Need to give some background on this.....
Been into hifi since my 20's, like 50 years come a long way. Been using a sub with DSP amp for the last 15 years....and I still learning how to optimise. Last episode came yesterday, when I spent the best part of a day going through many permutations. I got my setup sounding the best it ever has....but let me start at the the 1970's.

In those days, there was only once source....Vinyl Records (excluding FM Radio which had its following).....turntables were the transport.

I remember my first which was a Garrard SP25. This formed the front end of my first system ever. I soon became aware of its limitations, which mainly took the form of awful rumble. I really could not live with it and upgraded pretty quick...

This was a French turntable from ERA. It was a belt drive, and there was no rumble! What a relief.

I did notice, however, that the was a constant slight buzz from the motor. This was fixed to a very resonant steel plinth albeit isolated my neoprene. This was a limitation I could not live with for long.

My next deck was the iconic Pioneer PL12D. I loved everything about this deck. There was some slight motor noise which I found acceptable. Nevertheless, it wasn't with me long as I had bought it from a hifi shop that was owned by a mate of mine who wanted it back for another customer as they were in short supply.

He did replace it for me with one of these:

AR Research. Wow.......this was a fully isolated belt drive suspended deck. No noise from anywhere. However, I was not a fan of the primitive tonearm....anti-skate provided by the twist in the shielding cable as it exited the tonearm wire. This fussiness & fault finding was a sure sign I had been infected by the hifi-bug.

Around this time, I had a dabble with direct drives which were coming onto the market in the form of the Technics SL150. This was a perfectly engineered deck. Faultless finish and performance. It just had no soul, and sounded thin & uninspiring. I did discover later that this was partly due to the speed control, but that's another story!

Following on from the AR, Linn Sondek were grabbing all the headlines using a similar suspended sub-frame technique. I was fed up with all the hype, so went for the Logic DM101 instead. I was really impressed with the engineering and much preferred its industrial look vs the Linn. This deck stayed in my stable and was only sold recently.

Throughout all this time, I was really unaware of what I was listening to. I had not developed the skill to critically listen. It either sounded good, or sounded bad. My next deck changed all that:

What can I say? I felt real proud to have this deck in my possession. I was living in Hertfordshire at the time, and picked it up direct from the Borehamwood factory. John Michell told be how to set it up, and I had a grin on my face every time I played it. I felt this was the pinnacle of turntable development, and I was there. What made me want a Lenco?

This was one of those hifi moments that proved to be life changing. I started to get into hifi DIY as I had to make a plinth for it. There was a Lenco Heaven forum full of enthusiasts making these incredible plinths. This was my own first attempt and the story carries on from HERE if anyone is interested on how I came to develop my own turntable and eventually market it, along with my Terminator tonearm! Suffice it to say, I was hearing things in the Lenco that were not present in the particular detail & separation in the bass. Slam and dynamics that were missing in the belt drive. This is the thing with don't know what you're missing  until you hear it. While working on Salvation I developed critical listening. I could hear the differences between the Lenco & Gyro so knew what I was after. I went on to make my own turntable because the Lenco was noisy vs the Gyro. Salvation had all the slam & dynamics of the Lenco, but was quiet. It was also more refined & authoritative. It was a direct rim drive without speed control. I learned speed control was detrimental to the sound, as an example, the Technics sounded thin. Hearing the Lower & Upper bass advantage the Lenco had over the Gyro, I would play sound tracks that repeatedly showed this distinction, tweaking as I went along until I had maximised the separation and attack of the leading edges of bass notes. I came to appreciate the frequency range between 60-300hz. This gives the music its slam & dynamics, and makes a system sound dead or alive. The added bonus I was after was tone & detail. 

Anyway, you may ask what this has to do with setting up a subwoofer. With my HiFi DIY bug firmly taking hold, I had a go at developing my own speaker....also catalogued on the Lenco Heaven forum HERE. As you can see in this, I was working with a baffle-less subwoofer for years, and integrating this with a now commercial bookshelf speaker was the challenge....and this would apply to anyone trying to incorporate a subwoofer into their setup. The things I discovered on my turntable journey can also be applied to my sub-woofer journey!

My relationship with subwoofers goes back to the early Open Baffle Bastanis days when I was using a pair of boxed 12" sealed units. There wasn't much adjustment as it was controlled by a simple plate amp. I remember them bottoming out at the first sign of 'deep' bass. The sequence of pictures below starts with the Bastanis Prometheus with a 15" sealed sub, and finishes with my baffles-less clamshell arrangement that I use today in 18" format coupled to the Focal Shape Twin studio monitors.

