4350's: Very uneven frequency response

[j20056]

I have finished my room, I will post pics later. My setup:
JBL 4350's (studio version)
Mac Intosh MC7300 (low)
Mac Intosh MC7150 (high)
Mac Intosh C38 Pre-Amp
Wadia CD player
JBL active cross-over Model 5232

I bought a sound level meter at Radio Shack (low end unit) and measured the frequency response of the 4350's paying attention to the Left-Right balance.
I found that the system is massively out of balance, depending on the freuqnecies. I placed the meter at my listening posisiton, or 11feet from the 4350's. I have attached the graph of the frequency plot.
In some cases, like 126Hz, the differential is a much as 24db between left and right.
I wonder if there might be something wrong with the electronics that I use? Any ideas?

[Robh3606]

What are you using as a signal?? Did you take into account the FR of the meter?? Can you borrow an RTA??

Rob:)

[Zilch]

http://www.jblpro.com/products/recording&broadcast/LSR6300/RMCUserGuide.pdf

http://www.jblpro.com/products/recording&broadcast/LSR6300/White%20Papers.pdf

Also, the hump at 6 - 8 kHz is from the RS meter. I measured the frequency response here:

http://audioheritage.org/vbulletin/showthread.php?p=127276#post127276

[speakerdave]

Looks like that in the very least you could check the polarity on the 2235's and 2202,s; check the polarity on your low frequency amp connections, and turn up the tweets (although you may not be able to if you are using the 3107's).

Check carefully going into and out of that active crossover; JBL does not follow standard pin polarity conventions. And their woofer cones move forward with an upward moving voltage to the black terminal. By the way, you would very likely find it sonically advantages to upgrade to the 5235. They are not very expensive and are said to be a marked improvement.

The Radio Shack SPL meter is known to be down in the upper frequencies. It's good for general level measurements, but not really useful for frequency response charts (I know--I've tried it, and my ears told me different).

Also, it may be that your crossovers need to be rebuilt.

David

[j20056]

Robh3606,

I used ProTools to generate the signal. I have a digital mixer TASCAM DM4800 hooked up to my Mac Intosh Pre. There is a plugin in ProTools to generate a sine wave and I can dial the frequency in 1Hz increments.

[Robh3606]

Can you do an Pink Noise signal, narrowband like a warble tone or 1/3-1 octave bands. Using sine waves is tuff because you can excite narrow band resonances and small changes in microphone placement can make a big difference. Forget the measurements how do they sound???

Rob:)


This will help you on the lowend. Try a search if these don't work there are a couple of sources up on the net for the files

http://www.digido.com/modules.php?name=News&file=article&sid=16

http://www.digido.com/modules.php?name=Content&pa=showpage&pid=62

[Ian Mackenzie]

What are you using as a signal?? Did you take into account the FR of the meter?? Can you borough an RTA??

Rob:)

Borough...sounds like NY city regions.

I think you mean borrow.

j20056 try measuring the voltage drives per the JBL test jig to confirm the passive crossover is functioning properly.

Ian

[j20056]

JBL test jig? can you elaborate, not sure i know what you mean.

[Zilch]

http://www.jblproservice.com/pdf/Network%20Schematics/Standard%20Test%20Fixture.pdf

[Ian Mackenzie]

Yep,

Un-gated (time) measurements are meaningless in your room because the meter part from its lack of accuracy is reading the room as well the 4350..

Assuming your drivers and crossover wiring is correct it should be okay.

The 4350 is really a far field monitor incidentally. Meaning listening at anything less than 3 meters or so is not going to allow the system to integrate properly. This also makes it difficult to realise meaningful measuremnts in your house.

Ian

[Mr. Widget]

I have finished my room...Where are you located? It may be possible to have someone with some actual measuring gear pop by and check out your room/system.

In-room measurements can be quite problematic, but seeing the room, speaker location, and settings on your gear can answer some of your questions.


Widget