A Delicate Operation: Removing Tweeter Guards From Harbeth Monitor 40s

tmallin

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May 19, 2010
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Perhaps this is of historical interest only. This operation need not be done on the current series of Harbeth speakers because their tweeter guards have a much wider weave to the metal grill work. The guards thus don't obstruct the high frequency sound emanating from the tweeter nearly as much, if at all. But these directions should work on the Monitor 40.1, as well if anyone wants to try it. I don't think removing the guard could hurt the sound. It may not be audible, but it might help a bit.

I'm pretty sure that these instructions would generally apply to other Harbeth speakers as well, especially the M30 and M30.1 which use the same SEAS Excel tweeter as my M40s did.

Keep in mind that this operation involves extreme risk to the tweeter dome. It would be very easy to ruin the tweeter dome if you allow your fingers or a tool to slip. Proceed at your own risk!!

Here are the detailed directions I wrote back in April 2005. I have altered a few parts to update my thinking about the sonics, but all the mechanical instructions are unchanged.

By the way, the unguarded tweeters survived shipment and a new owner is still enjoying the Harbeth M40s upon which I did this operation. I also know that Robert Greene (REG of TAS) did this operation (he did it first) on the pair of M40s which he still uses as a reference. REG has kept his tweeter-guardless M40s all these years because they sound more accurate to him than the later M40.1s. You cannot go wrong with either speaker, I say, as long as you are prepared to equalize the bass, if necessary.




Removing the Tweeter Guards/Screens From the Harbeth Monitor 40s


I did it! The tweeter guards on my M40s are gone. I wouldn't have
believed such a change could result in such a significant improvement in
sound which I found hard to fault in the first place! Sometimes it just
takes a short example of something better to open your ears to what
could have been improved. That's the case here.

The Sound

REG's reference to pink noise led me to listen to the quality of FM
hiss as my first experiment. I did one speaker first and focused on the
quality of the background hiss. Sure enough, the hiss from the speaker
I had operated on sounded somehow cleaner and more detached in space
from the program and speaker with more of a pure ssssss sound whereas
the other speaker's hiss had a bit of shhhssssss sound and was less free
from the speaker location and the program. Listening in stereo, the
operated-on side seemed to image and stage larger in all three
dimensions, especially height.

A day later I removed the tweeter screen/guard from the other speaker.
Only then did the full impact of the improvement became apparent.

First and foremost is the improvement in overall coherence or
"of-a-piece"-ness; the sense that the drivers of each speaker and the
two speakers together are speaking with one voice; the sense that each
speaker is really a one-way, not three-way design and on mono material
the integrity of the center phantom image. The M40s were already second
only to the Quad 63/988 in this respect in my experience. Removing the
screens significantly narrowed, if not closed the gap. I'd have to
listen to the Quads again to know if there still is a gap. The Harbeths
were great for near-field listening before because you could not hear
out the individual drivers. Now they are even better. [Update: The M40.1s are yet better in these respects, even with the tweeter guards in place.]

The highs are yet cleaner, there is yet more inner detail. There is no
increase in brightness, but the high end seems yet more extended,
perhaps because the elimination of whatever resonance the guards were
causing reveals or unmasks the extreme highs.

Imaging is tighter, more focused and stable. But the soundstage is
larger in all dimensions. The entire presentation sounds bigger, more
generous, more spacious and airy.

As excellent as the M40s were before--and I really honestly could hear
nothing wrong or less than truly stellar with the mids/highs in any of
the areas I've mentioned above--the speakers are significantly better
once the tweeter guards are removed. The difference, to my ears at
least, is not subtle. Yes, the operation has significant risks, but it
also has significant rewards.


There is nothing "wrong" about the sound
of the M40s with tweeter guards attached. While REG may have heard
something which could have been improved, I certainly didn't. In the
mids and highs I found the un-doctored M40s the best I'd yet heard [as of 2005].

Perhaps an analogy would be lighting an artificial scene behind a thin
scrim. The speaker designer adjusts the scene so that the scene looks as realistic as
possible and in fact that is very realistic compared to other speakers.
But lift the scrim and it's more realistic yet. Those who have seen
scrims used in opera or other performances will know what I mean.

Or how about the world itself viewed through a window? Beautiful
scenery still looks beautiful even if the window is a little filmy and
you might not even notice a subtle uniform film at all until you clean
the window really well. Will nature look worse or better after the
window is cleaned? Will it not look still better if the window is
opened or removed?



Preparing For The Operation

I'm setting forth a detailed description of how I successfully
completed the surgery as safely as possible. It actually was easier
than I thought it would be. I'd estimate no more than about 15 minutes
per speaker. It doesn't take long. I do not regard myself as having
particularly dextrous or steady hands. In fact, I'd say I'm toward the
ham-fisted end of the spectrum. But the only part which got a little
tricky was replacing the first Allen (hex) screw upon reassembly.

Do the operation with the speakers vertical, perhaps on their stands or
any other steady support which puts the tweeter at a comfortable height
for you to work on.

