an open circuit at low freqs so therefore, as one impedance raises or lowers according to frequency, the other reciprocates, making the amp see a flat impedence response.

However, if you are using a "super tweeter" from Jaycar, then the tweeter impedance should be so high it is negligable (seeing as its actually a capacitor, not a coil). I guess that's y they call em super tweeters....

When you think about it, nearly all (cheaper) 6*9 speakers use this setup to get the same result. The only reason that the crossover (a non polarized capacitor) is used at all is to ensure the tweeter does not become damaged (by playing lower freqs).

So yeah, as long as it is set up like this then its O.K.

What this setup is doing is using the bass speakers natural rising impedence curve to negate the use of seperate crossover outputs to the bass and tweeter speakers.

p.s. If you again look at the focal spec sheet, you'll notice that in the FREQUENCY RESPONSE/ IMPEDANCE, the lowest line represents the bass speakers reative impedance in ohms to a given freq. The speaker shoots up to around 50 ohms at its resonant freq (100Hz) , goes back down again, then rises up to 10 ohms by the time the freqencies are above 5KHz. So, this can give you and idea of how the nominal impedance can really change according to different freqs.....

Thanks!

I had managed to figure that out just tonight, by reading a few textbooks. And that confirm my theory... something wrong with amp's power supply. I thought I'd given it a 2 ohm load in a bridged config and was slapping my forehead and calling myself names for being so stupid and installing at 1am.

Now I've got a whole big horrible mess of problems, and I'm going through them one at a time to see what else is fried. When the amp fried I took it out, and the sub amp, and sub kept playing just fine. But now when I hook up these super dooper splits, even with the head unit on 00 and the amp gain on 0... you get a zillion decibel shriek, and this time I'm positive it's not a wire off the speaker terminal. So, at the moment, fuses are out, and system is silent while I think and plan. One amp is dead, that's for sure, and I'm pretty sure that's Jaycars problem, not mine. Perhaps the thing just chose to die. But what else has it done.

Another question I raised in my mind tonight is... I have nothing connected to my head units speaker outputs. That means there's an (albeit small) amp driving nothing. Any thoughts to the ramifications of this? They haven't been connected to anything in a good while, and no probs. But just wondering. And no, they're not touching bare wire on chassis.

I'll start by checking the main fuse, and seeing what the current draw is. Then check all the current from everything. Then I'll check grounds, and then I'll check speaker to earth to check for shorts or bared wires. I'll also hook up dodgy speakers to the remaining 2 channel amp and use another input to test that. I might test the audio out of the head unit also and see if that's gone. The shriek sounds like a feedback loop. Though with no program signal, I'm not sure... however, of course the headunit only attenuates, it does not 'shut off' the signal at 00.

Anyway, thanks very much for the reply! At least I can stop kicking myself, and see what on earth is the problem now. The amps had been running perfectly happily for about 5 months prior to these front speakers, so I'm still VERY suspect of their install and a possible short or something else. There may be still good cause to kick myself.

Thanks again! :)

Yeah... Looks like your on the right track with regards to testing the amp....

Having the head units speaker outputs unused (seeing an open circuit) is perfectly fine and it won't hurt your head units internal amp at all. Head unit specs often rate the maximum impedance at 8 ohms. This is because at higher ohms than this, the volume output at the speaker terminals would not be very loud, even with the volume right up on the deck the speakers would become too quiet to listen to effectively. However in your case, you don't need to worry about it.

One thing you may take into consideration is a very small possibillity that the internal speaker amp may cause noise interferance with the preamp output of the RCA's due to the large voltage differences at the amplifier chip terminals (in particular at high volume). This normally happens at higher freqs, and is why some top head units have heaps of shielding around the internal amps, choose not to have driver amps at all or have a seperate housing for the driver amps altogether, away from the preamps.

Well!!!! Dammit.... it was the speaker terminals AGAIN, causing me hassles!!!!! I went over everything, and found the left channel 'positive' wire was earthing somewhere along the line. Undid the driver out of the door and it dawned on me that the distance that the terminals are from the door panel including the mdf spacer, puts them DIRECTLY in the vacinity of the door metal itself. And sure enough, ONE bit of solder was sitting on the door. *sigh*. So now all the metal bits are insulated and no more fuss there. My remaining amp works very nicely with the drivers, and they are REALLY amazing for the price. No, they probably won't keep up with anything really decent, but they're seriously amazing for what they are. The bass could almost be described as 'thunderous' from the 6.5" inch woofer. With those up front, the sub ain't gonna need to be doing much work. The tweeters are really nice too, very smooth and crisp without being harsh and sharp. I'm really impressed, and the door deadening really really worked. No rattles, and the bass holds good for the full range. The bottom notes sound like they're coming from a sub, and make your chest vibrate, with no artifacts. They WON'T do this at 140db... but I don't want them to. They will do it loud enough to hurt like crazy, so good enough for me!

Now I just have an amp with 4 fried power supply mosfets, and who knows what else. :( I don't know if it was from the speaker. I assume it quite possibly was, though the system was fine for at least 4 hours prior to things going awry. I remember that the system went NUTS when I went over a bump in the road. Perhaps it made contact and said a rather large hello. However, I don't know that that in itself would have caused the amp to fry. I turned it off within a split second. And it didn't blow up my remaining amp when I first plugged in the speakers again and noticed the squeal. I still think there's a fault with the amp's power supply. There was no power short. Earth was (and still is) good. Impedance was correct for amp. The only thing was that the amp was bridged, which I've never had it before. Obviously it drew a heck of a lot more power on it's supply rails, but why? The gains weren't up that much. The speaker shorting would certainly have given it a <1 ohm load and thus hitting it up for it's MAXIMUM power. But why didn't this blow the amps fuse? It did blow the fuse I installed for it... and here boys and girls is why I'm a BIG IDIOT... I replaced the fuse without fixing the problem, and that's when the smoke got let out of the amp!!!!!!!!!!! My amp would probably be in one piece still if I'd not done that. I already had learnt that lesson before, but I guess I just ignored it. Oh well.

Anyone who wants cheap splits... go the jaycar system. 200 bucks will get you a front system that will suprise you.

Goodnight all!


oh btw...anyone know if jaycar repairs amps? Obviously it ain't gonna be warranty as my stupid fault.

yeah, they do repair amps. However they send them off to melbourne or sydney. So you have to pay for the freight. A $50 deposit is taken to check the amp and that pays for the freight too from memory

heh heh... jaycar took the amp under warranty. I sounded dumb and said that it just stopped working and didn't blow any fuses. So we'll see what happens. I'm half expecting them to ring up and say, hey, this ain't warranty... but perhaps I'll be lucky.