PE curved cabinets concerns

[augerpro]

Hi all. I was doing some researching last night about the PE curved cabinets to see if anyone thinks they have a bit of resonance (I do) and what they did about. I came across a post by a guy who makes diy speaker kits and he said he measured the .38cf box to be .314 and the .5cf box to be .376 and speculated that the .75cf MTM box would .585 based on those other two. I've read Kevin H mention that the .5cf was smaller than expected for the Exodus speaker.

So I did my own measurements. I just used simple geometry to split the box up into a rectangle and some triangles and figured the volumes. I came up with .38cf = .381cf (10.8L), .5cf = .463cf (13.1L), and the 1.0cf MTM = 1.05cf (29.7L). So it seems the .5cf is a little small, although the others are fine. I was pretty happy to see this since the above quoted numbers are very far off and would drastically affect the sound if a person didn't know. I'm wondering if any of you have any experience with these curved boxes and wouldn't mind measuring yours to recheck my work? Hopefully this will be usefull info for anyone planning on using these cabinets.

Also does anyone know of a cabinet treatment to reduce wall resonances? For regular resonances I've been using soundbarrier, but that stuff is pretty spendy and shipping is making me rethink what I use. Anyone think using some 1/2" carpet pad and doubling up the thickness with 3M 90 spray would be a viable alternative? Maybe use the cheap asphalt sheet first for the wall resonance and then the carpet pad over that for the other resonances?

[rc white]

In this ESP article i look at several AES papers on the subject of enclosures..

http://sound.westhost.com/articles/ssl2.htm

These show that the most effective way to reduce resonance is to move it to higher frequencies by means of very stiff cabinet bracing reducing the effective panel size, this also greatly increases the stiffness of each panel leading to a reduction in vibration amplitude.
All that damping does is to broadband resonance, and not prevent, it because it does not increase stiffness.
The the key is making the box very stiff, in this context the best material is carbon fiber honeycomb, but thats a bit expensive, three quarter inch boiler plate is also good but thats a bit heavy.
rcw

[JJones]

You want to reduce cabinet wall resonances? (You're not asking about reducing internal standing waves, I mean?)

When you brace, break up the wall into different size sections by not putting the brace exactly in the center.

Use something like strips of wood cut along the grain, not strips of MDF or other such material.

Two layers of "roof repair tape" is going to be WAY more effective than carpet pad.

But, I agree "reducing panel size by bracing" is key.

[dlneubec]

Brandon,

Here is a crazy idea. :?? I would be a lot of work, but a cool looking and probably pretty effective treatment might be to add some contrasting hardwood elements or panels to the outside of the boxes. One might do a translam or translam effect of 3/4" hardwood stacked up the side. You could use the side of the box to trace the shape to make a pattern piece for each side. You would have to cut the pieces of harwood out of wider stock to accomplish the curve. It could be a monolithic panel or they could be stacked with a small gaps between.

[dawaro]

Someone on another forum measured the enclosues by using sand IIRC.
They measured the .38 cubic feet cabinet at .314 cubic feet and the .5 cubic feet cabinet at .376 cubic feet.

As I understand they brought this to the attention of PE but I am not sure if the information is going to be updated or not. One interesting note is that in future shipments the internal brace is going to be screwed in rather than glued. This would allow you to remove it and install more effective bracing.

I am not sure the exact name of it but there is a material you can buy at roofing supply stores that is an asphalt based material with adhesive on one side. It is made for areas with high rain/snow fall as an alternative to felt. When I was in the car audio industry we used it as an alternative to dynamat and it worked well. You might try looking around in your area. I would think any mass material like that would do what you are looking for.

[augerpro]

rcw&jjones> Thanks for the article rc. Bracing would be my first choice too, but the curved panels make that a bit of trick, that's why I was looking for an alternative. Even it involved only broadbanding and dispersing the resonance instead of actually pushing it above the woofer's pass band.

Dan>sounds interesting. Not sure my woodworking skills are up for that but I'll boucne soem ideas around and see what I can do. Thanks.

David>I think we read the same forum post then. Thing is my own calculation doesn't really agree, except the .5cf box being a tad on the small side. So I'm wondering if anyone else has done measurements on these. PE does have those asphalt sheets too, but hardware store would be cheaper I think. I'll see what HD and Lowe's has. I know there can be a concern with the vapor off these affecting the glue on some drivers, although the ones I've bought from PE didn't seem to really smell much, implying that it's probably not giving off much VOC's.

