enclosure too narrow?

[jc]

I thought I had it fixed, but no.

TL enclosure tuned to 21hz. (12' line with slight taper and moderatly lined walls)

Front baffle is 13" wide by 37.5" tall outside.

Inside is 11.5" wide by 14" tall.

Driver is Dayton SD315-88 DVC 12" Overall diameter is 12 3/8" cutout diameter is 10 3/4" Mounting depth 6" Xmax of 7mm.

Problem is a bad vibration in the driver at certain frequencies. I reduced this a great deal by removing a portion of the bracing where the driver is very close to the walls giving the driver a bit more room on each side. (I thought it was gone) But after carefull listening there is still an audible vibration at around 80hz and 30hz. More at the upper end.

It's not the box vibrating, it is the driver frame/basket.

This sub sounds amazing outside of the rattling frequencies. Sweet, tight bass and pure sounding below 30hz. I don't want to scrap the design. I've made two of them inside my listening room because they are well over two hundred pounds and hard to move around.

I'm hoping someone may have an idea or two. But think that it's simply too narrow for the drivers.

JC

[Pete Schumacher ®]

> I thought I had it fixed, but no.

> TL enclosure tuned to 21hz. (12' line with
> slight taper and moderatly lined walls)

> Front baffle is 13" wide by 37.5"
> tall outside.

> Inside is 11.5" wide by 14" tall.

> Driver is Dayton SD315-88 DVC 12"
> Overall diameter is 12 3/8" cutout
> diameter is 10 3/4" Mounting depth
> 6" Xmax of 7mm.

> Problem is a bad vibration in the driver at
> certain frequencies. I reduced this a great
> deal by removing a portion of the bracing
> where the driver is very close to the walls
> giving the driver a bit more room on each
> side. (I thought it was gone) But after
> carefull listening there is still an audible
> vibration at around 80hz and 30hz. More at
> the upper end.

> It's not the box vibrating, it is the driver
> frame/basket.

> This sub sounds amazing outside of the
> rattling frequencies. Sweet, tight bass and
> pure sounding below 30hz. I don't want to
> scrap the design. I've made two of them
> inside my listening room because they are
> well over two hundred pounds and hard to
> move around.

> I'm hoping someone may have an idea or two.
> But think that it's simply too narrow for
> the drivers.

> JC

If you're hearing the basket vibrate, it may not be mounted tight enough, or, you may need a gasket. Otherwise, you can deaden the basket by coating it with a layer of epoxy.

[jc]

> If you're hearing the basket vibrate, it may
> not be mounted tight enough, or, you may
> need a gasket. Otherwise, you can deaden the
> basket by coating it with a layer of epoxy.

I've tried everything but cork for gasket. And on one driver I drilled extra holes in the flange for more mounting holes. Even used a cross pattern to tighten it so as not bind it. Put little plastic washers on the bolt heads to stop any vibrations from rattling there. I had mounted an old set of generic 12's in both of these boxes and had no rattle or vibration. Just poor sound quality

I guess I'll have to try the epoxy.

Thanks for the answer.

JC

[Chris Roemer]

> I've tried everything but cork for gasket.
> And on one driver I drilled extra holes in
> the flange for more mounting holes. Even
> used a cross pattern to tighten it so as not
> bind it. Put little plastic washers on the
> bolt heads to stop any vibrations from
> rattling there. I had mounted an old set of
> generic 12's in both of these boxes and had
> no rattle or vibration. Just poor sound
> quality

> I guess I'll have to try the epoxy.

> Thanks for the answer.

> JC

If you've got a frame/driver rattle, you should be able to hear it out of the box. Why not try that next? Maybe the vc leads are flapping?

Are you SURE nothing's rattling inside your enclosures? You wouldn't hear it with a different woofer if the woofer won't go low enough to cause it to vibrate.

I've used 3 of those drivers with no trouble.

[jc]

> If you've got a frame/driver rattle, you
> should be able to hear it out of the box.
> Why not try that next? Maybe the vc leads
> are flapping?

> Are you SURE nothing's rattling inside your
> enclosures? You wouldn't hear it with a
> different woofer if the woofer won't go low
> enough to cause it to vibrate.

> I've used 3 of those drivers with no
> trouble.

