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Discussion Starter · #1 ·
This makes no acoustic or electrical sense to me:

I have a REL sub that has the option of a high-level input directly (parallel) from the amp terminals to the speakers. This allows the sub to be driven by the same signal as the speakers. There are two "hot" wires and one ground so you get to choose which speaker gets both. Shouldn't matter it seems. But it does! It appears as if the acoustic pattern is quite different just in the 50-80 Hz region.


Since the signal is the same from the Soundblaster card, how could the outputs be so different? (I will assume the Soundblaster is not defective nor is the Classe' preamp and amp nor the RadioShack meter.)
 

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I am almost as confused as Wayne. On at least one REL page, they seem to describe hooking the sub to the high level outputs of each front speaker -- which I guess lets the sub combine the bass signals to the two front channels. It sounds as if you are intending to connect to only one of the front channels, under the assumption that the two are identical; is this correct? Are you also connecting the LFE channel from the preamp to the sub directly?

In your graph, what are the two curves? Were these each taken with both front speakers driven? And you were connecting the sub to only one or the other front channel? Or do these graphs represent the two front speakers, each driven separately?

Bill
 

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Discussion Starter · #4 ·
Sorry for the wording.

There are three wires from the sub to the high-input on the REL sub. In the example in the manual, the red goes to right+, black to right-, yellow to left+. It is also possible to connect the red/black to left and the yellow to right. There are not four wires so one amp connector (-) is not connected to the sub.

The two curves represent those two possibilities. Both speakers are playing in the tests as is the sub. "Left-Sub" means that two wires are connected to two the left amp terminals.

I hope that is more clear.
Thanks.
 

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I am still a little confused as to what your doing here.

The high level connection requires your speakers run full range, is this the case?

Also, you should run the HL cables as described in the manual. If any bass is sent to one speaker but not the other (happens in music, not with dedicated music LFE), then the sub wont pick it up if the HL connection isnt going to both speakers. The Neutrik connector only needs to read the signal that goes to the speakers, it doesnt draw any power from them, and the 3 wires can simply connect to the amp, rather than the speakers themselves to make connecting easier.

Now with your measurements. Are these 2 measurements the same thing measured twice ending with different results, or a set of 2 measurements from 2 sweeps where you changed something for each sweep? I am reading this as left only is with all your HL cables connected to only the left speaker, while the other is with one cable going to the right as the manual shows.

Its quite possible for the sub to perform differently when only connected to one speakers vs 2. It really depends on how you amp processes bass signals and sends them to each speaker. With 2 feeds, the Rel will read the bass slightly differently than it will from only one speaker, which could result in a measurement difference like the one shown.

Which Rel sub is it BTW?
 

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That 3-wire connection REL provides assumes that the amplifier channels share a common ground. That is not necessarily the case with all amplifiers, if the amp's outputs are effectively isolated from one another then you will only be getting one speaker fed to the sub. To check that, disconnect the red wire so that you have the black wire on the negative of one amp channel and the yellow wire on the positive of the other and see if the sub produces any output. If not, you may be able to link the negatives of the amp outputs at the amp, but check your amp's documentation first.
 

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Discussion Starter · #7 ·
Moonfly: From my post, I am running both speakers in the tests (full range) and the sub cables are attached to the amp outputs not the speaker terminals. All as described in the REL manual. I have just changed from two wires on the left to two wires on the right. The diagram in the REL manual shows one of two possible connections that should, in theory be identical. Both speakers are connected parallel to the sub in both tests but in a different manner. One speaker has + and - and the other speaker has - only.

JohnM: Disconnected the red wire and sub works fine. That leaves black on L- and yellow on R+. By the way, the amp (Classe CAV500) is only red/black coded, not +/- and I match the REL wires to that.

I am only reporting this as weird not a problem. In one case I have substantially flatter response (a good thing).

BTW; I see mention of V5-beta. Is it time to upgrade from 4.1.1 or wait a little?
 

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V5 is pretty stable now and its been a while since anyone reported any bugs. The beta is due to close soon, so you can update now or wait till beta is over, it probably makes little difference. Depends whether you can be bothered to update again once beta closes.
 

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... I have just changed from two wires on the left to two wires on the right. The diagram in the REL manual shows one of two possible connections that should, in theory be identical. Both speakers are connected parallel to the sub in both tests but in a different manner. One speaker has + and - and the other speaker has - only. ...
It is bizarre. I don't believe you have mentioned which Classé preamp/processor you are using, and the manuals I have found are a little ambiguous about all the settings available. I am wondering if your two front speakers are at different distances, or were calculated as being at different distances during the processor's autosetup, and what you are seeing is different timing at the sub depending on which way it is cabled.

The difference between the two curves is consistent with what one might see in a conventional cabling, connecting the sub only to the LFE out and using receiver's bass management, were one to vary the sub distance setting in the receiver/processor.

Bill
 

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Discussion Starter · #11 ·
System: Classe' SSP30 preamp, CAV500 amp, Magnepan 1.6qr fronts, CC-3 center, 12 rears, REL Strata III sub. I have thick RealTraps in the corners for bass and thin RealTraps in all the first reflection points for the HF.

I am using the analog pass-through in the pre-amp so there is no electronic modification to timing or distance. I have the front speakers at equi-volume at the measuring point +/- 0.5dB.

Admittedly the planar speakers are complex with respect to their interaction with a room but I have been using statistically designed experiments to flatten the room response at selected peaks. This is a journey (as someone here said) but fun and interesting. One thing for sure is the amount of variation from day to day is significant and I believe that is due to changes in the room that I have not identified and controlled yet. I always compare data from about the same time/day.

I meant for my posting to be a warning to check on assumptions. I would not have guessed there could have been any difference, and certainly not this large or frequency specific.
 
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