1)measurements made up close include false bass INCREASES.
This is particularly present in large cabinets.
2)We measure using a swept sine wave via TEF. For subs in particular we measure at a distance of 10M with 28.3V input. So that comes back to a 2.83V 1M measurement.
3)The 6dB between continuous and peak is simply the increase in power to a maximum of the driver-with a 6dB peak based on the power capacity of the driver.
This is assuming no power compression-since that takes time.
The 137 will hold for a certain period of time-based on heating. Of course the actual levels without power compression will depend on the dynamic range of the signal.
4)We do no measure distortion at full output. But a horn cabinet will typically be less distortion than a front loaded/ported cabinet simply because the driver is not moving as far.
Dear Ivan,
1) Your statement is inconsistent with your measurement guru's dictum.
I'll cite it if you ask politely, but don't want to embarrass you with it, we all have our "drunk posts" that we have to walk down the "hall of shame" while holding the trophy with some appendage of our shamed existence held prominently for all to see.
Having far too many "shame walk" atrophies evident in my copious "drunk post" historical evidence, which progressively disappear from the inter-webs at the approximate rate of their initial propagation, I regret any "collateral damage" inflicted in my reply to your dissertation.
2) The "power capacity" of the drivers DSL uses are simply reprints of the AES rating of the driver taken in free air.
When the driver is loaded in a "tapped horn", the impedance of the driver is far lower than in free air.
Since the AES rating is based on the nominal impedance, not your DSL TH impedance, your power specification is inflated by a rather large factor.
As an example, let's use the DSL TH-118 loaded with a "4 ohm" B&C 18SW115 rated for 1700 Watts.
To drive a nominal 4 ohm load to 1700 W requires 82.5 volts, so we assume that is the voltage used for the AES test, even though the driver's average free air impedance is far higher- the driver is actually dissipating a fraction of the "watts" specified.
Put the same "4 ohm" B&C 18SW115-4 in your DSL TH-118 and apply the same "continuous" 82.5 volts at Fb, where impedance is as low as the 3.3 Re DCR of the driver and in about twice the time it takes Porky Pig to say " ba ba be hey hey hey, presto", the smell of burnt adhesive will start to be evident near the cone.
Leave that sine wave tone fixed at Fb another 30 seconds or so and the smell will be enough to drive you out of the room unless you have an air evacuation fan going full tilt for a cold December half hour (true story). Wish I had more than a 1500 Watt heater in the shop..
Now take that "warmed up" driver, and apply halfway between the "continuous" 1700 Watts (those Watts that used to be redundantly called Watts RMS) and the peak rating of 6800 Watts, "3400 Watts" requiring 106 volts.
I don't presently own an amp that can put out 3400 Watts continuously, but I guarantee the "poor little" 115mm double sided double wound 18SW115 voice coil won't last long even if you use 106 volts (RMS, not peak) pink noise rather than a sine wave at Fb.
Yes, cooling is better when the cone is violently flopping around, but we can't determine the musical proclivities of end users, EDM "drones" may have less crest factor than the "terrible" 3dB of a sine wave.
In weeks of abusive testing, and years of shows ranging from jazz to hip hop to EDM, I never had any problem with the B&C 18SW115-4 loaded in my Welter Systems Keystone Sub design, also "sporting" the same 3.3 ohm impedance minima at Fb the DSL TH-118 has.
The fellow I sold the original pair of Keystone Subs to managed to burn one up in the first week.
My guess is he accidentally panned kick and/or bass hard left, leaving one sub to do +6 dB more "heavy lifting" to achieve the level he became used to on the first several gigs.
Bass is addictive, I see +5, +10, and +20 addicts ruining our collective lives on an ever more frequent "bass"is.
A single mono bridged Crest CA 9 driving one Keystone sub can't put out more than 80 volts while drawing 37.8 amperes from a 120 volt line.
