taming the rising high freq response of FR drivers

[phase_accurate]

What about the use of diffusors ?

Regards

Charles

[MJK]

Originally posted by pforeman
I was wondering if most people do anything about the rising high freq response of full range drivers, or do you live with it finding the cure worse than the problem.
Specifically I want to make open baffle speakers hopefully with as small of baffles as possible with 18 inch H frames for support.

I have used Lowther drivers in boxes and on OBs. Lowther drivers are well known for having a rising response which can lead to a harsh, shrill, very fatiguing listening experience if they are used in any old box design. I have looked at three options and built and listened to two of them with my PM2A drivers.

1) An ML TL style of enclosure can work if you use a correction filter. The correction filter is required and improves the sound of the system making it extremely good sounding. There are no negative impacts of a properly sized filter other then a loss in efficiency. A correction circuit does not remove anything from the signal it just rebalances the SPL magnitudes and even corrects phase shifts associated with baffle step. In this type of system bass was limited to about 40 Hz, the design will not produce high volume subwoofer bass output.

2) An OB using two 15" woofers with my preference being high Qts woofers. All that is required is an active crossover set near 200 Hz, the full range driver produces everything above this point. I used my PM2A drivers without any compensation to offset a rising response. There was nothing between the amp and the PM2A driver. This was probably the best speaker I have had in my system producing a huge soundstage, amazing detail, good imaging, and tremendous dynamics. The downside was the size of the OB, I have now learned enough to believe that a much smaller baffle would have worked just as well (maybe a little of the bass would be sacrificed) and will rebuild the system at some point.

3) A hybrid TL/BLH that is corner loaded. I have a simulation design that yields a flat frequency response down to about 50 Hz for this style of enclosure. Because it is corner loaded the design has only one mouth and is not so large. Basically taking advantage of the corner the enclosure produces enough bass output to math the efficiency of the Lowther driver. This is on my list to finish and build. Unfortunately my list is long and my time is limited.

If you are looking to build an OB system with an active crossover to a large woofer or a pair of woofers I do not believe you need to be too concerned about the rising response of the full range driver.