10 Hz Gap Between Crossover Frequencies

Rikkimax

Hi,

Thanks for all of the great discussion! Given the nature of the DriveRack PA manual, this forum is invaluable.

I have a question for your indulgence...

Background - I have:
A DriveRack PA
High Speakers - pair of JBL SRX715m (800 watts each at 8 ohms)
Subs - pair of JBL VRX 915s (800 watts each at 4 ohms)
High Amps - pair of QSC PL 236, one per side (each one bridged - 2400 watts at 8 ohms)
Low amp - QSC PLX3602 (stereo - 1250 per side at 4 ohms)...yes, this is underpowered, but I figured it would be harder to destroy the 15's than the high frequency drivers in the top speakers...maybe I have it ass backwards!

Statement: Settings for these speakers that are in the DRPA wizard do not completely correspond to the specs specified on the JBL cut sheets for these speakers (no surprise). Also, looking at the DRPA processer setting chart for the SRX712m's available at jblpro.com, I noted that the high pass slope for the SRX712m in passive mode with a sub is ideally a Linkwitz-Riley 6 at 90 Hz (Ha Ha. DRPA does not offer LR6. So much for that suggested parameter edit!)

Question: In the DRPA processor setting chart on jblpro.com I note that the low pass slope for the SRX718 sub being used as an example is a LR24 at 80 Hz (according to the cut sheet, the low pass frequency of my VRX 915s subs can be set anywhere between 80 and 120 Hz) . As stated above, the recommended HP for the passive SRX712m (with sub) is LR6 at 90 Hz. It is interesting that there is a 10 Hz difference between the low pass frequency of the sub and the high pass frequency of the high speaker. I am assuming that the differing slopes of these two filters makes for a smooth transition. I am planning to do some experimenting with the crossover point. If you were me, would you try to keep this 10 Hz difference between the LP and HP filter (in spite of the fact that I can't use an LR6 for the HP (as it is not available on the DRPA)?...or... Would you just set the slope of both the LP and HP filters at LR24 and cross them both over at the same frequency (say, maybe 90 or 100 Hz)? If I try to keep the 10 Hz difference, what slope should I use on the high pass for the top speakers?
Thanks for your consideration of my question! --Rikkimax

Dennis

What are the individual output levels of the two pass-bands in question (sub out and mid/hi out) as listed in the tunings on the JBL website?

Dennis

Gadget

Hmmm,
I don't find that to be the case... In my findings, the PDF specs an LR24@80hz and a LR24@ 90 hz for the HPF/LPF for the sub/tops xover...The LR6 you speak of is the the tops LPF that you don't have in the Hi outs but you could ..and do in the mid and lo outputs on the DRPA, and the LR6 is usually spec'd where a smother response is desired when having to impose an LPF... The DRPA kinda says "let the speakers reproduce what they can on the top end, or let the frequency response limitation of the speaker be the natural LPF of the speaker...

What Dennis is getting at is there is an electrical xover point and an acoustic xover point.. in this case the gain structure specifies a gain for subs xover point and the tops xover point... in this case they are moot since you aren't using either the SRX718 (speced @ +1.7db) or the SRX728 (Speced @ -2.5db) since you are using VRX 915 subs...

In other words, as the xover gain is added or subtracted, the acoustical xover point will vary as well...so, IF you select a 90 hz frequency as the LPF of the sub, the actual point may be 110 hz...(simple example here no real actual numbers only examples), if you add gain to the xover point, that will raise the acoustical xover point as well... and conversely, lowering the gain will lower the acoustical center as well..OK

So to answer your (in this case moot question) query, if you get a suggested setting from someone, or JBL.. and want to see what this or that setting sounds like...try both, or multiple, but make sure you understand exactly WHAT they are saying, and NO you cannot use whatever "speaker they provide since yours is an 18" front loaded sub as well"...If it's the EXACT system they spec, you can feel comfortable that you will get the performance they spec from the design. Otherwise, we generally specify using similar adjacent xover types (LR24/LR24...BW18/BW18...etc) and often spec a same or small split for LR24 filters, and if you wish to overlap, use BW24 filters as they generally are a smoother transition...Just know that the xover region can cause all sorts of chaos frequency wise to the content in the xover region...

