Harbeth Monitor 40 domestic specific

[A.S.]

OK there are a number of issues here. First of all, you can not take a speaker like the M40 and plop it down into any and all rooms and expect it to work optimally. Just to remind you: it was designed as a specialist workhorse for use in treated BBC studios where there are no bass problems at all.

I think there is an unfortunate combination of room and speaker's bottom end. It happens. It happened to me in my new listening room (written up here: http://www.harbeth.co.uk/usergroup/showthread.php?t=154). Yes, Rockwool is similar to but not the same as fibreglass: both are used for lagging building walls. They are pretty much interchangeable. Rockwool is non-irritant though.

What I would do is this: remove the grilles and completely stuff the ports. A pair of socks one inside the other in one, either or both ports will do the trick. This will dramatically reduce the vent outputs. That is by far the most effective workaround. If that works, then make some prettier furniture foam bungs and job done.

[Ned Mast]

Casaross,

A.S. obviously knows these speakers better than anyone, so I would follow his advice to the letter. I'm a bit surprised, however, that he didn't comment on the height of your stands. 12" is very close to the floor to have the M40s sitting. I had 17" Sound Anchor stands for my SHL5s and put risers on them to get my M40s about 21" off the floor. This improved the bass reproduction, I believe. At any rate, room positioning is very important, so keep trying different configurations and ultimately you will be richly rewarded!

Ned

[A.S.]

... 12" is very close to the floor to have the M40s sitting

Yes, sorry, I missed this point. 12" is extremely low but of course, as with everything in life, compromise is necessary.

Reducing the port efficiency is the primary workaround and can be tested for free. Adjusting the stand height is of secondary effect. Here is a picture M40 on studio stands I designed. They lift the bottom about 970mm from the floor. The M40A rack-amp is mounted into the stand below the speaker. This works well.

[Ron Herbster]

Casaross,
I agree with Ned that you need to get the 40s anywhere from 20" to 23" off the floor and try a little less toe in. I currently have 20" Skylan stands and I know that Noel Nolan is currently working on a 23-24" stand for the 40s with a tiltable base which could better assimilate BBC positioning. Get in touch with Noel as he is a wealth of knowledge concerning bases for the Harbeths and a great guy to know. He has been a tremendous help to me with the 5s and 40s.

[Casaross]

Hi Alan and Ned,

Thanks to both of you for your responses. I did not expect to plop the M40's into the room and to have them magically optimize. I did, however, expect that some of the Harbeth group faithful would be able to guide me once I began to try to work these speakers into the best configuration. As usual, Alan suggested a trick that may well work and impose minimal expense. As for Ned's point on the stand height, I can easily make the stands go a bit higher just by installing the spikes. After that, I may be able to layer some wood blocks but want to take care not to send my significant investment tumbling, literally, to the floor.

Thanks again for your help. I will go to my drawer and withdraw my most suitable bass-damping socks. (All my high frequency attenuation socks are in the wash!)

Scott

[A.S.]

... I can easily make the stands go a bit higher just by installing the spikes. After that, I may be able to layer some wood blocks...

Noted. Now I've read here and there about making very small (by which I mean, say, an inch or so) height adjustments and I'd very much like to save you the hassle - there is almost no chance that such a small change would effect the very low frequencies. The reason is that the wavelengths are so long (about 30 feet) that in proportion, an inch or so is utterly insignificant unless, by some weird fluke, you hit some sort of sweet spot. But that would be luck indeed.

That leaves two options then, and this would apply to all speakers in all environments: put less energy into the room (attend to the port/ports) or absorb the energy from the port (room damping). Can we know something about the walls, floor, ceiling construction and who or what is below you? Not a double garage I hope. If you bang the walls with your fists, do they boom? Is that low frequency signature sonically related to the problems you have with music?

Could you confirm the ownership history of these speakers?

[Casaross]

Hi Alan,

My room is in the basement of my home, so the floor is poured concrete covered by a pad and carpet. One side wall and the back wall of the room are foundation walls with studs 12" on center for greater stability in holding up the gypsum board. The ceiling and side wall shared with the remainder of the basement are a double layer of gypsum board to give the wall greater mass and resistance to movement. Again, this wall has studs 12" on center and an additional course of fire stops to add structural rigidity.