37.8 amperes line voltage to a shade under 100 volts, when directly connected to a mains power transformer with about 40 feet of 4AWG to the mains panel, and 100 feet of 10AWG to the amplifier.
If the Crest CA 9 were run anywhere near that 80 volt output level the 20 amp circuit breaker the fellow's amp rack with two other amps of equal power draw on the same circuit would have popped, but the breaker didn't, the coil lost it's immortal soul.
The "take away" from all this is your specifications are not "real world", so you constantly have to inform your DSL clients to limit the speaker to some small fraction of the AES rating your DSL specs are based on, or they will let out the "magic smoke" and stink up the area surrounding the DSL cabinet.
This is the choice made when DSL wrote specifications based on fictional "power" ratings, like so many companies play the grid iron playing field here.
Yet you have always liked to play from the top of the hill, showering us with "trickle down" theories like a "golden shower" of truth on the 49% of the 99% inhabiting the USA;^).
2) I like to firmly bolt my drivers down, how far is "too far" for a driver to move?
Thanks for finally updating your TH-118 specs to the 18SW115 AES ratings rather than the 18NLW9600-4 that is still pictured and your tips six years ago about why the B&C is the better choice :^).
Sometimes I wonder if M.H's influence has shifted you, but I know the "force" is strong deep within you, Ivan- do not succumb to the "Dark Side".
Jokes aside, the reason the 15.2 gross cubic foot Keystone Sub "tapped horn" also loaded with the B&C 18SW115-4 delivers 6 dB more average SPL in the 40-100 Hz pass-band than the same driver in a 9.24 gross cubic foot "bass reflex" enclosure with the same low corner frequency is because the driver is forced into "doing more work" for a given excursion.
Work is hard, some "force" always will pay for any work done in the omni-spherical dimension we inhabit.
Yes, the Keystone Sub "horn cabinet" delivers more SPL for a given input voltage, but the TH will also have more distortion at that voltage than a BR.
Recently, while reviewing TH distortion and SPL compared to BR, while also comparing impedance curves, found the Keystone had "compression" at the upper end of the pass band at "only" 77.5 volts of sine wave input, while the BR was the opposite, due to "port compression".
The impedance curves made obvious "what went on".
Impedance is kind of like a variable frequency chastity belt, the upper reduction in the TH SPL was due to it's upper pass band low impedance dips "sucking, or demanding" power, while the BR has a steadily rising impedance "spurning, or rejecting" the Scottish Watt's "power".
The more power the voice coil "sucks" surrounding the pole piece, the hotter it becomes, which makes it's impedance rise, protecting it from the very "power" that heated it up, a cosmic entropic conversion of energy, - sex, drugs and rock and roll are not required to witness the conversion, but two of three are usually involved.
Since most of us audioholics test from "bottom" up, my sine wave tests were also started at the bottom of the pass band, that way you can only go "up".
The average increased excursion down low provides ample "heat pumping" (forced cooling), then proceeds to upper frequencies, which progressively pump less heat from the voice coil.
Ouch, too hot to touch- and that smell..
The upper pass band compression noted in the TH compared to the BR was due to the lower upper impedance causing voice coil heating, raising impedance, causing power compression- at 77.5 volts, after considerably less than 50% duty cycle over a few minutes time.
I know the duty cycle was less than 50% because I am "digitally challenged" and it took me more time to save each record than it did to let the SMAART screen settle down.
Data in post # 12 here:
http://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html"Full power" should have been 82.5 volts, not 77.5 volts.
77.5 volts is 1500 Watts into a nominal 4 ohm load, the B&C 18SW115-4 is rated for 1700 Watts AES. I accidentally substituted another B&C driver's AES rating, and conducted the test at a fraction of a dB "too little" power.
As the Immortal Carroll Shelby said: "Too much power is Just Enough".
I bet Carroll burned up a lot more 427 Cobra engines than I have drivers, but his drivers got paid more than mine ;^)..
Cheers,
Art
Welter Systems, Inc.