Cabinet Treatment Suggestions

[Loren42]

Greetings!

I am nearing the end of the journey with my DIY 3-Way system using a 15" JBL 2235H for a woofer in a 6 cubic foot vented enclosure (tuned to 28 Hz). The system is tri-amped.

I am about to veneer the outside with some awesome koa, so I am making the last minuted touch ups to the exterior and now is a good time to address any last minute items inside since I have to pull all the drivers.

My question is one of bracing and internal treatments to the cabinet to reduce resonances. I have braced every panel asymmetrically. The enclosure is made from 3/4" MDF. The mid and tweeter have their own cabinet.

Here is a rendering showing the overall cabinet. It is about 24" square at its widest, 20" square at the top, and the overall height is about 34".

http://www.mdbq.net/pyramid3d.jpg

Here is an isometric cutaway of the interior looking from the back. All the braces are 3/4" thick, either 1.5" or 2.345" wide.

http://www.mdbq.net/pyramidbracing.jpg

Ports are removed for clarity, but the two holes for the flared port tubes are shown.

Fill is 1" thick polyester over most exposed surfaces, I'd say about 80% covered, which may be a bit too much?

Any thoughts as to what else I should do?

Thanks!

Loren

[richluvsound]

Hi Loren,

nice degisn BTW. There are a couple of things you may want to consider !

Why not make the ports , either down or rear firing !

The other point is, " diffraction " This is where the sound interacts with any sharp edge on the baffle assembly.

There is plenty of information here and on the net regarding this theory !

Good Luck, Rich

[Mr. Widget]

I am guessing you are a little far along in the process for this conversation.

If your braces are 3/4" MDF they will do almost nothing, 3/4" hardwood or marine grade birch plywood would be better... some simple geometry changes better still and double the weight of the bracing also a good thing.

Beyond that, I really do not care for polyester batting. 1" fiberglass http://www.wrap-on.com/contact/contactus.html or 2" Sonex are both quite good. Either of these will reduce the amount of upper bass and midrange coming back through the cone of your woofer... even with a fairly low crossover frequency the added midrange clarity good damping offers is quite significant.


Widget

[Mr. Widget]

The other point is, " diffraction " This is where the sound interacts with any sharp edge on the baffle assembly.Good point, but it may be too late for this.... if each of these planes will be veneered, giving them a generous radius with the judicious use of a router may not be an option.


Widget

[Loren42]

Hi Loren,

nice degisn BTW. There are a couple of things you may want to consider !

Why not make the ports , either down or rear firing !

The other point is, " diffraction " This is where the sound interacts with any sharp edge on the baffle assembly.

There is plenty of information here and on the net regarding this theory !

Good Luck, Rich

What advantage would downward or rearward pointing ports be?

One reason I choose baffle mounted ports was to insure that there was no phase delay between the woofer cone and the port. I may not be right, but it would seem to me that a port's job is to either reinforce or cancel (in the case of a resonance) the frontal wave of the woofer.

If the port and woofer are not on the same baffle it would seem that there would be a further delay between the front wave and the back wave of the woofer. Would this not change the tuning of the cabinet?

I would like to know more about that if you can explain.

As far as diffraction, one of the aims of the top portion of the cabinet was to slope the side backward to ease diffraction. The woofer is another story. I guess rounding is a possibility, but what would be a minimum radius?

[Loren42]

I am guessing you are a little far along in the process for this conversation.

If your braces are 3/4" MDF they will do almost nothing, 3/4" hardwood or marine grade birch plywood would be better... some simple geometry changes better still and double the weight of the bracing also a good thing.

Beyond that, I really do not care for polyester batting. 1" fiberglass http://www.wrap-on.com/contact/contactus.html or 2" Sonex are both quite good. Either of these will reduce the amount of upper bass and midrange coming back through the cone of your woofer... even with a fairly low crossover frequency the added midrange clarity good damping offers is quite significant.


Widget

Interior treatments are easy to do. I was looking at something called Damplifier Pro (http://www.secondskinaudio.com/vibration-mat/damplifier-pro.php?category=70) as an option. Any thoughts?

Fortunately, all braces are either 3/4" hard wood such as poplar and oak, or cabinet grade plywood for the portions in the middle and top of the cabinet.

The lower cabinet uses 2-3/8" by 3/4" hardwood on the walls ant it trimmed to allow the port tubes to pass at the bottom.

MDF is only used for the cabinet walls.

Which product of the Wrap-On family are you recommending? The only thing I saw on the web page was a 6" wide fiber glass wrap for pipes.

I'll look into Sonex, too.

What are your thoughts on the amount of dampening material and where best to apply it?

[Mr. Widget]

Which product of the Wrap-On family are you recommending? The only thing I saw on the web page was a 6" wide fiber glass wrap for pipes.

I'll look into Sonex, too.