The wall behind the listening seat has three large cabinets with records in them - massively heavy.

I have a wool rug suspended on one side wall and a diffraction device to catch the first reflection on the other wall - roughly equalizing the reflectivity of each side wall.

Behind the speakers is a bass trap of unknown provenance and a couple of Michael Green acoustic treatments that catch higher frequency slap echoes but do little to the bass.

These are the general characteristics of the room. It is not badly configured for other speakers I have used there but I am sure that it can use more work.

Thanks so very much for your help. I appreciate it immensely.

[kevint]

Maybe I’m lucky, I use 12” height stand for M40 without any bass problem. My room size is similar to Casaross.
I suggest if your M40 is a brand new pair, perhaps give them more time to run-in, the bass unit need time to sound relax. I remember my brand new pair sounded boomy and congested at first day of installation, after a month or so intensive usage, the problem was gone.

[Casaross]

Progress...

I spent a lot of time this evening trying to improve the sound of my M40's. Following Alan's suggestion, I put rags into my M40 ports and that toned down some of the boominess. I also moved the speakers back in the room toward the front wall, away from the middle of the room. I followed the advice on the Cardas website under "Insights" regarding set up. In that article, Cardas recommends that the front speaker baffle come out from the front wall .447 x room width. They also recommend that the front center of the speaker baffle come out from the side wall .276 x room width.

I violated the distance from side walls recommendation by placing the speakers about 29" from the side walls but 5'7" from the front wall. This meant that my M40's were 92" apart from tweeter to tweeter. This combination of distances seemed to offer a good compromise of soundstage width and depth, while staying less boomy.

I also moved a couple of very large pillows into the room and that helped a very small bit.

Finally, I wired my speakers to the 4 ohm taps and biwired to the low and mid posts.

Frankly, my sound tonight was much better than last night. I have, however, changed so many things tonight that I cannot with any assurance say what made the major differences and what made the minor differences. I think that the port stuffing was the biggest difference. Suffice it to say, however, that I sat and enjoyed music tonight. Last night, not so.

For the next go round, I may put the Sound Anchor stands spikes in to more firmly anchor the speakers to the concrete floor beneath the carpet in my listening room. Perhaps that will damp their resonant qualities a bit, too.

As always, I am grateful for any recommendations that fellow M40 users have experienced in getting the best from these wonderful speakers. As Alan said, these cannot just be "plopped" down in a room and expected to sound their best. Rather, this is a project to be undertaken over the course of weeks or months. Even knowing that, however, I sometimes have difficulty being as patient as I should be.

[Casaross]

M40 placement and rationale.

Side wall and front wall positioning. In trying the Cardas recommended speaker placement, I placed my M40's at a distance from the side wall (.276 x room width from side wall to center of front speaker baffle) that comes close to the placement recommended in the Harbeth User's Guide (.75 meters from side wall to side edge of M40). The Cardas website, however, calls for the front baffle to be .447 x room width from the front wall of the room. The Harbeth User Guide calls for approximately 1 meter's distance from the rear surface of the speaker to the wall - a difference between Cardas and Harbeth of about 10 inches.

Rationale; Application to Different Harbeth Models. Cardas explains his approach according to "Golden Ratios" that apparently have worked well in a number of applications. Are there particular explanations for why the Harbeth placement works better for the Harbeth speakers? Also, do the various Harbeth speaker models differ in ideal placement? For instance, does the M40 require some variation from the HL P3 due to the more robust bass output?

Science and art for the non-scientist and non-artist. My own experimentation leaves me thinking that there is some science that can be applied to each room placement and acoustic treatment situation but that there is also a bit of art. Any guidance that Alan or other M40 users can provide will help as I am neither scientist nor artist!

[markus sauer]

I've read here and there about making very small (by which I mean, say, an inch or so) height adjustments and I'd very much like to save you the hassle - there is almost no chance that such a small change would effect the very low frequencies. The reason is that the wavelengths are so long (about 30 feet) that in proportion, an inch or so is utterly insignificant unless, by some weird fluke, you hit some sort of sweet spot. But that would be luck indeed.

Hi Alan,

may I ask you to expand a bit further on that? I agree that boundary reinforcement is boundary reinforcement, and that it doesn't matter much whether you get it form the florr or a wall, but I always thought the stand height had to be adjusted so that you could listen on the design axis of a speaker, i.e. at the most linear point of integrartion between the drivers.

