| Schaef |
I'm contemplating re-building a pair of subwoofers I made several years ago. They are currently set up similar to the sono-subs in a passive stereo pair. Since I now have a digital HT, I have been thinking of going to a powered single-sub configuration.
So, with that in mind, that means I have a pair of 10" peerless subs to use. I have been toying with a half-a-dozen different ideas/configurations. Recently I've been toying with the idea of using the two in one box to help with the bottom end in a sealed enclosure, and thought maybe the push-push idea would be interesting.
Here's some specs/limits:
The woofers are 10" Peerless 260SWR (831727)
The maximum box size is in the 3 to 4 cubic foot range.
The box will be place in a corner in the room.
Transmission line, while a neat idea, is more than likely out. (I don't think it'll fit in the space requirements.)
The amp hasn't been purchased yet, but am currently looking at the ApexJr plate amp.
So, any thoughts on doing a push-push with these limits?
In push-push, do the speakers have to be back to back? (What about 90 degrees to each other)
Will having one speaker fire into the wall kill the push-push idea? (Up/down is out, as it will be used as a quasi end table as well)
Any other suggestions for other arrangements that would be fun?
Thanks for the help and info! |
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| kneadle |
bump.
I'm interested in this project, even though I have no input. Here's hoping someone comes along who does have input.
Dave |
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| planet10 |
I heartily recommend push-push. Chris & i are working on V3. Pic is V1 using 2 x Philips 12". The box is about 2.8 ft^3, and in the cases of V1 & V2 are both aperiodic (the drivers would really like to see bigger boxes). The top 2 images show the brace used to ridgidly connect the 2 magnets together -- the blue foam is closed cel and quite thin and provides just enuff to tightly couple the magnet to the brace. It is important that the drivers are on oppossite sides & tied together mechanically.
Both V1 & V2 (customer supplied Foster 12s) turned out really well. Both use drivers that are more intended for midbass use than sub use. They go low cleanly and integrate very well with the sats (in both cases a quartet of BD-Pipes with RS 40-1197s). The push-push loading means very little mechanical energy transfer to the box.
dave |
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| planet10 |
A snapshot of the plans. If anyone wants a copy that are large enuff to read the dimensions and such, just email me.
Note: pics are of V1, plans of V2.
dave |
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| 7V |
I have two alternative subs for my new Nonsuch range. The Little Awesome and the Bigger Awesome.
The Little Awesome is like an oval barrel with the driver (Bandor 150) firing out of the bottom.
The Bigger Awesome is a Push-Push, comprising one Little Awesome mounted upside-down so that the driver fires upward and the other one normal-way-up on top of it, separated by 2" - 3". The sound comes out of the middle, between the two drivers.
Clear as mud? Sorry I haven't got any drawings to show you. I just figured that the vibration cancellation would be even more effective if I could get the two drivers close together.
Anyway, if you can figure out what I mean, I put this forward as another alternative because the drivers are in the centre so you could still put coffee cups on top.
If you don't want to go for this vertical approach, I still wouldn't recommend the 90 degree thing as you would lose the vibration cancellation benefit.
As for whether you can fire into the wall (presumably there will be a gap between speaker and wall), I believe that this depends on the highest frequency the speaker has to produce. Down in the deep bass I don't think the speakers will care (some disagree) but if they go above, say, 150Hz - 200Hz you may have a problem.
For the particular driver you're using and the volume required, Push-push would require double the box size of a single driver.
Hope this is helpful.
Steve |
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| planet10 |
| quote: | Originally posted by 7V
Clear as mud? Sorry I haven't got any drawings to show you. I just figured that the vibration cancellation would be even more effective if I could get the two drivers close together. |
Like the attached image? A very interesting design thou from a cosmetic point-of view.
Face-to-face is harder to get good coupling. The only way i can think of would be to use somesort of driver attachment that couples the 2 drivers together, but i can see complications with assembly.
Best is magnet direct to other magnet & the frame rims also tied together. If you can bolt the two drivers together even better.
If this had the magnets touching it would exemplify what i'm suggesting.
dave |
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| 7V |
| quote: | Originally posted by planet10
Like the attached image? A very interesting design thou from a cosmetic point-of view. |
Yup, that's the one Dave.
| quote: | | Face-to-face is harder to get good coupling. The only way i can think of would be to use somesort of driver attachment that couples the 2 drivers together, but i can see complications with assembly. |
Yes, I think you're right. So far all I've come up with is connecting the baffles together. Not ideal. I haven't tested yet so I'll see in the next few days. The closeness of the two baffles should provide some cancellation. we'll see.
Steve |
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| kneadle |
| quote: | Originally posted by planet10
Like the attached image? A very interesting design thou from a cosmetic point-of view.
dave |
I've seen this before, somewhere. Now, is the basket a contraption that is housing the drivers for some reason? Am I reading that correctly?
