Low-sensitivity speakers — What's special about them?

@phusis
My original post towards this subject was dealing with what it takes to design a true high sensitivity design that is capable of audiophile use. That is why I posted a few driver spec's in that post to make sure knowledgeable people knew that I was referring to drivers. 
Yes, in general,  I was speaking of cone speakers and woofers in general.  Many may not realize that MOST cone mid range drivers are woofers that have very good top and bottom extension.  The higher in sensitivity that you shoot for,  In general, the worst the top and bottom end extension gets. 

@timlub --

Somehow I got around to base my first post only on the quoted passage by you, and not the whole post (I quoted the passage early the day before yesterday to reply, but didn’t get around to actually write it until later on, and so blissfully forgot about the rest of it).

Now taking that into account I better understand where you’re coming from, though I fail to comprehend how you apply a "true high efficiency" design with direct radiators. It appears however that this is what you believe to be the best outset to work from as opposed to horn-loading, and so presents the specific challenges laid out by you - i.e.: if a sealed bass principle is preferred (less efficient compared to a ported alignment, not to mention horn-loading) and you seek to minimize cross-over points as well, then the challenges you find yourself placed in the midst of are certainly present and understandable in the context of aiming at high efficiency.

For what it’s worth: a friend of mine has build a pair of wood replicas of the Western Electric 12a’s (fitted with a Lamar driver), and they in themselves cover from ~100Hz to a few kilohertz (sorry, can’t remember the upper frequency cut-off). Add in a horn tweeter hung down in the midst of the 12a horn and a pair of horn subs beneath them, and you have yourself a very(!) high efficiency all-horn set-up, 3-way at that, with a range potentially from 25Hz on up. Apparently several who’ve heard this setup (though with twin 15" AE units in open baffles per side for the lower range) regard it as the best they’ve ever heard, not doubt in large part due the specific frequency range of the big 12a horn driven from a relatively small and very lightweight diaphragm.

Hi @phusis

Not sure what we’re doing here, but I’ll bite. I assume that you are simply saying that it can be achieved with horns. The Lamar driver is very good for sure. Its top end extension lacks, but its nice sounding, fairly linear (plus or minus 5db from 200 to 2500) and can cross as low as 80 hz. Yes, add a tweeter and you’re good to go. So, thank you for posting 1 horn driver that is capable The 12a horn is huge and you are correct, this has not been the target in my designs.Something a little more compact. I’ve been looking for a couple of parts... a 12 to 15 inch that is closer to plus or minus 2 from 40 to 1500. I’ve contacted 3 manufacturers, I’m told that it can be built for me, but as of now is not out there. The AudioTechnology Flex 15 is close but its only 93db. and its only getting 93db because of its very low QTS of .22. Another factor is trying to get a woofer.  I'd really like to have more like 97db and I need some xmax. Most every driver that comes close to what I’m try to achieve has a very low xmax. Again, I’m told that I can have it manufactured, we’ll see.

Hey, @timlub --

Not sure what we’re doing here, but I’ll bite. I assume that you are simply saying that it can be achieved with horns.

A combined effort perhaps of incorporating a horn/waveguide and letting an extra cross-over point come into play (downwards), hereby letting the two "main" driver elements better meet (like better power response at the cross-over point) as well as to achieve higher sensitivity and better control of directivity. Hybrid designs of both a direct radiator and an acoustic impedance transformer have their own set of challenges, but carefully implemented it appears good results can be had.

The Lamar driver is very good for sure. Its top end extension lacks, but its nice sounding, fairly linear (plus or minus 5db from 200 to 2500) and can cross as low as 80 hz. Yes, add a tweeter and you’re good to go. So, thank you for posting 1 horn driver that is capable The 12a horn is huge and you are correct, this has not been the target in my designs.Something a little more compact.

The 12a’s are behemoths for sure, and won’t cater to WAF/spouse factor or interior decoration aspirations, unless one for some reason fancies big horns. Have yet to listen to the Lamar-fitted 12a’s in question, but on my next trip to Brighton will.

I’ve been looking for a couple of parts... a 12 to 15 inch that is closer to plus or minus 2 from 40 to 1500. I’ve contacted 3 manufacturers, I’m told that it can be built for me, but as of now is not out there. The AudioTechnology Flex 15 is close but its only 93db. and its only getting 93db because of its very low QTS of .22. Another factor is trying to get a woofer. I’d really like to have more like 97db and I need some xmax. Most every driver that comes close to what I’m try to achieve has a very low xmax. Again, I’m told that I can have it manufactured, we’ll see.

Coming back to my first paragraph I’m wondering why you’re adamant in regards to 40Hz extension from a 12 or 15 inch that extends up high as well, while maintaining a sensitivity goal around 97dB’s - is it to avoid the use of subs and keep simplicity? 1.5kHz extension for this size of driver is a stretch as well (beaming, break-up). My first thought would be to give up extension down low to achieve the desired sensitivity (and then augment with subs), and next I’d think in the direction of a fitting waveguide perhaps (OSWG?) with a compression driver, for a variety of reasons really, but also to lower the cross-over point more comfortably to about 1kHz. I’m sure you’ve heard of Earl Geddes’ Summa and Abbey speakers (now apparently NS15 and NA12 respectively) - just to give an idea of a 2-way design, in the need of subs augmentation, and a sensitivity in the higher 90’s. Actually the first Summa iteration of Geddes used the B&C 15TBX100 - crossed at approx. 900Hz, if I’m not incorrect - the same driver I’m using in my pair of tapped horn subs.

EDIT: giving up extension down low from a suitable, say, 15 inch would not only raise sensitivity, but high-passing it at about 80-100Hz (for subs to take over) would make it even more agile/clean sounding up to its cut-off point.  

I have very specific design parameters that I'd like to achieve.