How to improve your system's stereo imaging -- Hint -- Center focus is key 

As many of you noted I neglected speaker toe-in, my bad! Of course that should be a part of the experimentation for optimizing stereo imaging.

Steve I moved my chair and how right you are. Convincing my wife must be in the next video. Please hurry!

I pulled my 32 years old Heybrook HB1 speakers (with refurbished woofer-rings), powered by an inexpensive Denon PMA 520AE, a bit further into the room (1meter / 3feet from the wall), 2 meters apart, left and right from my tv screen. Placed my lounge chair at an equal distance in the center, applied some 'toe-in' to the speakers to make them point right behind my head. This improved the direct/indirect sound ratio a lot, and also the quality of the low end. I then cut and shortened my old and long speakercables on all 8 ends to a more appropriate length and fitted all ends with new gold plated bananaplugs from Nakamichi. This seamed to increase the clarity and imaging even more! I'm very happy again with my old, simple, but effective, 'improved' stereo set and enjoy listening to music so much more! Thank you Steve for all your advice, tips and inspiring enthusiasm!

that Paris subway map t-shirt looks like a diagram of the speaker reflections in my 9x10 room

I'm a casual listener so your casual drawing at the beginning of the video is all the advice I need!

I use mono recording(s) to establish center focus, and found that with eyes closed while seated with recording playing, I have a better sense of which speaker needs correction. Thanks for the video and info !

After much experimentation I now have my Magnepan LRS positioned and my listening distance locked in the sound stage is spectacular. Vocals if recorded as so the artist is dead center like you can feel their peresence not just a representation but a feeling their right in front of you singing, a little un nerving after a long musical intro but very engaging after the jump factor fades. Room reverb in the recording is huge but forward solo instruments are pure sounding in their placement be it form either side to middle or front to back ,very impressive. Thank you Steve for sharing your knowlege and passion for music and gear ,I look forward to every video. Take care.

Thanks for the tips. I find the real challenge is achieving both dead center stereo imaging plus just the right distance for a nice balance of low frequencies. I switch up speakers every now and then, which means some extra tweaking, but it’s fun for me and rewarding when dialed in.

When I first heard my stereo with spot on stereo imaging, I couldn't believe what I was hearing. During the lockdown, I had been playing with my setup (measuring distance from the side walls, rear walls, distance between speakers, etc) and I use Chet Bakers Sings in mono while making any adjustments. I feel like it's also important to mention for vinyl listeners to ensure their anti-skating is set correctly on their table to achieve the most out of their LP's and stereo.

I've had zero issues with imaging with my first set of Hi-Fi speakers. Placed them 2ft minimum away from any wall boundaries with just a smidge of toe in. It's mostly because they're Uni-fi's, those concentric drivers image so well. Ordered KEF Q950's yesterday so I'll see how those compare. I'm excited!

That was the best and clearest description I have heard on this issue. Thank you. I’m wrestling with a very small room and a pair of Forte II’s so need all the help I can get. Cheers!

I take a great deal from your talks. i am not blessed with space or a good room but following your tips I have a listenable system. The change that made the biggest difference was tilting the front of the speakers upwards to just the right angle. A couple of degrees could make a huge difference. Thanks for your help.

Hey Steve, Love your channel . Although perhaps not 'audiophile' the absolute best stereo imaging I have ever heard (by incredible orders of magnitude) was with a couple of Minirigs held at arms length pointing towards my ears. It truly was holographic and astonishing. I wish everyone could have that experience. It shocked me. The music was just 'there' like a solid, organic entity you were in the presence of - spooky! I think that when you have that 'flesh' almost physically present its a quantum leap participation and enjoyment. You no longer care whether the lowest octaves are reverberating within you chest because the music is simply astonishing in its cohesive purity. Like a live performance it's simply happening and your senses are in jaw-dropping overload. It is simply an ecstatic experience to hear recorded music in that way. In a crazy way it is just 'right' and amazing fun just listening in an effortless and exhilarating way to your favourite music knocking your socks off like it was the first time you heard it but like you were there with your own breath a part of it.

Thank you Steve, ive spent months and months fine tuning my placement and have treatment etc. I never thought to use a Mono track before. I will try it now : )

I have been playing around with extreme toe-in on tower speakers to achieve this center image effect and wrap around sound. Seems to help.

