is this research on poly accurate?

As I am about to build my first Ported Box I am really in a tight Spot under my trucks back seat. But A link was found by a friend of mine. I wanted to run it by you guys before I got too excited. Thanks http://web.archive.org/web/20020808224043/integra.cyberglobe.net/caraudio/resources/fiberfill/I can't hear you!

That article is so last millennium - 15 years old! And hot air is "stiffer"?? I know it's less dense, but stiffer? And the fill vibrates hence absorbing heat - maybe we need a fully damped enclosure?     Alas I'm venting (pun intended) in a jesting way.... I'm not box nor fill knowledgeable, but stuffing was a common technique. Fill was recommended in my last box (domestic, ~4' x 1') but maybe to reduce harshness (crispness)? But it might be one of those "spouse-tales" practices - ie, all bullsh etc. But I do see its "logic". But I also see the logic of other things which - although logical - are wrong. I too am interested in the expert & experienced replies.... (What does WinISD indicate? I still prefer DI though.)

Yes, hot air is stiffer. For a given volume, hot air's pressure will rise more and faster for a given added volume of the same temperature air, than would cold air under the same circumstances. You cannot have "a" fully damped enclosure - you must have some volume remaining, AND every "fully damped" mark will be at a different point - depending on Fb and Vb. If you look at the first graph posted there, you will see that the cutoff for any gain is between 2.6 and 3.1 pounds per cubic foot; beyond 2.6 pounds per, you start to actually LOSE effective volume! This overstuffing loss actually happens faster than the gain happens in the "under" stuffing - it's by no means a bell curve! Your "overstuffed" point hits fast, and damages quickly! In this PARTICULAR volume's case, the "fully damped" stuffing density will be about 2.75 to 2.8 pounds per cube. This is the "fully damped" density for this driver/box combination. What is the "magic" density? Without anechoic chambers and acoustic analyzers or impedance measuring equipment, it's hard to tell! Additionally, if you read one of the very last lines in the article:

Tom Nousaine wrote: I also found that stuffing gets less effective as box size increases. The moral: The bigger your box is, the harder it is to fool your woofer.

Generally speaking, I agree with this last line, and I have seen this to be the case in nearly every larger enclosure I have ever built. (...and I've built a few, I assure you!) It means that the larger the enclosure to begin with, the less damaging a small error in judgement - size wise - becomes, and the less the driver will need or even notice any stuffing. Additionally, if you build your box EXACTLY to spec, allowing for all displacements, including driver CONE (not just magnet and frame), vent and bracing, your response will be the same as if you had built the enclosure 50% smaller and stuffed - there will be no difference. JBLSpeakershop has confimed this for me numerous times. This to me means that stuffing is a band-aid, one designed to help cover the open wound of either miscalculations or sloppy construction techniques. It CAN be effective for improving SAF (Spouse Approval Factor - smaller enclosure = higher SAF), but it doesn't mean that every box MUST be stuffed.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Thanks Haemo. But I think I can improve - isn't the SAF = zero (volume)? Or maybe I'm thinking of its limit - ie approval approaches 1 (or infinity in male less-dominant partner terms) as Vol approaches zero....? LOL. And now I understand the stiffness. I was thinking more in terms of density and "lightness" (like copper - hotter is softer but higher electrical resistance). But for air, as temp increases, speed increases (acoustic impedance decreases). (Greater stiffness is greater speed.)

oldspark wrote: Thanks Haemo.

There's a new one... It'll go in the list with hempy, haemph and physt... ;) A little close to "homo"... Just be careful! LOL

oldspark wrote: But I think I can improve - isn't the SAF = zero (volume)?

Ideally... This is what wives don't understand: There MUST be some amount of volume occupied. Sometimes they just don't wanna hear that! LOL I think this is why Bose is so successful with women, their SAF approaches unity! Sure, they sound like complete shiite, but the ladies are happy!

oldspark wrote: Or maybe I'm thinking of its limit - ie approval approaches 1 (or infinity in male less-dominant partner terms) as Vol approaches zero....? LOL.

See point two! ;)

oldspark wrote: And now I understand the stiffness. I was thinking more in terms of density and "lightness" (like copper - hotter is softer but higher electrical resistance). But for air, as temp increases, speed increases (acoustic impedance decreases). (Greater stiffness is greater speed.)

Yep. It's the very reason pressure increases when you add heat to a sealed container. The material inside gets "stiffer". The stiffness affects acoustic impedance, just as you said. Higher temperature = lower impedance.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."