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[Dan Gruner]

I am hoping someone will be able to shed a little light on something that has been puzzling me.  I understand that a lot of subs do not have the acoustic wadding material inside to absorb internal reflections of the sound, unlike mid/high cabs, which almost always do.  I have been told by some people that it is best not to use acoustic wadding in subs, for it will
>reduce their output and I suppose hard "sound quality"  My EV RX-118 and Xi series 18" subs all have acoustic wadding inside, but my RCF Event ESW1018's do not.  The ESW1018 is a cracking sub with plenty of output, but I think tends to sound a little "boxy" at times.  If I treated the cab to someacoustic wadding will this make a big difference, removing any "boxyness"
>but reducing the SPL?  This may also have something to do with the crossover/eq settings (using an EV DX-38 on the system)

Any help much appreciated.  

Dan

[Johan Rademakers]

There are basically 2 types of wadding used in PA:

Fibrelike materials, either loose or packed together (like BAF or glasfibre). These are mostly used to create a bigger virtual volume (it will appear to the speaker as if the volume of the box is up to about 10% larger than it actually is).
Don't use glassfibre in BR-cabs tho, the glass particles that will come loose due to vibration can be highly irritating on the skin and lungs.

Foam like materials (like Pritex). These are mostly used against standing waves in the enclosure and against "boxyness".
Both types have a certain overlap in their effects. For instance, if you use Pritex you will also create a little extra virtual volume.

More volume will extend the BR's lowfrequency response in exchange for less output. But we're not talking about significant differences here as some people appear to think:
Your f3 might go down 0.5 - 1.5 Hz, in most cases output will only fall 0.5-1 dB. That's a change you wouldn't even hear. It's next to nothing considered the fact that you finally did get rid of that annoying "boxyness"

Mvg Johan

[Too Tall (Curtis H. List)]

Dan G wrote on Mon, 25 April 2005 06:47

I am hoping someone will be able to shed a little light on something that has been puzzling me.  I understand that a lot of subs do not have the acoustic wadding material inside to absorb internal reflections of the sound, unlike mid/high cabs, which almost always do.  I have been told by some people that it is best not to use acoustic wadding in subs, for it will >reduce their output and I suppose hard "sound quality"  My EV RX-118 and Xi series 18" subs all have acoustic wadding inside, but my RCF Event ESW1018's do not.  The ESW1018 is a cracking sub with plenty of output, but I think tends to sound a little "boxy" at times.  If I treated the cab to someacoustic wadding will this make a big difference, removing any "boxyness" >but reducing the SPL?  This may also have something to do with the crossover/eq settings (using an EV DX-38 on the system) Any help much appreciated.   Dan

Hi Dan,
   Nice explanation by Mvg Johan.

   Reflections can only happen if the distance between the walls of the box (or room) are long compared to the wavelength of the frequency in question. So for 2kHz the wavelength is about 6". A typical box has walls much further apart. The reverse at 100Hz the wavelength is over 11'  and that is long compared to the typical ported sub woofer box so no reflections.

   As Johan explained adding stuffing makes the box look bigger to the driver for a sealed or ported box. You do lose some output. So if you can you make the box the right size and you don't need to add stuffing to make it work right. OTOH If you really need a smaller box for a truck pack for instance designing the box smaller and adding stuffing is often done.

[Dan Gruner]

Many thanks for all your help guys.  Mvg Johan applied that adding the wadding to my RCF Event ESW1018 subs may cure any “boxiness” they exhibit, but at the expense of slightly reduced output.  Following on from what has been said, if this material makes the box looks bigger that it physically is, by adding the material wont that effect the cabinet tuning and loading of the driver??  If I add a layer of foam like materials (like Pritex) this should cure any “boxiness”, but what thickness to use I do not know! ?

[Johan Rademakers]

Pritex will add that little extra volume to a cabinet, but then again it won't change tuning/output significantly. We're not talking rocketscience here, where a slight change will lead to drastic changes in performance. Subjective it will do more and that's often where the confusion starts. If you don't like it just take it out again

I only know of one thickness when it comes to Pritex, so that shouldn't be to hard to get.

