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new subwoofer king?


Jay481985

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The Royal Device is older than most members here. [:P] No doubt one of THE most impressive custom subwoofers,and the most costly. How many rearrange thier foundations to build a MASSIVE horn loaded sub with so much displacement...on a world wide level there are a few,very few...subs taht impressive.

The Danley Matterhorn is another "subwoofer" that would be in the same league,here even more displacement.In a compact "shipping container" with the amps mounted behind.

After..I will have to join with The Sealed Device...[:D] [:P] completed it will use 28 sealed modules,14 15" and 14 18" drivers powered by ~50KW.

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And about the DD subs (since I don't want to get OT in the HT thread), you're right about them being for SPL, but I think you'd be surprised at how good they sound. I use one 1508 (8 inch) sub in my car running on about 600 watts and, even in the terrible box it's it, it still sounds pretty good to me. Besides, as we speak, I'm building a new box that doesn't use a 2" pvc pipe as the port (it chuffs at any volume level, I hate it) and should be a big improvement. I can also tell you that my little 8 is just as loud, and much much cleaner sounding than the crap most people my age (17) are buying from the big box electronics stores. I had to pay a good bit for it, but it was completely worth it.

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  • 3 months later...

I'd have to see calculations to be
convinced that the fall off of pressure with distance within this
cabinet was enough to be a significant worry. I'd be interested to see
a subwoofer that supposedly took this into account. Most of the PR
subwoofers I've seen are close to square boxes with PRs mounted on
opposing faces.


I've been meaning to get
back to this thread now that I'm done with school and have time to
actually run some numbers on the specific design. Btw, I must confess that I initially thought it was some obnoxious floor to ceiling design with as many drivers as could be packed in. I guess that's what I get for skimming (I blaim it on the crazy workload of that semester).


Anyways, you mentioned a
height of ~60" - this will result in a rather steep dip in the frequency
response at about 54Hz. I think moving the active drivers to the middle
of the cabinet might push that up to 108Hz, but I'd want to
measure to know for sure. You're basically getting a 1/4 wave
reflection that puts a null behind the driver when the driver is trying
to move outward (so it's fighting against a vaccuum). When the driver
is trying to move inward, it's going to be running into a pressure
maximum. It's easier to fight a pressure max than a pressure min, so
you're going to get some second order distortion from this too. You'll
want to make sure your xover puts this frequency down about 20dB for it
to get completely masked. That'll also help reduce the 220Hz standing
wave from getting noticeably triggered from harmonic distortion at
100Hz.


As far as the location of the passive radiators relative
to the active drivers and all that shnazz...it mostly shows up in the
group delay. The T/S models assume that the pressure behind the driver
is instantaneously transfered to the passives. PR's are nice because
they don't have a tube making the delay longer. Anyways, the PR doesn't
do anything until the pressure wave reaches it - so in this design
(with the active in the middle), there's a delay of about a 2ms from
half the wave travelling downward and then about 8ms from the half that
starts upwards and then reflects back down. There really won't be two
distinct waves, but the point is that the energy driving the passive
radiator gets spread out over time. I think this is why we see PRs
becoming more efficient at louder volumes - basically, lower amplitudes
have lower energy to the point of not being able to overcome stiction
in the PR suspension. Spreading the energy out raises the SPL needed to
get the PR moving.


Also, 20Hz has a period of 50ms. If we assume
an extra 5ms of group delay caused by the propogation delay, then
you're looking at 36 degrees of extra phase difference between the
active and passive. This will cause about 1dB of attenuation compared
to the T/S model. A worst case of 8ms or so would cost over 3dB
(depending of course on the Q of the tuning). I have measured a few
different subs where moving the ports around can get rid of 1-2dB dips
in the frequency response that happen just above the tuning point.


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Dr. Who, I was really juggling with the crossover points for these cabinets at first, but put that on a back burner to the build. My main priority for these guys was to be the .1 channel in my 5.1 setup. At first, I was going to utilize these guys at 40Hz down, since my 6 Jbl 18's handle the overall mains and surround duty quite handily. I was going to start with the 5 main channels crossed at 35 and up and run the .1 channel 35Hz or so and down, but since the .1 channel is supposed to carry info up to 120Hz, I figured I would start the .1 channel at 120Hz down and work my way from there. I guess if the new subs were going to be used for overall music listening and sound reinforcement, I would have a lot more considerations to look over, but since they will primarily only be used for HT movie soundtracks with special effects, do you think they will be able to be integrated more easily?