[ThomasW]

The generic PE bituminous material doesn't off-gas enough to damage drivers. The killer for this stuff is it's heavy, so I buy it when PE has their free shipping offers.

I haven't used any of the new curved sided boxes. In the older straight sided boxes, the crossover boards were usually so densely packed they damped the sidewalls of the enclosure.

[jeff_free69]

I suspect they have to be a little smaller, since they have pretty much the same external dimensions as the non-curved, except for the back of course. But in person you can see the curve is very gentle so it's not as bad as you might fear . I should be finishing my RS150 system in the .25 curved this week, but its sealed so there's no port tweaks needed and I'm using a sub ...otherwise I'd be concerned.

I love the look of the piano black! . If it turns out to sound really thin, I may do something crazy like buy another pair and stack them into siamese twins by cutting holes in the adjoining top/bottom. That would give me double volume and make it taller without making it too deep like the .5 cab is for my HT.

[Dennis H]

I am not sure the exact name of it but there is a material you can buy at roofing supply stores that is an asphalt based material with adhesive on one side.

The most common in the US is Ice and Water Shield. A whole roll of it is pretty $pendy but you could probably get some scraps from a roofing contractor pretty cheap.

http://www.graceathome.com/pages/roofingprod.htm

[dawaro]

The most common in the US is Ice and Water Shield. A whole roll of it is pretty $pendy but you could probably get some scraps from a roofing contractor pretty cheap.

http://www.graceathome.com/pages/roofingprod.htm

That is exactly it. Thanks Dennis.

[collo]

Here's a tip for finding cabinet volume.

Put a plastic garbage bag (or several if bracing requires it)into the cabinet and weigh.

Fill the bags with water and weigh again.

Each kg of water (2.2 lb) is one litre.

[augerpro]

The most common in the US is Ice and Water Shield. A whole roll of it is pretty $pendy but you could probably get some scraps from a roofing contractor pretty cheap.

http://www.graceathome.com/pages/roofingprod.htm

I'll check that out Dennis, thanks!

[joetama]

Here's a tip for finding cabinet volume.

Put a plastic garbage bag (or several if bracing requires it)into the cabinet and weigh.

Fill the bags with water and weigh again.

Each kg of water (2.2 lb) is one litre.

Interesting idea there.

The only problem would be if your garbage bag leaked... I know most of mine do... Which is why I don't throw half full beer cans in them anymore. :roll:

[benchtester]

Interesting idea there.

The only problem would be if your garbage bag leaked... I know most of mine do... Which is why I don't throw half full beer cans in them anymore. :roll:

I never have this problem. My house rules are whoever opens a can of beer has to finish it. (No one seems to mind.) :rofl:

[Martyn]

I built two pairs of speakers (cherry and maple) over last Christmas using the 0.38 cu. ft. curved boxes. Yes, they do audibly resonate. I tried various solutions including adding stiffeners, bituminous felt, and constrained layer damping. Only the latter had any significant effect. The problem with adding bracing is that the boxes are laminated from mediocre quality MDF that won't hold a screw, and the interior is too cramped to be able to work in comfortably.

My solution was to apply patches of self-adhesive mass-loaded vinyl (of the sort used to damp car body panels) and then to bond pieces of light gauge aluminum sheet of the same sizes on top of the vinyl. I haven't yet measured the result and thus can't quantify the improvement, but it is significant and worth doing. If I were to do it again, I'd cut out the middle of the centre brace to allow better access.

The finished result is very good aesthetically, it's just a shame that they suffer somewhat from the made-in-China syndrome.

[joetama]

I never have this problem. My house rules are whoever opens a can of beer has to finish it. (No one seems to mind.) :rofl:

Good idea...

[ThomasW]

rcw&jjones> Thanks for the article rc. Bracing would be my first choice too, but the curved panels make that a bit of trick, that's why I was looking for an alternative. Even it involved only broadbanding and dispersing the resonance instead of actually pushing it above the woofer's pass band..

Might consider laminating the inside with fiberglass resin and several layer of fiberglass cloth. That should make the cabinet pretty stiff...

