[Danny Richie]

Did the title get your attention Tyson? 

Really though, Tyson is admittedly very sensitive to top end brightness and so am I. So he did a little tweak to his V-2's to soften them up a little more to his liking.

He outlined it very well right here: http://www.audiocircle.com/index.php?topic=86681.msg845739#msg845739

He also thought that my Super-V's at the show were a little hot too.    So it motivated me to see what result he was getting with that foam tweak.

Tyson gave me a couple of pieces of that reticulated foam that he used in front of his tweeters while he was at the show. So I thought I'd drop it in and see what it was doing that made him like it so well.

I don't have my listening rig set up yet and may not yet for a while as I am just too busy to get to it. But my measuring system is always set up and ready for action and it only takes me a few minutes to take some measurements. In fact I did all of it quicker than the time that it takes me to write all of this.

Anyway, I took some base line measurements then inserted the foam piece as instructed and took another measurement.

The Red line is with no foam and the Green line is with the foam.



The response shows the difference. It clearly soaked up quite a bit of output in the lower range of the tweeters response and also some energy across the board. If you want to lower the output in that range then this will do it.

Guys, the great thing about building a kit like the V-2 is that you can easily adjust it to sound any way that you want. And if Tyson is in heaven with this response that's fine by me.

I might experiment with a very small amount of this stuff to see if I can maintain a smooth response but just drop a little bit of the edge off at 1.5kHz. Who knows. I might like how it sounds too.

Thanks Tyson!

[Tyson]

Thanks Danny for doing that.  I'd say the top graph is slightly rising from about 400hz, overall, and the bottom graph is slightly dropping.  I measure the same dip at 1.5khz in my setup, so we're in complete agreement with what's going on.  However, from a subjective/preference standpoint, I find the speakers more pleasant with the foam, particularly since I usually sit about 5 feet away from the speaker, so any bit of extra energy will be magnified. 

I think you are right, that some experimenting with the foam could correct that dip just above the crossover, which I've been meaning to do myself, but other things have taken precedent (like veneering the V2's, painting them, getting the No Rez installed).  I'm in the middle of getting the side panels cut and finished (1.5 inch no void Baltic Birch), so the foam experiments will have to wait for a little bit on my end.  But, if you find anything out on your end I would LOVE to hear about it

[Danny Richie]

Hey Tyson try this.

I took what you gave me and cut it in half lengthwise and widthwise. So it is 2.25" long and only 3/4" deep.

I sprayed it lightly with 3M spray adhesive just to make sure that it wouldn't push in too far. I also wrapped it around a pencil when I installed it and made sure there was a good hole through the middle.

The frequency response suggest something that I might like.



I will try this in the pair and see what it sounds like in a week or two when I get my system hooked back up.

[jtwrace]

Posting some in room response curves with and without the foam would be really cool.

[TomS]

Yes, attenuation ~2-3db from 1khz up is part of it, depending on the foam. 

Here is the reference to Dr. Geddes' patent on the use of foam in waveguides
http://www.freepatentsonline.com/y2007/0102232.html. 

Certainly easy enough to compensate in a design 

[Danny Richie]

Wow, I can't believe that they can grant a patent on that.

Regardless, this is not something that I will be doing or selling, but if the end user wants to try tweaks like this, they can.

[Tyson]

Well, my wife and daughter are at a jewelry show this evening, and I am finished gluing and clamping the 2 sheets of 3/4" Baltic Birch together (for 1.5" total thickness).  While I'm waiting for it to dry, I find that I have some time on my hands.  So I pulled out the foam in my tweeters.  I kept it long, but I cut off some of the material to make it less thick when installed.   There's a small hole in the center.

Result, I'm getting a result about halfway between both of our original plots, and it sounds pretty good!  Danny is right you guys, THIS is why you DIY, because you can simply make adjustments and experiments until you end up with a sound that makes YOU happy.  Speaking for myself, this is my second set of DIY speakers, and I've also rebuilt my tube amp, and I will NEVER go back to pre-made products.  It's just too much fun and too satisfying to have the ability to this

[PDR]

OK.....I'll give this a shot.

What type of foam please......from a pet store for aquariums? correct?
Is there a number or brand name?

A picture is worth a thousand words.......

Thanks guys.

[Tyson]

Yes, from an aquarium store, they are usually in the filter section.  Just the most open foam you can find.  I like the thin sheets instead of the big square blocks, I find the sheets easier to cut to try different shapes and sizes.

[Wind Chaser]

I wonder how this foam affects how the speaker measures?

[Tyson]

Danny posted several measurements in this thread.

[Wind Chaser]

Thanks, I might be a little more attentive if I could resist the urge to multi-task while on AC.

[Tyson]

If I understand the theory correctly, what is happening is that most of the sound of the tweeter in the horn is a result of the soundwaves coming directly off the tweeter and traveling along the center of the horn/waveguide.  But, a small but significant portion of the soundwaves are bouncing off the walls, sometimes multiple times.  This is what Geddes calls a High Order Mode (HOM), and is very audible and gives horns their typical "horn sound". 

I've heard it in a Geddes system, and it works very well.  I've now also heard it in the V2's and like it quite a bit there to.  I think originally I had too much foam packed in too tight and it sucked up too much energy.  But after this thread I've adjusted my foam inserts to be much less dense and it's a lot more lively, but still not bright or "horn sounding". 

[Wind Chaser]

If I understand the theory correctly, what is happening is that most of the sound of the tweeter in the horn is a result of the soundwaves coming directly off the tweeter and traveling along the center of the horn/waveguide.  But, a small but significant portion of the soundwaves are bouncing off the walls, sometimes multiple times.

That description reminds me of how diffraction makes a mess of things with a series of secondary waves following the primary wave. 

[Tyson]

Which, ironically, is part of why I think waveguides work so well, they don't have the problem with baffle diffraction that flush mounted tweeters do.

[dvenardos]

You should see what they get patents on in the software industry. 

Wow, I can't believe that they can grant a patent on that.

[Wind Chaser]

Which, ironically, is part of why I think waveguides work so well, they don't have the problem with baffle diffraction that flush mounted tweeters do.

Somebody with the SP Tech Mini experimented with felt inside the wave guide.  He seemed to like the effect, but it sure looked odd.  For the foam to be as effective as it is, there's no way it can be 100% acoustically transparent.

[dBe]

Somebody with the SP Tech Mini experimented with felt inside the wave guide.  He seemed to like the effect, but it sure looked odd.  For the foam to be as effective as it is, there's no way it can be 100% acoustically transparent.

Reticulated foam is about 95% air and that is why the superpositions that are created along the walls of the waveguide are attenuated so well.  There is very little acoustical energy to deal with and the direct sound is "essentially" unimpeded.

I've used felt in waveguides before and it is quite effective.  What is interesting is that placement is not what one would expect.  Applying the felt at 90 degree increments (12-3-6-9 o'clock) is all that is required.  It is not necessary to cover the entire WG.

[Tyson]

After going active and making several upgrades to my tube amps, I no longer endorse the foam tweak.  The V2's just sound better with nothing in front of the tweeters.