Monolith Bass - how to get it

Hi Folks, this is a continuation of what up to this point had been a series of private exchanges with another Monolith owner. We initially were triaging some wiring and hook-up challenges on a set of Monolith IIIx with the EXOS active external plus three amps (two mono and one stereo).

Once the system became operational, the owner brought up the fact that the bass seemed lacking. Here’s the quote:

I am in business but the bass response is really not what I expected. I think my sequels are deeper which seems impossible. The bass isn't flabby it just doesn't have much gusto. I did not plan to run a sub but I might have to.

Click to expand...

And now, welcome to the dirty little secret of Monolith Bass: It’s really hard to coax some out of these. For one, like most ML’s, it has to sit out in the room (which lowers room reinforcement), two, the panels put out so much more energy relative to the woofer, that the woofer to panel balance is not the same as in smaller ML’s. This explains why Prodigies and Summits have dual woofers in their bases for increased low-frequency output.
And in any case, the factory woofer probably is >4db down at 30Hz. Higher if the driver is >8 years (which by now is most Monoliths).

You will likely need a Sub to get good deep-bass in your room. I had two Velodyne ULD-18’s and they barely kept up. Not until I went with my monster infinite baffle did I get the kind and quantity of bass that could keep up with the Monoliths’s at higher levels.

A good point to crossover the Monolith to the sub is around 60hz using a steep 24dB/Octave active crossover. More on that in later postings.

In the short-term, you need to tweak the controls you have available to you through the EXOS crossover.

Lots of settings and they do interact. So patience and an SPL meter are recommended.

Following are a couple of posts showing the effects of various settings on the EXOS crossover, the idea being to try several combinations of these in your room and measuring the results.

The measurement shown below display the range of bass section boost or cut available from the crossover.

The top line represents the maximum low frequency gain available by combining:

• +4 dB of boost on the “Boost/Cut” control on the front panel
• A +6dB gain using the dip switches on the rear
• A setting of 30Hz for “Frequency”

The mid line represents a good normalized setting for an 18x25x8 room, by combining:

• 0 dB of boost on the “Boost/Cut” control on the front panel
• A 0 dB gain using the dip switches on the rear
• A setting of 40Hz for “Frequency”

The Bottom line represents the minimum setting for reductions, by combining:

• -4 dB of cut on the “Boost/Cut” control on the front panel
• A -6 dB gain using the dip switches on the rear
• A setting of 30Hz for “Frequency”

What will work for you depends on where the room peaks or nulls are. But I’d stay away from the extremes.

This next graph shows the effect of setting the boost/cut frequency and of the various gain settings.

The blue traces show the effect of the frequency control at its three different settings (combined with a -3dB gain setting).
The red traces show the effects of the various gain settings via the dip switches.

Since the owner reports low bass output, first thing to check is the gain settings.

Given my experience with my Monoliths, I'd say the woofer needs at least 3dB of Boost, and probably 6 if you are currently dissatisfied with Bass output.
I use +5db of Boost on the woofers through my active crossover.

Another reason why boost and/or cuts might be unequal gain structures in your two amps.

But frankly, I just think it takes a bit more to drive the woofer to a balanced level. One would think the panel would be the one in need of more grunt, but no…

Check and adjust Phase

Another culprit of insufficient bass output is miss-matched phase.

Given the wiring complexities of active, bi-amped speakers, there is plenty of opportunity to get something reversed along the way.

And even if all the connections visible to you look good, it still does not guarantee that some component in the chain is inverting phase.

Therefore, one must ensure phase is set in both vertical and horizontal planes. That is, panel to woofer and woofer to woofer.

Best way to check and correct this is to start on the left speaker and follow these steps:

• turn off amps or disconnect input to the right channel
• play a wide-band pink noise through the system with both panel and woofer hooked up. Reverse the polarity of the woofer (if there is switch along the path, otherwise, turn off woofer amp, change wires, restart amp). And see whether the bass increases or decreases.

This works best if you can switch back and forth quickly.
Once the polarity between panel and woofer is established in the left speaker:

• Disconnect the panel (or turn off that amp).
• Reconnect the right channel feed to the amp that feeds the right speaker woofer
  
• Play the tone and toggle the polarity of the right channel woofer until the bass is maximized.

Now balance the right speaker:

• Disconnect the left channel feeds
• Reconnect right channel panel (or turn on that amp)
• Repeat steps above to balance panel and woofer, except that this time, you reverse panel polarity, not the woofer, as we are trying to keep all four drivers in synch to the polarity of the left panel.

