Gotham Review by Alan Taffel in The Absolute Sound

Petrov -- Sun, 09/14/2008 - 22:00

I enjoyed reading Alan Taffel's review in last month's The Absolute Sound. In his review of the Gotham subs he said: "I set out to achieve the best blend with my main speakers", and : The subs should not "intrude on midrange purity". In his article on sub setup he said: "Instead of trying to pressurize a room...focus on the natural integration of sub with both the room and the main speakers", and: Use "reference material and fine tune by ear".

I was wondering if a detailed account on how he actually achieved this blend could be helpful...what reference material, what songs and what exactly to listen for in the songs. I inferred that he places the subs close to the mains and then moves them in increments and listens to the difference. Could a diagram of the listening room with dimensions and speaker placement be insightful?

In a multichannel setup, does the process change? What crossover points do you use, what is the relative level between subs and mains.

When using a real time analyser, what do you look for?

I know that this is alot to ask; however, I feel that a detailed account of his setup process could be very helpful in the difficult area of 250 Hz and below.

Thank you,

Peter Wainwright
pcwainwright [at] bellsouth [dot] net
peter [at] theaudiowarehouse [dot] com

Steven Stone -- Mon, 09/15/2008 - 09:25

The issue Alan appeared to have was one of integrating a full-range speaker with ports with sealed box subwoofers.

Sealed boxes and ported boxes have different ways of propagating bass.

Alan also wanted to keep his full-range speakers running full-range.

In a more usual arrangement, with a crossover used on the mains, it's less difficult to integrate subs with full-range speakers.

I have no problems integrating four subs with my Dunlavy SC-VI speakers, which measure flat to 25 Hz. But I cross them over at 50 Hz using the internal crossovers in a Meridian 861.

In my other room I have Genesis 6.1 surround system (which have built-in servo subs in the front L&R speakers). I cross them at 60 Hz. This room has a two JL f-112 fathoms as well as two Genesis subs (in addition to the two in the mains). I run the subs in stereo with three on each channel. With a Lexicon MC-12 HD's internal crossovers I have no trouble integrating the subs and the mains.

In both systems I can turn the subs on and off while playing chamber music or a single singer and guitarist and you won't hear a smidgen of difference to the overall harmonic balance or midrange timbre.

I don't use an RTA, but instead a B&K reference sound pressure meter (which measures far more accurately than a the ubiquitous Radio Shack meter in the bass). You can also use your ear coupled with a good sine/sweep recording (the 861 has a built-in sweep).

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

Alan Taffel -- Thu, 09/25/2008 - 16:34

Mr. Wainwright,

I am glad you enjoyed my review of the JL Audio Gotham subwoofer. You are asking a lot of good follow-up questions, and I will do my best to answer them without writing a treatise!

Achieving proper blend between a subwoofer and main speakers is both art and science. I covered quite a bit of this in my "How to Set Up a Subwoofer" article. The science part has to do with avoiding corners (which excite every room resonance mode) and with choosing a subwoofer -- or preferably a pair of subwoofers -- that match the main speakers' characteristics as closely as possible. Since, as Steve points out, sealed and ported boxes propagate bass differently (not to mention having different decay and damping characteristics), it makes sense to stick with the same design for both main speakers and subs.

I also advocate placing subwoofers the same distance from the listening position as the main speakers in order to time align all sound sources. Note that time alignment is NOT the same as matching phase, as it is possible to have one with out the other. Having the subs flank the main speakers is simply a convenient means of ensuring time alignment, but it is by no means the only option. Other placement techniques -- described in this very Forum category -- are completely valid, but I'd add the criteria of maintaining time alignment.

Before I get to the "art" part of the equation, which seems to be the thrust of your questions, let me comment on Steve's post. I am somewhat of an obsessive purist when it comes to main speakers. I will not abide the addition of a subwoofer compromising main speaker sound even a little. For this reason, I would never subscribe to the approach Steve uses. ANY crossover on the main speakers will compromise their sound. If you use the high-pass filter included in many subs (though not the Gotham), you are subjecting the main speakers to a crossover circuit of unknown quality. Digital crossovers in upstream controllers are theoretically perfect, but if the source is analog (e.g. - a turntable or CD player), they require an A/D conversion of both the bass and the main speaker frequencies, and then a conversion back to analog. Obviously, this will compromise the sound, too. This, I believe, explains why Steve does not hear, in his configuration, a difference in the main speakers when he turns the subwoofer off: the mains are not running pure in the first place.

For me, the only way to avoid an impact to main speaker purity is to avoid crossovers, which means running them full range. That, in turn, means a substantial amount of subwoofer tuning by ear. Start with the specs of the main speakers and note the 3db down point at the low end. This is going to be the approximate correct area of the crossover between the mains and the sub, as set in the sub's low-pass filter. Here is where the "art" comes in, because the exact crossover frequency will have to be determined by ear through trial and error. Closely related, of course, is the relative level between sub and mains. One can get this set perfectly when using a digital controller and digital sources, but for analog sources and the mains running full range, it's got to be done by ear. Playing sweeps of test tones and monitoring them with a meter can be helpful in setting levels and identifying bumps or dips.

By the way, even without a crossover on the mains, some subs will still pollute midrange purity. This is because the sub has an ill-behaved low-pass filter that is allowing upper harmonics to "escape". I always make a note of this phenomenon when it occurs, as does JV, and I wish every reviewer did so.

