My thanks to Bennett Prescott, U.S. Sales Manager for B&C speakers for guiding me to the proper driver for my application from the huge variety that B&C makes.
Thanks to Charlie Tappa of Pro Sound Service Inc. (Pro Sound Service AV Sales Service Install 877-776-7631) for providing that B&C driver for evaluation, with prior knowledge of the abuse I would subject it to.
Thanks to Jack Arnott of Assistance Audio (Welcome to Assistance Audio) for providing the BMS drivers with prior knowledge that they most likely would not fit my needs.
For years I had wanted to hear BMS drivers, which use polyester diaphragms, a material primarily associated with awful clothing from the 1970s.
Finally, thanks to Bonnie T, love of my life who put up with my obsessions over the last month in particular, and the last four years in general.
This HF compression driver evaluation was undertaken for three basic reasons:
1. Advances in materials and design has led to higher power handling which may correspond to additional available output and lower distortion.
2. The DH1AMT / DH1A drivers presently in my speaker cabinets weigh 23 pounds, a weight savings of 10 to 20 pounds per 50 pound cabinet could be realized with other drivers.
3. Most of my sound work presently is in the dry high desert of New Mexico, HF air losses in hot summer temperatures require far more acoustic power to overcome those losses compared to similar heat at high humidity.
HF air losses are in addition to the inverse distance 6 dB per doubling of distance.
For example, at 90 degrees, 80 % relative humidity, HF air loss is only 2.4 dB per 100 feet, while at 20% humidity, 22.9 dB loss occurs.
To achieve the same HF response at 100 feet in the desert would requires a 20 .5 dB increase in SPL, over 20 times the power (without considering power compression).
Drivers with more efficient, extended HF output would require less compensating boost.
In the past two decades, LF driver technology has made large advances in linear excursion capability and power handling, resulting in more clean LF output per driver, although requiring more power to achieve that goal.
Thiele -Small parameters for cone transducers make comparison of cone speakers relatively easy, allow allowing reasonably reliable predictions of response in a particular cabinet alignment.
HF compression driver manufacturers do not publish TS parameters, at best one gets power, Fs (resonant frequency) diaphragm size and composition, exit diameter and response on a specific horn or plane wave tube, sometimes with harmonic distortion figures derived from a single frequency sweep at a small fraction of rated power.
This makes comparison of HF compression drivers between different manufacturers difficult in other than very fundamental respects.
Even comparing within the same company can be difficult, the newer EV DH7 can’t be compared to the older DH1AMT on paper, they used different horns in testing.
Having heard dozens of different HF drivers on dozens of different horns in different venues ranging from home theaters to arenas, with different arrays driven with various playback material and mixes by different engineers mixing different bands through different consoles, processing, and amplification, about the only conclusion drawn were various HF drivers can sound quite good or lousy.
The EV DH1AMT and DH1A HF drivers presently in my PA were chosen back in 1992 after extensive side by side testing comparing them to the JBL 2445 and 2425 drivers in use at the time.
A single DH1A had more extended, clean response than the pair of JBLs, at a considerable weight, size, and cost advantage, both in reduction of driver cost and elimination of a crossover point and amp channels.
In 2000, after comparison, Jack Arnott replaced his JBL 2450 drivers with BMS, and later became the North American distributor for BMS product.
I designed a series of tests that involves elimination of as many variables described above to determine how a variety of drivers compare to each other at different drive levels, all driven with the same program material through the same electronics chain. Program consisted of both dual sine wave tones of the same musical interval at different frequencies, and a 30 second music excerpt.
The dual sine wave tones have accompanying RTA screen shots so the difference in each driver’s harmonic and intermodulation distortion can be compared visually as well.
The results of the tests were recorded and normalized for level and are available for download.
The “Full Monty” report with all the facts and figures is here:
High Frequency Compression Driver Evaluation - diyAudio
Since you are a busy professional, I’ll cut to the chase and give you the results of what consumed 50.25 hours of testing, then another 84.75 hours to mix, analyze, write up and post the findings, a total of 135 hours of work in this project spent over the last month.
To be continued next post.
1A = EVDH1A
02= Eminence PSD2002
50= BMS 4550
52= BMS 4552
82+ B&C DE82
“DRPA630HiOutOnly” is a recording of the DSP HF output driven by a Phillips CD player.
The recordings below are an excerpt from Ed Kabotie’s song, “7 Cities of Gold”
Ed Kabotie Freedom Songs - DreamCatcher.com
with voice, acoustic guitar and wood flute used to compare the output of the various HF drivers all fitted to the same type horn.
The drivers were equalized as flat as possible from 630 to 16K using the three PEQ and 1/3 octave filters afforded by the DBX DriveRack PA. Each driver also used a specific delay compensation to align it with the LF track, slightly different delay and EQ were required for the 1250 Hz alignment.
The process was akin to aligning a dozen different PA systems, no small feat in itself.
The process “babied” the 1” drivers, allowing for the LF track to carry some extra “weight” around the 630 Hz crossover point. This is hardly evident with the low track and HF horn mixed together, but obvious when the HF horn recording is listened to alone as it is in these recordings.
The actual SPL and power levels for the recordings are:
1An0630 0, 630 Hz (7.3 watts, 116.7 dBA peak)
1Ap1363 +13, 630 Hz ( 146 watts, 128.9 dBA peak)
1Ap1763 +17, 630 Hz (367 watts, 132.4 dBA peak, oops)
1Ap1312 +13, 1250 Hz (73 watts, 127.8 dBA peak)
02n0630 0, 630 Hz (7.3 watts, 110.3 dBA peak)
02p0125 0, 1250 Hz ( 11.5 watts 113.8 dBA peak)
02p10125 +10, 1250 Hz (115 watts 118.9 dBA peak)
02p15 125 +15, 1250 Hz (367 watts 125.8 dBA peak, oops)
50n0630 0, 630 Hz (7.3 watts, 114 dBA peak)
50p13125 +13, dBA 1250 Hz (36.6 watts, 125.5 dBA peak)
52n0630 0, 630 Hz (7.3 watts, 116.3 dBA peak)
52p13125 +13, 1250 Hz( 36.6 watts 124.6 dBA peak)
82n0630 0, dBA 630 Hz (7.3 watt 113.2 dBA peak)
82p1363 +13, 630 Hz (146 watts 126.3 dBA peak)
82p1312 +13, 1250 Hz (73 watts 121.6 peak)
Not wanting to run the risk of burning up this antique driver, it was given less power:
PAp363 +3, dBA 630 Hz ( 14.6 watts 96.3 dBA peak)
PAp912 +9, dBA 1250 Hz (46 watts, 99.5 dBA peak)
More recordings are included in Posts # 2 and 3.
I suggest downloading "DRPA630HiOutOnly" (the high output of the crossover used for testing the HF drivers), first as a comparison to hear what the high end of the song sounds like before being recorded from the output of the HF drivers.
The sound files are in mp3 format, to open them change the suffix < .pdf > to <.mp3 >, then open with your mp3 app.