JBL PT 100x100 waveguides, any experience? MPro?

Hello Norman

Yes it just takes a little work. You need to countersink the adapter plate and use Flathead machine screws because the driver covers the screws that attach the plate to the horns.

So you have to mount the plate and then do a completely blind mate to the driver using the 1/4-20's. That was a real PITA ended up using tweezers to get them in there and starting them into the driver. I will post a picture.

It's nice though because with the mods to the adapter plate and helicoils you drop on any 1'5" driver with the same bolt pattern.

Rob :)
 

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Hello,

Take a look at the third photo above. The flange has 4 slotted holes for the attachment of the driver. With my handy ruler the slots will accept 3 ¼” to 3 ½” bolt circle drivers.

As far as I can tell 3 ¼” to 3 ½” bolt circle drivers will fit.

Both the D2430H and 2432H have a 3 ¼” bolt circle and fit the OEM flange and waveguide the same.

Thanks DT
 
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Wow, talk about a shallow horn.
I figure ideally it should be deeper to load down below 1khz even (1/4 wavelength).
But seeing what the pt does with a 4" driver, it may not have to load down below 1khz to measure flatish down there.
I though the pt was shallow (4" throat to mouth).

I see a jbl m2 horn flange for sale.

JBL M2 Horn Flange #5026224 - Speaker Exchange
 
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That's not the waveguide it's the compression drivers they are both in break-up modes above 10K. Here is a 476 on the older waveguide and it's clean up there.




It's the short phase plug that makes them hit or miss. You would get a notch in the response. The 2435 works well on the older PTH1010. We wrestled with this a lot on LH and it really was hit or miss I don't think we ever really built a list of "good' horns/waveguides.


Rob:)

Hello Rob and All,

I am going to be taking a closer look at the impedance curves of these 100 X 100 waveguides and CD combinations. Looking at cone drivers my impedance curves are turning out to be relatively smooth compared to the curves that I am getting with the CD PT H1010HF-1 (this is the newer one). My curves for the CD and PT waveguide combination is looking pretty much ragged especially related to the 1.7K ish impedance peak. See post #67

Looking at your attached impedance plot above you have the same 1.7K ish peak with a little related roughness. The edges on my plot look like a serrated kitchen knife.

I think that there is some instability going on with the CD diaphragm and or waveguide or both around that 1.7K ish impedance peak.

What are your thoughts and experience with this?

Thanks DT
 
yup, horn standing waves show up in the Z plot, throat to mouth, and across mouth also (even little ripples cause by reflections from edges in horn path), I think a compression driver's Fs is there somewhere, maybe not. It will not be as flat some drivers with a copper cap. So I hope others can chime in.

On google, you can look up images of "compression driver" impedence to see what we are looking at.

I've seen comments on AH forum about the pt (older) not loading much below 2khz (maybe 1.5khz, I can't remember).

replaced my 2420 + 2344A with 2435 + PT-H1010HF - Page 2

Flatter is better, but the big throat to mouth peak is probably unavoidable.
 

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In search of horn reflections

That is curious to me.

Some where I recall reading that where there is a resonance there is a resonance peak on the impedance plot. This seems to ring true today. For example if sound bounces around off of bracing inside the woofer cabinet there will be a tattle tale bump on the impedance plot. Worst still it is likely to be audible.

Speaking of the 100 X 100 waveguides I can’t say if can report hearing that throat to mouth impedance peak or not. I do know that I much prefer the sound of a 3-way speaker with a JBL 2123 or JBL 2119 dome midrange crossed over to the 100 X 100 CD/waveguide at 2K.

The APx analyzer that I am using has a raw data setting where all those micro reflections show up on the impedance plot. I have several old school Bi-Radial horns sitting around and a couple of 2” throat CD’s to test drive over the next couple or 3 weeks.

In search of horn reflections.

Thanks DT
 
Hello,

Take a look at the third photo above. The flange has 4 slotted holes for the attachment of the driver. With my handy ruler the slots will accept 3 ¼” to 3 ½” bolt circle drivers.

As far as I can tell 3 ¼” to 3 ½” bolt circle drivers will fit.

Both the D2430H and 2432H have a 3 ¼” bolt circle and fit the OEM flange and waveguide the same.

Thanks DT

Hello DT, your measurements are looking good. Maybe you have already seen this M2 adapter: Compact monitor - Page 6

Cheers,
Mitch
 
Hey Mitch,

Thanks I took a look at the adaptor flange in the link that you provided. I am still scratching my head thinking about it.

At this point it looks like that I can drill 4 new holes for the larger bolt circle required for the 2451 CD.

I do have the Aquaplas SL diaphragms to also tryout in the 2451’s.

I am also planning to tryout the D2 CD’s on the PT H1010HF-1 waveguides.

We are in the process of a long dragged out move a couple of counties north of us near the coast. It will be a couple of weeks before I get some time in Sparky’s Lab. (Sparky is the cat)

Thanks DT
 
I think that there is some instability going on with the CD diaphragm and or waveguide or both around that 1.7K ish impedance peak.

What are your thoughts and experience with this?

Thanks DT

Hello DT

Frankly I am not sure that is what's happening. If you take a common horn like the 2380 Flat Front Bi-radial and look at the impedance curves with different drivers the peaks are all over the place and not consistent in amplitude or location. If you had a strong horn resonance going on wouldn't you expect a bump in impedance curves in all drivers at that frequency?? Don't see that in the plots with 2427 2445 and 2446 drivers??

Rob:)
 

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Oh, ok, i see the z plot is the resulting combination of driver and horn.

I found a plot of a celestion cdx20-3075.
Its impedance plot then its plot on their 90 x 40 horn, notice it went from 1 Z peak to 2 smaller ones.

