Placement options – Impacts of location, orientation and treatments

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Well, logic dictates that you cannot "correct" a fundamentally flawed (distorted) sound from the speakers. Kind of like if you get the source signal wrong, all you end up doing is amplifying that flawed signal. The purpose of room correction is to minimize room contributions to the sound that you hear. If that sound is flawed or significantly distorted, that is what you will hear with good room treatment.
 
I have just ordered a couple of mondo traps for my small, 12 w x 14 l x 8 h, listening room to clean up some of the muddy bass. If I am understandidng the discussion thread correctly, the proper placement will be behind the speakers for these 2 traps. When I purchase additional traps, they can then go to the corners behind the listening position and between the speakers. Is this correct?

Also, if the back wave has such a strong effect, why is the general speaker placement recommendation 3-4 feet from the wall? Is there something to this or is this an old wives tale? Also, why hasn't the Martin Logan company not more strongly encouraged dealing with the back wave, or even attach a trap to the back of the speaker.

Finally, to educate the novices, I was wondering if someone could please describe the purpose of the different types of the charts in this thread. Why is each type of chart used? What is measured in each chart? What are the axes? What should the more ideal shape of each type of chart be?

Thanks!!!
 
I have just ordered a couple of mondo traps for my small, 12 w x 14 l x 8 h, listening room to clean up some of the muddy bass. If I am understandidng the discussion thread correctly, the proper placement will be behind the speakers for these 2 traps. When I purchase additional traps, they can then go to the corners behind the listening position and between the speakers. Is this correct?

Actually, for a couple of mondo traps, the best placement would be in the corners of the room, either in the front or the rear. This will help clean up the muddy bass, as you say, and is what these traps are designed for. I would get a couple more as soon as you can afford and place them in the other two corners for much smoother bass response.

However, I would not recommend using the mondo traps behind your speakers to absorb the rear wave, because these traps have a reflective membrane in them that will actually reflect high frequencies and cause time-delay smearing and comb filtering. What you want behind the speakers is a panel that absorbs fairly evenly from 250 hz to up above 15,000 hz. In the real traps product line, that is the High Frequency Mini Trap (or HF Mini for short). That is what Jonathan and I are using behind our speakers with excellent results.


Also, if the back wave has such a strong effect, why is the general speaker placement recommendation 3-4 feet from the wall? Is there something to this or is this an old wives tale? Also, why hasn't the Martin Logan company not more strongly encouraged dealing with the back wave, or even attach a trap to the back of the speaker.

I think the further that the speakers are from the wall (lots of people prefer five feet or more), the greater the time delay and diffusion for the rear wave and the less it interferes with imaging. I believe toe-in helps with this as well. Also, I believe that placing the speaker out from the wall helps to keep the wall/floor corner from over-emphasizing the bass from the woofers. Most high-end speakers require placement a few feet away from the front wall for similar reasons.

I can't answer why ML hasn't explored this more in R&D and made hardware adjustments or at least more specific recommendations for dealing with the rear wave of the speakers. If not handled correctly, it is certainly a flaw in the design of the speaker because it hinders the phenomenal imaging and soundstaging that these speakers are capable of. At one time, one of the acoustics companies (ASC) made an absorptive/diffusive backbox that was designed to go on the back of the ML Aerius speaker. I think there just wasn't enough demand to continue to produce that sort of product as it would have to be specific to each speaker. They did indicate an intention to produce them per speaker by custom order at the time, but I don't know if that still holds true.

For a description of this product, check out post #13 of this thread:

http://www.martinloganowners.com/~tdacquis/forum/showthread.php?t=1942

Finally, to educate the novices, I was wondering if someone could please describe the purpose of the different types of the charts in this thread. Why is each type of chart used? What is measured in each chart? What are the axes? What should the more ideal shape of each type of chart be?

Can't help you too much here, as I'm still learning about this myself. I'll punt this one to Jonathan.
 
David,

If I am understandidng the discussion thread correctly, the proper placement will be behind the speakers for these 2 traps. When I purchase additional traps, they can then go to the corners behind the listening position and between the speakers. Is this correct?

I usually advise corner placement first, especially when the complaint is muddy bass as you mentioned. The good news in your case is you also bought stands, so you can easily experiment with different placements and see which gives the best results for these first two traps.

