813B Perplexed

[David Ketley]

The Urei JBL 813Bs seem to break a fundamental rule to isolate bass and mid range drivers?
Also the Urei 813Bs use a E145 which JBL seems to recommend is crossed over below 800hz but the 2426 seems best crossed at 1.5khz? Been messing with mine running them active with a few additions and exceptions?
Dave

[Robh3606]

Also the Urei 813Bs use a E145

Somethings not right. The only Uries that used the 801C or E-145 based coax was the "C"s. If you have them in "B" cabinets with "B" crossovers you have the wrong crossover for that driver. You need the "C" crossovers for any of the E-145 based systems.

Rob:)

[David Ketley]

Must be me getting it wrong, one of the write ups on the 813Bs said the E145 was the mid range unit. If not then what did the 813B use?
I am going to build some speakrs based on JBL 2225s and the 2425s with the biradial horn. But as the 813Bs sounded so bad I decided to use my 3 amps and tri amp them with the 2225 in place of the old Eminence woofer and the 2425 and biradial in place of the horn.. To be quite honest Im just stunned at what Im hearing outstanding result with solid bass mid and the top end is very good. I do realise its not good practise to run the bass and mid in the same cabinet. How diid the 813B overcome that problem?


Somethings not right. The only Uries that used the 801C or E-145 based coax was the "C"s. If you have them in "B" cabinets with "B" crossovers you have the wrong crossover for that driver. You need the "C" crossovers for any of the E-145 based systems.

Rob:)

[Robh3606]

The "B" used either an Altec 604 type or possibly a PAS coax. Not sure of the exact lineage as it's not clear in the tables what the exact differences are between the A vs B versions. If you look at the 811 there are 4 different coax drivers there ending in the 801C. You can also see different networks as well.

Rob:)

http://www.jblproservice.com/pdf/Systems%20Reference%20Charts/UREI%20Series.pdf

[David Ketley]

Thanks for that I thought it was a JBL unit! Ive changed the connections round JBLs always were the opposite to everybody else.
Still don’t understand though the design philosophy of putting the bass and mid unit in the same cabinet with the same air loading as this causes feedback distortion between the units?
Thanks
Dave

[HCSGuy]

I will preface this with the disclaimer that I have never owned nor heard a Urei speaker, as far as I know. My understanding, though, is that they are not 3 way speakers as you suggest, but are instead what is considered 2 1/2 way. In a 3 way speaker, you have discrete bass, midrange, and tweeters, all in separate enclosures so that they don't react with each other. Speakers designed for midrange usually have a very small XMax, so that if they shared enclosure volume with a LF speaker, the LF energy in the enclosure may force the midrange driver VC out of the gap, or at least out of linearity - as you suggest a bad thing.

In a 2 1/2 way, you have two woofers and a tweeter, but one woofer is rolled off quickly so that it only handles bass, while the other handles bass and midrange. Although the two LF speakers are different types, as they are both reproducing bass equally, it is not horrible to share the same enclosure. That is to say the LF/MF driver cannot be modulated by the LF driver as it is already reproducing those frequencies. This assumes that both woofers are of fairly equal capability.

I think a modern construction would probably isolate the two woofers as you suggest, but Urei models seemed to have been engineered as an organic whole - if you break them up and start re-engineering parts of them, the magic of the whole disappears. I'll let the Urei fans chime in now, and welcome their corrections...

[David Ketley]

The 813B always seemed bass light when not soffit mounted. I was running it with a sub but now the sub is detracting from the more than ample tight bass the 2225 gives.
I know they can be re-coned to a 2235? But they do then loose that tight bass kick I like.
As I’m running the system active I can bring down the mid range nearer to the bass or even the same. I will also though try and put a mid range unit in and isolate it. I know the guys will think its sacralige to mess with the 813Bs but no harm in trying things out its easily put back.
Thanks
Dave

[BlueC5]

I have had 813Bs for many years and have made sure they are spec correct. the crossover tests accurate and the speakers are in good condition ,,,, ,,,

I recently changed the 813Bs to 4345 and the difference is quite clear,,,, the upper end is very apparent w the 4345s and the 18"s provide the lows that sould be there with the eminence 15"s but disappear someplace in the cabinet.

i have always suspected the 4345s were better but they were 10 miles between sound room locations and wouldnt allow for immediate A/B testing on the same amps etc...

I have 4333s in my bedroom that are excellent and the 813Bs seem to be weak in comparison ,,,

they do sound beautiful on strings and horns but triangle and cymbals are not as apparent....

so what i am saying is that i understand your experimentation completely and even with the taboo no no of an Eq on the "time aligned" Ureis, they still cant keep up with a tweeter....


i would like to understand why the 813Bs were not as "spectacular as i expected them to be...........


RN

[louped garouv]

i would like to understand why the 813Bs were not as "spectacular as i expected them to be...........


RN

kinda offshoot question....
what's up with the blue tape on your avatar's horn lip foam?

maybe that's a contributing factor?

[BlueC5]

Foam Repair................

yeah i was wondering if i taped a golfball in the throat of the horn ,if it might would work better.....

seriously ?

I was moving the cabinet to get the LF driver out and I tore the foam slightly so i used some of the woofer glue on the seam and taped it tightly to cure in the correct position...



kinda offshoot question....
what's up with the blue tape on your avatar's horn lip foam?

maybe that's a contributing factor?

[louped garouv]

Foam Repair................

yeah i was wondering if i taped a golfball in the throat of the horn ,if it might would work better.....

seriously ?

I was moving the cabinet to get the LF driver out and I tore the foam slightly so i used some of the woofer glue on the seam and taped it tightly to cure in the correct position...

makes sense... i did something simmilar to a pair of 809s I have....

well, that ain't it!

sometimes you read of crazy things going on in the forums....