Excellent guide! I would add toe-in and distance between the speakers regarding center of the image... if you put speakers to wide, then you have to do more toe in and vice versa

Great suggestions. With input from you and others I got great results by: 1. moving speakers 4-5 feet from the front wall 2. Moved chair closer to speakers (7 feet) 3. Used the same laser as you to lock in equal distance from ear to speakers 4. Used laser to align distance equally from woofers to mid/tweeters (big impact) 5. Laid some folded thick towels on the floor in front of the speakers 6. Increased the toe in 7. put some sound absorption into the fireplace cavity behind the speakers Clearly my room would benefit from sound absorption. I'll play around with this when the pandemic is behind us and trips to home depot are convenient/safe.

A wonderful, very informative lecture, and explanation on stereo imaging. As for myself, I suppose that behind my left speaker that is a bit further from the wall, and window, I'd put a MDF board, Masonite, or board of plywood behind that speaker. I have speakers that are two-way rear port design, therefore I understand what you are also communicating.

This is the first time I have heard of trying to achieve this affect. I look forward to experimenting!

One thing to keep in mind when it comes to distance between speaker and rear wall: You will get a comb filter function where the first / lowest dip in the frequency curve is two octaves below the frequency with wavelength corresponding to the distance between speaker and wall (very miserably explained). Or: 10 cm / 0.33 feet gives a first dip of 858 hz, 20 cm / 0.66 429 hz, etc. When you reach a distance of 1m / 3.3 feet, the first cancellation is 86 hz. Then there will be a new, slightly smaller dip of 172 Hz, 258 Hz, etc. The closer to the wall you place the speaker, the smaller part of the frequency range will be disturbed by the comb filter. Then there are two problems with placement near the wall: 1 You get a reinforcement in the bass. I do not think it does much. I usually listen to low volume and have small mini-monitors, so a little traction at the bottom is just a good thing. 2 This is a more serious problem: The reflection from the back wall is in a frequency range where the hearing finds much of the information it uses to determine where the sound is coming from. We also move in an area where the ear is sensitive to most of the abnormalities. Fortunately, we are also starting to get so high in frequency that absorbents of most thicknesses work efficiently. Thus, it is possible to get a good stereo image with speakers close to the wall when you have absorbents on the wall behind and between the speakers

I achieved it and I also have the La Scala's behind me too. I discovered it by accident when I was dem'ing a pair of JBL 112's fpr a buyer and I noticed the awesome imaging. The speakers were 3 feet away from the wall and equidistant between listener and speakers, a perfect isosceles triangle. Yamaha DSP-1!

Not knowing much about imaging at all, I accidentally got a center image with a basic setup. I was listening to a Celtic Women CD last year and was like "why does it sound like there's a speaker in the middle?" My quest for imaging has continued ever since. Now (after 39 years) I finally know what the balance knob is for! There's 1 album I have where the image pulls just left. Touching the balance a tad right worked like a champ. Imaging is fun.

great vid. i'm an audiophile newbie. i finally feel like this is an explanation of imaging for me that don't have experienced audiophile experience and vocabulary. many thanks!!!

We have been moving toward wide dispersion/omni directional mono sound for quite some time with single bluetooth and wifi speakers. Just stick them in a corner as they ooze and soothe...

Great video Steve , thanks! Lots of useful information. I have wasted a lot of money on modern stereo 180 gram re-pressings of classic jazz LP's, only to find that the earliest mono pressings of these records, while they cost 4 or 5 times as much as a new stereo copy, do sound more 'holographic', more musical and have so much more aesthetic appeal! Stereo only started to 'work', in my opinion, in around 1968 or so....

Hi Steve . As always a very educational video! I wish you a Merry Christmas and a happy, musical and ahealthy 2021! Greetings from Harald Amsterdam (the Netherlands)

I have notice the height of the back of your listening chair makes a difference. I switched from a high wingback chair to a low back chair and sound improved.

Very right! A symmetrical layout is key to good imaging.

So, so much difference with the placement details as you explain Steve. One of my best demos when I was in retail was to have a customer sit in a properly positioned listening spot and play the speakers. It could be so dramatic to hear that center space sound that is not physically there that some customers would doubt we weren't pulling their legs. Magic! BTW, the great print that is usually right behind you done by an artist with their initials P.P.? Just curious, I took a painting class he taught at Brooklyn College many years ago. Keep up the good work.... Joe G.

