Jbl 4345

Sorgenti, Amplificatori, diffusori acustici, ecc.
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Iscritto il: 18/05/2019, 16:34
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Jbl 4345

#1 Messaggio da Svarione »

You Guys are Amazing
I can't belive all the interest in this 30 year old system. It was never very successful during its life time primarily due to its size. Most people would get something smaller. It also had a reputation for less than detailed bass, which I have always thought was due to the enclosure not being quite large enough. I haven't thought about these things in years but since I have received a few requests for comments - here goes.

The system was and probably still is a stellar performer if you like the inherent sound of the traditional big JBL 4-ways. There is good news and bad news in the basic design. Good in that they are dynamic as hell and never get confused with intermodulation products of any type. They don't take much power to run and can swallow up a really big amp should you wish to do so. The weak areas of that type of design are several. First, there is a large time off-set between the 10" driver and the HL92 horn. This shows up in both the on-axis response, the directivity pattern and the homogeneity of the driver blending. The second problem is the use of a passive crossover between the top of the woofer and the bottom of the 10". Passive crossovers set to frequencies below about 500 Hz react badly with the motional impedance of the woofer/box combination and give substantial gain around 100 Hz. Gain out of a passive system is generally a bad thing. In the case of the High Pass, we have to work the passive network through a really large motional impedance peak resulting from the 10" fundamental resonance in the sub enclosure. This means that the actual voltage drive that occurs at the terminals of the 10" is less than ideal. There was the added complexity that the Marketing folks of that time required switchable bi-amp capabilities in which the incorrect setting of the switch was not allowed to hurt anything. These little things all add up to additional insertion loss for the woofer and loss of damping control. Now all of this sounds pertty bleak, but as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway.

My sonic memory of the big 4 ways, the last of which was the 4344MkII, is that they are effortless, dynamic, pretty low in coloration and really "alive". They are a little vague by today's standards in terms of precise imaging and although they are very low in intermodulation effects, they are not as detailed as really good lesser way designs. There is no simple answer to any of this and no one design statement that is best. Everything is a series of compromises, and the 4345 has a very good set of complimentary compromises.

I noticed a comment earlier in this string regarding the 2122H. It is a really good voice transducer. It always has been and always will be. Things just sound really natural through it. Another one that might be slightly better is the 2123. It is a little less smooth but perhaps a little more realistic on voice. Either are really good for that critical range from a few hundred Hz to about 1500 Hz.

I imagine you guys have talked about and tried lots of things to get the most out of the system. I will mention a few things that I would do if I had a pair at home for my primary system.

Get rid of the bi-amp switch. Hardwire it in which ever mode you want it. The switch is not that great.
If you can work out bi-amping do so. The difference in the 2245H and 2122H will be amazing. The crossover will have to be non standard. Neither driver is flat around crossover so the voltage drives will need to be adjusted to get proper acoustic bandpasses.
The network components should be updated and this isn't easy. All the capacitors should be polypropylene and you would want to use air core inductors where ever possible. I believe the 4345 used some tapped iron cores. Those are hard to replace with aircores because the surrounding network topology would have to change and all of the values have to be re-engineered. I would suggest leaving them alone unless you are really good at this stuff.
If you can swing it, go to a biased network. The difference is unbelievable.
The ring radiator hates passive networks. A major improvement in the upper range would be to drive the 2405 from its own little amp. You only need 3 or 4 v rms. The 2405 does 110 dB for 2.83v. It is padded way down in the system. There is little real power at those frequencies anyway. You only need to know the voltage output of the amp, power is irrelevant. The 2405 is about 12 ohms and won't draw much current. I would use some little chip amp with a 2ond or 3rd order low level highpass in front of it. Take off the passive network to the ring and just feed it straight. Make sure the amp doesn't make a DC thump on turn on or turn off. That will fatigue the diaphragm. The amp will also have to have really low noise characteristics as any hiss will be really loud directly into the ring. I used to use an old Marantz 1030 integrated amp to run my rings. I could separate out the power amp section and the tweeters always sounded really good.
The L-pads aren't so hot either, particularly after all of these years. Once you have your preferred balance, it is fairly easy to measure each leg of the L-pad and replace it with fixed resistors.
I notice from many of the pictures that the system is elevated on blocks. It is very good to get the 2245 up off of the floor to minimize midbass fatness.
For resale reasons, you should be very careful about doing as much of this as possible reversibly.

Before closing I should comment briefly about the 250 - 4345 comparison. Simply put, I prefer a 250. I like the bass quality of the LE14 woofer. Alway have and always will. The 2245 when used as a dedicated sub is one of the best sounding woofers ever. It has an amazing blend of speed, pitch and punch. So does the 14" but the 18" is better. Unfortunately the 18" dislike for passive networks hurts it more than the 14" is hurt by a passive network. I think the mid and high range on the 250 is smoother and much more open however the 4345 wins by a bunch in terms of effortless dynamic sound. I have made all of the above changes to 250 systems (except for separate amp on UHF) and the improvement is huge. I have not done so on the 4345 but I suspect that that system will benefit from theses changes more than a 250 would. If both systems were tweaked out to about the same level, I suspect it would be very hard to come up with a clear overall winner, but I think I might lean towards the 4345 as having the greater potential.

Thank you all for the interest in my work. I must admit I have been blessed with a really nice profession that has treated me well for a very long time. Remember that sound and music enjoyment are very personal things and that what makes you happy may or may not please others. Screw them. If you are happy and no one is geting hurt then go for it. No loudspeaker system even approaches real life so there is plenty of room for interpretation.