If you're of a mind this would be a good time to mold in flat mounting pads for the crossovers.

[jdybnis]

That sounds like a good first project for working with fiberglass and resin. Anybody have a link to a tutorial online?

[JJones]

The roof repair tape with the Aluminum backing really does make a big difference if you use two layers. To get it to stick very well here's the secret trick: brush on a layer of contact cement and let it dry, then the roofing repair tape bonds extremely well, far better than on raw wood.

Also, an easy way to attach braces is with good hot melt glue. Not all hot melt glues are the same, I'm sorry I don't recall which ones are best.

When using cross-braces made of solid wood, does anyone know if hardwoods provide any significant improvement over pine?

As a test once I built two speakers with the same internal volume, but one with 1/2" walls and one with 3/4" walls (both Baltic Birch plywood). Surprisingly?, the one with thicker walls had worse resonance problems. The somewhat extensive bracing and damping I was using seemed to be more effective on the cabinet with thinner walls.

[DaytonAudio]

Internal Volume of Dayton Audio Cabinets

...SNIPPET "As I understand they brought this to the attention of PE but I am not sure if the information is going to be updated or not...."

Information regarding the internal volume measurements was passed along to the product engineers here at Dayton Audio and we discussed things this morning. At the bottom of this post you'll find the actual manufactured internal volumes of both the traditional and curve cabinet designs.

Additional comments follow:

All cabinets are slightly larger than advertised with the exception of .5 ft³ cabinets which are .494 ft³ for the traditional and .477 ft ³ for the curved sided. The traditional is 1.2% undersized and the curved sided is 4.6% undersized. Although the .5 ft³ curved sided is undersized (slightly) it is certainly in the ballpark and would not change any aspect (f3, Qtc etc.) of a box/speaker combination, therefore we feel it isn't necessary to change how we advertise them.

Due to the shape of the curved sided cabinets it is almost impossible to measure within ± 5% using a ruler. Accurate measurement would require geometry and or calculus, another method would be to fill the enclosure with some material (small beads, popcorn, sand, water), empty the contents into a basic shape enclosure and measure the amount

Finally, we are working on getting all Dayton cabinet drawings up on the website. The drawings indicate the box volume so this may help, but even with the detailed drawings it is difficult to derive internal volume of the curved sided cabinet.

Feel free to pass comments, suggestions, or questions directly to us here at Dayton Audio. My email address is: richtATSIGNdaytonaudio.com

As always, we thank you for your patronage! :T :T

Rich Taylor
Brand Manager
Dayton Audio


MANUFACTURED DAYTON CABINET INTERNAL VOLUME

TRADITIONAL ft³

0.25 TWO-WAY 0.281
0.38 TWO-WAY 0.387
0.5 TWO-WAY 0.494
0.75 TWO-WAY 0.780
0.75 MTM 0.763
1.0 MTM 0.999
1.0 SUB 1.084
2.0 SUB 2.084
3.0 SUB 3.122

CURVED
0.25 TWO-WAY 0.283
0.38 TWO-WAY 0.392
0.5 TWO-WAY 0.477
0.75 TWO-WAY 0.788
0.75 MTM 0.763
1.0 MTM 1.010

[ThomasW]

Thanks for clarifying that Rich... :T

[augerpro]

Indeed, thank you Rich!

[kevinp.]

color me skeptical. I'd like to see some real third party measurements.

[joecarrow]

I thought it was a helpful response- and I'm glad that someone is paying attention and speaking to the community. If your speaker design is terribly sensitive to enclosure volume, then why trust anybody's measurements but your own?

[jkrutke]

Someone on another forum measured the enclosues by using sand IIRC.
They measured the .38 cubic feet cabinet at .314 cubic feet and the .5 cubic feet cabinet at .376 cubic feet.

I've measured all of the standard rectangular cabinets except the .75 cu ft models. All of them are close enough to be in the ballpark for which they are advertised. If someone measured the .5 cu ft model at .37, they did something very wrong. The "sand" method doesn't sound very trustworthy.

I modeled these on cad, using actual dimensions, and properly subtracted out gusseting. I even subtracted out the corner angle gussets and added back in the holes on the shelf gusset. My own numbers are within 1 cubic inch accuracy. That said, it's generally stupid to go after than kind of accuracy, I just do it because I'm a little obsessive. Trust PE's sizes. It's not like anyone's tuning predictions would be right on even if they had the exact cabinet and port sizes.

