As is said, variety is the spice of life.

 

SONY  5"  BLUE

 

Procrastination taken to a very high order of magnitude.

 

These speakers were purchased from PE Aug 11, 2010, a carton of 18 units @ $2.90 each. Although no longer available, a link to their still present page is given below.  A link is also provided for the BESTON ribbon tweeter added later. I just may buy the open back BESTON to find out how much of a difference, if any, it makes.  Opening the current ones and drilling holes in the back was considered and quickly abandoned although that me be the only physical difference between them considering the equal price tag.

The intent back then was to use them in a closed or vented line array but the design seemed way too large for decent bass so the idea was shelved, the intent of which was not supposed to be 7 years.  Time flies.  The idea of an open back hadn't occurred to me in the slightest.  That recently changed mainly due to talking with another Wharfedale aficionado regarding the Briggs' open back SFB-3

While SONY states the upper limit to be 4khz, it actually does quite well to about 7.5khz. (See FIG 1 black curve)

Sensitivity is given as 85dB 1w1m (See FIG 1 black curve)   Eight units will give an extra 9dB as compared to one if each of the 8 units receives the same power as the single unit. Alternatively, if 8 watts were fed to the total 8, the output (SPL) would be 94dB.  That 9dB difference would hold for any power applied to 8 identical speakers versus a single unit.

With a baffle of 7.5" wide, doublet action begins at about 1800hz.  However, by adjusting the electronic crossover point, it was found that not much audible change was noticed until the crossover point went below about 1100hz so it was set at 1200hz.  The 10" woofers in the cabinets under and behind the end tables cover 1200 and lower.  As can be seen in FIG 3, the response between 1khz and 7khz isn't bad at all, within 5dB.  That's the band of the 5" units above which they roll-off fast. (See FIG 2)

 

So, how do they sound.  AWESOME, once the tweeters are padded down about 3 dB.  The stereo image is stable and the speakers virtually vanish.  Phil Spector would like the "Wall of Sound" they create.  Offenbach's Gaîté Parieienne will put the listener into the Moulin Rouge.

 

https://www.parts-express.com/sony-5-dynamic-bass-replacement-speaker--299-011

https://www.parts-express.com/beston-rt002a-ribbon-tweeter--277-112

https://www.parts-express.com/beston-rt002a-dipolar-ribbon-tweeter-6-ohm--277-116

 

PHOTO 1

The almost finished baffle.  The bottom was later reversed to provide a larger center of gravity as a 20o backward tilt places the center of mass almost at the center of gravity.  The addition of the BESTON tweeter would have exceeded that.

The wood braces hold the two sections together; a temporary thing.  Later, a steel bracket will be applied inside and be provide an adjustable angle.  Right now, the angle is achieved with a wood block under the front angled baffle.

The front bottom baffle is tilted at 60o and the rear is at 72o.  The angle was to aim the highs from the two bottom units upward.

 

 

FIG 1

The black curve is that of one speaker at 1w1m.  The green and purple curves are the 8 unit line without and with the Beston tweeter.  No reference to power applied.  Those two are not gated, so room reflections are present.  They were run in my living room with the mic at ear level at the listening position and both arrays playing.  What surprised me was the linearity of the curve as much worse was expected.

The Tweeter is filtered at 6khz, first order.  A potentiometer was later added to tame the tweeter.  Despite it's 92dB 1w1m which is 2 dB below the output of the eight 5" units, it still sounded very bright, probably due to its beaming right at my ears while the 5" units radiate in a wider pattern.  A higher crossover frequency may well have fixed that since at 6dB/octave, the knee is already 3 dB down so at 3khz, it's 9 dB down.  While that may sound like a lot, 3khz to 4 khz is right in the band of highest sensitivity of the human ear.

 Then, there's personal preference.

See revision 1 in Fig.3

 

 

FIG 2

Another look at the system, both array's playing in the living room and without the tweeter.  The thin black trace is as the mic picked up the sound.  The pink and green are 1/10th and 1/3rd octave smoothed, resp.

 

 

FIG 3

The peaks and dips below about 700hz seem to correspond to room dimensions versus wavelengths and half wavelengths.

As for the dip at 9.5khz and the peak at 12khz I can only guess.  It could be a reflection from the hard faceplates of the tape recorders which is about 18" behind the mic.

The green curve was achieved after much tweeking, namely raising the tweeter crossover point, adding the potentiometer and phase reversal of the sections with the electronic crossover and the wiring of the tweeters.  The 5dB rise above about 1khz was very irritating due mainly to its bandwidth.  Attenuation of the tweeters was insufficient so the crossover point was raised to 11khz.

 

 

Revision 1

The Tweeter is first order passively filtered with a 2.3uf capacitor and a 50 ohms potentiometer wired similar to an L-pad.  The pad is set around 3 o'clock.(-4dB)  This high pass filter begins at about 11khz. This is quite an improvement over using the 4uf filter (6khz); it completely removed the harshness (stridency) in the treble, the reason being attributed to the slow roll-off and the interaction between the highs from the Sonys and those from the Beston.

