Must try MOD - Foam inside the stamped steel baskets - YES!

ChrisD06

plastic_avatar wrote: »

I wonder if BH5 in 2x4 strips on the side walls would be effective in the jr?

No clue, would rather not do any experimental stuff and just go with stuff that's been tried and written in stone.

skipshot12

^ Totally agree and understand but, that’s how the tried & true mods came to be… trial and error.

I’m still so considering this.
Only thing my brain is keeping me from trying this is the 16 friggin MW’s 😬

ChrisD06

skipshot12 wrote: »

^ Totally agree and understand but, that’s how the tried & true mods came to be… trial and error.

Excellent point! The only issue would be how much foam I'd add. BH5 is pretty known, 3x3, 4x4, etc, and with this armacell mod you line the inside of the basket with it. But with adding it to the sides... what size should each sheet be? Trial and error would be really tedious...

xschop

F1nut wrote: »

xschop wrote: »

Another F1 B-lister. Welcome aboard.

You must have missed the fact he removed an amount of BH5, which will make a HUGE difference compared to your hack idea.

You missed the fact that this inner-frame modification has ABSOLUTELY NOTHING to do with the BH5 modification.

skrol

The idea of reflections off the spokes of the basket kind of makes sense since we know there is reflection off the back wall of the cabinet. Even though I applied the foam to the spokes of the basket, I question if there is enough material there to really absorb the reflection very much. It is of no harm if it isn't interfering with the cone or spider movement, low (or no) cost and, as they say, everything matters. Removing the excess Sonic Barrier (BH5) likely did far more to improve the speaker over the way I had it.

Jazzhead

When I first tried this mod on my old 12's I had listened for months with my speakers unchanged, using 1&1/4 Sonic Barrier to completely damp the outer drivers (the successful westmassguy comb filtering mod):

https://forum.polkaudio.com/discussion/173834/westmassguys-idea-employing-damping-to-mitigate-comb-filtering-and-lobing)

and a 4x4 piece behind the inner drivers (along with uncompressed polyfill behind both drivers). To my ears damping materials like Sonic Barrier and BH5 mitigate midrange "shoutiness", loss of composure at higher volume levels, and generally clean up what sounds like backwave slapping around inside the cabinet. The stuff is so effective that I can now casually hear the frequency difference between the two drivers (the idea behind the westmassguy mod). Gardenstater's driver basket mod is a different animal that removes "smear", and brings clarity - most noticeably with vocals. I have noticed it takes a bit more juice to reach the same loudness the speakers produced pre-mod. After several months I reduced to a 3x3 inch piece of Sonic Barrier and found that to be the best combo. I haven't noticed any reduction of bass, or loss of liveliness, but I also can't measure anything. My rig and room produce a lot of bass and I would trade some of it to keep the foam mod clarity. That said, my speakers are old, with a somewhat flawed design, so YMMV.

Gardenstater

skrol wrote: »

The idea of reflections off the spokes of the basket kind of makes sense since we know there is reflection off the back wall of the cabinet. Even though I applied the foam to the spokes of the basket, I question if there is enough material there to really absorb the reflection very much. It is of no harm if it isn't interfering with the cone or spider movement, low (or no) cost and, as they say, everything matters. Removing the excess Sonic Barrier (BH5) likely did far more to improve the speaker over the way I had it.

I did it by itself with lots of ingrained aural memory of how my speakers sounded prior, ie. lots of time since the previous mod which I believe was a 6" x 6" square of BH5. Eva Cassady was the first listen and her vocals were cleaned up and I realized that "Live at Blues Alley" had lots cleaner reverb and it was clear that I was listening to somewhat distorted reverb prior. Further listening revealed that vocals that were very low level like background vocals often tend to be, became more discernible, as well as being able to decipher words to songs that I had been unable to, previously. Also, multiple singers and instruments were more separated and distinct. Very pleasurable.

You might go back in and do the area near the spider, between the spokes. Pretty significant amount of reflective area there.

Jazzhead

Clarity relative to understanding lyrics, distinguishing instruments etc. reduces listener fatigue.