Your post seems to indicate that stand height dosn't matter much with the M40. Do I understand this correctly?

[A.S.]

I did say "at very low frequencies". You are taking about driver integration issues in the mid/upper frequencies. That is a completely different issue.

[markus sauer]

Thanks for pointing this out (note to self: pay attention!).

[A.S.]

No problem. Actually, as I typed my original comment I should have italicised it as I had a sneaking suspicion that I'd be picked up on it - and was!

[Groovetracer]

Alan, I am using 2 completely different amps to power my M40's because I find the tube amp offers beautiful tone but lacks control, whereas the SS amp offers better control in the lower frequencies.
If the M40 is amplified below 200hz with a solid state amplifier and above 200hz with a tube amp, what tap should the speaker cable be connected to at the tube amp terminals, 4ohm or 8ohm, for optimal performance?
I realize matching the gain of 2 different amps in the process is critical.

[A.S.]

The gain and the phase must be checked or you are doomed. Are you sure about the phase? I've touched on this before here: some brands are (or were) phase inverting: QUAD is just one example: phase inverting QUAD preamps driving phase inverting QUAD power amps = a reverse of a reverse so the amplifier chain is altogether in-phase.

I'd go for 4 ohm on the bass/mid and 8 on the HF.

[Groovetracer]

The gain and the phase must be checked or you are doomed. Are you sure about the phase? I've touched on this before here: some brands are (or were) phase inverting: QUAD is just one example: phase inverting QUAD preamps driving phase inverting QUAD power amps = a reverse of a reverse so the amplifier chain is altogether in-phase.

I'd go for 4 ohm on the bass/mid and 8 on the HF.

Thanks Alan, no phase inversion on this tube amp. BTW, I should mention I own the domestic version of the M40.

Regarding choice of 4ohm or 8ohm tap, I am powering the mid and tweeter with the tube amp so what tap do you suggest I use for this configuration?

The 12" driver alone is powered with the solid state amp.

[A.S.]

I suggest .... bass alone 4 ohm, midrange/tweeter on 6 or 8 ohm.

By the way ... word of caution: This bi-amping arrangement I have not tried. As I've said before, the M40s bass crossover expects to be loaded by the midrange crossover (and vice versa) from the same amp source. You are in uncharted territory!

[Groovetracer]

As I've said before, the M40s bass crossover expects to be loaded by the midrange crossover (and vice versa) from the same amp source. You are in uncharted territory!

Thank you very much for responding Alan. Last weekend I listened for a few hours with the M40's bi-amped and heard no issues, in fact the reason I did this was to see if the bottom end could be better controlled and it was. There is no substitute for solid state power, although I still prefer the M40 with tube amplification even if the low bass is a little loose.
Do you think I should go back to a single amp source? IOW, Could I damage the crossover or speaker through biamping with 2 completely different amps?
I apologize in advance for the repetitive nature of my questions.

[tmallin]

What a long, strange trip it's been for me and my M40s, stand-wise.

Let me stress that for those who value the midrange and high frequency tonal truth, beauty, and natural detail which allow the most realistic vocal reproduction available--which have always been the very core of Harbeth's strongest suits--I suggest trying the Skylan stands if you are not already using them. In my case, at least, they have added considerable potency to my M40s' magic.

When I first bought my Monitor 40s a couple of years ago, my dealer offered me two options for stands. One was the Skylan.

The other, the one I chose, were a pair of custom-made one-off stands which were about 14" high and made of fiberglass with Delrin end caps and aluminum spikes. The stands supported the speakers only at about a two-inch-square area near each of the four corners and were otherwise open to the floor. I used felt pads as an interface between the tops of the stands and the speakers. I thus chose stands that were maximally open below the speaker to avoid any extra reinforcement of the bass from a solid stand structure. It was only after I bought the M40s that I became aware that Harbeth was touting the Skylans as their "recommended" stands. And now I finally hear why.

I did not go straight to Skylans from the custom stands I had, however. Along the way I tried homemade stands using plastic Supreme Crates and dairy crates purchased from The Container Store, with and without casters, either a single height or a double stack. As I experimented with stand materials, speaker/stand interfaces, and stand/floor interfaces, I soon learned that taller-than-14" stands really sounded better, at least in my system/room. A stack of two plastic dairy crates on casters, yielding a 23.5" stand, sounded really good--better than my original custom stands--for only about $30 each.

