Classic compression drivers internal throat geometries

[marco_gea]

Hello all,


After some deliberation, I decided that it would make more sense to start a new thread rather than dig up an old one that had a similar topic.
I hope this is OK.


So, basically, this post is to summarise the information that I painstakingly collected over the years on the internal geometries and flare rates of the "classic" JBL and (JBL-inspired) Pioneer TAD compression drivers.


The internal throats are all conical, but based on a hypothetical duct having the same length and entry / exit diameters, and assuming exponential or hyperbolic-exponential (hypex) expansion, one can calculate equivalent cut-off frequencies.


The reason that this is relevant is that for the best possible matching to a horn, one would want the horn (including throat adaptor) to have the same flare rate as the one that actually already starts within the compression driver itself.


So, here it goes:

Large-format drivers	Throat diameter [mm]	Throat angle [deg]	Equiv. Fc (Exp) [Hz]	Equiv. Fc (Hypex T=0.7) [Hz]	Equiv. Fc (Hypex T=0.6) [Hz]
JBL 375, 376, 2440, 2441, 2445, 2446	49.2	8	180	235	260
JBL 2450	49.2	10	217	290	320
TAD TD-4001, TD-4002	49.2	10	217	290	320
TAD TD-4003	39	8.5	225	300	340
Small-format drivers
JBL 275, LE85, 2420, 2421, 2425, 2426	25.4	8	350	450	480
TAD TD-2001, TD-2002	25.4	8	350	450	480

I hope someone will find this useful! :-)


Marco

[ivica]

Hello all,


After some deliberation, I decided that it would make more sense to start a new thread rather than dig up an old one that had a similar topic.
I hope this is OK.


So, basically, this post is to summarise the information that I painstakingly collected over the years on the internal geometries and flare rates of the "classic" JBL and (JBL-inspired) Pioneer TAD compression drivers.


The internal throats are all conical, but based on a hypothetical duct having the same length and entry / exit diameters, and assuming exponential or hyperbolic-exponential (hypex) expansion, one can calculate equivalent cut-off frequencies.


The reason that this is relevant is that for the best possible matching to a horn, one would want the horn (including throat adaptor) to have the same flare rate as the one that actually already starts within the compression driver itself.


So, here it goes:

Large-format drivers	Throat diameter [mm]	Throat angle [deg]	Equiv. Fc (Exp) [Hz]	Equiv. Fc (Hypex T=0.7) [Hz]	Equiv. Fc (Hypex T=0.6) [Hz]
JBL 375, 376, 2440, 2441, 2445, 2446	49.2	8	180	235	260
JBL 2450	49.2	10	217	290	320
TAD TD-4001, TD-4002	49.2	10	217	290	320
TAD TD-4003	39	8.5	225	300	340
Small-format drivers
JBL 275, LE85, 2420, 2421, 2425, 2426	25.4	8	350	450	480
TAD TD-2001, TD-2002	25.4	8	350	450	480

I hope someone will find this useful! :-)


Marco

Hi marco_gea,

Thank You for the summary data presented, though, large (2") format driver throat drivers are not so popular today, as most of them would expect to be used with large horns, and mainly limited to about 10~12kHz. I think the most important would be "soft" surface curves transition between the driver mouth and the horn throat, in order to prevent horn throat reflection. So very sophisticate curvature of the horn throat can be seen on the JBL 2328 , or on the H66k horns (throat).

Making my DIY horn 'inspired by JBL H66k horn' I have made (called JAN45-2.0 and JAN45-1.5) two different horn throat 'ready' to be connected with 2441...46(50), as 2" type drivers, and 2450-1.5 or 2451, and from the measurements, I have done, there seemed to be the reflections were quite low.

regards
ivica