What is better? Big diameter or long throw?

[mwmkravchenko]

You need alot of air to even hear the lower frequencies. You need approximately 2 litres of real not hopefull displacement to hear 20 hz. The lowest distorsion will come from a bunch of smaller diameter woofers. To figure out real x-max you need to figure out voice coil length minus air gap height then add 25%. That will give you real X-max. You will find that the diameter of a woofer is usually usefull to about half the surround width as a true piston. With this info do some more looking and you may be surprised at the volumes that you come up with compared to the advertised specs. One more note. To hear 16hz at the loudest levels I have ever heard of you need four 15" woofers displacing 4litres of air per stroke. Not chicken feed and pretty darn impressive if you have ever heard it.

Mark

[SimontY]

four 15" woofers displacing 4litres of air per stroke.

Four 15" sub drivers, presumably in a ported box. Yikes! That's one large cabinet! Did it make you feel ill?

It's a shame the laws of physics are the way they are
I'd love a little sub with a 10" driver or something like that, but it's just not gonna do squat. Ah well...

I still think 2x12" has to be a great compromise - for price, size, performance, versatility even(??)

The REL Studio II uses a couple of Volt 10 or 12 inchers. I bet that sounds nice. Has anyone heard volt bass drivers, or such a costly sub?

Has anyone tried their ARM (acoustic resistive matrix iirc) loading in a DIY project??

I've just remembered, some of the most impressive deep bass I've heard. Our city's cathedral is having a new organ built, costing millions £££. In the meantime they have a Hammond organ and large arrays of speakers on the walls. In one corner is a giant transmission line with 8(iirc) 15"(most likely, it's quite high up so could be 18") drivers!!! Sure it's a large building, but it can wobble the pews, and if you're feeling a little fragile after a big Saturday night, it makes you feel funny with the right hymns!!


-Simon

[Matttcattt]

Originally posted by SimontY

Four 15" sub drivers, presumably in a ported box. Yikes! That's one large cabinet! Did it make you feel ill?

I've just remembered, some of the most impressive deep bass I've heard. Our city's cathedral is having a new organ built, costing millions £££. In the meantime they have a Hammond organ and large arrays of speakers on the walls. In one corner is a giant transmission line with 8(iirc) 15"(most likely, it's quite high up so could be 18") drivers!!! Sure it's a large building, but it can wobble the pews, and if you're feeling a little fragile after a big Saturday night, it makes you feel funny with the right hymns!!

wow x2!

[BAM]

A new, linear-operating 10" driver is the SX10 at Creative Sound Solutions. It is designed specifically for CSS and features Adire's XBL^2 technology.

[kelticwizard]

Following is a chart I posted for how much air must be moved to produce which SPL at what frequency. The original chart is by Richard Small. There are two charts-one for real and one for Metric measurements.
Volume Displacement For SPL Chart

Just for reference sake, the air a woofer can move is it's area times it's ±excursion. So a 15 woofer normally has something like 132 in² and an excursion of anywhere between ±¼" and ±1½", (yes, the latter actually exist). ±½" is a nice long excursion, so 132 in² X ½" equals 61 in³.

According to our chart that will give us about 104 dB @20 Hz. Four of them will raise the SPL 12 dB, so it will be 116 dB @ 20 Hz.

This applies to sealed systems only. Properly configured ported systems with the correct woofer parameters can give a single ported speaker the same output as four sealed woofers.

[Jimmy154]

I think it sounds better when a 15" pushes air gently at say 30 Hz than to get the same SPL from a 12" trying get the same result at close to double the Xmax. I have realised this before I ever read it on DIY Audio sites.

I'm not sure what group delay is exactly or a lot of speaker terms. I think Ron E's quote somewhat applies here (no offense to any one ): "An expert is one who knows more and more about less and less until he knows absolutely everything about nothing. - Nicholas Murray Butler"

It's just simple physics, that moving air gently is a good idea. Depends what spl you want and at what Hz. Deep and loud bass on one 15" always sounds better to me than one 12" working twice as hard. Less SPL or more Hz a 10 or 12 might sound better to me. Okay maybe the guy is a bit too much. You know what I'm trying to say though

[Squalish]

Originally posted by EC8010
Group delay is the time by which frequencies within a group are delayed. If you had a group delay of 1s for all audio frequencies, it wouldn't matter (except for when cueing the stylus). There's only a problem when you have non-constant group delay - some frequencies are delayed by more than others. Filters are not only characterised by their amplitude vs frequency response, but also by their delay vs frequency response. The low-pass filter needed for a sub-woofer always implies substantial delay, and unless you also delay the audio to the main loudspeakers, the sub-woofer will always lag behind. Additionally, the LF alignment of the sub-woofer and its enclosure forms a high-pass filter and as as the volume of the box decreases relative to VAS, Q rises and delay between different frequencies increases. There's nothing like a big box.

A larger diameter driver can move the same volume of air as a small diameter driver, but with less excursion. Less required excursion means the coil doesn't need to be so overhung, and that increases efficiency. A larger cone will break up at a lower frequency because break-up occurs when the circumference of the cone is equal to one wavelength. The velocity of sound varies with cone material, but break-up frequency is broadly inversely proportional to cone diameter. You have to try quite hard to get a cone to break up at <200Hz.

Can the 'time delay' you speak of be absolved by making a dedicated sub amp that has a high pass filter in the feedback loop?

[kelticwizard]

Jimmy:

I kind of agree that bass from a larger woofer sounds better. But the larger the woofer, the bigger the box for the same cutoff. So it is a tradeoff.

I am glad that the poster came forward to explain group delay. It is a term that is getting increasing attention, an I am glad that someone came forward to tell us what it is. If you don't "get" the explanation, or simply feel unconcerned about group delay, that does not mean that the person does not know what he is talking about.

Some time back, the people at Stryke ran some tests and discovered that group delay for a sub is associated with transient response. The higher the group delay, the worse the transient response. So a low group delay is nice to have, if for that reason alone.

Back in the seventies, people were pooh-poohing phase relationships in speakers as a fad. Over the course of time, it has been accepted that phase is important for good reproduction. Just because something is new doesn't mean it is overrated.

[planet10]

Originally posted by SY
Multiple smaller diameter drivers can often be a good compromise.

I always like to use 2 drivers in a box push-push, 4 for a stereo pair. i have also been finding that i get better integration if the bass driver has an extended range and have therefore been heading towards older 12s (if you are patient they can be really cheap too ), or 10s or even 8s if i need to use new drivers. This often means giving up some ultimate extension on the bottom, but it isn't really missed.

dave

[subwo1]

I vote for high excursion smaller woofers in small boxes. Besides group delay as mentioned, the smaller box size is easier to make stiffer, resulting in less coloration from box vibrations. A vibrating box can be thought of as a distorted, poorly phased, passive radiator.