Subwoofer crossovers

[Randy Myers]

Sometime after being advised by Acoustic Frontiers (2015 dedicated room design) that most single box main speakers were incapable of producing true low end, and then reading the attached article, I incorporated a JL Audio F212v2 subwoofer and CR-1 active crossover into my audio system. I had been somewhat reluctant to do this because for years I thought putting a relatively lost cost CR-1 between my source equipment and main speakers would destroy the benefits of the high end equipment in my audio system.

Instead what happened after dialing the CR-1/F212 in with the help of JL Audio T/S, the main speakers midrange and highs noticeably improved because they and the stereo amp no longer had to try to produce lows below 30-40Hz, and the bass became a truly visceral low end extension of the main speakers. The subwoofer sounds like an integrated part of the main speakers sound field.

Soundoctor - all about subs (https://www.soundoctor.com/whitepapers/subs.htm)

I have been considering adding a crossover to my KEF / Rythmik (x2) setup. The JL Audio CR-1 looks impressive but I do believe it would be a bit over board in my much more modest system.

Are there other good choices that are not as over the top as the CR-1? Researching I have not found many other choices. About the only thing I have found that looks interesting is this:

Amazon.com (https://www.amazon.com/dbx-223xs-Stereo-Crossover-Connectors/dp/B004S2FVSM/ref=sr_1_1_sspa?crid=AKZPVKTK965X&dchild=1&keywords=dbx+223xs&qid=1628100242&sprefix=dbx+223%2Caps%2C218&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyMlhOMzQ4TU1TTlIwJ mVuY3J5cHRlZElkPUEwNDgzNTcySTJXWEZROFlRNEI2JmVuY3J 5cHRlZEFkSWQ9QTAxNzg5MzEzNUkzVDZFWTBOU1FYJndpZGdld E5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm9 0TG9nQ2xpY2s9dHJ1ZQ==)

223xs | dbx Professional Audio (https://dbxpro.com/en/products/223xs)

Is this pure junk? I know DBX used to be a top quality brand but I am not sure if they are even the same company as they once were. Would this be good in my systems or would it actually hurt my performance? I will be glad to hear any and all opinions or thoughts.

Is anyone aware of and recommend any other models?

Thank you.

[jadedavid]

Don't know if your pre has 2 outputs but if it does a simple capacitor in series to the main amp will provide a 6db roll off.
Vandersteen, Aesthetix, Raven and some others use this approach to create a high pass filter.
Several calculating sites online. Just need to know the amps input impedance.
Your subs already contain the low pass network in their plate amps.

[Randy Myers]

Yes, my pre has four sets of outputs. 2x RCA and 2x XLR. Currently I have a set of XLR to the MBL, another to the Woo and a set of RCA to the subs. I simply have the main and the subs off if listening to headphones.

So putting a high pass filter inline from the pre-amp to the main amp should work? Where do I find good one that will not diminish the sound quality going into the MBL amplifier?

Would something like this work?
Amazon.com (https://www.amazon.com/Shure-A15HP-High-Pass-Filter/dp/B00075VQRO)

[Jack]

Randy

You can order the DBX model through Amazon and then you have 30 days to try it and return it if it doesn't work. Other than a couple of high dollar ones like the JL and the Bryston most of what you will find will be in the Pro audio arena. May also find some in the Competition Auto Audio arena. There are some simple in line ones you can find from companies like Harrison that may also may be available from Amazon, AA and Crutchfield with return policies. Also over on Audio Circle you will find a large group of DIY speaker builders including the ones building kits from GR Research. I expect someone over there has tried most of these products. The Vandersteen method that jadedavid mentioned does work as I used it for years with their speakers and subs.

Bottom line is that if you can get the DBX unit from Amazon and try it out for 30 days then nothing to loose.

[2FlyingYorkies]

The MiniDSP products (like this MiniDSP 2x4HD (https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4-hd)) get plenty of love on some of the other forums. Some models even include room correction if you're interested in that kind of thing. They also come with pretty detailed instructions (https://www.minidsp.com/applications/digital-crossovers/subwoofer-integration-with-minidsp) on how to electronically program everything. I have no personal experience with these units, but considered them pretty seriously at one point.

[jadedavid]

The Shure model that you reference may work, and it is the proper idea. However it does not specifically take into account your amps impedance which is a critical piece in determining the correct capacitor(s) value.
Sorry but I am not good on being able to provide you with a proper link.
However a quick search for passive line level balanced high pass filter should provide you with further info.
Also I have found that the Brand/type capacitor has little variation in sound quality using this implementation.
Simple and works great.

