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Can I testify? DIY cab baffle.

rumblethump

rumblethump

Mar 25, 2000
1,096
17
80
Pioneer CA. 95666
#1
Thanks to the great help in this forum, I added damping material to one of my 2 12 cabs today to ab them. I used camp mat egg crate foam. I cut the back of each section first and stapled in then added a one piece side cut to exact. Started stapling at one end and it worked pefect.

Now on to the great news.

These are legion sound 2-12 cabs I have refurbed with metal speaker jack, t nuts for all the speakers and I have disconnected the horn and removed the original thin piece of damping material they thought was adequate. Up until now I was pretty happy with their sound. Especially 2 2-12s, but one has been plenty adequate, even with the 5 string. .

I could tell immediately how much this mod helped. The cab developed a (warmth/thickness) ?? OMG It sounds great. On the other hand the other cab sounds thinnner boxier in comparison. Itseems to have attenuated the harsh highs a pleasant amount. Thanks again for your assistance, I'll try and get pics up soon. I may even be able to post MP3 for comparison
 
#6
Didn't think about the camera until I was halfway done. :hiding:

bareside.gif


1stsidefinished.gif


finisheddampingmaterial50.gif


GigRig.gif
 
#9
Jazzdogg, cabinet damping can have a minor effect on low frequency output (measureable, but usually not audible), as a little bit of low-frequency energy is lost to the material. Too much damping material will result in an audible loss of bass energy, but lining the cabinet walls as shown above shouldn't fall into that cagegory. If you let damping material get too close to the inner opening of the port and impede the airflow, you can have a significant loss of low frequency output.

Most of the impact of damping material is in the midrange and high frequency region, where it effectively absorbs the short wavelengths so they don't re-radiate through the cone and impart a "boxy" signature that degrades clarity. Some cones are more acoustically transparent than others, so the audible improvement from adding damping material can vary significantly from one cab to the next.

Note that acoustic damping material will do nothing towards reducing mechanical resonances in the enclosure walls. That's a different problem calling for a different solution.

My preferred method of applying damping material inside a cabinet is to use loose polyfill, with mosquito netting used as necessary to keep it away from the inner port opening(s). In a vented box, 1/4 pound per cubic foot is a good starting point. The effectiveness of damping material is related to how thick it is in relation to a wavelength, so a foot and a half of fluffed-up loose filling is effective down to a lower frequency than is 2" foam along the walls. If you have a lower midrange "droning" resonance, 2" thick foam won't help much. But it isn't necessarily either/or; you can do both.
 
#10
Wow Nice.. I was thinking of doing this to an old peavey 1-15 cab, Where do you guys find the foam (damping meterial) will carpet padding work? I have a friend who lays carpet and they have this blue rubberized pad,about 1/4" thick with a waffle like texture,It is not as thick as that egg crate foam.

Eno
 
#11
eno50, you want to use an open-cell foam (that you can breathe through), because the material has its damping effect as the sound waves pass through it. I think that carpet padding is usually a closed-cell foam.

By way of illustration: You know how in a public urinal they often have a plastic or metal grid of some sort that you aim for? Well, in passing through that grid the energy of the stream is dissipated, so you get less reflection back at you. That's damping material in action.
 
#12
DukeLeJeune said:
By way of illustration: You know how in a public urinal they often have a plastic or metal grid of some sort that you aim for? Well, in passing through that grid the energy of the stream is dissipated, so you get less reflection back at you. That's damping material in action.
Click to expand...

Yes. Damping material prevents dampening material.
 
#13
DukeLeJeune said:
Jazzdogg, cabinet damping can have a minor effect on low frequency output (measureable, but usually not audible), as a little bit of low-frequency energy is lost to the material. Too much damping material will result in an audible loss of bass energy, but lining the cabinet walls as shown above shouldn't fall into that cagegory. If you let damping material get too close to the inner opening of the port and impede the airflow, you can have a significant loss of low frequency output.

Most of the impact of damping material is in the midrange and high frequency region, where it effectively absorbs the short wavelengths so they don't re-radiate through the cone and impart a "boxy" signature that degrades clarity. Some cones are more acoustically transparent than others, so the audible improvement from adding damping material can vary significantly from one cab to the next.

Note that acoustic damping material will do nothing towards reducing mechanical resonances in the enclosure walls. That's a different problem calling for a different solution.

My preferred method of applying damping material inside a cabinet is to use loose polyfill, with mosquito netting used as necessary to keep it away from the inner port opening(s). In a vented box, 1/4 pound per cubic foot is a good starting point. The effectiveness of damping material is related to how thick it is in relation to a wavelength, so a foot and a half of fluffed-up loose filling is effective down to a lower frequency than is 2" foam along the walls. If you have a lower midrange "droning" resonance, 2" thick foam won't help much. But it isn't necessarily either/or; you can do both.
Click to expand...

Thanks, Duke! Succinct & cogent! Very helpful. :)
 
#14
Thanks, Jazzdogg.

Now here's a little trick in case you ever decide to design your own speakers: Design (and tune) for a little bit more low bass output than you really need, so that you can then add enough damping material to get good midrange clarity without worrying about ending up a little bit bass-shy.
 
#16
Having a bit of time on my hands, I decided on Cabinet 2 to only add the dampening material (egg crate foam) to only the back of the cabinet first to compare against my first cab which has all sides and back done. First impression is its comparable sounding to the other but I will have to bring cab 1 home to do a direct a/b testing.
 

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