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In Reply to: RE: compromises - at what frequency is the first horn in the system most critical? posted by freddyi on October 16, 2015 at 01:14:27
Hi Freddyi
Horns do two things (at least), they can increase the overall efficiency which means for a given spl, the radiator excursion is less and since the motor non linearity is a primary source of distortion, it is less as well. Second they can confine the radiation pattern which means at the listening position, one is receiving more direct sound and less reflected / late sound which helps articulation and or intelligibility as measured via STIpa.
There are two problems with horns (at least), they are limited bandwidth devices and because they are large, a multi-way system places the upper and lower sources farther apart which is a larger distance than with direct radiators.
Two loudspeakers or acoustic sources CAN add together coherently like two close coupled subwoofers do but only if they are about ¼ wavelength or less apart, beyond that the sources radiate independently and produce an interference pattern (a series of lobes and nulls in the polar pattern) and each source has it's own individual arrival in time depending on the distances which harms musical articulation and measured intelligibility as predicted with STIpa.
The latter is why large concert style line sources become unintelligible or less intelligible even when operated outdoors or when modeled acoustically even if each source were text book perfect, time does matter for some things like intelligibility and articulation generally but not for all kinds of music.
Also, the familiar thumb rule of a mouth 1wl in circumference is not actually correct or rather not understood, that is the dimension where increasing mouth size offers little extra gain as it implies the knee in the radiation resistance curve. Horn gain does start at a much smaller dimension, for example an SH-50 has a cabinet / mouth that is 28 inches square but the gain over the direct radiating drivers begins at about 100Hz.
Hope that helps, what do you want to do?
Best
Tom
Follow Ups:
hi Tom - - out of curiosity I'd like to revisit a midbass horn and for use in a small cramped space, try to augment the bottom with simple small sub - result might be frustrating and bulk large to reach 80Hz solid - think it can be done with small K-coupler as midbass rather than horn.
Best,
Freddy
Karlson Evangelist
I know it will mark me as an apostate heathen to many in this asylum, but the problem of the great physical distance between the drivers in the various horns can be easily corrected by a good DSP. My three way horn loaded system has over 16 feet of separation between the acoustic centers of the 15" woofers in the Fitzmaurice HT Tuba folded corner horn subs and the AER drivers in the Oris 150 wide range horns. Using a DEQX HDP-3 DSP I can correct that so that arrival times for sound from the two are equivalent to having the acoustic centers of the drivers within less than 1/8 inch of each other.
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