[MGbert]

I think you've hit the nail on the thumb.

Directional control requires big ugly things because of the wavelengths involved. About 1' at 1000 Hz, 10' at 100 Hz. The waves just diffract around anything small.

One of the few exceptions to this -- dipoles and other phase cancellation designs, e.g., cardioids. But they have a limited effect.

You can make a small sound source directional by using ultrasonics and relying on the nonlinearity of the air to shift the frequencies down, and there are commericial directional speaker systems that work that way, but the SPL's are very high and there are some real questions about the health in long-term listening.

Near field listening can help, if that's OK in your setup. But it isn't a cure all.

This I think is one of the biggest unanswered questions in audio -- how do you take the room out of the picture without making something huge and un wife friendly.

One interesting possibility is to make fresnel deflectors, e.g., triangular wedges with absorption on one side. I believe there's one guy who does this in studios, his technique is closely guarded but I reverse engineered the idea from reading a description of what he'd accomplished.

BTW, speaking of dipoles, rather than adding the second barrier, why not just adjust the toe-in of the speakers so that the sidewall first reflection is at the dipole null? I've experimented with that and it works quite well.

Josh!

Thanks for the references.  Adding them to my reading list... maybe by Christmas I'll be able to start.

Ultrasonics... ouch! Hurts my ears just thinking about it...

I find nearfield to work quite well, at least in conjunction with FRTs.  It would be hopeless in a 11 foot square room otherwise!  Looking at the studio layout, maybe an octagonal room could work...

As to your point about eliminating the second set of FRTs by angling the speaker... I did that with the angled speaker setup of the initial post.  You're right, it did help manage the sidewall reflections.  The big problem is the rear wall early reflections, which I added weasel words to that post about human hearing doing better with rear reflections than the front reflections.  That was, as is so often the case, not having the imagination at the time to imagine an actual solution.     Too bad the solution I came up with is a bit ugly, but that's life.

MGbert

[Letitroll98]

The size shrunk when I realized that symmetry was important, so after moving shelves around my 19 foot length became 11 feet. 

Thanks for posting this MGbert, I've been following with great interest since your first post.  But related to the above quote, could you let us in on the why we are seeing the unfinished wall construction and why you needed to take a 19'x11' room and constrict it to 11' sq.  I'm sure you have good reasons for all, but curious minds want to know as on the face of it the solution to the small room problem seems to be use the 19' of the room available.  Could this be an attic space?

And for the materials, I was thinking something like Lowe's Pactiv 4'x8'x3/4" Extruded Polystyrene sheets.  Lightweight, easy to handle and cut if needed, fairly reflective in the frequencies we're talking about and a tiny bit absorptive in the frequencies below, and easy to make floor to ceiling in the spaces most people inhabit.  http://www.lowes.com/pd_304087-210-304087.0_4294858106__?productId=3122443&Ns=p_product_qty_sales_dollar|1&pl=1&currentURL=%3FNs%3Dp_product_qty_sales_dollar%7C1&facetInfo=

Anyway, thanks again for posting, it's been fun following the thread.

[josh358]

Jim,

You're correct, I'm making some generalizations here and in particular talking about RFZ rooms, which are most similar to what MGBert is doing. But studio design has evolved over the years, each room is different, and not all control rooms are designed to the highest standards -- indeed, most aren't.

BTW, minor correction, they aren't as dry as possible. That would be anechoic, which is unlistenable. They're just drier than the home environment. There have been variations on this over the years, e.g., "live end-dead end" rooms were popular for a while, RFZ rooms have diffusion on the rear wall, etc.

[Pryso]

Josh, thanks for your interesting input to Bert's valuable post.

Some time ago I was thinking about the 10 ms principle when reviewing sidewall reflection guidelines.  My conclusion was that all dipole speakers should be placed at least 5 feet out from the front wall (10 ms = 10' [approximately], then 5' to the wall and 5' back again for reflected sounds) to maximize clarity and minimize smearing.

