JBL PT 100x100 waveguides, any experience? MPro?

Not so different a setup to what I'm after. Are you using the 2119H as midrange because you had it or you purchased it for this project? I'm looking into 8" with the same xo points as you.

Hello,

I have been playing with this project for a long time with different woofers, mid-ranges and tweeters. Along the way I have become more focused on controlled dispersion.

For midranges I have tried JBL 2123h’s 10 inch, JBL 2108’s 8 inch, JBL 2118h’s 8 inch and JBL2119H’s 8 inch.

The 2119 is the higher power less efficient younger brother of the 2118, they look identical from 10 inches away and are otherwise pretty much the same. There are many 2118’s on ebay for cheap. Good luck finding 2108’s or 2119’s for any price.

Depending on how you measure the diameter (6.5 inches) of the JBL 8 inch drivers the calculation shows 100 degrees dispersion at 1907 Hz. XO at 2000Hz is very close.

Thanks DT

Mitch,

Thanks for the DSP insights and recommendation for the prophylactic capacitor. I have a pair of 30uf film capacitors I will use.

The phase correction shown in the DSP EQ could account for some of the dynamic breaking I have been speculating about. The resistors in the L-Pad may also help dampen resonate reflections in the CD / waveguide.

I am going to spend some time with the DSP programming information that you linked.

Thanks DT
 
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Hello,

Today I have been looking again at the impedance of compression driver attached to waveguides.

See the attached D2 /M2 plots. These plots are done with no passive devices; resistors capacitors or inductors between the amplifier output and the driver input. I know that real world there will be L-Pads and capacitor high pass filters to protect the CD. Also thinking about it, the L-Pad resistor is in series with the CD voice coil(S) and will shunt or damp CD / Waveguide resonance.

Tomorrow I’ll do Frequency Response plots.

Thanks DT
 

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Great thread.

Do the impedance plots change if you try to eq out some resonances?

Bill,

I do not know. I suspect that the impedance peaks will flatten out with the addition of some passive crossover and EQ parts. The passive network that JBL puts into the M2 attenuates the D2 input by 9dB’s, only 25% of the amplifier output power goes into the CD. Much of the Resonate Back EMF in the driver shunts to ground through the resistor that is in parallel with the driver Voice Coils. That resistor to ground is what Variable Frequency AC motor drives call active breaking. The damping comes at the expense of lost amplifier watts. The typical passive XO has higher dB output HF drivers than woofers and have HF watts to burn.

I plan to add more pieces to the puzzle and do more testing.

Thanks DT
 
Hello All,

This is the first look at the D2 CD and M2 Waveguide no equalizer and no filtering, on axis, ~ 22.5 degrees Horizontal off axis and ~ 45 degrees Horizontal off axis. I turned up the output a bit to swamp the analyzer’s fan noise. No smoothing.

Thanks DT
 

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So far, I can't see anything that can't be eqed.

Hello,

No problem; passive, active analog or DSP EQ are all good tools and help flatten out the D2 FR plots. What I see in the plots is the typical -6dB per octave mass break roll-off. I do not see any diaphragm breakup in the D2 plots.

I will sneak up on it with an active 30 band equalizer and active crossover.

Give Mitch credit, a little down the line I will try out the digital solution. The plots that Mitch has posted are like a ruler flat.

I think that this JBL D2 is well capable of 20 KHz and better output.

I believe that Rob is correct 15dB, of boost at 20KHz may be a strain. I am also of the thought that diaphragm breakup if present will contribute to UHF harshness.

See this link for a little background and history of CD’s and waveguides in monitors.

http://www.cieri.net/Documenti/JBL/Technical Notes/JBL Technical Note - Vol.3, No.1.pdf

Thanks DT

A little food for thought.
Waveguide JBL PT90 50 with JBL2408H-2 CD
 

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I use ~15 dB of CD horn equalisation relative to about 2.5 kHz on the JBL 2453h-SL/2384 waveguide. The large format 4" CD is good to about 19 kHz. Measuring at reference level (i.e. 83 dB SPL) at the listening position), the high frequency distortion is in the noise floor, even with the compensation eq in place.

DT, your measurements are similar to an M2 system measurement I recently received. After Audiolense correction, virtually a straight line (tilt) from 20 Hz to 20 kHz - impressive speaker system! Looking forward to your listening impressions on this waveguide/cd combo...
 
Has anyone ever measured a D2430 on one of the newer PT waveguides ?
I have once done so with a PT95 and the measurement looked very smooth (the expected CD rolloff. But within +- 1dB between 1.5 kHz approx and 5 kHz). But I have to admit that I didn't measure with the same resolution as DT used for measuring his M2 waveguides.

regards

Charles
 
That looks good too.

