Vicoustic Vari Bass tunable Helmholtz trap

[Washington]

Originally Posted by DanDan

It would be strange if you did not see a noticeable shortening of the modes addressed. It would also be extremely interesting us your curious fans here ;-)
DD

Agreed, but I actually dig the "reality" experience as Mr. Lagerfeldt has reported it. I'll confess I too got a sweet tooth for tech experiments and acoustic science, yet at the end of the day we work in studios, not labs.

This is not a Mary Poppins world, and reviews in magazines are dreadfully biased due to ad sales. When they aren't, they are limited to blissfull praise because of ethics (don't shoot at an ambulance) or because of principles (we'd rather show you good stuff than warn you off). This forum suffers from the occasional troll on a mission, but where else could we read a statement such as Lagerfeldt's?

In my book, his was a simple and effective review. Thanks Lagerfeldt!

[Brainchild]

The subjective report is interesting to read, but of course as DanDan says these things are precision devices (putatively) and need to be placed in the location where the pressure at their tuned frequency is highest in order to be most effective.
Considering the degree of engineering precision that went into all the equipment in that room [not to mention the room itself], it would be out of proportion not to apply at least a little engineering precision to determine where these devices should be located within the room.

[Nordenstam]

Originally Posted by DanDan

Give them the best possible chance. Measure again.

+1!

It's good to see this ears only report, but it probably doesn't tell the story as it could have been using measurements and an intensive effort to make the most out of those traps.

It starts with the issue of placement. The opening of the trap needs to be in a spot where there's a lot of pressure in the frequency that the trap is supposed to address. Standing on the floor with the opening on the top is probably not a good place. Sound is both velocity and pressure, with velocity being high away from boundaries and pressure being high close to boundaries. The SLM test will reveal such hotspots. When the traps then are inserted into the room, hopefully doing something to the sound, they'll change the modal response as they effect it! Which calls for a new round of retuning the traps to get the best response from them.

The main effect will be in the decay times. The best plot to use is the cumulative spectral decay. A +-1.5dB difference in the frequency response of a sine sweep seems to me to indicate a pretty large difference. Bet the change looks more spectacular in the decay plots!

The primary reason to be a bit sceptical to the results posted here is that placement have so much to say for such things. It's like diffusers; four of them at some arbitary position in a room will most likely not do enough to give an audible change. Four diffusers in the right spot will most likely make for a difference that most people will hear. Have a feeling the same goes for these traps.

On the other hand, it's fairly small devices with what I gather is a rather wide Q factor. Which isn't the best starting point to make a big change using such structures. It may very well be that they simply doesn't do much.


The big question is how it compares to other products, like RPG's Modex traps. They're 140-170 euro each, depending on target frequency range (price found at novatone uk). If we assume the Danish price to be twice the vat-less UK price specified for the Modex unit, it's about the same price for the vicoustic traps as the RPG product. Given RPG's excellent reputation in the acoustics field, I'd put my stocks on that option. It's also quite a more technologically advanced product. Though they do not offer tunability, which may be the strong point of the vicoustic traps.

Would also love to hear some comments from Vicoustics on this.


Andreas

[Lagerfeldt]

Thanks for the interesting comments. I think you and others who touched the subject have some valid points.

While the placements I tested weren't calculated they weren't exactly arbitrary either. There are some practical limits to where I can place them though so considering that I pretty much tested them everywhere they could realistically stand: corners, near walls, behind speakers, all in one place, spread out, etc.

I'll see if I can get the dealer - who also happens do to acoustic measurements - to do some testing with me.

In the mean time I'll experiment some more. As I wrote earlier they certainly do make a change although I'm not sure I prefer it like this.

[Seamus TM]

This is handy to find the best spots for them:
hunecke.de | Room Eigenmodes Calculator

An spl meter would help a lot, too.

[DanDan]

+1 to all recent posts. Take a look at your modes in that hunecke device. You will probably find the the mouths of your devices were close to or in a null. They need to be at a pressure max. That would be on the floor in a corner. A sine/SLM or even by ear, would confirm the hottest spot.
I only got some limited action when I inverted my trap or laid it sideways. LOL the double entendres....
DD