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Tweaks?IntroductionIf you want to colour your CDs green go ahead, its cheap (use a marker :)). Quite a few people claim to hear a difference, and What Hi-Fi actually conducted a blind test for the green stabiliser ring. 3 members of the public invited to the test actually said they heard a difference. The blind test involved a variety of tweaks including changing interconnects. It appears that the green ring produced a greater change in the sound than did the interconnects! Index and the revamp Part I: Isolation
PART I: ISOLATION For myself, the only tweak I would recommend is some sort of isolation platform for your CD player. I've installed Sorbothane feet on my player (which weighs 15kg) and decoupled the glass shelf its on from the rack via Black Diamond Mk3 cones. The sorbothane feet bring about minor improvements whilst the Mk3 cones are really impressive. At least it didn't make the sound worse! There're a lot of isolation products on sale, feet etc, but of course, ultimately, platforms are the way to go [I still haven't managed to save $640 for the Shelf yet... note: the price in Singapore is now like $900...]; in Singapore there's:
Can't afford it? (neither can I yet) The next best solution is to go for feet, and there's so much to choose from.
And speaking of isolation platforms, an Equipment Rack also works wonders and complements any isolation measures you take. This applies to isolation in general, but you get a lower noisefloor, more bass and tiny improvements in soundstage. I think the Americans take the view that glass shelves are useless, but then, they haven't experienced the 'Mana' effect yet. Mana is this company with a cult following in the UK (especially with Hi-Fi choice) making equipment racks and supports. Relatively expensive, they suprisingly, have a following with those involved in pro-audio. According to Stereophile, Sony demo-ed new equipment supported by Mana. And to the point, Mana uses glass tops decoupled from the rack by 'tuned' spikes (could that be the secret?) My own Target D3 stand also has glass tops decoupled from the frame by what appears to be 3M sorbothane stoppers. Target and Soundstyle are good, cheaper brands. (i.e., the sound definitely improves over placing it an ordinary TV/video rack). Update: I have just found out that Electrades has increased their UK rack prices by more than 20%! As they are the sole dealers of Target and Soundstyle, I can't call these 2 brands cheap anymore. I am in the process of looking for alternatives and the best bet so far appears to be to drive to Malaysia to buy a rack. Will update when I find out more. For more isolation, you can replace the sorbothane stoppers (or whatever it is for your rack) that decouple the shelves of the rack from the equipment frame (hmm, that seems to more prevalent in UK products) with RMS (Reference Music Systems) Carbon Fibre supports. They're small enough to fit, inexpensive, and do a good job (think of them as mini Black Diamond Pyramids). Of course, now that I've mentioned it, Black Diamond Racing Pyramid Cones [Review] are another value for money investment. They go under everything, including speakers. You may not be comfortable with 3 per component though. I can't find any sonic difference between 3 and 4 under the component so for the sake of stability, you might want to put 4. [also, over time, your equipment shelf is going to warp after a few years if you put 3 cones on a 15kg CD player :)] Ok, but personally, after some testing, I think that replacing the CD players/components feet changes the sound and that this might not always be for the better. Sure, there are soundstage improvements, but the sound changes as well. It appears that investing more in getting a good platform (Seismic Sink, the Shelf, Brightstar etc) is better then buying feet as platforms are more 'neutral' in the way they improve the sound. But if you like the improvements from special feet, sure. Currently, I'm retaining the original feet but I'm decoupling the glass shelves from the Target rack by Black Diamond Racing Mk. 3 cones.
Spikes and Speakers. Interestingly, some people claim to hear no difference whether or not their speakers and/or equipment have spikes installed. Well, thats possible, since I don't know what sort of room their equipment is in. But basically spikes are critical. Actually good spikes are critical. There was a What Hi-Fi test of cheapo IXOS spikes that were to be put under equipment. 3 members of the public were asked about their opinion. They didn't like the sound change. One explanation is that stuff vibrates at different frequencies. Some have a less deleterious effect on equipment than others. Spikes do not damp vibrations (except maybe the carbon fibre ones which do absorb some vibration), but they can tune the vibrations (definitely not out of hearing range, as some claim, but where it does the least harm). The alternative is to use Audioquest's big sorbothane feet for speakers weighing less than 20kg. Actually, nothing's stopping you from using both. Just put a marble slab in between them. But apart from regular spikes, you can try Black Diamond Racing Pyramid Cones (Mk. 4), or alternatively, Mana Acoustics Sound Bases. I like sound bases as they're basically stands for small floorstanders. They provide isolation, they raise the speakers 5 cm from the floor (if you have a woofer/floor problem, this could be a solution), and they allow you have a level base to place your speakers on [far easier than trying to adjust spikes on your speaker!].