When I got serious about tall stands, I initially went with a pair of 22" Sound Anchor four-posters. These just did not work well at all at first in my system. After much tinkering, I finally arrived at an arrangement which allowed the Sound Anchors to perform a bit better with the M40s than the plastic crates did. The saga of my battle with the Sound Anchors can be found at:

http://groups.yahoo.com/group/regsaudioforum/message/516

I used that arrangement for several months before taking a Linkwitz Orion detour for a number of months. Then, as a result of my own desire to return the M40s to my listening room, and at the urging of Noel Nolan of Skylan, who had read one of my comments hinting at this desire in regsaudioforum, I decided to try the M40s on a pair of Skylan stands.

Mounting my Harbeth M40s on Skylan stands seems to result in a significant improvement from the best sound I was getting from the M40s before. The naturalness of the midrange and highs have been further enhanced in important ways.

I really don't think I'm imagining that the Skylan stands are making a change for the yet better in the M40s or that I'm just reacting to certain things I've missed about the M40 presentation during my tenure with the Orions. When I first heard the M40s on the Sound Anchor stands, my first impression was extreme disappointment compared to the naturalness I had previously achieved with the M40s on makeshift plastic dairy crate stands or custom-built low sand-filled fiberglass stands. The sound was bright and gritty and lacked any semblance of the midrange magic I knew the speakers could produce. I had to work hard to get the Sound Anchors to allow the measure of M40 magic I'd previously experienced to come through.

This time, from the first moments of play, the M40s sounded wonderful. So much natural clarity and midrange detail. Such sweet yet subjectively more extended highs. If you love natural tonality and detail, especially in voices, the M40s are at the very top of the heap of what I've heard. But of course you knew that already. And the imaging and staging, areas where I thought the Orions surely bettered the M40s, were rock solid, expansive, and immersive, fully the equal of the Orions' presentation.

I believe the Skylan stands allow the M40s to both report more truthfully on differences among recordings in the mids and highs and still allow the music to remain more enjoyable. In other words, the Skylan stands further enhance the M40s' remarkable combination of mid/high truth and beauty.

Above the low bass, the M40s seem to be able to play louder cleanly now than before, and the sense of dynamic freedom (uncorking loud transients) is also better. And now the Harbeths are cleaner and more transparent, in the sense of natural presentation of small sonic details without false brightness.

These changes were evident from the first listen to the replaced M40s. I did not have to struggle to get the Skylan stands to perform at least as well as makeshift plastic dairy crate stands the way I had to with the Sound Anchors. The Sound Anchors come with their metal legs pre-filled with damping materials. With the Skyans, you add your own damping materials. I've filled each of the four pillars of each stand all the way to the top with sand. I'd estimate that this requires about 80 pounds of sand. That is what Noel Nolan at Skylan recommends for these stands with M40s. I'm just using the standard little rubber (neoprene?) bumpers that come with the stands as a speaker-to-stand interface. I'm using four of these little Skylan rubber bumpers per stand, one positioned over each sand-filled pillar. Using my tap-and-listen test, these spots are the deadest spots on the top plate of the stand.

The stands have no effect on the measured peak I got around 60 Hz in my room with these speakers positioned as they are with other stands. The peak is still measurably there to the same extent as before. Subjectively, however, it seems a bit reduced, but with the speakers and listening position as they are now, I still need to shave off bass with the 60 and 80 Hz sliders to restore naturalness to the midbass.

When so adjusted, the bottom octave of the M40s is still lacking both subjectively and in objective measurements, but much less so than with prior stands in this position in the room. Compared to 1 kHz, the low bass is -2 dB at 40 Hz, and -12 dB at 31.5, 25, and 20 Hz. So, the M40s still don't have much extreme bottom, but, otherwise, on the Skylan stands they are providing the best overall sound I've yet heard from them in this room.

I intend to try spiking the stands and try some of the other stand-to-speaker interfaces Noel provided with the stands. I may also try re-orienting the speakers to fire into the short (width) dimension of the room. This could allow me to position the Harbeths in positions more supportive of the low bass while still placing the listening position in the near field, the way I like it.