Thanks,

Robert

Please give any thoughts. I am open to any ideas and solutions.

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I'm just reading through this thread.

I have no idea what you guys are even talking about or even know if it is in english but it sure is interesting and great pics too.

You guys are insane (in a good way) and I cant even imagine how good these subs must sound on the lows in movies..

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Dr. Who, I was really juggling with the
crossover points for these cabinets at first, but put that on a back
burner to the build. My main priority for these guys was to be the .1
channel in my 5.1 setup. At first, I was going to utilize these guys at
40Hz down, since my 6 Jbl 18's handle the overall mains and surround
duty quite handily. I was going to start with the 5 main
channels crossed at 35 and up and run the .1 channel 35Hz or so and
down, but since the .1 channel is supposed to carry info up to 120Hz,
I figured I would start the .1 channel at 120Hz down and work my way
from there. I guess if the new subs were going to be used for overall
music listening and sound reinforcement, I would have a lot more
considerations to look over, but since they will primarily only be used
for HT movie soundtracks with special effects, do you think they will
be able to be integrated more easily?

I see movies and
music the same way....the goal is always accurate reproduction of the
source material. With that goal in mind, the setup issues are pretty
much the same.

Btw, there should be an LFE setting on your
processor that will let you send the LFE track to both the subs and
mains. This should be pre-xover, so you won't lose any information from
the LFE track - even if you do a 40Hz xover. Anything above 40Hz would
go to your mains and then everything below would go to the subs.

In
fact, if you're crossing that low, then you might as well keep the
super low tuning point since intermod won't be as big of an issue with
the narrower bandwidth. You should have the headroom to EQ up the
bottom end in that case too - I've not run the numbers, but I think
what you're proposing will be rolling off a bit early with some of EBS
alignment. A lot of guys are always aiming for "flat after room gain",
but I find that doesn't sound natural (and is probably why so many guys
are doing house curves over at the HTS). You'll want to be flat in 1/8
space, but that's often hard to measure....and it will be different
than what you see in 1/2 space.

Also make sure you hi-pass near
your tuning point. The suspension on the LMS drivers will let you smack
the VC against the plate. The insane cracking sound you get from just a
single driver will make you crap yourself - I can't imagine what 4
drivers would sound like bottoming out together. In fact, the last time
I saw it happen, it blew a fuse too (oops). That guy is on this forum -
I'll let him chime in if he wants...I believe we were watching Flight
of the Pheonix? Good times.

Btw, which JBL 18's are you running, and how high are you running them?

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Anyways, you mentioned a height of ~60" - this will result in a rather steep dip in the frequency response at about 54Hz. I think moving the active drivers to the middle of the cabinet might push that up to 108Hz, but I'd want to measure to know for sure. You're basically getting a 1/4 wave reflection that puts a null behind the driver when the driver is trying to move outward (so it's fighting against a vaccuum). When the driver is trying to move inward, it's going to be running into a pressure maximum. It's easier to fight a pressure max than a pressure min, so you're going to get some second order distortion from this too. You'll want to make sure your xover puts this frequency down about 20dB for it to get completely masked. That'll also help reduce the 220Hz standing wave from getting noticeably triggered from harmonic distortion at 100Hz.

As far as the location of the passive radiators relative to the active drivers and all that shnazz...it mostly shows up in the group delay. The T/S models assume that the pressure behind the driver is instantaneously transfered to the passives. PR's are nice because they don't have a tube making the delay longer. Anyways, the PR doesn't do anything until the pressure wave reaches it - so in this design (with the active in the middle), there's a delay of about a 2ms from half the wave travelling downward and then about 8ms from the half that starts upwards and then reflects back down. There really won't be two distinct waves, but the point is that the energy driving the passive radiator gets spread out over time. I think this is why we see PRs becoming more efficient at louder volumes - basically, lower amplitudes have lower energy to the point of not being able to overcome stiction in the PR suspension. Spreading the energy out raises the SPL needed to get the PR moving.

Also, 20Hz has a period of 50ms. If we assume an extra 5ms of group delay caused by the propogation delay, then you're looking at 36 degrees of extra phase difference between the active and passive. This will cause about 1dB of attenuation compared to the T/S model. A worst case of 8ms or so would cost over 3dB (depending of course on the Q of the tuning). I have measured a few different subs where moving the ports around can get rid of 1-2dB dips in the frequency response that happen just above the tuning point.

