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


I'm building a system for a smaller room (need smaller bookshelves), and I did a bunch of research and some listening. I am attracted both to the Dynaudio Evoke 10's (heard locally) and the Salk Wow1 speakers (ordered and I'm waiting on them for a trial). I have a Rel 328 sub.

Here's the thing — both of those speakers are 84db sensitivity. Several people on this forum and my local dealer have remarked, "You should get a speaker that's easier to drive so you have a wider choice of power and can spend less, too."

That advice — get a more efficient speaker — makes sense to me, but before I just twist with every opinion I come across (I'm a newbie, so I'm pathetically suggestible), I'd like to hear the other side. Viz.,

QUESTION: What is the value in low sensitivity speakers? What do they do for your system or listening experience which make them worth the cost and effort to drive them? Has anyone run the gamut from high to low and wound up with low for a reason?

Your answers to this can help me decide if I should divorce my earlier predilections to low-sensitivity speakers (in other words, throw the Salks and Dyns overboard) and move to a more reasonable partner for a larger variety of amps. Thanks.
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In the case of dynamic (box-type) speakers, as a general rule of thumb small physical size, deep bass extension, and efficiency trade off against one another. So among the kind of small "bookshelf" speakers you are interested in more efficient speakers will tend to have less deep bass extension than less efficient speakers. There are many exceptions, of course, but as I say that set of tradeoffs can be considered to be a general rule of thumb.

And regarding deep bass extension, especially in the case of smaller speakers, some users will prefer to augment that with powered subwoofers, while some will not due to space or other considerations.

Other tradeoffs are also involved, of course. Larger cabinets tend to cost more than smaller cabinets, everything else being equal. The impedance characteristics of a speaker can affect drive difficulty as much or more than efficiency or sensitivity. (If Stereophile has reviewed a speaker that is under consideration the measurements section of the review will be very informative in that regard). Amplifiers tend to sound better when driving high impedances than when driving low impedances. For a given level of amplifier quality, and within a given class of operation (A, AB, or D) higher powered amplifiers tend to cost more than lower powered amplifiers. So within a given class of operation a greater percentage of the dollars one chooses to invest in an amplifier will tend to go toward quality rather than toward watts if high efficiency speakers are used.

And of course how all of these factors are addressed comes down to individual preference and budget. Personally I prefer relatively large floor-standing speakers having relatively high efficiency and benign impedance characteristics, which therefore are very versatile with respect to amplification. But the opposite approach works well for many others.

Good luck. Regards,
-- Al

Are you building a system for this room from scratch or do you have an amplifier you wish to use?  It is the AMP/speaker combination that will determine suitability for your room. As Al stated the impedance issue is also a factor. I you have an amp which one? 

From my experience it is hard to find a small bookshelf type speaker that has reasonable bass level (50hz) and sensitivity rating above 87dB at the budget level of the Dynaudio Evokes (below $1000 I believe). Also finding ones that have do not drop below 4ohms somewhere below 200hz is difficult. 

If you don't have an amp purchase the speakers you like and find one that will drive them to the required level. The small room works in your favor. Also if you won't be trying to drive yourself out of the room with volume.  
Generally speaking if you do have to play the speakers at volume, lower efficiency speakers have something called 'thermal compression' where the voice coils can heat up, significantly curtailing musical peaks.


But if size is an issue and your room is not large (and so not requiring a lot of power), a lower efficiency speaker can offer better bass as Al pointed out.


But a nice sub option if space is an issue is the Swarm by Audiokinesis. It is 1 foot square by 2 feet high so its not the smallest sub around and there are 4 of them to be used to kill standing waves in the room. But they are unlike other subs in that they are designed to be placed directly against the walls, and work best if asymmetrically placed. So they can work very nicely in a small room. This allows you a smaller or more efficient main speaker, since that speaker only need to down to 80Hz. 
The really short answer:

Speaker designers can trade sensitivity for bass.

That is, by loosing power overall, we improve the bass to mid and treble balance.

