I was just wondering whether the total impedance of a speaker is still 8ohms when your using an 8ohm woofer and 8ohm tweeter. I'm not sure whether they are being connected in series or parallel. I was also wondering whether it's alright to use a 4ohm woofer with an 8ohm tweeter.
if u use a crossover 'correctly' (ie. high pass tweeter at frequency X and low pass woofer at frequency X), and both are 8ohm, you will have an 8ohm nominal impedance system
if the woofer is 4ohm, then it will draw more from the amp for mid-bass duties, but not for treble. not that it's a problem, but consider the sensitivities of those drivers, and the fact that the amp will output more at 4ohm than 8ohm in some (most?) cases (and apparently not for some amps due to some protection type circuitry - so i hear).
if the woofer is 4ohm, then it will draw more from the amp for mid-bass duties, but not for treble. not that it's a problem, but consider the sensitivities of those drivers, and the fact that the amp will output more at 4ohm than 8ohm in some (most?) cases (and apparently not for some amps due to some protection type circuitry - so i hear).
different impedances together
Using different impedances can make it easier to match the outputs of the different drivers,
I have a speaker that has 15 ohm tweeters, 8 ohm mids & 4 Ohm Woofers
(complicates Xover calculations a bit though)
Most tweeters are more sensitive than mid/bass drivers, so using a lower impedance woofer is OK.
Pete Mck
Using different impedances can make it easier to match the outputs of the different drivers,
I have a speaker that has 15 ohm tweeters, 8 ohm mids & 4 Ohm Woofers
(complicates Xover calculations a bit though)
Most tweeters are more sensitive than mid/bass drivers, so using a lower impedance woofer is OK.
Pete Mck
ok that sounds alright since i'm probably going to use a 4ohm woofer (87dB) and an 8ohm tweeter (93dB sensitivity). But i still don't understand how to work out what load the amplifier is seeing. Is there a way to calculate this.
However i can get an 8ohm Vifa woofer for the same price which seems to go lower than the Response one i was considering before.
Vifa: http://www1.jaycar.com.au/productView.asp?ID=cw2100&CATID=15&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=xxxxxxxxxx&Keyword2=xxxxxxxxxx&pageNumber=&priceMin=&priceMax=&SUBCATID=383
Response: http://www1.jaycar.com.au/productView.asp?ID=CW2102&CATID=15&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=xxxxxxxxxx&Keyword2=xxxxxxxxxx&pageNumber=&priceMin=&priceMax=&SUBCATID=383
I'm just not sure whether the Vifa woofer will be loud enough given it's higher impedance however it will probably sound better, i'm going to be powering it with about 50watts btw.
Vifa: http://www1.jaycar.com.au/productView.asp?ID=cw2100&CATID=15&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=xxxxxxxxxx&Keyword2=xxxxxxxxxx&pageNumber=&priceMin=&priceMax=&SUBCATID=383
Response: http://www1.jaycar.com.au/productView.asp?ID=CW2102&CATID=15&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=xxxxxxxxxx&Keyword2=xxxxxxxxxx&pageNumber=&priceMin=&priceMax=&SUBCATID=383
I'm just not sure whether the Vifa woofer will be loud enough given it's higher impedance however it will probably sound better, i'm going to be powering it with about 50watts btw.
yeah i have floor standers using a response dome tweeter and two of those midranges. i put the midranges in series to get an 8ohm load. i then put an lpad on the tweeter to attenuate it somewhere around 4dB (give or take due to available resistor values).
i felt like i was wasting amp power (which essentially i am) but attenuating the tweeter, but it's very hard to find woofers with matching sensitivity.
if your amp can't handle 4ohm loads, then i suggest ensuring that each frequency range is handled by a 8ohm load. if i were u i'd either use a single one of those vifa drivers and attenuate the tweeter a lot, or two of those response ones in series and attenuate the tweeter a little. obviously i went the second option. this is assuming these are your only options, which of course they aren't.
i felt like i was wasting amp power (which essentially i am) but attenuating the tweeter, but it's very hard to find woofers with matching sensitivity.
if your amp can't handle 4ohm loads, then i suggest ensuring that each frequency range is handled by a 8ohm load. if i were u i'd either use a single one of those vifa drivers and attenuate the tweeter a lot, or two of those response ones in series and attenuate the tweeter a little. obviously i went the second option. this is assuming these are your only options, which of course they aren't.
