Need Subwoofer Advice - Input Voltage Too Low?

[12Many]

I am working to set the levels of my subs and am at a point where I need some advice. My gear is blue node streamer into a BM DAC3 HGC (XLR output to amp and RCA output to subs), BM AHB2 Amp, Revel F208 speakers. The subs (2 Rythmik F12) accept a line-in signal from the DAC3.

1. How loud or noticeable should be sub be if only the subs are playing - (speaker amp is off)? I know this is hard to quantify, but my subs present very low output volume, even when the crossover is at about 60 hz and the volume is about 2/3 of the way up.

2. If I fed both RCA output line out level signals from the DAC into one sub, would those signals sum, meaning two times the voltage?

3. I noticed on the DAC3, the XLR outputs are at a higher voltage (24 dbu) on the jump setting I am using, then the RCA analog pre-out levels (2 V rms). Could this be a reason why my speakers are at a desired listening volume, but the sub output seems anemic? There is an internal jumper on the DAC that will attenuate the XLR output (10 db), which may result in a closer level match between the XLR and RCE outputs from the DAC.

Thanks for the advice.

 

[staticV3]

1. How loud or noticeable should be sub be if only the subs are playing - (speaker amp is off)? I know this is hard to quantify, but my subs are very low output volume.

About as loud as the mains when playing sine waves at either end of your crossover:

Though you have to be mindful of room modes of course. A single bass frequency is highly unlikely to be representative of the entire bass range.

A UMIK-1 really helps.

2. If I fed both RCA output line out level signals from the DAC into one sub, would those signals sum, meaning two times the voltage?

No. You cannot do that. You would be shorting out the DACs outputs, which can damage the DAC.

Edit: I read that as "into one sub input", so with a y-cable of sorts. That does not apply if your sub has separate L and R inputs and you use those.

3. I noticed on the DAC3, the XLR outputs are at a higher voltage (24 dbu) on the jump setting I am using, then the RCA analog pre-out levels (2 V rms). Could this be a reason why my speakers are at a desired listening volume, but the sub output seems anemic? There is an internal jumper on the DAC that will attenuate the XLR output (10 db), which may result in a closer level match between the XLR and RCE outputs from the DAC.

You have extra volume controls on both the Rhythmik subs and the AHB2, so even if the DACs outputs are uneven, you should be able to compensate.

 

[DVDdoug]

Most active subs have a level control.

1. How loud or noticeable should be sub be if only the subs are playing - (speaker amp is off)? I know this is hard to quantify, but my subs are very low output volume.

For "high fidelity" the frequency response should be flat... It should be as if you didn't have a sub and the bass from your main speakers didn't fall-off at lower frequencies. But from there you can adjust to taste.

2. If I fed both RCA output line out level signals from the DAC into one sub, would those signals sum, meaning two times the voltage?

Maybe, if the sub has two (left & right) RCA inputs and you're currently using only one. It depends on the internal circuitry. Just try it. And you won't lose any signal if you connect both inputs on both subs. But yeah, don't "short" the left & right DAC outputs together.

 

[12Many]

About as loud as the mains when playing sine waves at either end of your crossover:

Thanks. I think I am far below this. This gave me an idea though - run some low frequency signals through the speakers only and the sub only to check and compare output levels.

Maybe, if the sub has two (left & right) RCA inputs and you're currently using only one.

My sub does have this. Each sub has a left line-in signal input and a right line-in signal input. When I had just one sub, I feed both R & L inputs into one sub. It seemed louder - I can check again tonight.

You have extra volume controls on both the Rhythmik subs and the AHB2, so even if the DACs outputs are uneven, you should be able to compensate.

True. My amp is at the lowest gain setting. I am turning up the subs but I not sure it would be good to max out the sub volume due to possible distortion. And when I do this, when the DAC is in home theater mode, the subs output is far too loud during movies.

My thought was it might help if I attenuated the XLR output to bring the RCA and XLR output voltage closer together. Or I can feed the subs (has line level and high level inputs) with the high level input from the speakers.

 

[12Many]

I am writing to provide an update. As a test, I used the speaker level inputs on the sub instead of the line level inputs. The sub really came to life. Much better. So, IMO, with the DAC3 jumper set to 0 dB, the difference between the XLR outputs and the RCE outputs on the DAC is too large (RCA outputs are too low), resulting in too low a signal being provided to the sub, in relation to the signal provided to the amp. I have not tested moving the jumper to the 10 dB slot.

I may start another thread on this, but is this connection method OK? Using a three foot speaker cable, I connected the sub directly to the terminals of the speaker. It seems to work fine although I have not done any critical listening yet. Is this ok? The F208s have dual connectors on the back of the speaker with a large metal jumper between the terminals. Thanks.