You should look into 2.5 way speakers as a close alternative. Better sensitivity and more bass output in the same footprint as a 2-way.
Low sensitivity is a trade-off small size and deep bass to bigger size and not as deep bass.
Low sensitivity causes thermal compression that makes heavy, constrained, tiresome sound.
High sensitivity speakers, in contrast, produce easy going sound like a real musicians on stage performance.
It is sad, but a big part of audiophiles don't care about  thermal compression despite this phenomenon kills a real musical reproduction and makes music boring and tiresome.
Regards,
Alex.
It’s not just about bass, one needs to consider the source the root causal reason for higher output.

one form of higher output is achieved with a mechanical device to focus energy - imo at cost to fidelity. Horns are not everyone cup of tea. Since to appear focused on dynamic drivers, I will comment more about those..

for dynamic driver speakers, non pistonic motion creates higher output thru constructive and destructive interference. Check out the Utube video on the comparison of two 5” midrange, for a dramatic and easy to understand visual representation of in and out of phase behavior. That video is linked on the Vandersteen website. For a non pistonic driver ( most of them frankly ) A great deal of output is just in and out of phase trash. When a pistonic cone assy is fitted to the driver with equal mass, output drops. The bottom line is trash counts in the efficiency measures. Another reason to listen and not get too wrapped up in less than critical specification. Pay attention to impulse response tho!
IMO a fantastic speaker for you would be Vandersteen VLR signature on Sound Anchor stands with a Vandersteen Model 3 subwoofer with 11 bands of analog EQ for perfect bass at the listening position and a built in amp that takes load off your main amp yet preserves transfer function of the main amp

I've not bought any power yet. Thanks for the replies. I understand the technical trade offs better, now. If one had the bass covered by a subwoofer, it seems there’s no positive, specifiable, aesthetic reason to prefer low sensitivity speakers. I think that captured every remark so far, no?
+1 tomic601.  I have installed a  pair of Vandersteen Model 3 Subwoofers.  They are sublime.
What it comes down to is... really good mids with any type of top end extension without cone break up is hard to find in true high sensitivity speakers.  It has already been mentioned about bass.... The bigger the magnet/motor structure of a woofer, the more sensitivity and the more mass it needs to produce low fs/Qts.... these are attributes that lead to deep bass.  As you as you ad mass fs goes down and qts goes up,  but the trade off is that sensitivity goes down.  
Its not a perfect world.  I try to find the sum of parts as a whole to start the design process. Not being able to find any single part can kill an entire speaker project.  
Alot of people really like sealed box speakers for bass, I am one of them, but woofers that work well in a sealed box need a qts of a minimum of .4 and preferably .5 or even a bit higher.... Look at spec's on high sensitivity woofers,  you'll see .2 to .35.  This is just too low to produce bass in a sealed box system,  Although .35 can produce very satisfying bass in a ported or vented design.  You also have to consider that most good designers prefer to keep the crossover out of the vocal range,  so again,  it requires drivers with a fair amount of extension on the top end or bottom to pair with other drivers. 
There are plenty of excellent parts to design high quality low to medium sensitivity 2 or 3 way systems with great results. 
Every speaker, to some extent, makes some trade offs, and, at all price points, imo. The thing is, as a listener, we need to determine, what musical parameters of recorded music, are most desirable to each of us. And as explained above, the speaker / amp / room combination, should be matched as close as possible, to work together. Someone above, although appreciating the efficiency of horns, prefers other things. I, on the other hand, prefer horns, and the efficiency, is simply, icing on the cake. Advice : Take you time, and listen to as much gear as you can. Also, go listen to some live, " un-amplified " music, as this will give you an indication, as what to listen for, in audio gear ( speakers, specifically ). My best, and Enjoy ! MrD.
I’ve always gravitated to lower sensitivity speakers mainly because they were the speakers I enjoyed the most. Pluses and minuses either way I suppose. Dynaudio makes excellent speakers if you buy the Evokes I bet you would be quite happy. Down the road you could consider the opposite and drive a highly sensitive speaker with a low wattage tube amp, that is what makes this hobby fun.
Right now I am enjoying Magnepan LRS speakers that are quite different from box speakers. Could I go back to Dynaudio or Totem someday - probably. Anyway my point is buy what sounds good to you, no matter what you buy you’ll have to match it up with proper amps / stands / Dac anyway so don’t sweat it. 
The advice to get speakers that I enjoy and then find the amps to match is how I was initially going forward.  It was the warning that I might be boxing myself in that caused me to reconsider the speakers that I had heard and enjoyed. But there are more speakers out there and some of them might be higher efficiency...so there’s no harm in just doing more listening! Of course if some delightful and expensive tube amplifiers really make a big difference to the sound, well, then, it might not hurt to consider that as a potential orienting factor for the speakers! You see how I get turned around and around! Still, it makes sense to start with the speakers. 
I have a bedroom system w Sierra2ex 89db sensitivity. I run a pair of 80w class a monoblocks and a pair of REL t-zero. I can rock the entire house from that little system. I was worried about the same thing, but I gambled on this and won. 
For the past couple of years I’ve been happy running a SET/high-efficiency system but previous systems were all of the higher-power/low-efficiency type. Obviously, there are compelling reasons for setting up a system either way. One thing about the low-efficiency approach I don’t care for is the need to crank the volume for the speakers to come alive. Low level listening just sounds anemic otherwise. Of course, some people get around this using EQ or headphones. Something to consider nonetheless.
@andrew -- I looked long and hard at Ascend Acoustics. They have great deals and what seems like amazing speakers.

