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Need active crossover advice


DLStryker
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I have Marantz PM8005 2 channel pre amp/amp (2017 model)  driving La Scalas.  ALK crossovers and Fast Lane squaker horns.

 

For a sub, I have a JBL 4645b (single 18) cabinet with a Crown DSi 1000 (950 watts bridged 8 ohms).  Here are the specs on the JBL 18:

FREQUENCY RESPONSE :
Lower Frequency limits (no EQ): -10 dB: 18 Hz -3 dB: 35 Hz
Lower Frequency limits (with EQ): -10 dB: 20 Hz -3 dB: 22 Hz
Recommended Crossover Frequencies:
High-Pass: 20 Hz. 24 dB/octave
Low-Pass: 80 Hz to 120 Hz. 12 to 24 dB/octave
Enclosure Tuning Frequency: 25 Hz

 

Now I need guidance and advice on an active crossover.  My budget is around $400.  I am very new to active crossovers.  Any advice will be appreciated.  What model.  How to even wire the unit.  I assume I need a x over that will sum the stereo channels for mono sub??  I have quite a bit of money invested in my system (at least for me) and not looking for jerry rigged sub unit that just gets by.  I'm looking for high fidelity and good, rich, deep, if the volume is up...... controlled, pounding base.

 

I noticed most x overs in my $ range are for live performance systems.  Seems the lowest high pass filter is around 35 hz.  I'm guessing most bands don't care about anything lower than that and it is just wasting amp power.  If I am listening to predominately "music", do I even need the 20hz subsonic high pass filter?

 

Also have a Marantz UD7007 CD/Blue Ray player (the Blue Ray is for music videos).  Paid $1,200 for the Pre amp/Amp and $1,200 for the CD player.

Also have a Monster line conditioner/surge protector.

Interconnects and speaker cables are Morrow Audio

 

Thanks in advance for your help.

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I recommend connecting The Marantz PM8005 pre-outs directly to the Crown DSi 1000 input using a RCA to Phoenix adapter, then scroll down the DSi 1000's onboard menu and selecting the pre-sets for the JBL 4641, the newer version of your fine subwoofer. That should get your system playing just about right without buying an outboard crossover, since the La Scala does not really need a high pass filter (bass cut filter). Later, when you become more familiar with the Crown's built in DSP, you can select the CUSTOM mode to apply your own settings, the important parameters being JBL's "B6 filter", 6db boost @25hz Q2, Hi Pass Filter (subsonic cut) @20hz. Also select Low Pass Filter @60hz to the subwoofer since your La Scalas will handle everything above 60hz. 

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If you would like to time align your La Scalas, this is really straightforward:

 

Go inside the top hat of each La Scala and unscrew the mounting screws from the tweeters, then move the tweeter (still attached to the electrical leads) to the back of the La Scala top hat on top of the cabinet, facing forward.  Place some absorbent material down across the entire top of the cabinet, then rest the tweeter on top located 23.5 inches farther back from the its in-cabinet mounting position, elevated slightly above the top of the cabinet.  That's it.  Now listen to its greatly expanded soundstage. 

 

You can also mount the tweeters in a small custom-made baffle, like that shown below:

 

LaScala Mods SS -4.jpg

 

Chris

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8 hours ago, Khornukopia said:

RCA to Phoenix adapter

An adapter is not really needed with your existing hardware. Just take an inexpensive RCA wire set, cut off one end and strip the insulation, insert the bare wires into the Phoenix connector and tighten the set screws. The inner wire should be the positive + conductor.

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No, you don't need the high pass filter on the sub for recorded music.

Kick drums are mostly 50-60HZ, with some bass drums and big toms getting onto the 30's.  The lowest note on a piano is 27.5Hz, however even on an 11 foot grand, you're hearing mostly harmonics and sympathetic resonances on other strings.  The low E on a bass guitar is at ~41Hz, and the B on a 5 string bass is ~31Hz, or a half step lower at ~29Hz for the contrabassoon.  Synth drums, synth bass, subharmonic generators in some popular music, and movie soundtracks aside, there's not much "down there" that you will be wasting power on.

Organ music?

Pro musicians roll of below 30 or 40 or so because there are things like people walking on stage or things bumping around that can overload the system, especially with the amounts of gain they run in the LF for live music.  This is already done for you on recorded tracks.  There's no reason not to roll stuff off sharply in the LF for vocal or other instrument mics in the studio.  Everything down there is junk or hum or HVAC.

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On 12/11/2017 at 12:54 AM, Khornukopia said:

I recommend connecting The Marantz PM8005 pre-outs directly to the Crown DSi 1000 input using a RCA to Phoenix adapter, then scroll down the DSi 1000's onboard menu and selecting the pre-sets for the JBL 4641, the newer version of your fine subwoofer. That should get your system playing just about right without buying an outboard crossover, since the La Scala does not really need a high pass filter (bass cut filter). Later, when you become more familiar with the Crown's built in DSP, you can select the CUSTOM mode to apply your own settings, the important parameters being JBL's "B6 filter", 6db boost @25hz Q2, Hi Pass Filter (subsonic cut) @20hz. Also select Low Pass Filter @60hz to the subwoofer since your La Scalas will handle everything above 60hz. 

