Blast from the past! SpeakerWorks/USD Audio A-6.0 Testing

I was loaned this set of SpeakerWorks/USD Audio A-6.0 horns by a friend some time ago and recently came across them when shuffling some things around in a closet.  Even though these are circa 1995 (maybe earlier), I thought it might still be fun to test them out for “old times sake” to recapture some nostalgia.  Because, heck, reminiscing is fun and we can learn a lot from old designs.

Before moving too far ahead, I would like to address this specific horn and application given it’s age.  I contacted USD Audio to see if they could provide any insight on the product.  Eric Holdaway was kind enough to respond with some vital information that is crucial to understanding the implications of the preceding test results:

They are “A” models with the fiberglass body which are really, really old.  These should only be used with the original supplied EQ and compensation circuits or comparable devices for them to perform at their best.

Eric also added:

It sure was fun to “invent” the HLCD’s in the car thing with my Dad (Roger), Brother (Pat) and Great friend R.E Greene. Our U.S. Patent was amazing to get and lock in that we had created an original idea. This and the A-periodic subwoofer enclosure were a thrill to create.

 

I have to thank Eric for being kind enough to provide some info on a product that has been obsolete for nearly 2 decades and understanding the desire to still want to learn and revisit some nostalgic items back when car audio sound quality competition was in it’s “heyday”.  As Eric noted, these were designed to be used with an EQ/Compensation circuit.  However, this was not provided so please understand that while these results show the performance of the raw horn… that’s exactly what you are getting; you are not seeing the results as they were intended to be used from the factory as the above mentioned circuit is not tested as part of the kit here.  The owner said he might have this circuit somewhere so this test may be revisited later and updated accordingly.

 

With that said, let’s get started…

IMG_3972 IMG_3967 IMG_3979 IMG_3982 IMG_3980

IMG_3978As you can tell, these horns were treated with CLD (constrained layer damping – commonly known as “dynamat”, etc).  This was popular among competitors as it was used to reduce the horn body from resonating at higher frequencies.

 

Measurement Information

This horn was measured free-air.  This was not measured in a car nor was any sort of baffle used to mimic the bottom half of a dash, as these would typically use in an install to ‘extend’ the horn’s effect in the vertical plane.  It was attached to a 6×6 beam and measured both horizontally and vertically from -90 to +90 degrees.  For Frequency Response measurements, a signal of 2.83v was fed to the driver with the mic placed at 1 meter distance from the horn mouth.

 

Impedance Sweep

Results provided are obtained via Dayton’s DATS v2.

  • f(s)= 1325 Hz
  • R(e)= 5.789 Ohms
  • Z(max)= 14.54 Ohms
  • Q(ms)= 4.164
  • Q(es)= 2.754
  • Q(ts)= 1.658
  • L(e)= 0.8925 mH

USD Horn impedance

Frequency Response – Horizontal

I measured the A-6.0 horizontally, with the magnet side facing upwards from -90 to +90 degrees.  My 0 Degree axis was dead on the straight side of the horn.  Positive (+) degree measurements were performed going from 0 degrees to 90 degrees to the flare-side of the horn.  Negative (-) degree measurements were done going from 0 degrees to 90 degrees to the straight-side of the horn.  The polar mapped image below gives further illustration to help make this clear.

The second and third image are simply the 0 to +90 and 0 to -90 degree measurements broken out for easier viewing. Following these are some ‘comparison’ images at varying axes (i.e.; +15 vs -15 degrees).  Read the legends.

Horizontal Polar

0 to 90 hz 0 to -90 hz

15 vs -15 hz 45 vs -45 hz

Frequency Response – Vertical

I measured the A-6.0 vertically, with the magnet side facing upwards from -90 to +90 degrees.  My 0 Degree axis was dead on the straight at the horn.  The “bottom” is referred to as the compression driver side.  Positive (+) degree measurements were performed going from 0 degrees to 90 degrees to the top side of the horn (CD facing down side).  Negative (-) degree measurements were done going from 0 degrees to 90 degrees to the bottom side of the horn.  The polar mapped image below gives further illustration to help make this clear.

The second image is the 0 to +90 degree (top side) measurements broken out for easier viewing.

Vertical Polars 2

Vertical "top"

Harmonic Distortion

The following was done in the nearfield simulating 98dB @ 1 meter (1khz reference).  Note: Input voltage was 2.83v.

HD 2.83v 98dB @ 1m equivalent

The follwoing was done in the nearfield simulating 104dB @ 1 meter (1khz reference):

HD 104dB @ 1m equivalent

PS:  If you would like to help me keep up funds for testing, there’s a little ‘contribute’ button that goes through Paypal all the way at the bottom of every page.  Any little bit helps.

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