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Elsinore Mk 2 Crossover & Notes

The new HDS Tweeter is not as flat as the previous XT25, but it has much lower distortion and superior in every other way. The Mk2 now specifies the use of the Nomex version 830875. This has virtually an extra dB of sensitivity and the HDS tweeter means we can exploit that and yet still maintain a nominal 8 Ohm load, something that could not be claimed with Mk1.

OPTIONAL CONJUGATE FILTER: This has a dual purpose. First, it flattens out the impedance curve between 300 Hertz and 1500 Hertz. This means that the source impedance of the power amplifier is less likely to modulate the frequency response, such as non-feedback single-ended triodes and push-pull tube amps. Second, since the electrical first order hi-pass on the tweeter results (as is usual) negative current just below the crossover, the conjugate filter offsets this by drawing positive current, and hence the total negative phase angle (load wise) is reduced to -18 at 2200 Hertz. As the impedance is a high 9.5 Ohm at this frequency, this is quite a mild load.

Frequency Responses & Other Measurements











Above: 1 Metre Family of Frequency Responses - Red ON Axis - Blue OFF Axis 15 - Brown 25

Above: 2 Metre Family of Frequency Responses - Red ON Axis - Blue OFF Axis 15 - Brown 25

Because this has a rising response the optimum listening angle is Blue OFF Axis 15 where the 2Pi response is better than -/+ 2dB 60Hz to 12KHz (ignore microphone proximity effect around 150Hz).

This shows the system impedance and Pink electrical phase (using the optional Conjugate Filter). The Blue impedance stays well above 6 Ohm and hence qualifies as an 8 Ohm speaker system. The lowest phase angle is at 80Hz (-45) but the Z here is 18 Ohm. The other low is at 2200Hz (a moderate -18) and Z is 9.5 Ohm. As stated before, this is clearly an easy load and also suits the use of tube power amps as the modulation  of the frequency response will be mild.

2 Metre Impulse Response (simulated square wave @ 500Hertz)

This may surprise a few. There are not many speakers capable of this kind of result. The reverse electrical phase does not translate into a lack of flat phase response until near and above 10KHz. The beauty of this is that we are able to aim for perfect summing from 1M onward and a large lateral off axis spread. This is difficult to achieve with so-called in-phase drivers (believe me, I have tried for many years and it just doesn't work). The acoustic phase is correct until the top octave is reached. Because of this, and the time coincident mounting of the drivers, they are entirely in-phase at the crossover and maintain so over the whole overlap. Thus the drivers sum 100% all the time unlike conventional Butterworth which has a 90 phase error and hence susceptible to rippling of the response.


You may think that using a simulated square wave is cheating, but it is a difficult ask to do a full measurement as it requires that nearfield response somehow be incorporated. But an effort was done by going outdoors and minimising reflections and raising box well off the ground. Instead of 500 Hertz, a realistic and only slightly higher 700 Hertz proved achievable:

700 Hertz square wave captured at 2 Metres and 15 Off Axis

This is a remarkable achievement by any standard!

Step Response

Red is the Step Response, also captured at 2 Metres and 15 Off Axis

Effect of the Conjugate Filter

RED represents zero impedance and BLUE is 3 Ohm. The response shape is changed only very  little.

Diffraction Control

Recommended Room Positioning

At the preferred listening position you should be able to see the inside panels of the speakers (see red dotted line). It pays to experiment with the width between speakers. The rear of the speakers should be at least 500mm from the wall.


Total Design Responsibility, Joe Rasmussen of Custom Analogue Audio & JLTi

Part Financial Sponsor & Prototype Box Construction, Bernard Chambers of Sutherland

Sounding Boards, Michael Lenehan of Lenehan Acoustics & Brad Serhan of Orpheus Loudspeakers



Send mail to joeras@vacuumstate.com with questions or comments about this web site.
Copyright 2003-10 Joe Rasmussen & JLTi
Last modified: Monday June 08, 2015

Just had a terrible thought. If "intelligent design" is unscientific, then who will design our audio equipment?