Floor Loudspeaker Reviews

Manufacturer's Comment

Thank you for the review of the SourcePoint 888. I hope by naming it 888 it brings me the prosperity I need to one day retire. Until then I will continue using other peoples financing to design speakers . . .

I have some comments with regard to the technical evaluation. For most of the range, the impedance is quite even with a low phase angle. This is achieved through using impedance compensating elements in the crossover.

I did this both to minimize peak current demands and also reduce its sensitivity to frequency response errors when driven by high source impedance amplifiers. There is not much I can practically do at the lowest frequencies, but as John says, the peak current demand for most music doesn't occur that low.

Both the low-frequency balance, and the dip towards the mid frequencies are more a characteristic of measuring a large multi-driver system at such a close distance of 1m, allied with to trying to combine nearfield measurements with far-field without diffraction compensation calculations. At 1m, the differing distances between the woofers and midrange and the microphone contributes noticeable errors.

The balance evens out when measured at 3m and then referring the sensitivity back to the standard reference distance of 1m.

I was interested to find John stuffing one of the ports. In a regular vented box, with one internal chamber and two vents, stuffing one vent tunes the box a half-octave lower, and extends the response downwards at the expense of a lowering overall of bass level.

However, with the SP888 the chambers for each driver/vent pair are isolated. Stuffing just one port results in one chamber being closed box and the other vented. In this case, because the drivers are connected in parallel, the resultant response is better defined than if they were in series.

However, I did wonder if any odd low-frequency phase cancellations might occur by combining a second-order high-pass response with a 4th order. So I did the experiment!

We can all relax. It works okay. The difference between both open and one stuffed is a dip in response of almost 6dB around the tuning frequency, and no odd cancelations.

So it turns out that it is a useful fix for John's room. Just remind me to design some bass traps for your room before next Xmas, or my next speaker design review.—Andrew Jones, Chief Speaker Designer, MoFi Electronics