If you use a crossover with LP section to woofer & HP section to tweeter, then amp sees 4ohms up to crossover frequency, and 8ohms above that - the two impedences don't interact.
Cheers
For the sensitivity part… isn’t is that you just look to the sensitivity driver, no matter the impedance it has got, and match those sensitivities together (woofer and tweeter). If the sensitivity is 91dB @ 4ohm for the tweeter and the woofer is 90dB @ 8ohm the difference is 1dB, that the impedance is different isn’t important, the sensitivity is nearly the same. The only difference is that the impedance is different. Or do I miss somothing?
Properly this isn’t a problem, most amps can handle this (here I have a 8ohm woofer and 4ohm tweeter hanging on a Akai amp that is about 20 years old and I’m getting away with it, but I hope to own a NAD C320 BEE soon 🙂 ).
Properly this isn’t a problem, most amps can handle this (here I have a 8ohm woofer and 4ohm tweeter hanging on a Akai amp that is about 20 years old and I’m getting away with it, but I hope to own a NAD C320 BEE soon 🙂 ).
if u had a tweeter that was 8ohm, with sensitivity of 94db/w/m, and a woofer that was 4ohm, with sensitivity of 92db/w/m, then...
when the amp plays highs, it sees 8ohms and outputs X watts. when it plays lows, it sees 4ohms and outputs maybe 1.3X watts. this means the woofer will play at probably 92.5db/w/m EFFECTIVELY with regards to this 8ohm system.
if the sensitivity on the woofer however is 92db/2.83v/m, then it wont play any louder. 2.83v @ 8ohms = 1w, or close enough. so the way of presenting the driver sensitivity for 8ohm will give the same result, but not for 4ohms.
i hope i didn't stuff that up. also, i'm not claiming to be an expert at this, but this is how i understand it to be. i'd be happy for anyone to correct my mistakes.
edit: i guess i should also add that some amps will not output more at 4ohms, so such a speaker system may have a huge lack in midbass on those amps. each amp will behave somewhat differently when not presented an ideal load.
when the amp plays highs, it sees 8ohms and outputs X watts. when it plays lows, it sees 4ohms and outputs maybe 1.3X watts. this means the woofer will play at probably 92.5db/w/m EFFECTIVELY with regards to this 8ohm system.
if the sensitivity on the woofer however is 92db/2.83v/m, then it wont play any louder. 2.83v @ 8ohms = 1w, or close enough. so the way of presenting the driver sensitivity for 8ohm will give the same result, but not for 4ohms.
i hope i didn't stuff that up. also, i'm not claiming to be an expert at this, but this is how i understand it to be. i'd be happy for anyone to correct my mistakes.
edit: i guess i should also add that some amps will not output more at 4ohms, so such a speaker system may have a huge lack in midbass on those amps. each amp will behave somewhat differently when not presented an ideal load.
The impedance is more frequency dependent that we think, especially since we don't output pure sine waves into our speakers (unless we are testing or playing around).
Each driver regardless of sensitivity has it's own frequency dependent impedance curve. These combine with the XO filters to create a new overall impedance curve, which is dependent on the overall circuit (including the voice coils). On a purely mathematical level, impedance of the drivers is not important.
But at a practical level, I think phreeky is right.
I would add that it is also important to look at the driver's impedance curve and determine how it would interact with the signal from the XO. Both the SPL curve and the impedance curve are required for this and they are only a start since they are usually based on a sine wave frequency response. This is why I think XO design is so difficult and why I will stick with subs and line level filters.
🙂ensen.
Each driver regardless of sensitivity has it's own frequency dependent impedance curve. These combine with the XO filters to create a new overall impedance curve, which is dependent on the overall circuit (including the voice coils). On a purely mathematical level, impedance of the drivers is not important.
But at a practical level, I think phreeky is right.
I would add that it is also important to look at the driver's impedance curve and determine how it would interact with the signal from the XO. Both the SPL curve and the impedance curve are required for this and they are only a start since they are usually based on a sine wave frequency response. This is why I think XO design is so difficult and why I will stick with subs and line level filters.
🙂ensen.
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