UREI Speaker discussions

[DerekTheGreat]

Angela spotted a listing for a set of 811C's that were practically in our backyard, couldn't resist. When we got there, the gentleman said he had a third one he'd like to sell to us if we were interested. Yep, I have an addiction and couldn't turn these away. Actually wanted three, as the goal is to use these as L, R and C in the home theater. The fella had all kinds of groovy JBL stuff and we got to talking, we didn't leave until about two hours later.

[Earl K]

Wow, now that's real cool!!

[srm51555]

Good stuff

[DerekTheGreat]

Thank you, fellas!!

Pretty stoked about 'em.

..On a side note: why don't these have tuned ports like most other speakers? Why just little boxes cut into the cabinets? Isn't that just lazy? Would they sound better if tuned? For what these things cost new, I'm surprised they are this way.. For example, 4435's are tuned and look better aesthetically, yet those were significantly less $$$ than 813C's. What gives?

[hjames]

This past weekend my 813C's had puppies:

Yeah, you got it bad, and thats real good!
So ... collect the whole set!

[Riley Casey]

How are these not tuned ports?

Thank you, fellas!!

... why don't these have tuned ports like most other speakers? Why just little boxes cut into the cabinets? Isn't that just lazy? Would they sound better if tuned? For what these things cost new, I'm surprised they are this way.. For example, 4435's are tuned and look better aesthetically, yet those were significantly less $$$ than 813C's. What gives?

[DerekTheGreat]

Yeah, you got it bad, and thats real good!
So ... collect the whole set!

Just need me some 809's or another pair of 811C's and I can have a 5.2 UREI surround sound set up.

How are these not tuned ports?

They're just cut outs in the box.. Aren't tuned ports supposed to be tubular of a specific length?

[Mike Caldwell]

Just need me some 809's or another pair of 811C's and I can have a 5.2 UREI surround sound set up. They're just cut outs in the box.. Aren't tuned ports supposed to be tubular of a specific length?

Those are tuned as per the size of the hole in the box even if it does not have any ducting, well it has 3/4 inch of ducting. Among other things adding ducting length to a port lets you increase the port size while keeping the tuning frequency the same.

[RMC]

Derek,

A port or vent can be many shapes and still keep the name "port": round, rectangle, square, triangle, slot. Shape is not really a concern and as long as dimensions are not extreme (too large/long or too small). Some JBL SR boxes use triangular vents, mostly due to baffle space use.

The first consequence of using a longer tube (or other) is tuning the box lower, other things being equal. Then in order to make it shorter one may use a larger area port (e.g. increased diameter). In speaker software i play with both port area and length up until a combination does the trick for a specific project.

Without port covers its definitely a vented box, but if the port covers were on it would "flirt" with a sealed box, or at least be considered as a hybrid cab, not really a vented box.

Since there's fans for everything i guess one could mimic or so sealed cab operation/transient response when covering the vents with the foam plugs. If they're high density foam it could block vent action, but if low density foam it would be seen as a resistive vent.

As reported by Dickason, Thiele had nothing positive to say with regards to resistive vents, such as higher F3, lower efficiency, higher distortion, etc and concluded why bother? (I posted this before in my BGW thread).

I had a quick look twice at the JBL/Urei Tech Manual (813C) and owner manual (811C, 813C, 815C) for any info and explanations about the foam plugs use (when, why, etc) and to my surprise didn't see anything (or i'm blind). This apparent silence is very curious in view of the consequences (i.e. Thiele's). I find this inexcusable due to the implications.

Richard

[Robh3606]

Those foam covers add air resistance just like a port. Depending on the density and thickness of the foam you can shorten the duct lengths. JBL does this in the shallow cinema boxes where the duct length is restricted because of the depth of the box.

I wouldn't be so quick to just write the foam off as just covers without a better understanding of the box tuning. They could actually be a critical part of the "duct length".

Rob :}

[DerekTheGreat]

Thank you for the responses, fellas.

I've seen that image before, worth a chuckle for me as it's inaccurate as it suggests each woofer has it's own enclosure. They do not. As a layman, I'm just trying to understand why there is no port (and no seperate enclosure for each woofer) despite the high price tag these things carried. The port size is the same between the 811C and 813C, I figured the single woofer and lower cabinet volume might have lead to a different port design or size. They sound phenomenal to me, but sometimes I think, "Wow, they're just a super heavy black box with a coax driver and helper woofer. The profit margin on these had to be 80% or better..." Meanwhile, I look at 4435's and think, "Wow, these are beautiful. Nice wood veneer and Dolly Parton's likeness. However, their sensitivity is lower as was their price tag..."

I also thought the foam plugs were just cosmetic. Had no idea they could result in lower efficiency, although my 813C's plugs are missing. However, the entire cabinet of each 813 is STUFFED with wool. Same for the B460 clones. I never asked RustyJefferson why he did that, just took it as a beneficial mod from a sage. Figured if he took the time to fill the cabinets, it was for an improvement. So of course I've left that stuff in there and am wondering if I should fill the cabinet of the 811Cs with it as well.

