Query on Damping a cabinet to absorb all internal reflections

[TheFlash]

Probably a polyester type.

As they are ported, have you tried them with out? (the fleece like stuffing  ). As they seem to have dense foam lining the walls, maybe placing some eggbox foam directly behind the mid/bass drivers to help defract the soundwave from the back of the drivers.

Edit: I just noticed you said reinstalled  :doh:

Loving that edit! I used “replaced” instead of “reinstalled” at first pass, but thought someone might say “replaced with what?”!

Loving learning about this though. 👍

 

[greybeard]

Loving that edit! I used “replaced” instead of “reinstalled” at first pass, but thought someone might say “replaced with what?”!

Loving learning about this though. 👍

I know very little about the Posselts, are they a 3 way or 2.5? And are you unhappy with the sound in a particular area? Or are you just experimenting, as the weather is awful  

 

[TheFlash]

I know very little about the Posselts, are they a 3 way or 2.5? And are you unhappy with the sound in a particular area? Or are you just experimenting, as the weather is awful  

I enjoy the sound! They're not ATC actives of course, so I have to adjust my ears every time I'm in Kendal but they're a hugely enjoyable listen and have one of the best soundstages I've had. They're a 2.5 way with these drivers:

• Morel MDT30 (full specs available in this list https://site.diy-loudspeakers.com/datasheets/46-morel-datasheets/162-old-morel-driver-datasheets)
  
• Vifa/Scanspeak PL18WO-09/08 https://willys-hifi.com/products/vifa-pl18wo-09-08-woofer
  

 

[newlash09]

No, because it dampens the port tuned resonance too much.

I find it most beneficial with a 3 way sealed speaker, where the mid enclosure is separate from the Bass, and using a lot of damping, in the bass enclosure gives the illusion of a larger volume therefore increasing bass output, and in the mid enclosure a lot of damping helps stop reflected soundwaves reaching the back of the cone, and muddying the sound.

As with everything in this hobby it is personal choice on whether it is better or worse to your ears, so experimentation with the amounts used is essential.

Thanks a lot for sharing that sir

 

[Fatmarley]

In my bass units the most effective damping material was the aluminium foil/ rubber adhesive sheets used to damp sound/vibration in cars/vans ....proved it with REW analysis - OMG I’ve become a measureist 😁

Have you got a link to the measurements? Did you use it to damp the walls, or something else?

 

[MF 1000]

I’ll dig around my REW files later Matt ....but have a look at 



Page 29 shows the internal lining etc

But my recent experience in adding the balau hardwood cladding to the outside of the cabinet has probably had more effect ....though at a greater cost 

 

[Fatmarley]

I’ll dig around my REW files later Matt ....but have a look at 



Page 29 shows the internal lining etc

But my recent experience in adding the balau hardwood cladding to the outside of the cabinet has probably had more effect ....though at a greater cost 

Have you tried the bubble wrap / wadding and measured the port output by placing the mic in the mouth of the port?

I only ask because I had a bit of a disaster with my current build, and put far too much acoustic foam in them and it killed the port output.  It's down about 7db compared to my previous, lightly stuffed speakers. The bass sounds gutless

Since searching Helmholtz resonators etc, I'm starting to think bubble wrap might be a very good idea in ported speakers (sorry to say I thought you were crazy when I saw you were using bubble wrap lol). I'm guessing air gets trapped in porus materials and the slow release ruins the Helmholtz affect. I could be wrong about WHY it kills the port output, but I do know that dense, open cell, acoustic foam DOES kill the output. 

When I get a chance I'm going to cut the back panel off one of my speakers and fit quick-release case latches. I'm then going to put my microphone on the port entrance, and measure a numbers of materials to try and keep the port output as high as possible, but reduce resonance/standing waves as much as possible.

 

[MF 1000]

Hi Mark 

I’ve never done any port mic work.  I tried the fluted foam in a previous build but as you found I thought it killed the bass.  Incidentally on my smaller bass enclosure with the Volt driver it was improved by more wadding / bubble wrap ....in my 150 litre cab stuffing it to a similar level (inc a 4oz circle of wadding behind the driver) killed the bass.  So it think the effects are volume driven too as in the new cab the ‘van lining’ foil/bitumen layer works very well with minimal wadding/ bubble wrap in each cell of the cabinet. 

 

[greybeard]

Have you tried the bubble wrap / wadding and measured the port output by placing the mic in the mouth of the port?

I only ask because I had a bit of a disaster with my current build, and put far too much acoustic foam in them and it killed the port output.  It's down about 7db compared to my previous, lightly stuffed speakers. The bass sounds gutless

Since searching Helmholtz resonators etc, I'm starting to think bubble wrap might be a very good idea in ported speakers (sorry to say I thought you were crazy when I saw you were using bubble wrap lol). I'm guessing air gets trapped in porus materials and the slow release ruins the Helmholtz affect. I could be wrong about WHY it kills the port output, but I do know that dense, open cell, acoustic foam DOES kill the output. 

When I get a chance I'm going to cut the back panel off one of my speakers and fit quick-release case latches. I'm then going to put my microphone on the port entrance, and measure a numbers of materials to try and keep the port output as high as possible, but reduce resonance/standing waves as much as possible.

My understanding of Bass reflex cabinets, is to brace them well to stop resonance of the panels, applying bitumen sound deadening sheets would also help in this, and not take away too much cabinet volume, and then, either add egg box acoustic foam, to the back panel, and one side panel (you do not need to do both) or my favourite old fashioned felt carpet underlay around 2cm thick on all internal walls. Do not use any loose stuffing, as this could a: block the port exit and b: overdamp the tuning of the port frequency.

I tend to make sealed cabinets, where in my experience, bracing and damping the internal walls as above, but then stuffing the remaining space with as much loosely teased lambs wool as possible, gives the best results to my ears, but as always this will vary to peoples taste.

 

[Fatmarley]

With my last speakers I did something similar to the Royd Minstrel. Port on the side, just below the bass driver, and loose stuffing (Monacor mdm3) just below the port (Edit: just to add that these speakers were large floorstanders, so there was quite a lot of stuffing below the port). The bass was excellent, deep, tight, and powerful.

The Minstrel also has stuffing at the top of the cabinet, but my midbass driver was at the top, so I couldn't put any there.

I think dense foam is the real bass killer, but I'm sure anything porous is going to slow down the Helmholtz spring effect to a certain degree. 

In my experiments, I've also decided to try some freezer bags with a light bit of stuffing inside. 

 

[Fatmarley]

I'm on holiday at the moment, so don't have access to all my photos, but here's a thread with some pictures: (ignore the comment regarding the delta 10a not producing any bass, it's completely wrong).

http://techtalk.parts-express.com/forum/tech-talk-forum/1469381-boxy-bass-and-sounding-like-there-s-no-stuffing-inside-the-horrible-hollow-sound

 

[Alvolake]

FWIW I followed Fatmarley´s rec. of motorbike exhaust wadding made up of fibre glass and cotton I think. and took out all the Dacron polyester I had gone OTT with. in my sealed boxes. I reckon it´s definitely a step up.