Dope from Hope papers to build acoustic panels

[john4618]

Does anyone know where I can get the Dope from Hope papers for building acoustic room panels ???

Im told there was a web site, and I searched for it but could not find it ???

[Dflip]

Contact Justin at justin@soundwise.org. He made a pdf version of the files that he got from...(not sure who exactly had the files originally).

[DrWho]

Justin was the one who acquired all the papers and scanned them and created the adobe file. I would post a direct link to the file, but Justin asks for a small donation to cover the costs of producing it (it will then become free once his costs are covered at which time the link will be on his website).

You'll find him at www.soundwise.org

[WMcD]

Look at my 7/14/03 post in Technical Questions. There I managed to post the back page of the DfH. Evidently I didn't get back to the project as I'd said I would. Now file attachment isn't working.

I can e-mail anyone the two pages. The file is somewhere at the office.

Also, you should look at The Master Handbook of Acoustics. I've seen it in Borders. It has a few pages on polycylinders, and building them.

It cites to an article by a fellow with a Russian name who did some more study. He reports, with data, that stuffing the panels with fiberglass gives some bass absorption. Something I wanted to follow up on and get a copy, along with the Boner, Ph.D. article which is PWK's source. Time for an interlibrary loan.

Building more is a long postponed project for the apartment.

I did have some questions on the amount of bulge and how to build them out of Masonite. Masonite does bend better than foamcore. Looking at the MHoA, it looked like there was more bulge than PWK suggested. Also we have on the forum some picture of PWK's actual installation where the reflector is a half cylinder. I.e. a lot of bulge.

I've bought some maps and posters as cover material. Also I thought I'd make ribs in the form of a portion of circle to fasten them to. This is in distinction to the bow and bow string type construction shown by PWK and the MHoA.

Also, I thought I'd try a truncated arc where a flat side is up against a wall or ceiling.

In any event, I have a spreadsheet which starts with the poster size and the degrees of arc as input. Then it calculates the resulting "crown" bulge, the radius, and size of the back.

The next problem is how to cut the curved ribs. You could rig a big compass to draw the arc. But I've done some math to give data points.

Again, this is available by e-mail. Right now the spreadsheet is on Lotus wk1 format (my HP LX-200 palmtop, use on the CTA bus computer), and the graph will have to be redone if you use Excel.

Best,

Gil

[WMcD]

Look at 6/15/03 post in Technical Questions about Styrofoam.

Down near the bottom is a picture of a reflector I made out of foamcore. This was for my office, which is is square in floor plan and had a high pitched slap echo. I made two.

I think they helped.

I've seen some people comment that the surface should be made of soft material, or that hard material is not much of an improvement. My thought is that it is supposed to be hard to make the off axis reflection.

My other thought is that "bigger is better". At least it is easier to build one big one than two small ones. So I went to the poster store and ordered the biggest Monet posters available. Actually, they are not bad looking.

Gil

[DrWho]

Yikes! I just remembered something...

Artto was the one who put together the Dope from Hope papers (300+) and then Justin was the one who went about scanning them to get an electronic copy.

Just putting due credit to where it belongs

[Dflip]

When I got my version of all the Dope from Hope files in pdf, it was for a $5 donation to Justin to cover his costs. Pretty cheap when you considerthe size of the file and number of pages.

[WMcD]

I visited Borders to check the Master Handbook (4th Ed). It is not quite as I recalled and doesn't have the info on stuffing.

So I must be remembering something else.

Dang. This is the danger of relying on memory and using Borders as a reference library.

Gil

[WMcD]

Gee, this was annoying. I had to go back to Borders, again.

Yes, after all, the MHoA (4th Ed) does have a section (Ch. 9) on polycylinders stuffed with mineral wool. I suppose that is fiberglass. However it is in a different section that polycylinder reflectors and doesn't appear in the index with reflectors.

The reference to a Russian guy is not to an article but rather a book. Mankovsky, V.S., Acoustics of Studios and Auditoria, London Press, Ltd. This is a very widely quoted book. If you put it into a search in Amazon, there are many cites.

All of this deserves a closer look.

In the MHoA there is a section on making sound absorber panels out of building insulation and a comparison of the paper facing out and facing in, and different thicknesses.

It looks to me like the stuffed poly has bass absorption similar to the absorber. This is not quite clearly compared. I'd expect the high frequency diffusion is better with the poly cylinder surface added.

I note that Mankovsky (as in MHoA) is using a polycylinder with a bulge, or crown, of 1/3 of the back. The DfH design numbers are less.

However, if you look at some of the graphs, I believe that there is a lot of convergence in the pure absortion panel, the unstuffed poly, and the stuffed poly.

If you make a stuffed polycylinder to the indicated dimensions, you wind up with a rough appoximation of the absorber's depth.

Maybe what is going on is that the ply or Masonite hardboard surface of the poly is essentially transparent to bass and thus "looks" like a pure absorber.

The MHoA also has descriptions of tube traps to be put in corners. That is also a mass of absorbant material with a paper cylindrical surface. A variation on the same design. So, many of these designs are essentially the same.

My take is that if sound radiators in a corner are effient at radiating, and setting up room resonances, then the absorbers placed there will do the same, in reverse. Every one is fishing in the same water.

A final question is: Are absorbant / diffusers the magic bullet to ALL room problems? It seem improbable.

OTOH, maybe they are for most. This could be so if one considers that all rectangular rooms have the common problems, in general, created by walls facing each other. Anything which alters that by absorption and diffusion may tend toward a more favorable condition.

Best,

Gil