[serengetiplains]

I've been poking around OB threads with interest anticipating I will build OB speakers.  One issue I'm unclear on is how driver mounting affects resulting sound.  I've read that mounting the driver to the baffle will cause the baffle to vibrate.  This seems uncontroversial to me.  I've also read that mounting the driver by clamping the magnet, then soft-touching the basket to the baffle will reduce baffle vibration.  I'm not sure this is the full story.

First, it seems to me that Newtonian reaction energy will transmit as effectively through the magnet structure as through the basket mounting flange.  These two form one solid unit, after all.  This energy will then transmit into the structure to which the clamping method is attached, this structure being either the baffle per se, or some other assembly that itself must be either attached to the baffle or closely aligned to it.  In either case, the assembly, and the floor, and possibly the baffle will receive this energy, and vibrate.

Second, magnet mounting seems to me less solid, less secure than basket flange mounting.  To the degree magnet mounting flexes will the driver's ability to produce sound be compromised (magnet-mount flexure is lost cone vibration energy).  Further to this, I would assume that increasing the weight ratio of basket-to-cone results in more faithful cone vibration.  Where the driver is attached to the baffle, baffle weight adds to basket weight.  Wouldn't a heavier baffle be therefore better?

Am I wrong about either of these?

Tom

[454Casull]

The vibration energy still gets transferred through a magnet mount, but the structure of a magnet mount tends to be stiffer than the baffle, so there is less sound-producing displacement.

On the contrary, magnet mounting is more secure. In either case (flange or magnet mounting), you have a cantilevered mass off the fixed point. For a baffle mount, the cantilevered mass includes both the basket and the motor, where the basket can act as a spring [SL] and therefore produce resonances. For a magnet mount, the only cantilevered mass is the basket which is significantly lighter than the motor. As long as your magnet mount is secure, there's no reason why it would be weaker than a baffle mount. As to the other point, I don't have hard figures, but it seems to me that the energy lost (regardless of which mounting type) is negligible.

My two cents.

[serengetiplains]

Hi 45, I think, yes, amount of energy lost is in any case minimal, but let's inquire into what aspect of cone movement this energy loss might affect.  It would seem to me acceleration would be the primary compromised element, and more so the higher the acceleration.  This compromise would seem to me to compromise transients.

[serengetiplains]

Also, looking at the bottom-most diagram here, the wood support used to increase stiffness of the magnet mount would look to me to create just the thing an OB wants to avoid, a sound-reflecting surface (here, essentially a half-box) adjacent to the rear of the cone.

[454Casull]

Hi 45, I think, yes, amount of energy lost is in any case minimal, but let's inquire into what aspect of cone movement this energy loss might affect.  It would seem to me acceleration would be the primary compromised element, and more so the higher the acceleration.  This compromise would seem to me to compromise transients.

If you post in the same general time period, just modify one of your original posts. It's easier to quote just one post.

In what way will the diaphragm lose energy? Remember that for SPL to be compromised, the diaphragm's acceleration relative to "space", or ground, must drop.

For the other post: there are many ways to implement magnet mounting.

[gainphile2]

Hi, I have been thinking about this too. Can anyone advise how audible is the change between normal mount vs. magnet mount. I am also worried about the resonance created by the magnet mount (the panels used to mount the magnet).

[serengetiplains]

In what way will the diaphragm lose energy? Remember that for SPL to be compromised, the diaphragm's acceleration relative to "space", or ground, must drop.

To the extent the magnet/basket assembly, and with this, anything to which it is attached (baffle, etc.), moves or vibrates has the diaphragm lost energy.  When the cone is propelled forward, the magnet assembly is propelled back.  Any resulting movement back subtracts from cone movement forward, meaning the cone moves less relative to air.  Transients would thus be compromised.

The above is irrelevant to the extent basket vibrations constitute resonances passing through the suspension.

