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Setting up Magnepans

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Posted on September 27, 2016 at 07:53:34
ceulrich@fastmail.us
Audiophile

Posts: 7
Joined: September 27, 2016



Hello All,

This is my first post, but I have been trolling through old posts for a number of months looking for information on setting up Magnepan speakers. I did find a lot of useful information, so I thought I would share my experience in the hope that it will be useful to someone else.

I have been a Magnepan owner for many years, starting with the 2.5R model and more recently with the 3.7i model. I have always done the setup by ear, and in my previous house I had a dedicated listening room so I had complete control over speaker placement. However, in my current house I am much more constrained, see the attached scaled drawing (room height is 8 feet). At first I tried the speakers along the 14' wall, and just did not like the sound, not sure why. Next I tried them along the 12' wall, sound was ok but the arrangement disrupted use of the room as a normal living room. Finally I settled on the arrangement shown, with a 5 degree toe-in. Reflections off of the front wall from the out of phase sound from the rear of the speakers is not a problem, because there is not a direct path to the listening position. Reflections off of the right-side wall and from the rear wall might be problems. Reflections off of the ceiling and floor may also present problems. I have found one drawback to this arrangement, the image seems to be pulled back into the corner. This effect is much reduced when listening in the dark or with my eyes closed. I am not sure if this is psychological or a physical acoustic effect.

The sound was pretty good but I always wondered about the reflections and what problems I created with the listening position back in the corner. Some time ago I acquired the REW software and thought I would see what the measurements told me. I have a number of graphs that will be too much for one posting, so I will dribble this out over a week or two.

Cheers,

Chuck

 

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RE: Setting up Magnepans, posted on September 27, 2016 at 09:05:15
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 Do you have window treatments on the bay window? Bay windows are often a problem and I think with heavier curtains the window reflections can be suppressed enough to match with the open space on the left.

 

RE: Setting up Magnepans, posted on September 27, 2016 at 09:06:18
6bq5
Audiophile

Posts: 4393
Location: SF Bay
Joined: August 16, 2001
 Set up looks good- however I might try one or the other of the following-
Move your listening chair out from the corner a bit- or put some traps behind the chair...

In the end - it is the sound - so if it sounds like the best config for the room- Keep it-
Happy Listening

 

RE: Setting up Magnepans, posted on September 27, 2016 at 18:50:11
ceulrich@fastmail.us
Audiophile

Posts: 7
Joined: September 27, 2016



Hello All,

Thanks to Satie and 6bq5 for their comments. Yes, there is minimal window treatment on the bay window, but about 80% is partially open mini blinds. I will present some data later on early reflections which may clarify that point. Regarding moving the listening chair out from the corner, yes I experimented with that a bit, but it disrupted use as a living room too much. Regarding the use of traps, I put that decision off until I was sure there was no alternative.

Attached is a plot showing the room response to the Magnepan 3.7i's set up as shown in the previous post. I used a calibrated microphone (Dayton EMM-6), positioned at the listening position, 3 feet from the corner and 2.8 feet above the floor, which is the approximate position of the listener's head when seated. Room responses for left channel only, right channel only, and left plus right channels are shown. The excess bass energy with the combined channels was clearly audible, particularly with string bass on jazz recordings. I attributed that mostly due to the right channel, which is positioned very close to a corner. Magnepan's are generally considered to be lacking in bass energy, but that was not my problem with this arrangement.

I listen predominately to classical music, concertos, trios, quartets, vocals, acoustic jazz and folk music, essentially no organ or rock music. So, I wanted to tame that bass energy a bit. In the next post I will explain my approach.

Cheers,

Chuck

 

RE: Setting up Magnepans, posted on September 28, 2016 at 08:31:24
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
 Great job...

It looks like you have an imbalance right to left. Particularly critical in the 300-1KHz area of your graphs. A lot of this can be because of you being in the corner, coupled with the arrangement of the loudspeakers. You can test this with a band limited pink noise signal for each channel. You can use you balance control to correct this. The Corner seat location is also the woes of your compressed image. The left speaker is also first reflections off the wall to the right and the reverse is true for the right speaker as well. This means you are receiving stronger than a traditional layout opposite channel reflected signal to your ears... The best way to resolve this id to move the chair out from the corner - physically. Or acoustically be adding absorbing material to the corner walls. Note: to be useful down to 300 Hz you need 6 inch wedges - but start by using far less with some double stick tape to see if you get you imaging back with just high frequency attenuation.