BTW- this process works for those of you who bi-wire your speakers as well. I’ve seen folks get that wrong and wonder where the bass or the imaging went.

The system that got me into panels was precisely a pair of Monoliths ca. 1994. It was a jaw-dropping revelation. If I recall correctly, they were vertically bi-amped (or was it quad-amped?), with Krell for the woofers, Jadis for the panels. Bass wasn't lacking in any way--in fact, it played much better than another combination I heard at that same event that consisted of Magnepans (some model comparable to today's 3.6R) driven by Levinson and Proceed gear. I guess the high-end tubes in the panels made a big big difference, plus I am sure that the crossovers were very carefully tuned (in other words, patience pays off...).

Edit: I forgot to stress my initial point--no subs were used.

Actives + Sub

To hook up a subwoofer in conjunction with an active crossover, the cabling is a bit more complex, as we need to first send the signal to the sub crossover and then take its outputs and feed those to the EXOS.

The real challenge is going to be to keep hum and noise out of the long run between processor and sub and back. This is why I always liked the old Velodyne ULD designs that had the separate AMP/Crossover unit and the sub box. One could keep lines short.

Here’s my recommended cable between pre and sub and back for its low capacitance and good RF shielding:

Blue Jeans Cable LC-1 http://www.bluejeanscable.com/store/audio/index.htm

Here’s the diagram:

OK, I think that covers the basics.

Time to stop talking to myself and wait for questions, flames, etc.

oh and yes Paulo, the Monoliths were what got me hooked on Martin Logan back in 1993. Wonderful sound as I recall.
But it is sooo much better now than when I first got them, it's not even funny.

These guys can be tweaked to no end. A good speaker processor is the key.
I still plan to publish my DriveRack guide one of these days. Patience grasshopper.

JonFo said:

OK, I think that covers the basics.

Time to stop talking to myself and wait for questions, flames, etc.

oh and yes Paulo, the Monoliths were what got me hooked on Martin Logan back in 1993. Wonderful sound as I recall.
But it is sooo much better now than when I first got them, it's not even funny.

These guys can be tweaked to no end. A good speaker processor is the key.
I still plan to publish my DriveRack guide one of these days. Patience grasshopper.

Click to expand...

I wish I could tweak my Vantages with the same ease I read about Monolith tweaks (or, even more, Magnepans). But then, I don't think I've settled on this particular model of ML (dying to see and hear the CLX!) . If I had a pair of Monoliths I would probably settle, just because they are a classic...

[/QUOTE]
Hi Folks, this is a continuation of what up to this point had been a series of private exchanges with another Monolith owner. We initially were triaging some wiring and hook-up challenges on a set of Monolith IIIx with the EXOS active external plus three amps (two mono and one stereo).

______________________

My sincere thanks to Jon for his help thus far and for once again going way beyond expectations to help a less than adept member get his system right.:bowdown:

I am the problem child and Jon helped me initially hide my shame when I enthusiastically purchased a pair of mono blocks to us with the Monolith IIIx EXOS only to find out that I was a couple of amps (at least one) short of what I needed to do to use the EXOS.

Long story short, I am going to try to trouble shoot all of Jon's recomondations and see where it nets me. That will of course be after the Mothers day hyberboil and when I can find the energy to try to lift off my HD tube TV (very heay and very ackward) off the cablinet which now hold sseveral hundred pounds of beautiful blue lighted power etc so I can try to pry it away from the wall to begin the fun.

Sigh!

Hi John, sure anytime.

Before you move too much stuff, you might want to try setting the EXOS dip switches such that you have +6db of gain.
Keep your 50 Hz Frequency setting and the +2 of Boost cut you've dialed in.

Give that a whirl and let us know.

I will try that for sure but I am away from the house for a day or two (have to earn a few dollars) and the interconnects are not long enough to manuver the xover without pulling the connections out. I will have to go the hard route of moving stuff anyway to get to it properly.

Sorry to leave you hanging and this is killing me so I am anxious to try it all. I ping you as soon as I have access and time. I am hoping you will feel the thumping from Seattle to Atlanta and you will know we have fianlly given justice to those freakishly large beasts.

Well I am back and just tried the lazy mans approach so far with just checking the phasing on the speakers. No appreciable changes flipping them as it turns out and the only thing that seemed backward was the left panel and they are so awsome I did not even notice that might not be perfect.

With a great deal of contorsionary skills I managed to get to the EXOS dip switches which had 2 + 2 prior to flipping 6 as suggested. That did net a notable difference but not huge. I am now in full mode with all the dips switches activated on the bass attenuation. Sounds a little better but still not the punch or movement I would expect on the woofers I would expect at volume. I played around with the boost and cut on the front and that still sounds best at the 45 hz and 2 db setting.

