Help understanding this crossover

[larryfff]

Sorry, Newbie question:

I have five Optimus pro 88av speakers that I use in a 5.1 HT set up. These are the RadShack ones with 5" woofers and the Lineaum tweeters. One the cases the speakers are rated for 8 ohms.

I opened the box and found the drivers each marked 6 ohms. They have a simple 1st order crossover with an inductor marked .84mH and a 4.7MicroF tweeter cap.

When checking with an online calculator that looks like it would yield low pass of about 1100Hz and a high pass off about 5500Hz.

Here's my question:

That seems to leave a big gap in the mid range. Does that make sense? Am I looking at this the right way?

Thanks,

Larry

 

[augerpro]

You have to take into account the ACTUAL impedance and frequency response. The calculated poles of the crossover may not be anywhere near the crossover point.

 

[hermanv]

Here are the results from the LTC simulator (free at Linear Technology)

I got the best answer using 8 Ohms for the drivers. I used a pure resistance which will cause an error since drivers are never pure resistors. The drivers are connected out of phase.

 

[Thawach]

hi

augerpro you are right.
The impedance will be changed when the voice coil gets the some freguency respond. it is true that the freguency respond cannot
flat. sometime it is increase. sometime will be drop. sometime
i think the calculator softwares are not better than my ears.
But the calculator softwares helps me thihks the simple xo. it
is quickly.


thanks

 

[Svante]

As said, there are large differences between oversimplified theoretical crossover design and pragmatic practical dito. It might very well be that the values of the components are optimal for the given drivers, since the drivers have a non-resistive and frequency dependent load, and also because the do not have a flat response in themselves.

Then again, there can also be a potential there for improvement. The only way to find out for sure is to do some acoustic measurements.

 

[larryfff]

Thank you for the helpful replies. I was just curious.

I understand what you are saying.

The only equipment I have is a DMM so I won't be doing any acoustic measurements.

The speakers are OK for watching movies. Someday I'd like to replace them with something better.

If I build speakers I will opt to use a proven design by someone who knows what they are doing.

Cheers,

Larry