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Should i fill my Speaker cab up with foam or something similar?

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Well yes, short question but gets it across! I saw someone on another thread building a cab and it was full of roof insulation looking stuff?

What does that do and should i do it?

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Posted (edited)

Cabs should be lined with either open cell urethane foam, rigid fiberglass board insulation, or polyester furniture upholstery batting, 2 to 4 cm thick. Sealed cabs may benefit from being totally filled with pillow stuffing, not foam, and absolutely not fiberglass building insulation. That depends on details about the drivers that you're probably unable to find if you have a store bought speaker. If you're building a cab with plans from a professional designer they should tell you what should be used. One can rightfully infer that if they make no mention of it that they're not from a professional.

Edited by Bill Fitzmaurice

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Stuffing cabs is relatively complex in theory easier in practice. Stuffing in the cab space can act to break up standing waves in the air in the cab. At a slightly higher density it can alter the way the air works so that the air mass seems bigger to the speaker. Heavy damping material on the back of the cab could be there to damp reflection off the panel which is otherwise reflected straight back out of the thin paper cone. HiFi cabs often have a mineral loaded bitumen sheet on the walls of the cab. This mass loads the panel and damps resonance in the panel itself.

Generally speaking I don't bother much with damping materials in instrument cabs. The little sheets of white polyester in a lot of commercial cabs are there for show IMO they are far too light and thin to make much if any difference. If you feel inclined it might be worth experimenting with a good thick layer on three opposite panels. You need to achieve densities of around a couple of pounds per cu ft (google that if you are young :) )

Alternatively you could try concentrating it all on the rear panel to stop the reflection thing

Have a good listen before and after and be prepared to experiment, it's a cheap way of tweaking your speaker and you can pull it all out if you don't like it

If the cab is ported keep any stuffing well away from the ports or you will lose your tuning.

 

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If its big enough you could fill it up with those squashy balls, and have a sort of play ball pit, as well as a speaker!

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1 hour ago, Phil Starr said:

. Stuffing in the cab space can act to break up standing waves in the air in the cab. At a slightly higher density it can alter the way the air works so that the air mass seems bigger to the speaker.

That's old school theory, long ago abandoned. Modern speakers are too small for standing waves to arise. If they were large enough for that to happen the wavelengths would be too long to be broken up by stuffing. The air mass with sufficient stuffing density doesn't seem larger to the driver. That said, the effects of both damping and stuffing are real, easily measured, and with sufficiently advanced speaker modeling software predictable.

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BTW this is in my Harley Benton amp i changed the speaker on a while back... 

First experiment: take the front off, shove a pillow in there. Result: less honky mids, but a bit dull. Took it out again. Heard neighbours crashing about, decided to watch the Handmaid's tale instead.

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To simplify, all cabs need damping for smoother mids. Sealed cabs that sound boomy may be improved with more than just being lined, some may require being fully filled to adequately tame the boom.

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Fill the thing with shaving foam. 🕺🏻

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3 minutes ago, xgsjx said:

Fill the thing with shaving foam. 🕺🏻

It's already full of quantum foam.

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5 hours ago, Bill Fitzmaurice said:

That's old school theory, long ago abandoned. Modern speakers are too small for standing waves to arise. If they were large enough for that to happen the wavelengths would be too long to be broken up by stuffing. The air mass with sufficient stuffing density doesn't seem larger to the driver. That said, the effects of both damping and stuffing are real, easily measured, and with sufficiently advanced speaker modeling software predictable.

Oh dear, the wavelength of a note at 1000Hz is just over 34cm and the first standing wave is half that, clearly that is nowhere near the size of a bass cab back to front. Modern bass cabs are sooo small. No, wait that's exactly the size they are. 

Air mass to the driver, well if you want to do a detailed explanation of adiabatic process to people here then be my guest. This was my simplification to help someone who wants to try something out to improve their speaker. 

As to the idea that we have good modelling software that will adequately take into account all the variables and make accurate predictions, well let's just say I've yet to be convinced, perhaps you can point me to the maths behind it.

I'm watching he Handmaids Tale tomorrow. I'm old school, I recorded it. 

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Standing waves are a low frequency issue, not midrange. Adiabatic process has nothing to do with how damping and stuffing work. That's also old school theory that tried to use thermodynamics to explain how damping and stuffing functioned before the actual acoustical processes were understood.

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Come on now, we've all had a few drinks, let's not spoil it for the bride and groom. 

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Standing waves certainly exist in loudspeaker cabs and most good designers spend time trying to minimise them. Some go to extreme lengths trying to try to get rid of them. They are particularly problematic in tall, hi-fi cabs, where standing waves occur at frequencies around 200 to 300Hz. There are a number of different ways that a designer can measure them. Dealing with them is more tricky.

A typical bass cab isn't exactly small, and they tend to suffer from standing waves between 170 and 300Hz. These are critical frequencies for bass guitar and will colour the sound unless some steps are taken to keep them under control. I've found that felt is quite good at taming standing waves and flutter echos inside cabinets.  It's also fairly cheap. Place more damping material at the end of the longest dimension of the cabinet because that's where the biggest problem is.

 

 

 

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18 hours ago, Bill Fitzmaurice said:

To simplify, all cabs need damping for smoother mids. Sealed cabs that sound boomy may be improved with more than just being lined, some may require being fully filled to adequately tame the boom.

Great name for a band! :D

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4 hours ago, Teebs said:

Great name for a band! :D

Or a porn film. 

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