Update . . . .

I did some reading and found that I need to be careful which dip switches I turn off and on. I was assuming the more you set to on the deeper the bass but it would apear that if I read correctly that the correct setting would be to turn off everything on the left side of the low-pass attenuation switches other than the #4 and #2 and everything on the right side other than #8 which should give me the + 6.0 dB Gain you are talking about.

Before I go through the all the steps to get to the back of the EXOS again, is that right?

I also checked my Sub Woofer that I might use for the system and do not see any outputs. I have balanced and unbalanced inputs but no outputs to feed back into the EXOS.

johnwa said:

Update . . . .

I did some reading and found that I need to be careful which dip switches I turn off and on. I was assuming the more you set to on the deeper the bass but it would apear that if I read correctly that the correct setting would be to turn off everything on the left side of the low-pass attenuation switches other than the #4 and #2 and everything on the right side other than #8 which should give me the + 6.0 dB Gain you are talking about.

Before I go through the all the steps to get to the back of the EXOS again, is that right?

I also checked my Sub Woofer that I might use for the system and do not see any outputs. I have balanced and unbalanced inputs but no outputs to feed back into the EXOS.

Click to expand...

John,
The low pass switches should only have switch 8 ON. All others should be off to get the +6db gain.

The sub you have does not seem to have an active crossover output, so it can not be used as I describe above, as there is no way to high-pass the L/R.

Now if your pre-amp/processor has a Sub/LFE output and can be configured for a sub/mains crossover of 60hz, you might be set. But if I recall, you are using a 2-ch pre, correct?

In which case you’d need something like the Bryston 10B crossover as well in your circuit.

This is why I keep recommending a speaker processor. A DriveRack 260 can do all the bass management for your system in that one box. Also, you can put multiple EQ’s on the woofer and sub outs, play with phase in 1 degree increments, add the 1.75ms delay to panel necessary to align to woofer, and finally, add the roughly +5dB gain the woofer needs.
Not that I think you need to stop and switch to one now, but I just wanted to reinforce the point that even with a factory crossover, it’s never simple to do actives.
Maybe it’s me and I’m just enamored with complexity or am overly anal-compulsive about tuning…

Keep plugging away at this, you’ll get it right and be blown away by the results.

Thanks for your continued patience and help and as even I am growing tired of my questions. I now have both #8 switches on and everything else is off. Do I have that right or should I only have one of those on? I am using the Genesis SACD CDs you had mentioned and they seem to be the least responsive to the bass tunes.

The sub I currently have in my HT set up has no outputs for certain so that is a shame as I was going to see if the additon of a sub on the Mono's warrented the purchase first. I hear you about the fine tuning and will happily get the additoanl electronics if it will solve the issue.

John, I think you have the switches right now.

Must play around with palcement and room treatments to get better results.

Seperate sub still recommended.

10-4 will do. Thanks again!

John, or anyone else inrested in a great sub crossover and sub room correction, you need to track the release of this product:

http://www.svsound.com/CES2007/SVS_AudyessyRelease.pdf

It does everything you need to give you the best bass in your room with a minimum of fuss.

At $750, it's quite reasonable for what all it does.

Moving on to Speaker processors

Resurecting this thread to continue the discussion of how to take this to the next level with a speaker processor.

JohnWA, As you asked about this in this other thread, I thought I’d continue it here, as it’s more germane to this topic.

The question was: How do you transition from your current setup to a Speaker Processor based approach?

The answer is:

Step 1- Sell the EXOS (Just Kidding-might want to hang on to it for a bit until you are satisfied).
Step 2- Obtain a DriveRack 260 processor.
Step 3- Obtain a Jensen ISO-Max DM2-RX
Step 4- Wire it up as follows (see attached Image)
Step 5- Load up preset I’ll send you (baseline Monolith 2x5 crossover config with EQ’s flat).
Step 6- Measure the in-room responses and tweak settings
- Requires a measurement setup of some kind. Details can be found on the REW forum here. http://www.hometheatershack.com/forums/spl-meters-mics-calibration/

The wiring is pretty straightforward, with a need for a few new balanced cables from the Jensen to the DR 260. I recommend BlueJeans cable balanced.

I believe your Mac’s have balanced conenctors for inputs, so you’ll need additional balanced cables from the DR 260 to the Mac’s. And finally a Balanced cable from the DR 260 to your Sub’s LFE (no crossover in sub) input.

Simple, eh?