Maths help :(

[shudster]

Hiya Guys

Just after some confirmation on my maths for wiring speakers.

So if I put an 8ohm and a 4ohm in series, and two 4ohms in series, and then wire them together in parallel, do I end with a load of just under 5 ohms? 4.8 to be exact?

Is it safe to wire to different loads in series, and then into parallel like that?

Any help on that would be great.

Cheers,
Shud.

[moamps]

Originally posted by shudster
[B]
So if I put an 8ohm and a 4ohm in series, and two 4ohms in series, and then wire them together in parallel, do I end with a load of just under 5 ohms? 4.8 to be exact?

Yes.

Is it safe to wire to different loads in series, and then into parallel like that?

Resistive loads? Usually yes.
Loudspeakers? Usually no. The speakers have complex, frequency dependent impedance. If speakers have different caracteristics, the power distribution between speakers will be also frequency dependent.

Regards,
Milan

[shudster]

Originally posted by moamps


Yes.



Resistive loads? Usually yes.
Loudspeakers? Usually no. The speakers have complex, frequency dependent impedance. If speakers have different caracteristics, the power distribution between speaker will be also frequency dependent.

Regards,
Milan

Thank you Milan, but as you can probably tell, I'm a bit new to all this, so I don't understand some of the terminology.

What is a resistive load as opposed to the load from a loudspeaker?

By the way, two of the speakers in the configuration I've mentioned are 2-ways, with a passive (?) x-over inbuilt, and the other two are single drivers. When you talk about the power distribution being different depending on frequency, is this simply a matter of balance between speakers? Or can it actually cause damage to the amp or speakers?

Thank you,
Shud.

[tnsguy]

Yes, 4.8 Ohms is correct.

1/(1/12+1/8) = 4.8.

[nunayafb]

two of the speakers in the configuration I've mentioned are 2-ways, with a passive (?) x-over inbuilt, and the other two are single drivers.

Could you elaborate on the 2-way part, and what are the drivers that you are adding.
If the separate drivers will be playing the same frequencies as the 2-way you will have a series of serious peaks and nulls in the frequency response, my gut tells me you are adding 2 woofers to a 2-way that lacks bass. Am I right?
Let us know what specifically you are doing so we can provide an actual answer.

[shudster]

Originally posted by nunayafb



Could you elaborate on the 2-way part, and what are the drivers that you are adding.
If the separate drivers will be playing the same frequencies as the 2-way you will have a series of serious peaks and nulls in the frequency response, my gut tells me you are adding 2 woofers to a 2-way that lacks bass. Am I right?
Let us know what specifically you are doing so we can provide an actual answer.

Ok, this is the embarassing part. I know a lot of you are hardcore audiophiles, and what I'm doing is probably a little bit of a no-no.

I'm actually working on an arcade cabinet for a music game called "beatmania IIDX". Initially it just started out as a bit of fun, and not knowing a lot about anything I picked up some car speakers from ebay, just because they looked cool I then started to learn a bit more about how audio works exactly, and realised I'd have to learn a lot more.

So, I have two JBL GT122 subs from my old car stereo, and I bought four cheap 3-way 6 1/2" car speakers from ebay. I also bought a cheap car box that has 2 tweeters, and two 6 1/2" speakers (this box has a channel for each set of two speakers).

I want this thing to sound ok, but I mainly want it to have a lot of punch and to be "loud". Most of the music being played is club type stuff. I'm not overly fussy about it being top quality.

I realised I'd need a bit of power to drive these speakers, and even though everything except the subs is pretty crappy, I also decided I wouldn't mind spending a bit on amps, as I've always loved my music, and upgrading from the crappy speakers will be less costly then upgrading amps.

So at the moment my plan is this:

From source to Sub Amp, which will power two of these

Then using the outs on the sub amp, I plan on running the signal to a Behringer A500. The A500 has to power these:

On each channel:

2 x 6 1/2" 3 ways (2" mid, 5/8" tweeter) - 200w peak, 100w continuous, Freq. Resp. - 65hz to 20khz, Sens. - 92dB, 4ohm.

And one half of the box = one 6 1/2". plus one tweeter (I'm assuming it has a x-over built in) - the stats on the back of this box are exactly the same as the the stats for the 3-ways.

So, however I do the math, with the those three speakers on each channel of the A500, the load is always below 4 ohm, or its 12ohm correct? So I thought if I add a home speaker I have that is rated at 8ohms, I can get to the 4.8ohm calculation I had.

Wow, this post got very long very quickly. Anyways, I know thats all very ugly, but that is what I"m working with.

So have at it. Just excuse my ignorance

Cheers,
Shud.

[AndrewT]

Hi,
try putting a chip amp onto each speaker, no interaction between the speakers then.
A balancing pot on each input to the chipamps allows you to adjust for sensitivity.
Even add a low pass, passive filter in front of the bass unit chip amps to use them as bass only units. Will help to raise the volume a bit.

I would not recommend series connecting speakers.
Parallel is OK but then you are limited to the lowest power handling or you risk blowing it before the others.

[myhrrhleine]

The 4 ohm or 8 ohm rating is an approximation.
The 'ohms' will be all over the map, depending on the frequency.
And the 'ohms' will be different for different speakers at the same frequency.

Additionally, the electrical phase will come into play. Different speakers at different frequencies will draw different currents because of the electrical phase.

That's why the ohms-impedence doesn't combine like it would for resistors.