I pilfered this comment (not from Lynn) from Lynn Olson's website:

What an interesting subject. I followed the timedomain links (interesting English) and what is mentioned there makes perfect sense to me; Separating the loudspeaker ground from the enclosure. After all, that’s what we do with amps, separating signal ground from chassis ground.

Any action will result in an equal opposite reaction. The action would be the loudspeakermembrane and the reaction the loudspeaker chassis+enclosure. Expressed in grammes, the difference is huge. But what if we use logaritms like we do for voltage, then the numbers appear less favorably.

Let Mm be the moving mass of the system and Ms the stationary mass of the system. Then we could define the mass ratio dBM as 20 x log(Ms/Mm). For the Fostext208∑ the equivalent moving mass is 12g, the stationary mass is 3800g. The mass ratio would then be 50.0dBM, and the Fostex has a very low moving mass and very heavy magnet system. A typical loudspeaker has a higher moving mass and much lower magnet system weight, so 50dBM is already on the high end of the scale.

Does this make any sense? I mean, could this dBM number be used to predict the amount of cabinet resonances? A sort of signal to cabinet energy ratio?

[454Casull]

In what way will the diaphragm lose energy? Remember that for SPL to be compromised, the diaphragm's acceleration relative to "space", or ground, must drop.

To the extent the magnet/basket assembly, and with this, anything to which it is attached (baffle, etc.), moves or vibrates has the diaphragm lost energy.  When the cone is propelled forward, the magnet assembly is propelled back.  Any resulting movement back subtracts from cone movement forward, meaning the cone moves less relative to air.  Transients would thus be compromised.

Nothing is infinitely stiff, but a well-designed magnet mount should not allow the motor to move significantly. If that's not what you're talking about, then I fail to grasp your point.

[serengetiplains]

45, language like "should not allow the motor to move significantly" is not sufficiently precise for me.  I'm here wondering to what degree music is affected by just those kinds of movements.  My questioning wants better to understand what movement is or might be there and what aspect of sound is or might be affected by that movement.  If my questions are irrelevant, then they're irrelevant.  I'm not convinced they are. 

The difference between a good and a great speaker is found, IMO, in those kinds of details.

[454Casull]

45, language like "should not allow the motor to move significantly" is not sufficiently precise for me.  I'm here wondering to what degree music is affected by just those kinds of movements.  My questioning wants better to understand what movement is or might be there and what aspect of sound is or might be affected by that movement.  If my questions are irrelevant, then they're irrelevant.  I'm not convinced they are. 

The difference between a good and a great speaker is found, IMO, in those kinds of details.

Well, I have nothing further to add that is of use. It is, however, my opinion that such an effect is negligible.

[owenmd]

Hi Tom,

I too have been contemplating this question for some time as I need to construct some new baffles for my Hawthorne Sterling Trio's.

I still haven't read any solid and confirmatory information that magnet mounts are superior.... somehow, it also just doesn't "feel right" to me...?  From the perspective of loss of micro information through adverse canceling driver movement, basket mounting solidly to the baffle feels like the way to go, but this obviously can lead to coloration from sympathetic baffle resonance.

I believe a high-mass baffle is better than a low mass baffle from what I've heard, as it will obviously lower the unavoidable resonate frequency to a less audible area.  I plan to use a laminate of 3/4" birch plywood and 3/4" MDF joined with green glue for additional damping.

Right now, I'm leaning toward mounting my drivers to a minimalistic and highly damped sub-baffle and isolating this from the main baffle using Herbies Audio lab isolating washers and bolts.  I'm thinking this will be a good compromise between minimal micro-movement and isolation.  The other option is bolting solidly to the baffle and mass-coupling, in which case I would add another layer of MDF and green glue to further increase the obsorbant mass.... probably in combination with some form of sand or lead shot vibration sink.

I would love to hear if anyone can comment on direct sound quality comparisons between a magnet mount and more traditional mounting methods using the same baffle....?