Steve, I moved my speakers out from the front wall a little more. Imaging is even better. Good info

God bless you Steve for that mono advice. It helped alot and I didn't previously know about it. Luckely I have one Decca Opera in mono that I used.

Thank you Steve for this video...I think in reality there is no perfect room...I'm not leaving in a perfect room, but just happy with what I got...

Another useful vid. Thanks Mr G. Keep on plugging.

For that “rock solid center” you’re talking about I recommend using a mono system and a single speaker. Stereo systems are all about soundstage, placing the instruments in the right spot (not necessarily center) and keeping them there.

I had to chuckle when you talked about the one speaker set up. We're talking the 1950s here and I was about seven years old with my father brought home for my teenage sister a 45rpm record player which he wired into our 1940's cabinet style radio (one speaker) that we had in our living room, you know the radio that sat there and your phone (party line) sat on top. So then was my teenage sister an early audiophile? It was just a thought.🤔

I find that the ability to generate a good center is directly related to the ability of the speakers to throw a good soundstage in general. Some speakers are very forgiving, like my old B&W DM220s, or my new SVS bookshelf speakers in my theater. My Magnepan .7s had to be toed-in just right in order to focus the center. So, to me, it starts with the speaker and you adapt the room and the placement to suit.

I’m running a 3.1 Klipsch setup, Denon receiver, Mini DSP, to control dual SVS subs, streaming Tidal, sitting about 6’ away from center channel, sounds magical in my 330 square foot room.

I would like to add to Steve's good remarks that the angle of the two speakers can be important. There is no one recipe for all. Some speakers, e.g. LS3/5a only need 7 degrees, others need more...depending on how focused they radiate and so on. But it should be taken into account in each individual case.

Great video. Im still working on this as my imaging does pull a bit to the right.

Excellent Steve! Thank you! I suggest to add an acoustic guitar music to check the center image focus.

Thanks Steve. I love your videos.

Good poop. I *think* few things show up faults in your vinyl playback system quicker than playing a good mono record and listening closely to it in stereo. This especially exposes speaker placement issues, but also cartridge/arm/turntable issues. All must be perfect *!* to hear the music come from a spot in space.

Better than just a mono track - use a mono pink-noise track (some test CDs, like the first Stereophile disc, have them). You may discover a room/setup issue than means different frequencies are "sprayed" around the room. Fixing those through repositioning your speakers will prevent the effect where, say, a centered soloist or vocalist will seem to "move" on different notes.

i'm not a audiophile but getting imaging from my modest TLS floor standing speaker is effortless, no room treatment, nothing fancy. just 3meter away from the speakers. at first i thought my center Channel were alway on until i realized it was just the left and right channel. i would really love to hear how the so-called audiophile imaging sound like someday.

At my village, earlier years, my uncle had a small radio cassette player over the fireplace....

Paradoxically I tried reflecting speakers, full range Lowther 1 foot towards the front wall additional to big direct speakers and I am having a great centered image.

Thanks for the tips, Steve. Mono is fun and gives you a different perspective. However, sound field placement of instruments, and consequently what is being played, can be critical to fully enjoying what the production team had in mind. Many Steely Dan recordings serve to illustrate this exceptionally well. Cramming everything into the center keeps the listener from hearing the parts as intended, which can often make or break the aural phenomenon. Oh .... no mention of length of wires, what do you think .... anything to that?

My experience has been the recording will make the biggest difference. I can play a CD where the sound appears to magically appear from a 3rd dimension space between the speakers, and the next CD doesn’t provide this nirvana.

I've noticed the recording itself also makes a big difference regarding center image

Not sure if I missed it. But perfect gain match the left and right. Some amps has a gain knob so it can be dialed in perfectly.

Stevemo, You'd enjoy experiencing Danley's Synergy models, in an extreme toed in positioning. Time/Energy Exchange ... whereas moving off center left increases proximity to left, but increases the on axis energy from the right. As with any controlled directivity design, aggressive toe angle creates this situation. Widest sweet spot imaginable via conventional forward radiating loudspeakers. So the Danleys, they pass a square wave, so they're phase/time accurate. Since they're point source, phase accurate ... as you slowly approach one speaker ... progressing all the way until your head is nearing the cabinet, you have ZERO perception of proximity. It's freaky, freaky good. Few years ago, many of us traveled from all over the country to participat in a day long, double blind shootout. The entry level Danley Synergy, up against a (Don Keele) CBT line array from Selah Audio, Seaton Cat12c, JTR Noesis, the latter two are both 3way coaxial designs. The relatively tiny Danley SM60, a 20"x20" box, punched WAY above it's weight with many picking it first place.