The only tools you need are a #2 Phillips screwdriver for the four
outer tweeter plate screws and a small metric Allen/hex wrench for the
four inner screws which hold the plate to the tweeter body. I suggest
using a combination Allen/hex wrench set rather than in individual hex
key since the combination set will give you a better grip and better
control of the wrench to keep it away from the magnetic pull of the
tweeter.

I don't want to make too much of the magnetic field strength. Yes,
there is a pull, but if you are expecting it, it is nothing that you
cannot resist in the sense of controlling your tools and the screws. I
suggest testing the strength of the field at all the inner screws with
your hex wrench in hand BEFORE you remove the tweeter guard so you will
know what to expect.

One obvious goal of all the precautions here is to avoid touching the
tweeter dome or surround with any tool, screw, or even your fingers.

Remove the speaker cabinet grills.

Attach a small bit of masking tape on the circular tweeter mounting
plate to indicate which side is up before you start the disassembly.
The orientation of the plate must be correct with respect to the actual
tweeter body when you replace the plate. There are two small nipples on
the back side of the plate. The two nipples are different sizes and fit
into two differently sized holes on the face of the tweeter body. If
you rotate the plate 90 degrees or 180 degrees and try to reattach it
that way, it won't mate up properly with the tweeter body. The masking
tape will ensure that you get the orientation correct the first time you
rejoin the parts.

The Operation Itself

Loosen the four inner hex screws by a turn or two first. Then loosen
all the outer Phillips screws. Remove three of the inner hex screws.
Then remove three of the outer Phillips screws, leaving one of the two
bottom Phillips screws. Before removing the last Phillips screw, place
your hand against the bottom of the tweeter plate since if the tweeter
breaks free from the cabinet, the bottom end will tend to jump out of
the cabinet, not the top. Then remove the last Phillips screw.

If the tweeter plate does not separate from the cabinet at that point
(mine didn't), use the Allen/hex wrench to gently pry the bottom of the
tweeter plate away from the cabinet just enough so you can get a finger
grip on the edge of the tweeter plate. Insert the end of the Allen
wrench into one of the Phillips screw holes to do the prying.

With tweeter plate in hand, pull the tweeter out of the cabinet just
far enough so that about 1/2 inch of the round body of the tweeter
itself is exposed, just enough so that you can now hold both the round
tweeter body and the somewhat larger tweeter plate in the fingers of one
hand. Now use your other hand to fully loosen the last Allen/hex screw
holding the tweeter to the tweeter plate. There is no need to remove
the screw from the hole in the plate. Just pull the plate away from
tweeter and set it and your hex wrench on top of the speaker. Then push
the tweeter back just a bit into the speaker until it is balanced on the
front cabinet panel and won't tend to fall into the speaker cabinet or
out of the speaker cabinet when you let go of it.

You will now notice that the circular tweeter body has protrusions on
the left and right where the wires attach and are soldered. These
protrusions fit into cut outs in the cabinet front. There is thus no
real danger that the tweeter orientation will rotate.

Pick up the tweeter plate and move it away from the speaker before
removing the guard from the plate.

There may be no need to use a tool to remove the tweeter guards. Mine
both detached easily when I held the tweeter plate in my two hands and
pushed a bit with my two thumbs simultaneously on the back side of the
tweeter guard. Yes, there will now be a slight cosmetic "defect" in the
front side of the tweeter plate since the black paint on the tweeter
plate will be removed in a narrow circular line where the tweeter guard
was once attached and was pried free.

Now the tricky part. I put one Allen/hex screw back in the tweeter
plate. I put a finger over the head of that screw just to make sure it
didn't come out of the plate as I brought it back to the tweeter. I
then carefully aligned the hole in the center of the plate with the
tweeter (also paying attention to the orientation of the plate marked by
the bit of masking tape) and brought the plate up to the tweeter. I
then got the fingers of one hand around both the edge of the plate and
the circular outer edge of the tweeter body. The screw should be
magnetically attracted toward its hole. I then used the other hand to
CAREFULLY use the hex wrench to tighten that screw just enough to get a
connection between the tweeter plate and tweeter body so that the
tweeter body would not be able to fall back inside the cabinet.

Push the tweeter plate back into the cabinet so it is more or less
flush with the front of the cabinet.

Before trying to attach any more screws, check that the screw holes in
the tweeter and cabinet are all lined up with the screw holes in the
plate. Rotate the plate a bit if necessary to line up the Phillips
screw holes. To line up the Allen/hex screw holes in the tweeter body
with the Allen/hex screw holes in the plate, insert the end of the hex
wrench into one of the vacant holes and nudge the tweeter rotation just
enough to line up the holes.

Now you're ready to reinsert all four Phillips screws. You can do this
by hand, or by holding each Phillips screw against the tip of the
screwdriver as you approach the tweeter. Get all four hand tight.

