Chris,
Having actually tested the above, I would say no.
Ivan and I seem to be slightly at odds regarding this point.
Over the course of forty years professionally listening to and testing hundreds of BR, FLH, and recently TH, I have found the various cabinet types to all conform to the inverse distance law.
The inverse distance law, simply stated says every time we move away from a sound source, doubling our distance from it, the sound pressure level decreases by 6 dB (6.02 precisely).
In single units of the above, this has been true even from one meter onward, while in large arrays, it has been true from a distance roughly the diagonal of the array on out when the array has been roughly square .
The inverse is also true, half the distance to the source sound pressure level increases by 6 dB, though when one measures quite close to a large radiating source the “law” breaks down, at some point the level will no longer increase.
In May 2010 I tested a small ported Lab 12 compared to a 15" "CHorn", Phil Lewandowski tested a JBL SRX 718 compared to a Growler. The C horn and Growler are similar size and shaped horns with path lengths of around 2 meters.
Although the acoustic origin from a time alignment standpoint is approximately the same as the horn path length, the output drops with the inverse square law once it leaves the horn.
Rog Mogale of Void Acoustics also tested horns compared to bass reflex and they both found they followed the inverse distance law, within one dB in Rog's more controlled testing.
Rog Mogale's test used a small 4th order bandpass sub with a single 12" woofer compared to an 18” horn loaded design, and found it only 1 dB louder from 8 meters and beyond.
http://www.voidaudio.com/pdf/lffaq.pdf
Josh Ricci has extensive testing experience documented on his Data Bass website.
He wrote:
"The diaphragm may be further inside the horn but that is completely irrelevant to the listener or end user other than perhaps for setting delays between cabs. When you simulate something in Hornresp or another program it calculates the acoustic performance at some specified distance from the final radiation point of the cabinet, not from a driver sitting 3m or whatever inside. “
The exception is when the the horn mouth diameter is larger than the measurement distance, but the same exception holds true for a large direct radiator array, when the measurement distance is within the array diameter, going closer to the source no longer increases level.
In regard to full range frequency measurements, Pat Brown wrote :
"A working “rule-of-thumb” for determining the boundary between near-field and far-field is to make the minimum measurement distance the longest dimension of the loudspeaker multiplied by 3.
He then writes:
"It is often thought that a remote measurement position is necessary for low frequencies since their wavelengths are long. Actually the opposite is true. It is more difficult to get into the far-field of a device at high frequencies, since the shorter wavelengths make the criteria in Item 4 more difficult to satisfy.
Item 4:
4. The distance from the source where the path length difference for wave arrivals from points on the device on the surface plane perpendicular to the point of observation are within one-quarter wavelength at the highest frequency of interest ."
This is an important distinction between high frequency and low frequency measurement, criteria #4 can be satisfied at 95 Hz for a subwoofer of one square meter measured at one meter.
At any rate, the diameter of the subwoofer, not the path length of the horn determine when the inverse distance law kicks in.
Art