What I mean is: are those baskets the things actually absorbing the mechanical energy, or are the drivers still driving against each other?
Dave |
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| planet10 |
| quote: | Originally posted by kneadle
I've seen this before, somewhere. Now, is the basket a contraption that is housing the drivers for some reason? Am I reading that correctly?
What I mean is: are those baskets the things actually absorbing the mechanical energy, or are the drivers still driving against each other?
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The ultimate push-push is based on the PEARL PR2 woofer.
The magnet assembly sits inside the basket and it is designed to be bolted thru the polepiece. This is a very rare driver. With more accessible drivers some compromises or other tricks would need to be enabled. But if you are getting an OEM batch of drivers it is worth thinking about using these features.
dave |
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| leadbelly |
A lot of woofers frames' extend out enough that I think a few holes could be drilled close to the magnet and sleeve-nuts used to bolt the two magnets solidly together.
So does cabinet tuning differ for a push-push, or do you just design as if it was a regular dual woofer sub? |
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| planet10 |
| quote: | Originally posted by leadbelly
So does cabinet tuning differ for a push-push, or do you just design as if it was a regular dual woofer sub? |
Tune like any dual woofer box.
BTW. The PR2s were designed & manufactured in Calgary.
dave |
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| leadbelly |
I'm sure that would blink at the price, even if shipping charges were $0.50 of gas.
Is there a rock-bottom price sub driver out there? If I buy 2 Shiva's, I won't be drilling holes just to try a new idea out... |
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| planet10 |
| quote: | Originally posted by leadbelly
I'm sure that would blink at the price, even if shipping charges were $0.50 of gas. |
You got that. For the price of a pr of those you'd could get 4 Stryke SA1024s.
dave |
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| Schaef |
So let me see if I have everything straight... to model the push-push I just use a two woofer in parallel configuration in the modeling software. (I'm switching between winisd and unibox) My only concern with the sealed box is that the software shows these drivers having an F3 of about 50Hz in a sealed configuration. Since they're being used for a combo system (HT and normal music) I'm a little concerned about the bottom end for music. Will the corner loading really help make up for the high F3? (I'll also be using the sub-out from the AV unit, a Denon digital, which I think starts a roll-off around 80Hz)
Also, when it comes to the physical connection between the two, it just really needs to be a tight, solid connection between them, and not necessarily actually touching magnet to magnet. (I know this would be better, but I'm just trying to clarify things) As to bolting the baskets together, what do you think about lengths of all-thread between the two, or would there be vibration problems? As to bolting through the pole-piece, I don't have enough experience/confidence to try that.
As to the gap between the one woofer and wall, we're talking only a couple of inches, unless a build a top that really stretches out.
On to Steve's (7V's) design, it sounds interesting, but a couple of questions. Have you had a chance to listen to it yet? How does it sound? Also, what's the air gap between the two subs, and is it open on all sides, or did you design it to be similar to a port between the two? (Only one or two walls open)
I know, I have a lot of questions, but right now I don't have the time to build it, only design it and I might as well get as many ideas as I can before I have the time.
Thanks for the help and suggestions! |
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| 7V |
| quote: | Originally posted by Schaef
On to Steve's (7V's) design, it sounds interesting, but a couple of questions. Have you had a chance to listen to it yet? How does it sound? Also, what's the air gap between the two subs, and is it open on all sides, or did you design it to be similar to a port between the two? (Only one or two walls open)[/B] |
No, I haven't had a chance to listen yet. I'm picking it up over the weekend from the company that's finishing the enclosure.
The gap is 6cm (2.5"). It's open on all sides (well 'cabineted' at the back of course), connected by four steel rods. If it isn't open you may have to increase the gap size.
Steve |
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| kneadle |
Keep us posted Schaef.
Dave |
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| leadbelly |
Shaef,
If by "all-thread" you mean threaded rod, then yes, you could use this, but you would have to cut it to a suitable length to avoid the chance of the cone snagging on it. And vibration would be an issue, but epoxy should cure that, maybe silicone as it's less permanent.
I would do it with a long threaded sleeve if I found one at the HW store.
