Hills and Valleys (another subwoofer thread)

I just bought a sub to augment my B&W CDM1Ses. During setup, using an RS SPL meter and the excel spread sheet that includes the response corrections for the meter, I was astonished to find that the B&Ws excite the lowest room resonance at 31.5 Hz! Equally there's peaks at 63Hz and 126Hz. There are relative low points at c. 45-50Hz and also at 100-110Hz. I've been playing around with speaker and sub positions and I've found that moving the speakers closer to the front wall diminishes the troughs relative to the peeks. I've also been drawing the sub out of the corner, it's actually about 90cm from the left side wall and the front of the sub is about 60cm from the front wall. The sub is positioned just to the left and just behind the left speaker.

In the beginning I set the crossover at 30Hz, but I think it's now closer to 70Hz, the markings on the frequency adjustement are (30Hz - min, 180Hz max). I set the gain, originally, on the sub by getting the same reading at 80Hz on the SPL meter from the main speakers and then from the sub.

Can anybody give me an idea of what I should move and how I should move it to get the troughs to come up in level ? Short of the Behringer Feedback destroyer, that is.

What about the gain setting, less or more ? I know I can fiddle that as much as like and at the end of the day it's a question of taste. For the moment I'm trying to minimise the nulls rather than fight the resonant nodes.

 

In general, the troughs are far less obtrusive than the peaks and are also harder to correct. So my advice would be to concentrate on reducing the peaks.

 

You might have a look at www.cara.de. Their software is a bit of work but I'm told the results are very accurate.

 

Peter,

two things. Have you tried reversing the phase of the sub? And secondly, what re the room's dimensions?

 

7_V,

Ok I'll see what I can do with the sub position, ease it further into the room and see what happens, that should lessen bass boost ?

Markus,

I'd originally used version 2.0 to set up the main speakers, but since I've lost the room plan, I think it got lost when I changed hard drives. I think it works well, but it's a chore modelling the room :-(

 

I set the phase on the sub to get highest output, I haven't tried a sweep with the phase reversed.

The room's dimernsions are essentially 5.23m x 4.75m x 2.42m. The room is not quite rectangular tho' it has a little bite out of the corner where the doors are (not). Opposing walls are parallel. The doorway opens to a hallway and the kitchen.

 

The best way to deal with troughs is to avoid sitting in them. Your main trough at around 45 Hz will occur at 1/3rd of the room length from the back wall. If this trough bothers you then put your listening position (your head) 1/4 of the room length from the back wall. At this position you will miss most of the trough (but you will enjoy the second harmonic peak at 110 Hz ).

Edited to add: that second harmonic probably won't bother you too much. Peaks tend to be most troublesome on sustained notes and in the bass region these tend to occur at 40 - 60 Hz.

 

With Music the peaks are not too obvious, perhaps with sustained notes. I think that the listening position is about 6/10ths of room length. I could try moving the sofa back or foward a little, but the room config makes more than 20cm subject to WAF control.

 

i also think that you should cross it much lower than 70 Hz.

cdm1nt probably produce decent bass at 50 Hz and perhaps even a bit lower......

i find REL's setup recomendation very usefull - take a look:
http://www.rel.net/setup.htm

 

I've been using a setup guide I found on AV123's forum, which suggests a sub position about 1m from side or front wall. I thought at first that 30Hz which is low as I can go would be best with the CDM1Se. But the 31.5Hz output from B&Ws is very surprising to me, since quoted specs are -3dB and -6dB at 58Hz and 46Hz respectively. I suppose I'll have to find positions for the main speakers that diminish that 31.5 Hz peak before looking for a definitive sub position.

 

i think that this 1m recomendation is a nonsense.
RELs usually need about 3-5 inches.

i don't know about other subs - but it just shows me that there is no general recomendation can be given.

did you read rel's setup guy?
it mught clear few issues for you.

 

I read it a while a go, and getting the sub into a corner is not possible for me, there's a humungous plant in the way. But, I will look it over again.

I'll give their POPI method a go tonight.

 

The typical advice is to set the phase for the maximum bass output. It's good advice, particularly if you are using the sub in a corner to maximise gain.

However(and somewhat leftfield), in the past I have switched the phase and overlapped with the mains. Recently did it with the Velodyne. Carefully applied (and with a lot of tweaking), this approach can cause the subwoofer to act like an EQ by sending an out of phase signal to cancel out the main's peaks. It is important to place the sub to avoid any significant dips in its response, so prefereably a corner. The evidence on the Velodyne screen showed a much flatter response, although the sub's output needs to be set higher. It's a bit heath robinson but it can work well for smoothing out the room's resonances.

Croc is right - that 1m thing is very misleading

 

i had a strata 3 and never really liked it. the only place it seemed to do the job was in between the speakers slightly to the rear. this was ruled out for one reason or another.

REL's set up instructions seem to suggest that the sub is a low low bass supplement ,that needs the cut in to be set very low, as oppossed to the way they seem to be marketed which is a device that builds the curve up from a small speaker roll off at say 50/60hz.

my advice - buy some floorstanders

 

You :JPS: mais bon, I don't believe good floor standers can be done affordably. But I can see what you're getting at.

 

Is it already or can you get the computer into the front room?

If you can then download the demo version of Spectra RTA from Sound Technology. You get 30 days IIRC unless you decide to buy it (quite expensive). The Radio Shack SPL will be good enough to use as the microphone and I can't remember but spectra might take the SPL correction files that you can download places.

As it runs in real time the whole setup thing goes a lot quicker than plotting graphs and setting the phase is a breeze (at least it was when I tried the software a year or so back).

From my experience position the mains first, as you like them to sound, or the only place you can put them. After that do the sub.

 

Matt,

I'll look that over, I can take the portable home ...


Peter

 

de rien

what about secondhand?

 

I've done this with my MJA Pro 50 and my Dyn 1.3MkIIs and got the best results that way. Using ETF software it was clearly giving me the flattest response (and subjectively it was the best aswell).

Michael.

 

Ah yes, well I don't actually want floorstanders in the 'ouse. In fact I'd like to try some ProAcs Tablettes or Dynaudio Contour 1.1s, 'cept I don't have enough oomph, yet, to drive 'em.