GRANITE SLABS
UNDER SPEAKERS In assessing the sound, I was aware that since the tweeter height changed, I might be hearing differences because of this, so I adjusted my listening height to 30mm higher. Of course, increased distant from the floor also causes changes due to speaker/floor interactions; but that is part of the point of putting speakers on something... its not really the mythical properties of marble/granite anyway. Oh yeah, just to repeat, my floor is parquet, very different from granite, so I would expect to hear some change. For those who have granite/marble floors, any difference would probably be a change in speaker/floor interaction (if any). Anyway, the sound did become a bit brighter which annoyed me a bit since my system leans on the bright thin side. I had to break out my AQ ferrite clips and the TDK EMI filter (which I removed after installing the Vansevers) to tame the sound a bit. After doing the tuning, I could put my finger more accurately on the sound. It does sound more 'thrilling' with a better pace and more importantly better timing. The music takes on a greater precision (perhaps because of the increased speed seems to make notes attack with greater snap). Listening to Mary Chapin Carpenter's Come On Come On, on the first track, I was pleasantly surprised with better treble detail and a delightful 'shininess' to the instruments that I have associated with the metal-coned Monitor Audio PMC series. Though the pace has increased, this does not mean that the treble cuts off abrubtly; in fact it still 'shimmers' delightfully in space. So provided you're able to compensate for the increased brightness (or your system is not bright to start with), granite tiles are highly recommended in the 'cheap and good' category :)
PART II: ELECTRICITY Electricity Power Cords Hmm, are we in the twilight zone already? I've read the discussions in rec.audio, but I still have no idea whats the scientific basis behind power cords improving (or even changing) the sound. Anyway, Stereo Electronics at Causeway Point (previously at Beauty World Centre) (yes, the one that sells Wadia and Classe amongst other things) advertises weekly in the classified ads offering 1 week trial with full cash refund. They offering 3 grades of power cords; $100 [multistrand], $200 [solid core], $400 [even thicker solid core]; add $20 for a Hubell plug [without a fuse, its supposed to sound better as well]. They're supposed to be 'UK handcarfted' but I have my suspicions - especially - the box has no CE marking required by EU law [maybe the shop gets the cords in bulk and puts it in the box]. I opted for a $100 with the normal 3 pin fused plug (you can trade in 100% of the value in 3 months). A-B-A-B testing is relatively simple, just plug in and out the cords. Plugging in the cord into my integrated amp, I though I heard a big difference, then plugging back the old cord, I realised the difference was not that great. Furhter plugging in and out showed a consistent (but yes, subtle) difference. OK, lets do the clearer differences first:
More subtle than that was a perceived sense of a larger soundstage. I would not want to gamble my money on detecting this on a blind test (I would for the crisper transients) so it may all be the power of suggestion, I'll have to listen more closely and get back to you after becoming more familiar with the sound. And this is just a cheap power cord. I wonder what one of those $500+ wonders will do for my system [considering diminishing returns, not much], still I can always go for a free trial with the $200 solid core cables they're offering. For $100, its a bargain, and you get a free cash refund trial for 7 days. Who cares if no one has heard of the brand before.. Trust your ears :)
Remove the fuse on the 3 pin plug You see all those UK magazines recommending removing the ordinary fuse and replacing it with a gold plated fuse as it sounds better. Obviously, if you remove the fuse altogether, it should sound even better. In my experience of blowing stuff up, I am pretty sure that the fuse on the 3-pin plug is pretty useless. I mean, we have tons of 2-pin plug equipment without fuses, and in the US, their 3 pin plugs have no fuses as well. The protection is actually provided by fuses inside the equipment or faster acting circuit breakers/ MOVs on your power distribution strip. These items will blow way before the 13 amp fuse on the plug blows. To get rid of the fuse, you have to get 2 plugs. Basically, the neutral connector has no fuse and the live connector is the one with the fuse. Pull out the live connection and replace it with the neutral connector from the other plug. You may need to drill/cut a bit of the plastic to allow the live wire to access the new connector. But the new connector itself is a 'drop-in' replacement for the old one. Ferrite Rings over Power Cords Ok, we are really in the twilight zone with this one. Theoretically, by adding impedence to the cord , you are supposed to suppress radio frequency interference because, in effect, your power cord is a antenna.