When that is not possible due to room size or other constraints, we must then begin thinking of other ways to delay the back wave from our dipole speakers, along with sidewall reflections, to better separate them from the direct radiated sound from our speakers.

Great food for thought guys.

[josh358]

That's been my experience, and that of many others. You *can* use them closer to the front wall, but they start to come into their own at 5' and continue to get even better as you move them out, for works recorded in larger spaces, anyway.

Side walls are less critical with dipoles because the dipole null reduces the first lateral reflection. You can actually tune that out entirely by rotating them so you're seeing them edge-on in a mirror mounted on the wall. I've done that and you can easily hear when it "clicks in," but it may not be the best position overall owing to other factors, e.g., you might not be listening on axis (or at the recommended angle).

For this reason, I've found that Maggies are less sensitive to side wall than front wall proximity. Usually the limitation is bass response, it starts to climb when they're a foot or so away from the wall because the reflection increases the effective baffle width and drops Fequal, throwing the design assumptions off. (An exception would be the Maggie woofer, which is designed to use the proximity gain.) Two feet is better and of course further better still.

However -- front wall reflections give you a sense of depth, and side wall reflections give you a sense of width, what the concert hall acousticians call ASW or apparent source width. Dipoles are "depth speakers" in that they don't much illuminate the side walls. Omnis have a larger image than either dipoles or conventional boxes (which are omnidirectional in the bass, cardioid in the treble) since they illuminate both the side and front walls. If sufficient distance can be had to the side wall, it may be beneficial to orient the speaker so as to illuminate it. Side wall reflections are also the most pleasing, according to subjective comparisons.

Ideally, we'd be able to delay the reflections from all the walls to match the size of the hall. A huge, directional speaker like the Sound Labs could do that to the lower midrange, but to be directional, a speaker has to be larger than a wavelength, so it's hard to do that with a more reasonable form factor. One possibility I've thought about would combine a directional mid/tweeter with electronic cancellation for the low frequency reflections. This kind of cancellation is practical only when wavelength is long, because otherwise head movements would throw it off. But that's exactly where we need it. And once a loudspeaker is sufficiently directional, HRTF correction of the kind they're doing at Princeton becomes much more effective in even a room with household acoustics. You can also use a phased array approach to direct the delayed ambiance to the side walls.

[MGbert]

Thanks for posting this MGbert, I've been following with great interest since your first post.  But related to the above quote, could you let us in on the why we are seeing the unfinished wall construction and why you needed to take a 19'x11' room and constrict it to 11' sq.  I'm sure you have good reasons for all, but curious minds want to know as on the face of it the solution to the small room problem seems to be use the 19' of the room available.  Could this be an attic space?

And for the materials, I was thinking something like Lowe's Pactiv 4'x8'x3/4" Extruded Polystyrene sheets.  Lightweight, easy to handle and cut if needed, fairly reflective in the frequencies we're talking about and a tiny bit absorptive in the frequencies below, and easy to make floor to ceiling in the spaces most people inhabit.  http://www.lowes.com/pd_304087-210-304087.0_4294858106__?productId=3122443&Ns=p_product_qty_sales_dollar|1&pl=1&currentURL=%3FNs%3Dp_product_qty_sales_dollar%7C1&facetInfo=

Anyway, thanks again for posting, it's been fun following the thread.

Glad to hear you're following/enjoying the thread!  It's been quite the little research project at my end - the fact that no one else seems to have tried this with Maggies still has me shaking my head.  In hindsight, it seems so obvious!

I'll apologise for the length of this post in advance, but a good answer to your questions requires a summary of a 2 year long process.  So here goes...