And for irony, I was looking around for pictures of woofers with frames suitable for this mod, and I found 2 with a perfectly shaped frame sitting on my shelf...2 old 10" cheapies that planet10 told me to consider a push-push for back in Dec.! :) |
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| planet10 |
| quote: | Originally posted by Schaef
F3 of about 50Hz in a sealed configuration. |
But what is the F10. With room gain this is a far more important number. Many a sub is designed to be flat way low in the modeling software and ends up being a big lump once it gets into the room.
| quote: | | Also, when it comes to the physical connection between the two, it just really needs to be a tight, solid connection between them, and not necessarily actually touching magnet to magnet. (I know this would be better, but I'm just trying to clarify things) As to bolting the baskets together, what do you think about lengths of all-thread between the two, or would there be vibration problems? As to bolting through the pole-piece, I don't have enough experience/confidence to try that. |
The tighter the coupling the better, magnet to magnet is impracticle in most cases (but there are tricks). A bolt thru the polepiece in a driver not designed for such is potentially harmful to the driver (ie get the spacing wrong by a bit and you could pull the magnets off the drivers).
dave |
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| planet10 |
| quote: | Originally posted by leadbelly
If by "all-thread" you mean threaded rod, then yes, you could use this, but you would have to cut it to a suitable length to avoid the chance of the cone snagging on it. And vibration would be an issue, but epoxy should cure that, maybe silicone as it's less permanent. |
all-thread (aka ready rod) is exactly what i had in mind -- sheathed on the inside with a couple layers of heat-shrink to kill off potential resonances -- it should be tight enuff that resonances will be fairly high in frequency, but the potential does exist for this to act like a guitar string.
dave |
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| usekgb |
If anyone is feeling daring, you could use two woofers with center vented pole pieces. Carefuly cut away the dust cover, and you have a hole ready to accept a rod. Run the rod through the center of both pole pieces, and secure the rod with locking washers or nuts. If you wish, you can re-attach the dust cap to make everything look pretty. This would also work with the solid aluminum spacer between the magnets as was posted earlier. You wouldn't need any speacial driver for this configuration, as vented pole piece drivers are very common.
Any comments folks? |
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| planet10 |
| quote: | Originally posted by usekgb
If anyone is feeling daring, you could use two woofers with center vented pole pieces. Carefuly cut away the dust cover, and you have a hole ready to accept a rod. Run the rod through the center of both pole pieces, and secure the rod with locking washers or nuts. If you wish, you can re-attach the dust cap to make everything look pretty. This would also work with the solid aluminum spacer between the magnets as was posted earlier. You wouldn't need any speacial driver for this configuration, as vented pole piece drivers are very common.
Any comments folks? |
Just that if you do this you have to be careful that you have the spacers the right size. If you have any gaps there exists the possibility of cranking things down to the point where you pull a magnet off. You also loose any cooling or venting effect of the vented pole piece (althou some find that plugging up the pole piece is a good thing sonically anyway.
dave |
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| Schaef |
Sorry for not posting earlier, but things have gotten busy for me. Thanks to all for the info! (Just as an FYI, yes, all-thread is the same as a threaded rod)
Now, I just have to sit down and think about some designs to build. I'm still pretty busy until June, but the money for the amp showed up the other day, so I should be ordering that in the next couple of days. (Then I can play and experiment a little with the existing setup!)
I'll post more details after I have a design and start construction! |
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| leadbelly |
| quote: | Just that if you do this you have to be careful that you have the spacers the right size. If you have any gaps there exists the possibility of cranking things down to the point where you pull a magnet off. You also loose any cooling or venting effect of the vented pole piece (althou some find that plugging up the pole piece is a good thing sonically anyway.
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So guess what, my woofers came today, and they have vented polepieces.
Since I was just planning to cut a wooden donut and epoxy two of them to this donut back to back, this comes as a surprise.
Does plugging up the vent affect the T/S parameters significantly? I have no measuring equipment, so I'm using the manufacturer's specs to determine crossover point, and have to play it safe to avoid changing them too much. Would it be safer to cut vent holes in the donut, or maybe use a thick donut? |
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| pinkmouse |
| Blocking up the vents will change the compliance of the speaker a little, but more importantly, if you are running the sub at high levels, the cooling will be greatly compromised. If you can cut some vents in your doughnut, then I think it would be worthwhile. You could always block them up later if you want to experiment, but if you don't have them and you find they are needed, you're stuffed;) |
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| leadbelly |
Thanks pinkmouse.
Would the type of wood for the donut actually make any difference in the effect of the push-push? Would a non-dimensional wood such as MDF be required, because a grained wood would take one woofer's vibration and impart a directional vector to it along the grain when pushing against the other woofer? Or is even something much less elastic than wood like metal required? Or is this just insane overkill because I'm using $14 woofers? :) :D |
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| pinkmouse |
| quote: | Originally posted by leadbelly
Would the type of wood for the donut actually make any difference in the effect of the push-push? Would a non-dimensional wood such as MDF be required, because a grained wood would take one woofer's vibration and impart a directional vector to it along the grain when pushing against the other woofer? Or is even something much less elastic than wood like metal required? Or is this just insane overkill because I'm using $14 woofers? :) :D |
Insane overkill...Nah...This is DIY!:)
However, strangely enough, I have no experience of this, I am going on guesswork.