(or something like that, I'm no science student :)) Once again, Stereo Electronics gives you 7 day cash refund trials for a pair of Ferrite clamps at $30 per pair (no brand). Pertama, Musicbox sell Audioquest Ferrite rings in nicely sealed packages. Home trial? You wish. Once again, trust your ears. Myself? I can't hear any differences I would care to put money on in a blind test, but the perceived changes have piqued my curiousity such that I'll keep them for further experimentation. The changes have got to do with the sound being more 'closed-in' with the ferrite rings over my CD players power cord. [of course, 'closed-in' is a negative effect, but If theres a removal of the high-frequency haze that surrounds many vocals, it might be beneficial] Will report further. For fun, I clamped it over the connection to my subwoofer.Bass seemed to sound worse. Of course, I could be making all this up in my head. For what its worth, quite a few people have e-mailed by saying that they hear an improvement with ferrite rings too. Stay tuned... :() TDK EMI filter This is also covered elsewhere, and is here for completeness. Basically, its a black box that plugs into a US shaped socket and has another US socket for you to plug it stuff. 3 amps max. I didn't like it with my CD player plugged directly into it as there seemed to be some high pass filtering that removed some 'space' and made some tiny nuances like breathing, (listen to Mary Black's Shine. I heard a breath
Power Conditioners So far, I have had comments about the Chang Lightspeed 6400 and the Audioprism Foundation 2. Recently, I went back to Stereo Electronics at Beauty World (where I bought my power cord) to try out their $140 filtered power distribution strip. Its just a ordinary looking power distribution strip with apparently minimal filtering ability (at least compared to the $500++ Powerwedges and Changs) and a very thick power cord. There are 4 sockets for standard Singapore/UK 3 pin plugs (i.e. not the US Hubell type.) Bottom line: it does work, but you get what you pay for and I'm still saving up for a Powerwedge. Also, the thick power cord is too long for my room. The components are about 5 ft from the wall outlet. The amps power cord is 5ft long and plugs straight into the wall outlet. With the filter strip's power cord at 6ft, you can imagine the mess of wires (don't mention the cables for my home theatre). There was a bit more blackness when music was played, and placing my ears next to the speakers with no music playing (of course), the slight hissing sound was different (not softer just different). Of yeah, the hissing sound from the speaker is influenced by the digital components. With my SDP-EP9ES plugged into my amp, the hiss is also different (noisier too). What this means, don't ask me though. Playing 'Song of Reconciliation' from the Ashton/Becker/Dente album 'Along the Road', I detected a increased fullness in the sound. Quite unexpected, but A/Bing showed this to be the case. Volume setting was of course constant. Elsewhere, there were tiny improvements in soundstaging, focus etc. When I A/Bed, I am certain there was a difference. But there were difficulties in quantifying the sort of improvements there were. I have apparently contradictory opinions about treble extension. On Mary Black's Circus, the vocals became a bit harsher perhaps because of increased treble detail, yet on Holly Cole's bright 'Don't Smoke in Bed', the vocals seemed fine, or even better. Sibilance did not increase at all. However, I'm in the market for a Powerwedge, and even the shopkeeper states that the $140 is still not as good as a $600++ wedge (though at least equal to the Power pack of Chang 3200) and the differences here. Bought a Castle
Line Conditioner for fun Therefore, the amp is still plugged direct into the socket and the CD player & subwoofer (with TDK filter) are plugged into the Castle. There is only the tiniest of improvements over my lovely Winstar distribution strip. (note: I have a Winstar and Wonpro distribution strips - the Winstar sounds better - more controlled bass). But with my system becoming a touch brighter with the installation of Nordost Blue Heavens, the Castle is actually quite welcome. But note, the Castle has 8 outlets in a neat package. A winstar/wonpro with 8 outlets would be unbelievably long and would cost like $50/60. So the Castle doesn't cost all that much more. Recommended? Yes. Still, the 7 day money back trial, compatibility with Sinapore 3 pin plugs (Hubell adaptors cost about $7 and worries of poor contact [these adaptor are cheap stuff meant for hairdryers etc] arise), audible though small improvements make this item highly recommended for those with cheaper systems or those who want an improvement, but will never spend $600+ on power conditioners.