As to the incredibly shrinking listening room... it's a prefab shed I bought when we moved here.  It has a 11'-4" X 19'-4" inside footprint, it has to function like a basement or attic since our house only has neither.  The wife also made it clear that no aspect of the big rig was going to be in the house, and besides we have cats who love using furniture as scratching posts...  The shed has power and is climate controlled, and I added the insulation.  But since it is after all "only a shed", I never felt the need to do aesthetic stuff like drywall.  If I become convinced that sonics would improve, then perhaps.  I'll definitely look into the product you recommended.  Moving stuff around to do it would be a big PITA at this point, however.

Problem with the shed acting like a basement/attic is it has to store a lot of stuff, and that stuff is impossible to arrange symmetrically (one item for instance is a metal cabinet which actually rang when certain noted were played) - and we all know how Maggies love symmetry when it comes to throwing a realistic soundstage. 

I had my pre-owned MMGs (we met on Audiogon - they were a local sale) for about a year before getting them Gunned, but when they came back and I STILL had soundstage problems, I decided to bite the bullet and see if the non-symmetric stuff could be hidden from the listening area.  To that end, the only arrangement that works is arranging tall LP and CD shelves into faux walls spaced 11 feet apart in the middle, leaving 4+ feet width of storage space behind each set of shelves.  When I realized that, it took me a while to bite the bullet and do it, since I knew that any improvement in soundstage would be accompanied by different problems due to the short width.  In the end I decided to make this a research project, figuring that if I could finally figure out how to make Maggies sing in a small space, that knowledge would be really cool to share with the Planar community.  (OK, corny, but that's how I feel)

It took months of trying different speaker positions based on everything I could find by googling "speaker placement", then trying spaces between those.  Each spot had issues.  Then one day, reading Josh expound once again  about the benefits of 10 msec delay time for first reflections, it finally dawned on me that a) 11 feet was simply too small for that criteria to be met and b) one should be able to rig something up to trap and delay reflections by giving them a new surface to bounce off of.  A quick trip to Home Depot to get some pieces of paneling and a few cinder blocks to raise them off the floor led to my first success, which I posted about at the start of this thread. 

For the better part of 2 months, I was frankly afraid to move anything thinking I'd jinx it.  But of course engineers tinker, so eventually another trip to Home Depot for some larger panels led to the current configuration.  I also put sliders under the cinder blocks raising the MMGs off the floor to facilitate trying other placements, but there doesn't seem to be a need to try other MMG locations - they sing pretty darn well just where they're planted.  Replacing the two smaller panels with the 6 foot tall panels made a small improvement, but it was introducing the second set of panels outboard of the speakers that really cemented the deal.

Oh by the way the MMGs are shimmed to be fully upright - as you know, the Gunn mod has them tilted back by design - and tweeters in.  And as far as raising the MMGs off the floor - conventional wisdom says this should kill bass response, but no such thing happens in my room, FWIW.  Here's a dirty secret: I use a Behringer DEQ2496 for room EQ as well as a DAC and balance control for my passive preamp.  Here is the frequency response at the listening seat.  Sorry for the blurry pic.  Each horizontal dashed line represents a 2.5 dB change.  Note that the average level is about -60 dB, and that the response at 45 Hz is only down by 5 dB at -65dB.  Not shabby at all, and even though the FRTs help I have to give the Gunn mod a lot of credit.  And no, the EQ settings do not boost any frequency below 80 Hz; in fact, I cut the level at 63 Hz by about 4 dB, there is so much power there!





Sorry for the long-winded response; you've probably noticed I have trouble being any other way (in print at least).   