--Ethan
 
Actually, for a couple of mondo traps, the best placement would be in the corners of the room
LOL, we both posted the same advice at the same time. :D

I would not recommend using the mondo traps behind your speakers to absorb the rear wave, because these traps have a reflective membrane
This is another advantage of David having stands. If he turns the MondoTraps around so the rear is facing the room (toward the back of his speakers), that mimics what an HF style MondoTrap or MiniTrap will do. I imagine in this case that having the traps backwards behind his speakers will clean up the mids and highs, and having them forward across corners will clean up the bass. If this is indeed the case, then he can get HF Mondos or Minis next.

--Ethan
 
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I own a pair of ML Summits and still have a lot to learn about audio fidelity. I found your postings on room treatments enlightening, and I was hoping you could clear up some concerns I have about the quality of the Summits that may be reflected in your measurements.

I recently came across Richard Hardesty's www.audioperfectionist.com online publication where he argues that Martin Logans exhibit poor (quasi-anachoic) frequency responses, poor time and phase performance, and significant energy storage issues that are inherent to their design. He argues that it makes them inaccurate speakers and listeners confuse this with being highly-detailed. DTB300 seems to refer to this effect as "one of the biggest myths in ESL circles -- that the rear wave of the panel provides an "ambiance" that is beneficial to the sound". Hardesty's measurements were taken for a Martin Logan Aerius.
...

OK, those are some significant claims, so let’s deconstruct them bit by bit.
First measuring a line array is different than a point source speaker. Measure a dipole Line array (any ML ESL) is even more different.

For line array’s one must be at least a meter away and usually 2 to really capture the full effect of the line source (i.e. the summing of all the drivers, or the entire panel).
And at 2m, the room is providing a big influence on the measured response.

Now, since any line source will be >4’ tall, the mic will be picking up signals from varying angles emanating from the speaker, this will show up as some comb filtering on the frequency spectrum. But the benefits of a deep soundfield plus an even energizing of the room at mid and low frequencies (for line arrays of dynamic drivers) provides greater benefits than penalties.

My tests of the SL3 panel (a new one in my center) shows they have excellent time response, and the phase is not an issue either. If you do no absorb the rear wave, then yes, there can be all kinds of issues. But then those are room induced and not inherent in the speaker.

As for ‘energy storage’ I’m not buying that, as an ESL has vanishingly low mass in its diaphragm, so where is this ‘energy’ being stored?
Now, A bad panel element can resonate (or buzz) if the spars are not set right or the tension in the mylar is off. But then so can a cone driver that’s not well attached to its voice coil. Spurious claim in my book ...

So fundamentally, a good ESL is a very accurate transducer, much more so than cone drivers that’s for sure.
The challenge, as this entire thread is trying to address, is how they will operate in the various listening environments we put them in.
There I’d agree that just plopping the speaker down and hooking up the amp will yield measured responses that do feature problems we’ve been documenting here.
The good news is they can be dealt with.

My question is whether you know of any published quasi-anachoic response measurements for the Summits? Whether the Summits perform as poorly on the speaker response tests as the Aerius? And if so, whether it's best to start with a better (anachoic) performing speaker in the first place before investing in room treatments or any other improvements?

I guess ultimately my question is whether room effect treatments can overcome speaker performance deficiencies? Or are room effects so much more important than speaker deficiencies among “decent” speakers that fixing room effects has a bigger incremental benefit than starting with better performing speakers?
...
A good performing speaker is an important starting point, but ideal anechoic is not necessarily required. Because as I’ve been documenting, the in-room response is affected by the room to such a large extent, that how the speaker is designed to interact with the room is just as important (if not more so) as good anechoic numbers.

The ‘deficiencies’ of speakers are many. For instance box resonances, the non-linear effects of acoustic suspension alignments, port resonances on ported speakers, horn directivity and ‘glare’ issues with horns, and of specific interest, the management of dipole radiation from Maggies, ML’s, Soundlabs, etc.

The question is: how are they managed and how do they interact with a room?

Good design mitigates many of them, but room interface is critical. These are mostly under user control and therefore subject to huge variations.
So my bottom line is that any pair of good speakers will still face a huge challenge as we try and interface it to a room. No one design is a winner in all cases.

