Seas hexagrid...

[jaberwocky6669]

Hi,

I was just wondering if it were possible to remove the hexagrid from in front of my Seas tweeter? Is it a good idea? Any ideas, thoughts, revelations, comments would be greatly appreciated!

Thanks!,
Matthew

[qwad]

this is strictly a no-no not advised to tamper with it though l understand M A [ monitor audio did have a removable mesh on one of their models back in the 80's] youll just have to learn to live with it, sorry TC

[ch83575]

I have removed the grid on my H1212 tweeter. It is easy, just grab on and pull... it is just glued on. I had to scrape the glue off with a needle, but that was cosmetic. I was having problems with the diffraction in my speaker design and had a post about it a while ago (Is this normal diffraction?) and there are a few plots with and without the cover in there. They are just on axis plots though. I have been recently looking at the contribution of the grid (and phase shield) off-axis, and that is much more compelling. If removed the FR starts a very slight high end droop very low in frequency (it looks to be 1 or 2dB / octave starting at about 3k), with the cover it stays flatter much higher in frequency and farther off axis. I have not been able to really test a stereo pair of speakers yet, so I can not be positive, but my initial impression was that I liked the sound better without the cover. I will be doing more testing on the subject over christmas shut-down. I will keep you posted.

[jaberwocky6669]

Well, for now I am going to err on the side of safety. I will wait and see if there are any more developments and wait for when I can afford an extra tweeter just in case before I go ripping my tweeters apart. =) It seems to me like you should not have to yank it out should you? I was imagining that you could probably just undo those four hex screws that hold onto the driver and from there just pull it out of the back.

[ch83575]

You can put the cover back on as easily as it came off. All you need is a dab of glue and it will be just like new. You can even just let the magnet hold it in place (thats right, it is ferris ) if you want to take it on and off. JM Lab/Focal uses a very similar cover for their tweeters that you can remove and replace that is held on by the tweeters magnetic field.

I did some testing this morning. Here are some detailed off-axis measuremets (from 0-45 degrees in 5 degree increments):

With the hex-cover:

Larger version HERE


Without the hex-cover:

Larger version HERE

Unfortunately the images on this page did not come out to the same size and it is really hard to scale them without making them look really bad, but the larger versions in the links are the same size so I recomend opening them both in seperate explorer windows and flicking back and forth between the two if you want to really see the differences.


This also shows the effects of baffle diffraction off-axis which I find interesting. This is the same cabinet shown in the post I linked in last post.

I also did some more listening tests. Today I was much less conclusive. Sometimes I felt that it sounded like there was something blocking the sound with the cover on after listening without the cover (psychosomatic perhapse?). But other times I felt that I could definitly hear the lack of high frequency energy without the cover.

Now for some questions for the more experienced members out there. It almost seems like the phase shield flatens the power responce of the tweeter to a higher frequency where it then just falls off into nothing. Am I reading that right? Does it work simply by eliminating phase cancelation from the center of the radiating area? Do driver manufacturers not use phase shields often with cloth tweeters because the center of the dome is not acting like a piston at the frequencies where there would be phase cancelation with the sides, or is there some other reason? I guess I need some more basic knoledge of how and what the shield is doing before I explore further.

Right now I still do not know wether I like the tweeter with or without the cover, but I think I am leaning towards leaving it on... we shall see.

-Chad

[dlr]

It almost seems like the phase shield flatens the power responce of the tweeter to a higher frequency where it then just falls off into nothing. Am I reading that right?

It's more the on-axis response. Note from your measurements that the extreme off-axis, though slightly higher for a bit, eventually takes a steep dive.

Does it work simply by eliminating phase cancelation from the center of the radiating area?

Yep. Simple as that.

Do driver manufacturers not use phase shields often with cloth tweeters because the center of the dome is not acting like a piston at the frequencies where there would be phase cancelation with the sides, or is there some other reason?

That and the better ones have closer to optimal damping, not just being no longer pistonic. The best ones work more like a ring radiator as the frequency goes up. The best example is probably the Hiquphon OW1.

dlr

[bidland]

Have a look at some measurements in this tread:

http://www.htguide.com/forum/showthread.php4?t=22214

Bjorn

[jaberwocky6669]

Fascinating indeed! I can manage to crawl my way through those technical terms and somehow in the end I usually get a good idea of what is being discussed! =) I think I will definately leave the hexagrid firmly in its place. Who am I to question seasoned acoustical engineers?

As an aside, I have never before posted in such a helpful forum as this for any topic ever! Thanks yall!

[ch83575]

Just in case anybody was wondering, the hexagrid does not seem to affect distortion very much. I thought that there might be some distortion due to compression behind the grid/shield. I had seen this said elsewhere before, but I dont remember where. Well, I did some distortion sweeps, and they show a slight drop in distortion (about 3db in 2nd and almost 6db in 3rd) from 5k to 10k when the grid is removed. BUT, this comes with a 2-3dB drop in sensitivity in that range when the cover is removed (this is the same problem Zaph runs into, these plots are not relative to output level, they are absolute. So if the tweeter puts out less fundamental and less distortion, they could be at exactly the same persentage, but look like the distortion is rolling off).

With grid


Without grid


I personaly suspect that this is probably a non-issue as it is pretty high in frequency and only really affects the 3rd harmonic (which would make the actual product VERY high in frequency), but I do not have enough experience to say for sure. I only report the facts .

-Chad

[keyser]

Whoever might have something useful to add to this thread: please do! I am very much interested.
ch83575, keep up your posting!