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In Reply to: RE: JBL L250 posted by Rpower on March 01, 2018 at 05:46:10
Here is another pic of the L250s
Follow Ups:
I have read about them but have never heard them. I do know that JBL's can have very good sound. I had a pair of Lancer 77 speakers which I enjoyed very much until they were displaced by my current Spendor BC-1's. My brother-in-law is still enjoying them. Even the studio monitors I have heard sounded very good to me.
I sold JBL in the 80's. The other speakers in you picture look very much like what I sold.
I strongly suspect you have a fine pair of speakers that were well worth the effort!
Dave
they break fundamental directivity guidelines running the 5" midrange too high - 5 kHz which translates to a 2.75" wavelength. Image width would clamp down severely at the top of its range only to transition to a wide dispersion dome tweeter sitting in its sweet spot.
Perhaps I'm overly sensitive as a coherency freak but I've heard that hourglass shaped frequency-dependent directivity weirdness before. Note that current JBL designs like the LSR6332 cross 5" midranges a full octave lower to avoid that problem. I have to smile when I look at the manual which plots the polar response at 2 khz (about where the xover should be) and 12 kHz completely missing the problematic area where the results would surely be different.
You raise a legitimate objection. I agree that keeping directivity smooth is desirable and very audible. however, the effects can be minimized by listening on axis and having the speakers well away from reflective surfaces. Of course this can not always be done. The flip side is that the hight you make the, crossover, more it is out the area where your ear is sensitive. I believe that this is why many listeners prefer full range drivers, with all of their problems.
I have wondered about crossing a whizzer coned driver with a conventional tweeter/crossover to keep the dispersion even. Would this be superior sounding to a conventional mid woofer-tweeter. I know Electovoice and others did this, but I have not had a chance to listen to any examples in depth.
Since there are so many imperfections in even the best speakers, they have to be looked at as a whole system. A design might not work for all systems/rooms/people and still be a viable design if setup where the weaknesses are recognized and minimized while the strengths are maximized.
Dave
The flip side is that the hight [higher?] you make the, crossover, more it is out the area where your ear is sensitive. I believe that this is why many listeners prefer full range drivers, with all of their problems.
Perhaps for some, but the first time I heard L110s I was immediately struck with the weird imaging. At first, I couldn't put my finger on the cause, but found it distracting. For me, it's the overt discontinuity in a sensitive area even close to axis.
I think the lure of full ranger dynamic drivers is not as much the lack of a crossover, rather NOT having a "show off" driver on top vividly contrasting how well it does around the xover. Their directivity fades off gradually into the sunset as frequency rises...
For the L110's (at Jerry's), were you sitting dead center? Were the speakers out in the open?Well, even if this was the case, I suspect the design will have some affect on the image. My JBL Lancers didn't image well but they did other things very well. I enjoyed having them. They had a very natural quick sound. They weren't neutral like my Spendors, but I wasn't bothered by their deviations. They did rock and they were very efficient.
I am working on a pair of L110's so I will be able to speak with more authority about the sound.
Dave
Edits: 03/02/18
Perhaps not dead center but they (like his Advents) were in the open.
When I told him what I heard, he was a bit puzzled but I think he later caught on to my observation. I'm pretty sure he has subsequently retired both in favor of a 2 way mating the neutrality and top end extension of the L110 with the consistent directivity of the Advent.
There was a SEAS dome tweeter that could go very low. He was using it in both Advents and Dynaco A25. I still would expect a lot of directivity in a 10 driver crossing to a 1" dome.
Jerry is a little older than me, but there is some overlap. I don't recall people talking or worrying about imaging until the 70's. Both of us started with mono hifi's. I now enjoy a nice solid image, but I also still listen to mono records.
Dave
I don't recall people talking or worrying about imaging until the 70's. Both of us started with mono hifi's. I now enjoy a nice solid image, but I also still listen to mono records.
The type of imaging to which I refer is not stereo related. It's the hourglass shaped frequency presentation of an instrument. It seemed most noticeable with piano where the instrument seems to be reflected in a fun house mirror - with some parts sounding one way and other parts of the same instrument differently.
Visually, it is represented by a directivity plot like this - although the funneled down response in this example lies between 1.5k and 3k.
I get that you are talking about a drop in output due to the increasing directivity of the midrange driver with frequency. Then when you switch to the tweeter, which has wide dispersion at the crossover, there is a discontinuity.Are you taking about a loss in perceived volume before rolling off to the tweeter?
By the way, L110's crossover at 4000 kHz.
Dave
Edits: 03/03/18
Are you taking about a loss in perceived volume before rolling off to the tweeter?No, what I perceive is not a tonal balance thing. Which is why I refer to it as an imaging flaw. One that creates an unnaturally shaped "scene" as Siggy Linkwitz would call it of instruments that span those drivers.
By the way, L110's crossover at 4000 kHz.
Four megahertz! :)
Still too high. Even the modest Polk LSi7s used in the HT crosses its 5" driver over to the tweeter at 2.2 kHz. Just like the current JBL and higher end Revel models - influenced by Floyd Toole's research. Start about 24:30 for his discussion on uniformity and directivity index.
Edits: 03/04/18
Maybe the solution is as simple as a wave guide for the tweeter when you want to cross a midrange driver high. I am working on putting together an L110. If I am bothered by the problem you describe, the solution could be a waveguide. I conical waveguide would be easy enough to construct.
Dave
Perhaps. Restrict the inherent directivity of the tweeter to match the scrunched response of the midrange at xover.
While not an ideal solution, it would serve to facilitate consistency.
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