I have no earthly idea. The rubber-cork pads simply raise the front end of the baffle about1". The bulk of the baffle bottom plate stays in contact with the floor. I have wall to wall carpeting so there's that to. Raising this small amount does not adversely effect the bass response of speaker.

HK

This frequency response doesn't jive with what I am hearing.  I have a pair of Fast 15 that I am breaking in using the "big betsy" ZF15L baffles.  My first impression was I was less than impressed with the spongey bass, abiet a lot lower it was slower and lacked texture.

That said, I have been running the hours on them to see where they land.  It has been hard for me, becuase I simply removed my seasoned pair of F15's and installed these new fast 15's in their place.  Besides the bass quality at first, the midrange was hard to digest. As well the top end.  I am just comparing them to the previous drivers, and the baffles have not been moved.

The response is peaky.  It has discombobulated my highly resolute sound stage that now changes from track to track.  Some things are way better than I've heard them and some are way worse.  The driver is somewhat re-mixing the recording by peaking midrange and treble frequencies thus moving things way forward in the sound stage, and dropping other things way back.  There are certain recordings that finally after 40 years shined and sounded right to me for the very first time.  However there are a lot more that are getting wrecked.  

This may change as I get the hours on them.  We're at about 150 hours so far.  The bass has improved a lot since the first two hours, and by that I mean it has tightened up, which I didn't expect.



After awhile I had to look up the response shown above and frankly that's not really what I am hearing in my room.  

Today I measured them in the F15L baffles and was completely stunned to see the -3dB point is 30Hz!  And from 30Hz to around 400Hz was impressively flat.  That might be worth trading a little speed and texture for, because the F15 in the same baffle in the same location goes silent at 50Hz.

Today I measured the speakers to see the gated response in my room, which is not that far off anechoic.  Consistent with what I've been hearing. A tilt in the midrange and a large presence peak.

Frankly compared to the F15 in these baffles, it's going to be a no go unless it can be improved.  In fact I almost removed them and gave up until I measured them and saw how flat the bass response was and down to 30Hz in a baffle is a first.  So I will continue to burn them in and am playing with very simple 6dB crossover coils to see if I can tame it.  I didn't have the right value to get it where I want, so I have ordered more and will continue next week.

Meanwhile here is the raw response after 150 hours.



click to enlarge

To get the reference/honest sound stage of the F15 in these same baffles with these drivers the response is going to have to be tamed.  To have my open baffles drop to 30 Hz and actually have a touch more presence and upper midrange and treble extension would be exiting. So lets see what we can make happen!

Steve

I have been doing as much listening to the Fast-15 drivers as time will allow over the past few days.

They have smoothed out a bit, but as Steve observed, they can be "recording dependent" at this point.

On a "hot" or "thin" recording in my room and system, they can be unpleasant ..... but on a good recording they are a revelation.
Happily for me, I have spent a good part of the past 15 years searching for music that is well recorded with a good tonal balance.

I can say that I thoroughly enjoyed a two-hour session with the Fast-15 drivers last night.

One of my customers who lives about 100 miles away (and has become an audio buddy) has told me that he really didn't care for the F-15 drivers at first. His original speakers had Betsy drivers and he added a second pair of baffles with the F-15 drivers.
He stated that it took about 500 hours of playing time in his system before the F-15 baffles sounded good to him ..... and now he loves them.
He will be visiting tomorrow to do an A/B between the F-15 and Fast-15 baffles in my room.

I'm looking forward to his thoughts .....

If the worst-case scenario happens and the drivers do not "mature" as hoped, Steve's inductor fix might be the answer.

However, based on the good things that I have heard so far ..... I am willing to be patient to see what some break-in time will reveal.

Best wishes,
Randy

While I don't expect any early Fast 15 adopters have 500 hours on their drivers, does anyone want to provide an update? I am particularly interested if the elevated upper midrange and treble response that Steve measured has dissipated with additional hours. What say you folks?

The Lii Audio free shipping extended offer ends tomorrow. Is the driver a real upgrade from the F15 driver or not in your opinion?