We just pick our favorite compromises and deal with them
 
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LOL, we both posted the same advice at the same time. :D


This is another advantage of David having stands. If he turns the MondoTraps around so the rear is facing the room (toward the back of his speakers), that mimics what an HF style MondoTrap or MiniTrap will do. I imagine in this case that having the traps backwards behind his speakers will clean up the mids and highs, and having them forward across corners will clean up the bass. If this is indeed the case, then he can get HF Mondos or Minis next.

--Ethan

Agree with both of you on that. The Mondo’s , with their reflective face directed at the speaker are not recommended, see plots of this on post #104

Interesting that reversed, the Mondo might work OK. But then the mounting braces are visible. Better to get an HF version of the Mini to put right behind the speaker, and use Mondo’s in the corners. They even have a corner Mondo that looks good in that config.
 
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I got ten more boxes delivered today. :cool:
But long day at work, so no fun with those until the weekend. :(

Also, I’ll answer the plot descriptions question in the am.
 
...
Finally, to educate the novices, I was wondering if someone could please describe the purpose of the different types of the charts in this thread. Why is each type of chart used? What is measured in each chart? What are the axes? What should the more ideal shape of each type of chart be?

Thanks!!!

David,

Sure, let’s try and clarify this, so without adding dozens more posts here, I’ll try and summarize and link to external sites with good descriptions of the type of metrics.

There are two types of views, time domain centric (impulse and waterfall) and frequency domain centric (bode and general frequency response).

All plots are taken from a basic MLS burst measurement and the audio measurement tools then apply algorithms to that captured sound to create the various output plots.

I'm separarating the various descriptions into individual posts to make it easier to read.
 
Impulse response

Impulse response

This is the basic test to detect the phase and time energy of a signal. As I’ve shown early on, it’s one of the best ways to ‘see’ if the rear wave is being reflected back at the speaker (or listener) and whether it’s affecting the sound in deleterious ways.

What you’re looking for is a clean initial impulse and then as smooth a tail as possible, That would indicate no reflections or resonances (some of which could be speaker induced).

The scales are normalized linear amplitude levels, showing positive and negative phase swings centered around a normalized base level is plotted vertically, and the horizontal is the time dimension (usually in milliseconds) of the signal and it’s decay over time.

Of course, in a real room, there will always be some level of reflection, the idea is to manage those and yield the balance of direct and reflected energy the listener desires.

This article further explains this metric.
http://en.wikipedia.org/wiki/Impulse_response
 
Bode response

Bode response

This is a complex frequency domain metric that shows the unsmoothed frequency (horizontal log scale in Hz) vs amplitude (vertical scale in SPL).

Since it’s unsmoothed, unlike the 1/3 octave graphs usually printed in magazines, it looks pretty bad, but it’s a great way to see comb filtering effects induced by rear wave reflections or other room resonances.

Ideally, it’s a straight line, but that never happens with ANY speaker (maybe an in-ear headphone, but even then … )
http://en.wikipedia.org/wiki/Bode_plot
 
I got ten more boxes delivered today. :cool:
But long day at work, so no fun with those until the weekend. :(
You do not look so good Jon...:think: You will need to call in sick and take care of yourself. More than likely you will be able to return to work on Monday. :D
 
Psychological Frequency response

Psychological Frequency response

This one is a corrected 1/3 octave smoothed frequency response plot. With amplitude (in SPL on the vertical ais and the log frequencies along the horizontal axis (in Hz).

The ‘corrected’ has to do with adjusting for the Fletcher-Munson human hearing response curve. Ideally, this one is also a straight line. But any speaker in most any room (except anechoic) will never be flat.
 
Waterfall plots

The waterfall plot is probably the most useful view to visualize the areas of modal ringing stemming from room resonances or from system induced resonances (box resonance, crossover EQ ringing, etc.).

More than a quantitative measure, this one should be viewed as a relative qualitative metric. As the goal is not so much to flatten the initial frequency response, as it is to reduce the long ‘mountain peaks’ (from back to front) that represent significant energy storage in the room (or system).

A waterfall plot has a time component that is derived from windowing the original impulse measurement. So it is trying to represent how much energy is measured at the various points in time, but it is not a frequency response over time measure. As noted above, it is indicative of the decay levels at various frequencies.