Thanks, Steve ! Now I need to recheck that my speaker toe-in is equal .

Steve, I always enjoy your videos, especially the one today on speaker placement and center imaging. However, it would be nice and I realize this address’s only a small percentage of your audience, the placement of corner, Khorns, i.e. AK Sixers. Roy Delgado and his team have done. A really beautiful job on designing the latest iteration of this speaker, they’re enclosed box desighn allows one some latitude in placement as far as a corners are concerned. However, best imaging is still achieved with full corner placement on the K horn, and a few other speakers, the disadvantage of this, of course is your sweet spot is very narrow, which is fine with me since I’m usually the one in the sweet spot. I’m going to experiment a little bit with placement having the box a little farther out in the room and I’ll report in if you like on this Subject sometime later.

I actually used a tape measure/level for mounting my TV, centering the audio rack and speakers. My leather chair is smack in the middle.

Another great episode!

I have it Steve! Klipschorns and the equilateral triangle technique makes it easy. With tube gear its even better because I still have pin point center image plus wider and deeper holography!

i Think people keep there speakers against the wall because you get more bass and purely practical purposes. I have a set of AR3 about 3 feet from the wall with a little rel subwoofer to give me the bass I want. I'm driving them with a fisher 400 which I know is underpowering them but I like the sound. I have been playing around with room treatment the last couple years and it has made a difference. Acoustic Fields has some great videos on how to achieve better acoustics. Another good video is "how to set up and treat a listening room" by Ethan Winter That's a great one to start with. Over the summer I rented a place in the outer banks with my whole family and the living room was huge with high ceilings the acoustics blew my mind. I had my little Klipsch 3 Bluetooth speaker connected to my Astell and kerns mp3 player and it sounded fantastic. It was mind numbing how good it sounded. I use the set up in my bedroom at home and it sounds nothing like it did in that big house. If you have a big room with high ceilings you are off to a great start!!

First, I always make certain my speakers are in phase - easy and fast to do, and I do it unless I'm uncertain. I always do it when I'm assisting someone else. Getting them out of phase should really be difficult to do these days, but it's still possible. If they are not, the rest of this is of questionable value. I normally use a stereo source with a vocalist that should image in the center - easy enough to verify using headphones. There is reflection and absorption. Some sound reduction panels will absorb 90% of what hits them - practically nothing reflects from them, but it is in any case what does reflect will be different than what would be reflected in the examples where there are adjacent similar walls at equal or different distances - and it isn't just the timing. It seems the problem is both the arrival timing of the reflections from left & right, but also the volume being returned to the user. Also, there is the case of a speaker in or near a closed corner vs. the second speaker along an open wall, or open corner (opening into open space). However you have your speakers, they should as related to reflecting surfaces in all respects be as much as possible the same. Same materials, same distances all around, etc. Adjust for other sound parameters, but keep them the same in terms of reflecting surfaces and distances.

My left speaker is a few feet away from wall while right speaker is much farther away from its side of the wall. Since I have to move the cat furniture out of the way anyway, I tried moving it a few feet away from the right speaker to partially simulate the effects of a wall. In effect, it makes the room smaller. Maybe this is a placebo effect but I could swear imaging is better and more focused. I am not sure if the cat likes it though. I agree with the added suggestion of speaker toe-in. The manual to my NHT C3s suggests no toe-in because of the 3-way design. I disagree and find imaging and sound in general are better with slight toe-in but the toe-in is less aggressive than needed with a 2-way design. Another suggestion for good imaging if you have stand mount speakers is good speaker stands. Preferably you should fill them with sand or lead shot.

Another great topic Steve

What you describe is exactly the reason I hated Bose 901’s. With rear mounted speakers on an angle, it was impossible for them to create s realistic center image. They said they wanted to create a “wall of sound”. I wanted voices and instruments spread across a sound stage. I agree with all your suggestions, especially moving the speakers away from the wall behind them.

