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.
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.
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! |