@melvinjames The goal for me would be to avoid exactly what you describe by buying enough power. My understanding was that if there’s enough "headroom" then one does *not* have to crank things up to get the response needed for engaging sound. Perhaps I had that wrong, but that’s what I thought I learned in this video: https://www.youtube.com/watch?v=th8CxTk22pY
1++ Almarge and Atmasphere:)
It's really about component matching. If have decided upon a speaker system you like, then you need to match them with an amp that will drive them adequately. Conversely, if you have found an amp you like, match it with a speaker system. In other words you don't want a low powered amp driving inefficient speakers nor waste a high powered amp on high sensitivity speakers.
@aewarren Can't argue with your logic. For me, the key factor is the most revealing order-of-discovery, if you will.
I get a better sense of speakers by swapping them in and out and keeping the amp constant.
I am not sure if the experienced change would be nearly as great if I kept the speakers constant and swapped out the amps.
This latter factor is difficult because I am not sure which speakers to get yet! I need to choose them first. Then, I'll choose among a few amps for the best component fit/match.
Down the road, I can upgrade/change speakers as long as I have enough power or a fairly flexible kind of power.
OP did you watch the video ? Red cone movement is out of phase to the input and 100% distortion....
@mrdecibel as always I so enjoy our measured and reasonable exchanges based on mutual respect for different tastes :-)
More and better bass out of a smaller package with the right beefy amp capable of delivering it. 
I think it’s a common misperception that smaller speakers mean you can have a lesser amp to drive them. The exact opposite is case if the speakers are good quality and you want to get the most out of them. 
I listen to music using Magnepan 20.1s, which are a 4 ohm and 85 db sensitivity speaker. Yes, they require some power to drive, especially if you don't want your amp to overheat. But you don't have to pay a fortune for an amp that can drive them. Emotiva has the A-300 amp for $400 right now and it has 150 wpc at 8 ohms and 300 wpc at 4 ohms. The 300 wpc is enough to make the Maggies sing.
What it comes down to is... really good mids with any type of top end extension without cone break up is hard to find in true high sensitivity speakers.
The Classic Audio Loudspeakers use a beryllium diaphragm with Kapton surround in their compression drivers; the first breakup is at 35KHz. The model T3 which I have at home is 97dB and 16 ohms, flat to 20Hz owing to dual TAD 15" woofers.
All transistor amplifiers (except class A) have thermal distortions (similar to low sensitivity box speakers). The transistors parameters change with changing of temperature.  
This distortions have inertia. As result you can't fix these distortions by feedback.
Our brain is very sensitive to these kind of distortions. These distortions cause tiresome and decrease enjoyment from listening music.
So, if you use combination of low sensitive  sensitivity box speakers with powerful  transistor amplifiers you get thermal distortions in a square.
As a result, you have a tiring, depressed, suffocating, annoying sound.
I think this combination is the worst delusion of audio industry.
Sadly, most of audiophiles don't understand it. 

