The effects of mid-bass drivers

[andrew]

I have, over the journey, keep combing back to speakers with large mid-bass drivers. My current study set-up - which is a bit of a play-pen - has subs for low bass (<80Hz) and main speakers (Gale 401) that run >80Hz. The Gales have twin 8”drivers that product good bass | mid-bass but adding 18”mid-bass module for the 80 to 300Hz region makes the mid-bass a lot more impactful - despite the fact that I’m using EQ to get to the same target curve over the region. Am I dreaming or is this real? And, if so, then what is the cause? Also, the mid-bass modules are being used as stands for the main speakers which I guess has a benefit that there is little floor bounce cancellation. I’m wondering though if there is any benefit to be hand from attempting to re-arrange to get centre of the mid-bass module to be at ear height. Is this likely to be of benefit?

 

[andreasmaaan]

I suspect that the differences you are hearing are partly attributable to the differing ratios of direct to reflected sound. The baffles/boxes of the 18" mid-bass modules will be a lot wider/bigger than those of the Gales, so less of the lower midrange/upper bass will be spilling to the back of the cabinets. Therefore, if you EQ to the same target curve, a higher proportion of the sound will be direct sound from the drivers.

Whether there is a change in floor bounce cancellation depends on the height of your Gales and your listening distance. If you're listening distance is less than 4m, then yes, the primary cancellation from floor bounce is likely to at least partially fall under or around 300Hz.

Another possible factor is distortion. No doubt the 18" units produce far less of it, and additionally the Gales will be producing less IM distortion higher up in frequency as a result of having the sub-300Hz range taken off their hands.

There is unlikely to be any benefit in getting the mid-bass module at ear height. To do this, you'd have to place them besides the Gales, which would skew the horizontal polar response (which is arguably more important than the vertical polar response, which is what is skewed when the drivers are arrayed vertically as you have them now). Moreover, if your listening distance is close enough that having the 18" units on the floor actually is ameliorating the effects of floor bounce, then placing them at ear height will undo this.

 

[andrew]

I suspect that the differences you are hearing are partly attributable to the differing ratios of direct to reflected sound. The baffles/boxes of the 18" mid-bass modules will be a lot wider/bigger than those of the Gales, so less of the lower midrange/upper bass will be spilling to the back of the cabinets. Therefore, if you EQ to the same target curve, a higher proportion of the sound will be direct sound from the drivers.

Whether there is a change in floor bounce cancellation depends on the height of your Gales and your listening distance. If you're listening distance is less than 4m, then yes, the primary cancellation from floor bounce is likely to at least partially fall under or around 300Hz.

Another possible factor is distortion. No doubt the 18" units produce far less of it, and additionally the Gales will be producing less IM distortion higher up in frequency as a result of having the sub-300Hz range taken off their hands.

There is unlikely to be any benefit in getting the mid-bass module at ear height. To do this, you'd have to place them besides the Gales, which would skew the horizontal polar response (which is arguably more important than the vertical polar response, which is what is skewed when the drivers are arrayed vertically as you have them now). Moreover, if your listening distance is close enough that having the 18" units on the floor actually is ameliorating the effects of floor bounce, then placing them at ear height will undo this.

Thanks for the comprehensive response.

 

[andrew]

I suspect that the differences you are hearing are partly attributable to the differing ratios of direct to reflected sound. The baffles/boxes of the 18" mid-bass modules will be a lot wider/bigger than those of the Gales, so less of the lower midrange/upper bass will be spilling to the back of the cabinets. Therefore, if you EQ to the same target curve, a higher proportion of the sound will be direct sound from the drivers.

Whether there is a change in floor bounce cancellation depends on the height of your Gales and your listening distance. If you're listening distance is less than 4m, then yes, the primary cancellation from floor bounce is likely to at least partially fall under or around 300Hz.

Another possible factor is distortion. No doubt the 18" units produce far less of it, and additionally the Gales will be producing less IM distortion higher up in frequency as a result of having the sub-300Hz range taken off their hands.

There is unlikely to be any benefit in getting the mid-bass module at ear height. To do this, you'd have to place them besides the Gales, which would skew the horizontal polar response (which is arguably more important than the vertical polar response, which is what is skewed when the drivers are arrayed vertically as you have them now). Moreover, if your listening distance is close enough that having the 18" units on the floor actually is ameliorating the effects of floor bounce, then placing them at ear height will undo this.

Since this post I’ve tinkered with the system but, ultimately, always come back to preferring Gale + Mid-Bass setup over running the Gales full range - and especially so having used Audiolense to build the x/o in the digital domain.

The reason that I chose 300hz for the x/o was that both speakers have a flat response either side of this frequency and I believe it’s below the point at which the 18” starts beaming. Does this make sense or, put differently, is there a case to move the x/o up or down from this point?

And, out of interest, how do you think some of the small well measuring pro audio monitors (such as KH80) would go as a replacement for the Gales? I look at the measurements of these in awe, and the option of just limiting to >300hz solves the limitations in the bass region, but wonder how stitching these together would go in terms of off-axis performance etc.