JBL Master Reference Monitor

[pos]

Frequency response on axis measured at 4 meters.
The two gray lines indicate the frequency range of 100 Hz to 10 kHz for the evaluation of the waviness of 3.97 dB from Min. To Max.
The orange line shows the transmission range (-6 dB) of 36 Hz to 21.3 kHz.

Single measurement of LF (red) and HF path (blue) without filter; in orange and light blue, the associated filter functions in DSP System

Maximum levels based on 1 m distance with maximum 3% distortion (red curve) and at not more than 10% distortion (blue curve) for the low frequency range to 300 Hz.
The course is determined by the limiter at the final stage with 400 W for the woofer and 50W limited for the tweeter.

Spectrogram of M2 with a total low-resonance behavior

Horizontal Directivity
The level has dropped during the transition from yellow to light green by 6 dB relative to the central axis.
The central aperture angle in this case is 113 ° with a very small fluctuation width of only 10 °.

Vertical Directivity with an opening angle of 93 ° average.
At the crossover frequency at 800 Hz, a slight constrictions can be seen.

Measurement of intermodulation distortion with a multi-sinusoidal signal with EIA-426B range (green curve) and 12 dB crest factor at 91 dBA Leq at 8 m distance (red curve).
The peak level Lpk amounted to 106 dB, also at 8 m. The distortion components add up to 3.4%.

Averaged frequency response measurements on each 30 position for the left and right speakers to the listening (blue).
Below 150 Hz the room modes are clearly visible.
From the measurements a EQ (green) has been derived for room correction.
Below are the average curve with EQ (red)

[srm51555]

Thanks for posting and translating this POS.

On another thought has anyone contacted the thread originator Ti-Dome and informed him parts are available for projects?

[Valentin]

Thanks Pos

Does the magazine say under what conditions thy do the measurements

is it a freefield, gated what resolution , semi anechoic or anechoic etc

[pos]

No, that is all there is.
The rest is a classic loudspeaker review.

Maybe someone used to reading this magazine could shed some light on their measurement methods...

[ivica]

Thanks Pos

Does the magazine say under what conditions thy do the measurements

is it a freefield, gated what resolution , semi anechoic or anechoic etc

Hi Valentin,

What kind of differences You would expect ?

regards
ivica

[pos]

I got the universal adapters from sebackman last week (thanks Rob!), and ordered the studs and nuts to fit the 2435, D2430K and 2450SL-Be
But now that I think about it, I am a bit worried: can the 8 plastic inserts withstand the 10lbs of a 2450SL, especially if the loudspeaker is moved around, etc?
I mean, these insert were made for the much lighter D2430K, and are probably just (and perfectly) adequate for this kind of weight...
Obviously I would hate to see the horn fall apart!

By the way, what kind of screw do you guys use to bolt the adapter to the horn?
I think JBL is using wood screws, and I would not mind using such screws myself as when using studs and nuts the adapter should never have to be removed from the horn when changing driver.

I think 4313B is using M5 machine screws, and sebackman is using M6 machine screws. In both cases the holes have to be tapped to the selected threaded.

[4313B]

I always support the compression drivers with a cross brace regardless of what horn or waveguide they are bolted to. I put a piece of felt between the compression driver and the brace.

[Don C]

I have Mcmaster 95893A368 for screwing the plate to the horn. These are flat head torx, you have to counter sink the holes on the plate to use these. These are thread forming screws made for plastic. Eight screws and 1, 1/2 inches of screw length gives a lot of strength. These bite hard into the plastic and need a lot of torque to install. You need a good torx T20 driver. You don't have to tap the horns. The size is #10-14
Due to the short length of the horn that is not giving the driver a lot of leverage, these will probably support a 2451 just fine. The lighter 2452 is definitely no problem at all.

http://www.mcmaster.com/#95893A368

I also have a box of McMaster 99512A465 these are similar, but are pan head torx, (T25) for fastening the horn to the cabinet. You could use these for the plate also if you have D2 drivers and don't see any reason to countersink your plates.

http://www.mcmaster.com/#99512A465

[pos]

Thanks a lot to both of you for your good advices

The 2450SL is around twice the weight of the 2452SL, and it also deeper (ie more leverage).
I think I would definitely be more relieved with a proper cross brass.

Of course I am not worried about the strength of the screws themselves, nor am I worried about the grip they can have on the horn (like when trying to pull the driver off the horn).
I am worried about the strength of the plastic insert themselves.
So in that regard it looks like the best solution would be to go for the longest possible screw (probably around 2") to reduce leverage and distribute forces on the entire insert, and the thinnest possible thread diameter (while still having enough grip) to avoid weakening the insert when forcing them in.

Or maybe I am unnecessarily concerned?...

4313B, are you using machine screws? Did you tap a thread?
http://www.audioheritage.org/vbullet...l=1#post375138

[Robh3606]

I had #10 heli-coils put in and chamfered the holes on the plate to accept flathead screws. Worked out really well Rob

[pos]

Thanks Rob,

How long are those heli coils?
Do you feel it is safe to hang the 476 without support on those 8 inserts?

I am using Robert's "universal" adapters with the holes already chamfered, so that part is already taken care of.

[Aaron]

I used 12-24 machine screws and a sharp, unused tap. That's probably the best option for a light weight driver that you know you're never gonna pull off of the horn...otherwise even I would've used the helicoil idea if I had them in hand.

In other news: My woofers are on their way!...and I won't be home for four months. =o[

[Robh3606]

Hello Pos

It really is no big deal to support them. I am sure that many screws would be fine but why take the chance not like you can find this stuff just anywhere.

Rob

[Cappelen]

I got the universal adapters from sebackman last week (thanks Rob!), and ordered the studs and nuts to fit the 2435, D2430K and 2450SL-Be
But now that I think about it, I am a bit worried: can the 8 plastic inserts withstand the 10lbs of a 2450SL, especially if the loudspeaker is moved around, etc?
I mean, these insert were made for the much lighter D2430K, and are probably just (and perfectly) adequate for this kind of weight...
Obviously I would hate to see the horn fall apart!

By the way, what kind of screw do you guys use to bolt the adapter to the horn?
I think JBL is using wood screws, and I would not mind using such screws myself as when using studs and nuts the adapter should never have to be removed from the horn when changing driver.

I think 4313B is using M5 machine screws, and sebackman is using M6 machine screws. In both cases the holes have to be tapped to the selected threaded.

Is this universal adapter for sale somewhere? Is sebackman a forum member?

The adapter wasn't available when I ordered the waveguides. I was hoping that maybe someone could share the dimensions of the original adapter and then I could have it machined somewhere. Anyone who can help me out there?

I doubt there will be any problem with supporting the weight of the 2450SL in the waveguide without any other support with good screews. 8 bolt holes of this length will have plenty of strength, even in plastic.

[10 Watt Street]

Is this universal adapter for sale somewhere? Is sebackman a forum member?

The adapter wasn't available when I ordered the waveguides. I was hoping that maybe someone could share the dimensions of the original adapter and then I could have it machined somewhere. Anyone who can help me out there?

Do you mean this:
http://reconingspeakers.com/product/...lange-5026224/