SUB Crossover Settings

[brothermalzone]

We've recently purchased the new RCF 932 Tops and we'll be using 1 x RCF 8003 AS II. This will be for our wedding band at small/medium size gigs and everything goes through the PA (Vocals, Bass, Guitar, Drums etc). 

The SUB manual mentions the following settings and I was wondering which would work best for our situation? 

 

EXTENDED LOW PRESETS (more extended and linear frequency response):
L1 30 Hz – 60 Hz
L2 30 Hz – 80 Hz
L3 30 Hz – 100 Hz
L4 30 Hz – 125 Hz

HARD PRESETS (less extended frequency response, more pressure at 50-60 Hz):
H1 40 Hz – 60 Hz
H2 40 Hz – 80 Hz
H3 40 Hz – 100 Hz
H4 40 Hz – 125 Hz

CARDIOID PRESETS (in combination with L presets)
C1 30 Hz – 60 Hz
C2 30 Hz – 80 Hz
C3 30 Hz – 100 Hz
C4 30 Hz – 125 Hz

[David Morison]

Well, you can ignore the Cardioid set of presets as you're only using one box - they are used when combining (usually) 3 boxes in a certain way to reduce LF spill backwards from the PA.

As for the others, it's really a matter of taste - get them set up at a practice and try them out for yourself.

A couple of general thoughts do occur though...

1: using the Extended Low presets may give the perception of more bass even at more modest volumes, but it also uses up a bit of headroom - so if you're trying to run quite loud, this would be counterproductive. It's likely to result in the tops outrunning the bass bin given your 2:1 ratio of boxes - again, if you need to run loud.

2: the higher the crossover frequency you select, the more work the bass bin does and the less work your tops do - if you were really trying to max out the volume you can run at and still keep the tops nice and clear sounding, you'd probably get slightly better result using the higher crossover therefore. However, for small to medium wedding gigs, I'd imagine you're not likely to be pushing the rig hard enough to need to worry about that.

3: remember to run your mixer's L & R outs into the bass bin first, then jump up to the tops, so that the crossover between the 2 is correctly handled - otherwise your tops are going to try and play the whole spectrum including the low end.

 

HTH,

David.

[Keith_]

Have a look (if you did not already) at the freq response published by RCF https://www.rcf.it/en/products/product-detail/sub-8003-as-ii?p_p_id=it_dvel_rcf_products_frontend_web_portlet_ProductDownloadsPortlet&p_p_lifecycle=2&p_p_state=normal&p_p_mode=view&p_p_resource_id=downloadProductFileEntry&p_p_cacheability=cacheLevelPage&_it_dvel_rcf_products_frontend_web_portlet_ProductDownloadsPortlet_productCode=STP0145&_it_dvel_rcf_products_frontend_web_portlet_ProductDownloadsPortlet_profileId=239890

You will see it drops about 10dB from 50 to 80Hz and keeps going down at that rate as f increases. Your 932s are good down to 70 or 80Hz, so I expect L2 or L3 would be best, but agree with David from the Granite City above about experimenting.

 

Also to note (if you want) the 932s are roughly cardioid polar pattern (horizontal) above around 1kHz, so 40 degrees or so off axis (of either of them) will be a bit wooly (especially with audience absorption) - beam width quoted as 90 degrees at 1k. As a rule that is not a big issue in small venues; it may be best to point them slightly inwards, not parralel (depends on where the walls are). I imagine you are putting the bass box in the middle FOH. The 932s are a bit less dB, so I don't expect them to be out of balance with the bass. You can use some pan to help avoid standing waves and feedback from the tops (it might make a bit of difference in some tricky, cramped situations). Returning to David's advice, I would play some familiar music through the system and walk around to see how it sounds in different parts of the venue, tweeking to taste. The speakers should serve you very well.

 

[David Morison]

Hi Keith, that frequency response curve appears to assume the 60Hz filtering is in place.

