# JBL 4000w JRX125 DUAL 15" PA SPEAKERS



## Steazo (Jan 17, 2007)

In a couple of weeks I am going to buy these speakers from an eBay store. Does anyone own these or has owned them? How do they sound and what would be a good amp for these speakers? They have an RMS rating of 500w per channel @ 4ohms. I have read good reviews about these speakers but I am always skeptical when reading reviews from sites that actually sell the same product that is being reviewed or discussed. Also what is the difference between a speaker that has a rating of 500w @ 8ohms vs. 500w @4ohms? Which is better to use?


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## Eboy87 (Jan 17, 2007)

A Crown XS900 would put you in the ballpark for those, it's rated 900w @4ohm A QSC PLX3102 would also work well for powering those. THe only thing I don't like about the XS series is the fan noise, but it'd only be a problem if it was a small, intimate, quiet gig.

I can't speak for the sound quality, but I have heard through the grapevine that you're better off saving up for the SRX or MRX series. As for the 4ohm versus 8 ohm, I think, and don't quote me on this, that the twin 15" drivers are wired in parallel to make it 4 ohm. Sharyn? Is this right?


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## soundlight (Jan 17, 2007)

An 8 ohm speaker has a higher impedance than a 4 ohm speaker. If you hook two 8 ohm speakers together in series, you get a 4 ohm total impedance. Four 8 ohm speakers or two 4 ohm speakers, 2 ohm total impedance. Amplifiers have to work harder if there is a 4 ohm load. Generally, a speaker that has two woofers will be wired inside for 4 ohm impedance, but this is not always the case. If your speakers say that they have a 4 ohm impedance, they are wired this way, so you need to use them with an amp that has the rated RMS value at 4 ohms stereo or bridged. If you get an amp that has 500W RMS value for the 4 ohm stereo spec, then you only need one amp. If you get an amp that has a 500W value for the 4 ohm bridged mode, then you need two amps (one for each speaker). I recommend the QSC PLX3102 or the Crown XS900 or XS 1200.

Wow! By the time I finished that, Eboy87 recommended the same amps as me.

EDIT: I have been corrected. It's PARALLEL not SERIES for those impedances.


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## Chris15 (Jan 18, 2007)

Just to make a slight correction if I may. When you wire two 8 ohm speakers in SERIES, the impedance will be 16 ohms, you add the values. Two 8 ohm speakers in PARALLEL will be 4 ohms. The sum works as 1/total R = 1/R1 + 1/R2 + 1/R3... Where R is impedance.

Very few amps will take a load less than 2 ohms and there are some that will go no lower than about 4. Read the documentation for the amp. 2 4 ohm speakers in parallel on a 4 ohm minimum impedance amp is going to be a problem... (Wire them in series if this is a problem). And for reference, double the minimum impedance per channel if you are running in bridge mode.

Do not I recall previous discussions recommending that you use an amp 1.5 - 2 times the speaker wattage so as to give proper headroom and reduce the likelihood of damage? So a 500 watt amp on a 500 watt driver probably ain't the best move...


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## Steazo (Jan 18, 2007)

The 900w @ 4 ohms is that 450w left 450w right or 900w left 900w right? As I said I am a newbie DJ and some of this has to be explained to me as if I am 4 years old. Thanks for your reply and patience!!!


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## Eboy87 (Jan 18, 2007)

Chris, you're right, I had a slight brain fart. Spent quite a few weeks in my audio class discussing that.

Steazo, the amp's rating in stereo is per channel. The XS900 is rated at 900watts per channel in 4 ohm stereo operation.


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## SHARYNF (Jan 18, 2007)

the JRX LINE is Jbl's low end. There are some of us that joke and say the J stands for junk. I would definitely try to save up for the m or s lines if you could. There are other companies that offer better value at these price points. Yorkville for instance has a good reputation, and some people also like the Yamaha club line

In general I would recommend not going with a dual 15 top but look at 12's and putting more money into subs
I usually like to get the tops up high pointing downward, and keep the subs on the floor. The higher end of the JBL line has been designed to use massive amps, so they work great but unless you really have the amps to drive them I would look at yorkville probably being the next best choice, and then the Yamaha line 

Sharyn


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## Steazo (Jan 19, 2007)

I am also not too familiar with all the terminology or the sound tech jargon. What does it mean to hook your speakers up the paralell method? Is that the same as when you "daisy chain" speakers (power one speaker from another that is powered directly by the amp? Also wouldn't an amp the has a rating of 900w @ 4ohms blow a speaker that is rated at 500w @ 4ohms? What if I only want to run 700w @ 4ohms into the 500w speakers but the amp is rated at 900w @ 4ohms is there a way to regulate how much power one puts into their speakers? I noticed that some amps have meters and others don't. How can one tell if your are putting too much power in the speakers. I am nervous about paying my hard earned money for speakers and amplifier only to mess them up. So I want to make sure I know what I am doing.