I use a variety of test material throughout the fine-tuning process. Different tracks tell me different things. "Ghosthack" on Kenji Kawai's "Ghost in the Shell" CD allows me to listen to the decay of a single drum note and assess whether it is natural or truncated. The electric bass solo at the end of Peter Gabriel's "Don't Give Up" from "So" has a distinct resiny character that should come through cleanly. The Michael Wolff trio's "Jamaica Turnaround", from their indispensable "2 am" CD, has an acoustic bass line that jumps up, down, and all around. The key here is that the timbre and volume of the bass notes should not change with their frequency. Finally, as noted in the review, the organ at the end of the "Pie Jesu" from the Atlanta Symphony recording of the Durufle Requiem is a great test of bass extension, power, and accuracy.

I hope the above proves useful. When you do get the blend right and locked in, with no midrange impact, all the trouble feels well worthwhile!

Alan Taffel
Senior Writer
The Absolute Sound

Alan Taffel
TAS Senior Writer

bherlihy -- Wed, 01/27/2010 - 07:10

could someone tell me what TAS Number this article was in?

Paul D. (not verified) -- Thu, 02/25/2010 - 20:37

Alan,

I am in the process of purchasing a pair of JL Audio subs and was reading your article again on the Gotham's to see what your procedure was to set them up in your room. You reference an article you wrote "How to set up a subwoofer" but I cannot locate it on the AVGuide website. Can you provide the location where I can find this article online?

Thank you,

Paul D.

Paul D. (not verified) -- Thu, 02/25/2010 - 20:47

Alan,

I am in the process of purchasing a pair of JL Audio subwoofers for my 2 channel system and decided to read your article on the JL Audio Gotham again. I was looking for information on how to set up a subwoofer and you provided the web address for an article you wrote on this subject. The problem is that the web address is no longer valid. Can anyone provide me with a new web address that contains this article or send me a copy?

Thank you,

Paul D.

Steven Stone -- Thu, 09/25/2008 - 16:55

Alan Writes: Quote:Digital crossovers in upstream controllers are theoretically perfect, but if the source is analog (e.g. - a turntable or CD player), they require an A/D conversion of both the bass and the main speaker frequencies, and then a conversion back to analog. Obviously, this will compromise the sound, too. This, I believe, explains why Steve does not hear, in his configuration, a difference in the main speakers when he turns the subwoofer off: the mains are not running pure in the first place.

While this is certainly true for analog sources, for digital sources, which are already in the digital domain, there is no initial A/D conversion, so the "not running pure" is not entirely correct.

I maintain that with digital sources using a digital crossover (especially the ones in the Lexicon MC-12 HD or Meridian 800/500/G series) will improve a system's sound, not detract from it.

Some adjustment by ear is and will always be necessary to get the best blend, but by removing low bass chores from the main's amplifier and from the mains themselves you gain substantial head-room and dynamic agility.

Why ask a midget to lift 500 lbs. when the strongman is just standing there waiting to do the job? :)

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

Miguel Esteves (not verified) -- Thu, 05/28/2009 - 14:45

I understand both positions and would like to implement a mix of them in my new media room.
I would like to know if there is any subwoofer that allows me to have both an high level connection coming directly from the sub ouput of the pre/pro (using its digital crossover) and at the same time have a low level connection between the loudspeakers terminals and the subwoofer. In this last case the loudspeaker would be run full range and the subwoofer would be there filling the bottom octaves.  
Both would be always connected, since they don't seem to be mutually exclusive.
What do you think ? would this work ? What subwoofer would allow me to implement this successfully ?
 
 

Steven Stone -- Thu, 05/28/2009 - 18:03

 That methodology will work just fine.
 
I've had that kind of set-up on my Genesis 6.1 speakers and Genesis 12/2 subwoofers for several years with no problems. You merely need to find a subwoofer that has two independent inputs with independent level controls and crossover adjustments for at least one of the two independent inputs.
 
All the Genesis subs have the controls needed and I suspect that it is not uncommon on other subwoofers as well.
 
 
 
 

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

sheepherder -- Fri, 05/29/2009 - 05:55

REL subs allow those connections and that is how I have my REL subs set up.

Sheepherder
Shenandoah Valley, VA

Miguel Esteves (not verified) -- Fri, 06/05/2009 - 18:08

Alternatively I could connect two subs to the two main speakers (FL & FR) through the low level inputs (taking the signal from the secondary output from the stereo preamp) or high level (from the speakers). In the pre/pro I would put the FL and FR channels full range and would insert a crossover frequency for all the other channels At the same time I would select the no subwoofer option in the pre/pro therefore routing all the bass from those channels to the main FR&FL speakers.
Do you think this would be a workable option ? From all this possibilities which one do you think would give me the better sound ?  My main interest is music (stereo & multichannel) movies are important but come next.
 Do you think it is important to choose a subwoofer with integrated room correction/equalisation or is it possible to achieve good results without it?
 

Steven Stone -- Fri, 06/05/2009 - 18:17

Bot of the methods you mention will work.
 
The question as to which would sound better depends on several factors. In the end the only way to know for sure its to try them both out and decide for yourself.
 
A sub with built-in EQ makes it easier to achieve even bass response. B even with a sub that doesn't have built-in Eq you can do it , but it may require more time and more careful placement to get the best results.
 
Even with a sub with built in EQ, the first goal is to find the best placement that delivers even bass response and then use the EQ for the last bit of touch-up.
 
 
 
 

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

Miguel Esteves (not verified) -- Fri, 06/05/2009 - 19:13

 That was a prompt reply :)
Thanks.
There are a lot of questions and options which result in a lot of doubts about which way to go ...
 
 

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