Sub for Full range horns

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For what its worth, I use an autotuba currently with a set of line arrays. Good to around 30 Hz. I used to use (and still have) a 12" ported adire shiva tuned to 17Hz but that simply isn't efficient enough for an efficient set of speakers. It also doesn't seem to match "tonally" . I tried the same shiva in a sealed enclosuree but just didn't like the sound.

YMMV
 
The 'usual suspects' for horn subs are the labhorns or the Bill Fitzmaurice stuff (tubas).

You need to work out if you have enough space for horn subs as they're not small.

If space is an issue maybe try the punishers down to 40hz and use something more conventional for the bottom octaves.



Rob.
 
Dave,
I considered the apex Jr. push-push sub several weeks ago but it was too small for my application because they needed to do double duty as sofa end tables in my small HT (13'x14' room). I had all but decided to build a pair of single driver 12" or 15" sealed subs probably using the Dayton RS series drivers when I saw your new Extremis based design. Tell me about your new design and its suitability for my application.

Ray
 
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Dave,
As I understand it the benefit of this configuration is that the cone excursion is cut in half and vibrations are reduced along the lateral line of the box. Is there anything else?
I noticed that you set the drivers high to get as close to the satellites as possible. Will placing the subs on each side of my couch, which is across the room from my front speakers, undermine the sub's performance?
I think that I may be enamored with the bipole push-push configuration and therefore considerating an inappropriate application. What say you?

Ray
 
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Ray Collins said:
the cone excursion is cut in half

That happens any time you use 2 drivers

vibrations are reduced along the lateral line of the box.

This is the big one... most of a driver's newtonian force is along the central axis of the cone/voice coil. This energy is usually transmitted to the box (and in some cases becomes so large that subs have been known to "walk". In a push-push arrangement we are attempting to actively cancel this force. How successful we are depends on how ridigly we can couple the drivers.

An extreme example is this coupling arrangement:

pushpushPR2.gif


using these drivers which have a built-in provision for bolting thru the pole-piece to the cabinet

pr2_bass.jpg


In practise we usually just align one of the internal (plywood) braces so that the magnets are tight up against the brace. Most of the lower frequency vibrations are coupled to the other driver where they cancel, and higher frequencies are dissipated in the brace and anything that does get to the outside walls has so little energy that it doesn't do anything untoward.

Besides a small potential improvement in fidelity because the driver is not allowed to rock the box, a dramatic reduction in the energy mechanically coupled to the box occurs. This means that almost all box wall resonances have to be excited by internal air pressure and that energy is significantly less. The net is a bif reduction in box coloration. A side effect is that because less mass is needed to counter driver movement, we can use thinner box material further pushing up the panel resonances (where there is even less energy to excite them), lower cost (less wood), fewer strained backs (less weight), and marginally smaller box size.

With a push-push woofer we have no hesitation of building with 12 or 15 mm plywood.

I noticed that you set the drivers high to get as close to the satellites as possible.

This was specific to the application, where the sealed FE167s are being actively XOed to the stereo woofers at 106 Hz (using SY's gyrator based tube XO -- i can hardly wait for him to publish that article). In this specific application i expect room gain to get these things to reach into the high teens and that they will need to be throttled back by using aperiodic damping in the port (system just being installed so i don't know how it will work out in the end)

Will placing the subs on each side of my couch, which is across the room from my front speakers, undermine the sub's performance?

You just need to make sure that you adjust the box so that the drivers aren't firing into the couch (ie one forward, one back, or some arrangement where the exit for the drivers is actually in the middle of the box (figure 8 or torus topology)

I think that I may be enamored with the bipole push-push configuration and therefore considerating an inappropriate application.

At the frequencies a sub operates at, it is acoustically omni-polar and this is the case no matter how many drivers we use -- 1, 2, 20...

dave
 
Dave,
Thanks for the comprehensive reply. I apologize for the delayed response but my wife priortized my agenda and.....

Is the push-push configuration suitable for a sealed enclosure?