PART III: OTHER TWEAKS THAT COST MONEY Bedini Ultra Clarifier Over the holidays, my friend brought his Bedini Ultra Clarifier (BUC) to my house and lugged along an unsuspecting non-audiophile. At first, we thought we heard significant differences. But, I've kept the BUC for several days and I've been doing more methodical A/B testing. The main problem is that it is difficult to do A-B-A testing as you cannot 'unclarify' the CD. A-B-A testing frequently reveal that there are actually no differences, or that the differences are far more subtle than initially thought. Ideally, you should have another person 'clarify' the CDs with the caveat that he does not clarify it 50% of the time. You then have to guess whether or not the CD is clarified. Given that you have a 50% chance of being correct, I think a high rate of success would be required to be statistically significant. If you don't have a 2nd person available, you could have 2 copies of the same CD (listen to them to make sure they sound the same first :)), so that you can do A-B-A testing. Myself, even when doing A-A-B testing, I found myself not really hearing any difference for most of the CDs I listened to, and for those where I heard some difference, the effect is so subtle I'm note sure I would successfully detect them in a blind test. My A-A-B test was designed to minimise the effect the noisy motor would have on my hearing. It is possible that the Clarifier's noisy motor messes with your hearing. First, I listen to, say 1 min of the track. Then I pause. I act like I'm clarifying the disc, i.e., maintain a 1 min pause, turn on the clarifier on another disc. Then relisten to the CD. (I have to admit that after listening to the jarring motor noise, I thought the CD (which was not clarified and was just sitting in the CD player) sounded different) Then I actually clarify, then listen. Hence: A-A-B testing. Occasionally, vocals and/or instruments would seem better seperated and more spacious. But I really couldn't hear anything else. Perhaps it just doesn't work on my CD player. Further, this is just some flimsy black plastic box with a motor; production costs can't possibly be a fraction of the S$190. At that price, I would agree with critics that its a con job. [not because it doesn't work, but because its ridiculously overpriced] In addition, since I haven't heard of a single shop offering home trials, and the fact that this product doesn't work in all systems/CDs, it can't really be recommended, given the fact that $190 can buy lots of CDs or worthwhile tweaks (like isolation).
Contact Enhancers I use Pro-Gold to treat all contacts, including power plugs and the fuses in the plugs. In addition, after watching my dealer do it, I've removed my woofers and treated the connectors connecting internal wiring to the woofer with pro-gold. On my speakers, they appear to be ordinary nickel and would be vulnerable to oxidisation. I treat my computer contacts with pro-gold as well. Pro-gold is highly recommended since you can use it for all sorts of electrical equipment. In addition, it is heat-resistant and can be to treat tubes. According to the Audio Research website, some brands of contact enhancers cannot take heat and form into some kind of gunk if they are subjected to heat. Note: there are 2 types of Pro-Gold, G5 which is only 5% Progold or G100 which is 100% Pro-Gold. Get the G100 from Soul of Music as they have the best price.
Anti-Static Spray
Demagnetising Discs. Certain manufacturers like XLO/Reference Recordings, Sheffield Labs, Densen, make CDs with tracks that demagnetise your system. What Hi-Fi, Hi-Fi Choice, & Hi-Fi News and Record Review all endorse its use. I have the XLO/RR disc. It works. After demagnetising (it acutally randomises magnetic fields rather than demagnetises), vocals become clearer as high frequency response is improved. The most significant improvement came when I demagnetised a 7 year old Sony/Carver/JBL system. This was done for 2 non-audiophiles. They heard the difference clearly. Makes sense that old equipment will show the greatest improvement.