[Randy Myers]

Thanks jadedavid and Jack. I was thinking the same thing about the DBX. It does not look like there are a lot of higher end products out there (except the JL Audio). Hopefully the DBX is decent quality.

I was also thinking maybe try the Shure XLR High Pass Filters. The whole idea is to free up the amplifier from dealing with low frequencies and only sending 100hz and above to the amplifier/speakers... letting the subs have the low frequencies. I did not find any higher quality ones that did this sort of thing, but still looking.

I found Harrison Labs (HLAB) offers XLR FMOD hi-pass filters that you can choose the frequency you want. I decided to pick 70 hz. I figured this would be a good try in line hi-pass filter and I think I trust Harrison labs more than the Shure.

[Randy Myers]

The MiniDSP products (like this MiniDSP 2x4HD (https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4-hd)) get plenty of love on some of the other forums. Some models even include room correction if you're interested in that kind of thing. They also come with pretty detailed instructions (https://www.minidsp.com/applications/digital-crossovers/subwoofer-integration-with-minidsp) on how to electronically program everything. I have no personal experience with these units, but considered them pretty seriously at one point.

Thanks. It is important for me to keep in the balanced world for this process. I am using balanced outputs form the pre-amp and balanced inputs on the MBL amplifier!

[Jack]

Randy

Once you have done the measurements for that room and determine where the big drop off is for the KEF's then maybe reach out to to either your preamp guy or maybe even EJ or one of his people and see what would be involved with putting a resistor across the outputs like Ayre does for Vandersteen owners. The resistors would be based on the desired cutoff frequency and the input impedance of the MBL. Also this method could easily be un-done if you needed to sell the preamp. Seems like their are enough guys in your Audio club group with the background and skill to help you get this done. The Harrison FMods are just an external attempt to do the same thing but since they don't take into account how their internal resistor will react with you amps specific input impedance then picking the right one may be hit or miss to some extent as you don't know what "baseline" input impedance they are using in their calculations to determine which value resistor to use. Chances are good they are using something common like 100k ohms.

[NekoAudio]

You could look for a used Bryston 10B-SUB (http://old.bryston.com/products/other/10B-SUB.html) with XLR jacks (it's either RCA or XLR, not both). It was recently discontinued.

The full-size miniDSP SHD (https://www.minidsp.com/products/streaming-hd-series/shd) has balanced I/O but there is an issue with it not accepting above reference line-level voltage on analog I/O and you can also accidentally go above 0dBFS on the digital output. Which could be a problem if you're using it in the analog domain since the analog output from a preamp or receiver can easily go above that, or if you don't introduce an appropriate level cut for any PEQ boosts you use. For digital-only, you can use the SHD Studio (https://www.minidsp.com/products/streaming-hd-series/shd-studio) but you'll need an extra DAC for your subwoofer.

A more full-featured option would be the Trinnov ST2-HiFi (https://www.trinnov.com/en/products/st2-hi-fi/).

With the miniDSP or Trinnov, you could use it as analog I/O like a traditional crossover box, but you could also use its digital input right after your source and connect its digital output to a DAC and amplifier for your main speakers and connect its analog output to your subwoofer. You would need to control volume at the miniDSP, Trinnov, or upstream at your source. This would let you use your highest-quality audio playback for your main speakers, but the DAC of the miniDSP or Trinnov for your subwoofer. And you get the benefit of a digital crossover implementation instead of an analog one.

Besides dbx, Behringer is another pro brand with crossovers like the CX2310 (https://www.behringer.com/product.html?modelCode=P0CCS). Although I would make sure I could try and return the dbx or Behringer just in case, given this is going into the signal path of your main speakers.

[2FlyingYorkies]

Thanks. It is important for me to keep in the balanced world for this process. I am using balanced outputs form the pre-amp and balanced inputs on the MBL amplifier!

The next model up the MiniDSP range (4x10HD (https://www.minidsp.com/products/minidsp-in-a-box/minidsp-4x10-hd)) is balanced but is otherwise fairly similar to the one I referenced earlier. You'll find these units in quite a few home theater installations, as well as used for active speaker crossovers. The SHD model Neko mentioned is very similar, but adds streaming capability that I don't think you're looking for in this component, unless you were really looking to replace your preamp, which I doubt.

[Randy Myers]

All good suggestions and much appreciated. I think I will try the inline hi-pass filter first to see how it works. All of these other suggestions are great ideas. The Behringer is actually less expensive than the Harrisons FMods, but I think I prefer to try the Harrisons first to see how they work. Thank you for all of your replies!