HK

Bit of a lurker finally checking in... thanks everybody for all the discussion. I'll also be interested if anyone has any updated reflections before the free shipping promotion ends today. I'm no stranger to full range drivers with presence peaks, having lived with Lowthers for some time before I got my F-15. So, I'm not really looking to upset the apple cart in terms of the exceptional balance and coherency of the F-15s.

I was searching for a response curve to compare with Steve's measurements of the new fast 15 drivers. Can't post the link/image here directly because it's my first post but it's #965 on page 20 of the Steve's Big Betsy Project thread. There are peaks and troughs of course but overall there's no "rising" response like with so many FR drivers.

The value of the resistor will be critical. The resistor will overpower the capacitor and reduce the phase shift so we want to get it somewhere between the blue peak and the red hole.

After clipping in different values I realized it's going to have to be dialed in perfectly, so I got an adjustable resistor and simply slid the adjustment around between each measurement until I got as good as it was going to get.

And here it is with the flat reference line.  We still have a hole but the overall response is far more listenable.



click to enlarge


Final value for the resistor was 36.5 ohms.  Here is the schematic:  The switch is so the network can be disabled.

It's good you bring that up, because I can assure you they will firmly stand behind their original voicing.  They make many versions each different and listen to them, choosing the best 100% by ear.  A presence peak can be very appealing, especially from a 15 inch driver.  

But, in my room as an amplifier designer, I need a flat speaker that doesn't EQ the response.  I have that with the F15.  I will test this network over the next week or two and see if it can win me over.  The drivers have great potential even for me.

Steve

As mentioned in my previous post .....

"One of my customers who lives about 100 miles away (and has become an audio buddy) has told me that he really didn't care for the F-15 drivers at first. His original speakers had Betsy drivers and he added a second pair of baffles with the F-15 drivers.
He stated that it took about 500 hours of playing time in his system before the F-15 baffles sounded good to him ..... and now he loves them.
He will be visiting tomorrow to do an A/B between the F-15 and Fast-15 baffles in my room."

Here are the results of the visit .....
We spent several hours doing an A/B of the F-15 and Fast-15 drivers in identical baffles.
I asked him to share his thoughts during the session without providing any of my opinions or observations in advance.
The results were that his observations were nearly identical to mine.

The following is just my opinion (in my listening room with my equipment and playing music that I enjoy and consider "well recorded") and should be taken as such .....

The Fast-15 drivers certainly are "lively" sounding.
I still have some music in my library that is "hot" or "thin" and if a person's music falls into this category, these are probably not the drivers for you.

On the vast majority of the music in my library, these drivers are a revelation.
They combine the lower midrange / upper bass response of the original F-15 drivers with the speed and upper frequency response of the Lii Audio Silver-10 drivers.

They create a HUGE soundstage / stereo image when the recording contains such information.

The separation and space between instruments and vocalists is excellent.

My system includes a third baffle with a Lii Audio W-15 bass driver which adds a nice "foundation" to the music and has to be factored into my final take on these drivers.

The addition of a ZROCK2 in the mix works very well ..... at least for me.

So, there you have it.
I also expect them to improve with additional break in.
Based on my experience, every Lii Audio driver has a "raw" sound until well broken in.

Conclusion - if a person has reservations about the suitability of these drivers for their system, go for the original F-15 drivers.
If the solution to "tame" these drivers that Steve is working on pans out to his satisfaction, that will be an answer for many buyers.

Happy listening,
Randy

what is the phase plug made of ? acrylic or wood.... hard to tell in photos.

Hi Palomino,
If it's not too much trouble, could you elaborate on how you augment your F15s with the upfiring tweeter?
Thanks so much,
Chris

As if by magic!

Pal,

I cheated is what I did!

Went to your link, copied the picture address and then put it in my Imgur account, resized it to large thumbnail, copied the picture address by right clicking on the picture, then pasting it between the IMG thingies on here.

The secret is the right clicking and copying the address there, I can never get their links to work.

Well thank you.  Now everybody can see my tweeter balls.

I'm using a better tweeter now and a better cap.  I don't know how much high end extension I am getting but I hear more more "air."

Awesome; thank you, Palomino!
What tweeter are you using currently?
best,
Chris

Thanks, Palomino!