I really had little clue what I was doing with the above designs. These open baffles have nothing in terms of slam vs boxed units, and operating the subwoofers to cross with full range units meant they were crossing near 300Hz. I mean they worked, and at the time I thought they were great....but the sound they achieved does not come close to my present day set-up. As i said before, you don't know what's missing until you hear it! I have to insert a little caveat here  that hifi is such a personal subject, one size does not fit all. For me and the type of music I listen to, getting the upper bass right, ie., slam, dynamics, detail, texture is the foundation for a system that is a pleasure to listen to every time I switch on. Important the sub is not overpowering or obstructing the rest of the frequency range.

There were a few things about choosing the boxed speaker that were important in achieving the best integration. I needed to have control of the lower extremity bass it put out so as not to incite modes in my room. I have one at 50hz. If you dont know where the Modes are in your room, I can suggest a frequency generator app you can download to your phone and connect to your system. I use the app "HZ" which can be downloaded from Google Play. This will generate a sound wave at any frequency you want. You will find the room modes usually between 20-80Hz. You will know its a mode because the frequency will get louder. Make a note on where its loudest. That is your room mode, and you could have several. 

Many of the bookshelves I tried tended to extend too low. I guess the manufacturers would try to compete with who could produce the most bass from a small box, but the quality tended to be loose and bloaty. A few of the smaller boxes really suited my room insofar as they didn't incite any room modes  and rolled off nicely. Unfortunately, they would bottom out before they reached the SPLs I was after. This was the main decision that made me go with an active speaker. Most of the active designs had built in High Pass Filters (HPF) where you could actually select where you wanted the speaker to cut off. I tested several of these including Acoustic Energy AE1's, Kali Audio In-5, Elac Navis and Focal Shapes. The Kali's & Focal's are classified as Studio Monitors.

I dismissed the AE1's early on because they had a fixed HPF and I had no control over selecting cut-off frequency. The other 3 had controls so I could cut the bass extension and avoid inciting the room modes. I eventually selected the Shapes  because I preferred the bass from the passive radiators rather than the reflex port on the Navis & Kalis. Listening critically I could notice the bass from the ports tended to veil the mids. The Shapes were also more forward and dynamic which I preferred.

Now I have laid the groundwork, I can finally start on the subs. You know I have been through many designs, from boxed to open baffle, U frames, the Bastanis Ripole and Baffle-less. Keeping it short, I stuck with the baffless Clamshell arrangement because this was the most room friendly and produced the most uncoloured and open bass I ever heard. Don't take my word for it though. A whole thread HERE on other people's experiences.

The first thing I did was to run the Focal Shape Twins on their own and set the HPF to the lowest point that did not incite any room modes. I found the 60Hz setting to be perfect. You really want the Twins to produce as much of the bass as possible as this is what gives the detail and dynamics to the system. The subs are only going to produce rumble and shake, but you don't want this to encroach on what the Twins are doing in any way.

At this point, a frequency reading of what the Twins look like would be useful. The program I use for this is XTZ Room Analyser Pro which is obsolete now, but serves my purposes. Most people are using REW.

The critical part is the roll-off and slope. We can see this happening at 63hz. We want to try to get the subs to blend in with this seamlessly. I am using a Behringer NX6000D amplifier with built in DSP.  This is connected to my laptop via USB & all parameters  can be accessed in real time by a free simple Windows downloaded  from Behringer called "NX Edit". 

There are dozens of permutation you can chose, for example crossover slopes:

In addition to these slopes, the crossover point can be moved to best match the  Twins. This would be a trial and error process than can take the best part of the day involving changing the parameters and listening to a track you know well.

One of my favourite test tracks is the band Monolink's  "Rearrange My Mind". This track is rich in upper bass detail, texture & dynamics as well as deep bass. There is plenty of detail going on elsewhere too.

I found too gradual a slope missed out on the floor rumble, and too high a cross over obscured detail from the Twins. The gain also needs to be adjusted to give the correct balance between Woofer & Bookshelf.

This process is time consuming and down to personal preference.

In my case, I narrowed it down to these slopes:

Of the 2 selections, I preferred the bottom steeper slope which was better defined and gave a cleaner result. The top selection gave a warmer less detailed sound.....again, personal preference.

After further listening tests, I noticed room modes were getting in the way affecting performance.
This track,  Variations by "Sunmotion Orchestra" toggles between 40 & 50hz bass riffs, and will tax room modes! I found the 50hz too loud, and the 40hz too quiet.

I opened my PEQ page and corrected with a slight boost and notch. This is how it affected my crossover:

My other setting involves some no baffle compensation to give the bass a boost and compensate for woofer roll-off. I use the Dynamic Eq page for this and it works similar to a loudness button where bass lift is increased at lower volumes:

The final result on graph looks something like this. Bear in mind I had to position the mic low down to capture the woofers so the mids are skewed....but sonically, this gives me a great real-world result.

I will live with this setup and tweak further if I find it necessary.

I hope you have found this blog interesting and informative. If you feel there are sections that need clarifying, please send me a contact email at