[jadedavid]

Randy

Once you have done the measurements for that room and determine where the big drop off is for the KEF's then maybe reach out to to either your preamp guy or maybe even EJ or one of his people and see what would be involved with putting a resistor across the outputs like Ayre does for Vandersteen owners. The resistors would be based on the desired cutoff frequency and the input impedance of the MBL. Also this method could easily be un-done if you needed to sell the preamp. Seems like their are enough guys in your Audio club group with the background and skill to help you get this done. The Harrison FMods are just an external attempt to do the same thing but since they don't take into account how their internal resistor will react with you amps specific input impedance then picking the right one may be hit or miss to some extent as you don't know what "baseline" input impedance they are using in their calculations to determine which value resistor to use. Chances are good they are using something common like 100k ohms.

I first encountered the method of high pass by capacitor when I got a Dahlquist dq-lp1 many years ago. A neat unit that I modified and used for quite a while. The owners manual has a chart for capacitor substitution that also includes necessary (when needed) resistance additions. From both this early information and any subsequent info I have found it appears that if you design for 80hz or less that a resistor is not necessary. I would be interested in obtaining any further info you may have that could shed more light on the addition of a resistor.
I have found this method to be the easiest and least detrimental to sound quality than any of the other active crossovers that I have tried.

[Randy Myers]

I first encountered the method of high pass by capacitor when I got a Dahlquist dq-lp1 many years ago. A neat unit that I modified and used for quite a while. The owners manual has a chart for capacitor substitution that also includes necessary (when needed) resistance additions. From both this early information and any subsequent info I have found it appears that if you design for 80hz or less that a resistor is not necessary. I would be interested in obtaining any further info you may have that could shed more light on the addition of a resistor.
I have found this method to be the easiest and least detrimental to sound quality than any of the other active crossovers that I have tried.

Hey Jack and jadedavid; here are the specifications on the MBL amplifier. I am out of my league in understanding in the area you are discussing. To start I am going to try a Harrison Lab 70Hz High Pass Filter and see how that works and then go from there. Thank you guys for your input. It is always appreciated!

Peck Pulse Power [Mono] : 500 W
Rated Power [Mono] :
120 W at 8 Ω
185 W at 4 Ω
Output Voltage: 35 V
Output Current max. : 20 A
Input Sensitivity: 1,5 V (185 W, 4 Ω)
Signal-to-Noise Ratio: 115 dB
Total Harmonic Distortion: less than 0,006%
Damping Factor: 300 (4 Ω)

The one thing about the KEF Meta's (for me anyway) is they are the first speaker I have had that appear to completely disappear in my room, including my Maggie's! My thoughts are to see if they can be opened up even more when the MBL no longer has to deal with the very low frequencies. I know my friend from our audio club noticed a huge difference in his system when he added amplifiers to handle low frequencies and had his main MBL amps handle the rest. Granted a completely different level then what I am dealing with :D.

[Jack]

Randy

I input impedance on that amp for both SE and Balanced inputs is 10k ohms.

[Randy Myers]

Randy

I input impedance on that amp for both SE and Balanced inputs is 10k ohms.

Thank you Jack. Good sleuthing :P. What I posted was the only specs I could find on the amp :).

Is this input impedance a fairly normal figure, or is it an outlier?

Here is a spec I found on Harrison Labs site. I admit to having very limited knowledge on this:

WHAT IS AN FMODtm ?
THE FMOD IS AN ACTIVE CROSSOVER SIMULATOR. IT IS BETTER THAN A MUCH MORE EXPENSIVE ELECTRONIC CROSSOVER THAT REQUIRES POWER TO OPERATE. FMODS ARE PACKAGED IN PAIRS AND AN FMOD CAN BE COMBINED WITH OTHER TYPES OF CROSSOVERS TO CHANGE THE SLOPE (DB/OCTAVE) AND CROSSOVER FREQUENCY POINT.