Gardenstater

Try covering some aluminum flashing with some Armacell on one side and speak at it with a high tone of voice. Now flip it around and do the same thing. I hear a subtle difference. With two layers of Armacell still subtle but slightly more of a difference. It is more pronounced when you hold the flashing at an angle to a wall and do the test that way. In the speaker basket there are reflections back at the cone and there could also be transmissions through the steel that could have an audible effect as well. If they did not have an audible effect, then the constrained layer dampening material (Dynamat and others) wouldn't be audible. Also, I know you know this but have to point out that changing two variables at once and drawing a conclusion that what you hear is due to only one of them is a definite no no in science and engineering

Edit - how would the following experiment go if the 2nd tuning fork were covered with Armacell?

https://www.youtube.com/watch?v=aCocQa2Bcuc

gp4jesus

Very interesting

xschop

This is why you should also butyl-mat your drivers that have the magnetic shielding shroud attached to the magnet as well. It is just a ringing bell hanging off the back.

xschop

Bump for @inanortherntown.
Inexpensive yet very effective modification. Should be a sticky here.

odcics2

Wonder how great an MW would sound modified to look like an early KLH woofer??
Very minimal reflections!

xschop

It would also increase the speed of the cone during lower frequencies, no?

inanortherntown

xschop wrote: »

Bump for @inanortherntown.
Inexpensive yet very effective modification. Should be a sticky here.

Thanks much! Will take a look

-Tony

odcics2

xschop wrote: »

It would also increase the speed of the cone during lower frequencies, no?

It would allow the cone to follow the sound wave more effectively, decreasing distortion.
The reduction in back wave reflection would be helpful!
A good fabricator could make a large ring to hold the surround, 4 stilts, and a small ring to hold the magnet assy.
It would be a great experiment.

gp4jesus

Interesting…

One of the higher-end tire manufacturers, attempting to attenuate ~200hz road noise using a similar execution of foam on the interior

Hansvelton

Not against fun experimenting, but have to wonder, if this was a thing, would someone else not have know about it by now, I mean we have Kippel measurements for years, and not a single speaker manufacturer has ever employed this "Mod".......

Gardenstater

Do you know what everyone on the planet "knows" LOL?

Ask ya another question.......does CLD ie. Dynamat etc. on the basket work to clean up the detrimental effect of vibrations upon the clarity of the driver? Why didn't and don't you see manufacturers doing that?

Manufacturers have largely solved both of these problems another way, by going with cast baskets with minimal spoke area and ventilated designs behind the spiders.

F1nut

Manufacturers have largely solved both of these problems another way, by going with cast baskets with minimal spoke area and ventilated designs behind the spiders.

A cast basket does solve the ringing issue of a stamped steel basket, but so does Dynamat Xtreme.

The minimal spoke area of a cast basket does not absorb sound waves like adding pieces of foam inside a stamped steel basket.

The purpose of ventilated spiders is to increase power handling, it's got nothing to do with anything else.

xschop

So why doesn't Polk send a sheet of DynaMat extreme with every Legend speaker?

F1nut

xschop wrote: »

So why doesn't Polk send a sheet of DynaMat extreme with every Legend speaker?

Silly question back at ya. Why doesn't Polk send a sheet of foam to line the inside of the basket with every Legend speaker?

xschop

That was my rhetorical question.

But I'll answer both: It is because of price point and the target customer.

xschop

When Polk starts building a driver that doesn't require Dynamat or foam inside the frame, I'll be a customer.

Gardenstater

Here's a good picture of a driver designed for minimum back wave reflections that would reflect back at the cone, including back wave that transmits through the spider:




Polk stamped steel MW driver with spider cutaway (photo by forum member I forget the name of sorry). How much projected area for reflection is presented to the backwave here?

xschop

Started foaming another set of B&O drivers this weekend...

odcics2

Note green felt to absorb back wave directly in front of the magnet. The rest goes into the enclosure.

Imagine an MW65xx designed like this.

Gardenstater

odcics2 wrote: »

Note green felt to absorb back wave directly in front of the magnet. The rest goes into the enclosure.

Imagine an MW65xx designed like this.

That's totally the Vandersteen Midrange design in the patent. Backwave from the cabinet "possibly" becomes a major problem in a 2 way with passive radiator design because you might be limited in how much damping materials you can apply to the cabinet, but I wouldn't use BH5 because it may load, I would use No-Rez and you would have to experiment.

That design is really for a 3 way speaker design where this midrange unit would be in an isolated chamber with damping material I think.

odcics2

That’s why I said imagine.

It would be designed as a 6.5” mid woofer for a Polk Monitor 5, 7 or 10, for example.

xschop

Imagine no foam or Dynamat frames.