Greg timbers

http://www.audioheritage.org/html/people/timbers.htm

Buon divertimento
EDO RC24
Messaggi: 379
Iscritto il: 01/12/2016, 16:09
Località: albano laziale

Re: Jbl 4345

#2 Messaggio da EDO RC24 »

sì sono quei monitor tanto discussi da i non adetti a i lavori cioè gli ascoltatori che in certi casi putroppo arrivavano a asportare le lenti acustiche alle trombe coniche con risultati disastrosi Marcello Croce in un'altro forum di alcuni anni fà ha illuminato se così si può dire tecnicamente i presenti sul problema che affligeva questi monitors..il salto di dispersione tra il 10" e la tromba conica all ìncrocio..considerando la posizione in asse montati on wall nelle regie audio
figuriamoci nell'ascolto a pavimento e in campo lontano..
Svarione
Messaggi: 1276
Iscritto il: 18/05/2019, 16:34
Il mio Impianto: K.heresy,audion silver night 300b,cdi naim
In estate causa calore valvole preferisco un ampli rega brio, e systemdek
Iix con testina wos 100

Re: Jbl 4345

#3 Messaggio da Svarione »

Mai sentite, sorry
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armonica
Messaggi: 13
Iscritto il: 16/10/2020, 17:48
Il mio Impianto: Completamente in digitale in multiamp attiva a 3 finali Yamaha MX-2 pilotanti jbl 4345.
Località: Tirano

Re: Jbl 4345

#4 Messaggio da armonica »

EDO RC24 ha scritto: 21/10/2020, 17:26 sì sono quei monitor tanto discussi da i non adetti a i lavori cioè gli ascoltatori che in certi casi putroppo arrivavano a asportare le lenti acustiche alle trombe coniche con risultati disastrosi Marcello Croce in un'altro forum di alcuni anni fà ha illuminato se così si può dire tecnicamente i presenti sul problema che affligeva questi monitors..il salto di dispersione tra il 10" e la tromba conica all ìncrocio..considerando la posizione in asse montati on wall nelle regie audio
figuriamoci nell'ascolto a pavimento e in campo lontano..
Mi sembra che Marcello Croce si riferisse alle 4350 e non alle 4345 che in comune i due hanno solo il STW 2405.
Le 4345 sono piu' simili alle 4344 ( evoluzione delle 4343 ) che differiscono solo dal woofer da 18' e mobile piu' grande ovviamente.

Marcello enfatizzava che le 4350 negli studi avevano problemi di mixaggio soprattutto per il disallineamento temporale tra mediobasso e medioalto e che erano state sostituite con le UREI o IBL-UREI ( 813 -815 ) che queste non avevano in quanto i crossover inserivano un ritardo sul mediobasso allineandoli, oltre alla tromba in coassiale .

Con questo, le 4345 hanno un sacco di difetti non utilizzabili oggi in grandi studi , e ci mancherebbe altro , si parla di un progetto e drivers del 1981 di 40 anni fa , ma con le oportune modifiche possono ancora dire la loro in ambienti domestici senza spendere cifre folli.

Le 4345 sono state le ultime grandi monitor 4 vie di Greg Timbers uscite 1982 con tutti i drivers aggiornati che come ha scritto lui stesso sopra, non avevano avuto grande successo ai tempi perche' uscite alla fine dell'era grandi monitor , e poi IBL aveva acquisito UREI per cui spingeva quelli. Tuttavia come per tutti i monitor 43xx esistono innumerevoli estimatori disposti a compromessi .

Di 4345 ne esistono pochi esemplari originali senza modifiche in quanto nel tempo i possessori mantenendo i drivers originali hanno apportato modifiche prese proprio dai suggerimenti di Greg del post sopra di 15 anni fa e da altri progettisti , molti sono descritti in JBL HERITAGE.

A differenza delle 4350 che vengono quasi tutte da studi le 4345 vengono la maggio parte da privati, hanno drivers poco sfruttati e si prestano a modifiche o realizzare cloni a un minor costo dei drivers se servisse ripararli ( a parte il woofer le altre tre sono comuni a molti monitor ) .

Per esempio la mia coppia di 4345, 10 anni fa il precedente proprietario ha fatto sostituire il cabinet di truciolato da 2,5cm che risultava non sufficientemente rigido con un multistrato di betulla da 3cm. Il crossover portava via volume interno e non era di qualità ( bobine avvolte in ferro, condensatori, potenziometri e commutatori di biamp ) . Tolto tutto e fatto esternamente mediante crossover digitale in multiamplificazione attiva su tre canali allineando le emissioni di Woofer/mediobasso /medioalto , crossover passivo solo per medioalto alto con componentistica audiophile, nessun commutatore o potenziometro, ma attenuatori a trasformatore Coral AT-70 sui TW.

Le 4345 riesce a regalare un impatto notevole a basso volume come le 4350 , diversamente da quest'ultime sono più piccole e si montano verticali, per cui riescono a stare anche in ambienti domestici di media grandezza .
Un saluto
Tito
EDO RC24
Messaggi: 379
Iscritto il: 01/12/2016, 16:09
Località: albano laziale

Re: Jbl 4345

#5 Messaggio da EDO RC24 »

sì mi sono confuso.. il problema era tra supertweeter e tromba 2311 le 4345 montano una tromba più lunga 2308 mi pare.. la quale però senza la lente rimane sempre un piccolo fucile acustico che fà a cazzotti con la dispersione orizzontale di almeno 100° del "naso" che io tanto adoravo da ragazzo.. :) comunque sì al di là di tutto rimane oggi un gran bel sistema che però io lascerei suonare così come mamma l'ho ha fatto senza storpiature e sopratutto con filtro originale il quale se non sbaglio non recupera l allineamento dei centri acustici tra driver e naso\supertweeter..ma come ripeto l originalità non và intaccata..riguardo al mobile io avrei scelto mdf o hdf per la costruzione..
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