Polyfill ampeg

kr3w1664 · #1 09-21-2010, 12:07 PM

Just going to do a little experiment. I'm planning on putting polyfill into my svt215e. The walls are already lined with some flimsy wool type material, and not even on all the walls. Has anyone done this to their cab? I'm not looking for negative feedback, this is strictly an experiment.

Wes Whitmore · #2 09-21-2010, 12:14 PM

Most ported boxes use sheet batting so it doesn't blow out the port...

kr3w1664 · #3 09-21-2010, 12:22 PM

Yea, but There only batting on 3 of the walls and it's really flimsy material. I'm obviously going to glue it so it's not puffing out the vents lol. I'm just curious to how it will affect the frequency response.

62bass · #4 09-21-2010, 12:53 PM

You don't want any negative feedback, so all I can say is-great idea. Give it a try and report the results.

kr3w1664 · #5 09-21-2010, 03:55 PM

Negative feedback is alright as long as you can justify it. Most people on forums just end up opening their mouth to release a hot steamy s**t and somehow the topic always ends up changing. Lol.

KramerBassFan · #6 09-21-2010, 04:34 PM

I like mattress foam.

$10 for a huge sheet from walmart, a staple gun later, and most any cabinet is lined in under half an hour. Mid hump? Good-by. I've done it a few times now.

SlingBass4 · #7 09-21-2010, 04:42 PM

Quote:

Originally Posted by KramerBassFan

I like mattress foam.

$10 for a huge sheet from walmart, a staple gun later, and most any cabinet is lined in under half an hour. Mid hump? Good-by. I've done it a few times now.

+1 to a much better solution. IF you can find some of the egg crate type pads - so much the better!

Jerrold Tiers · #8 09-21-2010, 07:41 PM

If the stuff in there is white, we used that until the factory for it blew up from dust...... later we used a gray stuff out of the automotive industry. The gray stuff was much nicer.

You really don't need a lot for the basic purpose of cutting sound reflections. if you put a lot in it will change the effective volume of the cabinet, which may not be a good thing. So we put in the least that got it done.

If you stuff the cab, then, aside from needing a way to keep it out of the speakers, you will also have a somewhat larger cabinet, effectively, and that may not work well with the drivers.

The effective size increase comes from the difference of compressing air which is free to heat slightly with compression, vs compressing air which loses its heat to the fiber stuff. The first way, the pressure rises slightly faster/more. When it loses heat to fibers, a given volume change results in a lower pressure, and so acts like a larger cabinet. It is actually significant, even though your first reaction is to blow it off.....

billoetjen · #9 09-21-2010, 07:47 PM

Quote:

Originally Posted by SlingBass4

+1 to a much better solution. IF you can find some of the egg crate type pads - so much the better!

Not an expert, but I've seen quotes here by them that point out that the research shows negligible effect from the egg crate foam. Wish I knew more about it.

rpsands · #10 09-21-2010, 07:51 PM

I am a really big fan of quilt batting. Cheap and it works.

PDGood · #11 09-21-2010, 07:56 PM

I think it's an interesting idea, and one that you can un-do if you don't put too much glue on it. Pretty safe experiment really.

I wish people would get more inventive. (Myself included). I remember the first time I heard that a guy had put piano strings on a bass it sounded like a crazy idea. It turned out to be Chris Squier with Yes and the sound became part of that band's signature. Maybe not the sound I'm going for but I like that he had a vision and tried something different and made it work for his music.

If you have an old cabinet that you want to experiment with, one thing you can try is fiberglassing it. I heard a dual 18" cabinet that had been fiberglassed and it had the clearest bottom end you could imagine. The downside here, of course, is this can't be undone - so don't practice on your good stuff.

billfitzmaurice · #12 09-21-2010, 08:43 PM

Quote:

Originally Posted by kr3w1664

Just going to do a little experiment. I'm planning on putting polyfill into my svt215e. The walls are already lined with some flimsy wool type material, and not even on all the walls. Has anyone done this to their cab? I'm not looking for negative feedback, this is strictly an experiment.

Do a search. This is a recurring topic, and the feedback from those who do it is always positive.

Quote:

Originally Posted by billoetjen

Not an expert, but I've seen quotes here by them that point out that the research shows negligible effect from the egg crate foam.

I am an expert, and IMO anyone who says that most definitely is not. No such 'research' exists. OTOH many examples of research that show the positive effect of damping in general and foam in particular do exist.

