Pass the wrench.

While browsing around the countless audio websites I found a recommendation for a track which was considered perfect for matching subwoofer bass to the speakers.

Just out of curiosity I connected my old 16-46 PCI/NSD SVS cylinder sub to the Front speaker output sockets on my Creative SB Live! sound card and switched on: No speakers. Just the sub. Normally the speakers dominate the reproduction but this time I wanted to compare how the SVS and the IB sounded when working alone on the same bassy track.

First I rattled most of the loose objects in the room with the SVS while reading an average of 85dB(C) on the Galaxy 140 SPL meter at the listening position. Then I swapped the cables over to the IB subwoofer via the Naim preamp and EP2500. I didn't bother to turn on the Naim speaker amp. Though I could just as easily have muted the Main speakers on the CX2310.

The difference in presentation from the IB was immediately apparent and really quite shocking. The percussive leading edge of each note played on the bass guitar was suddenly fully exposed by the IB. There was no hint of this from the SVS. At times one could (almost) describe the bass guitar on this track as a drum with multiple tones as the bass player plucked very near the bridge of his instrument. The reproduction was lighter on its feet with seemingly much more upper bass present. Yet the guitar and vocals I could clearly see on the monitor were completely absent. All I could hear was a realistic sounding bass guitar. The SVS had sounded very deep, soft, muffled and rumbly without any speakers to support it. The IB on its own was playing the same track at exactly the same level but seemingly reaching into a higher register.

The strange thing is that the IB has a 24dB/octave active crossover while the SVS uses only 12dB/octave on its low/line level connections. Both were set to 80Hz on their crossover's respective scales. There was no lack of powerful, deep bass from the IB but it sounded far more open and natural despite the absence of speakers. You wouldn't want to listen to the SVS for very long on its own since it sounds almost monotonically boring even when playing only a bass guitar. The IB sounded as it was playing full range but was obviously not. An unexpected result of this straight comparison.

I used to love the SVS when it was my only subwoofer. It sounded so detailed, powerful and expressive on both music and films. I even put a website together to try and explain its amazing performance. (now erased by Orange as it ate up earlier ISPs like a killer shark hunting baby seals) Now the IB leaves the SVS completely for dead on sound quality, accuracy and its incredible ability to reproduce a believable version of reality.

The percussive leading edges were finding some rattles around the IB manifold which were easily cured by re-tightening all the driver fixing screws with an Allen key/wrench. Almost all had loosened slightly and responded to a turn, or two, to snug them enough to grip the rubber driver seal without distortion. The nice thing about furniture screws is that they use a hex socket which is very safe in use. Even a clumsy mechanic would have a real struggle to poke an Allen key through a cone. He would also have to be truly brutal to mar the nice chromate finish on the large diameter heads of these screws. They hold their finish very well and still look like new.

It is odd how one's ears become educated over time as components arrive in one's system only to be replaced by others later on. My old, home-built pair of 6th order series, passive, bandpass subs sounded great to my ears. I used them to support Linn Kans for quite a number of years until I bought the SVS. Then suddenly they sounded woolly, muffled, soft and rumbly compared with the SVS. I would say on this particular test the IB is an order of magnitude better than the SVS. The SVS has no reason to continue its existence in our AV room but my wife likes it and won't let me sell it. This, despite it never being l played from one year to the next these days. It is so eclipsed by the IB that I would have no reason to listen to it except perhaps to supplement my silly little computer speakers. Though only when I can't be bothered to turn on the entire audio system to listen to one track I might find on the internet. Usually the full system is playing anyway while I browse, scribble my blogs and post my nonsense on the forums.

If it is of any interest the Galaxy SPL meter was reading around 100dB(C) at the IB manifold mouth for the 85dB(C) average at the listening position about 9 feet away. Meter settings were C-Slow and the top scale of 80-130dB. The SVS was reading several dB lower at the skirt at around 93-95dB(C) at 8 feet from the listening position for the same level as the IB. Perhaps I should also have read the SPLs coming from the port at the top but it would probably have been outside the bandwidth of the bass guitar.

Interestingly? My wife complained of the loud repetitive bass down in our lean-to greenhouse/ conservatory. Whether this was a result of the SVS playing at frequent intervals I have no idea. Normally she doesn't moan about the IB bass. For some reason the SVS carries more despite having a very similar response curve and shorter LF reach. It rolls off roughly 8Hz Hz higher than the IB. Perhaps being down firing it puts more energy into the rather flexible stage on which it rests? Though it made no audible difference to my ears to place it on a massive, round, concrete slab resting on carpet off-cuts for better isolation. So I got rid of the slab again.

The perceived difference in frequency range really demanded further examination with REW.

Here are the traces of IB and SVS superimposed using (all) Measured: I used the Galaxy 140 SPL meter at my normally seated ear height at the listening position as the test mike: I also ran a few sweeps on both subs to give a firm line to the graphs and to ensure no errors had crept into my testing methods. These were the settings I had lived with for quite a while. In case of doubt the SVS is the green line. The IB is the wider, purple curve.

The difference in upper frequency range is very obviously in favour of the IB. It is also more extended into the deep infrasonics. While the big SVS cylinder rolls off very rapidly below its nominal tuning point. Which is only to be expected from a reflex enclosure. The IB being a (large) sealed box follows a much more gentle slope.

