1'' vs 2'' compression driver

[quochuy0202]

Hello Everyone,

I am a new member of this forum.
I am impressed by JBL vintage speakers, especially jbl 4345, so i decide to build an 4345 model.
I consider between 1'' driver such as 2425, 2421 or 2'' driver such as 2446, 2441 and 2440 for the mid-high.
Would you mind give me your opinions about the sound of 1'' vs 2'' driver?

Thanks in advance!

[ivica]

Hello Everyone, I am a new member of this forum. I am impressed by JBL vintage speakers, especially jbl 4345, so i decide to build an 4345 model. I consider between 1'' driver such as 2425, 2421 or 2'' driver such as 2446, 2441 and 2440 for the mid-high. Would you mind give me your opinions about the sound of 1'' vs 2'' driver? Thanks in advance!


Hi quochuy0202,

You can find some physical explanation about expectable behaviors 2" and 1" drivers in JBL Technical notes Vol.1, No.8. in few words it would be expected that 1" driver ( VC=1.75") would have almost two times 2nd harmonic distortion larger then 2" diver (VC=4"), under 'the same conditions', for 3rd HD it seems the same results ( that can be seen on figures 9B and 10B, where SPL is over 100dB...THD on the 1"driver is about 6bB larger.....then on 2" driver).

For your 'new project-4345' may be it would be interesting to be considered also JBL 1.5" drivers ( VC=4") too, such as 2450SL, 2451SL or 2452SL, connected to the some kind of "newer faster-flaring" 1.5" horns such as 2352/53 ( see: JBL Technical Notes Vol.1, No.21) or PT-F95H (PT-F64H) ( see: JBL Technical Notes Vol.1, No.31), where even less THD can be expected,
but some tweaking has to be done on the VHF part of the 3145-like network.

In 4345-like projects, it would be expectable that compression driver would be operating over 1000 Hz...... up to 10kHz,
as a sort of mid-bass driver would be present ( 2122, or 2123, or 2202, or 2251, or 2012..) in order to 'cover' the rage from say 300Hz to 1.5 kHz.

Regards Ivica

[quochuy0202]

Thank you for you reply.
I have a pair of 1 inch drivers 2470 with phenolic diaphragms. I don't have a chance to listen to 2 inch drivers, so i don't know which one is better to use for the 4345.

[more10]

One inch drivers have a voice coil of 1,75 inch. Two inch and 1,5 inch drivers (large format drivers) have a voice coil of 4 inches. 1,75 inch VC drivers go higher than 4 inch VC drivers. If you use a 4 inch VC driver you will probably need a supertweeter above. 4 inch VC drivers go lower than 1,75 inch drivers. JBL 1,75 inch drivers typically reach 15 kHz, so you don´t need a supertweeter. The bigger the voice coil the lower the distortion, etc, etc.

In the 4345 JBL used a 1,75 inch driver as well as a 2405. Probably the economy department was involved in the design :-).

If you can afford it, go for a large format driver. The 2447 is a good choice (cheap and 1,5 inch exit) as Ivica suggested. I would pay 150€ for such a driver. You can improve the driver by using a 2450SL (aquaplassed) diaphragm, a truextent beryllium diaphragm or even a Radian aluminium diaphragm. The original titanium diaphragm will start to break up at 4 kHz.

You will have to choose a horn that matches the 2405 radiation wise, the thread Questions about 2352 and 2381 Horns (http://www.audioheritage.org/vbulletin/showthread.php?4655-Questions-about-2352-and-2381-Horns) lists some facts. Or some other horn of your choice.