Wall Speaker

[Paul Joppa]

I just posted about the Climax and Straight-8 crossovers, noting among other things that simple theoretical crossovers were not suitable because the drivers did not have a sufficiently wide overlap of flat response.

Almost three years ago I posted about a two-way design that used fullrange drivers so that there was a substantial overlap. This permits the use of a simple first-order crossover, though of course the deep bass and high treble will retain the limitations of fullrange drivers. The design is a flat panel, intended to be mounted flush to the wall. Here's a link to the original thread:

http://db.audioasylum.com/cgi/m.mpl?forum=bottlehead&n=116387&highlight=wall+speaker+Paul+Joppa

Bottlehead tsingle999 actually built a set, and has posted about the experience, but I haven't located the other threads yet.

I wrote an article for VALVE many years ago giving a passive line-level crossover (first order) that would be suitable for bi-amping this design.

 

[Paul Joppa]

I copied my posts from the old forum on this design, in case it disappears:

====================================================

OK, here's the idea. I have a nasty cold right now so I'm not up to making a drawing and finding a place to post it - I'll take the easy way out with an ASCII diagram.

Basic idea is two panels about 2 ft wide and 4 ft tall - these are often available pre-cut at lumberyards. (Or buy a full sheet and heve them quarter it!) Then get some boards about like 2x4s. This is the hard part, finding dimensionally stable boards that have flat finished surfaces and a precise width. You'd like them to be around 3.5-4" wide, and at least 1" thick. You cut to size and glue them on edge in this pattern to one of the plywood sheets:

 ----------------------- 
 (port)     |     (port) 
 -------    |    ------- 
 |          |          | 
 |          |          | 
 |          |          | 
 |          |          | 
 |          |          | 
 |     WOOF | WOOF     | 
 |          |          | 
 ----------------------- 
          TWEET 
 ----------------------- 
 |          |          | 
 |     WOOF | WOOF     | 
 |          |          | 
 |          |          | 
 |          |          | 
 |          |          | 
 |          |          | 
 -------    |    ------- 
 (port)     |     (port) 
 -----------------------

Cut holes for the woofers and tweeter in the other sheet and glue it on top like a sandwitch.

The "tweeter" is now installed in a short transmission line - actually a dual line, both sides being about 12" long. Stuff it with Acousti-Stuff or long-fiber wool or whatever you like. George Augsberger has published design methods for these, both in Audio Xpress and in the AES Journal, which will help choose the area of the line and the stuffing density.

Each of the four woofers has its own chamber, with a large and long port (gives more unconstricted bass). The port dimensions depend on the chamber volume, which in turn depends on what you can find for the 2x4s. "Boxplot" and other speaker design freeware can work it out. If you will be using an SET, be sure to increase the QT of the speaker by 30% to account for the low damping factor. Line the area behind the woofers with a good absorptive material, like 1" acoustical fiberglas - but keep it a couple inches away from the port. You may not need to line the edges or the front. Wire the woofers in series-parallel to maintain the 8 ohms impedance.

A first order crossover at about 800Hz will work well, because the tweeter is a fullrange with plenty of excursion, and the drivers are very close together in terms of wavelength. Plus, the drivers are flat for a couple octaves on each side of the crossover so you don't have to account for phase and amplitude anomalies. In some back issue of VALVE I published an adjustable passive line-level crossover which would probably work pretty well if you want to biamplify; I would thing the tweeter amp should be about the same power as the woofer amp, or at least half that much power. I'd bring out the woofer array and tweeter wires and use an outboard crossover, to allow for bi-amping at a later date.

When I find my notes (they are in a file somewhere in the office here...) I'll try to fill in some blanks about the chamber tuning and crossover details.

For refinement, you might want to put a "belt" of felt across the middle section, probably 1/4 to 1/2" thick - go full width, and at least 12" tall. Wouldn't hurt to do the whole surface, but that might get costly. I always planned to search out some grille cloth the same color as the living room walls and cover the whole thing so it sort of disappears.

 

[tsingle999]

I built these 8 years ago and I just pulled these out of my garage after 6 years of being idle. Ran them with 2a3 paramounts yesterday. Decided they needed more power so I switched to the quicksand today. Actually I think the 2a3's are fine with these. These things throw a really wide sound stage. They are pretty sensitive to where you sit meaning if your off center the sound shifts to one side. They are probably to close together. So I did break these in but it sounds like I need to do that again which I have been doing. But here's the thing: the fostex driver seems too loud compared to the mcm drivers. There is not much bass especially compared to the Abby's. I'm using a 1.8 mhz inductor and 26uf cap. I adjusted the fix (noticed differences in fic adjustments much more than any other speaker) and it definitely helped tame the fostex. The fostex sound like they need a couple more hundred hours of break in but beyond that I feel like I should be getting more bass out of these speakers. Anyone have any suggestions?