The IB really was playing much higher in frequency than the SVS due to gross inaccuracy in the marked roll-off point on the CX2310 dial. This required the adjusting knob to be reset right down to an indicated 50Hz! The SVS needed to be raised just a little to 90Hz on the crossover dial to match the REW 80Hz roll-off curve. Unfortunately the blue line representing the roll-off curve on the REW graphs doesn't show on (all) Measured. The graph (below) shows the results of careful adjustment of both sub's responses to follow REW's indicated 80Hz roll-off curve as closely as possible. (even if it doesn't look like it!) :-)

In the next REW graph (below) the response levels have been adjusted on the graphs to match each other for a better response comparison over the major power band. There isn't any obvious meeting point between the two curves at higher frequencies. It is difficult to confirm whether there is any difference in the steepness of the upper roll-off curve of each sub. Comparing crossovers of 24dB/octave against 12dB/octave one might have expected the IB to take more of a nosedive with rising frequency.

I think the adjustments required adequately explain the not-inconsiderable, perceived difference in frequency range between the SVS and IB. I really wasn't being fair to the SVS on my listening tests on the bass guitar track. Since it rolled off so much earlier than the IB with the previous settings. Now I will have to do another listening test of that same track. I'll update when I have had a chance to do this properly tomorrow. A quick listen suggests the subs are much better matched now. i.e. both sound very deep, rather soft and rumbly!

BTW: All REW traces have had 1/3 octave smoothing applied. Calibration and test level was 75dB for both subs. With slight adjustments to levels applied later to the graphs shown above.

Update after new listening tests: Rain stopped play! After I managed only a couple of exchanges between the IB and the SVS a terrific thunderstorm passed over. The forecast was for warm sunshine all day! Grrr?

Initial impressions are that the situation has been reversed. With the SVS now having a wider bandwidth. At least that's how it sounds subjectively. The hard attack of the leading edges was almost absent from both subs now that they were similarly rolled off. I could hear strange singing in the background from the SVS but the IB remained totally silent to all but the bass guitar. The SVS port can be made to act as an organ pipe if fed suitable material. It is proving hard to kill the buzzes produced by the SVS in the objects beside which the cylinder stands. The IB excites no such unwanted effects on this track. I had a chance to run a couple of REW sweeps to confirm the rough match in their nominal 80Hz roll-offs. Nothing had changed overnight from the graphs which appear above. I shall investigate these subwoofer comparisons further when time allows.

2nd Update: I have had much more time to listen to the SVS and IB together and separately. I'm now running the SVS from the Subwoofer Out XLR on the back of the CX2310 active crossover. This gives me "remote control" over the roll-off point and gain from the listening position with the SVS' own crossover bypassed.

I have also run a number of REW tests on the effect of adding the SVS to the mix and played about with phase adjustments. I discovered that since the last changes to my IB it now works better when the phase is reversed to the speakers. I have also pushed my speakers back by a foot or so.

The SVS is certainly powerful low down but completely lacks the IB's clarity. On certain organ works (like the Franck double CD mentioned earlier) with the big pipes playing the SVS can be turned up far enough to make the room shake really violently. It is just that the SVS plays only loud tones. Without any indication of timbre or the interplay between the great pipes. There is just no suggestion (at all) of the pipe's character or how it actually speaks. I played the same little piece of a heavy pedal section over and over again. I tried with and without the SVS and on its own and at many different levels. Try as I might I simply cannot get the SVS to sound like an organ. It sounds more like a soulless tone generator. It cannot manage the complex waveforms at the low frequencies at which the IB excels. One particular big pipe had a hard edge on the IB but this went completely unnoticed on the big SVS cylinder. It is probably just as well there is no real comparison or the work involved in building and installing an IB would be wasted. It might be entertaining to try an SVS Ultra to see if it has what it takes to play like a real organ. Other IB Cult member's comments would suggest otherwise.

My latest listening tests have proved yet again that it is not enough to play deep tones very loudly. It must also be done with finesse and clarity if it is to mean anything at all. Those who enjoy organ music need have no doubt that the investment in time and effort to build an IB will be well rewarded.

Now I know that having another subwoofer in the room does not wreck the response curve I may finally go ahead and install four more drivers in two separate manifolds. My earlier tests seemed to suggest that a massive trough would be produced in the frequency response. Depending entirely on the second sub's separation from the IB. Reversing the phase of the SVS relative to the IB solved this problem to perfection resulting in a broad, flat response at the listening position when both subs are working. See: the Port open 180 curve below. This is with the SVS just inside the right speaker.

Click on any image for larger version. Back click to return to the text.

Pottering around amongst the You Tube videos I discovered a huge variation in SQ so it pays to choose tracks carefully. I have discovered videos of many of my favourites by Clannad and Loreena McKennitt. The latter has such perfect breath control and wonderful variations in her voice. I never tire of listening to her CDs. Her version of "Greensleeves" on the "The Visit" CD album is very emotive and powerful. Reminding me rather of Kate Bush's stunning rendition of "Women of Ireland" on the first of the Celtic Circle double CD series (on CD2). Sinéad O'Conner has similar abilities to sound all soft and "girly" one moment and hard edged the next. I am not a great fan of hers but do like some of her work.

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