Same Vd, different size drivers - is bigger better?

[rick57]

Some have suggested (IIRC at the AA's High Efficiency Speakers or here) that bass from larger, lower xmax drivers, sounds better (more effortless? ~ lower IMD??) than from a smaller driver of the same Vd.

If beaming is not an issue, in would the same Vd from eg a 15" be preferable to that Vd from a a higher xmax 10/ 12"?

I was thinking of a dipole over 70 - 400 Hz, but don't know that dipole would change the answer; maybe over 70 - 400 Hz would in part.

thanks

[wigginjs]

The theory behind that, I believe, comes from the idea that with a lower xmax driver cone movement remains more linear because the VC doesn't stray as far from the field generated by the drivers magnet. That said, it's my understanding that dipoles generally require significantly more displacement than conventional boxed speakers, but I don't think that it matters how you get that displacement. For instance, I believe that the output achievable from two drivers with the same Vd in a dipole configuration will be similar regardless of their Sd, but that generally there would be more distortion produced from the higher xmax driver. However, I think best way to compare two drivers for a dipole configuration would be to download the spreadsheet Sigfried Linkwitz has available on his site and model both of them.

Side note: A 15" driver used to cover 70 - 400Hz doesn't seem like the best fit to me, even in dipole configuration. Try perhaps an 8"?

[richie00boy]

Some good points there. One often overlooked fact is that although the two drivers may have identical Vd, the larger one will have better impedance match to the air load, so will be a little bit more efficient for the same movement.

[sreten]

Originally posted by richie00boy
Some good points there. One often overlooked fact is that although the two drivers may have identical Vd, the larger one will have better impedance match to the air load, so will be a little bit more efficient for the same movement.

Hi,

Aren't you just confusing matters ? Vd = Vd whatever the driver.

/sreten.

[richie00boy]

Vd = Vd, yes. However, as I said, the actual output in practice will be a little greater from the bigger driver.

There is also the thinking that the larger driver moving less will produce less doppler distortion. See the Klipsch article on my website for more info.

[rick57]

m0tion

You're probably right, the benefit is cone movement remains more linear.
(Yes, in a dipole for a given baffle size, more displacement is required as Hz decreases).

Linkwitz has made available the fundamantals of dipoles, but not the relative benefits of different ways of achieving Vd. (That probably means either that he thinks it matters little, or maybe he hasn't got to it).

Dipoles partly aside, does Vd = always Vd whatever driver size?

Does a larger driver moving less, have benefits, eg less IMD??

Cheers

[badman]

Think about the way a musical instrument produces bass sounds- how big is a string bass, or kettle drum? They're not deforming wildly, they're large areas vibrating (reasonably) gently.

Lots of surface area has lots of advantages, as said, lower distortion, better impedance match. There are also drawbacks, with generally higher Le, and a lower top end cut off, not to mention directional behavior at a lower frequency.

It's all a matter of picking your poison, as in everything HiFi.

[kelticwizard]

They'll be less cone flexing with a 12" than 15", but more IMD.

It comes down to a subjective judgment, and in my opinion most people like the sound of large surfaces vibrating. So I'd go with the 15.

[rick57]

If you're within the top end cut off and beaming range, what are the benefits of smaller diameter drivers?

thanks

[MBK]

The proof is in the pudding... I just surprised myself when I switched from two 10" "HiFi" drivers in push-pull a la Linkwitz, covering 20-100 Hz crossed to a 6.5", to a 15" pro driver crossed at 300 Hz to the same mid (same baffle, same everything).

The 15" is more efficient but more to the point, the 15"+higher x-o to the mid has:
- much tighter bass
- much better intelligibility
- much cleaner midrange and even upper midrange, way beyond its operating range
- subjectively more realistic by quite a margin - piano sounds like piano, which is very hard to achieve, etc

I do not completely understand yet why this is so. While I suspect that often a bit of higher order HD can appear to give more detail, distortion measurements indicate that the 15" is indeed very good and low on HD (as it should - a top of the line 18Sounds 15ND930 with all the gizmos, demodulation rings, neodymium). The 15" should have more resonances, cone flex etc but the increased intelligibility belies this. The tighter bass - well in principle the new driver is EQ'd to the same specs as the old ones. So on data it should be rather even. But it is much better.

The higher x-o, from 100 to 300 Hz, surely reduces the load on the midrange significantly and this should be a big advantage for clearer mids and upper mids. But some of the effects were noticeable even in first tests, when crossing at the old 100 Hz point.

So I conclude that the various mentioned factors - IMD, doppler distortion, efficiency, BL, and low HD on a good model - really do add up to significantly better sound from a 15" pro driver crossed high, as compared to smaller HiFi spec'd drivers and a mid that has to do bass duties as well. I can recommend it with a big smile at least...

And specifically for the 70-400 range: that is just the range large 12" and 15" pro drivers are built for. The above may not be true for a 15" spec'd as a "HiFi" subwoofer, I can't comment on that. But 15" pro drivers, often spec'd to usage beyond 1000 Hz, will do the trick remarkably in your range. If you choose a good model from a good manufacturer, you won't regret it and I'd even venture to say, you might never look back. Not to mention you might even save money.