PART IV: THINGS THAT COST (ALMOST NOTHING) Ambient Noise While the equipment is warming up, cool the room with air-con at full blast, then turn it off for critical listening. Alternatively, try to get a super silent air-con. I have a Sanyo multisplit and its relatively nosiy. So remember to choose your aircon wisely. I minimise the noise by switching on the air-con in a adjacent room and opening the adjoining door to let the air flow in :) Also, things like ticking clocks also have to go... [you don't notice the ticking until you really get into the listening session :- does it mean that the listener also has to 'warm up' his ears :)] Warming Up Well, its been objectively shown that total harmonic distortion (THD) in equipment that has been switched on for like 10 minutes is higher than in equipment that has been running for several hours. Equipment needs time to reach correct operating temperatures (even speaker cones) I can hear quite clearly the difference in equipment thats been turned on for 10 minutes and equipment thats been running for 2 hours. The former sounds bright and thin. Warmup times do depend on several factors so the only advice I can give you is to let your equipment warm up before serious listening. I let my system warm up for at least 45 mins (about the time to play 1 CD) before any kind of listening [while waiting, I'll do things like edit my webpage :)]. Do you need to leave your equipment on all the time for best sound? The answer for equipment appears to be yes, according to some manufacturers, but I do not have personal experience in this. Personally, I don't bother, why waste electricity, and if lightning strikes... booom. I'm sure you know some people who had surges due to lightning, quite often, their whole computer is fried. For serious listening sessions, the warm-up time for my equipment will be at least 2 hours. Sometimes, I turn it on on Saturday night (but of course, while I'm sleeping, no music is played) and leave it on till Sunday. It sounds wonderful. Speaker Adjustment / Sitting Position. Placed last not because its unimportant, but its soooo painfully obvious and probably the first advice given by any self-respecting audio enthusiast. But sometimes, the advice is sooo general that newbies have no idea. So I'll just give my own experience: (front, rear, right, left is with reference to the listener's position) I do not have an ideal room (what an understatement). Its a tiny 12' x 13' effectively 11' x 13' because of a large bookcase on the sidewall. The flooring is parquet. On the front and back walls, there are curtains. There is a half-height cabinet on the rear wall. The right wall is bare except for a small Ikea pine table (not the 'Lack' table -- subject to a prolonged [and as usual, very painful] debate in r.a.o as to whether such a table has audiophile properties :)). where I dump my CDs (standing upright of course -- well, Laserdiscs warp if you lay them flat, so... ) Toe-In : The minimum
possible (Feb'99) For toeing-in, my advice would be to try and use the least amount of toe-in possible. Ideally, you should not need to have any toe-in. Basically, most of the top of the line systems I've heard did not have much toe-in as they already had fantastic imaging, so they can just point nearly straight ahead to maximise soundstage. So don't forget, if you do a tweak or an upgrade that greats focus and imaging, you might want to reduce the toe-in of your speakers to see whether you can have increased soundstage and good focus at the same time. Basically, after adding Blue Heavens to my system and mass-loading my speakers again, I found that the sound was incredibly focused but a bit relentless. Then I realised that I had recently increased my toe-in of the speakers (I think while the Blue Heavens were still breaking in). After reducing the toe-in considerably (I think this is the least amount of toe-in I've ever used), I still get strong central imaging, a wider soundstage, and the music gets pushed back deeper into the soundstage.
Update: I've moved my roomstuff here. Mass Loading Speakers Someone wrote into Stereophile extolling the virtues of stacking massive amounts of lead shot on speakers. Though we might not go to his extent, there appears to be some benefit in mass-loading speakers. There may also not be any effect at all, as I've discovered. It depends on the speaker and the floor. On regular spikes & parquet floor, my speakers did not seem to benefit from placing 7.5kg of weights on them. When I replaced the spikes with cones, the sound improved slightly, and when I then placed 7.5kg, it improved a little bit more. I can see that weights might cause the sound to worsen if the weight is made of material that amplifies the resonances/vibrations of the speaker. I put a metal weight on the speaker (with a book in between to increase the distance in case things get magnetic :)). The weight 'sings' along with the vibrations of the speaker. However, if I put a piece of foam between them, the weight stops vibrating as the speaker vibrations are soaked up by the foam. I cannot honestly say that I can hear a difference I would be able to detect in a blind test though, but I leave the foam in, because it makes sense that the weights you use to load the speaker shouldn't vibrate along. > Lest you all think I've stacked a stack of weights 2m high, the foam+weights is about 4 cm high. I can't hear any deterioration in soundstaging which should theoretically occur :) To test whether or not mass loading benefits your speakers, play some bass heavy track loud. Mass loading should tighten the bass. My test track is the Mo-Fi remaster of U2's Joshua Tree. More Bass = More
Mass Needed< (Feb'99) Prior to that, I was using 7.5kg of weight per speaker. Afraid that the stacks of metal weights may affect soundstage but obstructing sound and other general worries, I did an A/B at that time and couldn't hear any difference between 5 kg and other heavier weights. So I removed some weight and kept 5kg of weight on each speaker. After 100 hours of breaking in the Blue Heavens, I sat down to contemplate the sound. I was troubled and worried by a seeming lack of focus. Eventually (thats about several days of tweaking), I placed some more weights on the speakers and suddenly, the music snapped into focus. It was quite amazing. This suggests that where more bass and louder volumes are involved, mass loading becomes more essential. If you had previously found mass loading not important, you must reconsider this each time you tweak your system and increase the bass/volume.