The fact that you're using an ESW 1018 slightly changes things tho. When it comes to wadding basreflex, you don't want the wadding to block the air-flow to/in the reflexport (or speakervents for that matter).
The ESW mainly is a gigantic port, so there is not much space to put Pritex on.
(You could also see it as some type of backloadedhorn, but it would model out about the same).

Quote:

Nice explanation by Mvg Johan...Mvg Johan applied that

Mvg is a Dutch way of ending a post/letter. Met vriendelijke groet it means: With kind regards.
(exactly translated it would be: With friendly Greetings)

Mvg Johan

[Gary Perrett]

Hi,
What about an 'applique' of thin higher density ceiling pannel 'glass'.

I took the plastic sheet off of ceiling panels (those 1/2 inch or so fiberglass ceiling panels) and glued them into the boxes suggested on the FANE website for the Colossus XB 15's. I could not believe the sound, those things rocked! I christened them the LBD series (little but deadly). I have just recently started using Smaart, and will attempt to measure these little
be-hemouths! Runnibg with a 50HZ highpass and an RMX 2450 these things really impressed me (my main speakers in the sub region are LABsubs) That said these things REALLY CRANK! I didn't even try them without the 'pannels' but I guess I will when I try the 18" version of these.

As for the LABsubs, my son tells me the ones we built without the sound absorbers (I used poly 'pillow material')are louder, and have less heat in the chamber behind the woofer. I cannot verify this though...yet.

Has anyone measured a lab with/and without 'pollyfill or glass fill' behind the baffel? I know mine kick some major ASS, and really pound the hell out of the room, to the point that I am "finally" the only one allowed to do bands @ that site( an all-together to often trade-off in many venues where the almighty dollar is more important than good sound!)

Gary Perrett, owner
Twilite Zone Productions
Grand Rapids, MN

[Too Tall (Curtis H. List)]

Gadget69 wrote on Thu, 19 May 2005 21:19

Hi, What about an 'applique' of thin higher density ceiling pannel 'glass'. I took the plastic sheet off of ceiling panels (those 1/2 inch or so fiberglass ceiling panels) and glued them into the boxes suggested on the FANE website for the Colossus XB 15's. I could not believe the sound, those things rocked! I christened them the LBD series (little but deadly). I have just recently started using Smaart, and will attempt to measure these little be-hemouths! Runnibg with a 50HZ highpass and an RMX 2450 these things really impressed me (my main speakers in the sub region are LABsubs) That said these things REALLY CRANK! I didn't even try them without the 'pannels' but I guess I will when I try the 18" version of these.

Hi Gary,
   If you decide to measure the change with the 18” with Smaart I would like you to send me the files. Smaart will export the measurements as an ASCII (text) file that I can import into Praxis. A picture will do me no good since I need to combine port and driver. Also I can’t easily overlay pictures like I can with data files.

Do one set before and one after adding the insulation.

For Frequency response measure about ¼” from the cone dust cap and another measurement right in the middle of the port with the mic right at the entrance of the hole.

Also do an impedance curve measurement. Each time you set up to do the impedance measurement first measure a resistor of known value so you know the setup is working correctly.

Snip-

Gadget69 wrote on Thu, 19 May 2005 21:19

Gary Perrett, owner Twilite Zone Productions Grand Rapids, MN

[Johan Rademakers]

I would say that wadding gives a change in sound that is mostly subjective and works for just the same reason as why subs often sound better behind or a side than in front.

Simulated the changes are very little, so little, theoretically you wouldn't even hear a difference. The absence of the higher frequencies tho would also explain why people swear it lowers the sensitivity so much, while it doesn't.

I would really like to see the measurements tho, so if you can post em, don't hesitate

Mvg Johan Rademakers

[Antone Atmarama Bajor]

Theres this stuff that you can buy from Home Depot in the carpet department ( I forget the name).  But its made from recycled matress material and they using for undercarpet padding.  Its relativly harmless.  You can staple it to the inside of your cabs for a little extra deadaning!!!!