Safe crossing point (6dB/oct)

Sony

Member
2004-09-10 7:16 pm
Europe
Two drivers in question:

1. Tweeter with manufacturer specification: Cross at 2KHz or higher, 12dB (2nd order)
- Will it be safe to cross at 4KHz 6dB (1st order)?

2. Midrange with manufacturer specification: Cross at 800Hz or higher, 12 dB
- Will it be safe to cross at 2KHz 6dB?

Note: "Safe" means: 1. Safe for the driver; 2. Does not compromise the sonic result.

Thks, Rgrds
 
Sony,

I am still learning, but as written in Van Dickerson's Loud Speaker Cookbook, "Speaker building is an art form".

For tweeters and first order networks, it is best to cross over at least 2 octaves from the Fs with an even higher frequecy being regarded as "safe". 1st order (6dB) can still let low fequencies through (attenuated none the less) which at high levels can damage the tweeter's voice coil.

Woofers on the other hand (including mid-range drivers) need to be crossed with-in their band. They have their own roll off and an audible hole may be formed by crossing over too high to the tweeter.

Why 1st order and what drivers?

Mark
 

jomor

Member
2004-02-20 1:36 pm
Athens
Safe about tweeter: The more you cross near the tweeter's Fs, the more harsh sound you ll get, and the more dangerous it will be for damage.

Safe about the woofer: There will be sonic problems if you cross too high. Many woofers have strong cone break-ups at frequencies appox. between 4Khz - 8 Khz ( hard cones mostly). Look at Seas Excel woofers for example.. If you cross too close to the breakups, you ll get a real distorted sound
(the cone doesnt act like a rigid piston at breakup)

May I ask why 6dB/oct ? you enjoy living in danger ? :D
 

wintermute

Administrator
Paid Member
2003-08-03 11:43 am
Sydney
If you are considering 1st order, check your tweeters impedance plot, if it has a high peak at resonance, you would do well to add impedance compensation so your filter is effective at the resonant frequency... otherwise you may not get the attenuation you think you will.....

Also Time alignment is much more critical with 1st order crossovers, so you would be wise to look at that aspect as well :)

Tony.
 
Without knowing the drivers, it looks like you're creating a 3-way. Rather than hitting the low-end of your tweeter, have you considered crossing the tweeter/mid at around 5-10kHz, and then your mid to your midbass at around 1.5-2kHz? Depending on the midbass you've got, you'll probably still need a zobel and a notch filter as well (unless you've got really a well behaved cone).

Have you thought about a series first-order? There are slight advantages to series when you're going first-order (check out Rod Elliot's article at http://sound.westhost.com/parallel-series.htm and Andy Graddon's - a DIYaudio member - pages at http://users.tpg.com.au/users/gradds/SeriesXO/series_cross-overs.htm).

Also, how are you initially designing the crossover? Trial and error, or are you using a software package?
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
You cannot assume that 1st order at 4kHz is save knowing that 2nd order at 2kHz is save.
The roll-off is too shalow and first order filtering doesn't correct the bump to an
acceptable degree, so this is more dependent on the power of the amplifier
and the use of notch filter.

Assumming you use a common high power bipolar amps, a notch in 1st order speaker is
almost always required when you seek for an optimum speaker (you are since you have
compared with higher order ones).

Tube or class-A amps of less than 15W do not need the notch IMO (but may be there
are other design issues with low amplifier output impedance). Personally, even with
25W I don't need a notch, but often I needed one for high volume listening.
 
Here is how I would compare to see if the crossover point is safe.

For tweeter, it is recommended to be at 2k or above, 12 db/oct. Here is the db level below the 2k crossover point, down 12 db per octive.

-12 db @ 1000 hz
-24 db @ 500 hz


You wanted to know about 4k crossover, 1st order, 6 db per octive.

-6 db @ 2000 hz
-12 db @ 1000 hz
-18 db @ 500 hz
-24 db @ 250 hz


Close, but the tweeter may get too much low end at loud levels. A 1st order at 6kHz should be safe.

Does this answer your original question?