help understand this Tannoy 2nd order crossover

[noviygera]

Greetings!

I traced out the crossover for the Tannoy CMS1201 celing speaker.

Please help me figure out how to shelve the tweeter by about 3 db without messing up.
Also, what is the function of the pair of 24 ohm resistors (they are 30 watts each)?
I see this is a 2nd order high and low pass crossover but the tweeter network is confusing me since this does not look like a zobel.

thanks!

 

[adason]

3dB lpad calculator
You can fuse it with 1 ohm resistor
http://www.sengpielaudio.com/calculator-Lpad.htm

 

[noviygera]

Oh thank you but what about the other questions?

 

[olsond3]

A really good way to adjust a crossover is to make measurements and load them into crossover design software. I like Xsim. It is free and will handle this job easily. You can then put the existing crossover schematic into Xsim and see how it performs. Then it is easy to make changes in the software. Those resistors are adjusting the Q of the crossover network. There is no Zobel network shown. This is Do It Yourself Audio, and that's where the fun is. Almost any microphone will work for crossover design, as you only need it to have a flat response at the crossover frequency range. I've seen Part Express selling measurement microphones for as little as $20 in the last few months.
You can make the required measurements with Arta and Limp software using a cheap microphone and two resistors. Of course you can just add some resistance across that tweeter, 16 ohms or maybe 8 ohms, and adjust the level by ear.

 

[noviygera]

Thanks, I’ll try it tonight!

 

[wolf_teeth]

If it's a conventional dome tweeter, just up the 20W resistor to 4 ohms or there abouts. Should be close.

 

[adason]

What other questions?

Oh thank you but what about the other questions?

Perhaps some impedance correction apart of high pass 2nd order

 

[noviygera]

If it's a conventional dome tweeter, just up the 20W resistor to 4 ohms or there abouts. Should be close.

It's a compression driver tweeter -- the Tannoy is a 12" pro coaxial driver.

 

[WhiteDragon]

Please help me figure out how to shelve the tweeter by about 3 db without messing up.
Also, what is the function of the pair of 24 ohm resistors (they are 30 watts each)?


thanks!

for 3 dB with single series resistor it would be 1.65 ohms
So use the nearest standard value available either 1.5 or 1.8 ohms

change the current 1 ohm resistor to the higher value 1.5 or 1.8 ohms

The pair of 24 ohm resistors are parallel for more power handling
And would provide a value of 12 ohms.

Placed in series as shown with the inductor, will change the filter Q at cutoff.

 

[AllenB]

A compression tweeter? Considering the complicated looking impedance plots they often throw, that's a simplistic crossover. I'd therefore be looking to add a resistor in parallel, and unless you plan to change anything else that also means increasing the series resistor.

 

[Davor D]

To my understanding this is 1st order for tweeter and 2nd order for midbass. Such combination helps with phase alignment around cutoff frequency when acoustic center of tweeter is behind acoustic center of midbass. You can see that in other large Tannoy coaxials.

0,3mH and two 24ohm resistors looks like response correction, since compression tweeters often have rising response towards lower frequencies.

1ohm resistor is for tweeter level adjusting.
So, if you want to lower the level increase resistor to suitable value.