Steve, I know you're not a book reviewer, but I think you should do a review/recommendation list of what are good informative or entertaining books on audio/audio equipment. A nice book on a persons favorite hobby is a good gift. Especially with Christmas, now that people are more at home with this pandemic going on, people have more time to read.

I know I have everything set up correctly because I had to keep getting up to make sure my center panned material on my 2 channel playback was not actually coming through the center speaker. That mono Sgt Pepper cd though - completely different experience. Sounds like a real rock band, and I actually hear more distinct playing on a track like She’s Leaving Home in the mono mix. Multi channel guy, but the Sgt Pepper mono mix is a real thing.

Just bought a Carver HR 742 and has a button holographic and , wow! Don't care what anyone says it's nice. Saving up for a good powerful Carver amp to crank but work construction and ain't rich but the receiver makes my old Infinity RS 5s sing. Can't wait to get my 7kappas new polydomes and be back in bit- Ness! Enjoy the music my freinds.

Lots of good advice here, I would like to add the center focus will disappear if the volume is too much for the room, so don't play it too loud if you're only six feet away.

I bought my last Classical music cds in the early 90's and most of those and favorites then were Deutsche Grammophon, Telarc, Decca, MMG and a few lesser known brands. Which are the ones that are known to be above average today? Thanks.

I disagree that the center imagine needs to be as tight as possible. It can get too tight and too condensed that it is not lifelike and things in the middle sound too small. Should get the center imagine to sound lifelike. Such as a voice and see if it sounds as big as life. Not blurred though. But also not too small

Nearfield listening helps tremendously to rid of all room anomalies at least many of them. It's a bit too close for my taste but it happens to work.

Properly placed Quad ESLs. Of, course you have to sit in the perfect place.

Steve, I have all in my music room when listen my speakers just disappear and the music is al around me. Room is 14 x 17’ . I am. So lucky’

this is the reason I bought JBL LSR305 because of the class d amplifiers that it has (idk much technically, but assuming this makes the difference) I don't have to be always in the center to have the sound "centered"

I have some dcm timeframe tf-350 that image incredible slightly toed in and 18 off the wall, they have sure surprised me, their pretty tough to beat lately.

So many variables based on sound principals - I guess it all depends whether your table is in front of the band or up the back of the room... ✌️🇦🇺

I have my system on a set of pulleys and use block and tackle connected to my roof to keep center image dead rock solid center.

What are your thoughts on Center channel speaker and the type like MTM? Place it vertically or use a bookshelf instead?

I actually needed it to be a bit off to the left cuz thats were my tv is and it actually worked putting it off just a bit. Not because I watch TV in stereo but because when the center image wasn't coming from directly in front of the TV even when just listening to music it annoyed me lol

Just looked this up today. Certain recordings seem to favor the left channel on my turntable. The soundstage is livelier and fuller on the left. But I can hear pops in the vinyl far right. Just slightly less expansive nusic on that side. My solution? Started playing cds.

Are there recordings where you just can’t get that center? I get it with say - The Talking Heads but with say A Love Supreme by Coltrane Stereo it’s a hard pan. Sorry for the dumb question. Cheers.

Having both speakers EXACTLY the same distance from the wall is critical. I was getting cancellation of voices in the center image and measured my speakers (right and left of each speaker) from the wall and found that they were off by about 5mm. Doesn't seem like much, but when I made sure they were the same down to the mm the center voice in my music reappeared! I must have had a comb filter cancellation of the vocal frequency when they were that distance off. Not saying you can't have the speakers angled in, you just have to have both the same.

How about for a home theater system? Do you need to do that as the center channel can probably handle that imaging issue

my old philips 457's have tweeters on the right side of the front panel, so they are always 10 cm visualy off center and I hate that lol

I’ve got a question for ya sir, I’ve got pretty bad room dimensions, 10x11 w9’ ceilings. I use the ikea kallax bookshelves for record storage and they completely line one wall all the way across. Is it an issue for me to bring my speakers ZU DW’s out into the room in front of the shelves? Would the individual shelve openings create individual boxy reflections? My gear is pretty decent Kinki studio p7, M7 and DAC1, vpi scoutmaster.... my room is my restriction at this point....