PART V: ROOM TREATMENT (old layout. sans waffles, weights on speakers, and the DNA) Some Tools we need for speaker placement
Yes, if one speaker is one inch nearer than the other, I can hear the difference (at my 7' listening distance). No kidding. If the speakers have differing toe-in angles, you can hear the difference too [but its more subtle than different listening distances]. If your floor is uneven, your speakers may not be level. Thats where the bubble level comes in. In addition, if you have a high seating position or you're sitting close, you may want to angle the speakers upwards a bit. And Yes, the point about keeping speakers level also applies to all other components (pretty obvious), especially your CD player. Sitting Position Related to the placement of the speakers is the placement of yourself. The ideal listening position is about 1.5 x the distance between the speakers. Thanks to room rearrangement and the removal of a small bookcase at the rear wall, I now enjoy a 1.5 x listening positiong. . Also, your ears should be roughly tweeter height. (of course, this depends on the design of the speaker) , but needless to say, there is an optimal height, and its up to us to find it :). Any piece of advice is that you should not sit too near the rear wall, but given the Singapore-style room space constraint, you have to compromise. If you want the speakers far away from the front wall, you'll have to move your listening position backwards. Personally, I find moving the speakers away from the front wall more important for the soundstage. As for being too close to the rear wall, you can treat your rear wall with thick acoustic panels. If you put your speakers against the rear wall, you have minimal soundstage, no matter how you treat the front wall. Caveat: I'm not asking you to lean your head against the wall; the bass will sound reallly funny :). My listening positiong is about 2 feet from the rear wall. (update: now about 3 feet from rear wall - much better)
Room Treatments aren't really tweaks, they're essential for getting the best out of your system. Imaging, focus, and soundstage are affected tremendously by room acoustics. If you can't hear the difference when you install new interconnects/power cables etc, the reason could be that the room reflections are masking the differences brought about by them. With treatment, I can hear problems with my speaker positioning very clearly :- things like small differences in toe-in angle and speaker distance. With some treatment, female vocals become 3-dimensional and the soundstage ranges far and wide. Of course, with cheap equipment, the soundstage impression is that of 'back' and 'front' whilst for others the impression is of true depth with back, front, and everything in between... If you have problematic room acoustics, it becomes difficult to hear the differences between equipment as spurious high-mid frequency reflections mask the sound. Generally, room treatment involves placing items that absorb and diffuse sound.
(2) At the sides (sidewalls) (3) Behind the listener (rearwall) (4) On the floor (5) Ceiling midpoint between you and speakers (6) Ceiling corners If you're sitting near to the rear wall, rear wall treatment obviously makes the most difference. In my room, rear wall treatment makes the most difference, followed by front wall and lastly side walls. Which goes against conventional wisdom that says that side walls are the most important place to treat; but then I have a small room :) The effect of sidewall treatment is difficult to discern until :-- you treat only 1 side of the wall, then you'll notice your perfectly place stereo image wander a bit :)
It should be noted that such treatments generally affect 100Hz and
above. I can't comment on bass treatments yet because I don't have
a bass problem :) (dunno, after I isolate my components more, I'm
sure to get more bass) Such items are manufactured by RPG, ASC, Illsonic
and Michael Green (Mr. Room tune). Roomtunes takes a different approach
to room treatment which I feel is more suited to larger rooms. Treating
any of the above will bring about improvements though I can't predict
which will bring about the greatest improvements. It depends on the
room. Its also important to note that these items (well, at least
my Illsonic panels -- but then, all these items have standardised
NRC ratings, so performance is similiar) are far more effective than
thick curtains, which I've also tried.
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