Well, I'm quite sure it's not the enclosure. I built the first one and got the rattle. 3/4 MDF and line walls every 4.75" with every corner having a brace. So I thought something was loose in it. So I built the next one with much more bracing. It had the same rattle. Two boxes, two drivers, the exact same rattle, same frequencies. (I have to scrap the first one now because they are not identical with the extra bracing)

more weird things- Both boxes I played with damping material to tune/remove standing waves with the top (or side depending on view) having minimal screws. In other words, leaky. There was little rattle and what there was I assumed was the loose top. Also, when I LOOSEN (make leaky) the drivers, the rattle is reduced. I have had them in a small box and what rattle was there I thought was coming from the flimsy boxes. (old pair of cheap floor standing 3-way speakers) I'll try them in open air. I did test them with a PC program and they tested very close to manufacture specs.

I have had others listen and look with no answers.

Needless to say, this is very frustrating and I have brought my axe into the house. If they must go they will go in piece's.

I don't know why it would make a difference but it almost HAS to be the close inside dimensions.

Thanks for your thoughts.

[jc]

The design is very simular to this only wider and not as tall with two more folds on both sides of the driver. From Transmision Line Speaker page.

[marlboro]

Its a TL. I would contact ML King, the guru of TL's and see what he says. It sound less like you have a rattle, and more like you have a specific frequency resonance based on the the dimensions of the box. If anyone can assist you with this, its King. Google Transmission Lines and ML King and you find his email address somewhere. He also posts here, but unless you have Transmission Line in the title, he probably won't see the discussion.

Kind regards,

Marlboro

p.s.: If you are going to paint the speaker itself, I'd go with that rubberized dipping paint that they use for putting rubberized coatings tool handles.

> The design is very simular to this only
> wider and not as tall with two more folds on
> both sides of the driver. From Transmision
> Line Speaker page.

[mgh]

Try laying the box on its side first. I did the down firing calculation and at 7mm XMAX and an Fs of 25 this driver exceeds the 5% sag figure (5.7%). I suspect you've compounded the problem by tuning the TL so low (below driver resonance). Even tuning the box at 35 Hz, you would still have a solid output for the last octave with a slow rolloff and room gain. Regardless, you can do these calculations to determine if you are exceeding XMAX.

Murray

> I thought I had it fixed, but no.

> TL enclosure tuned to 21hz. (12' line with
> slight taper and moderatly lined walls)

> Front baffle is 13" wide by 37.5"
> tall outside.

> Inside is 11.5" wide by 14" tall.

> Driver is Dayton SD315-88 DVC 12"
> Overall diameter is 12 3/8" cutout
> diameter is 10 3/4" Mounting depth
> 6" Xmax of 7mm.

> Problem is a bad vibration in the driver at
> certain frequencies. I reduced this a great
> deal by removing a portion of the bracing
> where the driver is very close to the walls
> giving the driver a bit more room on each
> side. (I thought it was gone) But after
> carefull listening there is still an audible
> vibration at around 80hz and 30hz. More at
> the upper end.

> It's not the box vibrating, it is the driver
> frame/basket.

> This sub sounds amazing outside of the
> rattling frequencies. Sweet, tight bass and
> pure sounding below 30hz. I don't want to
> scrap the design. I've made two of them
> inside my listening room because they are
> well over two hundred pounds and hard to
> move around.

> I'm hoping someone may have an idea or two.
> But think that it's simply too narrow for
> the drivers.

> JC

[mikec]

some thoughts about the mechanical part of the problem==

Play them for a while, then inspect the drivers for "wear points" where parts are rubbing.

Try putting dabs of lacquer/cheap nail polish across joints and see if any crack --if they do you've found what's moving.

Maybe run a bead of epoxy across any suspected joints.

Run a brace behind the driver and pad it (silicone?) so that it supports the back of the driver when installed.

Are both of them doing it? If just one, could the driver be faulty?

interesting problem - -

________
party Cam

[billfitzmaurice]

I can see a number of reasons for the problem. The xmax is shy, the driver Bl is low, the frame isn't strong enough. A TL that long has a lot of air mass inside the pipe, and it takes a lot of effort for the driver to push it. There comes a point where additional power applied doesn't result in additional excursion, but instead results in mechanical distortion. You need a driver that's robust enough to stand up to the job, something along the lines of Titanic 12.

[mgh]

Temporarily mount the driver on the outside of the box facing inward. This will eliminate the possibility that the volume directly behind the woofer is causing a constriction.