Interesting stuff Bentz. I'm not so sure how severe this 54hz null will be. I also have a cabinet with a dimension of around 60" but my driver is located in the bottom corner and the cabinet is well broken up internally with the driver bracing and port system preventing any real straight line paths from wall to wall. I don't have any bad FR or cabinet resonances below 100hz that I can tell. Are you sure that 54hz is the correct frequency for that null? It seems like it would be much higher above 100hz with a length of 60"?

The only thing that I don't like about the LMS drivers is that the motor and suspension will allow the vc former to slam right into the back plate easily. It seems like they could have added more clearance there in the back plate and allowed the suspension to clamp down on things in a more graceful manner.

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It's a quarter wavelength cancellation, Peavey writes about it in a
slightly different application, although it is still applicable. It
also applies to the cabinet dimensions in that you can only get the
drivers so close to the walls of your room...

http://www.peavey.com/support/technotes/soundsystems/boundarycancellation.cfm


54Hz has a wavelength of 1132/52 = 21ft. One quarter of that is 63inches.

(speed of sound divided by the frequency is the wavelength)


I have found that it is more audible than room modes because you
pretty much always have the null present - same with early reflections.
Room modes can have phase rotations greater then 360, which would mean
the cancelling effect is delayed - so you get a smearing/ringing of
something that is there part of the time.


Also, the 54Hz null is
going to come with nulls at 108Hz and 162Hz. You will see +6dB spikes
at about 72Hz and 144Hz - just basic comb-filtering. You also get your
first standing wave happening at 216Hz and every harmonic above that,
which even with a perfect low pass filter can be triggerred by harmonic
distortions and is then attenuated by its ability to transmit out of
the cabinet, and it modulates the impedance on the active driver too.


Btw,
bracing and what not looks very small to the wavelengths we're talking
about, so it really doesn't affect these natural cabinet behaviors very
much. You have to get dramatic and redirect the waves - think of it
like pouring water through the bracing...it just keeps on flowing. If
you've got a larger baffle, it'll deflect and wrap around. If you've
got a really large baffle, it'll splash and then get the majority of
its momentum redirected.


As far as the VC slamming the plate -
that's what happens with a very linear suspension. Also, moving the
back plate will reduce your Bl slightly and it will also just push the
mode of failure onto something else. My bet is that the spider is the
next weakest link. While bottoming against the back plate is scary as
all get out, I think it's one of the least damaging failure modes....as
long as you don't hit it so hard as to deform the VC former or
windings. I guess the problem is that the source material that will
cause you to hit
the backplate don't occur very often, so you can't tell
when you're just barely touching it. Putting filters in place to
prevent this from happening is really the best approach - and if you
get creative, you can make sliding filters with variable rolloff so
that you're limited to peak excursion at all frequencies and
amplitudes. This also has the benefit of dramatically reducing intermod
distortion caused by low frequency signals that aren't perceivable, yet
tax the driver real hard.


Btw, all cabinets have the above effects that I've mentioned. The
trick is to get these effects out of the passband so that you don't
trigger them. Large cabinets are absolutely required for deep efficient
bass, but you gotta lower the HF corner with the lower LF corner.

One
other side comment...I wouldn't be writing about all this if I didn't
think it was audible. I've done some measuring and listening of my own
and strongly believe that there is an audible correlation. The problem
is that it is very difficult to do an A/B.

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I don't know whether or not I have a pre-xover. I have large and small speaker selections and crossovers for each.

If you have a Denon receiver, there is a setting that you can set to "LFE: Subs + Mains". The other option is "LFE:Subs Only"

If you've got a Sunfire processor, then the setting is "Bass Mode: Enhanced".

If you've got a Yamaha, it's something like "LFE: Subs Plus" or something to that effect.

It's been a while since I've played with various receivers/processors, but I'm fairly certain they all have it. It should be built into the AC-3 decoder chip that everyone is using a flavor of. Even my brother's nasty cheap Sony receiver has this setting.

I think you might have to have the speakers set to large though for this to work...and if that's the case, then it's bypassing the xover and you'll have to tune the sub xover to fill in where the mains naturally roll off. One of these days I need to sit down and just measure what all these receivers are doing so that I can know for sure how exactly to dial in the xover settings.

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