Re: Discussion on speaker upgrades on DCS (and similar) machines

On Feb 13, 7:12 pm, RJBAudio <ro...@xxxxxxxxxxxx> wrote:
On Feb 13, 5:30 pm, "cody chunn" <cchu...@xxxxxxxxxxx> wrote:



So...uh...how does it sound (compared to original)?

--
-cody
--CARGPB4

"RJBAudio" <ro...@xxxxxxxxxxxx> wrote in message

news:830c0e7c-ae13-4644-b50b-fba4fb64ed2f@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I've read quite a few posts recently regarding speaker upgrades on
different DMD machines and I would like to discuss a few things.  I'll
first note that my other hobby involves designing high-end speakers
(www.rjbaudio.com) so I have a bit of experience on the speaker side
of things to some degree.

I recently upgraded the speakers in my Demo Man machine but did some
tests prior to choosing replacement drivers.  This machine uses the
DCS sound system which basically means that it has an active crossover
at around 300 Hz which splits the signal prior to amplification and
then uses one amp for the lower cabinet subwoofer driver for
frequencies below 300 Hz and another amp for the higher frequencies
that drives the backbox speakers.  The original configuration for the
backbox speakers uses a full range driver on the left side and a
smaller high frequency driver (filtered using a series 10uF capacitor)
on the right side (which means that there is an emphasis on high
frequencies in general because this range, approximately above 4 kHz,
is produced by both speakers).  So one complaint about this type of
backbox speaker configuration is that the imaging is poor due to the
fact that sounds below 4kHz only come from the left speaker.

The first thing that I did prior to ordering new speakers was to
disconnect the original speakers and run those wires to a few sets of
high-end speakers (for the backbox speaker lines I used a pair of 2-
way bookshelf speakers and for the subwoofer line I used a ported 6.5"
driver tuned to have an f3 of around 40 Hz).  I actually found that
the backbox speakers when run to a set of fairly neutral high-end
speakers sounded a bit muffled due to a prominence in the lower
midrange.  Also, it seemed like extreme high frequencies weren't
present in the original signal.  The subwoofer speaker didn't reveal
that much more bass than the original lower cabinet woofer which made
me think that it would be a waste of time to use a driver capable of
producing very deep bass based on the assumption that the raw signal
doesn't even produce frequencies that low.

What I gathered from this experiment was that the backbox speakers
didn't need full frequency extension all the way to 20kHz like home
stereo speakers do, but what was most important was the frequency
balance of the drivers used so that the sound from the machine was
reproduced with a level of clarity and neutrality.  I also thought
that there would be a point of diminishing returns with going with a
subwoofer driver capable of producing very deep tones due to the
limitations of the signal sent to it.

Based on this information I learned that it is not so important to get
the highest "quality" drivers, but to choose drivers best suited to
the application to provide the right synergy.  This means choosing
backbox speakers that cover the 300Hz to 10kHz range well yet have a
tonal balance that reproduces the signal sent to them in a way that
preserves clarity and presents neutrality.  It can be important to
find a subwoofer driver/backbox driver combination that provides a
good balance between the levels of those drivers and this is
determined by looking at the sensitivity of the drivers involved but a
good alternative is to use an L-pad on the backbox drivers so that you
can lower their volume level relative to the subwoofer to get a bit
more impact in the bass region.  Choosing a very high sensitivity
subwoofer driver can sometimes result in a sacrifice in bass response
due to the trend that higher sensitivity drivers "tend" to have higher
resonance frequencies due to lighter cones.

