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|7th July 2006, 02:46 PM||#1|
Join Date: Jun 2005
Location: The Netherlands
Random horn questions
Currently I'm trying to design some horn speakers. I've got 6 midbass units, two of them have a Qts of 0,25 and a Fs of 45 Hz. The other 4 could be used as midrange speakers. I'm curious about the following:
A) According to Dindale's article about horn loudspeaker design, he mentions that in case of a BLH the direct radiation from the unloaded front of the cone is only a few percent of the sound coming from the horn. If the horn takes care of the bass frequencies (say up to ~350 - 400 Hz), then apparently the direct-radiating side of the cone doesn't produce any bass frequencies. Is it then possible to see it as a 'midrange speaker'?
If so, could I substitute the BLH for a FLH, and the direct radiator for a 'real' midrange unit? Thus: FLH up to ~350 - 400 Hz, then a midrange unit from ~350 - 400 Hz up to tweeter frequency.
The FLH will be more effective around Fl (BLH start to fall off ~10 Hz earlier than the calculated cutoff freq.), and it offers greater ease regarding placement. Also the midrange unit won't receive any low frequencies, so less excursion etc...
B) With Keele's math, you can adjust the throat chamber (between driver and horn) to a desired frequency. Because the horn's usually optimized for it's bandwidth (Fl to Fh), should the throat chamber rolloff frequency be set to Fh, or is it better to adjust it to a higher frequency?
C) Are there any specific requirements for loudspeakers that will be hornloaded at midrange frequencies? Thiele/Small parameters? Dinsdale provides a method for designing mid/treble horns. According to his article the throat diameters of these horns should be equal to the speaker's (nominal) diameter. Also, I read somewhere on this forum that the cutoff frequency should be set significantly lower than the lowest frequency of it's bandwidth (Fc << Fl) in case of midrange horns. Could someone verify these statements?
*D) Well this question doesn't have anything directly in common with the subject. Anyway, are there any (dis)advantages of using a midrange unit or a tweeter with an open back (AMT) in a dipole/OB arrangement?
Thanks in advance.
|17th July 2006, 08:08 PM||#4|
Join Date: Jan 2005
Location: Rotterdam, NL
The direct radiation from the front of the speaker is producing bass frequencies (depending on size of the rear chamber) only at a much lower level. If one side is producing bass so must the other side.
The frequency which 1/2 wavelength is equal to the distance from the front to the rear of the driver, through the horn will partially cancel, creating a 3- 8 dB dip centered around that frequency. The use of multiples will flatten that out.
However it would be unfortunate if the cancellation would take place in the mid area.
With BLH meant for bass, known as "scoops" it's often around the 70 -90 Hz area, meaning lack of kick.
The front side of the speaker is capable of mid frequencies. The back of the driver still radiates the higher frequencies but they will get "lost" or delayed in the horn and/or (stuffed) back chamber.
Some designs use the mid capabilities of the speaker to make the enclosure cover the entire bass-mid range up to an tweeter. Not all speakers are up to that task as producing bass frequencies desires different T/S-parameters than producing mid.
Also the delayed mid coming through the horn might bother you.
With kind regards Johan
Impossibilities we do immediatly, miracles take slightly longer.
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