Since we deal here with a mostly newbie to novice level of user we usually ask that they select a LR24 filter @24db/octave, and further, that since the xover gain skews the acoustic center, that they leave the xover gains @ unity and utilize the amp attenuators for setting the gain structure. See this post:
viewtopic.php?f=61&t=959
for further clarification on our stance here...Suffice it to say that we also understand that the actual xover point is affected by that amps attenuation as well, and thus the greater the difference in gain level of the amp/xover gain the greater spread may be necessary to avoid excessive interaction of the frequencies in the crossover region...

BTW JBL puts a split in that can sometime seem unreal.. like even as much as 400-500hz or more, rest assured there is most likely a reason for this, and their R&D budget and tool set is most likely far superior to ours... Now there are a lot of folks out there with oodles of skill @ tuning systems that would disagree with JBL or (insert speaker de-our name here) but suffice it to say if your not really good at the whole tuning thing (like Dennis or Mikey) Suggested settings by the MFG are going to be at least a good starting point...

I also inserted the 260 setups provided by JBL (SRX715-SRX718subs) into the GUI and there they speced
LR48@88.4hz at 0db
LR48@91hz at -1.7 for the tops
BTW have you seen the FAQ section?
viewforum.php?f=60
Gadget

Rikkimax

Dennis wrote:

What are the individual output levels of the two pass-bands in question (sub out and mid/hi out) as listed in the tunings on the JBL website?

Dennis

0 db

Gadget

:shock:
Um... :?
Where did you find THAT figure?
No comment on my diatribe :?:
hmmm

Rikkimax

Gadget:

I wasn't ignoring your message. It just took me a while to formulate a response. I posted it a few minutes ago, but haven't seen it pop up yet...

Here is where I got the specs I was referring to:

http://www.dbxpro.com/Download/Speaker_ ... 0DR_PA.pdf

If I understood Dennis' question correctly, the level of the LP filter for the SRX718S sub is 0 db with a LR24 at 80 Hz, and the level for the HP for the SRX712M passive (with sub) is 0 db with a LR6 at 90 Hz. Am I mistaken?

Rikkimax

Dang it,
I think I lost my long reply to Gadget's message...sigh. Here I go again.

Anyway, Dennis and Gadget, thanks for your quick and comprehensive replies. I was using the specs from JBLPro for the DriveRack PA with SRX712M tops passive with SRX718S subs, dated 2/3/05. Yesterday I also found the Driverack260 specs for the SRX712M passive with SRX718S subs, dated 3/9/07, and the suggested specs were different!!! The 260 specs have an overlap and call for a LP on the subs at 88.4 Hz using a LR48 at 0db, and a HP on the SRX712M's at 85.9 with a BUT18 at 0db. Very confusing, as I didn't know the laws of physics could change in two years!

At any rate, I just plan on using a LR24 for both the LP on my subs and the HP on my tops at about 90Hz, and see (hear) what happens.

A last question: If you had to underpower something, would it be your tops or your subs? I have plenty of power for my top SRX712M's (2400 watts rms at 8 ohms for each 800 watt, 8 ohm speaker), and less for my VRX 915s subs (1250 watts rms @ 4 homs for each 800, 4 ohm speaker).

Thanks for everything, Rick.

Gadget

Use the power for the subs... raise the HPF for the subs/tops xover to somewhere over 100hz...use LR24 filters and split them a little, Say 100 hz for the sub and 118hz for the tops.

I think your misreading the specs/setups. As I said the LR6 is a tops LPF(HIGHEST point we want the tops to go) , and I don't think ANYONE would be crazy enough to put different xover types on adjacent xover points...

DON"T try and use your subs in place of the ones they speced... the VRX are different!!! Instead, follow the instructions you already have. Al the info you need to tune your system is in the previous posts
g

Rikkimax

Thanks!!!