Hi All
Fwiw, on the origin Jericho horn, I mean in more recent times like the last few years, some genuine credit is due for it’s existence to two of the LAB folks.
A few years ago at Infocomm trade show, both Doug Fowler and Craig Leerman both suggested we try to make a larger Synergy horn, large enough so that you could use one per side in a decent size live show.
The next year at the same trade show we had a working prototype Mike noticed the door in the demo room opened to a large parking lot and he arranged an impromptu demo in the parking lot at the end of that day.
While building security closed it down, a few important people were there and it was enough to get them specified into two sports stadium jobs and that lit the fuse.
At the first installation, the designer wanted a lot of subs, like 16X TH812’s or something. Mike talked him down and the designer was hesitant but willing to try 6 which is what I heard when I was out there. 6 can easily shake the far side of a 70,000 seat football stadium .
I am not sure if comparing a 2X18 to a TH-812 is fair as they are very different beasts intended for different uses. For one thing, the TH812 having a low frequency “knee” nearly an octave lower and not having a tilted frequency response would make them sound VERY different subjectively.
Also, since “peak output” is most likely to be the least accurate spec, I am not sure that focusing on one number is very useful either .
Unless one actually measures, one has no idea where one runs out of linearity relative to it’s thermal capacity, in other words, at what fraction of rated power does the device become unlistenable / unusable and at what frequency?
Keith posted something I have heard before about measuring in full space.
Without a crane or silent helicopter, this is a rather hard condition to achieve for a subwoofer.
In fact, while they don’t say what space it is on the pdf on line, if you model the two drivers in that 2X18 in a box that size, you find they published an honest HALF space measurement. If you model that system, like any system, you can see at what power you would run out of Xmax, how the port choking nonlinearity rolls off the low end with increasing levels .
When a company is forthright enough to publish a measured 1W 1M response curve, then one can go a step farther than a one number comparison by examining the systems sensitivity vs frequency, for example, it’s sensitivity at 30,40,50, 60 Hz etc.
Our curves are usually taken at 10 meters and at 28.3Vrms which into an 8 Ohm load, produces a conservative 1W1M equivalent even for “big” cabinets. For a 4Ohm nominal cabinet like 812, one has to subtract 3dB to get the 1w1m loudspeaker rating.
A quick eyeball off the TH812 data sheet and accounting for the load shows the 1w1m sensitivity to be;
http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/TH812-spec-sheet.pdfAbout 105dB at 30Hz
About 107dB at 40Hz
About 107dB at 50Hz
About 108dB at 70Hz
Perfect world Max Level at rated power, 39dB over 1W, calculated peak +45dB over 1W
From a dual 18 vented box spec sheet, 1w 1m sensitivity
About 92dB at 30Hz
About 96dB at 40Hz
About 97dB at 50Hz
About 97dB at 70Hz
Perfect world Max Level at rated power, +32 over 1W, calculated peak +38dB over 1W.
Peak levels based on a noise signal which has a peak to average ratio of 6dB, thus peaks are +6dB greater than an average.
If one could also drive both systems at rated power at all frequencies in question and had no power compression, the difference between the two would be;
About 20dB at 30Hz (100X)
About 18dB at 40Hz
About 17dB at 50Hz
About 18dB at 70Hz
Now, obviously on paper one can make up 18 dB by having 8 subs and 8x the power instead of one but then you run into the problem that dominates live sound speakers, the sources interfere with each other, even can partially cancel each other out.
With a “line array”, to the degree the sound actually falls off more slowly than an omni point source, it is because the individual sources increasingly cancel each other out in the near field in a complex interference pattern as you move closer to the system.
Two or more sources can add coherently into one new source like two subwoofers can IF they are close together BUT this only happens when the sources are close enough together, about a quarter wavelength or less apart.
Coherent summation sounds simple but even at low frequencies, it is hard to place direct radiating drivers that close together to avoid an interference pattern, consider that to add coherently at 100Hz, the sources can’t be any farther than about 33 inches apart so for a 50Hz high cutoff, the subwoofer radiators need to me within a 5 foot circle.
For those interested in playing around with what happens with “where the sound goes” when you array woofers or sources etc, there is a free modeling program you can download called DDT which is fast, powerful and fun and Doug Jones has made a couple some “how to” videos also on the company website. It’s a work in progress and Doug keeps adding features and doodads but it’s already proven useful.
http://www.danleysoundlabs.com/support/ddt-files/AS one might picture a wall of subwoofers produces a wall of sound but it also is an array of individual sources which are not adding coherently but partially canceling each other out in an interference pattern. That array produces many time arrivals at the listener when fed a single impulse and has frequency dependant directivity and if the array is large enough it’s response also changes with location even outdoors (where there are no room effects)..
The sort of “purest” approach I have taken is that if you feed the sound system a single impulse, that single impulse is all you should hear / measure no matter how powerful or large it is. The more strong individual arrivals there are (all other things being equal), the poorer the “fidelity”, the more complex the interference pattern, the more obvious it is when the wind blows etc). It is not like aligning a bank of spotlights for even illumination, it is more like projecting a single image with several projectors.
Anyway, the point is that once you have enough sources, even subwoofers, they don’t add per the simple assumption, you are radiating an interference pattern comprised of lobes and nulls and spreading out impulsive events in time.
Part B of the interference pattern is a strong factor in commercial sound indoors, you do not want the sound projected to the sides, behind , above or below the speaker system. One might think a large array has a lot of directivity, but in reality, one can make a large horn system that sprays / wastes less sound in the wrong or counterproductive directions by avoiding an interference pattern. Doug wrote a White paper that covers that part of it;
http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/01/line-array-paper.pdfNot radiating an interference pattern is very audible too or maybe more importantly is audible as that is what brought in all the stadium work.
If you have Face book and headphones on your computer, go to the company facebook page, hit " recent posts by others" and scroll down to “Mike posted a video” on July 31.
http://www.facebook.com/DanleySoundLabs?ref=tsIf I remember right, that stadium has 4 or 6 TH812’s and a couple Jericho horns, the speakers are in the two score boards, the video taken at the far end (like 750 feet away from the speakers). The sound level is within + - 1 or 2 dB (depending which meter you looked at) and to the ear, sounds the same everywhere over the seating area, no comb filtering and very little effect from crosswind.. The coolest part other than the difference in sound quality I think is when all the sources add coherently into a single source in time and space and avoid an interference pattern and you confine the sound to the desired pattern, it takes far fewer drivers, amps, DSP, EQ and everything else to do a given size audience plane and SPL.
Best,
Tom Danley