Low- vs. High- Order Active Crossover

[askbojesen]

Low- vs. High- Order Active Crossover

Hi!

I'm building a 2-way sealed speaker using two Scan-Speak drivers: 15W/8530K00 and D2905/9900.

The active crossover is going to be somewhere around 2 kHz, but I'm not sure if it's going to be 12 dB per octave or 24 dB per octave.

The advantages I can think of are the following:

Advantages for low order:

• Easier and cheaper to build
• Less distortion because of the simpler design
• More frequency overlap gives more contact in the sound picture between the midrange and the tweeter

Advantages for high order:

• Less frequency overlap gives less interference from the two sources
• The excursion of the tweeter is reduced
• Less requirements for the midrange/tweeter above/below the crossing frequency

My question is now what is your experience?

Especially your experience dealing with my weak formulated advantage for the low order active crossover:

• More frequency overlap gives more contact in the sound picture between the midrange and the tweeter

Please Help!

[thylantyr]

My question is now what is your experience?

Build both and try both, not complex at all. Everyone
will have different tastes just like drinking wine.

[LineSource]

The frequency plot for the 15W Revelator shows the off-axis response starting to fall at 2K Hz. If you are constructing an enclosure with a very narrow baffle, you may lose some imaging "magic" with a low slope crossover. If you construct a low slope crossover, you may also need to compensate for the mechanicall 12db/octave fall off at 7Khz of the 15W.

These are popular drivers, and you will likely find passive 2nd order crossover designs on the internet which you could build for a reference.

[Bose(o)]

Wouldn't the high-order (24dB./oct.) filter net you less distortion? More specifically, less Intermodulation Distortion. Considering, the filter will block more low frequencies from the tweeter and thus reducing the tweeter's excursion. IMD is the distortion I'm refering to, what's your's?

[amo]

Originally posted by Bose(o)
Wouldn't the high-order (24dB./oct.) filter net you less distortion? More specifically, less Intermodulation Distortion. Considering, the filter will block more low frequencies from the tweeter and thus reducing the tweeter's excursion. IMD is the distortion I'm refering to, what's your's?

I doubt that Intermodulation Distortion within the tweeter will be a problem due the great difference in sencitivity of the two drivers. In other words, the woofer will reach its IMD limits much sooner the the tweeter (85.5 dB vs 91 dB). I would recommend to read up on Group Delay distortion and to decide how important it is to you and your application, because the 24 db/oct slope will have much greater effect on the waveform. Weather this will be audible or not is a matter of debate/taste/etc. If however you decide to go for an MTM or another dual woofer 2-way configuration, I think you would benefit from a higher slope and less IMD distortion at higher volume levels.

[Dave Jones]

Originally posted by askbojesen
Low- vs. High- Order Active Crossover

Hi!

I'm building a 2-way sealed speaker using two Scan-Speak drivers: 15W/8530K00 and D2905/9900.

Why are you using the 15W/8530K00 in a sealed enclosure, rather than the higher Q 15W/8530K01? I assumed that the 00 was designed for ported boxes and the 01 for sealed.

D.

[askbojesen]

15W/8530K00 has a bigger magnet than 15W/8530K01 which implies a lower Qes and Qts:

Qes(K00) = 0,29 and Qts(K00) = 0,27
Qes(K01) = 0,38 and Qts(K01) = 0,35

This means that fb (the resonans frequency for the box+driver) is higher for the same Q using the K00 because:

fb/fs = Q/Qts,

and fs = 30 for both K01 and K00. Therefore K01 is better making low frequencies in a sealed box, but since I'm planing to make a 3-way system later, I choose the K00.

------------------------------------------------------------------

Now Back to The Track!

What is your for experience with low- vs. high-order active crossovers between the midrange and the tweeter?

[phase_accurate]

High order usually means less IMD and low order ususally means better transient response.
There might be a compromise: Because the tweeter is generally more susceptible to IMD caused by lower frequencies, opposed to a midrange that is fed with high frequencies, a constant-voltage subtractive filter might be your choice.
They have asymmetrical slopes, i.e. 2nd or 3rd order in the highpass and 1st in the lowpass, or vice-versa, depending on topology. They are transient-perfect and offer a linear frequency response.

Regards

Charles

[askbojesen]

The filter I had in mind for my projet is the 24 dB/oct. or the 12 dB/oct. Linkwitz-Riley crossover, but maybe some other filter is better...

Originally posted by phase_accurate
... a constant-voltage subtractive filter might be your choice...

I found one link explaining something about a constant-voltage subtractive filter:

http://www.geocities.com/kreskovs/John1.html

Where can I read more about it?

/Ask

[phase_accurate]

See:

http://www.passlabs.com/pdf/phasecrx.pdf

or

Active Subtractive XOs

Regards

Charles