Using the pad to attenuate the tweeter with the 6khz filter didn't work as too much attenuation was required to bring down the wide rise above 3khz resulting in far too much attenuation in the higher register above about 9khz..  A technique used in an earlier design was implemented with great success.  That technique was to spread the low pass section of the mid-range and the high pass section of the tweeter.  In this system, the tweeter is filtered at 11khz as stated earlier.  The natural roll-off of the Sonys was sufficient and needed no filtering.

 

 

FIG 4

Curve 56 (green) was obtained by making many changes recorded in curves 29 through 56. See Fig 3

This curve 56 includes the polarity reversals of the Sonys and the Bestons.  See Figs 5a & 5b

Green is what the mic 'hears'; red and blue are 1/10th and 1/3rd octave smoothed, resp.

The 1/3rd smoothed blue curve is what one would see when using a 31 band 1/3rd octave analyser.

 

 

 

FIG 5a(L), 5b(R)

Left.  8 Sonys reversed polarity (red) with respect to woofer

Right. Tweeters reversed polarity (green) with respect to Sony's.

Keep in mind, the tweeters are passively filtered so reversing the polarity of the Sonys with respect to the woofer by the two way electronic crossover has no effect on the tweeters polarity with respect to the Sony's.

 

  

 

 

FIG 6

Green is a single unit free air impedance.

Black and red are each system (just the 5" arrays).

The blue is with a zobel impedance equaliser.  That was done before I realised I was going to use these on an existing 2 way bi-amped system, rendering the use of a zobel unnecessary.

 

 

PHOTO 2

The pair in the living room along the 17ft wall, well, about 30" in front of the aforementioned wall.

Electronically crossed over at 1200hz, done by ears, the woofers are in the 3 cubic feet cabinets under the end tables.

The corner cabinets were built in Dec,. 2009 for a Wharfedale W15CS and is 6 cubic feet internally.  The Super 8 and Super 3 drivers are facing up in the top housings.

The painting was done by me back in 1972; oil on canvas.  The story surrounding that is HERE

 

 

 

PHOTO 3

Another view of the room from under the arch between this room and the dining room.  The listening position is between the TEAC (light brown) and the two Revox A77 tape recorders.  That's about 9 feet from the mid point of each array and subtending an angle of 60o.  That puts my line of sound within a few degrees of perpendicular to the center of the line arrays.

A description of the paraphernalia is at the bottom of this page.

 

 

FIG 7

Actually, this room is only 2 walled.  the divider that goes to the ceiling making the foyer by the front door is only 4 feet; the last 3 feet is only 4 feet high.  One could say its dimensions are 17' by 20' since it opens into the foyer and hallway. It could also be said that it's 34 feet long as it opens into the adjacent dining room.

There is 5 feet of wall on the left partially separating the two rooms.  The arrays are in front of the end tables, labeled as "T" under which are the 10 inch woofers.

 

 

The paraphernalia and associated description

On the left, two AKAI GX280-D tape recorders.  Underneath are the two ADCOM amplifiers for the two way system; the electronic crossover is on top.  On the upper right is a home made patch bay that will connect 7 recorders to the preamp. It also will allow recorder to recorder transfer.

In the center is a 9 cubic feet bass reflex built by a half-brother in 1957 which I was given in 1972.  The top chamber houses the W10FSB and Super 3.  The crossover is on the right.

To the right again is an EICO HF30 mono block and an ADCOM GFA-555 power amp.  Under that is a modified EICO HF30; it's now single ended and 15W and that's what drives the Wharfedale.

The black d'Appolito towers belong with the black cabinet in the rear right corner.  The lower half of these are sand filled as without that, they are top heavy.

In the right corner is the 190 pound bass reflex which is two 6.5 cubic feet cabinets internally, each housing a floor firing 15".

On top is a Thorens TD124-II which I bought in 1963 along with the Shure SME3009 tone-arm.  Beside that is a  Rek-O-Kut N33H (Rondine) turntable.  The cabinet in front of that under the TEAC reel to reel houses the EICO HF60 preamp, the ADCOM preamp, a professional CD player, 3 NADY parametric equalizers and a 31 band graphic EQ.  The ADCOM preamp drives the ADCOM power amps individually via a switch I rigged.  The two way system has no access to any of the equalizers.

The forward cabinet on the right holds two REVOX A77 recorders.  The upper is a half track, high speed (15/7) and the lower one is quarter track (7/3.75).  The A77 on the floor near the coffee table is a low speed (7/3.75) half track.  There are three more in other rooms and one on the way to be converted to a full track. The TEAC (there's 2) and all A77s have new heads.  Two actually exceed original factory specs.

All cabinetry with exception of the center one under the small tree are built by me as well as all refurbishing/restoration of the tape recorders. There's also an AKAI GX4000 near the left corner cabinet.

 

 

 

 

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