[BrunoB]

It seems that no one knows when the CDWG will available for purchase separately. I am too curious to wait, therefore I am trying to build one myself.

I put a  diffraction slot on the midrange and tweeter of my modded 626R. It is made  of pieces of a rubber sport  mat covering the side of the drivers. I put a layer of cotton fibers (about 1 cm thick) between the rubber mat and the midrange driver to adsorb sound coming from the midrange driver. The mat compresses the cotton. I did the same for the tweeter but with less cotton which covers the remaining horn part of the tweeter (I had removed the horn a long time ago for another reason). The slot on the tweeter is narrower than on the midrange. I can change easely the width of the slot. Everything is attached with black strings around the speaker. It looks ugly. But at the moment I don't care. This is for experimenting. The operation took about an hour of work this morning.

Sound changes:
- tonal balance is changed: less treble  coming from the midrange and less volume from the tweeter. For me, the midrange driver is too bright and the slot somehow corrects this. The sound level from the tweeter decreases when the slot is narrower. It is easy to compensate with the variable L-PADS.
- I can place the speakers closer to the listening position (4 - 5 feet) while still having a very large soundstage.
- larger sweet spot: I can  move my head arround without being bothered by a big image shift. It feels more like in a concert hall. I still loose a lot of treble when standing up, but this doesn't bother me.
- speakers dissapear more
- more wrap around sound
- more 3D effect, more depth information


I don't have 180 deg constant directivity - based on  my observation that the sound changes when moving my self  forward between the speakers.


If there is enough interest, I will borrow a digital camera and take picts of the "device".

Note: these results are preliminary. I have only listen the modified  system for two hours during which I have changed my speakers positions several times. It could be that some of the effects I have noticed are due to a different speaker position. YMMV.

Bruno

[mjosef]

I would like to see some pics on how you did it...I was thinking of trying some thing similar for my RM1s, seeing that this is a discontinued model it sure won't score high on the CDWG-to-be-made list. Since I did the SR71 and vitrified passive upgrades, my RM1s have the tightest bass I have ever heard, so I am itching to take it to another level.

[warnerwh]

That's pretty impressive Bruno.  I'd like to see pics also.

It seems like something like these waveguides would be best made on a machine that could make all the cuts as perfect as a machine can do. Then again you may be able to do a good enough job that an improvement has been clearly made.

[Skynyrd]

Bruno B said:

tonal balance is changed: less treble coming from the midrange and less volume from the tweeter. For me, the midrange driver is too bright and the slot somehow corrects this. The sound level from the tweeter decreases when the slot is narrower.

[/color]


This is truly good news.

I'll stick with the 4" wedge foam that is about 8" or 9" wide that I've double-sided taped on my RM40's for now.

Thanks for your pioneering modification work, Bruno.  I'm sure this will lead to others bettering their in-room speaker performance.
And your prices are good, too!

Skynyrd

[BrunoB]

Here are some pictures: DIY CDWG album


For the midrange:    
I used some cotton and two pieces (8x21 cm)  of   Sportcraft Fitness Equipment Mat (bought at Wall Mart). I folded the cotton twice to get the right thickness. My goal is to have a maximal height of 0.75 cm for cotton plus the mat when the mat is compressed on the cotton. The position of the two mats is adjusted visually such that only 3 lines of aluminium remain visible (see picture in my  DIY CDWG album).
Instead of cotton, one could use some wool felt, which would be easier to cut and place.
The cotton plus the mat  fits under a speaker grill and can be hidden.

For the tweeter:
I tried to line the inside of the remaining horn with two small pieces fo felt (triangular  section). I don't have a mean to cut the felt precisely enough, so I gave up on this idea. I might try with foam. I am still working on it.

Bruno