What are your thoughts on the amount of dampening material and where best to apply it?
I use Wrap-on fiberglass insulation. It is virtually identical to the stuff used in the classic JBLs. It is 1" non shedding, and yes it is yellow. You can get a 24" wide by 50' roll in a box (part number 16550) shipped to you for around $30. Contact http://www.wrap-on.com/ and they will give you the name of a near by stocking distributor or as in my case a distributor willing to ship it to you.

I have used this stuff for years and it is by far my favorite. Unlike house insulation it doesn't sag with time and since it is non shedding it is much nicer to work with.
I would use a 1" layer on all surfaces except for the front baffle.


Widget

[4313B]

What advantage would downward or rearward pointing ports be?

One reason I choose baffle mounted ports was to insure that there was no phase delay between the woofer cone and the port. I may not be right, but it would seem to me that a port's job is to either reinforce or cancel (in the case of a resonance) the frontal wave of the woofer.Mounting on the front panel with the woofer also maintains efficiency.

Using fiberglass insulation goes a long way in reducing the noise level of all the spurious resonances that will emanate from it. If you use some other kind of fill besides fiberglass then put the port on the back to help mask all the "noise" that will emanate from it.

Note that JBL used rear ports on many of their designs for one reason, it would look like crap if it were on the front instead. A nice grille negates that issue.

Fiberglass also negates pretty much all internal driver and bracing displacements so the box you build usually ends up with gross and net effective volumes being pretty much equal providing it is well braced and sealed (other than the port) to minimize loses.

[Ian Mackenzie]

I reasonable amount of fibreglass amounts to absorbing 99% of the sound energy so it helps deal with all the issues.:)

[Loren42]

I am looking at rock wool for a fill material, too.

[Ian Mackenzie]

I suggest you buy the 7th Edition of the Loudspeaker Cookbook.

It dispell's all the what if diy questions and voodoo from the nonsense facts based on a lifetime of real experience.

The only real negative issue for front mounting the ports is where the woofers mid range output can cause comb fltering effects with the midrange leakage via the front port or vent (as in the Onken style enclosure).

Enough fibre glass fill and sensible placement of the port should minimise this type of problem. I agree front ports are not visually appealing and they can cause diffraction issues if placed near HF transducers.

With rear mounted ports the above is less likely to be an issue but rear mounted ports can augment the effect of port output. This can be used to advantage in hi efficiency systems that are not typically extended LF woofers.

With the bracing I would run a front to rear 3 x 1 hardwood or oak material from the point just above the woofer to the rear panel. Also run diagonal braces from adjacement panel surfaces and interlock for nominal panel stiffeners (3 x 1 inch).

You will also need to trim your ports as their proximity to the side walls will probably cause a shift in tuning at Fb.

[Mr. Widget]

Interior treatments are easy to do. I was looking at something called Damplifier Pro (http://www.secondskinaudio.com/vibration-mat/damplifier-pro.php?category=70) as an option. Any thoughts?I somehow missed this part of your post before. Sheeting like this is particularly useful in very rigid enclosures with minimal mass... think rigid fiberglass or metal walled cabinets or even one made of thinner hardwood. For a box made out of MDF it really won't make much of a difference. The MDF is already more of a sponge than a bell and it has a fair amount of mass. For damping sheets to be effective they must have a fair amount of mass relative to the ringing surface they are to control.

I agree with Ian's comments on the additional bracing. Realize that MDF has a structural integrity closer to al dente pasta than a steel I-beam.


Widget

[Loren42]

I suggest you buy the 7th Edition of the Loudspeaker Cookbook.

It dispell's all the what if diy questions and voodoo from the nonsense facts based on a lifetime of real experience.

The only real negative issue for front mounting the ports is where the woofers mid range output can cause comb fltering effects with the midrange leakage via the front port or vent (as in the Onken style enclosure).

Enough fibre glass fill and sensible placement of the port should minimise this type of problem. I agree front ports are not visually appealing and they can cause diffraction issues if placed near HF transducers.

With rear mounted ports the above is less likely to be an issue but rear mounted ports can augment the effect of port output. This can be used to advantage in hi efficiency systems that are not typically extended LF woofers.

With the bracing I would run a front to rear 3 x 1 hardwood or oak material from the point just above the woofer to the rear panel. Also run diagonal braces from adjacement panel surfaces and interlock for nominal panel stiffeners (3 x 1 inch).

You will also need to trim your ports as their proximity to the side walls will probably cause a shift in tuning at Fb.

Thank you. Maybe the 7th edition is a good idea. My 6th is falling apart. ;-)

I am a little fuzzy on the brace you cited that runs just above the woofer. The current cabinet has a square 3/4" thick piece of cabinet grade plywood that sits horizontally above the woofer that is fully attached to all four sides of the cabinet. The plywood has two holes cut into it so that the upper portion of the cabinet is open to the woofer. You can see it in my cutaway drawing (see my first post) as the dark green plate. Is that okay? Of course the midrange/tweeter enclosure is fully sealed from the woofer.

I like the idea of diagonal braces sub-dividing the larger panels. I can easily do that.

