>Note that your exponential horn, which has a mouth diameter of about 15ft
and the speaker was almost certainly less than 2ft, which implies and
exponentiation of 2, Since the length is 17', the cutoff frequency is 1/2pi
8'= 1/48' which is about 20Hz. Ie, your horn speaker will produce very little
sound below 20Hz.
Thank you! I'm happy your calcs agree with mine. My original design goal was physical limit of fc=20hz or thereabouts. Beyond the physical size I indicated construction, transportation becomes a serious problem, so my hope was to force the system to work below it's natural limit of 20hz by equalization, sub-bass boost, etc. This is where I became interested in linux/alsa, IIR filters etc.
I don't plan on trying to build a football-field-size horn; I'm fairly certain I can make the 20hz horn produce the sensation it's working much lower that that, but if my "experiment" fails, I'd be happy to have a true 20hz loudspeaker -- pretty sure I'd be one of the few on my block with one.
My attention turns to what Alsa/Linux-sound can do to help me manage bass and subbass.
Rgds,
Ronan
On 2/2/07, Bill Unruh <
unruh@xxxxxxxxxxxxxx> wrote:
On Fri, 2 Feb 2007, ronan mcallister wrote:
>
> On 2/2/07, Gene Heskett <gene.heskett@xxxxxxxxxxx> wrote:
>>
>> The individual pipe may not, but the harmony or beat between two 32 foot
>> pipes can easily reach considerable energy levels well below 20 hz. Even
>> the 16 footers can 'shake your guts' at the right close harmony notes.
>> Our own organs 16 and 32 foot pipes rank each other across the backdrop
A 32 ft pipe is still only at 16-17Hz, not 5Hz
>>
>> They can be built, and in much smaller cabinets than the famous Altec
>> Voice of the Theater sizes which were actually built huge for efficiency.
No. They are built huge to bring down the resonance of the speaker in the
box. Even with zero frequency resonance of the cone itself ( which is of
course never the case), the frequency goes as the square root of the the
area of the cone squared times atmospheric pressure divided by the mass of
the cone times the volume of the box. The smaller the box, the higher the
frequency. Those speakers i believe tended to be horns for efficiency, but
the horn cutoff was probably still about 50Hz.
You cannot get good bass out of a small box, no matter how to tweak it.
(Or ratehr if you are happy with one note bass, then you can design a
Helmholtz resonator at whatever freq you want, but that is not a speaker.)
>> We once rebuilt the relatively small box the Bozak floor model came in,
>> about 28" tall by 24" wide, 15" or so deep, an infinite baffle design.
>> Replacing the 10" B305 driver with a B305AL which had a 2" throw,
>> stiffening up the box with cross bracing till it clicked like marble when
>> tapped with a mallet anyplace on it, and added about 3x the normal sound
>> absorber material inside it. Cook used to make some 78 rpm lp's intended
>> as demo records for us 'hi-fi' peddlers to use, and one of them had
>> several tracks of percussion solo's. The tympani track was a favorite to
>> demo that speaker with as it went on for about 45 seconds, then you could
>> hear the squeak of the peddle linkage as he let the drum skin go slack
>> after the last strike at the end. A normal OOTB speaker did the squeak
>> and that was the end. With the rebuilt box, the room went up and down
>> several times after the squeak. This was 47 years ago, using a 30 watt
>> McIntosh amplifier, or a Dynaco of about 20 watts.
That speaker still had a resonance at about 20Hz probably, and with that
sized box the resonance in the box was far higher.
Note that your exponential horn, which has a mouth diameter of about 15ft
and the speaker was almost certainly less than 2ft, which implies and
exponentiation of 2, Since the length is 17', the cutoff frequency is 1/2pi
8'= 1/48' which is about 20Hz. Ie, your horn speaker will produce very little
sound below 20Hz.
To get 5Hz requires a horn about three times as large. At 5 Hz the
wavelength is 64 meters-- about the size of a football field.
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