Over 24" joints

[Craig Che]

I am looking at building some speaker boxes out of 3/4" solid wood and want to do some nicer looking joints like dovetails. The problem is one of the joints would be 34" long, is there an affordable jig for this or is by hand the only way to go? I would like to use these joints because they will allow for growth/shrinkage throughout the year (am I correct here?) and add a nice visual effect. Any help is greatly appreciated. Craig

[Rick Gooden]

You should reconsider the "solid wood". No reputable manufacturer makes speakers from solid wood regardless of price. It has to do with resonance. MDF or BB plywood is the proper choice.

[glenn bradley]

Rick is on base. The resonance in solid wood panels is very undesirable for speakers. $50,000 speaker cabinets are medium or high density fiberboard with veneering. Even in the "old days" 13ply marine plywood was the desired medium.

If you are not wanting to get into large panel veneering, consider MDF with 1/8" veneered plywood laminated on. Your corners will be the challenge with this method. I have seen folks route a rabbet along each edge and add a 1/4" x 1/4" piece of matching or contrasting hardwood.

There are many locations on line and I have no affiliation (just did a Yahoo search) but start here:

http://forums.audioholics.com/forums/showthread.php?t=8645

[Mike K Wenzloff]

Hi Craig, Welcome!

As Rick said, all manufacturers I am aware of do not--and have not for a very long time--used solid wood for the reason Rick mentioned.

This seems like a good time to hone your veneering skills. That is the method I would advise. Either veneered MDF [if small enough HDF] or Baltic Birch. High layer count and voidless is what you want in the BB ply. Klipsch used 9 layer Apple ply for a while, don't know if that is what they are still using on the corner horns or not. That is what mine are.

Take care, Mike

[Jamie Buxton]

The Keller dovetail jig isn't too expensive. The jig isn't 34" long, but it can be stepped along the workpieces to do the job you're describing.

[Jim O'Dell]

If you want the look of the real wood cabinet, go ahead and build the MDF speaker, the clad it with the real wood. Veneer doesn't have to be 1/8" or thinner. Only thing is, you might need a tow truck to move them!!:eek:
But use the MDF OR HDF (never seen that, but I know it exists) for the cabinet. Your ears will thank you! Jim.

[Tim Sproul]

No reputable manufacturer makes speakers from solid wood regardless of price. It has to do with resonance.

I'm going to disagree about this. There are many fine instruments made of solid wood.

The problem with solid wood and resonance is the unpredictable nature of solid wood panels and their individual resonance 'pattern.' Each speaker would have to be custom tuned for the wooden panels and speaker drivers and cones and shape and size and such to acheive good sound if solid wood panels were used. This is a factor for why certain instruments - along with the skill of the maker - can command such high prices while others are just thrift store dust collectors.

MDF is a great choice for speakers because it is so predictable, along with having good resonance characteristics. Solid wood panels can have good resonance characteristics, you just have to sift through 1,000 panels for every one to fit a certain speaker.

[Tim Sproul]

....want to do some nicer looking joints like dovetails. The problem is one of the joints would be 34" long, is there an affordable jig for this or is by hand the only way to go?

I'd miter the joint and then cut in keys to make it look similar to dovetails. The jig is a shopmade sled that holds the box at 45 degrees to the table of the saw or router table. Many joinery books have this type of jig.

You could still do this type of effect after veneering the mdf. Another option is to think about doing something like a string inlay to add interest or simply to use nicely figured veneer.

[Gilbert Vega]

I can't remember where I came across it but I read on some internet site where one could make dovetail over 24". The only way I can imagine this to be done would be to take the stops off on a Leigh jig. Maybe someone else has come across this article.

[Joe Jensen]

I'm going to disagree about this. There are many fine instruments made of solid wood.

The problem with solid wood and resonance is the unpredictable nature of solid wood panels and their individual resonance 'pattern.' Each speaker would have to be custom tuned for the wooden panels and speaker drivers and cones and shape and size and such to acheive good sound if solid wood panels were used. This is a factor for why certain instruments - along with the skill of the maker - can command such high prices while others are just thrift store dust collectors.

MDF is a great choice for speakers because it is so predictable, along with having good resonance characteristics. Solid wood panels can have good resonance characteristics, you just have to sift through 1,000 panels for every one to fit a certain speaker.

I built custom speakers commercially for years. Instruments use solid wood to color the tone and they are carefully "tuned" to acheive the right "color". Speakers are supposed to be neutral so they don't alter what was recorded.

The most interesting set I built were made from "Studio Glass" a non-resonanant glass. Beautiful, but I never liked the sound. Sold them to somone who didn't know better....joe

[Jim Becker]

The Keller dovetail jig can be used essentially for "unlimited" joint length. (Through dovetails only, however)

But I also agree that for speaker enclosures, manufactured goods are the best choice for the carcass for consistent sound.

