Friday, August 24, 2012

Dahlquist DQ-10 Loudspeaker Stacking Stands

I've always been into vintage stereos.  

About 5 or 6 years ago I came across my first pair of Dahlquist DQ-10 loudspeakers

The bass speaker on a Dahlquist DQ10 is mounted in its own speaker cabinet.  The driver used is the same one used in the famous "Large Advent" speaker, which really revolutionized high fidelity due to its new (at the time) "acoustic suspension" cabinet where air compressed inside the box dampens the movements of the bass driver, providing tight, accurate bass.  Much like the Large Advents, the bass on the Dahlquists is deep and warm and round. Although somewhat lacking in it's accuracy and its ability to reach way down into the depths of synthesized musical sounds and some of the very low bass effects common on today's pop music, its ability to accurately produce wooden bass sounds such as the electric bass guitar, string bass, drums and reed instruments is absolutely stunning. 

There are four other drivers reproducing the higher frequencies. All of these drivers "float" in space on melamine baffles without boxes. A large 2" softdome midrange and a 1" hard dome tweeter share tweeter duties, while a traditional midrange woofer handles frequencies in between. 

A fairly cheaply made piezo horn tweeter is fed all frequencies in the very, very high register. Perhaps it is the quality of the speaker driver, or the combination of the horn and the dome tweeters, but many DQ10 fans, including myself, does not care for the sound contributed by the horn tweeter. I, and many others, have it disconnected. 

I believe it is the combination of the free-floating speakers producing mid-range and treble vs. the warm and round bass emerging from the acoustic suspension cabinet which gives the DQ10 its distinctive sound. It is almost the ideal acoustic music speaker and reproduces voice, wind and wood instruments with clarity and precision. 

Because the sound emerges from the front and back of the speaker, for best sound the speakers need to be placed at least 3 feet from any rear or side walls. With two DQ10's arranged in stereo, two-channel stereo recordings emerge from a soundstage which not only has a left and right component, but also a depth of field.  Music also appears to emerge from places outside the sound stage, for example to the left of the left speaker, or to the right of the right speaker. Two-channel stereo recordings of small jazz ensembles, chamber music and pianos and vocals are utterly lifelike. 

Dahlquist expanded this idea by introducing something he called "phase array", placing the speakers at different distances from the listener's ear based on the frequency. He speculated that the human ear hears higher frequencies "sooner" than bass frequencies. Thus be placed the higher frequency drivers further away than the bass speakers. 

The problem with this boxless design is that the speakers are very inefficient. DQ10s will soak up 200 watts and not produce volumes sufficient to satisfy a listener (well, me at least!). 

The answer is to stack two DQ10s together, two on each left and right sides.  In this way, you can drive the speakers together to produce more volume. (Note the distance the speaker is placed from the rear and side walls, for the best sound.)


The Upper speakers are flipped upside down to place the speaker array in close proximity to the lower array.  

These two photos are off the internet.   When I started researching stacking DQ10's I realized that my idea was not new.  This design that you see here appears to use 1/4" flat steel bar for the side panels and legs. A novel idea, but I dont think it is very sturdy and looks like it would wobble side-to-side.

After aquiring a 2nd pair of DQ10s early in the summer and restoring them, I decided to make my own stacking stands. I will blog about the speaker repair later.

First let's make some legs. 
I cut some 1/4" x 3" flat steel bar and began drilling some holes. I'm halfway through the drilling process in this photo.
Then, I cut some round stock in 2.375" x 0.156  and 2" x .125". The big 'uns are 4" long and the short ones are 3".
I also sliced up some 1/2" bar stock.
I welded the bar stock bits in between the flat bar to make "feet" for my stands. 
I welded inside the holes to make invisible welds.  Then I filled the holes with weld and ground them flat. 



I added a nut bung on the back of the tube and welded the feet to the base tube.

With the bases built and somewhat functional, I decided to focus on the "arms" that would hold the speaker racks.  Since the speakers are not a predefined width, I decided to make arms that could vary in width.

One arm is fixed and the other pivots.

I cut some parts and laid out them out on my welding table.

The most complex part is the center clamp/pivot.

Once that was tack welded, I made up some arms.

At the ends of the arms, the stands and rack "interface" using a shaft and tube connection. This same system is also used to construct the hinge on the pivoting arm. 

Holes were drilled and roll pins inserted to keep the hinge pins in place.

The stands so far.

The one arm pivots out on its hinge to accommodate a wide range of speaker widths.

Now that the stands were mostly done, I began to focus on the speaker racks themselves.

I wanted to construct a rack that could be used with one pair of speakers...or two pairs of speakers, stacked one on top of the other with the speaker set on top being "up side down".

I did not want to drill into the speakers or modify them in any way. I made rails that used the existing grille bolts (which are quite heavy duty).

To this rail, I added a tube which mates with the "pin" on the two arms on the stands (seen in the photo directly above).

Trying out the first set of speaker racks for the first time! 

Looking good!!!

Once I had the lower speaker rack made, I focused on making a pair of racks for the upper speakers. These are made in such a way so that the upper speakers are flipped up side down. Both the upper and lower speaker racks sit on top of one another on the same pin, as seen in the photos below.

Trying out the second, stacking set of racks for the first time. 

I'm 5'11", so these speakers are pretty tall!!

Once I had the entire speaker put together, I realized that they are pretty heavy.  I decided that I needed a safe way to level them on the floor so that they sit plumb to the floor.

I cut out some semicircular bits and drilled a hole. Then I welded a nut to this piece.

I flipped it over and welded it inside the large tube on the bottom of the stand base.

So I could screw in a screw-jack style leveling foot.

I did a similar thing with the fronts.

Now that everything was built and tested, it was time for paint. 

Except for the mating pins (which have a close tolerance fit and can't be painted), and the aluminum main posts, I painted the entire rig rustoleum black. 

After it was dry I got to move it into the living room!

First, let's try one set of Dahlquist DQ-10. 

These were freshly restored, repainted, the ends refinished and the grilles reupholstered in very attractive antique white, burlap material. 

Now let's try TWO pairs! 

They sound as good as they look. 


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