How to calculate depth of a slanted panel absorber?

[Armans]

Hello! I have been reading the resources on the site and am finding them very helpful so thank you. I am interested in learning more about low-end panel absorbers, especially the angled front ones like these http://johnlsayers.com/Recmanual/Pages/ ... encies.htm. I know you need to use the depth of the panel to calculate the resonant frequency but:

1) How do you calculate the height of the panel if it is angled? Do you take the measurement where the panel is at its highest?
2) Why are these panels perforated in John Sayers designs?

thanks again

[Armans]

24 views nobody here know the answer to this? I thought these angled panels were popular treatments over here

[Gregwor]

Sorry, I haven't had much time to write on here otherwise I wouldn't have left you hanging.

1) How do you calculate the height of the panel if it is angled? Do you take the measurement where the panel is at its highest?

I don't entirely understand your question. The height of the panel has no affect on any parameters here. Like all acoustic treatment, the bigger the foot print, the larger the impact. Do you mean the deepest? The beautiful thing about angled treatment is that it creates a wider Q factor. Ex: at the most shallow point, let's say the affected frequency is 230 Hz. At the deepest, it is 70 Hz. In theory, that treatment will affect those frequencies and every frequency between them.

2) Why are these panels perforated in John Sayers designs?

Perforated or slot panels create a Helmholz effect in a sealed/tuned device.

Greg

[Armans]

Thanks for the your reply and apologies for my terminology. I meant deepest, not highest. Over on John Sayers site there are instructions for building "Panel Absorbers". In the instructions it says:

The two factors determining the frequency of absorption are:

The mass or density of the panel.
The depth of the air cavity, i.e. depth of the sealed timber frame.

You kind of answered my question though because you said that if the panel is angled and the depth varied then the Q factor widens meaning you get a wider absorption range. What calculation can I use to figure out what depth corresponds to what frequencies? Like say I want to absorbe 60 - 240. I will need to use both those numbers in the calculations right?

[JasonFoi]

http://www.mh-audio.nl/acalculators.asp#showcalc