[augerpro]

color me skeptical. I'd like to see some real third party measurements.

I am a third party :

Although my measurements were roughly close, I did not use a CAD or any volume filling method. Rich's posted numbers seem pretty reasonable.

[kevinp.]

ok, if you guys say so I'll beleive you; I just have a hard time understanding how a curved box that comes to a point 4 inches narrower on the longest dimension measures almost exactly the same as the straight one which is only .5 inches deeper.

[augerpro]

kevin I believe the depth listed is incorrect for the curved boxes as most are the same as the square ones. Don't quote me on that since I haven't measured that dimension yet, but I believe that is the case.

[Rick Craig]

I have both the standard .5 cubic foot and curved back .5 loaded with the same design (sealed box). I'll run nearfield curves to see how they compare.

[jmb]

The curved cabs are actually 1.5" deeper.
12.5" for the rectangular, 14" for the curved.

[Landspeeder]

I'll upload a picture very soon, but if you have a router you can very quickly make 2 Aluminum braces (or plywood?) and either polish them (or stain them). They will wrap around the outside of the box (top/back/bottom) with an agressive curve that compliments the box. They will also have a hole drilled for a treaded rod to extend through the box to basically 'clamp' this bad boy down. If you wanted to, you could also use automotive adhesive to bond the entire brace to the box for a very perpement attacment.

[kevinp.]

The curved cabs are actually 1.5" deeper.
12.5" for the rectangular, 14" for the curved.

well that makes more sense then

[jmb]

Posted at Tech Talk

"Update

Well the resonace issues proved to be non-issues. A little Dynamat
on the side walls was more than adequate.

This issue involves mounting the baffles permanatley.
It may just be the 2 cabs I have, but when I was gluing the baffles on this weekend, using a two part epoxy, I noticed that there was no squeeze out.
This baffled me because I was pretty liberal with the epoxy, and expected some excess after tightening the screws. I did a little investigation with the second cabinet and found the baffle recess to be at least a 1/8" deeper than the edge of the baffle that should make contact
What is the baffle suppose to "grab" onto?
Are the screws and a little weather stripping suppose to do the job?

Beware
Before gluing, measure the recess and baffle edge and make sure that these two parts will actually meet and make contact."

[Martyn]

With my cabinets, mass-loaded vinyl alone wasn't sufficient (and I tried adding a few other materials as well) - it wasn't until I added a constraining layer that I saw the big difference.

On the subject of the fit of the baffles, both of my pairs have a slight taper on all four sides of the rabbets. Thus they are not intended to bottom out in order to seal - the seal is made by the taper. Nonetheless, I found some differences in construction between my two pairs, so yours might be different.

Edit: Incidentally, don't torque down those socket caps too much or the baffle will deflect. Just pull them down evenly and let the taper do its job.

[Landspeeder]

This probably no longer applies... but:





quickly make 2 Aluminum braces (or plywood?) and either polish them (or stain them). They will wrap around the outside of the box (top/back/bottom) with an aggressive curve that compliments the box. They will also have a hole drilled for a treaded rod to extend through the box to basically 'clamp' this bad boy down. If you wanted to, you could also use automotive adhesive to bond the entire brace to the PE curved box for a very permanent attachment.

[Hdale85]

Wow I like that a lot actually! Problem is getting those made in aluminum at an affordable price Probably would be at least 100 bucks.

[augerpro]

Looks cool landspeeder! Great way to use the curved cabinets for a center channel. Hmmm, I can just see using chrome braces on a bright red cabinet for futuristic Jetsons' look

[Hdale85]

Or the piano gloss black cabinet.

[Landspeeder]

mmm... That could be very sexy...
oops on the aluminum price
.75" Aluminum Plate 6061 T6 is $150/square foot
Well... 1" ply would work... spend some time on prep and paint... and it could look nearly as good as polished aluminum

[Hdale85]

Nah it would have to be aluminum

[Landspeeder]

Or.... you could first wrap the PE case in a couple of sheets of Carbon Fiber... a ton of resin, sand it down and clear coat it.... then Aluminum braces and endcaps.