Good luck!


"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: Setting up Magnepans, posted on September 28, 2016 at 11:10:44
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 Your left channel is whacked in the mid bass and lower mids. The midrange lump would be particularly annoying over time.
.
The suspicion on the midbass is the lack of wall loading on the left speaker. you might get the dip reduced by moving the left speaker towards the corner to get its edge closer to the wall. That is assuming you have them aligned with tweeters in.

Since it is a living room and you likely need the seating section treated, consider hanging a quilt or rug on that corner.

In moving the L speaker closer to its wall (moving it back and towards the left) you might want to move the listening seat a few feet to the left to retain equal distance to the speakers and a less bass heavy listening location which might help with the deep bass peak.. There is a reason for placing bass traps in corners.

 

RE: Setting up Magnepans, posted on September 28, 2016 at 16:24:46
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I would add DIFFUSION to the corner walls.
Too much is never enough

 

RE: Setting up Magnepans, posted on September 29, 2016 at 06:26:52
ceulrich@fastmail.us
Audiophile

Posts: 7
Joined: September 27, 2016



Hello All,

Thanks for your comments BigguyinATL. I was particularly interested in your comment about first reflections. The first reflections illustrated in the room diagram were derived from the classic mirror on the wall technique, I had not considered the reflection path as you describe it. I will be showing some first reflection data later, which may shed some light on this. I will be giving some thought to your other ideas.

Thanks for your additional comments Satie. I agree completely on your comments about the left channel mid bass. The tweeters are on the inside. I did some experiments a few months ago by hanging a quilt in the corner, and did not see much improvement. When I finish presenting this series of data, I might duplicate that experiment and present the data.

Continuing on from my last post:
I thought for a long time on how to tame that bass. Bass traps were not an option because they would be too large to do anything useful at 40 Hz. While I was considering an electronic equalizer, it dawned on me to think about a simple first-order high-pass filter with a corner frequency around 60 Hz. That would slowly roll off below 100 Hz, and bring down that 40 Hz peak. If I used the input impedance of the power amplifier as the resistive element, then all I would need would be a series capacitor between the preamp output and the power amp input. Since the right channel is more of a problem than the left, I could use different corner frequencies for each channel, and improve the channel balance at the same time. The power amp is a Mark Levinson 431 with a 100K ohm input impedance. After some calculations and test measurements I decided 50 nF would bring down the 40 Hz peak by about 5.5 dB, and 100 nF would reduce it by about 2 dB. As luck would have it, I had some 100 nF WonderCaps left over from a previous project. I put two in series to get 50 nF for the right channel and used one for the left channel.

The attached figure shows the room response for each channel, with and with out the high-pass filters. The actual in-room response was close to the calculated levels, the left channel response at 40 Hz was down about 1.6 dB, while the right channel was down about 4.6 dB. Channel balance at 40 Hz was within 1.2 dB.

With the next post I will show the left plus right room response with and without the filters.

Cheers,

Chuck

 

RE: Setting up Magnepans, posted on September 29, 2016 at 16:13:03
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 Looks like your L with the filter will match better with the R without the filter. If that combo introduces too much of a phase difference problem then you can set the R channel filter to a lower freq - bigger cap - say two 50s in parallel.

Edit
Looked again at your post, you should have had the two 100nfs in parallel to have a lower fc for this high pass on the more even R side. You are dealing with the deep bass hump - this approach can't fix the broad midbass suckout on L. Only serious EQ or reworking the placement to introduce more boundary reinforcement will work. Moving the R speaker away from the wall might get you a similar dip in the midbass on that side - more symmetry but worse overall tonal balance.

PS - I suspect your midrange hump on the L is more of a problem overall.

 

RE: Setting up Magnepans, posted on September 29, 2016 at 16:33:19
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I would experiment with DSP.
You can even, with more advanced models, experiment with PHASE FREE filters. FIR filters will do away with driving yourself nuts with phase experiments as you work thru all the OTHER options and settings. I think you can even specify time delays per output.

