Speaker Asylum: RE: 6 - 7 octaves if you're into low fi... by Thorsten General speaker questions for audio and home theater.

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Posted by Thorsten (M ) on July 11, 2012 at 11:16:34

In Reply to: 6 - 7 octaves if you're into low fi... posted by villastrangiato on July 11, 2012 at 10:35:18:

Hi,

> Similarly, use of large drivers (12- 15 inch) has serious drawbacks
> when implemented in two ways and crossed over from 1500 hz up.

Not really. It has some fundamental design requirements that need to be understood, considered and implemented, as has every engineering project under the sun.

> Wide variations in off axis response when transitioning from an
> oversized driver to a tweeter

Are an indication of very poor design.

Let us take an example of a good design, that originally derived in the mid 40's from german designs but moved beyond the original.

In this case we have a driver that is coaxial and uses the cone as waveguide.

(an interesting aside, in the 1980's then new Cepstral analysis and extensive listening confirmed the cone shape originally derived from german designs as one of the absolute best waveguides, over all the the then and even now fashionable "CD" geometries)

This driver has a near constant directivity index between 500Hz and 5KHz, above 5KHz DI increases and below 500Hz (depending on box size and mounting) it decreases.

When mounted and placed correctly the system has a flat on and off axis response from the LF Cutoff to around 5KHz with a falling off axis response above 5KHz.

The driver in question BTW is a 15" 2-way Tannoy coaxial from the same era as the JBLD130.

> (whether a five inch crossed at 3.8khz or a 15 inch crossed at 1.5khz)
> kills imaging performance.

Actually, using a driver/system with insufficient DI is what kills imaging, or large changes of DI over a narrow bandwidth.

The problem you suggest can only happen in hamfisted designs turned out by those who fail to understand the first things about speaker performance and design.

BTW, once you understand the action of the D130 Cone system you will understand why it actually offers a 40Hz-6KHz usable bandwidth with a pretty flat power response (that is integrating on and off axis response) and in fact a rather flat response at the listening position, without needing massive room treatment to control the reverb caused by poor speaker directivity.

Ciao T

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