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## Radman (Jan 19, 2007)

Simple way to not overdrive the speakers: don't turn the volume knobs all the way up!

As stated in previous threads, you will be more likely to cause damage to the speaker by underpowering it than you are overpowering it. It is much safer to get a bigger amp and simply turn the volume knobs down.

The "daisy-chain" jacks on speakers are wired to be parallel. It usually says that in writing on the connection panels of the speakers.

Parallel and series are less sound tech jargon and more wiring and electronics terms. Simply put, series would be connecting + to - in a circuit, and parallel would be connecting + to + and - to - in a row. Further explaination can be obtained via WIKI!


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## Eboy87 (Jan 19, 2007)

I'll take a stab at it. First off, on the power ratings, the rule of thumb is to have an amp that's 1.5 to 2x more powerful than the rating on your speakers. So, for a 500 watt speaker, you would need anywhere from an 800 watt (rounded up) to a 1k watt amp. If you have an amp that's rated at 500 or less watts, it could damage the voice coil inside the drivers, especially if you drive the amp into clipping. There's plenty of reading at PSW about that. Don't worry about regulating power to the cabinets, the extra power is just there so you don't clip. Very rarely, if ever, will you be sending the full 900 watts to the speakers.


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## SHARYNF (Jan 19, 2007)

To further add to the comments, a good clean signal to the speakers even beyond the so called power rating is less likely to cause damage than lower level distorted signal. Reason is it really the heat generated that causes the damage, and a distorted signal, tends to be closer to a straight dc signal as all the distorted frequencies clip and become less "sine wave" and more flat line.

I again personally think there are better deals out there than those JBL's that's why you tend to find them on ebay, the dual 15's don't really put out the bass you need, the combined format reduces your flexibility in placement. Typically the better setup is tops with smaller speakers, not attempting to cover the lowest end, and a sub this allows you to tri amp the signal, clean up the sound and works far better.

Sharyn


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## Eboy87 (Jan 19, 2007)

You could also look at Carvin's TRX series http://www.carvin.com/products/single.php?ItemNumber=TRX153B&CID=TRX. If you do a search over at PSW, you'll find a few people who really like them. They should be nicer than the JRX, and near the same price range. If you use a Yorkville sub with them, it should sound excellent. (Yes I've been reading PSW too much. Not much else to do on a month long break.) 

Just beware, buy once cry once. Trust me, it's better to get good gear the first time. And if you're going down the road of putting together your own PA, it's gonna get very expensive very quickly. Take it from someone who's already done it


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## SHARYNF (Jan 19, 2007)

I think you will also see that another the favorite is Yorkville. You could look at a system with a single 15 as the mid/low and a sub the unity line for instance There are the subs on ebay and the u15 speakers also 

Sharyn


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## Steazo (Jan 19, 2007)

Actually I did take your advice and I am starting to look at the Yorkville and Yamaha speakers that you suggested. When you say smaller speakers do you mean like 12" speakers that you have recommended mounted on top of a subwoofer? Are these two way speaker or three way speakers ? If possible could you give me a link to the type of speakers you are talking about so that I can get a visual picture. Sorry if I am being a pest about this.


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## Eboy87 (Jan 19, 2007)

There's the S112V from Yamaha. It's a two way with a 12" driver in it.


They make it with a 15" driver too, as well as a three way, but you can get away with a two-way, 12" cab with a sub under it (well, maybe not under it, but that's a different topic in itself, one we can go into if you wish). Here's the link for the Club series page from Yamaha.http://www.yamaha.com/yamahavgn/CDA/ContentDetail/ModelSeriesDetail/0,,CNTID%25253D43807%252526CTID%25253D560500,00.html

Here's the comparable models from Yorkville. http://www.yorkville.com/products.asp?type=29&cat=1 I believe they also make powered speakers too if you want to spend the extra money and go that way, and eliminate the extra (and heavy) amp racks.

I've not heard the Yorkies before, but I have used the Yammis and find them pretty good for small to medium events. Not sure they'd do a concert for 1500 outdoors (that's large for me, at least right now), but it seems that for what you want to do (I like perenthetical remarks) they'll work.

Oh, and sorry for the picture size, it's right from Yamaha's website.


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## SHARYNF (Jan 21, 2007)

Here is a link for the Yorkville Unity series
http://www.yorkville.com/products.asp?type=29&cat=38

Eventhough they do have 15's you would want to run a three way system, highs, mids (using the 15's in these "tops") and then the subs.