Try facing your L and R against LS and RS in a home theater setup 👌

Very Helpfull Tips I just need a bigger room perhaps one day but am Casual Audiophile

Equal length opposite walls are best (as in a rectangle). However, avoid square rooms.

there is Audio Test Tones by Audiolab album on Spotify if anybody wants pink noise in and out of phase to work on their setup.

Establish the listening position based on room modes first and then dial in your speaker placement - if possible!

With planar type speakers if set up with little to no toe-in, is it still possible to achieve a satisfactory center image? Or does one need to be on a axis to achieve a solid center image, regardless of speaker design?

Did Steve say to angle the drivers “in” to point directly at the listening position? Or does it not matter and the speakers can point parallel to eachother? With love, A guy who primarily uses headphones.

While setting up your system for optimal phantom center channel location using music is fine I have found that starting with test signals works best for me. A pure 1Khz mono test signal is a good place to start. Then use 500Hz, 2Khz, 5Khz, 8Khz and 10Khz will initially center things up. Test signals outside that range are less useful. The next signals to use would be White, Pink and Brown noise test signals. These three signals should center up dead center. It'll take a while to get things right but after the techy stuff then move on to your favorate music. Also building a little short between the inputs between your Preamp or Power amp inputs absolutely will center things up. Test signals are widely available for free download off the internet.

Because of my room constraints l have my .7's Maggie's 4 feet from the wall 8 feet apart and 11 feet from my listening position When have my non audio friends over for a listen they are amazed at hearing a proper center sound stage They always tell me it's like being at a live event

When you say 3’ from the rear wall, do you mean the front baffle or should I measure from the back of the speaker? Also, when I toe the speaker in, should I measure the angle of the speaker to the rear wall or measure directly from the back of the speaker to the rear wall as if it was straight ahead?

You don't mention anything about single drivers. I've got a pair of Caintuck Lii-15s that throw a deep and wide pinpoint image and I'm not measuring much of anything. Could this be due to them being open baffle?

Doesn't it help to put your head in a vice? I like imaging and try to set up my speakers symmetrically and I use some room treatment, but I have never heard "precise" imaging in a concert and I still think music listening is more enjoyable as a social activity (My next speakers will be Ohm omnis.) So, while I am a serious music listener--when I sit down to listen to music I focus completely on the music--I usually won't go to extremes to play equipment sound games. I guess that makes me just a music lover and not a true audiophile equipment hobbyist. That said, I really enjoy Steve's advice on how to better reach my goals of getting the most realistic sounds possible (admittedly, never fully achievable) of instruments and voices from my systems.

When I get too close to the speakers the drivers don't get a chance to integrate. Happens with 2 way bookshelves and big towers.

I used to make a fuss about all this at home. However, when I started spending a lot of time driving around the country I got less concerned with "laser focus" and such. Most of my music listening time was in the driver's seat of a car. You sit where you sit and the speakers are where they are---among the doors and glass all around. There ain't a whole lot of tweaking. I just overwhelmed the space with loud dynamics to cover all the problems. I had no complaints, you gotta do what'cha gotta do and I didn't enjoy the music any less. Some of that carried over to home and I got sloppy and hardly touch the speakers anymore.

Absorbers and diffusors can also cause problems and kill frequencies, that is my experience. You have to measure exactely which effect you want to have or what your soundproblem is. I solved my soundproblem with removing all absorbtion I put on my walls. (-; Sometimes it is a question of 1cm of speaker positioning if your sound is perfect in your room or unlistenable. If you have a problem with too much low frequencies, in average living rooms: Forget about absorbtion: Theese waves are about 10-12 meters, you can only "break" them with about 4 meters of absorbtion. And keep in mind that with absorbtion you also absorb frequencies that were good before absorbing, but bad after absorbing. Speaker positioning and listening positioning is, with the "matched" speakers to your room and music taste- right- the key to success. Don´t mess around with absobtion and diffusing if you are not satisfied at least 95% with the sound, move your speakers, move your...ears, that´s for free with better results. My experience.

What about speaker orientation? I just got my first pair of speakers (Kef R7) and I'm just setting them up now, but unsure if the cones should face you directly or if they should be facing straight forward with you in the middle. Thanks!

It would be cool to get a center image wherever you are in the room so that everybody can enjoy the sound the way it is meant to be heard.

A bit off topic question: I got my ls50 Meta last week and they came with sponge pucks for the rear ports. When and why would I want to use them?