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

Gardenstater

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

plastic_avatar

[goes to make something similar for my speakers]

[stops]

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

[sad]

Gardenstater

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):



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



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

Gardenstater

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

xschop

Do you think this is preventing any diffraction off the phase-plug?

Gardenstater

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.

xschop

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).

Gardenstater

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

Sumbrada69

I have 7Bs with non rabbbited MW and PR. Would the VR3 wool pieces help the Peerless tweeter? I can understand the oval cutout but why is it saw toothed? How about the foam piece under? The foam looks like the soundcoat 1/2" thick M&K uses (quite expensive and huge piece has to be ordered) for so little needed.

F1nut

If you think the Peerless needs help you have problems elsewhere.

The foam looks like Sonic Barrier available at Parts Express.

Gardenstater

Sumbrada69 wrote: »

I have 7Bs with non rabbbited MW and PR. Would the VR3 wool pieces help the Peerless tweeter? I can understand the oval cutout but why is it saw toothed?

In my experience (and others here), absolutely it helps with the clarity of the harmonics region of the highs. Something that is overly bright to the point that I didn't enjoy it much previously, like Breakfast In America, was now greatly improved. I'm certain that felt tweeter pads control the dispersion and thereby reduce baffle edge diffractions, and probably even help with reflections off of the magnet screws on the Peerless and reflections off of the MW flange. I beveled the edge of the round cutout with sharp shears and didn't go with the oval cutout. The sawtooth I believe is something that Wilson Audio does. I don't get it personally.

to be continued....

VR3

I found the saw tooth pattern helped with a more even response versus a flatter pattern back when I was making adjustments from a circle to an oval to the saw tooth oval

Gardenstater

Sumbrada69 wrote: »

How about the foam piece under? The foam looks like the soundcoat 1/2" thick M&K uses (quite expensive and huge piece has to be ordered) for so little needed.

That is what Rob used. I had the felt pads already installed on my tweeter and MW and didn't want to remove those; just add to them. What I did was use a piece of 1.7 lb/cu ft. polyethylene (polyurethane?) foam that was really old and a bit crumbly to be honest (need some newer denser stuff) and it was about 2" thick initially. I scrunched this down to a 1-3/8" round piece that was held to that shape by the steel mesh and the tangs on the mesh held it to my felts.

I guess this is what you are referring to on the M&K speakers (found these on eBay)? Does look like the same stuff Rob used. Maybe thicker than 1/2".

Looks like they are trying to control vertical dispersion of the tweeters like I was trying to do, presumably to reduce reflections off of the baffle and domes and grille. Maybe it also helps with reducing some of the comb filtering from interference between the drivers. Also reduces floor reflections as I noted above. My image got higher and instruments more separated.