Murray

> Try laying the box on its side first. I did
> the down firing calculation and at 7mm XMAX
> and an Fs of 25 this driver exceeds the 5%
> sag figure (5.7%). I suspect you've
> compounded the problem by tuning the TL so
> low (below driver resonance). Even tuning
> the box at 35 Hz, you would still have a
> solid output for the last octave with a slow
> rolloff and room gain. Regardless, you can
> do these calculations to determine if you
> are exceeding XMAX.

> Murray

[johnnail]

> Temporarily mount the driver on the outside
> of the box facing inward. This will
> eliminate the possibility that the volume
> directly behind the woofer is causing a
> constriction.

> Murray
nt

[johnastockman]

MGH's suggestions are spot-on for troubleshooting, but I have to agree with Bill F. about this driver being adequate for this application. Not a good candidate for down-firing (if that's how it's oriented), the tuning is below Fs, and probably not appropriate for a TL. I've used the 10" and 12" SDVC's in a few subs I've built and never had any issues with them, but I used them in sealed and vented boxes, not a TL type. This is a fairly inexpensive driver...maybe an RS series or Titanic sub would work better for this type of enclosure (maybe even a Quatro). Let us know if you find the source of the vibration/rattle.

John A.

[jc]

How about this?

These are sheilded. Is it possible that the close proximity to the inside walls is directing sound waves at the magnet sheild? The shield seems quite acceptable but thin enough to definatley resonate if waves were directed at them. Metal resonates quite easily. In a larger enclosure waves would not be directed so heavily at the magnet/shield assembly so this would not be a problem.

Thoughts?

[jc]

Okay, some clarification.

It's not up firing or down firing. I put more folds in it so that it is wider than tall (as per the example I posted) so that these will lay down like a table with the driver and ports facing the listening area.

Also, while the line is long with a small taper and the wall lined it will add a good bit of damping on the cone. But I hardly think that it would be near that of a sealed/accoustic suspention.

I have not been able to test because of the rattle but my F3 should be at 21hz. I may be mistaken as I'm new to this but generally a TL should be tuned 5hz higher or lower than the driver Fs Depending on Qts. That is why I chose these drivers. Less of a impact on the wallet if it turns out I'm just crappy at speaker building.

Also, this rattle is as present at low volume as high volume. I have not bottomed these drivers out. The only difference higher volume makes is loader rattle.

Keep the thoughts comming, I appreciate the help.

[jc]

> Temporarily mount the driver on the outside
> of the box facing inward. This will
> eliminate the possibility that the volume
> directly behind the woofer is causing a
> constriction.

> Murray

Good idea. I'll try it tonight.

[billfitzmaurice]

> Also, this rattle is as present at low
> volume as high volume.
That indicates a mechanical vibration in the frame, the magnet covers or something beneath them could well be it. I'd remove them.

[dick]

But does it rattle when NOT mounted? Take one out and sweep it free air. Lots of subs have rattles that have nothing to do with the cabinet!

Dick

[jc]

Okay, I mounted the driver facing in (magnet out). Immediatly and at very low gain the same rattle is present.

Took a firm hold of the magnet shield, cupping it in both hands and the rattle is gone. Added gain and repeated with the same results.

Loose magnet shield.

The other driver is not as bad with only a small rattle. (it hasn't been in as long) For two drivers to have this problem I assume the tight enclosure must have started the process.

I don't need the shields so how do I remove them? It appears they are glued on.

Thanks for everyones help. This was driving me bonkers.

JC

[mgh]

If all that's holding the cup on is magnetism, work the cup off, glue on a layer of rubber insulating material inside the cup and on the back of the magnet and pop it back on. I have two things that could work: one is a layer of dense foam that you put under flooring to pad it. The other is a waterproofing material that paints on. It's waterbased and at homedespot it's called RedGard.

Murray

> Okay, I mounted the driver facing in (magnet
> out). Immediatly and at very low gain the
> same rattle is present.

> Took a firm hold of the magnet shield,
> cupping it in both hands and the rattle is
> gone. Added gain and repeated with the same
> results.

> Loose magnet shield.

> The other driver is not as bad with only a
> small rattle. (it hasn't been in as long)
> For two drivers to have this problem I
> assume the tight enclosure must have started
> the process.

> I don't need the shields so how do I remove
> them? It appears they are glued on.

> Thanks for everyones help. This was driving
> me bonkers.

> JC