[tomlinmgt]

I'm considering a build that will use a coax driver for mids and highs with a few helper LF drivers playing up to 250-ish Hz. Are there any particular sonic characteristics that would make either a 12" or 15" driver of the same model more desirable in an OB scenario if I'm transitioning mids to highs around 1.2kHz?

[FullRangeMan]

I'm considering a build that will use a coax driver for mids and highs with a few helper LF drivers playing up to 250-ish Hz. Are there any particular sonic characteristics that would make either a 12" or 15" driver of the same model more desirable in an OB scenario if I'm transitioning mids to highs around 1.2kHz?

For OB you will need drivers with Qts above 0.9 as Alpha15A.
With Qts too low you will need EQ or DSP.
15'' woofers start attenuate at 60Hz.
12'' woofers start attenuate around 110Hz.

[tomlinmgt]

For OB you will need drivers with Qts above 0.9 as Alpha15A.
With Qts too low you will need EQ or DSP.
15'' woofers start attenuate at 60Hz.
12'' woofers start attenuate around 110Hz.

Right...but like I said, the coax driver will be tasked to play down to around 250-ish Hz, so I have plenty of wiggle room with a 12" or 15" even if I wanted to push them down to say 150 Hz...but I was thinking I'd let the LF drivers (Acoustic Elegance IB15) handle the entire bass range.

What I'm trying to determine is if there are things inherent to the different sized drivers that makes one a better choice than the other for reproducing mid range.

[FullRangeMan]

Right...but like I said, the coax driver will be tasked to play down to around 250-ish Hz, so I have plenty of wiggle room with a 12" or 15" even if I wanted to push them down to say 150 Hz...but I was thinking I'd let the LF drivers (Acoustic Elegance IB15) handle the entire bass range.

What I'm trying to determine is if there are things inherent to the different sized drivers that makes one a better choice than the other for reproducing mid range.

What I'm trying to determine is if there are things inherent to the different sized drivers that makes one a better choice than the other for reproducing mid range.
By the size alone no IMO. There is mid-ranges in various sizes, from 6'' to 12''.
An freq range graphic analysis would give you a idea on how it could perform.
However avoid fake Freq Range charts as what Eminence usually show.
These graphics are Software  Predicted Freq Response in a such box (usually BR box) at max power or medium power.

[David A]

Hi, If you've not seen Perry Marshall's OB speaker designs, you may consider to check his coaxial designs, https://perrymarshall.info/speakers/.  Perry frequently contributes to the diyaudio.com community, and there are several threads regarding his designs.  Good luck with your build!

[FullRangeMan]

This empirical table may give you some idea on the cone voices.

[tomlinmgt]

Hi, If you've not seen Perry Marshall's OB speaker designs, you may consider to check his coaxial designs, https://perrymarshall.info/speakers/.  Perry frequently contributes to the diyaudio.com community, and there are several threads regarding his designs.  Good luck with your build!

His Bitches Brew design is what got me headed down this path.

[kd4ylq]

TomlinMGT,
                 be sure to explore all of the designs by Perry Marshall! The Bitches Brew is the most ambitious, large (and most expensive to build), but his others are also very much worth serious consideration as alternatives. I've acquired beautiful Butternut slabs to build his CottonWood design with, and when I have some RMD money to buy the drivers with I'll be getting to work on it. His superb designs are very well documented and free to the individual builder for their own personal use. Good choice! Please share your progress here and on DIY. 

[tomlinmgt]

This empirical table may give you some idea on the cone voices.

Thanks for sharing this

[tomlinmgt]

TomlinMGT,
                 be sure to explore all of the designs by Perry Marshall! The Bitches Brew is the most ambitious, large (and most expensive to build), but his others are also very much worth serious consideration as alternatives. I've acquired beautiful Butternut slabs to build his CottonWood design with, and when I have some RMD money to buy the drivers with I'll be getting to work on it. His superb designs are very well documented and free to the individual builder for their own personal use. Good choice! Please share your progress here and on DIY. 

Yes, I had considered copying his Bitches Brew recipe but decided to dip my toes in the water using drivers I already have sitting on the shelf...including four AE IB15-8's and a pair of Radian 475PB that have Hawthorne Audio open back plates...leaving me only needing some sort of mid driver and I like the idea of a virtually point source coaxial. I'm looking at larger drivers because my space is large and I'm accustomed to listening to speaker systems that have significant dynamic range and appreciate  their ability to convey large dynamic shifts at high SPL with minimum distortion and strain.