When calculating the box volume for the push-push dual driver do I simply double the volume for a single driver subwoofer? (Accounting for braces also)

I am an advocate of the build it light and build it strong school so I really favor the push-push configuration. I suppose it derives from having built an airplane.

My need to employ the subs as end tables puts dimension restrictions on them. They must be about 24" tall and about 14" wide with the length/depth up to 30". This will provede enough top surface for remotes, drinks etc. Can your new dual Extremis 6.8 design be adjusted to work?

Ray
 
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Ray Collins said:
Is the push-push configuration suitable for a sealed enclosure?

yes

When calculating the box volume for the push-push dual driver do I simply double the volume for a single driver subwoofer? (Accounting for braces also)

yes

I am an advocate of the build it light and build it strong school so I really favor the push-push configuration. I suppose it derives from having built an airplane.

My use derives from having -- over the last 35 years -- figured out that that is what sounds best (and a big side benefit that you don't strain your back as often)

My need to employ the subs as end tables puts dimension restrictions on them. They must be about 24" tall and about 14" wide with the length/depth up to 30". This will provede enough top surface for remotes, drinks etc. Can your new dual Extremis 6.8 design be adjusted to work?

You just need to keep the net internal volume to 42 litres + the port (i prefer the long, high aspect ratio slot ports -- that is if you go with the reference ported design). I have at least 4 configurations drawn up, and i'm sure more will follow (the idea of having the drivers facing openings in the middle of the box (figure of 8 topology) is one i'd like to have a look at.

Given that the volume you need to fill is quite a bit larger than the skinny dual extremis (~10x20x22") that might be a way of helping to fill up the space.

I'll do a quick and nasty sketch in sketchup to give you an idea of what i'm talking about.

dave
 
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Originally posted by planet10 the idea of having the drivers facing openings in the middle of the box (figure of 8 topology) is one i'd like to have a look at.

Given that the volume you need to fill is quite a bit larger than the skinny dual extremis (~10x20x22") that might be a way of helping to fill up the space.

I'll do a quick and nasty sketch in sketchup to give you an idea of what i'm talking about.

Driver pair is the cylinder in the middle. Top could be glass or wood or stone or what-have-you.

dave
 

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Thanks....now I have something to chew-on for the next few days.

Am I correct in assuming that you prefer ported/BR
encosures over sealed enclosures when using the push-push configuration?

I agree concerning the high aspect ratio slots; it just looks apropos.

In your sketch the drivers are not positioned so that the magnets are coupled;
does this still provide the same vibration control?
 
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Ray Collins said:
Am I correct in assuming that you prefer ported/BR
encosures over sealed enclosures when using the push-push configuration?

I agree concerning the high aspect ratio slots; it just looks apropos.

I am actually not a big BR fan. This particular config for the extremis works well. The long high aspect ratio port pushes the box towards aperiodic and if necessary a bit of foam in the port pushes it to completely aperiodic -- this allows for tuning once the box is in the room (there is a specific blue foam i use that comes as part of the packing in Apple parts boxes). With room gain low 20s is possible.

In your sketch the drivers are not positioned so that the magnets are coupled;
does this still provide the same vibration control?

If you dimension the cross part of the 8 appropriately, you can actually get the magnets to touch. Imagine the cyclinder as the extent of a pair of woofers stacked magnet-to-magnet.

dave
 
Hi Ray,

My old 3 ways used 2 x s-speak 8565-01's per side. Each cab was ~120L sealed. The sound quality was excellent, but for me they were not subwoofers. They do get deep enough for music (not home cinema), but do not go particularly loud. For home cinema I ended up using 3 x tempest 15" drivers below 40Hz, crossed to the scans at 24dB/oct.

Eventually the SQ of the tempests got on my nerves and I moved onto labhorns. Much happier now.

For a music only system, if you don't want 'live' levels then 4 x the scans could well be the ticket.

Hth,

Rob.

My old scanspeaks


Thinking out loud, maybe use 4 8565-01's per side crossed to a pair of 15's (maybe servo driven ?) at around 25Hz may well sound nice, and do dynamics.
 
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