Modyfying the parameters of a 15" woofer

[noviygera]

After a long search I could not find a 15" or 18" woofer with parameters am I looking for:

High Qms (over 20)
High BL
High Vas
Low Mms
Low Fs (under 30hz)
Low inductance

This is going to be a multiple driver 8-12 vented or T/L subwoofer for impactful, dynamic bass at very low listening levels.

My question:

I found a driver that is close but Fs is too high and Vas is too small
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WITHOUT adding moving mass, what can I do to lower the Fs on this driver?
Change or cut the spider? Soften the spider?
Anyone had experience with such a situation?

[PeteMcK]

the 15" drivers on this page come close, but Qms is lower;
etone PROFESSIONAL SOUND
methinks your cabinets are going to be about the size of a bus....

[vacuphile]

Fs and Vas are communicating vessels with Qt as their middle man.

A driver with a higher Fs and smaller Vas, may operate similarly in a vented enclosure of similar size, as a driver with lower Fs and larger Vas, provided that the Qt of the latter is lower.

Therefore, you need to feed the parameters of the speaker you are looking at in the right formulas to help you decide if they will work in the enclosure size you are looking at.

This is an easy site for all kinds of calculations:

http://www.mh-audio.nl/spk_calc.asp


vac

[CharlieLaub]

You can modify apparent physical driver parameters by using the ACE-BASS circuit designed by K. Stahl. His U.S. patent from about 1980 or so has a good explanation of the circuit. You can model it using the program "Basta!".

-Charlie

[CLS]

I've experimented cutting the spider and surround of a driver. And softening the spider, too. (by silicon oil).

They are aiming the same goal - softening the suspensions, and all of them indeed lower the fs to some extent. But, by the very different structures and materials of all drivers, I believe there's no answer to which part is the most effective.

Some drawbacks:

1. Not reversible. Cut is cut. So you'd better do it bit by bit and examing by measurement, say, WT3 of the likes...

2. There're 2 suspensions in a woofer. The overall stiffness of the entire driver might be dominated by one of them, or pretty evenly distributed by the 2. Trying to find out which is stiffer in the first place might help.

3. The oil for softening the suspensions might gradually damage the adhesive. Generally, thicker (sticker) oil tend to be more stable; thinner one would be a better solvant... (actually I'm not 100% sure of if the glue for driver's suspension can be dissovled by oil, yet, I encountered this problem in some other things... ) And once the fabric parts get wet, they also get dirty more quickly.

4. Overall effect of moding a driver like this is not very predictable, or fitting in your purpose very well. And obviously not cost-effective. Once you fail, you simply destroy a driver. Trying (practicing) it on the cheaper one can't be a promise of sucess to another (more expensive) one.

for impactful, dynamic bass at very low listening levels.

-- my suggest is building a real bass horn.

[noviygera]

I am intrigued by the idea of softening the driver suspensions. Any other solutions besides silicon oil?

Which type/brand of silicon oil is recommended?

Thanks for all replies,
Herman

[CLS]

No brand. Nothing is marked on the plastic bottle. Ah! I remeber the oil is identical to the oil-filled gauge of Autometer. LOL ! (no! I'm not saying go buy an Autometer stuff)

Think this way. Spiders are mostly made of thick fabric. When in motion (stretched), there'd be friction among the fibers in the fabric. Oil (or any possible lubricant) in the fabric is to reduce the friction, thus the effect of softening. So, it doen't have to be silicon oil.

Eventually, softened by lubricant alone is not very effective. To achieve something more measurable, you have to cut something.

But, still, all these mods are not going to give what you want.

Impactful and dynamic bass at low level are not only relying on soft suspension. It might help a little under some conditions, but there're so many other factors. Look at those guitar drivers, their suspensions are so stiff that seem enough to stop any motion. But, how do they sound? Full of snaps !

The suspension provides not only damping, but also acts like a spring. At a transient note, VC gives the initial force, and then the suspensions pull it back right away. In this regard, suspensions are not only stopping the motion, but also contributing some of the actions. So, subjectively, I feel many stiff drivers sound "fast".

Again, I'd suggest rethink the whole thing. It's not the best route to achieve your goal.

[noviygera]

Ok, CLS I agree with your reasoning regarding spider softness/stiffness. It may not be the right direction to approach. But what am I trying to accomplish?

My goal is to have great transient response at quiet listening levels. To do that giving priority to the following specs (within reason):

Rms (less than 2) which is related to:
Qms (over 20)
Mms (low)
BL (high)
these relate to transient response. Now...
I need some low bass as well, but there is no free lunch. So to have good low bass I need low Fs but at what expense? There is only left Vas and Qts. As a trade off they must be high.

Correct?

[tinitus]

AE Speaker's Lambda Dipole 15 has Fs/22Hz with only 90gr mms

if you don't play loud, or use multiple drivers, maybe it would make sense to try and get it with shorter Xmax by making voice coil a bit longer
with a dipole bass design its probably the most responsive bass for lower SPL you will ever get

I may have misunderstood
but I'm not sure I understand your project, using multiple big woofers for low SPL
a single 18" pro woofer would be more than enough

or use 12" hifi woofers

[tinitus]

or RCF-L18P200-N looks like a good candidate

I have thought about it myself
for a closed design
I see no point in using BR
shallow cone for a studio speaker
and it has enough Xmax for adding exstra mass/coating

RCF - L18P200-N