Advice on JBL 8" alnico midwoofer

[Alexander_S]

Hi All,
I used for a long time 12" JBL 123A drivers in self made closed box 3-way system (130 L for 123A). As the mid driver I tried various speakers: original alnico LE5-2, LE104H, varous fostex drivers (87E, 107E, 120fx), modern 5" seas 1262. Honestly speaking, the seas was the winner in terms of distortion and tonal balance. What I didn't like with it - its comression (perhaps comming from Qms=1.5 and modern surround). It is a modern driver, and sound like all other modern speaker, even there are much better among them, i.e. scan-speak revelerator.

Among all other mid drivers I used I liked most of all original alnico LE5-2. But this is a quite problematic one, peaking arround 7 kHz. An excellent review on it can be found at Troels Gravesen site, who made the recreation of L100 crossover.

The second problem with LE5-2 is it is the upper midrange. Trying varous combinations of crossover points I believe now the heavy 12" bass driver should never go up to 800-1000 Hz and no way to 1500 Hz as in the original JBL L100 (old style desing). L100 is simple but the cost of symplicity is it sounds wrong.

I want now to make 4-way system with a 8" midbass between 12" 123A and 4.5" LE5-2.
Can You advice on the midbass driver for this? It will work from 300 to 800 Hz. Having the bass and mid from JBL, it will be reasonable to use JBL again. My original thought was 16 ohm JBL 2118J, but it is not alnico. Any other drivers?

Thanks,
Alexander

[ratitifb]

alnico is not the matter !

2118 is a great mid. Why not the 2108 but hard to find ...

800Hz lowmid/mid transition seems to me a little bit too low.
Take a look on 4315 design

[Alexander_S]

alnico is not the matter !

2118 is a great mid. Why not the 2108 but hard to find ...

What about 208H from G300, Is it good enough?

[speakerdave]

The only Alnico JBL 8" I can think of that is still supported by JBL is the LE8T. Earlier examples of it are Alnico and it also has an underhung voice coil. The cone is aquaplased, but I believe it will play well to 800 Hz. If you are willing to take a chance on unsupported drivers there are two possibilities. The LE8T-2 aka 2115 has the same frame, but a lighter, unaquaplased paper cone. The cleanest ones of these are often scavenged from Aquarius S109s and have lansaloy surrounds, which can be replaced. Rarer is the 2108/112A which has a three inch voice coil and was used only in the 4315 and L212. It is said to be quite outstanding, however. The price of sticking to Alnico within JBL can be hunting up clean examples of no-longer supported drivers.

Potentially the cheapest solution might be the D123 in your three-way configuration instead of the 123A. With a 130 liter box you have almost exactly the right volume for this driver, based on the opinion of those who liked it best, and it will play well up to 800 Hz. How did you arrive at that size box for the 123A?

[badman]

Seems a waste to use an Le8T only to 800Hz, it's a spectacular driver between 100Hz and 5k or so, so a 123A on the bottom and a supertweeter (horn please, nothing with wide dispersion) crossed at or about these frequencies should yield a very excellent speaker system....

A good 8" would be the peerless Exclusive 8", for 100-800Hz. A very great driver (not alnico, but has shorting paths) and is optimized for that range.

[4313B]

I think there are a pair of 112A's on eBay at the moment.

*****

Nevermind, someone must have just won them.

[Alexander_S]

Thank You for all your comments!

How did you arrive at that size box for the 123A?

Well, Qts=0.5, Vas= 230 L, fs=25 Hz, so in sealed box V=130L have

Q=0.5*sqrt(1+230/130)=0.7, f3=35 Hz.

This agrees with 3D simulation in box 40 х 40 х 100 cm and measurements too (f3 arround 40 Hz).

[speakerdave]

OK, I think that's an interesting solution. That box would be ported for the D123. Good luck with your project.

Thank You for all your comments!


Well, Qts=0.5, Vas= 230 L, fs=25 Hz, so in sealed box V=130L have

Q=0.5*sqrt(1+230/130)=0.7, f3=35 Hz.

This agrees with 3D simulation in box 40 х 40 х 100 cm and measurements too (f3 arround 40 Hz).

[Alexander_S]

BTW, could anyone clarify please: 123A1 has ribbon copper voice coil or round wire cooper voice coil?

[badman]

BTW, could anyone clarify please: 123A1 has ribbon copper voice coil or round wire cooper voice coil?

Edgewound (ribbon) I believe.

[badman]

Thank You for all your comments!


Well, Qts=0.5, Vas= 230 L, fs=25 Hz, so in sealed box V=130L have

Q=0.5*sqrt(1+230/130)=0.7, f3=35 Hz.

This agrees with 3D simulation in box 40 х 40 х 100 cm and measurements too (f3 arround 40 Hz).

Win ISD models this as a Q of .8, but it'll still dig plenty deep with a 30Hz F6 and a 20Hz F12....

With room gain, subs shouldn't be very necessary.... but on the other hand, if you cross it over at anything above 200Hz or so you're going to get quite a bit of modulation from the big bass cone swings.

GREAT drivers though