Sub drivers: diameter vs. throw length?

[newmz]

I've been looking around at drivers suitable for building a sub, I'll most likely go for a 4th order bandpass box.

When comparing the specs for drivers and the required enclosures my software comes up with (I use WinISD), I started wondering about the comparitive importance of xmax ("throw") and cone surface area.

I read and hear over and over that maybe the most important factor in a sub driver is its ability to "move lots of air". At first I thought that this just meant buying the biggest diameter driver I could afford that wouldn't need to be housed in in an unreasonably huge box.

A few weeks ago I got the specs for a 15" that a local supplier has started stocking and it's quoted xmax value is only 3.5mm. Is this typical for bigger drivers? Will I be better off with a smaller, long throw driver?

I guess ideally I'd like to find a 10" or even 8" "long-throw" driver so that the box doesn't have to be refrigerator sized but I'd guess that this would mean paying really big $'s, is that right?

Also, if anyone in Australia can tell me where I can buy decent (but not astronomically expensive) long throw drivers I'd be really greatful. I have looked at whats available at Jaycar and Altronics and the only possibilities I can see are the "response" brand one they call high-power drivers.

 

[f4ier]

Cone area and excursion capability aren't enough to go by, you have to consider all the parameters in order to make good driver selections. Consider the following subwoofer brands.

Adire Audio drivers are available from Acoustic Concepts (in Melbourne), which is the only Adire Audio distributor in AU.

One of the Peerless distributors (for the XLS drivers in particular) is WES Components (in Sydney).


Cheers 🙂
Isaac

 

[cocolino]

I read and hear over and over that maybe the most important factor in a sub driver is its ability to "move lots of air".

Hi newmz,
moving lots of air is indeed what one would want for a sub.
As the "moved air" is a product from cone surface area and xmax both parameters are equally important for this.
For sub applications nothing beats big high (linear) xmax drivers unless still bigger drivers with still bigger xmax.
Regarding the plain result of amount of "moved air" it does not matter if You have a big diameter driver with lower xmax or a smaller higher xmax driver.
However bigger drivers theoretically have some advantage regarding IM-distortion due to the fact that they have to do less excursion for the same amount of "moved air" , but I believe this does not matter too much for a sub only application where the frequency range is limitid to less than 100Hz. Of course this is valid only if not overdone for instance raping a high xmax 5" driver to do the same what the (accordingly lower xmax) 15" should do.

A few weeks ago I got the specs for a 15" that a local supplier has started stocking and it's quoted xmax value is only 3.5mm. Is this typical for bigger drivers? Will I be better off with a smaller, long throw driver?

Many drivers of that size have somewhat limited xmax when compared to smaller ones. Note that many of them are optimized for instrumentation application and not Hifi. Those are not intended for use as a sub but for mid-bass range often with high(er) sensivity. To achieve the high sensivity they have low compliance cone surroundings and spiders and therefore also lower xmax.
Second, the reason why big (15") AND high xmax driver (with still reasonable sensivity) are rather rare also may have to do something with relatively complex (and costly) construction. It is difficult to achieve that a big and therefore high mass cone can move over a high linear xmax-range and at the same time to maintain that the voice-coil is still centered into the air-gap. When the coil becomes off-centered (over time) this can lead to scratching in the air-gap in the worst case.
You`ll not find a "cheap" 15" sub-driver with high linear excursion capabilties and with good longterm stabiltiy regarding centering.
Therefore I think Your best bet would be in the 10" or 12" driver range. If this is not big enough for You, You can use a second driver, or a third, or a........

I guess ideally I'd like to find a 10" or even 8" "long-throw" driver so that the box doesn't have to be refrigerator sized but I'd guess that this would mean paying really big $'s, is that right?

I`m sure there is plenty of choice in the 10" drivers range with reasonable xmax but without paying big$$.
As You can`t have every advantage at the same time, to say:
low fs, high xmax, high sensivity, small box, cheap.....there is to make some sort of compromise.

When Your primary goal is rather reduced box size choose a driver with a rather heavy (and rigid) cone with somewhat reduced compliance (smaller Vas) which often still can have reasonable high enough xmax and sensivity.

originally posted by f4ier
Cone area and excursion capability aren't enough to go by, you have to consider all the parameters in order to make good driver selections. Consider the following subwoofer brands.

Hi Isaac,
cone area and (linear) excursion capability IMO are the most important parameters for subwoofers.
Followed closely by stiff/rigid diaphragms (in subwoofer applications whitout the disadvantage of cone-breakup resonances as this sometimes can be the case for very stiff driver cones in higher frequency ranges).
Also big diameter voice coils may be important for high power consumption and low thermal modulation.
High sensivity isn`t at the first places in my book of priority for low frequency drivers as high linear xmax and high sensivity is not only a contradiction to some extend (or very expensive) but (good and not too expensive) high power amps (for sub frequency) are readily avaiable.