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TAD 4002 crossover advice

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Posted on November 4, 2009 at 08:32:25
ThomasG
Audiophile

Posts: 12
Location: Copenhagen
Joined: February 2, 2009
 A friend got a set of TAD TD-4002 2" 16 Ohm drivers with 800 Hz exponential horns (TAD clones), plus TL-1601a 15" 8 Ohm woofers in Onken cabinets.

It is possible to use a 1. order 6dB/octave filter at 800 Hz, or would it have to be a 12dB/filter at that x-over frequency?

We found these online calculators:

http://www.diyaudioandvideo.com/Calculator/XOver/

http://www.diyaudioandvideo.com/Calculator/LPad/

The horn is 110dB, the woofer 97,5 so a damping of 12.5 dB is required. According to the Lpad calculater above, this requires a serial resistor of 20 Ohm, and a parallel resistor of 5 Ohm. What do you think?

Would it be a better solution to use an autotrafo, and what does that set up incorporate, and does it sound better than (high quality) fixed resistors?

He will eventually consider other horn types, maybe a 400 Hz, and other cabinets, suggestions are welcome.

Thanks in advance for any help!

Thomas
RE: TAD 4002 crossover advice, posted on November 5, 2009 at 05:56:43
JLH
Audiophile

Posts: 639
Joined: June 25, 2000
 If you are using a TAD exponential horn or TAD clone you are better off staying with a resistive L-pad. That horn was designed and voiced with heavy resistive padding to mate to a direct radiator. This became painfully obvious when one of my friends tried to bi-amp. The TAD horn and TD-4001 was so peaky and over dynamic it was unlistenable. We couldn’t stand to listen to it for more than a few minutes before it felt like it was splitting our scalps. If you try to use an autoformer attenuator you will get the same over bearing sound. If you want to use an autoformer attenuator you will need to switch to a more neutral sounding horn like a tractrix, conical, or Le Cleac’h.

Voiced Drivers and Neutral Horns, posted on November 5, 2009 at 08:08:12
AstroSonic
Audiophile

Posts: 814
Location: SE Pennsylvania
Joined: January 25, 2003
 If the TAD driver is 'voiced' for 10-12db of resistive attenuation, and for the response anomolies of a specific (TAD) horn, then the best way tio ensure neutral response is to use the driver under the same conditions it was voiced for (same horn and method of attenuation), as you said. Using non-resistive attenuation alters the driver voicing by substantially decreasing Qe (essentially this strengthens the motor). This is much like using non-resistive attenuation on a horn-loaded cone driver that has been voiced for a specific horn with series resistance used for attenuation.

What I don't understand is why a more 'neutral' horn would resolve the driver response deviations that might arise due to not using resistive attenuation. If the driver has been voiced with a specific horn or horn family, so that it has built-in compensation (response anomolies) for response errors in the horn, then using the driver with a different horn or family of horns leaves the drivers built-in voicing response changes (peaks and dips) without a corresponding (and opposite) horn response error. For example, built-in driver peaks have no corresponding horn dips to cancel out, so they are left exposed as peaks. It would seem that switching to a 'more neutral' horn would consistently result in improved response only in the case of a 'neutral' (non-voiced) driver. For voiced drivers the result would be a hit or miss proposition. While this oversimplifies things (there are many other design considerations including compression chamber shape and volume, phase plug design, diaphram mass and stiffness, surround damping, etc.), the motor strength is an important determinant of driver performance, so substantially changing it should produce response changes. It would be interesting to see the response graphs of a voiced TAD driver (into a plane wave tube) with and without resistive attenuation, just to see the impact of changing the motor strength.

Of the commonly used drivers (TAD, Altec, JBL, B&C, Radian, etc.) do you have any idea which drivers are voiced and which are 'neutral' (for example, designed for flat response with a plane wave tube). If we don't know this, then driver-horn selection is a try it and 'see' proposition.

Regards,

Bob

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