While most effective with bi/tri amping, running the output to a SINGLE amp per side will allow a custom curve per speaker. You could EASILY shelve down the side with the higher bass output.

The MiniDSP can have as many as 5 parametric EQ setting PER INPUT or OUTPUT.
Too much is never enough

 

RE: Setting up Magnepans, posted on September 30, 2016 at 10:14:33
ceulrich@fastmail.us
Audiophile

Posts: 7
Joined: September 27, 2016



Hello All,

Thanks for more comments Satie. Regarding the capacitor size (amount of capacitance), these are high-pass filters, so the higher the capacitance the less low frequency attenuation (frequency for -3 dB attenuation =1/(2 * pi * C * R). Connecting capacitors in parallel will increase the capacitance. My intent was to bring the left channel amplitude at 40 Hz down a little bit and then make the right channel amplitude at 40 Hz approximately the same (and doing this with the capacitors I had on hand). This may become clearer from the data with this post. I agree completely, this will not fix the broad mid-bass suck out on the left channel, and indeed it may be the biggest problem overall.

Thanks for your comments pictureguy. I agree, digital processing brings a lot more power to bear on the problem. Unfortunately it also brings a lot more expense.

Continuing on from my last post:
Attached is a figure showing the room response for left, right and left plus right, with the high-pass filters discussed in post 3. I did succeed in bringing the bass down about 3 dB at 40 Hz, and reduced the differences between left and right room responses in the low-bass region.

Acoustic Frontiers has published a white paper titled "Acoustical Measurement Standards for Stereo Listening Rooms" which provides guidelines for various acoustic characterizes for a good listening room (it is easy to find with Google). These guidelines, relative to this discussion, are as follows: 1 - In- room one-third octave smoothed frequency response measurement at the listening position for each speaker should be within +/- 3 dB from 250 Hz to 4 KHz, and each speaker should exhibit a deviation no greater than 3 dB from each other. 2 - Low frequency response measurement at the listening position should be within +/- 5 dB for one-third octave smoothed frequency response from 20 Hz to 250 Hz for both speakers measured together. My goal was to see how close I could get to these parameters with the room arrangement shown in my first post.

I just about met the first guideline except for the 400 Hz hump in the left channel. Even though my left plus right room response looks pretty bad, it just meets the parameters for guideline 2, accepting the fact that I will never get any very low bass without subwoofers.

I am thinking about trying BigguyinATL's idea of using band-limited pink noise to try and determine how audible the aberration at 400 Hz is. I am thinking that neither bass traps or absorptive panels will be very effective at this frequency.

I will present some data on first reflections in my next post.

Cheers,

Chuck

 

RE: Setting up Magnepans, posted on September 30, 2016 at 11:26:31
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 How about a DWM to reinforce the L channel? Should be able to fill in the midbass. Of course it also takes up more space and has a cost.

 

RE: Setting up Magnepans, posted on October 2, 2016 at 07:36:01
ceulrich@fastmail.us
Audiophile

Posts: 7
Joined: September 27, 2016



Hello All,

Thanks again Satie for you comment. A subwoofer is on my list to consider.


Continuing on from my last post:
Attached is a figure showing the early reflections for the left and right speakers individually and for left plus right. The table in that figure presents the actual difference in time between the direct sound and the reflected sound. The sound travel-times were determined using a laser tape measure. Just point the laser at the speaker and read the distance, or point the laser at a mirror showing the reflection of a given speaker and the laser dot also reflects and can be seen on that speaker, and again, just read the distance. Very cool. The difference between the two distances divided by the speed of sound yields the time difference.

The burst of reflections around 1.0-1.8 ms are mostly due to reflections from the back of the listening chair. The listening chair is a classic Eames chair, where the back is solid and comes up a few inches above the listener's ears. These reflections disappear when a person is seated in the chair. The reflections around 2.5 ms are due to the left speaker, and are probably reflections off of the wall on the right of the listening position (as was suggested by BigguinATL a few days ago). The reflection at about 4 ms is due to the right speaker, but I am not sure of the travel path. Similarly, I am not sure of the travel paths for reflections at 5 and 7.2 ms. These reflections are somewhere between -6 to -9 dB down in amplitude from the direct sound.