Personally I like multiple 10's or 12's for the mid lows, think they offer a better sound usually a smoother sound in the important mid levels below the horns.

If you want to be able to expand over time and do larger venues, then what you want is a speaker where you can add multiples. Here is where the horn pattern becomes important, you definitley do NOT want to get a 90x40 horn, you want to get a horn that is 60x40 or narrower.

Reason is the comb filtering and just interference of the horns side by side if there is extensive overlap is not good.

What you wind up with is start out with one on each side, then go to two then three, then 4 then 6 when you get beyond 3 you stack or hang them that one is upside down woth horns over one another, so in the final 1500 person venue you would have subs on the bottom probably 3 per side and then two rows of 3 per side one over the other,again horns to horns.

Actually works quite well and makes for a good system as an alternative to a line array design

Sharyn


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## Chris15 (Jan 21, 2007)

Eboy87 said:


> ...and eliminate the extra (and heavy) amp racks.



Now I can't argue that amp racks don't take up additional space, but with modern amp design, the weight is coming right down. The new Lab.gruppen stuff is 2x6500w or 4x2500w (at 2 ohms) in a 2RU chassis weighing 26.5 lbs or 12kg...

Now I do not know whether this is the case with the speakers in question, but have I not read previously gripes about the fact that with many powered speakers, manufacturers are not building in headroom? Ie. a 200 watt driver is getting matched with a 200 watt amp, not the 300 - 400 watt amp that would normally be specified with such a driver. Just something to consider.


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## Eboy87 (Jan 21, 2007)

True, I was exagerating trying to make a point. The I-Tech 8000 weighs what, 20lbs? Yes, modern amps are lighter, but before I posted that, I was pushing a friend's rack with Macro-Techs around; heavy SOBs. As for power specs, I can't speak to that since I've never looked at active speakers in depth. I always use the old JBL SR whatevers I got for free. But for beginners, I could see where having active speakers could be beneficial. I was rying to make a point that it's less gear, and less racks that need to be moved around at load-in and strike.


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## Peter (Jan 27, 2007)

I was just about to jump in here and make a plug for EAW speakers, especially the LA325, (which are an UBER versatile and great sounding speaker) and then I looked at the price for a 325 and well, I think it's abit above your budget. But if other people stumble across this thread, EAW is really worth a look. they are used alot in higher end systems and have great customer support even for smaller customers!


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## PhantomD (Jan 27, 2007)

I will definitely plug for Yamaha - speakers guaranteed to be pretty much PERFECTLY IN PHASE and they are real workhorses that sound amazing and have everything you'd expect for a bit less.

I had a wonderful experience with a pair of "JBL Professional" unpowered speakers I hired recently - amazing and full/rich sound I was blown away absolutely. That was with a Soundcraft desk too!


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## BillESC (Jan 27, 2007)

IMHO, active speakers would eliminate many of the potential problems a novice can run into.

No having to match an amp with cabinets, no having to worry about Ohm ratings, just simple plug and play.

I'd suggest looking at the EV SxA 250 or SxA 360 for tops and the SbA 760 for subs. This also eliminates the need for an outboard crossover and the associated learning curve.

If you have more in your budget, the KV2 EX 10's paired up with the EX 2.2 will simply rock your world.

www.kv2audio.com


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## Chris15 (Jan 31, 2007)

Eboy87 said:


> True, I was exagerating trying to make a point. The I-Tech 8000 weighs what, 20lbs? Yes, modern amps are lighter, but before I posted that, I was pushing a friend's rack with Macro-Techs around; heavy SOBs. As for power specs, I can't speak to that since I've never looked at active speakers in depth. I always use the old JBL SR whatevers I got for free. But for beginners, I could see where having active speakers could be beneficial. I was rying to make a point that it's less gear, and less racks that need to be moved around at load-in and strike.



Point taken. I agree that any amp rack that includes amps from what may be termed the good (or bad) old days is going to be HEAVY. I've pushed them...

Active speakers as a concept have benefits, less to move around etc. but in some cases there are the aforementioned amp driver matching problems but also some of them weigh more than I like to be lifting onto a speaker stand and in some cases I wonder if the speaker stand will be happy taking that much weight...


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## solutionrs (Feb 25, 2008)

My son and I have been looking at those JBL's and thanks for the input as we are just getting started.

I have a 17 yr old son just starting with his band and I need to get him a set of PA speakers. He has a Peavy 8.5c Amp that will supply 425 at 4 ohms.
He's found an EBay offer of JBX MBX 2520 speakers at a very low price but I can't find these JBX speakers or reviews anywhere. 

He did find a used set of Yamaha S115H II as well.

Any help or suggestions? He's got 300 - 550 to work with.


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