Natural wood is most resistant to compression along the grain, so you could just chop a round slice out of a treetrunk, such as Maple, Beech, or Iroko, and use that. Metal, unless you have the tools to work big chunks of it accurately, is probably too difficult, so I suspect it comes down to MDF. Just make sure it is never under tension as it will peel right apart...
BTW, the directional vector that MDF imparts is to that of artistic taste, which it sends into the fourth dimension, as can be seen on many tacky TV makeover programmes that use the stuff all over the place!:) |
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| planet10 |
| quote: | Originally posted by leadbelly
Would the type of wood for the donut actually make any difference in the effect of the push-push? |
Yes. A hard-wood is recommended... the more accurately the material passes the vibration in-tact from one woofer to the other the better. I wouldn't use MDF -- it's too squishy.
dave |
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| leadbelly |
Thanks Dave.
So, the widest sonotube I can find is an 18" at UFA for $36, which seems not worth it to me, since there's all that work stabilizing for a cut and the radius is not all that great for 12" woofers either. Still considering it as a maybe.
So, for the push-push dipole, are there any special geometry issues to worry about, or can I make an H-frame baffle and be done with it? |
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| leadbelly |
| More specifically, would any of these shapes be superior to the others (ignoring baffle width, I know they are not equal): |
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| planet10 |
The south-east one wouldn't be push-push... if i were doing one i'd be thinking along the lines of the NE one -- I don't like the idea of the parallel sides on the front facing portiom. There would be lots of variations. Of course -- bigger the better. One could use plexi for the wings. Don't forget that the shortest path could also be over the top.
dave |
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| kneadle |
| quote: | Originally posted by planet10
The south-east one wouldn't be push-push
dave |
south east? Now I'm confused. Which one is south-east?
Dave |
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| planet10 |
| quote: | Originally posted by kneadle
south east? Now I'm confused. Which one is south-east?
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Bottom-left.
dave |
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| kneadle |
| That one is not push-push because of the alternating mouth area, right? |
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| leadbelly |
As I understand Dave, it's not push-push because the driver's rear forces are transferred to the enclosure without being cancelled by the other driver.
Looks cool, though. I like the symmetry. |
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| planet10 |
| quote: | Originally posted by leadbelly
As I understand Dave, it's not push-push because the driver's rear forces are transferred to the enclosure without being cancelled by the other driver.
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Yep... it would be push-pull, tending to cancel non-linearities in the way the driver moves in vrs how it moves out.
dave |
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| leadbelly |
OK, well your answer has really made me rethink what I had planned to do.
I had planned to just epoxy 2 woofers magnet to magnet, making 1 unit, and then just screw the 2 flanges to the rear surface of two pieces of wood, as shown in the drawing, to begin making the baffle.
Is this technique still push-push?
If it is, would threaded rod bolted through the entire assembly from 1 wood surface to the other be necessary? Or else a threaded sleeve cut to length to fit tightly between the woofer flanges, bolted through from the baffle. |
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| planet10 |
| quote: | Originally posted by leadbelly
OK, well your answer has really made me rethink what I had planned to do.
I had planned to just epoxy 2 woofers magnet to magnet, making 1 unit, and then just screw the 2 flanges to the rear surface of two pieces of wood, as shown in the drawing, to begin making the baffle.
Is this technique still push-push?
If it is, would threaded rod bolted through the entire assembly from 1 wood surface to the other be necessary? Or else a threaded sleeve cut to length to fit tightly between the woofer flanges, bolted through from the baffle. |
yes it is push-push. With the magnets touching, any force thru the magnet and pushing against the other speaker is cancelled to a high degree. When the force is pulling the driver away it is much less effective. By gluing the magnets together you have a greater effect when the drivers pull apart. The threaded rod -- with bolts inside and out, are effective for both push towards & pull-away plus they spread the load over a larger part of the driver -- it is all a matter of how nuts you want to go.
dave |
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| leadbelly |
Well, here's hoping an old thread will wake up:
I never built the above designs because I just can't live with the footprint of any significantly-sized-baffle dipole. But it is warm in my garage workshop now and I already have the drivers, so it just a matter of time before I build something with them.
Dave's comment about adding stuffing made me think about the following design shown. Much nicer footprint for my needs.
My question is, what happens to the reponse as compared to a plain dipole? In other words, I can punch in this smaller baffle size into the same response calculator I was using to estimate the base case (no stuffing) response. More important is how the reponse curve shifts as the stuffing is increased. |
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| Bose(o) |
I was just running some Vector Mech and still don't know why you need to "tie" the woofers back-to-back. All of the mechanical forces are applied symmetrically about a baffle and is transferred to the sides and top and bottom. The enclosure is essentially a dictionary definition for Newton's Third Law.
I did figure that the magnets would have to mounted perfectly within their regions...i.e, center of drivers coplanar. |
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