The Nightingale

By Lars Mytting
02 Nov 1996

Crossover Suggestions

Crossover suggestion 1
I have two suggestions for crossover. The first one contains the least components, and they are of fairly small value. The response from 200 to 20,000 Hz is within +/- 2.0 dB. The filter gives a lively sound, with a added sense of attack and clarity, because it has more level in the region where these tonal illusions exist. This which may be either annoying or useful. It demands good midrange behaviour of the rest of the system. If not, the sound may be "thin" and without body. On a poor amplifier, the added level in the midrange may be unbearable; saxophones will sound like grinding wheels and any female voice appear as if the singer has just approached a situation of crude violence. It is also more difficult to implement in a "hard" room with wall reflections.

------1.35 mh----|--------------------- +
|
3.3uf
|
0.25mh                  W17EX002
|
1ohm
|
-----------------|-------------------- -

-------3.3 uf----|-----3.7 ohm ----|------- +
|                 |
0.47 mh         (opt. RLC)   2905/9900
|                 |
-----------------|-----------------|------- -

The measured response from 200 to 20000 Hz is shown in Fig. 9. SPL response.

The waterfall plot for the complete system in Fig. 10. Waterfall plot. Some room reflections affect the response to 1k. No smoothing is used on the lines in the plot.

Crossover suggestion 2 (more relaxed, very coherent)
This filter will suit cabinets with woofer and tweeter mounted on the same plane. It differs from the previous in having a lower crossover frequency (1800 Hz), and in having a more flat overall response and 2dB less average sensitivity. The 1.5 uf capacitor is optional, and provides more level in the upper frequencies.

------ 1.5mh ------ 0.65mh -------------- +
|              |
|            0.4mh
|              |
18uf          2.7uf      W17EX002
|              |
|            2.7ohm
|              |
----------------------------------------- -

|- 1.5uf-|
|        |
---- 6.8 uf-------|-3.9ohm |------------- +
|              |
|              |
0.35mh         15ohm      2905/9900
|              |
|              |
----------------------------------------- -

I am very satisfied with the overall sound from this filter, and it is the best choice for most systems. It sounds more coherent, not so aggressive, and is easier to implement with subwoofers and "hard" rooms.

The Calsod-simulations in Fig. 11. Filter function, crossover 2 and Fig. 12. SPL and Power, crossover 2 show the electrical response of the filter and the total SPL and power response.

Resistor types
I use metal film resistors for the tweeter circuit. These are non-inductive, have good high-frequency response and less noise than regular wire wound types. They are also inexpensive. Lately, big-money, "low-inductive" 25 or 50 watt power resistors with fancy gold plating has been praised by audio salesmen, but I would strongly advice to listen to metal film first. I use 4 resistors of 2 watt in parallel, giving a total power handling of 8 watt. The resistors does not get hot, even after two Wagner operas at extreme SPL. Each resistor in the paralleled pack should be of the same value (no tight matching is needed). If they have different values, the resistor with the lowest value will handle more power than the other.

Bass filter/highpass filter
I do not use passive circuits for the bass systems, as a they require large component values and have no good means of adjusting the level if the bass sensitivity is higher than the rest of the system.

I enjoy to cross a bit high, often around 250 Hz, to get more "snap", "bang" and energy from the 10" in the lower midrange. For experimental purposes, I use a active crossover that rolls off at 12 dB/octave. This blends fairly well with the rest of the system, but for maximum performance, the crossover should be closely optimised to the lower rolloff of the mid/woofer.

To achieve better power handling, I have placed a simple highpass filter on the input of my power amps. This filter consists only of a series capacitor. The formula for this is the same as for a speaker 6dB highpass filter, only that you substitute the speaker impedance with the input impedance of your amp. For a 200 Hz filter on a 10 kohm amp, you need a 0.08uf cap, for the same on a 50kohm amp, you need a 0.016uf. Note that many amplifiers already use input capacitors to block DC, and a good solution is to replace this cap (usually large) with the value giving the required rolloff. Many preamps also employ output capacitors for the same DC-blocking purpose. Use the best quality you can find for this capacitor.

My amplifiers have 600 ohm input impedance, and this graph shows the rolloff caused by 0.47uf and 1.5uf capacitors Fig. 13. Passive line filter.

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