@hilde45 .. I should have been more specific. I have a pair of Mark & Daniel Ruby speakers which the manufacturer specs at 82.5 - rather inefficient. The Rubys are a small monitor (2-way design with an AMT tweeter) which puts out a tremendous amount of bass - love them. I’ve run these with numerous amps including a 100 wpc class d and a 110 wpc class a/b. Both amps could drive them to ear-bleeding levels in my room but for late night and early morning listening the drivers simply needed to be played louder than wanted to come alive. I had the same experience with other inefficient speakers as well. Perhaps spending more cash on a bigger/badder (at least 200 wpc) amp would have worked but, ultimately, I chose a different path.

Thanks. I'll try to watch the video. Extended auditions are in order. 
@tomic601 , Happy Valentines Day to you too, sir ! LOL. We all have a story, so I hope my story is interesting, and not too long, so, I apologize. I have stated in many posts, that personal taste, is what this hobby is all about. The arguments between SQ differences folks have, have been ridiculous, as far as I am concerned. The earlier someone finds their cup of tea, the easier it will be to build a system around that, tweak it, get it closer to their ideal. During my childhood ( before 10 ), my dad had a Fisher 500C, Dual 1229 with Shure cartridge, feeding AR3a speakers ( all of which I had acquired after his passing, and just recently sold, very reasonably, to a listener who would enjoy them much more then I ). My dad, wanted to move away from the Fisher, with the onslaught on these ss Japanese receivers, and replaced it with a Sansui 881 Deluxe. At that same time, I had just received my pair of Klipsch Cornwall Verticals from my singing coach / music teacher ( he upgraded to Khorns ), and I used the Fisher, along with an AR table. That was the time, when my ears became " tuned " to the horn sound. I found the AR3’s amazing, do not get me wrong. I became a tweaker, sold and managed at a few audio stores, became a rep for a short time, and then became an independent audio consultant, helping people spend their money on systems. Not everyone liked Klipsch, Altecs, JBL’s, etc, as much as I. I understood the varied differences between all of the speaker designs, and at the same time, I understood the weaknesses. I owned multiple systems, having owned Vandies, Maggies, MLs, DQ10s, Gale 401s ( a wonderfully musical, yet very inefficient speaker ), and so many others, and heard a plethora of others during my travels. Same with the front end gear. Before, and during the intro of digital, I was enamored with open reel tape, which was fabulous, in every sense of the word. I also realized and understood, at an early age, that recorded music, will never sound like real, unamplified music. Once the instrument, or voice, reaches the microphone, it is a done deal. Those listeners who keep changing equipment, like I, underwear, fall under several categories. ( 1 ) Have not found their flavor, ( 2 ) Are looking for a " sound that does not exist ", meaning, very high expectations, ( 3 ) Does not have the auditory expertise in system matching and development, ( 4 ) Have not spent enough money on the equipment, ( 5 ) Have spent too much money on equipment, to the point, they are hearing every weakness of the recordings, which are many, and is why, what they listen to, are only the best mastered, and not necessarily, the most musical, ( 6 ) Does not have a " reference " of music reproduction, to guide them, ( 7 ) Have a serious, neurotic personality, ( 7 ), Can simply, never find happiness in a system / room........There are more, and of course, a combination, of many above. I am not trying to sound like, or appear to be, a know it all ( although to some extent, I do know a few things, lol ). Again, I apologize to all. Enjoy ! MrD.
I would go with the SALK speakers.  When you talk to Jim Salk tell him Larry Edwards from Denver sent you,  His speakers are just incredible.  You will love Jim.
A phd in a post, out for beachside valentine lunch. Our path similar!
will write more later!!!
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@larry5729  I will. I’m glad you think the Salks will be good. I went listening today to some amps... and heard some Spendor A4s and some Elacs S61. They didn’t do much for me, though they sounded good. Looking forward to getting the Salks, someday. I ordered them Jan 9. 
With the vast majority of typical speakers one can make a speaker's impedance more linear by lowering it's impedance, which can allow amplifiers to provide a more linear frequency response through those speakers. But doing so will decrease the speakers sensitivity.