Cheers,

Mark

[Bob in St. Louis]

I cannot comment about direct A/B comparisons regarding magnet versus basket mount. My baffle builds have been sufficiently different from one to another that fair comparisons are not possible.

I do believe that the ONLY part of a driver that should contribute to the sound should be the cone. Not a "ringy" basket, not the weight of a magnet hanging "way out back there", and certainly not a strictly magnet mount. Seems to me, the worst would be supporting the magnet exclusively and allowing the weakest part of a driver basket (the flimsiest part in comparison) and flange to flap around out there in the breeze.
So, in my very humble opinion, a combination of magnet and flange mount would be best.

Mr. serengetiplains, The way I think of it, is that if you can't properly hold the entire driver firmly, then there will be some part of it contribute to the sound in some negative way. Now, that being said, if you never listen to volumes over low(ish) levels, this might not be an issue. However, if you're "giving it some", then it is my belief that things should be held in a vise like grip. All of it, not just the front or the back of it.
At least, that's my line of reasoning.

Bob

EDIT: By the way Mark, welcome to the Hawthorne club.  aa

[markC]

Maybe I just got lucky, but recessed flange mount with gasket, damped basket ribs and cork on back of baffle is working great for me. The baffles do vibrate a little when held onto, but not rapidly. Therefore I feel that the vibration is below the "critical" frequencies. My baffles are just 3/4" Baltic birch with 1/8" cork. They are pretty though, if I do say so myself.

[Bob in St. Louis]

Show 'em.  aa

[serengetiplains]

Bob and Mark (owen), my sentiments follow what you both say.  I'm thinking flange-bolting to a massive baffle supplemented by an L-arm assembly bracing the magnet---the ole everything and the kitchen sink method---would probably work best.  Sand and lead shot seem apropos.  I'm tentatively thinking of a marble-lead-marble sandwich on a relatively small, narrow baffle: heave ho babies!  The magnet brace will require some thinking.

Tom

[Bob in St. Louis]

Wow, that will be heavy! 

How about a marble-lead-marble sandwich with Green Glue?????  aa

It's been several years, but "Mr. Content" is the first (I've seen) to implement flange and magnet mounting at the same time. I think the photos where on the old version of the Decware forum. It was a b200 driver if memory serves.

Sorry for the wild goose chase if you decide to go searching. 

Bob

[owenmd]

Tom,

I was also thinking of two layers of 3/8" birch ply sandwiching 1/16" lead sheet with green glue for my small sub-baffles holding the drivers.... with additional car panel damping sheet followed by felt, it should be pretty quiet...?  You may want to research the marble baffle thing.... I read somewhere that granite/marble "rings" and may sonically smear.... plus, because its so dense, its difficult to successfully damp...?  Although wood/MDF may exhibit more noise on its own, its also more responsive to damping.

Thanks for the welcome Bob.... much appreciated.... Diana and Darrel are good people with great products.

EDIT: By the way Mark, welcome to the Hawthorne club.  aa

[Bob in St. Louis]

There's a fella on the Hawthorne forum that used marble (or was it granite) with good results. It is one of those "controversial" baffle materials though. If memory serves, his name is "ole".

I'd find the thread for you, but it's movie time right now. Gotta go.  aa

Bob

[serengetiplains]

Granite might be too heavy, and I agree from what I've read it's considered controversial.  Here is one speaker manufacturer that uses granite.  What tips the scale to yes for me are the beneficial sonic effects I hear from using these.  They're basically constrained-layer granite and aluminum composites.

I'm thinking two lines of bolts down the length of the baffle, with a thin middle layer of lead, will kill the ringing. Of course, the granite should survive a fall through my floor to the room below, so that's a bonus too.  "Honey, the speakers fell through again," or, "Look, they're still playing."

By the way, Mark, I think lead is the way to go for damping.  It has, if I recall correctly from some speaker design book I read years ago, off-the-map damping characteristics.

Tom

[Bob in St. Louis]

Here's the link I was referring to about the granite baffles.

Bob