So, did you use this tweeter:
https://www.daytonaudio.com/product/1166/amt2-4-air-motion-transformer-tweeter-4...

OR this one:
https://www.parts-express.com/search?keywords=275-094

Just to be sure I have the right one.  Also the 3.3uF cap is being used with this Dayton tweeter; correct?
Thanks so much,
Chris

Hi Chris,

I used the second one, but only because I had it lying around.  I am thinking about researching and buying something else.  Having heard a high quality tweeter in Steve's house speakers has left me thinking a better tweeter might help.   Not that the AMT is a slouch, but its not in the league with what Steve had.

The AMT Pro4 is also large, not as efficient and does not go as high as I would like.   The little vifa tweeter in the photo goes higher and is more efficient, but was not as good a quality.

Now that I've done the proof of concept A/B testing, I do think an up firing tweeter does help the sound in my room.  Now to find the right tweeter.

Also, yes, the 3.3uf goes on the positive terminal of whatever tweeter you use.

See the house speaker build thread.  I don't know the specs on this one to know if its a candidate but I though it sounded great and I heard details I haven't heard in a number of recordings.

ScanSpeak Revelator R2904/7000-09 Tweeter. - $345 ea.

Loic has them. Just a short clip for now—hopefully detailed impressions soon.

https://youtu.be/7boJ-tIUuME

I'm going to build a large barrel open baffle speaker with the Lii Fast-15 drivers.  I'm curious if anyone has an opinion about MDF vs plywood and a single 3/4" sheet versus gluing two 3/4" sheets together.  Obviously, Decware uses thick hardwood but that is beyond my abilities.

I've built MDF and Baltic Birch Ply baffles and like the livelier sound of the Baltic Birch.

I also made my Betsys out of hardwood stair treads which I like, but I should have doubled up on the treads.

If I had the money/skill I would make the thick hardwood baffles as Steve did. Steve's go lower and sound fuller than mine.

I think you can see pictures of my construction process on the original Big Betsy thread.  The countertop idea is far less complex.   I don't know about the cost vs the treads - especially if you doubled up.

I was at the hardwood store the other day and if you went three wide by 42 tall, it would run around $450 as the price of wood remains relatively high.

I don’t know about a hybrid. It could be ok.  I’d suggest that over double MDF.  I just thought that sounded dead.  Maybe try some good plywood.  Baltic is expensive but maybe something just below that could be the ticket.

I have a hard time letting go of anything but I burned my doubled mdf baffles.

Paul, I used what materials I could find locally.
And yes I do believe that using a more dense product (MDF) for the middle layer adds to some stability required. None of what I used is going to add up to enough to compete with some thick, solid hardwood, however.

As I mentioned, this mock up was an early phase of "try things out and see what happens" with something new to me I had just acquired, which was the Original F15 drivers.
Which I absolutely hated at first, BTW. Love them, now!

They will need a great deal of break in time.
Then, you will have a difficult time ever turning them off!
They sounded thin and transistor radioey at first, but after a thousand hours or so, they sound rich, thick, detailed, precise and Established.

Mine have a home, now.

I do not mean to discourage you again, Paul. I feel I was a bit harsh with my first post to you. Sorry, but that part was more about physics.

I have a little over a thousand or so hours on mine. So, they are newish to me still and they have sounded pretty darn good for more than half that time.
Some guys say a hundred hours was fine for them. One guy said his sounded great right out of the box.
Mine did not sound fine right out of the box, but rather disappointing.
I received my pair with a very high Fs, which did not match the advertised specification by more than an octave.

I beat the crap out of mine for about three weeks and they reached a more palatable low range with a much more smooth mid range during that time.

Last I read about Steve's experience with his new Fast 15 drivers, he was still breaking them in. They looked great down low on a response curve, not so smooth up through the spectrum, but he is still working with them.

As I mentioned before, I have no experience with the newer Fast 15 drivers. When I went to try for my own experience with the Fast 15 drivers they were out of stock with no availability timeline offered.
So, I bought the older F15 model. Those arrived in about a week.

YMMV!

Don't let one guy on the internet bother you. I was just relating my still very fresh exposure to these things while trying my best to be honest.