I sent the note below to Energy Loudspeakers of Canada (highly
reputable, I might add) to see what they might have to say about their
old ESUB2, two of which I've played with for years. Then I thought,
there's likely as much expertise here as with the supplier so why not
post it here, too. I'll post any answer I get.
FYI, these ESUB2's are vented, "1/6 order" subs with small 6 1/2 inch
(I think) drivers and I think they are sold in pairs. Specs claim
only 37 Hz for the low end. The driver units face a closed box (air
spring loaded) and the back of the driver is in another enclosure with
tube tuning to the outside. There is no speaker cone facing the
outside world, all sound comes out of the tubes. Also, they contain
an odd X/O - a 650 uF cap and a 15 mH (or so) choke all in series with
the nominal 6 ohm voice coil (no shunt caps across the VC.)
BTW, I am fully aware that you can't get useful SPL from a vented
enclosure below vent resonance (and in a simple bass reflex design you
can damage the driver as it is unloaded at VLF) but, since this driver
is air loaded down to "zero Hz", I left them with the question to see
what they might say.
All comments welcome.
To: Energy Tech support or Development group.
First some history, then some questions...
Some years ago I acquired a couple of Energy ESUB2 subwoofers to
augment my home theatre system. At that time I had nominally full
range mains (1 cu.ft), Radio Shack Minimus 7 rears and no centre
speaker. I ran the ESUB2's from a separate 20+20 watt amplifier fed
from the "sub out" (below 300 Hz) output of my Yamaha RXV1070
receiver. All phasing done carefully with a SPL meter. Results were
quite good but subs were not very "deep" at 37 Hz lowest response and
did not integrate very well (too high X/O, I think.).
As time went by I did various modifications and changes as follows:
1. Improved the front speakers and moved the original ones to the rear
2. Added a matching centre speaker
3. Introduced an electronic crossover before the sub amplifier (the
separate amplifier); designed it for 90 Hz with 12 dB/octave rolloff.
Results better, subs now well integrated.
4. Increased sub amp to 150+150 watt Yamaha M4 (bought used) with same
X/O. Had to add about 10 dB of gain in the pre-amp stage (M4 needs
about 1 volt RMS for full O/P.) Results much better, more punch, but
still not very "deep" at 37 Hz, of course.
5. Replaced two ESUB2's on my main system with a single 12 inch
closed box sub powered by a 200 watt sub amp (purchased separately
PartsExpress in the US - model #300-804, a linear MOSFET design, not a
class D switcher.) Results definitely better, much more punch, faster
response and down to below 30 Hz (on SPL meter.)
6. Moved the ESUB2's to my electronic piano to extend the range of the
bookshelf speakers being used. Used a second PartsExpress #300-804
sub amp (you will note that I like this unit!) to simply drive the two
ESUB2's in parallel. Problem is, the piano goes down to 27.5 Hz! (Low
7. Minor concern! The ESUB2 are labeled as "6 ohms nominal, 4 ohms
minimum" so was a bit concerned about current demand. The "300-804"
amplifier will drive 2.7 ohms for a short while at about 290 watts so
it was safe for the piano application (it never cuts out.) So, not a
8. Checked the DC resistance of the ESUB2's to be sure. Big surprise,
infinite! There must be a series capacitor in there!
9. Decided to take look inside after all these years (warranty well
over!) I was not surprised to find the capacitor (650 uF) but
intrigued as to why it was there. I also found a series choke (looks
like 10 to 15 mH, not measured), all in series. The choke has a DC
resistance of 1.1 ohms, and the speaker, IIRC, 4.7 ohms, so it can't
below about 5.8 ohms, can it? Your spec says 4 ohms minimum.
10. I also noted that the chamber in front of the driver is sealed.
Good! I was concerned that, as a ported speaker, it would be unloaded
below resonance but this is not so for the ESUB2.
11. Since my sub amp is band limited (20 Hz up to 40 Hz - 180 Hz
variable), i.e. no DC or subsonic, I removed the caps (shorted them).
My sense is that this improves the response just a bit but still not
below 37 Hz.
That's the end of the experiments.
1. Were the pair of ESUB2's designed originally to be simply wired in
parallel with small satellite speakers so that the combination forms a
full range speaker? If so, I imagine the combined impedance gets
rather low for an average quality power amplifier. Also, this would
be difficult to balance.
2. Is there any change to the internal X/O that you would recommend
if the ESUB2's were used on a dedicated, band limited subwoofer
3. Can they be pushed below 37 Hz by any means? I can't think of
anything, there's no free lunch! Simply, low subs must be big.
4. Generally, how might I best deploy the ESUB2's in a world of "below
30 Hz" 200 watt plus subs?
On Sun, 12 Dec 2004 17:15:02 -0500, "Engineer" <firstname.lastname@example.org> wrote:
>FYI, these ESUB2's are vented, "1/6 order" subs with small 6 1/2 inch
>(I think) drivers and I think they are sold in pairs. Specs claim
>only 37 Hz for the low end. The driver units face a closed box (air
>spring loaded) and the back of the driver is in another enclosure with
>tube tuning to the outside. There is no speaker cone facing the
>outside world, all sound comes out of the tubes. Also, they contain
>an odd X/O - a 650 uF cap and a 15 mH (or so) choke all in series with
>the nominal 6 ohm voice coil (no shunt caps across the VC.)
The subs are basically bandpass loaded, with LC elements in series in order
to define a higher order bandpass function. The series C also protects the
drivers from large excursions by cutting very low bass.
"Engineer" <email@example.com> wrote in message
> Hi, group.
> I sent the note below [above] to Energy Loudspeakers of Canada
> (highly reputable, I might add) to see what they might have to say
> about their old ESUB2, two of which I've played with for years.
> Then I thought, there's likely as much expertise here as with the
> supplier so why not post it here, too. I'll post any answer I get.
Here's the reply from Energy Loudspeakers with my reply to them.
----- Original Message -----
From: "Steve Hipgrave" (address deleted)
Sent: Tuesday, December 14, 2004 9:39 AM
Subject: RE: ENERGY - CANADA - SUPPORT: ESUB2 discussion
Let me first start by pointing out that that the "some years ago"
that you acquired the ESUB2 subwoofer would be 12 -15 years ago. The
technology at the time was limited and the ESUB2 was designed as a
passive subwoofer for emerging Home theater market. As to your
questions, yes this sub was designed to be wired in parallel with the
matching sats. We can not recommend changing anything on the crossover
as the cabinet, woofer and crossover as all were designed to work
together. To push the sub below the 37hz without major loss in output
would require a larger woofer and cabinet. Your primary limiter here
the woofer size. Your best bet is to upgrade to one of our newer 10"
12" powered subwoofers which are capable of going down to 30 Hz with
appreciable power and output.
Parts and Service Manager
Steve, many thanks for you reply. Yes, time flies - thanks for the
I agree with all your points. BTW, I've designed speakers for years
but not subs, only standard bass reflex and infinite baffle types.
So, it's eBay for the ESUB2's and a search for a large passive 12 inch
sub as I want to use my excellent 200 watt FET linear amplifier, class
AB (I don't like class D amps, had one by Infinity burn out, that's
when I got the "300-804" unit from PartsExpress!)
Very best to the "Energy team" (definitely among the good guys!)
To the NG: Disclaimer - I have no commercial connection to Energy