 

[Paul Joppa]

That's stretching my memory  :^)  but I think it was designed for SET drive, with a modest damping factor of 2 or 3. Driving with the Quicksand would therefor not work as well in the bass. You could put a 3 to 4-ohm resistor in series to see if that makes an audible difference.

It's possible that sitting for a few years allowed the suspension to stiffen up, which would also affect the bass. Breakin is the answer to that.

You might also check the woofer series/parallel wiring in case one of them is accidentally out of phase with the others. Seems unlikely, but it can happen - we've all been there and done that at one time or another.

 

[pboser]

This might be a dumb question but did you try them up against the wall?

 

[Paul Joppa]

This might be a dumb question but did you try them up against the wall?

Good catch!

 

[tsingle999]

OK so the wall definitely helped lol (thanks! it makes me feel like when I'm at a store and ask a clerk where something is and I am standing right in front of it.). Also I have been running them hard for long periods of time and they are a lot better. I guess they needed a rebreakin.
PJ - The resistor is for the quicksand only? I went back to the paramounts and they def sound better.
As far as the series-parallel wiring of the woofers i know I def had my thinking cap on when I did it - both speakers sound the same. I tried switching the red and black at the speakers but that sounded worse. So I attached the diagram that I used to wire the woofers. Can you verify that is the way I should have wired it? Thanks!

 

[Paul Joppa]

Yes, that looks right.

 

[tsingle999]

These are sounding better. Watched a movie last night. The voices are reallly centered on the screen.
Couple questions now that i know i like them:
Is the resistor suggested for the quicksand only?
The fostex 126e that is in their have some damage on the cone. I was thinking of dropping the new 126en in instead. Then i noticed that there are other 4" fostex' drivers like the fe 108 sol. Which one would work best? Thanks! Taran.

 

[Paul Joppa]

The resistance is for any amp with a high damping factor - usually that means solid state with lots of feedback (like Quicksand). Seductor is on the edge - I don't recall the exact damping factor but it's higher than our SETs but still less than 10.

The smaller Fostex speakers are less efficient, with cleaner treble. I chose the 126 to match the woofers' efficiency. If you used a line-level crossover to biamp, then different efficiencies would not be as much of a problem.

 

[tsingle999]

Thanks Paul! I will try the sol's and see how they sound. (I can resist anything but limited editions) I am in a position to biamp now so i could end up doing that. Debk is working on a gigantamount for me (300b paramount 1.1 with fs100 plate chokes and tfa2004 nickel. That might get some more bass out of the speakers i have been listening to them all week. They are pretty cool speakers! Inhabe the feeling the mcm drivers have a long breakin. The metal driver subs from Blumenstein took a long time to break in. one day a few minths in i was like wow ok thats what they are supposed to sound like.

 

[tsingle999]

Just finished finishing the speakers. Makes a big difference! A lot of the imperfections are unnoticeable now.
I switch back and forth with the abbys. They always surprise me a bit when i hook them up again. They are better for movies as the sound seems like it comes directly from the tv.
Anyway i am really glad i built them - i learned a lot!

 

[tsingle999]

So i put the fe 108 sol drivers in. The speakers are really good now. the new drivers are much more balanced, smoother more delicate sounding. They have a more pleasing treble presentation more like the orcas. The fe103's were a bit harsh.  I think the lower sensitivity of the sol's lets the bass standout a bit more too.
I would definitely recommend these sol drivers.
So now that i really like these speakers maybe its time to try biamping with the 2 pairs of sr45's?
What would be the best way to do this PJ? Thanks. Taran

 

[Paul Joppa]

See my first post this thread for line-level crossover which will work well. I will try to attach a simplified circuit so you get the idea.

 

[tsingle999]

Ok I have a question. So the treble and bass out center posts go to a 10k and 50k potentiometer? That's what the arrow to the resistor means? So the idea is that the crossover gets put in after the preamp and then you can adjust the volume for each bass and treble as they go to the amp. Please correct me if I am wrong. Thanks, Taran

 

[Paul Joppa]

Got it in one!

I found the article I wrote for Valve in 2000, showing an adjustable crossover. You can ping me - paul <at> bottlehead.com - and I'll send a word file. I'm not sure whether it actually appeared in the newsletter, it was towards the end of VALVE.

 

[Paul Birkeland]

Ok I have a question. So the treble and bass out center posts go to a 10k and 50k potentiometer? That's what the arrow to the resistor means?

Yes, the arrow is part of the symbol for a potentiometer, and is used to symbolize the wiper (middle lug on most pots).

So the idea is that the crossover gets put in after the preamp and then you can adjust the volume for each bass and treble as they go to the amp. Please correct me if I am wrong.

Yes, you'll need to match the levels of the drivers depending on the amplifiers used.

 

[tsingle999]

Thanks guys!