driver impedance matching

[jpizzle]

Hi, I'm reasonably new to speaker design and was wanting to make an MTM design for home theatre application. The drivers I would like to use for this design difference in impedance however, (tweeter 6 Ohm & midwoofers 8 Ohm 2 in parallel = 4 Ohm). How does this effect my system?? I've seen other design where impedances don't match but do I have to do something in the crossover to account for this?? And what is the final/overall speaker impedance? Any help will be greatly appreciated! Cheers

 

[MacManNM]

You can compensate for different Z in the crossover. I would recommend X-over pro. It is a program that will help you design your crossovers. It's available at PE for ~$70. There are a few online that aren’t nearly as good but you could try them.

This site has some good info on it.

http://www.kbapps.com/

 

[j_garcia]

You will at least need a volt meter to measure the combined impedance of the drivers and the crossover so you can hit, or at least get close to, your desired nominal impedance.

 

[MacManNM]

You will at least need a volt meter to measure the combined impedance of the drivers and the crossover so you can hit, or at least get close to, your desired nominal impedance.

You can't measure impedance with a volt meter.

 

[annunaki]

You can with a Digital Multi-Meter.

 

[MacManNM]

You can with a Digital Multi-Meter.

No you can't. You can measure the DC resistance. A multi-meter is a part of the process though. Here is an example of one way to measure impedance. This is probably the cheapest and easiest for the DIY'r.

http://sound.westhost.com/tsp.htm

 

[j_garcia]

Didn't realize that. So when you put a capable DVM on the "Ohm" setting, it is giving you DC resistance?

Mac, IIRC, wasn't it you that measured the RTi8s or 10s with a DVM right on the posts and showed top 8 Ohm, bottom 8 Ohm, combined 4 Ohm? Does that mean that was not the impedance of the speaker?

 

[MacManNM]

Didn't realize that. So when you put a capable DVM on the "Ohm" setting, it is giving you DC resistance?

Mac, IIRC, wasn't it you that measured the RTi8s or 10s with a DVM right on the posts and showed top 8 Ohm, bottom 8 Ohm, combined 4 Ohm? Does that mean that was not the impedance of the speaker?

That was Buck that did that. This was a measure of the DCR. Usually, the DCR of a speaker "system" is close to the total Z. But that was not the correct way to measure the Z of the system, just a way to get a ballpark estimate. Also impedance follows Ohms law.

 

[zumbo]

Here it is.

http://i19.photobucket.com/albums/b152/tpc3416/9-4-05041.jpg

http://i19.photobucket.com/albums/b152/tpc3416/9-4-05042.jpg

http://i19.photobucket.com/albums/b152/tpc3416/9-4-05040.jpg

 

[Buckeyefan 1]

Those are Polk RTi10's. When the straps are off and I'm running the top half (the towers become RTi6's), they sound amazing and the Denon 3805 is able to drive them to reference levels (two channel only - no sub).

When I run the bottom half, I get amazing bass that almost mimics small subwoofers (2 channel only - no sub).

When I run them strapped with the 3805 (2 channel only), it's immediately obviouse the receiver needs an amp to get them both to reach their potential. I can max out the volume without any distortion, but the speakers don't reach refernce levels. The Denon runs fine, but there's still a lot more room in the Polks.

The RTi10's and 12's are too much for standard receivers. The Pioneer Elite 59 or HK AVR7300 may run them with their huge capacitors, but it would be much more economical to invest in a beefy two channel amp.

IMHO, the RTi10's dip well under 4 ohms with demanding, dynamic music and movies. Impedance always varies with music passages. Starting out with 4 ohm DVC isn't celebration time when you're throwing a 6 hour party without a separate amp.

 

[zumbo]

I always thought that you checked with a multi-meter. Learn something new every day.