One will be hard pressed to find high sensitivity speakers that can produce respectable step response or square wave response.


There's a lot more to speakers than sensitivity alone.
Thanks, unsound. That helps me make a bit more sense of the measurement which the page for the speakers I ordered list. I bought them for the reputation and reviews --and the notion they'd be sized well for my listening room, which was confirmed by the maker. It was only later on that I realized the sensitivity was low. Here are the stats/landing page for that speaker. http://www.salksound.com/model.php?model=WOW1
@timlub --

What it comes down to is... really good mids with any type of top end extension without cone break up is hard to find in true high sensitivity speakers.

Perceived really good mids and upper range extension (i.e.: "any type of top end extension" leaves room for quite a lot) is readily available with true high sensitivity speakers - without necessarily requiring exotic cone materials. Being so I gather cone break-up, in whatever shape it may present itself (or not), isn't an issue. 

@unsound --

One will be hard pressed to find high sensitivity speakers that can produce respectable step response or square wave response.

Question is whether it holds significant correlation in regards to perceived sound quality, not least depending on who you're asking. There's hardly consensus here, but transient behavior in (time aligned) all-horn set-ups, representing the best efficiency, are hardly the ones to fault the most in this regard. Even so, relevance/correlation is required. 

There's a lot more to speakers than sensitivity alone.

Sure, but I'll definitely side with poster @alexberger's above posts on the significance of high sensitivity (and headroom) as an aspect highly overlooked by the audiophile community at large, and that it's an essential ingredient in achieving a live sound imprinting. Those who've heard a well-implemented all-horn system covering most of the audible range will know this kind of sonic ignition, scale, presence and ease simply doesn't exist in low to moderately sensitive speakers; they just sound restrained and malnourished by comparison, not that they can't be highly capable in other areas. Yes, high efficiency and full-range requires BIG size, but you want to eat your cake too that's the pill to swallow. Personally I find it's definitely worth it. 
That aspect @phusis "a live sound imprinting" is significant. Thanks for putting it that way. Another, good metric to judge speakers by; very useful.
@phusis 
So you say "Percieved" and that these mid and bass drivers with good extension and little cone break up are readily available.... recently I've shopped a few hundred drivers looking for such.  Please list the model numbers.  
@timlub --

So you say "Percieved" and that these mid and bass drivers with good extension and little cone break up are readily available.... recently I’ve shopped a few hundred drivers looking for such. Please list the model numbers.

Perhaps we’re addressing this matter differently by now. Initially you wrote "really good mids with any type of top end extension without cone break up is hard to find in true high sensitivity speakers," so I set out to express my impressions from a complete speaker system - not focus on a single driver. Cone break-ups can be more or less challenging depending on your design goal and overall requirements, and nothing yet has been specified into the nature of a given design to illuminate your context.

Where "true high sensitivity" goes horns seem to be dictated, and with midrange compression drivers I’d wager their upper range (clean) extension isn’t a bigger issue, if as much as their lower end limitation in a given horn. Knowing what one is dealing with here would dictate what to work around rather than against, and with horns in particular it’s not exceeding the bandwidth of each horn element to main good power response etc., so a full-range all-horn system would typically require a 4 or 5-way approach.

With true high sensitivity speakers an excellent midrange can be had via a range of designs, so why would cone break-ups be a particular issue here if the design accommodates inherent challenges? You’re addressing and calls for the existence of specific midrange (and now bass) drivers with good extension, so what’s your context, specific use and related issue?
@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.  
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