Something in the 2408 bothered my ears, maybe the 15 and 23khz slight resonance, idk.

The 2408H or the 2408H-2?
I have been running the 2408H for the past 10 years or so on the JBL 6x6 PT waveguide and have no problems with mine. I can hear to 16.4khz and the top end on mine sounds fairly smooth.
This is an old measurement, used 3 eq bands from a MiniDSP. 5db/division.
 

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Hello All,

It is interesting looking at and listening to these JBL D2 / M2 CD and waveguides.

There are several options to equalizing these things.

So far I am keeping it active analog. I like listening to old vinyl and do not want to jump just yet into the DSP.

I have taken the CD’s and waveguides out of the lab where I use PPE hearing protection to the listening room where I keep a SPL meter on the table next to me. Thanks Mitch the reference is 83dB SPL.

Using the M2 waveguides and PT H1010HF-1 waveguides with the different; D2, 2432H and 2451J CD’s there is concept taking form. The better I do equalizing the combinations to the target curve, the more they sound the same.

The D2 M2 combination seems to have a more precise soundstage and more natural sounding solo voices and instruments. It is easy to get lost in the music.

The target curve that I am using is downward sloping to to 2KHz at 0.9dB’s per octave and 1.2dB per octave from 2KHz to 20KHz. This target is not too different than the Harmon Curve.

I have plotted the target curve on the D2 M2 Frequency Plot. There is not any extreme EQ being done with the Rane AC23S 30 Band Equalizer. Oh I almost forgot. The AC23S has CD Mass Break roll off compensating bypass capacitors installed on the PCB.

For fun I went to ebay and ordered 4 new to me, used, Crown COM-TECH amplifiers

See the attachment below.

For Fun!
YouTube

Thanks DT
 

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DT Nice!

Re: Using the M2 waveguides and PT H1010HF-1 waveguides with the different; D2, 2432H and 2451J CD’s there is concept taking form. The better I do equalizing the combinations to the target curve, the more they sound the same.

Yes, I have found the same in my experiments. In some respects, it levels the playing field as one can evaluate other aspects of the SQ without the variant of frequency response.

Re: The D2 M2 combination seems to have a more precise soundstage and more natural sounding solo voices and instruments. It is easy to get lost in the music.

Cool. Looking into the D2 M2 combo over the past year, I see others have made similar comments on various forums (AVS, Lansing Heritage) on precision soundstage and natural sounding.

Keep going! :)
 
Really smooth just right out of the box.

Hello,

I get more and more tempted by this little combination.

https://faitalpro.com/en/products/HF_Horns/product_details/datasheet.php?id=903010100

https://faitalpro.com/en/products/HF_Drivers/product_details/datasheet.php?id=502010305

Really smooth just right out of the box.

A large feature is that it is not visually dominating in the speaker stack. You are not looking down the orifice of a pair of Butt Cheeks.

There was a little concern about a lumpy frequency response curve like the 2342 has, no such problem.

At best this little tractrix is controlled dispersion not constant dispersion. Cross it over from the 8 inch midrange about 2000Hz for a smoothly tapering Dispersion Index.

Thanks DT
 

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Because someone sent me a PM asking.

I have been crossing over to the PT 1010HF-1 at 2K and above because there is typically a huge ragged acoustic impedance peak right about 1.6KHz. The depth of the waveguide is right at ¼ wavelength at 1.6K. About 4.3 inches. That makes for one huge reflection or family of HOM’s, if you are a believer, centered around 1.6KHz.

A resistor equal in value to the voice coil resistance placed in parallel to the voice coil plus enough series resistance with the parallel resistance will start to tame the impedance peak of the driver/waveguide combination. These days JBL and Crown use a dose of DSP to further tame the phase distortions caused by the impedance peak. (Done in the M2).

Attached are 1010 HF-1 impedance plots with JBL 2432H, JBL2451SL J and D2 drivers. There are also 1010 HF-1 frequency plots with mostly the same drivers.

Thanks DT

I added the last FR Plot of the PT90 with a JBL2408H2 because I like the looks of it.
 

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ty.

any idea for a nice tractrix or spherical that can go down to 1,200hz ?


If I remember correctly, djk said I'd need a 600hz stereo lab horn if I wanted to cross at 1,200.
We were looking at the 400hz horn for me to cross at 800hz................


Just because there is a huge Zpeak, it may not be a resonance (showing up on a waterfall or csd).
But others know more.
 
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