Did not know that, thanks for the prod in the right direction.
 

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Hello DT

Frankly I am not sure that is what's happening. If you take a common horn like the 2380 Flat Front Bi-radial and look at the impedance curves with different drivers the peaks are all over the place and not consistent in amplitude or location. If you had a strong horn resonance going on wouldn't you expect a bump in impedance curves in all drivers at that frequency?? Don't see that in the plots with 2427 2445 and 2446 drivers??

Rob:)

Hello Rob,

I like your puzzle.

In the old day we kids on the block used to argue about how they made potato chips. After tiring of the argument I asked my grandmother. She is not around anymore.

If I painted too simple of a picture perhaps I should have used a broader brush.

I don’t know. I will take a SWAG at it.

This is my approach to technical problem solving. I take a piece of paper or white board and draw a line down the middle. The known possibly related stuff goes on the left side. The stuff that you want to know goes on the right. Then you read study and experiment then the answer comes to you in a dream or when you are standing in the shower in the morning.

Limiting this to JBL bi-radial horns and drivers that I have here at the house this is what I know.

Each horn has its own physical shapes, dimensions, resonate surfaces and cavities. Each horn model is unique. As you say you might expect a particular horn model to have a typical resonance response pattern. Hard telling without a driver attached.

Each model compression driver has its own physical shapes, dimensions, resonate surfaces and cavities. Each driver model is unique; you might expect a particular horn model to have a typical resonance response pattern. Hard telling without a horn attached.

Another known variable is the diaphragm. Different type diaphragms can be swapped in and out of a driver; different metals, manufactures and coatings. Lots of variables here. Lots of money to spend too.

Now to toss a little theory into the mix, not a horn still stuff about resonance. We know that a particular woofer has a measured impedance peak with a known Q. We also know that we can put that known driver in a sealed enclosure of known volume and we know or can calculate a new combined Q and shifted resonance peak. This is how we test for Thiele Small Parameters. This is assumed technology.

To bring Mitch into this, I recall over on the Lansing pages Mitch and other folks talking drivers with and without a snout and adding a ½ inch thick spacer between the CD and the horn to shift or otherwise adjust the phase plot of a particular driver horn combination.

Is it a surprise that there are multiple impedance peaks and dips and that shift and move around as we mix and match CD’s, diaphragms, spacers and bi-radial horns? Short answer, No.

On the right hand side of the page what I want to know.

Can we predict and control; add and subtract, reduce the impedance peaks and dips in magnitude and shift the peaks and dips outside the band width we are designing.

Second and not least important; what are those little saw tooth ripples? Are they audible? I don’t want them in my midrange output.

Thanks DT
 
Can we predict and control; add and subtract, reduce the impedance peaks and dips in magnitude and shift the peaks and dips outside the band width we are designing.

Second and not least important; what are those little saw tooth ripples? Are they audible? I don’t want them in my midrange output.

Thanks DT

Hello DT

That is an interesting question. If you were just looking at a box program for tuning a reflex enclosure you can do quite a bit of that except for moving all the peaks out of the bandwidth because Fb is always between the double peaks so one will always be in bandwidth as an example.


Now what about the whole speaker system? Well think about this for a minute. We are looking at CD on Horn plots as a separate entity. We need those impedance plots to design our networks. Just as you would for a woofer in a box program.

Once you add a crossover network the whole game changes and those peaks are essentially not part of the overall system impedance curves. You can see all this is a good network design software program. They essentially just get swamped out by the network.

So what does this all mean?? To me I don't really get too concerned about individual driver impedance plots especially CD horn/waveguide unless there is something obviously wrong. An example being large variations between a pair of drivers you plan on using.

As far as your plots I can't imagine those sawtooth serrations are audible. To me it looks like an artifact from the measurement that would just go away with smoothing.


Here is a completed system curve for electrical phase and impedance. That's a 3 way with two compression drivers on separate horns. The impedance curves of the driver and horn combos looked kinda ratty but in the end I think it's the overall system curves that are the most telling and most important. The overall speaker system sounds very good.
 

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Rob,

I get the sense that you are changing directions, okay.

We were speaking of the nature of the CD /Horn impedance curve and how the irregular impedance affects the output including the frequency response. Resonate frequencies likely add standing waves that have a reverberation, or a persistence that will color the sound. You know the kind of resonance that makes my vowels and consonants sound different than yours.

External networks do not change the resonance of the horn.

Thanks DT
 
Rob,

I get the sense that you are changing directions, okay.

We were speaking of the nature of the CD /Horn impedance curve and how the irregular impedance affects the output including the frequency response. Resonate frequencies likely add standing waves that have a reverberation, or a persistence that will color the sound. You know the kind of resonance that makes my vowels and consonants sound different than yours.

I think we are actually on the same page I just don't look at an impedance curves as the tell all smoking gun. All three of the curves on the 2380 are different and if you drop on another 3 drivers in all likely hood that will repeat.

External networks do not change the resonance of the horn.

From an electrical standpoint those curves get lost with a network. That system measurement is just as valid as the horn and CD measurement.

I don't think the CD/horn curves tell us what is really happening. I think time domain measurements such as wavelets or a CSD are the way to go.

Rob
 
I think we are actually on the same page I just don't look at an impedance curves as the tell all smoking gun. All three of the curves on the 2380 are different and if you drop on another 3 drivers in all likely hood that will repeat.



From an electrical standpoint those curves get lost with a network. That system measurement is just as valid as the horn and CD measurement.

I don't think the CD/horn curves tell us what is really happening. I think time domain measurements such as wavelets or a CSD are the way to go.

Rob
I agree and that's what alluded to earlier. When you add a network the impedance curve will change.