[RMC]

Since you mention the entire cabinet of each 813 is STUFFED with wool. The absence of separate enclosures might be linked to the wool stuffing. The increased absorption from a lot of wool may actually render another chamber unnecessary, the drivers back waves may be absorbed anyway.

Wool stuffing is typical on sealed box systems. In vented boxes wool is typically lined on the panels, not stuffed. But there's an exception: more wool to generate additional box volume (see below).

Here, the wool stuffing and the standard port covers could be clues the box should normally be used with these on, mimic a sealed box or simply a resistive port. In that view removing the port covers would be sort of an exception, maybe to satisfy vented box "hardliners" on efficiency, distortion, cone travel, etc. Hard to say for sure when JBL/Urei has failed to explain their intent and purpose in the docs i have.

I don't know Jefferson's motivation with regards to stuffing of the B460 clone. A possible explanation that comes to mind is that he possibly wanted to create virtual volume for the box (larger size). By adding a fair amount of wool in the cab the woofer then "sees" the box as if it was larger than actual due to increased absorption. For even lower F3, flatten some bump or to mitigate a resonance ?

Richard

[rusty jefferson]

Derek,

As mentioned, the vents are tuned even though they don't use port tubes. This wasn't uncommon at the time these speakers were developed and other companies did similar things, mainly speakers of high efficiency with large box volume and low-ish woofer excursion. I've never seen what they were tuned to anywhere but nobody made speakers that went deep during this period of time.

More important than the port (imo) is the placement of the speakers. They were designed to be soffit mounted or at a minimum, be mounted in a 2pi space. Bass from the speakers is very different mounted in a soffit compared to what you're hearing in your living room (or mine) with them in 4pi space. That's why I built the b460 clones even before we updated the UREIs. The 813s are rolling off at about 100hz in 4pi (even higher with the 811s). You can see this in the FR graphs in the manual.

As far as the fill goes, I think filled is a better descriptor than stuffed. I removed the standard wad of polyester fill that was packed around the woofers probably by the studio that bought them or possibly JBL, I don't know. There are different reasons to adjust the fill of speakers and I have no idea what the original intent was but I know this was pretty common in that era and I'd seen it done to several pairs. I lightly refilled the cabinets with a couple pounds of the loose wool fiber in there now. What looks like a lot of fill could be compacted down into a large ziploc bag. They aren't stuffed tight, just filled loosely. My intention was to reduce the back wave of the woofers and the port output because I was crossing over to the subwoofers. Slightly overdamping the cabinets really helped keep the bass clean and tight in my room, something important to me (but not everyone). No overhang or boominess. They measured remarkably flat in my living room and had nuanced bass.

[rusty jefferson]

... No overhang or boominess. They measured remarkably flat in my living room and had nuanced bass.

The whole 'system' that is, the UREIs and the subwoofers.

BTW, there's not a lot of difference between the 813C and the 4435 to warrant moving from one to the other (imo) except for appearance. Both were intended to be soffit mounted and are only playing flat to 50hz-60hz in 2pi (without eq)(see link below) and really need those subwoofers to be full range. I've seen several 4435 users here who have systems like yours, with 2245s (or something similar) underneath. They both use the 2425h compression drivers and sound slightly different but not a better or worse scenario. And certainly not like comparing either of the older models to something current. A comparison here between 4435 and 813C:

http://www.cieri.net/Documenti/JBL/T...1,%20No.15.pdf

[DerekTheGreat]

I appreciate the responses, learning stuff here!

Oh, I measured the thickness of the cabinets and they're 1" thick, if not more! The lip where the foam plug would sit adds about a 1/4", I assume it's 1" thick everywhere else. Certainly helps explain the weight of those cabs.

Rusty, the bass on the entire system is TIGHT. The tightest bass I've ever experienced. The 813C's themselves have this dry, tight thwack to them that adds to my experience of drum kits (and probably everything else in that frequency range) and overall enjoyment of music. It truly feels as if I'm in the same room as the drum kit. The 2425h adds to that, I've never heard cymbals/hi hat sound so.. life-like. Not a super huge fan of The Police, but looove "Walking on the Moon" for the way ole Stewart plays his kit. Nice tight kick drum with huge sound or fill accompanied with the tickling and crashing of the cymbals. Love it.

When I auditioned those 811C's, I used Fleetwood Mac's "The Chain" to shake 'em down. I noticed a lack of detail, clarity and realism. It wasn't super huge, but I did notice something was missing. Could have been that there was no low reinforcement or the signal or the equipment and/or room. Not sure, but the crossovers are original and there's no wool. Gotta fix that. Rusty, where did you get the wool you used? Wondering if I could find some at Joane's.

I have read that tech article, before that I had no idea those were competing systems or used the same HF driver.