a simple question about speaker Impedance??

[Minion]

Hi Folks, I was just recently given a set of Koss Active Studio monitors but one of the speakers was blown and it needs to be replaced with an 8 ohm speaker but the only one I have that will fit in the Box is a 4ohm...

So my question is can I just put a 4ohm resistor in series with the speaker so that the amp sees 8ohms?? will this work OK?? and will it sound OK??

Thanx a Lot!!!

[Minion]

Over 40 Views and no reply!!!

Is my question really stupid or is it really hard or do you guys just not know the answer??

[Nigel Goodwin]

Originally posted by Minion
Over 40 Views and no reply!!!

Is my question really stupid or is it really hard or do you guys just not know the answer??

Yes, it's really stupid!.

You 'could' put a high wattage 4 ohm resistor in series with the speaker - the resistor will dissipate the same power as the speaker. So if the speaker is rated at 100W at 8 ohms, the 4 ohm speaker gets 50W, and the 4 ohm resistor gets 50W.

There are MANY problems with this:

1) The resistor is going to be expensive, large, and almost certainly require a large heatsink, plus it's going to get HOT!!!.

2) It destroys the damping factor of the amplifier so makes the speaker sound poorer.

3) Presumably this is a stereo system?, so this channel will sound nothing like the the other one, and the volume level will be different.

4) 4 ohm speakers are far rarer than 8 ohms ones, except for in-car speakers - which are generally pretty crap and VERY over specified.

[Scottmoose]

A little drastically put perhaps; no question is stupid if you don't know the answer, but sadly, I'd tend to agree with Nigel's analysis of the problems you'd encounter. To say nothing of the fact that you design a cabinet for a specific driver (or you should) so trying to drop another with completely different parameters into it is unlikely to work. And if there's a crossover, things are just going to get a whole lot worse as it's designed for a specific driver's electrical and sonic characteristics, and chaning it will screw thing up something chronic. Unless it's you're lucky day.

Hate to say it, but you'll be better off either saving for the correct replacement (or for the driver to be repaired), or salvaging what you can for use as test boxes or garage etc., listening, and buying or building yourself a new pair. Sorry.

[planet10]

Hey Minion,

Where are you on the Island? Perhaps we can look at your problem 1st hand?

If you are going to change the woofer you need to change both.

Given that it is an active speaker, a change in impedance shouldn't affect the XO, but if you go with lower impedance, you do have to worry about whether the amp can handle the exta current required. You also have to worry about any EQ built into the amp.

On top of that you need to ensure that the new drivers will work in the existing box.

dave

[tinitus]

Active .... I overlooked that too

Some detailed specs on that speaker might help!

And maybe some pictures to see what kind of drivers we are dealing with

[Minion]

Hi Guys, Thanx for the answers....I figured that might be the answer I would get but me being totally ignorant of speakers I had to ask....

The Speakers have two 4in Woofers and a neodyne tweeter in each Cabinet....The back of the Monitor says that the speaker impedance is 4 ohms but when I pulled the speaker out and looked at it , it said that it was an 8 ohm speaker so I suppose that the two 8 ohm speakers are in Paralell so the amp sees 4 ohms.....The amp is Rated at 40 watts total per side and each of the 4in woofers are rated at 20watts.....

planet10 : I live just south of Duncan in Cobble Hill so about 45 minutes from Victoria.....Were on the Island are you at??

If you live close to me maybe we can get together and work on something together as none of my friends are into DIY but they do have a Bad habbit of Calling me up every time something breaks and expect me to fix it....lol

PS: i just realized you are from Vic....
Thanx Guys.....Cheers

[planet10]

Originally posted by Minion
The Speakers have two 4in Woofers and a neodyne tweeter in each Cabinet....The back of the Monitor says that the speaker impedance is 4 ohms but when I pulled the speaker out and looked at it , it said that it was an 8 ohm speaker so I suppose that the two 8 ohm speakers are in Paralell so the amp sees 4 ohms.....The amp is Rated at 40 watts total per side and each of the 4in woofers are rated at 20watts.....

Those sound like an active version of the passive speakers my mom has. As an MTM if you have to replace 1, then you have to replace all 4 -- if they are they likely didn't do anything fancy

planet10 : I live just south of Duncan in Cobble Hill so about 45 minutes from Victoria.....Were on the Island are you at??

I'm about 15 min south of you... a left thru Goldstream Park and 3.3 km up Finlayson Arm Road.

I may well have some 4" that can do the job.

dave

[Minion]

Originally posted by planet10

I'm about 15 min south of you... a left thru Goldstream Park and 3.3 km up Finlayson Arm Road.

I may well have some 4" that can do the job.

dave

Hi Dave, thats cool that you live really close to me, and if you happen to have some 4in speakers that will work then maybe we can work out a trade or something...
I do have quite a Bit of DIY electronics stuff that I can trade with you Like pots, caps, PCB material, transformers ,opamps ect....

here"s my e-mail:

mr_sevs At Yahoo Dot ca....

Please e-mail me and then maybe we can work something out...

Thanx a Lot!!!