 

Wow!  I had no idea the DSP had so much functionality.  I saw a few basic crossover points in an owners manual.  I thought that was it!  Thank you for the information.  Seems like I am pretty much set.  I'll have to read up on the advanced DSP functions.

 

Thanks again!

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You may want to download the Crown HiQnet System Architect software and then plug your Crown into your home computer via USB cable. This is not required, but will be easier to navigate the menu and read your settings, compared to the tiny front panel display on the amp. I have not used a DSi, but I think it should do what you want.

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17 hours ago, Andy W said:

No, you don't need the high pass filter on the sub for recorded music.

I agree, in fact this will significantly affect low bass enjoyment for good recordings like DVD-As, audio BDs, and multichannel SACDs that haven't already had extreme low frequency roll-off.  (The one exception is phonograph records/turntables/cartridges, which must be high passed due to record warps, but the bass in records necessarily has been severely affected by the transfer to the phonograph format, in any case--the original case for "mastering, in fact.)  See the following thread for more discussion:

 

17 hours ago, Andy W said:

Kick drums are mostly 50-60HZ, with some bass drums and big toms getting onto the 30's. 

Actually, kick drums are uniformly in the 30s on every recording that I've demastered (about 11,000 music tracks to date).  See the linked thread above for more information. 

 

17 hours ago, Andy W said:

The lowest note on a piano is 27.5Hz, however even on an 11 foot grand, you're hearing mostly harmonics and sympathetic resonances on other strings.

This is mostly correct before the recording is mastered, but for the fact that almost all piano recordings have been mastered to a turnover attenuation frequency of about 450 Hz (-3 dB/octave).  That adds up to a -12 dB at 30 Hz of artificially introduced attenuation for virtually all CDs and phonograph records.  Multichannel SACDs and DVD-As/BD are a different story, however.

 

17 hours ago, Andy W said:

Synth drums, synth bass, subharmonic generators in some popular music, and movie soundtracks aside, there's not much "down there" that you will be wasting power on.

This is also not entirely true--at least for the tracks that I've demastered.  In fact, I've found many pop and rock recordings that have been simply rolled off during mastering.  Once they are demastered to restore the deep bass, then the idea of a "music subwoofer" must be able to faithfully reproduce down to at least 20 Hz, if not lower (pipe organ performances are especially true of this). The idea of "wasting power" is particularly surprising coming from a Klipsch employee--which is known for highly efficient loudspeakers in the industry, in fact the industry leader in terms of consumer models.  I don't recommend that sort of viewpoint, actually.  The effects of high passing music tracks are always audible in low frequency group delay growth.

 

17 hours ago, Andy W said:

Pro musicians roll of below 30 or 40 or so because there are things like people walking on stage or things bumping around that can overload the system, especially with the amounts of gain they run in the LF for live music.

This is true for most the recordings that I've demastered...but clearly not all, as the best recordings that I own have plenty of energy below 30-40 Hz in the bass line, kick drum, and other instrumentation. 

 

It's easy to rid yourself of microphone bump transients during demastering: just use a low-Q notch filter over those short time periods in the recording where there are microphone bumps (they're easy to see in the spectrograms due vertical lines below 25 Hz in the spectrogram).   Once you select the time period of the recording with the bump/thump, then you can apply the notch filter on just that short instance in time, thereby retaining the low bass spectrum (and proper low bass low phase relationships due to the minimum phase nature of the domain) for much increased listening pleasure.  Recommend calibrating your horn-loaded subs in-room to remove as much group delay growth as possible.

 

17 hours ago, Andy W said:

This is already done for you on recorded tracks. 

Yes, but this is easily undone via demastering those tracks.  I recommend it highly.  If you want to listen to any recordings where this has been done, let me know. 

 

17 hours ago, Andy W said:

There's no reason not to roll stuff off sharply in the LF for vocal or other instrument mics in the studio.  Everything down there is junk or hum or HVAC.

Well, I suppose I'll have to agree to disagree--sharply.  I would recommend that you update your setup to accommodate frequencies down to sub-20 Hz, and I recommend horn-loaded subs instead of direct radiators for the reason cited above.  HVAC is spectral , and is easily removed using notch filters (usually at either 21, 27, 31, 37, or 41 Hz, I've found.)  They're easily seen in the spectrograms and easily removed.  This is the easiest task in demastering, I've found. 

 

Hum is always at 60/120/180 Hz (North America), and 50/100/150 Hz elsewhere--well above the normal mastering deep bass roll-off frequency for good recordings.  Sometimes I see 30 or 25 Hz sub-harmonic frequencies but these tend to be rare.  

 

Chris

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Ah, yes...ported boxes. 

 

They really do need low high pass filters to keep the woofers from unloading at frequencies below the port tuning frequency.

 

If you're using a ported box, you already have audible group delay growth at low frequencies, so adding more with a preamp high pass filter probably won't be any more audible...

 

Chris

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