[Craig Che]

I didn't realize resonance could be a problem, would it work if I did a 1/4" mdf box and layed the solid wood on top of that (3/4" hickory)? I am trying to build the speakers to match my future tv stand to be made of solid hickory. I built the last ones out of 3/4" mdf with an oak veneer but wanted a better look than veneer and I don't know where to buy hickory veneer with lots of color variation.

Thanks for info on the Keller and the resonance, great forum with tons of info.

[Wilbur Pan]

Regarding resonance control, some resonance is good in a speaker. For ported speakers, it is the resonance of the speaker cabinet that adds to bass extension.

One approach to help control resonances is to add internal bracing to the cabinet (http://www.bwspeakers.com/index.cfm/fuseaction/products.techfeatures/ObjectID/3A7556CF%2D4779%2D11D4%2DA67F00D0B7473B37), somewhat like a torsion box. This approach is a bit complicated, because if you just built a typical torsion box, compartmentalizing the interior of the speaker, you would alter the bass extension (the "good" resonance) that the speaker cabinet would contribute.

[Rick Gooden]

There are so many factors that go into speaker design that the chances of getting it right without serious engineering is akin to going to Las Vegas and pulling a lever one time and winning a million dollars. Ported speaker designs are generally designed for efficiency allowing less power to produce higher SPL. The port needs to be engineered to do as little damage to the sound as possible. The size of the cabinet and the Q of the speaker (amoung other things) will determine the diameter and depth of the port which then will determine at what frequencies you will get regenerative feedback and which you will get negative feedback. The regenerative feedback (in phase) is placed in or around the 200hz level which produces a pleasant sound to most of us because we generally like a "bump" around that area. Sealed cabinets generally produce the most accurate reproduction however to produce good quality low end requires a large driver and the design is not concerned with efficiency and that translates into more power. Bracing will certainly help reduce the dimensional resonance of the large cabinet by essentially creating a series of smaller cabinets (with higher resonate frequencies). I would build the units out of MDF and veneer them. I do believe that if you built the boxes out of MDF (3/4") and then apply solid wood you would probably be OK if you mounted the drivers on the MDF with no contact with the solid wood. On a side note, I have witnessed people doing things with audio and video that are completely wrong with marginally good results - go figure.

[Craig Che]

Any more tips for doing the joints that are greater than 24"?

I talked to the guy who helped me with the original design of the speakers and he said it should be fine if I do bracing and do some of the sound proofing inside the cabinet along the walls. I am going to use the same size cft cabinet as I currently have, sounds great right now.

[Jim Becker]

I didn't realize resonance could be a problem, would it work if I did a 1/4" mdf box and layed the solid wood on top of that (3/4" hickory)? I am trying to build the speakers to match my future tv stand to be made of solid hickory.

1/4" MDF will not offer much in the way of the properties you are looking for in a speaker enclosure. 3/4" MDF boxes with a 1/16" hickory "thick veneer" might be a better choice. You want the solid stock thin to minimize wood movement issues. Anything thicker and you're going to have a problem if you just glue it to the MDF substrate.

[Joe Jensen]

Regarding resonance control, some resonance is good in a speaker. For ported speakers, it is the resonance of the speaker cabinet that adds to bass extension.

One approach to help control resonances is to add internal bracing to the cabinet (http://www.bwspeakers.com/index.cfm/fuseaction/products.techfeatures/ObjectID/3A7556CF%2D4779%2D11D4%2DA67F00D0B7473B37), somewhat like a torsion box. This approach is a bit complicated, because if you just built a typical torsion box, compartmentalizing the interior of the speaker, you would alter the bass extension (the "good" resonance) that the speaker cabinet would contribute.

Wilbur, it's not actually the resonance that extends bass with a ported speaker. The port makes the air restance that the woofer sees seem like that of a larger box. Generally, the right size sealed box is best, but the right size is huge. Ports let the small box look like a large one. The downside, is that there can be airflow sounds from the port, and those need to be managed with port diameter and length (all of which need to be carefully tuned to the box and woofer). Many speaker manufacturers put the port in front because most customers expect the port to increase bass and of course the bass needs to face the front, but in reality the location of the port doesn't matter, and generally the bass sound coming out of the port is 180 degrees out of phase, (decoded, means that the port can cancel the woofer).

Craig, If you want to build speakers there are some excellent books and a couple of good web forums. IM me if you want some pointers...joe

[Joe Jensen]

Craig, one more input. For the speakers I built I used a 1.25" thick particle board that was made from white pine and had extra high resin content. I forget the name, but it weighted over 100 lbs for a 4 by 8 sheet. The boxes were also heavily braced and then veneered. Each 36" tall, 15" wide, and 12" deep speaker weighted around 100 lbs. The current speakers I have are slimmer and a little taller (these are commercial speakers), and they weight around 125lbs each.

Last thought. Designing speakers can be very fun and at the same time very frustrating. If you are more interested in building them, I would hunt the web forums for some of the well proven designs and build one of them as some hobbiests have spent years refining these designs. I got lazy the last time and just bought a set...joe