An ideal waterfall plot is one that has a relatively smooth initial frequency response line, followed by a rapid decay (each successive line is substantially lower than the one previous) and with minimal ‘mountain ranges’ indicating ringing areas.


And this page describes them in greater detail. http://www.libinst.com/wattlar.htm

And finaly, Ethan posted some great descriptions of the ETF measuring tool and its graphs and uses in this article:
http://www.realtraps.com/art_etf.htm
 
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Thanks for the links Jon - day off today watching the cricket. Think there will be some rain delays so will check out these links.

Kevin
 
Excellent work, Jonathan.
Indeed, the best documented product endorsement one could hope for:bowdown:

...You have also debunked what I believe is one of the biggest myths in ESL circles -- that the rear wave of the panel provides an "ambiance" that is beneficial to the sound.
I have also come to this conclusion myself lately.
With 3-4 inches of acoustic foam right behind the panels I have found clarity to have risen quite a bit. Soundstage is much better too.
The only downside is the extra power needed to achieve the old sound levels: 2-3db have been lost according to the preamp volume control.
But hey, can't have everything eh, all this extra energy absorbed has to be replaced somehow...
 
The only downside is the extra power needed to achieve the old sound levels: 2-3db have been lost according to the preamp volume control.
But hey, can't have everything eh, all this extra energy absorbed has to be replaced somehow...

I hadn't really noticed or thought about it, but it makes sense that this would be true. Lower reflected energy should certainly mean lower spl's at a given volume level. However, I have found that with the extra clarity produced by absorbing the rear wave, I am enjoying listening at lower volume levels than I did before. And if I do decide to crank it up to the upper 80's to lower 90's (db levels), the sound is still crystal clear, and imaging and soundstaging don't fall apart. Maybe this is why I prefer a more powerful amp on the Summits than a lot of people think is necessary.
 
However, I have found that with the extra clarity produced by absorbing the rear wave, I am enjoying listening at lower volume levels than I did before.
Yep, you can hear more detail without having to turn it up as much.

Same effect with better power, less reflections, less bass boom, etc. With things such as lower noise floor and other noises or congestion removed makes you able to hear more of the music.
 
You do not look so good Jon... You will need to call in sick and take care of yourself. More than likely you will be able to return to work on Monday.


He he, good one there Dan.

However, while it's good to be the boss, a good boss sets a good example, so I've been working hard and all ten are still safely boxed in the garage.

It's driving me nuts though ;)

Saturday morning, we start Phase 2 !
 
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I hadn't really noticed or thought about it, but it makes sense that this would be true. Lower reflected energy should certainly mean lower spl's at a given volume level. However, I have found that with the extra clarity produced by absorbing the rear wave, I am enjoying listening at lower volume levels than I did before. And if I do decide to crank it up to the upper 80's to lower 90's (db levels), the sound is still crystal clear, and imaging and soundstaging don't fall apart. Maybe this is why I prefer a more powerful amp on the Summits than a lot of people think is necessary.

Rich, it is indeed a lower overall level in the room. One can see some of that via the lowered levels in the frequency graphs as well as the less dense waterfall plots.

Essentially, the traps are mitigating the rooms modal ringing. This ringing is clearly visible as the long mountain crests from back to front of the waterfall plots.
By getting rid of that excess (and distorting) energy, the system will sound a little softer, but much, much clearer and balanced. This as you note, allows us to turn up the volume a bit more and hear a more satisfying result.

Looking at the waterfalls and attacking the most egregious ‘mountain ranges’ (the modal ringing) is the goal. Using a combination of room treatments and EQ can be quite effective.
But I now note that without treatments, EQ is not enough. Matter of fact, some EQ induces ringing of its own. I saw that in the Sub EQ, which with all the new treatments is set wrong, yet it was inducing huge ringing artifacts visible in the low frequency plots.

The best setup is to start with good placement of the speakers, followed by adequate room treatments and only then, some mild EQ. But always checking by measuring the response to see if the ringing is improved or not.

I’m concluding (although probably prematurely) that going for flat frequency response is not the main goal. One should go for the most balanced energy levels in the key listening areas.
That means waterfall plots that decay quickly and have minimal ringing visible.
 

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