KramerBassFan · #13 09-21-2010, 08:59 PM

Quote:

Originally Posted by billoetjen

Not an expert, but I've seen quotes here by them that point out that the research shows negligible effect from the egg crate foam. Wish I knew more about it.

An expert is good at designing things, but can they really tell you what sounds GOOD to YOU?

All i know, is my 2x15 sounded like an entirely different cabinet when i loaded it with egg crate type foam from pillows. my source? Walmart.

billoetjen · #14 09-21-2010, 08:59 PM

Quote:

Originally Posted by rpsands

I am a really big fan of quilt batting. Cheap and it works.

Me too. Just tonight, I completely double lined an Ampeg combo with polyester quilt batting. To me, the foam stuff looks like it'd reflect more mids and highs than absorb.
This may be unscientific, but, when I get done, I stick my whole head inside the cab and everything seems very, very quiet; the way NYC subways used to sound in the 70's, after a night at CBGB.

Jerrold Tiers · #15 09-21-2010, 09:59 PM

Well, if you change a design, it may work better, or worse...... Or it might be "worse" but YOU like it better..... You never know.

Usually it seems to work better for a couple weeks, then if there is a problem, it starts to show up...... After you've got over the "I did it myself and it sounds great" thing.... But it's pretty easy to undo.

billoetjen · #16 09-21-2010, 10:55 PM

Quote:

Originally Posted by Jerrold Tiers

Well, if you change a design, it may work better, or worse...... Or it might be "worse" but YOU like it better..... You never know.

Usually it seems to work better for a couple weeks, then if there is a problem, it starts to show up...... After you've got over the "I did it myself and it sounds great" thing.... But it's pretty easy to undo.

Dis de truth

dmusic148 · #17 09-21-2010, 11:14 PM

Quote:

Originally Posted by billoetjen

This may be unscientific, but, when I get done, I stick my whole head inside the cab and everything seems very, very quiet; the way NYC subways used to sound in the 70's, after a night at CBGB.

LOL!!!!

Quote:

Originally Posted by Jerrold Tiers

The effective size increase comes from the difference of compressing air which is free to heat slightly with compression, vs compressing air which loses its heat to the fiber stuff. The first way, the pressure rises slightly faster/more. When it loses heat to fibers, a given volume change results in a lower pressure, and so acts like a larger cabinet. It is actually significant, even though your first reaction is to blow it off.....

That... just... blew..... my mind. I never in a million years would have thought of that, but it makes sense. Wow. Really?

billoetjen · #18 09-22-2010, 06:45 PM

Counter-intuitive.

billfitzmaurice · #19 09-22-2010, 08:14 PM

Quote:

Originally Posted by dmusic148

LOL!!!!

That... just... blew..... my mind. I never in a million years would have thought of that, but it makes sense. Wow. Really?

No, not really. That was accepted theory in many circles as recently as 5 years ago, but it's been found to be erroneous, along with the idea that stuffing a sealed cab duplicates making it larger.
Stuffing a sealed cab lowers system Q as a product of the higher impedance load given by a stuffed enclosure versus air alone. Lowering Q tames a midbass peak, which resembles in some ways what a larger box does. But a larger box also increases sensitivity and LF extension, stuffing does not. Heat is generated in the process, as stuffing fibers have a higher friction coefficient than air. But it's a byproduct of the process, not the process itself.

Quote:

This may be unscientific, but, when I get done, I stick my whole head inside the cab and everything seems very, very quiet; the way NYC subways used to sound in the 70's, after a night at CBGB.

Unscientific, but it works. If you stick your head inside an unloaded cab and hum, varying the pitch, and find a pitch where the cab resonates the cab is under-damped.

Jerrold Tiers · #20 09-23-2010, 08:55 PM

Well, well......

Interesting.....

I will say that stuffing, done properly, has always resulted in pretty much the theoretical effect for me, however....... if you keep it away from the close-in speaker cone and vent areas it does not seem to affect the Q particularly.....

I have for instance, actually USED the effect to get a slightly smaller box to act larger, and it did , without appearing to flatten out the box resonance......

Presumably the overall effect is sufficiently close to appear to work as described...... Most things acoustic are known to only 10% at best in production....... there is considerable room for variation in that.

I am also not quite with you on the higher impedance when stuffed..... it does not seem to fit on an energy balance basis...... or with the lower Q.