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Old 30th December 2003, 11:07 AM   #1
ViPER is offline ViPER  Australia
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Default speaker ohm question


Im making a set of hi-fi speakers and have a few questions.

I have 2 10inch drivers and a tweeter for each speaker with a crossover for the tweeter.

My question is is regards to the ohms of the speakers. The 2 10inch drivers and rated at 8 ohms and the crossover is rated at 8 ohms, is there a way i can get 8 ohm over all the speakers ??.

I have read some where that u can just put another 8 ohms resistor in the circuit to get 8 ohms, can this be done ??.
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Old 30th December 2003, 03:37 PM   #2
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Hi Viper,
the best solution would be to adjust
the cross over.
But if you can accept less performance, then additional resitors will also work.

If you have 2 speakers you can generally connect them in series or in parallel.
a) series connection:
two times 8 Ohms will result in 16 Ohms.
in order to come back to 8Ohm overall you must put another 16Ohms in parallel to the series arrangement of the two speakers.
b) parallel connection:
two 8hms in parallel will result in 4 Ohms.
in oder to achieve 8 Ohms overall you must connect in series to the parallel arrangement another 4Ohm in series.

both arrangements are poor in efficiency, because half of the input power is only used to heat the resistor.
also the damping will be affected.
in fact my experience with cross overs
which were not really matched to the specific box were poor....
to get a real good result you will need much more speaker details than the nominal impedance if you want to caculate it proper and a lot of patience during tuning. normally i need about 6months for the practical tuning.
for basic adjustment one day....
ears and patience are important instruments for tuning.
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Old 30th December 2003, 09:30 PM   #3
ViPER is offline ViPER  Australia
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Join Date: Dec 2003
Location: Brisbane
Thanks for they reply,

When u say adjust the crossover, do u mean make it 16 or 4 ohm.

Also how would i do this?
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Old 31st December 2003, 11:13 AM   #4
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if you go to adjust the crossover, then I would prefer to connect both drivers in parallel and go for a 4 Ohms configuration.

Well, if you change an existing crossover from 8 Ohms to 4 Ohms then you can follow this rule of thumb.
As the speakers impedance is half, all
other impedances should be also divided by two.
==> capacitors: double uF (reziproce behaviour of capacitance and impedance)
==> inductors: half mH
==> resistors: half Ohm

Please note that you might have to use
thicker wire for the chokes because of the higher currents.

Just to understand you right.
You plan two bass drivers and two tweeters per box? All the speakers
8 Ohm types?
Then you could also simply buy ( or solder yourself) two additional crossovers for 8 Ohms as you already have.
Then you could put two "setof8Ohms speakers+cross over" in each box.
You could give 4 terminals for each box.
Then you would stay flexible to wire this box in a 4 Ohms or 16 Ohms configuration from the outside.

Have fun and a happy new year!
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Old 1st January 2004, 06:16 AM   #5
ViPER is offline ViPER  Australia
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Join Date: Dec 2003
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Happy new year to everyone too.

Actually i will be using the following,

2 x 8ohm 70 watt 10inch drivers
1 x 8ohm 100watt tweeter
1 x 80hm crossover
for each speaker.

I was thinking of running one 10inch and the tweeter through a crossover and running the other trough a low pass crossover.

Seeming as the box im gonna make is seperated in the middle with one 10inch in the bottom and the other 10inch with the tweeter in the top.

The bottom 10inch is ported for lower frequency response.

Does this all sound (pun intended) like it would work ??
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Old 1st January 2004, 05:50 PM   #6
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Join Date: Dec 2003
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The good thing with speakers is that you will always get some sound out of it and there are plenty of "screws" to adjust the system.
So just try it.
Don't be disappointed if it does sound poor during the first sound check. Thats's normal.
Even if you are experienced proper adjustment will take some days.
Fine tuning about 6 months...

Have fun!
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Old 1st January 2004, 11:23 PM   #7
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Location: Chicago area
Someone sent me this link a few days ago, in reply to a similar question I had. Great info
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Old 4th January 2004, 09:14 AM   #8
ViPER is offline ViPER  Australia
diyAudio Member
Join Date: Dec 2003
Location: Brisbane
just finished putting it all together,

it sounds great on some music tracks but realy bad on others, manly in the bass speaker, which i think is because i am using the wrong size port.

Thanks for the info
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