32L in a volume without any absorption gives Q of 0,75 with the manufacturers TSP and Qtc 0,86 with what I measured.
While 0,86 is higher as I like to build it's far from 5dB hump, more in the 1-2dB area.
Get WinISD and do some simulations. Vas only has meaning together with Q of the driver.
While 0,86 is higher as I like to build it's far from 5dB hump, more in the 1-2dB area.
Get WinISD and do some simulations. Vas only has meaning together with Q of the driver.
Yes. Buddy of mine gets F3 <40hz with 2 Textreme versions in vented box about that size. Sounds excellent.
I didn't think so when I heard them but the answer would depend on what you like listening to, how loudly and the room.
The Textreme versions have different T-S Parameters. 60 liters could still work for two of the W024-P in a ported box but it's a bit small and you would want a larger port. It would be a good size for them is the box is sealed. I made a sealed box about that size with them and it's great.
If they're sealed then it's a good size. If it's ported then that's a bit small but still workable with a larger port.
TBH, I think it was vented. Maybe it wasn't?! It was a very short visit. 🤔
An excellent tool for enclosure and baffle simulation is Basta!
Use the serial number D4E5-EEA9-A5CE-8BD0 to get it started.
T/S param Basta files of the drivers can be found in the loudspeakerdatabase
60l vented for two WO24P-8 is too small, 60l closed and +100l vented are OK
Here are the sims for two WO24P-8 in parallel:
60l vented:
120l vented:
60l closed:
Use the serial number D4E5-EEA9-A5CE-8BD0 to get it started.
T/S param Basta files of the drivers can be found in the loudspeakerdatabase
60l vented for two WO24P-8 is too small, 60l closed and +100l vented are OK
Here are the sims for two WO24P-8 in parallel:
60l vented:
120l vented:
60l closed:
Everyone likes that woofer... It offers $500 performance for $300 price... 🙂
Some construction photos:
Above is the back panel and one side panel. For the purposes of assembly, most of the bracing is attached to the rear panel. There are two U-braces which will connect the front baffle to the sides, and these two are attached to one side panel. I am applying butyl rubber damping material on the back, sides, top and bottom panels.
Above: this is a trial fit to make sure that the side panel and rear panel fit together. I need to ensure that the damping material does not interfere with the joint fit.
Below is another view.
Above is the back panel and one side panel. For the purposes of assembly, most of the bracing is attached to the rear panel. There are two U-braces which will connect the front baffle to the sides, and these two are attached to one side panel. I am applying butyl rubber damping material on the back, sides, top and bottom panels.
Above: this is a trial fit to make sure that the side panel and rear panel fit together. I need to ensure that the damping material does not interfere with the joint fit.
Below is another view.
How much does this change the "knock test"?
I also like to add some dampening but to be honest in a proper braced cabinet the effect is often pretty small.
The effect of the Butyl sheets is following:
The sound blown into the enclosure by the drivers hits the cabinet panels from inside (more or less evenly distributed over the whole area/surface) and excites them to swing (most critical at frequencies corresponding the internal modes when pressure knots of the standing waves get supported by the walls).
With the Butyl sheets you put viscoelastic material between the exciting sound waves inside and the cabinet panels that sucks then out and converts part of the energy to heat.
So, the effect cannot be well tested by a knock test because 1. mechanical excitation on one point vs. acustical evenly over the surface and 2. excitation from "hard" outside, not from inside where the sound arrives and the Butyl is applied. Knocking from inside onto the butyl might be a more realistic test to get a feeling.
Additionally you can suck energy out of cabinet panels unwanted bending motion when you build a sandwich; I once glued additional steel sheets onto the buty with bending stiffness sized ~equal to the cabinet panel stiffness (~1mm steel sheet for 18 mm birch plywood) to get the neutral fiber of that sandwich located in the buty layer. So when the wall bends the shear forces occur in the viscoelasic Butyl, and this also suck some energy out.
For excitations caused by the vibration counterforce to the cones/domes excitation by the driver baskets, which are introduced directly to the structure mechanically, the Butyl has no relevant effect.
Further trivial effect is that just mass is added, so the sound power from inside must excite heavier panels, and the excitation is then reduced ~linear to the mass increase. (The sound goes not "through" the walls how many imagine, but excites the walls which then act as a large membrane)
Best regards
Peter
It is a perceptible change in the sound of the knuckle knock.
The type of cabinet I build is heavily braced and very rigid. My goal is to drive the first mode cabinet structural resonance to a high frequency (where there is less musical energy), and to couple all six cabinet walls together so there is just one dominant resonance, rather than each wall having its own resonance. Another goal is to arrange the bracing in ways which restrict the out of plane motion of each wall. Not all structural resonances will produce an audible cabinet signature, and those which cause a cabinet wall to move in out-of-plane bending are most likely to produce sound. A resonance which primarily deflects panels and bracing in the axial and shear directions are much less likely to produce sound.
With this kind of highly rigid structure, I have found that a layer of foil-faced butyl rubber damping does reduce the magnitude of whatever resonance remains. The damping material adds mass, which reduces the resonance frequency a small amount, and this is the opposite of what I want. However, I have found this to be an acceptable tradeoff.
I want to be clear that I do not intend this kind of construction to be a constrained layer damping. This damping material is applied to the interior wall surface, and it is not effective enough to be called "CSD". But it does help reduce any small resonances that remain.
Fixing cabinet structural resonances after the cabinet is built is very difficult, and sometimes impossible. Therefore, I feel it is prudent to take whatever steps I can to prevent a hard-to-solve problem later.
My thoughts on the effectiveness of foil-faced butyl rubber damping:
Some thoughts on structural damping.
When I built my textreme (TXT) system, the mid/tweeter box was well braced, with ¾ inch plywood walls, and a double layer baffle. As an afterthought, I added two layers of 80 mil Noico butyl rubber damping material to all interior walls. I did not think it would do much good, but I had it on hand, so I used it. The result was a very low signature cabinet, both from a measurement standpoint and subjectively.
Later, I followed @augerpro and his cabinet resonance research and thread. I began to consider if that butyl rubber material...
When I built my textreme (TXT) system, the mid/tweeter box was well braced, with ¾ inch plywood walls, and a double layer baffle. As an afterthought, I added two layers of 80 mil Noico butyl rubber damping material to all interior walls. I did not think it would do much good, but I had it on hand, so I used it. The result was a very low signature cabinet, both from a measurement standpoint and subjectively.
Later, I followed @augerpro and his cabinet resonance research and thread. I began to consider if that butyl rubber material...
I am not sure I agree that it has no relevant effect. The majority of structural resonance in a cabinet is driven by the direct mechanical vibration of the driver frame. Acoustic transmission to the other cabinet walls is secondary. A plywood panel in resonance has a relatively high Q. It does not take much damping to reduce the Q and thus the magnitude. I can lower the magnitude of a vibrating cabinet wall (i.e. dampen the panel) by touching it with my fingertips. So it makes sense to me that butyl damping would have an effect.
I have built similar boxes both with, and without butyl damping. With these highly braced boxes, there is a subjective improvement with butyl (the knuckle knock test), and a measurable improvement with butyl (nearfield scans of the cabinet wall).
It is a complicated subject. With more lightly built and less rigid cabinets, it is possible that adding mass and damping might make the cabinet signature worse: Lowering the Fn of a panel resonance often puts the resonance where there is more energy available. Lowering the Q can make the resonance easier to excite. Nonetheless, with the high rigidity cabinets I build, I have found a technique which works well.