Yet another mod to my 7Bs.........Tweeter Dispersion Controller (?)

Not sure what to call it frankly but my goal is/was to try to reduce reflections of tweeter output off of the structures of the MW such as basket flange and phase plug. A side benefit is that it will also reduce floor reflections.

I'm very happy with the even greater holographic imaging I'm now getting and clarity is off the charts. My scalp is tingling with what I'm hearing and I was happy with my sound before. Very live music like. Listening to Eva Cassidy "Live at Blues Alley" right now.

Seems to be successful and they aren't coming off except to try a better acoustic absorber material when I obtain one. Just medium density polyethylene foam scrunched up a bit within the encapsulation mesh (?). The wire tangs are bent somewhat outward and they are embedded into the wool pads. I had to secure my pads better for sure. There are now velcro pieces everywhere I can put them and it is holding nicely.

I may cover the mesh with some crafters felt or simply paint it matte black. We'll see :)

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George / NJ

Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Crown D150 amp
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform

Comments

  • [goes to make something similar for my speakers]

    [stops]

    [goes back to work drudgery, puts this off til another day]

    [sad]

    The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * Ye Olde college stereo in the garage
  • Gardenstater
    Gardenstater Posts: 4,136
    edited December 2022
    This would be easier for other people to try by just sticking a 4" long x 1" thick x 1" wide piece of open cell foam between their tweeter and the MW.

    This started for me when I observed a little dip in my tweeter response at around 7kHz when testing with a 5s sweep tone and measuring response at approx. 1" from dome, on axis. The hypothesis was that perhaps structures of the MW like the basket flange (mine are not rabbeted) or even the surround or phase plug, could be causing some destructive interference due to time delayed (by the distance from tweeter) reflections.

    The next thing I did was to place a barrier up against the baffle between the two drivers, angled downward about 45deg. I used a piece of 3/4" thick siding underlayment styrofoam with a layer of 1/2" cotton matting on top of it. The test showed a bit less dip at 7kHz which was promising and led to the construction of the contraption to hold a piece of foam against my felts.

    Although the thing gave me a much better more stable image and better soundstage (higher up from floor) and better clarity and separation of voices and instruments, I didn't really get much diminishment of the 7kHz dip to be honest. So although I will leave this thing on because I am enjoying the sound too much, the dip is still eluding me. It *may* have something to do with the oversized tweeter cutout which leaves a groove which can cause out of phase reflections, and it just happens to be at a distance on L and R which is 2", which happens to be the wavelength of a 7kHz sound wave. So that will be next, to fil that with some clay. Coincidentally (?) the basket flange is also about 2" from the center of the tweeter. Hmm...perhaps some better foam, like maybe 4lb/cu ft stuff instead of this ratty old piece that is only around 1.7 lb/cu ft might produce better results too.

    1" from dome of L tweeter before mod (yellow):

    4ry5ojw8c77y.png

    1" from dome of L tweeter with temporary styrofoam and cotton deflection barrier (yellow):

    d1ddis5rmrjb.png

    1" from dome of L tweeter with Tweeter Dispersion Control Mod (yellow):

    atwhrxie1fwj.png

    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Gardenstater
    Gardenstater Posts: 4,136
    Still enjoying this a lot. Looking at the 3rd graph again and comparing to the first one, there is a greatly improved response from 15kHz and above. Perhaps that is the only physical evidence I have so far of what I am hearing which is the greatly improved imaging (?).

    I think that other people who do not have the felts could very easily stick a piece of No-Rez or the like to their baffle and try this out. Experimenters welcome :)
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschop
    xschop Posts: 4,636
    Do you think this is preventing any diffraction off the phase-plug?
    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,136
    xschop wrote: »
    Do you think this is preventing any diffraction off the phase-plug?

    I 'think' in my case it is a combination of that and the reflections off of the basket flange, since mine are not rabbeted.

    I don't have a way of doing the proper measurements at 1m distance on axis from tweeter which would exclude room effects. I'm sure the room effects in my room are disastrous to getting a meaningful measurement. I need software that allows me to do what is called a 'gated' response.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschop
    xschop Posts: 4,636
    edited January 2023
    Interesting tidbit. I set up the modded 5Bs in the living room and did some extensive listening over Christmas break. I preferred the small foam strip between MWs and tweeters over the oval-cut out tweeter felts (which sound better than the simple round-hole cutout tweeter felts).

    dfj2bwev2tvl.jpg
    Don't take experimental gene therapies from known eugenicists.
  • Gardenstater
    Gardenstater Posts: 4,136
    xschop wrote: »
    Interesting tidbit. I set up the modded 5Bs in the living room and did some extensive listening. I preferred the small foam strip between MWs and tweeters over the oval-cut out tweeter felts (which sound better than the simple round-hole cutout tweeter felts).

    That's pretty meaningful I think :)
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform