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Studio SOS: Lack Of Low End

Paul Allen
Published July 2017
By Hugh Robjohns & Paul White

Some acoustic treatment was already in place, but the sound from the monitors was still cause for concern.Some acoustic treatment was already in place, but the sound from the monitors was still cause for concern.

A reader’s home-studio monitoring suffers from a lack of low end and poor stereo imaging. Can the Studio SOS team track down the cause?

Paul Allen must have the ultimate keep-fit recording space — built into the loft space of his Southport house, the studio is accessed via two flights of narrow stairs. As is often the case with such spaces, one wall slopes from ceiling height down to around a metre or so above the floor to accommodate the slope of the roof, and in this instance there is also an alcove off to the right-hand side housing a wash basin. Overall, the main part of the room measures five-metres long by three-metres wide and two-metres high, with the side alcove occupying just over one square metre.

Paul called us in as his mixes were not translating well when played on other systems. He was also unsure of how to get the best guitar sound using amp simulators, as he always found the results too ‘fizzy-sounding’. His general setup seemed OK, with small Genelec 1029A active monitors perched on top of a pair of Audio Pro hi-fi speakers sitting directly on a home office-style desk. These speakers all fired down the long axis of the room with the sloping ceiling behind them. Some soft furnishings at the far end helped reduce sound reflections. Paul had also stuck some fairly thin acoustic foam to the sloping part of the ceiling above his desk, and had a few sheets left over, but in reality the acoustics of the space still left a lot to be desired. We chatted about the problems and potential solutions while Paul offered us coffee and cookies (he also had some Chocolate HobNobs in reserve just in case).

The core of Paul’s system is a PC running Sonar with a Focusrite Saffire Pro 24 interface, though he also has a fair amount of outboard gear including a rackmount Line 6 Pod Pro rack, an E-mu Proteus 2500 and a PreSonus Digimax D8 eight-channel preamp (used to expand the Saffire via its ADAT connection). A Fostex VM200 mixer acts as a secondary monitor controller for the Audio Pro speakers, which are powered by an old integrated hi-fi amplifier. Paul had also acquired various second-hand Pro Tools interfaces including a 002 Rack and a brace of 96 and 192 I/O interfaces — although none were in use at the time of our visit.

Lofty Ambitions

As usual, we started by trying to get an idea of the sound of the room and monitoring by playing various tracks from Hugh’s test CD, and it became immediately apparent that the imaging was extremely vague and unfocussed, and the bass sounded very odd. The first thing to check was the response controls at the rear of the monitors, as unmatched settings can cause weird acoustic effects like this sometimes. However, the dip-switches on both speakers were set the same, with only the HF roll-off option engaged, as they seemed a little bright for the room when set to the flat position.

Poor imaging can be caused by strong local reflections, of course, and that was quite a likely issue given the untreated side walls and that sloping ceiling. The oddly weak bass could well have been a result of the fact that the desk (and thus the Genelecs) was about a metre from the back wall. As low frequencies tend to radiate omnidirectionally, spacing speakers away from the wall effectively creates two sources of low-frequency sound: direct sound from the speaker, and a reflection from the rear wall. These two signals arrive at the listening position at slightly different times and thus with different relative phases, resulting in a substantial dip in the low-frequency response at a frequency related to the spacing between speakers and back wall.

The obvious solution was to move the table back closer to the wall (which moves the response dip up in frequency and makes it much weaker), but we put that on hold until after we had sorted out other room treatment work, as access was needed to the rear of the desk to plug things in.

The fact that the desk (and monitors) were pulled some way away from the wall wasn’t helping!The fact that the desk (and monitors) were pulled some way away from the wall wasn’t helping!

On Reflection

Our initial listening made it very clear that we needed to tame early reflections from the front and side walls of the room, and we also felt that the Genelec speakers could use a better means of support to provide vibration isolation from the desktop. Fortunately, Universal Acoustics had kindly given us a box of two-inch by two-foot square foam panels plus a further quantity of one-foot square panels to use on this job — a big thanks to UA's Paul Eastwood for getting these to us at short notice. We deployed a mixture of these two panel sizes on the wall behind the speakers, with two more of the larger squares on the right-hand side wall, forward of the alcove, to cover the mirror point. The left-hand mirror point coincided with a pair of cupboard doors so we glued a number of the smaller panels directly to the doors so that they could still be opened. A couple of sheets of Paul’s thinner foam were also fixed to the back wall of the alcove above the sink. At this point we went out for a break in the fresh air to escape the glue fumes!

Polarity Ensues

Once I resumed sticking up tiles, Hugh investigated the odd imaging issues from the Genelecs, which he thought might be down to some form of phase issue. This kind of problem is trivially simple to track down given a monitor controller with polarity reverse and mono buttons... but sadly neither the Saffire Pro 24’s hardware nor control app provided these functions. Consequently, there was some faffing around ripping the test CD into Sonar, and then splitting tracks to allow a polarity reverse to be switched in and out on one channel, and a mono sum to be created. However, when this was achieved it was easy to confirm that, with a dual-mono signal going to the monitors, a reasonably solid and focused centre image could be created when a polarity reversal was introduced in one channel — but the headphone output on the Saffire interface definitely sounded right without the polarity inversion. So, clearly, there was a polarity reversal in one channel somewhere between the Saffire’s outputs and the Genelecs.

With some extra acoustic panels put up, the monitor speakers placed on stands slightly nearer the wall and — most importantly — the faulty monitor identified, the sound from the monitors was considerably more stable.With some extra acoustic panels put up, the monitor speakers placed on stands slightly nearer the wall and — most importantly — the faulty monitor identified, the sound from the monitors was considerably more stable.

A quick visual inspection of the cables suggested they were both OK, and this was subsequently confirmed with a digital multimeter. This left us with the only possible conclusion — that something was amiss in one of the speakers — but Hugh has been to Genelec’s factory in Finland a few times and confirms that their quality control is extremely good, so the speakers were very unlikely to have left the factory with such an obvious phase problem.

It was at this point that Paul volunteered that he’d bought a single used Genelec 1029A off eBay as a spare, but in moving his studio to the new room it was possible that he’d accidentally mixed up the original pair with this spare. So we set about swapping the spare for each of the Genelecs on the desk and quickly found the original pair as they produced a nice solid, focused centre image!

At a guess, it would seem probable that the ‘spare’ 1029A had received a new driver or amp pack at some point in its history, and when put back together the wires to one or both of the drivers (but most likely the bass unit) had become swapped somehow, introducing a polarity reversal. A polarity reversal of just one driver would also account for the rather odd sound that was not quite completely out of phase, but definitely wasn’t right. Frustratingly, we didn’t have the required Torx screwdrivers to get inside the speaker to find and resolve the problem, nor Hugh’s acoustic test set, which would have identified which driver was out of phase. So the rogue 1029A was labelled as dodgy and put back into storage awaiting further exploration.

Paul White has a word with one of Paul Allen’s guitars...Paul White has a word with one of Paul Allen’s guitars...Certainly, this odd phase problem would account for why Paul’s mixes weren’t translating correctly to other speakers, partly because everything sounded spacey and unfocussed, but also as the low end from the two speakers was doing its best to cancel itself out, making it impossible to judge the low-end balance of mixes at all.

Once Hugh finally professed himself happy with the stereo imaging — which should be one of the major strengths of small speakers like the 1029A — we moved on to providing a more solid mounting for them. Paul already owned some Studiospares adjustable speaker stands, so we moved the Audio Pro hi-fi speakers onto them, positioned directly behind the desk, and then raised the Genelec 1029As to ear height on a pair of IsoAcoustics platforms (thanks to IsoAcoustics and SCV London for arranging these), which we assembled using the longer of the included bars. We then angled the speakers in slightly so as to aim them at a point just behind the monitoring position, with the hi-fi speakers directly above and behind them to provide a useful alternative checking system.

