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Double Bass Old School Box Design: The LDS 1x15"

Wilbyman

Wilbyman

Sep 10, 2003
3,834
108
49
Parkersburg, WV
#1
So I fired off Don Oatman an email about getting a shallow, small 1x15 box loaded with an older driver. I wanted to base it on an old Polytone box. He was his reply.

Hi Will, Don't expect much low end from a box less than 12" deep. The old Polytones were not very bass happy and we have come forward a lot in small box design using 15's that work pretty well in a smaller cube. The older 15's---JBL, E.V. etc would work pretty well because voice coils were smaller ( better high end ) and the cones were thinner as well. and they were more suited to a sealed box. Have you thought about a 15 co-ax ? these work very well for upright players and we have designed and sold quite a few. Don Oatman----LDS

The old Polytone box was only about 9 inches deep so I'm just wondering if thinner wouldn't be better for this application. I really don't want big low end from an upright box. Anybody have any ideas or comments re: drivers and dimensions?

Will
 
#2
Wilbyman said:
So I fired off Don Oatman an email about getting a shallow, small 1x15 box loaded with an older driver. I wanted to base it on an old Polytone box. He was his reply.

Hi Will, Don't expect much low end from a box less than 12" deep. The old Polytones were not very bass happy and we have come forward a lot in small box design using 15's that work pretty well in a smaller cube. The older 15's---JBL, E.V. etc would work pretty well because voice coils were smaller ( better high end ) and the cones were thinner as well. and they were more suited to a sealed box. Have you thought about a 15 co-ax ? these work very well for upright players and we have designed and sold quite a few. Don Oatman----LDS

The old Polytone box was only about 9 inches deep so I'm just wondering if thinner wouldn't be better for this application. I really don't want big low end from an upright box. Anybody have any ideas or comments re: drivers and dimensions?

Will
Click to expand...
The old Polytone amps were anything but flat and most of the lowest frequencies were filtered out, so they weren't amplified and never reached the speaker. At the same time, the old Polytone amps emphasized the upper bass giving the characteristic warm tone. The cabinets were small (and shallow), since they were not trying to reproduce any low bass (which the amp didn't pass anyway). I have used my Walter Woods amp with a Polytone 1x15 extension cabinet, and it sounded OK at low volume, although it got boxy and honky sounding pretty fast (no matter how much clean power was available to drive it). Polytone used a very inexpensive (cheap) speaker in those amps.

The Eminence Alpha 15 from their American Standard series is probably the most like the older Polytone speakers. Better quality Eminence drivers such as the Delta and Gamma range sound rather different as do the Eminence Deltalite and Basslite 15's.

Along with the right driver, a small sealed box is what is needed to get a Polytone-like sound (assuming that's what you want). You might want to watch eBay for a used Polytone extension cabinet. I've seen them turn up occasionally.
 
#3
I suggest reading my design article at bedtime:

Invalid Link Removed

My hypothesis is that a sealed box is not necessary for the classic tone. There is nothing magical about a ported speaker, but the port allows a somewhat smaller box, and lets you work with contemporary drivers that are mainly designed for ported systems.

The depth of the cab doesn't affect tone, so long as the cab is lined with foam or fuzzy stuff. However, limiting that dimension makes it hard to provide sufficient volume without making the box look ungainly. That's probably what Don is getting at.

I suspect Don could take a look at my design, and build something along similar parameters, or suggest alternatives based on drivers that he favors. I am happy with my little 17-pound box. It gets stupid loud. Also, our clink has built one of these, and has posted his comments.
 
#4
Wilbyman said:
So I fired off Don Oatman an email about getting a shallow, small 1x15 box loaded with an older driver. I wanted to base it on an old Polytone box. He was his reply.

Hi Will, Don't expect much low end from a box less than 12" deep. The old Polytones were not very bass happy and we have come forward a lot in small box design using 15's that work pretty well in a smaller cube. The older 15's---JBL, E.V. etc would work pretty well because voice coils were smaller ( better high end ) and the cones were thinner as well. and they were more suited to a sealed box. Have you thought about a 15 co-ax ? these work very well for upright players and we have designed and sold quite a few. Don Oatman----LDS

The old Polytone box was only about 9 inches deep so I'm just wondering if thinner wouldn't be better for this application. I really don't want big low end from an upright box. Anybody have any ideas or comments re: drivers and dimensions?

Will
Click to expand...

Will,
Well if I were going for something vintage, mind you this is my personal preference, and way of the subject, I'd try building a 10" 0r 12" cabinet based in the original Ampeg Portaflex Cabinet with a Wizzy speaker. I loved the tone of the 15" Portaflex and marvled at how little amplifier power it took to acomplish it. At one point I had two of them running into a 100 watt Walter Woods MI 100 8 and it really sounded good, at least to me.
EA has really already done this already with the Wizzy 10 and 12. To me that's what I'd consider if I were you.

Ric
 
#5
Lest we miss the real point here, the Polytone-style speaker cabinet has a rather high cutoff frequency, which means it doesn't reproduce any low bass. In other words, it's an acoustic high pass filter. It's also incredibly simple. Efficiency and extended bass response are not part of the design goals.
 
#6
That's a good point. A really small 15" system probably has a cutoff above 100 Hz. For well over a decade, a small sealed 15" was my main speaker, but I ended up wanting a bit more low end but also a smaller box.
 