The reverberation time as measured by the Topt parameter of the REW software was 0.346 seconds for this room.

Based on the work of Floyd Toole we know that reflections in the 0 - 10 ms range that are between -2 to -15 dB down add a sense of spaciousness to the perceived sound. One of the reasons I continue to enjoy this rather unusual arrangement of speakers and listening position is the great sense of depth, height and width of the sound field, which is probably primarily due to these reflections.

One last evaluation I conducted was with Stereophile's Concert CD using the last track titled "Mapping the Soundstage." For this track, John Atkinson walks around a recording venue (a church) clapping his hands. In the associated booklet he describes in great detail what the listener should hear in relation to the movement of the image of the clapping. I was not sure if a planar speaker would be able to generate as detailed an image as a cone-type speaker, and thus how useful such an evaluation would be. But I was pleasantly surprised to find that I could very easily follow the image just as described.

In conclusion, I would advise anyone setting up planar speakers not to be too constrained by the conventional wisdom on speaker and listening positions. In my case I was constrained by the need to share a living room with a listening room, and ended up with a good if not great listening space. I still need to work on my left channel problems, mid-bass suck out and the 400 Hz hump.

I will sign off for now, but I will be pleased to read any additional comments anyone would like to offer.

Cheers,

Chuck

 

RE: Setting up Magnepans, posted on October 9, 2016 at 21:10:35
farfetched
Audiophile

Posts: 963
Location: Cleveland!
Joined: October 13, 2010
 I enjoy a somewhat similar room layout, and I too have my maggies set up on the diagonal as you do.

The only piece of advice I would suggest is, experiment moving the chair out into the room *while listening*. In other words, go for a more "near field" presentation.

I find everything opens up, air increases, the clarity increases, and there is no corner "boom", when I move my chair about 3-4 feet out into the room.

For reference, I do *not* listen at loud volumes, and also am not bothered by how soundstage "gets smaller" because of my setup.


By the way! try listening to really fantastic mono recordings as part of your listening calibration. I would **highly** recommend the mono mix of Jefferson Airplane Surrealistic Pillow. Put on "Today" and be amazed. It is my reference mono recording, even though any good pre-stereo recordings will do.
/ optimally proportioned triangles are our friends


 

RE: Setting up Magnepans, posted on October 11, 2016 at 20:10:10
ceulrich@fastmail.us
Audiophile

Posts: 7
Joined: September 27, 2016




Hello All,

Thank you for your comments farfetched. My current listening position is a bit shy of 3 feet from the corner, so I agree that is a sweet spot for this arrangement.

I have tried a more "near field" listening position, and have taken some measurements as shown in the figure. However, in my room I get a very steep roll off in bass response below 100 Hz, and a lot of room mode ups and downs. By putting the listening position back in the corner, I recover a lot of that lost bass energy, even to the point where I had to apply some electronic equalization as described earlier.

I will check with some of my friends for the Jefferson Airplane disk.

Cheers,

Chuck

 

RE: Setting up Magnepans, posted on October 12, 2016 at 06:42:57
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 I am assuming that you are moving the seat parallel to the back wall at these alternative seating positions, do you adjust the speaker toe in and location at all for these?

You obviously have very strong nodes at 40 hz (bump) and 70hz (cancellation) - and an overall lack of pressurization at the 6-9 ft positions along the back wall, have you tried sitting further out into the room?

 

RE: Setting up Magnepans, posted on October 12, 2016 at 09:25:56
ceulrich@fastmail.us
Audiophile

Posts: 7
Joined: September 27, 2016
 Hello All,

Thanks for your comments Satie.
Sorry for the confusion, I moved the microphone (listening position) diagonally out into the room, in a North-North-West direction referencing back to my original room layout diagram. I collected this data many months ago when I was just starting to try to get a feel for what I could and could not do in this room. I positioned the microphone by eye at a midpoint between the speakers, but actually measuring the distance back to the corner. The speakers were positioned within a few inches as shown in the diagram. From the data presented in the last post, it looks like my eye-ball distance estimate for the 6 foot location was not so good. At that time I was not thinking about the subtly of toe-in, so I am not sure what that might have been.

Cheers,

Chuck

 

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