Going back to the test CD showed that not only had we got back the missing low end, having resolved the phase issue, but the sound was now noticeably tighter and much better focussed with the early reflections under control. Paul made a wise choice in the 1029As because they don’t have too much bass extension for a smaller room, but having said that, it is still surprising how much low end you can get from such small speakers once they are mounted on a good platform.

...And My Axe!

...while Hugh Robjohns threatens an electric bass with a soldering iron....while Hugh Robjohns threatens an electric bass with a soldering iron.Paul seemed relieved that his mixes now stood a better chance of sounding right outside of the studio, so we spent the remaining time resolving some of his other issues.

He had some problems with his guitars — his Mex Telecaster and his Epiphone Les Paul needed both truss-rod and bridge-height adjustments to cure fret buzz and other action-related problems, which was easy enough to sort out once we’d found the right Allen keys. While I was doing that, Hugh picked up one of Paul’s basses to play with and noticed it had a loose output socket and volume control. In dismantling the control plate to tighten the pot and socket with an adjustable spanner it also became clear that their previous movement had caused the soldered joints of the internal earth wiring to fracture in a couple of places, so he fired up a soldering iron and remade all the connections to restore the instrument’s reliability.

Going back to Paul’s ‘fizzy’ guitar-sound problem, I suggested that instead of getting the computer or Pod to do all the work, he might get better overdrive sounds using an analogue overdrive pedal playing into a cleaner amp simulation. To test this theory we used one of Paul’s analogue overdrives and then patched that into his audio interface, loading up a few different guitar amp models to try. Paul particularly liked the combination of the analogue overdrive in his T-Rex Soulmate and the Scuffham S-Gear amp sim, which is included as part of the Slate ‘Everything’ bundle. Repeating the test relying entirely on emulated amp drive didn’t sound as good to our ears, so it seems the theory held up in practice.

After that it was just a matter of clearing away the chaos we’d created, and setting the Satnav for home.

Reader Reaction

Paul Allen in his studio.Paul Allen in his studio.Paul Allen: “I’m really grateful for Paul and Hugh’s help and can’t thank them enough for sorting out the issues in my home studio. I think it would have taken me a long time to identify the phase issue with the monitor and I’ve learned a valuable lesson about testing second-hand equipment before incorporating it into my setup. I think I will be purchasing a phase tester in the near future!

“The acoustic treatment and IsoAcoustics speaker stands have made a significant difference to my mixing environment and I’m now enjoying a much more focussed sound with improved bass definition. Even though I have read it many times in SOS, I’ve underestimated the difference such treatment can make and I would recommend to anyone before they reach into their wallet to purchase more equipment to invest in some acoustic treatment first. Many thanks to Universal Acoustics for the acoustic foam panels and IsoAcoustics for the speaker stands.

“I appreciated the time Paul and Hugh took repairing and setting up my guitars and I think we managed to achieve some very convincing guitar tones with the combination of my analogue pedals and amp sims. I love my new setup and I’ve already started to notice a real difference in my mixes. Thank you SOS.”

The Studio SOS Book

The Studio SOS Book is on sale in the SOS web shop. Have you got your copy yet?Using case studies to illustrate common problems, this 306-page book brings together a wide range of real solutions that are both affordable and easy to implement.

Written by Paul White, Hugh Robjohns and Dave Lockwood, the SOS team impart easy-to-understand, organised troubleshooting advice on a range of topics. Learn how to rid yourself of monitoring problems so you can accurately hear what you’re mixing, how to enhance the sound of your recording space, and how to perfect your instrumental and vocal recordings. Spend less time re-recording and mixing, simply by improving your room with advice from the guys who have seen it all when it comes to make-do small studios.

Get your copy from: www.soundonsound.com/shop/books/studio-sos-book

Published July 2017