The higher settings do extend it out appropriately so if the 932's happened to sound better with a 100 or 125Hz crossover, there shouldn't end up being a hole in the response.

Fortunately RCF do publish an Ease GLL file for this - I've extracted the FR curves for each setting here:

 

HTH,

David.

Edited April 7, 2023 by David Morison

[Keith_]

That's very good, David. I thought the graph I was looking at fell off a bit hard. RCF are underselling themselves in their advertising lit. 

By the way, I recently started lusting after some Funktion one horns ... that is until I saw the price of them. Fabulous kit, but you could buy a yacht for that kind of money.

[mojo filters]

I think @David Morison et al have provided all pertinent details needed to help you set up your system. 

I would just add that as a regular user of RCF, and as someone with an interest in system alignment in general - you should check out the various frequency response charts for those specific speakers, in order to get the best results. 

Unfortunately we all have different ideas of what nebulous terms mean, such as small and medium venue sizes. I'm familiar with the 8003 sub, it's a popular box where I work. Although the 932s are new, I'm sure my experiences with other 9xx RCF boxes indicate they'll be as good as, if not better than, the popular 7xx models. 

The recent RCF speakers in the Art, NX and HDM formats are beating the MI competition in Europe and UK, with keen pricing and chunky HF drivers capable of lowering crossover frequencies well into the sub-1000Hz territory. More importantly they sound good, whilst each incremental improvement lets them gracefully get a bit louder, maintaining sound quality before they crap out. 

When using that pretty potent combination of 932s over one 8003 for a rock'n'roll band in "smaller" venues, I'd attempt to account for the inherent difference between the electrical crossover frequency between your sub & tops (ie the sub's filter setting) and pay attention to the acoustic crossover frequency which inevitably will vary, depending on the relative volumes between your sub & tops. 

In all but the tiniest venues, I'd run the 8003 WFO, dialling back the tops to achieve more manageable levels within fader travel at FOH. This should let you get a satisfactory and coherent crossover integration by underlapping the preset HPF frequency feeding the top boxes. 

If you run the sub hotter than the tops, the paper spec electrical crossover frequency (eg 60Hz or 80Hz) might be lower than the actual (acoustic) crossover frequency, where the sub aligns with the tops. 

Acoustic crossover alignment will vary depending on the relative differential outputs of each type of speaker. For a rock'n'roll band, I'd stick with a 40Hz high pass filter on the sub. Lowering that to 30Hz only forces it to work harder, inherently reducing overall output capability without providing any tangible benefit.

60Hz or 80Hz electrical filters still allow higher frequencies to pass through (depending on volume) hence if the 932 tops have a natural -3dB rolloff around say 70Hz (please check, just an educated guess) then the 60Hz sub filter choice makes best sense, when run wide open at a higher level than the tops. The sub happily allows plenty of content above 60Hz through, thus we potentially get a better complimentary acoustic crossover frequency coupling between both boxes.

I don't have the specs for either box at hand, so please take my theories with a healthy grain of the proverbial salt. I've worked with the 8003 sub many times. I've always been impressed in small venues, though for my idea of medium sized spaces, I'd want 4 boxes tight-packed and centrally arrayed.

Nevertheless regardless of how good both types of speakers are, I would always approach setting up and tuning similarly spec'd boxes with these acoustical objectives in mind, regardless of manufacturer. 

My main point is simply to reinforce why even with complimentary pieces of kit designed by the same people to easily work together, you should be aware of the differences between electrical crossover frequencies (ie those on spec sheets, derived from filter design) and acoustic crossover frequencies, whereby the latter is derived from how the gear is used, as well as any kind of measurement - which could be as simple your own hearing, right through to a full SMAART rig. 

I hope this makes sense. I only intended to write a couple of sentences...obviously that didn't happen!

The TL;DR point is simply that relative changes in amplitude affect the actual frequency extremes, produced by different loudspeakers designed to reproduce different pass bands. There should be plenty of learning materials on the web which do a more complete and efficient job of explaining how these factors will affect your system.