MGbert

[*Scotty*]

I admit to being more than a little confused about just where the undesirable reflections that MG-bert is trying delay are coming from. It appears that the front wall,ceiling and sidewalls are covered with at least 4 inches of fiberglass insulation with a layer of craft paper facing into the room. Surely the front wall, so covered cannot be source of significant reflections with exception of those whose wavelengths that are short enough to be reflected by the craft paper.
 Perhaps moving the racks of CDs and records from close proximity to the MMGs and placing them against the side walls beside the MMGs would be an interesting experiment. This would greatly increase the time it took for reflected sound from the media storage racks to reach the listening position. By moving the CD storage racks on the right side of room to a position directly against the wall the time for the first reflection from this location would be increased by over 8ms.  The mean distance of the MMGs from the front wall appears to be 4 ft., if the panels were moved 1 ft. closer to the listening position the time for the reflection from the front wall will be increased from about 8ms to roughly 10ms. In fact it appears that a 10ms delay or greater could be achieved from all surfaces with the exception of the floor, by a simple relocation of the media storage racks relative to the MMGs.
Scotty

[medium jim]

I admit to being more than a little confused about just where the undesirable reflections that MG-bert is trying delay are coming from. It appears that the front wall,ceiling and sidewalls are covered with at least 4 inches of fiberglass insulation with a layer of craft paper facing into the room. Surely the front wall, so covered cannot be source of significant reflections with exception of those whose wavelengths that are short enough to be reflected by the craft paper.
 Perhaps moving the racks of CDs and records from close proximity to the MMGs and placing them against the side walls beside the MMGs would be an interesting experiment. This would greatly increase the time it took for reflected sound from the media storage racks to reach the listening position. By moving the CD storage racks on the right side of room to a position directly against the wall the time for the first reflection from this location would be increased by over 8ms.  The mean distance of the MMGs from the front wall appears to be 4 ft., if the panels were moved 1 ft. closer to the listening position the time for the reflection from the front wall will be increased from about 8ms to roughly 10ms. In fact it appears that a 10ms delay or greater could be achieved from all surfaces by a simple relocation of the media storage racks relative to the MMGs.
Scotty

Scotty,

I agree, well placed objects or "clutter" can be all the room treatment needed to nail the 1st wave reflections.

Jim

[Letitroll98]

But since it is after all "only a shed", I never felt the need to do aesthetic stuff like drywall.  If I become convinced that sonics would improve, then perhaps.  I'll definitely look into the product you recommended.  Moving stuff around to do it would be a big PITA at this point, however.

No Bert, the material linked was a suggested replacement for your paneling.  Not that you should replace the paneling you set up, but for someone beginning anew, maybe even me.  And as mentioned in a thread above, the unfinished fiberglass batting can only be a help sonically.  The only thing I would do to the walls is replace the fiberglass with rockwool, the Roxul Safe'nSound would be my choice, again, not suggesting you do it, but if starting fresh.     

Oh by the way the MMGs are shimmed to be fully upright - as you know, the Gunn mod has them tilted back by design - and tweeters in.  And as far as raising the MMGs off the floor - conventional wisdom says this should kill bass response, but no such thing happens in my room, FWIW.  Here's a dirty secret: I use a Behringer DEQ2496 for room EQ as well as a DAC and balance control for my passive preamp.  Here is the frequency response at the listening seat.  Each horizontal dashed line represents a 2.5 dB change.  Note that the average level is about -60 dB, and that the response at 45 Hz is only down by 5 dB at -65dB.  Not shabby at all, and even though the FRTs help I have to give the Gunn mod a lot of credit.  And no, the EQ settings do not boost any frequency below 80 Hz; in fact, I cut the level at 63 Hz by about 4 dB, there is so much power there!

I have custom stands for my MMG's and also have them dead straight up with no tilt back or forward.  I did have them tilted forward a couple of degrees and it can sound pretty good.  I also have them in a small room (13.5'x10') and have been bedeviled trying to make them sound good.  I've found several solutions, all with at least a minor drawback, nothing perfect yet.  Funny, I had them in a worse room in my old place and they sounded great, go figure. 

And your frequency response looks like the typical MMG in room response I've seen in a zillion plots, including mine.  The saddle response of upper-mid bass suckout and just above the crossover dip is quite common.  As is the boost in the 60hz region. 

Thanks for the answers and I'll keep following the thread.  Oh, and BTW, you're not nuts or anything, almost all MMG owners do these crazy things.  You're right in the middle of the bell curve. 

