Rear-loaded horns: disadvantages?
Hi, everyone. I'm considering a rear-loaded horn design for a pair of floorstanding 2-way loudspeakers. I know this is the full-range forum, and none of my drivers are running close to full range, but this is the area of the forum that seems to have the most experience with rear-loaded horn enclosures.
So, aside from build complexity, what are the disadvantages of a rear-loaded horn design?
An intrinsic problem is time smear. Sound from the backwave arrives delayed with respect to the front.
Opinions differ about the audibility and importance of this effect, but it is unavoidable.
I read somewhere that in a BLH there is usually a dip in the response around the mid-bass region (70-90hz) because of the delay, is this true?
I doubt it is unique but Tannoy, in their Autograph and Westminster adopted a front horn that went down to about 200Hz and used the folded rear horn to extend the response to a claimed 18Hz to 20Hz (-6db).
That system keeps the delayed rear wave to only the lower frequencies and maybe that hides some of the audible effect.
There are some threads looking at clones of these two speakers and as far as I can recall none/few builders commented on hearing time smear/delay/slowness in the bass.
Reviews of the Westminster actually major on the bass impact and reproduction of bass transients as a major advantage of the combined BLH FLH system. They say there is nothing like it from any boxed speaker.
Assuming a BW below ~250 Hz (though some claim as high as 400 Hz) and if you XO it below the 3rd harmonic dip, then nothing since the time delay will be minor and down in our rapidly rolling off hearing acuity BW.
WRT the dip's location, it's a function of the horn's design, so not necessarily in the 70-90 Hz BW.
Agreed, if a HE single driver is used in a relatively low impedance system, a BLH works best with a FLH to cover the acoustic XO BW between the driver's front and rear radiation since otherwise you have to either accept the broadband dip in the response or suffer the time 'smear' of a too high acoustic XO.
The way around all this though is to design using either a relatively high Qts driver or a HE driver with significant added series resistance to lower its effective Qts/mass corner/acoustic XO point or use a matching impedance amp.
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