JBL MIDs / 2169 , 2250

[Anti K]

Hello,

Midwoofers 2169 or/and 2250.

These are designed for HornSystems for very high SPL.
Is somewhere RAW drivers spec available, sensitivity of raw driver, graph etc?
Are they usable without horns?

2169 is named even one of best articulate Mids ... with horn though.

[AveDalang]

Hi....the 2169 is a 8-inch cone-driver made for horn-utilization, and with a JBL phaseplug giving it a 4-inch exit. The Seos horn is made explicitly for the driver. In the event that you need something for homegrown utilize and can live with a pass band of 250–2250ish, at that point it is very acceptable.

[RMC]

Hi Anti K,

2169H Thiele-Small parameters are available in JBL's 2012 parameters list (see pic). I'm assuming these numbers are correct, i.e. no typos.

As for sensitivity of raw driver, the same table gives efficiency at 1.3%. According to JBL John Eargle's conversion table from efficiency to sensitivity 1.25% = 93 db (1W, 1M, half space loading, piston band). So 93 db is pretty much what it is.

That's relatively low for a sound reinforcement driver. This is probably why they doubled the number of 2169 in the MD2 cab to increase sensitivity, then horn loaded it to further increase it, elevating it to 109 db 1w 1m. So the 2169 is not a high sensitivity driver by itself.

"Are they usable without horns?" Due to their very high Qts of 0.61 they might be more appropriate using a sealed box. But the question is also a tricky one. I'm even surprised it can be horn-loaded!

The cone driver suitability principles for horn loading have been known for a while, thanks to D.B. Keele, J. Eargle, etc. Discussing Mid-frequency Cone Driver Horn Systems Eargle indicates: "The design aim in these drivers is to keep the resonance frequency, Fs, high and the Qt low. ( RMC: Qt here being Qts) As shown in Figure 6-4, the requirements for response out to 2 khz is that the mass-controlled upper frequency, fhm, be no lower than about 1 khz."

The details of the design aim here are not really known, other than guessing. Such as why JBL departed from usual horn suitability criterias? Didn't see in the documents read (Marquis Dance Club series, MD2) any discussion about driver particularities for or about its unconventional horn loading. This is somewhat surprising.

(Fhm is one of the various driver response breakpoints, more specifically at the higher frequencies, where it starts to roll-off initially at 6 db/oct., then progressively steeper.)

He further adds " fhm = 2Fs/Qt. For high fhm, we require high Fs and low Qt. Typically, Fs = 100 hz and Qt = 0.2. Thus, fhm = 2(100) /0.2 = 1000 hz." (Handbook of Sound System Design, P. 122)

Applying this to the 2169 we get 2(320) /0.61 = 1049 hz which is pretty close to Eargle's example.

Other things being equal, had the 2169 Qts be 0.2 as in above example then fhm would have been a pretty high 3200 hz, possibly too high for an 8" driver to be used (Eargle, Loudspeaker Handbook, P. 113 & 205: an 8" driver at 2190 hz already shows a Directivity Index of 10 db, while at 1460 hz its DI 6 db, the latter pretty matching the 2169H XO for MD2 cab at 300 hz and 1500 hz.

Once its determined driver Fs is higher than usual, then you're bound to need a higher than normal Qts otherwise the above equation (fhm = 2Fs/Qts) won't lead to a satisfactory result (as for 3200 hz above). The other way around is also true, faced with a high Qts driver then a higher Fs than normal is what will make the equation work for you. I think this explains why driver Qts is abnormally high for horn loading, i.e. to get proper results from the fhm equation once Fs was set.

Another way to look at it is driver EBP (Fs/Qes). EBP around 50 is said to be more suitable for a sealed box, around 100 for a vented box, and around 200 for horn loading. Driver Qts should also be considered they say, i did. Well, 2169H EBP (320/0.68) is a whopping 470! Possibly the highest number i can remember. Would such number mean horn loading and absolutely nothing else?? I still think it could be used in a sealed box in view of high Qts. Don't forget, fhm equation doesn't apply when driver is mounted in a sealed box, makes things easier.

A little "weird" driver on Fs & Qts aspect, not a conventional device, however like for every rule there seems to be an exception or two. Design Engineers being smart and clever fellows, they pulled a rabbit out of the hat, abracadabra...

Note two other items are mentioned as characteristics of cone drivers for horn loading: low cone mass and high BL product.

Richard

88601

[Bassdabob]

Hello,i know again its an very old post and people might not like it but:2169 is a sealed out of the box driver thats why it has 320HZ Fs in this small chamber. 2250 could be used without an additional back chamber but usually was not. so keep this in mind. 2250 seems to be the way better driver but the 2169 is more cost effective and has better overall heat dissipation als less power compression.

[toddalin]

I use the 2251J in a rear ported cabinet even though it was also intended for a horn. I let them roll off naturally on the low end (to a 2241H crossed at ~360 Hz with some additional mfd), and to a specially modified Great Heil at ~3kHz. They are extremely articulate and revealing of every detail. And the soundstage and imaging are unbelievable, like none I've ever heard! Much better than I think could be achieved with a/any horn. https://youtu.be/M0jCSqRPPr4