#9
Wilbyman said:
Hey guys, thanks for all your input. I would like to try a new box (still) but am thinking about something off the rack. The old style Wizzy might be worth checking out, thanks Ric.
Click to expand...
Not trying to discourage the LDS 15 idea, but you did say Wizzy maybe and off the rack, so ...

I spent much of the weekend palm-muting a Lakland Bob Glaub w/ Labella flatwounds. And lovin' it. :D I don't know precisely how the Wizzy sounds compared side-by-side to a Polytone, but I dig "old school" and the Wizzy kind of has that mojo. Plus real well-defined mids / bark. And excellent projection. I don't associate those last two things so much w/ the Polytone sound I remember.

I was playing thru an iAMP-200 Wizzy combo. FWIW I was happy with that as my DB rig for 3+ years. Again, I lean to what I call kind of old school tone-wise on upright too.
 
#14
If I confused ya, my apologies. I agree the regular Wizzy has more of a vintage thing. Strong low-mids and prominent upper mids. Lots of mids. That sound turns my crank w/ a P bass, fingerstyle and w/ a pick.

The M-line has much the same vibe (that I call "thickness and clarity at the same time"), but a little more on the top and bottom. Probably more balanced overall. It sounds awesome IMO w/ upright. With the M-line, the upper mids are less up front, and the highs seem a little more prominent as a result. (Others came up with that descriptor, and I'd agree.) The M-line also goes deeper, which I notice mostly w/ a 5-string EB.

And the different transmission line in the M creates this cool off-axis low-end feel and dispersion. In fact I think that's the only thing that's physically different about the two cabs, aside from their overall dimensions.

They both sound great to me and project out into the room extremely well.
 
#16
Freddels said:
Do you have any pics/drawings of how you braced this box made with the 1/2" ply?
Click to expand...

Sadly, I don't, as I did it by the cut-and-try method. After I assembled the basic box, I cut a 1/2 x 2" plywood shelf brace for the rear panel, and simply glued it in. Then I reasoned that the box was so small, its dimensions are comparable to recommendations I had seen for the distance between braces. So I left the side panels alone.
 
#17
fdeck said:
Sadly, I don't, as I did it by the cut-and-try method. After I assembled the basic box, I cut a 1/2 x 2" plywood shelf brace for the rear panel, and simply glued it in. Then I reasoned that the box was so small, its dimensions are comparable to recommendations I had seen for the distance between braces. So I left the side panels alone.
Click to expand...

So there's only one 2" brace (I'm assuming horizontal) across the back of the box. Also, in your writings you mention that the next time you were going to go with the shelf port rather than the circular. Any other thoughts on that? Also, is the baffle board 1/2" ply too?
 
#18
After getting myself totally confused, I got out the speaker and made this sketch:

smallbox.jpg


Here is a sketch that I just made. Note that it is "schematic" and not necessarily to scale. The top picture is the front view. The bottom picture shows a side view with the sides removed.

A challenge with really small boxes is that the port can end up wanting to be longer than the depth of the box. As you can see from the side view, my shelf port effectively goes around a bend to give it just a bit of added length.

Looking at the front, the shelf port is 8-3/8 x 1-3/8, and the shelf extends to within two inches of the rear panel. The way that the shelf sticks out the front allows the port to be a bit longer than it would be, if it was flush with the baffle.

G is effectively a brace on the bottom panel, and also sets the width of the port. It goes all the way to the back, where it joins up with brace H.

F is the shelf, made from some 1/4 inch masonite that I had sitting around. It sits on top of G, and just butts up against the other walls. I reinforced all of the seams with cleats on the inside.

The baffle is 1/2 plywood, like the rest of the box. It has so little area, and the driver is so lightweight, that I figured on getting away with a relatively thin baffle. The baffle is set 1-1/4 in from the front of the box.

Working out the pieces (check my math before cutting):

A = 17 x 12
B = 14 x 12
C = 14 x 14-1/8
D = 14 x 16
E = 14 x 1-3/4
F = 8-7/8 x 7-3/4
G = 1-3/8 x 11-1/2
H = 16 x 2
Blank = 5-1/8

My recipe is to cut all of the pieces except the sides using a single rip setting on my table saw, cut the port hole with a saber saw,and assemble using ordinary wood glue and some long furniture clamps.

Then I put in G and the blank.

Then re-measure, cut the sides, and glue the whole thing together. Re-measuring is necessary because 1/2 inch plywood is not exactly 1/2 inch, and small tolerance errors build up.

Long story short: All of this complexity is why I might opt for a circular port. I made the mistake of not measuring the port tuning before gluing it in, and I was off by a few Hz. But that's not really a big deal.
 
#19
Nice schematic (Wiley E. Coyote would be proud) and helpful.

Now behind the blank, the port is still open and air goes in but nowhere to escape except back out where it came from. Any problems with turbulence due to that "dead area"?

I'm going to have to build one of these in a few weeks (just to see if I can).
 
#20
Quite a few years ago, I made a small 15" cab by copying the bottom of a Carvin PB-150 combo. Basically, it was a box with a shelf port in the back. Looks like the schematic here, but the rear shelf port allows building a smaller cab with the baffle board just a bit bigger than the speaker.

I think in a small cab, the shelf port does a good job of bracing, too.

That little cab got sold to somebody on another discussion board. By surprise, a couple of years ago a friend was looking for a small cab to go with a Bassman 50 head, I posted to that discussion board, and was offered that cab again, although the seller didn't remember he'd bought it from me.

The little cab sits in the friend's basement, where I occasionally use it for practice. Does a good job of an old school sound.
 

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