WHY ARE FMODS BETTER?
FMODS HAVE VIRTUALLY NO NOISE OR DISTORTION
FMODS DO NOT CAUSE TURN ON THUMPS
FMODS ARE VERY RELIABLE
FMODS ARE 24KT GOLD OVER BRASS
FMODS ARE COLOR CODED AND
MADE BY HLABS IN THE U.S.A.
12 DB/ OCTAVE

FMOD COLOR CODE
High pass Fmods (filter modules) have red labels
Low pass Fmods have black labels
The color ring indicates Hlabs standard crossover frequency (-3db point)
There is an 8%(LP) / 25%(HP) frequency increase at 10K ohms and 8%(LP) / 15%(HP) frequency decrease at 47K ohm load. Otherwise all color design values of crossover frequencies are standardized at 22k ohms. Keep in mind that exact crossover frequencies are seldom noticed or necessary.
20hz black bands (25hz @ 10K / 17hz @ 47K)
30hz 2 black bands (37hz @ 10K / 26hz @ 47K)
50hz brown band (54hz @ 10K / 46hz @ 47K) (62hz @ 10K / 43hz @ 47K)
70hz purple band (76hz @ 10K / 65hz @ 47K) (87hz @ 10K / 60hz @ 47K)
100hz has no band (108hz @ 10K / 92hz @ 47K) (125hz @ 10K / 85hz @ 47K)
150hz 2 blue bands (162hz @ 10K / 138hz @ 47K) (187hz @ 10K / 128hz @ 47K)
200hz blue band (216hz @ 10K / 184hz @ 47K) (250hz @ 10K / 170hz @ 47K)
300hz 2 white bands (375hz @ 10K / 255hz @ 47K)
500hz white band (540hz @ 10K / 460hz @ 47K) (625hz @ 10K / 425hz @ 47K)
1000hz light blue band (1080hz @ 10K / 920hz @ 47K) (1250hz @ 10K / 850hz @ 47K)
2500hz light green band (2700hz @ 10K / 2300hz @ 47K) (3125hz @ 10K / 2125hz @ 47K)
3500hz gray band (3780hz @ 10K / 3220hz @ 47K) (4375hz @ 10K / 2975hz @ 47K)
6500hz orange band (7020hz @ 10K / 5980hz @ 47K) (8125hz @ 10K / 5525hz @ 47K)

[Jack]

Randy

That is definitely an outlier. The lowest I have ever owned is 22k ohms with the Odyssey amps. Normal is somewhere between 47-100k ohms. I look over that chart and see what I can make of it but it may be hit or miss like I said to find what you like. There is a method Vandersteen uses with test tones and a meter to determine which of their passive crossovers gets you closest to the desired 80hz with their subs. It used to be listed on their website. 80hz would seem to be a reasonable starting point though. In fact on KEF's website they indicate 79hz to be a target but to allow for personal taste and room interactions.

Tips For Integrating Your Subwoofer and Speakers (https://us.kef.com/blog/tips-for-integrating-your-subwoofer-and-speakers)

[jadedavid]

Randy, From the specs you provided on the FMOD's the purple band at 70hz should do the job.
As Jack indicated, 10K is pretty low for a balanced input.
However I just received a VTV Purifi amp to try and it is 12K balanced on the input. Whereas my Pass is 30K balanced input.
Jack, do you know where I can find additional info on the addition of a resistor as you have previously mentioned?

[Randy Myers]

Randy

That is definitely an outlier. The lowest I have ever owned is 22k ohms with the Odyssey amps. Normal is somewhere between 47-100k ohms. I look over that chart and see what I can make of it but it may be hit or miss like I said to find what you like. There is a method Vandersteen uses with test tones and a meter to determine which of their passive crossovers gets you closest to the desired 80hz with their subs. It used to be listed on their website. 80hz would seem to be a reasonable starting point though. In fact on KEF's website they indicate 79hz to be a target but to allow for personal taste and room interactions.

Tips For Integrating Your Subwoofer and Speakers (https://us.kef.com/blog/tips-for-integrating-your-subwoofer-and-speakers)
Thanks Jack. I definitely do not understand the electrical engineering aspect of this hobby :). I have learned many things through my many years, but that is one that I have never grasped well. I appreciate your input and knowledge.

I have ordered (which they have not confirmed as of yet), XLR 70hz (purple) high pass filters. From the chart it looks like it would best approach the desired 80 range. It is a start and hoping for some improvements. It works good as it is but I've always thought the idea of having the main amp and speakers do what they do and letting subs do what they do without over lapping would be a more desirable way of running things :).

[Randy Myers]

Randy, From the specs you provided on the FMOD's the purple band at 70hz should do the job.
As Jack indicated, 10K is pretty low for a balanced input.
However I just received a VTV Purifi amp to try and it is 12K balanced on the input. Whereas my Pass is 30K balanced input.
Jack, do you know where I can find additional info on the addition of a resistor as you have previously mentioned?

Thank you. I appreciate the assistance. Hopefully the purple band FMOD's in XLR will work well!