Then reinsert the other three Allen/hex screws. Don't do this by hand.
Insert the hex wrench into each screw and hold the screw in one hand
and the tool in the other as you mate the screw to the hole. Tighten
each hex screw a few turns.

Then snugly tighten all four Phillips screws. Go round and round a few
times since you will continue to be able to tighten this wood/metal
boundary as you snug them down. Don't be a gorilla, but do get them
really snug.

Then tighten down all the Allen/hex screws, holding the tool near the
business end in one hand while holding the back end of the tool in the
other for maximum control as you work in the strong area of the magnetic
field.

Carefully remove the bit of masking tape, replace the speaker grill,
and you're done and ready to enjoy your "new" Harbeths!




 

GaryProtein

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Jul 25, 2012
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Wouldn't the manufacturer design the tweeter to sound a certain way WITH the supplied guard in place and wouldn't removing it change the sound the listener was intended to hear?

If not, why would they sell the speaker with a known design flaw???
 
Last edited:

tmallin

WBF Technical Expert
May 19, 2010
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Wouldn't the manufacturer design the tweeter to sound a certain way WITH the supplied guard in place and wouldn't removing it change the sound the listener was intended to hear?

If not, why would they sell the speaker with a known design flaw???

Sometimes I think that manufacturers are more concerned over accidental damage to delicate drivers than absolute best sound quality. A replacement driver might cost a few hundred dollars. As I said, I heard nothing wrong with the sound before the "operation." The speaker does not have a "known design flaw."

You might as well say that speaker manufacturers should not sell speakers with grills because in most cases removing the grill allows the speaker to sound a bit better. The cosmetics and driver protection qualities of speaker grills can outweigh absolute best sonics if the grills allow the manufacturer to sell more speakers. I suppose that's not the best analogy in the case of the Harbeths since most people agree with the designer, Alan Shaw, that Harbeths sound best with the grills ON. But you know that that is not the case with most speakers.

Or let's say that you're convinced that the speakers would sound best if the binding posts were eliminated in favor of pure bare copper pig tails and that the manufacturer could supply the speakers upon order with any reasonable length of pig tail (made from the same wire used inside the speaker) exiting the speaker to allow you to eschew binding posts and extra wire connections altogether. The trouble would be, how does the average owner keep the bare copper end from soon oxidizing and thus perhaps degrading the sound the speaker had originally. Cleaning bare copper, especially stranded bare copper, is no easy feat. Thus, most manufacturers opt for plated binding posts and soldered or plated internal connections to the binding posts, even in the face of audiophile claims that such binding posts and their related connections impair achievement of the best sound quality which could otherwise be had from the speaker. Besides maintaining the connection quality at a stable level over time, cosmetically binding posts are a superior solution for most owners and many owners would feel "cheated" in not being able to use their favorite speaker cables if the speakers were supplied with "hard wired" cabling of "unknown quality."
 

GaryProtein

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Jul 25, 2012
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I have no problem with grills or guards. They serve a good purpose and they don't have to adversely affect the sound if they are designed well.

I just think or hope that the designer/manufacturers have taken them into account when they produce a speaker for sale. By removing the grills, are you hearing a brighter sound than the designer wanted? How do you know what the designer was thinking when he was at work?
 

Addicted to hifi

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I don’t think harbeth should use a tweeter guard on such a good speaker It spoils the looks and properly effects the sound as well.most speakers don’t have a guard over there tweeters.
 

tmallin

WBF Technical Expert
May 19, 2010
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I don't think tweeter guards are a bad thing at all. It would be very easy to damage a delicate tweeter from handling, especially handling a heavy bulky speaker which must be lifted up onto a stand, like the Harbeth M40 series.

However, as I state at the very beginning of this thread: "Perhaps this is of historical interest only. This operation need not be done on the current series of Harbeth speakers because their tweeter guards have a much wider weave to the metal grill work. The guards thus don't obstruct the high frequency sound emanating from the tweeter nearly as much, if at all."

This operation was only intended as instructions for how to improve the sound of the original Harbeth Monitor 40, NOT the later M40.1, M40.2, or M40.3. All those speakers have tweeter guards with wide-enough weave so as not to obstruct the emerging sound to any significant degree.
 
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Addicted to hifi

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I don't think tweeter guards are a bad thing at all. It would be very easy to damage a delicate tweeter from handling, especially handling a heavy bulky speaker which must be lifted up onto a stand, like the Harbeth M40 series.

However, as I state at the very beginning of this thread: "Perhaps this is of historical interest only. This operation need not be done on the current series of Harbeth speakers because their tweeter guards have a much wider weave to the metal grill work. The guards thus don't obstruct the high frequency sound emanating from the tweeter nearly as much, if at all."

This operation was only intended as instructions for how to improve the sound of the original Harbeth Monitor 40, NOT the later M40.1, M40.2, or M40.3. All those speakers have tweeter guards with wide-enough weave so as not to obstruct the emerging sound to any significant degree.
It’s good Know the guard does not effect the sound.
 

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