Anyway, what I ended up doing with my Demo Man machine was first using
the Dayton 6.5" shielded 4 ohm woofer as a replacement for the
original subwoofer driver because I liked the fact that it fit
perfectly without any screw modifications and the Dayton drivers are a
pretty good value.  I went with a pair of HiVi B3N 3" fullrange
drivers for the back box speakers.  I didn't want to have to cut a
hole in my speaker mounting panel but instead made a "reducer" panel
for the left speaker.  I had used these drivers before in another
project so I knew that they sounded decent for the price and based on
distortion and frequency response tests I knew that they could cover
the 300-10kHz range well. I added a simple filter to them so that I
could adjust the tonal balance (a common baffle step filter consisitng
of an inductor in parallel with a resistor, with this configuration in
series with the drivers and adjusting the resistor allowed me to tweak
the amount of high frequency attenuation that I desired).  I liked the
fact of using two fullrange drivers which improved the imaging
significantly (all of the sounds seem like they are coming from the
middle of the machine now).  I didn't have to add an L-pad to the HiVi
drivers because they are a very low sensitivity set of drivers which
made the Dayton 6.5" woofer more prominent (but if I had just replaced
the subwoofer and used the original backbox speakers I probably would
have found the subwoofer driver to be too quiet).

So, that's my experience with drivers in a DCS machine.  One thing
that I would like to know for sure is the actual frequency content of
the signals sent to each driver.  I made estimates based on using
drivers that could cover frequency ranges well beyond that of the
signals but it would be nice to know based on real data, for example,
how low in frequency the bass sent to the subwoofer driver actually
goes.  I'm sure this may vary from game to game, and that would be
another neat topic regarding which machines have sound that goes the
deepest in frequency.   On a side note, I thought that it might be
interesting to use a subharmonic generator (a processor that takes
bass frequencies and generates duplicate ones an octave lower in
frequency) to artificially deepen the bass of a machine.

I'll wrap it up there but please comment.- Hide quoted text -

- Show quoted text -

I sort of have mixed feelings about the new sound.  One thing that
changed is that I have to turn the volume up louder to get the same
sound pressure level (SPL) as before but this doesn't bother me at all
because I've never come close to turning up the volume to the max (I
think I have it at 15 now).  This was due to the fact that the Dayton
woofer is slightly less sensitive than the orignal sub, but more due
to the fact that the HiVi B3N drivers are very low sensitivity (around
80dB IIRC).  I actually think that the relative sensitivities worked
out well because it made the subwoofer a bit more prominent giving the
sound more impact.  The other improvement is having the audio imaged
centered rather than having only the high frequencies centered and the
lower-to-mid midrange frequencies only coming from the left.  I guess
my main complaint is that the sound isn't as crisp as it was before
but some of that is due to the baffle step compensation filter that I
added.  However, sometimes I found the original sound to be a bit
"too" crisp and it could be a bit harsh on my ears.  The current sound
is a bit mellower but not to the point where voices are muted or
muffled due to too much lower midrange sound so I guess I found a good
compromise but I may mess around with the filter that I added.

I forgot to explain how that filter works, and it is pretty
straightforward.  It involves an inductor in parallel with a resistor
and this circuit is in series with the drivers.  The inductor only
passes low frequency sound below a certain frequency (I'm guessing
around 1kHz in this case) and the resistor acts as a bypass to the
inductor so that at high frequencies where the inductor pretty much
blocks all sound from passing through it, the resistor allows that
sound to pass by the inductor at a level determined by the value of
the resistor.  So if a higher value resistor is used then you will
have more attenuation of the higher frequencies and vice-versa with a
smaller value resistor.  So with my case above, if I wanted to try to
reduce the amount of attenuation on the high frequencies to make the
new speakers sound more like the older speakers (more crisp) then I
could reduce the value of the resistor that I used in that circuit.

So, back to the sound, I'm pretty happy with the sound of the new
configuration but what I realized after doing all of this work is that
the signal sent to the speakers isn't the greatest to start with which
takes us back to my original post where I said it doesn't matter that
much about the quality of speakers used but more about how well the
speakers work with the signal presented to them.

With that all said, I'm not rushing to make an upgrade to the speakers
in my Shadow machine that I got recently because the sound seems fine
and I think that any modification will sound "different" but whether
or not it will be better is hard to determine especially after
becoming accustomed to how the original sound was.

Aren't your HiVi B3N 8 ohms? Did you hook them up in parallel?
.

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