New Subwoofer - Best Upgrade To My System

[Andrei]

One thing that is odd is that in the past I have found randomly added subs have added airiness in the midrange, no idea why,

I have a hypothesis about this: If the midrange driver has too much work to do in terms of going from the crossover at the tweeter down to the bass; then adding a sub will take away some of its workload and thereby improve its midrange. I have no references to quote about this - just an idea of mine.

[Jazid]

hi Andrei,
I thought the same, but in this case the sub is working with the mid/bass unit attenuated below 67Hz thus should be producing this airiness, whereas in the past I have used the sub as a reinforcement for the mid/bass drivers so the airiness came without any change to their behaviour. So it must be something else in this case. Maybe a shallower crossover slope? Who knows!

Hi Paul, long time no talk
Using full range drivers with digi frequency shaping and a SET is a recipe for disaster IMHO. The main achilles heel of SETs being output trafo saturation at low frequencies the last thing I'd need to do is shove more energy down there. Also I'm still not convinced of the benefits of driving a small driver very hard vs. a large driver more gently or at least in its 'comfort zone' which is what I am doing with the sub. I hear you re. simplicity and integration, just thinking I prefer a big unit to shift the air around and the resources kept for the lmid-bass and upwards.
So saying I have got the sub flat to mid 20s, and a cabinet based roll off below. There is still plenty of output at 16 Hz however which is where the patio windows start shaking and I am petrified that a small scratch might spread and crack one pane so I am not going any lower with the signal genny!

[Reffc]

hi Andrei,
I thought the same, but in this case the sub is working with the mid/bass unit attenuated below 67Hz thus should be producing this airiness, whereas in the past I have used the sub as a reinforcement for the mid/bass drivers so the airiness came without any change to their behaviour. So it must be something else in this case. Maybe a shallower crossover slope? Who knows!

Hi Paul, long time no talk
Using full range drivers with digi frequency shaping and a SET is a recipe for disaster IMHO. The main achilles heel of SETs being output trafo saturation at low frequencies the last thing I'd need to do is shove more energy down there. Also I'm still not convinced of the benefits of driving a small driver very hard vs. a large driver more gently or at least in its 'comfort zone' which is what I am doing with the sub. I hear you re. simplicity and integration, just thinking I prefer a big unit to shift the air around and the resources kept for the lmid-bass and upwards.
So saying I have got the sub flat to mid 20s, and a cabinet based roll off below. There is still plenty of output at 16 Hz however which is where the patio windows start shaking and I am petrified that a small scratch might spread and crack one pane so I am not going any lower with the signal genny!

Good posting James, and spot on.

As to the question of small V's large drivers, the issue is less with absolute sizing and more to do with distortion V' frequency & SPL. Smaller drivers by definition need greater excursion for similar SPL levels to smaller drivers. They're not working any harder per se to generate the low frequencies as that is a function of their resonant frequency limits (easier to achieve lower Fs). You can have say a 7 inch unit with an Fs of 27 Hz or a 12 inch unit with an Fs of the same...in either case they both may generate a similar low frequency response. However, limiting excursion is usually a good thing as it is harder to control a driver moving 10mm than one moving 4mm and depending on motor design and cone material, distortion is usually higher for higher SPls for smaller units moving with greater excursion. This is not always the case, as a large driver is harder to engineer with sufficient stiffness yet retain a low mass, so there can be greater cone distortion with the larger drivers, hence driving them loud with low bass can also generate significant levels of distortion. As a general rule, if using small drivers for bass, they need to be of very high quality and specifically engineered for this application. There are very good examples of some superb bass drivers out there which are only 7 or 8 inches in diameter, ditto for drive units twice that size.

There is some truth also in one driver doing everything (ie full range units) perhaps not sounding as coherent as purpose designed drivers handling separate bands. It largely depends on bass group delay/control and resonance point at the lower end (without overhang into midrange) and prevention of beaming at higher bands which is simply a function of driver diameter. Eg, an 8 inch drive unit starts to beam on axis roughly from 1.7KHz; a 5 inch unit starts beaming from 2.7kHz so its not hard to see why full range units are a compromise really unless listening on axis and accepting bass limitations.