My ports are just below the woofer, so they are as far from the mid as they can get. I am adding black flush mounted flares to the front of the ports. I think the look is pretty good with the ports, but that is just personal taste.

One upgrade would be a better 6.5" midrange. Currently the Eminence LAR-MR is used, but I don't feel quite satisfied with the performance. Any recommendations for a ~6.5" midrange?

[Mr. Widget]

One upgrade would be a better 6.5" midrange. Currently the Eminence LAR-MR is used, but I don't feel quite satisfied with the performance. Any recommendations for a ~6.5" midrange?I don't know enough about your system to actually make a recommendation, but this is an excellent mid.

Audax PR170M0 6.5" Midrange


http://www.madisound.com/catalog/product_info.php?products_id=90


Widget

[Loren42]

I don't know enough about your system to actually make a recommendation, but this is an excellent mid.

Audax PR170M0 6.5" Midrange


http://www.madisound.com/catalog/product_info.php?products_id=90


Widget

Thanks!

right now I have:

JBL 2235H
Eminence LAR-MR
Morel MDT-37

System is tri-amped. Active crossovers set at 400 Hz and 3,500 Hz using an Ashly XR2001.

As far as I can tell, it should not be a problem to raise the lower crossover frequency to 500 Hz, but I don't really know how the 2235H behaves at that frequency. Anyone with experience there?

I have a 22" wide baffle on the woofer, so I should get a baffle step at 210 Hz or so. My room complicates things because it is 13' by 33" and is pretty live. In Florida everything is tile and drywall and my home is no different. Speakers will be placed along the 13' wall, but due to their size they live pretty close to the corners, so room reflections are going to be something we have to live with.

The mid is in a sealed enclosure about .25 cubic feet (not subtracting drivers). The woofer is an a 6 cubic foot enclosure tuned at about 28 Hz. Actually, I have been experimenting with 24 Hz and boosting the bass electronically.

We have played around with three different types of woofers and the 2235H has proven to be a damn great woofer. It would be nice to build the rest of the system to compliment that.

[allen mueller]

Has any one used recycled cotton insulation in a cabinet. I was wondering if it could be a good alternative with out the hassles of dealing with fiberglass insulation. Below is a link to what I'm talking about.

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100661753&N=10000003+90015+531841


Allen

[Mr. Widget]

I have used UltraTouch in several in-wall applications and am even using it in my garage to reduce sound transmission... it might be excellent in speaker cabinets. No harm in giving it a shot, though I'd look for a more respectable place to buy it. I can't see giving those folks the sale. :)


Widget

[badman]

Biggest problem with ultratouch is sourcing. Both in terms of getting the amount you want (though it's not pricey) and finding the stuff.

It's been used for a variety of acoustic damping purposes including in-box use and those who have used it (that I've seen) regard it as about the best absorbtive material available. This is likely due to it's inconsistent fibers and density, helping increase the bandwidth. As we know, absorbtion changes with frequency for all materials.

[Mr. Widget]

Biggest problem with ultratouch is sourcing. Both in terms of getting the amount you want (though it's not pricey) and finding the stuff. My local lumber yard stocks it, though you have to buy it by the bail... no problem when you are stuffing walls or ceilings, but there would be quite a lot left over for most speaker applications.:)

Thinking about it a bit more, I bet it would be good for in cabinet use, though it is tough to cut to shape and it is a bit dusty. It is also rather heavy which typically is not a concern.


Widget

[speakerdave]

I haven't done price comparisons, but looks like these guys will send it to you. They have packages of various sizes.

http://www.soundaway.com/Ultratouch_Insulation_s/79.htm?gclid=COz6_v-w05sCFRlcagodfyyHLA

[4313B]

Has any one used recycled cotton insulation in a cabinet. I was wondering if it could be a good alternative with out the hassles of dealing with fiberglass insulation.:dont-know

We would have to build several test boxes and see how it performs.

It doesn't appear to be available in 1" thick rolls.

[Mr. Widget]

It doesn't appear to be available in 1" thick rolls.Good point... and as much as I dislike the fiberglass itchies, the Wrap-On product is easy to get, use, and store... and it does work extremely well and predictably.


Widget

[badman]

I don't know enough about your system to actually make a recommendation, but this is an excellent mid.

Audax PR170M0 6.5" Midrange


http://www.madisound.com/catalog/product_info.php?products_id=90


Widget

It is indeed an excellent midrange. Just don't go mistaking it for a midwoofer, it's extremely Xmax limited, and wants to play 300Hz-5kHz or so. You don't necessarily need a filter for the top end of it, which is fairly well-controlled, despite the breakup, it's inoffensive.

Max Speakers PR65Neo is a monster mid, extremely dynamic, but has a nasty 4.5kHz breakup that needs some work to control.

Also, yeah, you have to buy a lot of the cotton, and it's not the easiest thing to work with, but it's not expensive, and doesn't give you cancer....

[allen mueller]

Thanks for the input about the cotton. I don't have any projects coming up, but the next one I think I'll give the cotton a shot at least at the test phase.

Allen