[Jack]

jadedavid

I was always using Vandersteen subs with Vandersteen and other brands of speakers when I was using the high pass system so I just used the X1 filters that were sold through Vandersteen dealers. Over the 15+ years I used the subs I went through so many different amps I owned pretty much every value of X1 they sold from 10k to 100k. I still have the subs and the most of the crossovers but they are all SE. They are spec'd for the input impedance value of the amp on the outside but I don't know what values of parts on the inside. When you order from Ayre and Aesthetix the dealer tells them what the spec is for your amp and they add the resistor/capacitor to match to what the Vandersteen subs need before shipping. It is required that you use the high pass system with Vandersteen subs but when I switched to the Rythmik subs I just connected them high level and ran the mains full. One of the speakers I ran with the Vandersteen subs were the Offrande's and both they and them amp seemed to benefit from the high passing. I suspect your final version of the Offrandes would see some benefit too. I found this article and calculator on line for making the parts determination and wiring diagram but the actual calculations I will leave to someone with more EE background than I have. We've got several members here like Ralph(Atmasphere) and others that probably have a better understanding of this than I do as I depended on Richard Vandersteen's expertise.

[jadedavid]

Thanks Jack.
I am using a .o22 cap in series to my line magnetic amp which has an input impedance of 100K. This gives me a 6db roll off starting at 70hz.
Works really well with my Reynauds. This is in a single ended application.
A calculator is available at Learningaboutelectronics.com/articles/high-pass-filter-capacitor-calculator.php#answer1

[Jack]

The Offrande's are a great speaker. I actually owned the review pair from Bob's PFO review back in 2003 for about four years. When I bought my Abscisse Jubilee's I was actually calling Bob to buy the last ever pair made of the Offrande Supreme V2 that were sitting in the warehouse of the Canadian distributor. Over the course of a half hour discussion Bob talked me into buying the Acscisse Jubilee instead as he had just sold his Supreme V2's and swapped to the Abscisse. I currently have my eye on the new Grand Voce which would be the replacement for the Offrande as Jean Claude could no longer get the parts necessary to continue with the Offrande and no idea what parts he has in reserve though that should never be an issue. Will have to be after the first of the year though as currently far too many speakers around already.

[Jack]

Randy

I think you are probably going to be pretty close with the first try but your ears will tell you in the end. One thing to consider though as from looking at the picture of the balanced Fmods on the Harrison web page they look to be fairly long. So like the balanced Rothwell's they could over time put stress on the amps XLR connectors so best to start looking for something simple to prop them up like a piece of foam, etc. I ran into that issue with the Vandersteen X1's and had to swap out the SE input connectors on a Belle's amp after a couple of years.

[Randy Myers]

Randy

I think you are probably going to be pretty close with the first try but your ears will tell you in the end. One thing to consider though as from looking at the picture of the balanced Fmods on the Harrison web page they look to be fairly long. So like the balanced Rothwell's they could over time put stress on the amps XLR connectors so best to start looking for something simple to prop them up like a piece of foam, etc. I ran into that issue with the Vandersteen X1's and had to swap out the SE input connectors on a Belle's amp after a couple of years.

Good suggestion Jack. The Audioquest cables come through a cutout in the center of the rear metal panel. It is about half way up the height of the shelf. There is also a considerable amount of space behind the Hattor so I am thinking that the cables will get extra support.

The only unit that does not have a lot of space behind is the MBL. That sucker is deep!

[Jack]

Do the Fmods go on the amp or preamp end? The Vandersteen units went on the amp end. With the Rothwell's you could order them either way.

[Randy Myers]

I believe they go on the pre-amp end.

[Randy Myers]

Harrison Labs appears to be a good company. I left a message just to verify if they received my order. A nice lady called me back to tell me they did get my order and make these to order. Mine will be shipped Monday!

[Randy Myers]

So the High Pass filters arrived on Monday. Therefore the lady who called was incorrect :D, they didn't get shipped on Monday they arrived on Monday! I can't remember the last time something actually arrived ahead of schedule. :)

I listened for a little bit last night, only in mood for digital... didn't feel like changing records, etc. Hard to describe the differences and I am sure like most things break-in is going to come into play (the KEF's are probably not totally broken in yet :) ). I definitely liked what I was hearing. I would say everything sounded a bit more relaxed and open. Definitely added to the amazing disappearance act of these Meta's, it was even more so (which I was surprised about). The mid lows and bottom end was more defined with a complete lack of any kind of muddiness.

I have to pull out some of my better vinyl and really put this through its paces, but on first listen I have to say it is nothing but good improvements!

I also cannot say enough about the quality and service from Harrison Labs. I highly recommend their products.