[MGbert]

I admit to being more than a little confused about just where the undesirable reflections that MG-bert is trying delay are coming from. It appears that the front wall,ceiling and sidewalls are covered with at least 4 inches of fiberglass insulation with a layer of craft paper facing into the room. Surely the front wall, so covered cannot be source of significant reflections with exception of those whose wavelengths that are short enough to be reflected by the craft paper.

Well, there were enough of those reflections to cause a fair amount of comb filtering which needed to be dealt with.  And with the FRTs, the delayed reflectons are doing a nice job of increasing the apparant size of the room.

Perhaps moving the racks of CDs and records from close proximity to the MMGs and placing them against the side walls beside the MMGs would be an interesting experiment. This would greatly increase the time it took for reflected sound from the media storage racks to reach the listening position. By moving the CD storage racks on the right side of room to a position directly against the wall the time for the first reflection from this location would be increased by over 8ms.  The mean distance of the MMGs from the front wall appears to be 4 ft., if the panels were moved 1 ft. closer to the listening position the time for the reflection from the front wall will be increased from about 8ms to roughly 10ms. In fact it appears that a 10ms delay or greater could be achieved from all surfaces with the exception of the floor, by a simple relocation of the media storage racks relative to the MMGs.
Scotty

Don't I wish I had the latitude to make the room larger!  I tried using the maximum amount of floor space at first, but it simply didn't work out - see my response to Letitroll98 for details.  And there is nearfield and there is TooCloseField, that the extra foot from the front wall would create.  I know, I tried - it messed up the bass response also.  Not to mention the rear wall reflection delay would be even shorter!  So for now, I'll stick with the FRTs.   

MGbert

[MGbert]

Time for an update.  I changed the front FRTs so instead of being "ears" to the bookshelf in front, they now are in the front corners of the room forming 30 degree angles to the front wall.  I had come to realize the bass emphasis from the previous arrangement was a bit much.  The new arrangement has the following advantages:

1) The new placement is a lot less intrusive, since it is closer to the front wall.  Potentially higher WAF, too.

2) By changing the angle the front and side wall make to each other, it seems to act a bit like a bass trap, smoothing out the bass.

3) It works in conjunction with the other FRTs on the outer side of the MMGs to delay the propogation of the early reflections, drastically reducing comb filtering effects.  However, unlike the previous arrangement, it offers no real advantage without those additional side FRTs.

I'll post a new floor plan and photos soon.

MGbert

[MGbert]

@Josh358:  it occurs to me that this latest config might actually work in your fireplace room as a way of taming the influence of the fireplace. 

MGbert

[josh358]

@Josh358:  it occurs to me that this latest config might actually work in your fireplace room as a way of taming the influence of the fireplace. 

MGbert

Thanks, sounds interesting. I'll be interested to see the sketch when you post it, it's kind of hard to visualize what you've done from the description -- I'd have to go back and reread the thread since you've used differential encoding.

[MGbert]

Thanks, sounds interesting. I'll be interested to see the sketch when you post it, it's kind of hard to visualize what you've done from the description -- I'd have to go back and reread the thread since you've used differential encoding.

Here is the sketch.  Computer problems delayed my being able to post sooner.



The advantage to this arrangement is that the front wall FRTs are less obtrusive, but this will only work with the side FRTs in place.

MGbert

[josh358]

Don't you get bass reinforcement from the side traps? Not that that would necessarily be a problem with the MMG's . . .

[MGbert]

Don't you get bass reinforcement from the side traps? Not that that would necessarily be a problem with the MMG's . . .

Not as much as the second arrangement, interestingly enough.  I realized that the bass reinforcement was too much, and started searching for a way of naturalizing it while maintaining the advantages of reducing comb filtering effects.

MGbert

[MGbert]

I have split this off into a new thread:

http://www.audiocircle.com/index.php?topic=118512.new#new

MGbert