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Don Sawall
18-08-2008, 08:00 PM
Hi Alan,

I was wondering if any of the Harbeth speakers are shielded especially the C7es3 and the SHL5? I'm considering putting together a system in a small room 11.5 ft by 13.5 ft by 7.5ft H. This is our television room and because of its small size and the way it is laid out, will require the speaker to be positioned right along each side of a 32" tubed tv. I had placed an old pair of ProAc Response 2 in that position and the speakers affected the picture of the television. I was told to look for speakers that are shielded. I want to be able to enjoy quality music in addition to watching television in that room and have read wonderful things in regards to the Harbeth line of speakers, but have not been able to read anything as to if they are shielded.

Thank you for your help.
Warmest regards,
Don Sawall

A.S.
19-08-2008, 01:20 PM
Hello -

The SHL5 and the C7 both have what is called an 'anti-magnet' glued to the back of the bass unit. The P3 has an anti-magnet fitted to both bass unit and tweeter plus a steel shielding can over the entire bass unit magnet.

The anti-magnet significantly reduces the stray magnetic field but does not eliminate it. The shielding can of the P3 reduces the stray field even further. However, I recall demonstrating the P3 at a show years ago as a dialogue speaker sitting atop a large CRT TV. When there was a really loud passage over the P3 there was (to my surprise) a fluttering modulation of the TV picture following the audio signal to the speaker.

It seems to be impossible to say in advance just how much influence the speakers will have on the TV - you'll have to try the speakers to be sure. It would be worth enquiring if the other speakers had any magnetic reduction technique applied at all.

I lament the passing of really good, CRT based TV's since the skin tone was, to my eyes, superior to almost all flat screens. Sony, who produced some exceptionally good CRT sets, seem to produce some singularly unimpressive flat screens - neither detail, skin tone nor contrast look right. Added to that, the shadow mask in the CRT sets seems to subjectively sharpen the picture, which in Freeview, is desperately needed. Interesting to note that for the first time in the history of a television, the new technology (digital Freeview) replaces a mature older technology (analogue UHF TV) with a picture quality which is far, far worse. Yet, who notices? Who complains? The public seem completely blind to vision quality.

Keep that CRT set as long as you can and enjoy UHF TV from a good aerial until they switch it off in just a few years.

Don Sawall
19-08-2008, 11:21 PM
Hi Alan,

Thank you so much for the quick reply. Also, I think it is really great to be able to talk with the actuaul designer...so thank you for taking the time as well as giving us the opportunity.

Do you know if a person's speaker were to give interference with a CRT TV, would the speakers do the same if it were along side of one of the new flat screen tv's such as LCD, DLP, or Plasma TV?

Also, I've been told (not by the designer though) that the ProAc Response Two speakers were unshielded that I had next to the CRT television.

Thank you again,
Warmest regards,
Don Sawall

s.a.b.
20-08-2008, 12:18 AM
I use my C7s with my Sony 40 inch LCD and have never noticed any interference. (Speakers are about one foot either side and placed just in front of the TV.)

Allow me to make 2 ancillary comments:

1. Just using the 2 channel audio outs from the HD Digital cable box, I am still continually amazed as to how good the sound is (and I generally don't even bother using my Velodyne servo sub).

2. At least with respect to the Sony XBR series, assuming the set is calibrated correctly and a good HD signal, the picture can be stunningly good. [I loved my Sony CRT for many many years but even the black levels don't bother me on the newer set; however the newest, and most expensive model XBR 8 will be released in the next few months and will be the first commercial Sony to use their Triluminous LED backlight system for supposedly even better blacks and contrast.]

Enjoy.

A.S.
20-08-2008, 10:14 AM
Interesting follow-up comments from you. Yes, my own experience with a big CRT set is that about 1 foot (say, 30cms) from the side of the TV case to the side of the speaker cabinet dramatically reduces the influence of the speaker magnets on the TV screen. Two foot (600cms) and the influence is practically zero.

A.S.
20-08-2008, 10:23 AM
Pleasure to help. Some days I can squeeze the time to reply, but others not because of my workload.

Do you remember physics at high school?! Once of the experiments I recall was showing how the path of electrons in a vacuum could be bent as they travelled according to a magnetic field placed near to their path. A CTR screen is nothing more or less than a big amplifier tube (valve) on its side with one end open and covered in luminous red green and blue phosphors. Right at the back of the CRT set - and the very reason those sets are so deep - is the electron source (the heater) and the electrons it generates are accelerated towards the screen where they collide with the coloured phosphors and the result is a picture. If you look through the vent holes at the back of the set when it's on you may be able to see the heater glowing as it produces billions upon billions of free electrons.

To make the electron beam scan from top left to bottom right as it builds up the picture every fraction of a second, magnetic coils are arranged around the heater by the tube neck, and these deflect the electron beam by bending it in a precisely controlled way, left/right, up/down. You can imagine that if there are any stray, unwanted external magnetic fields, such as a loudspeaker in close proximity, the electrons in transit from the heater to the screen will be pulled towards the speaker and the picture bent out of shape and/or strangely coloured. Flat screen TVs and monitors are not based around thermionic valves and hence are uninfluenced by magnetic fields: the speakers can be touching the screen.

Well, the C7s at least have anti-magnets to somewhat limit the stray field.

Don Sawall
20-08-2008, 10:51 PM
Hi Alan,

Thank you for such a descriptive and informative reply. It has been a long while since I've been in school. I only wish that more of our teachers would answer questions in the manner that you have just done. School would have been much more interesting and effective.

Unfortunately, the way the room is laid out (accordingly to my wife's wishes) the speakers need to be right along each side (within an inch) of the television. I realize that this is totally not ideal for soundstaging and I can accept that. But, I still would like to be able to appreaciate the great tone of various instruments and voices in my TV room just as I do in my designated listening room.

I have been using a pair of Phase Technology speakers with buildt in subwoofers that are adjustble in sound level. These speakers are shielded and do not affect the CRT. They work fine for watching movies, however for listening strickly to music, they are unenjoyable.

I am not aware of any Harbeth dealers in my area, therefore unable to try in my home. However, it gives me hope knowing that when the time comes to switch to the new flat panel tv's that the Harbeths can be part of that system.

Thank you again and continue the great work and service that you provide.

Warmest regards,
Don Sawall

Crantzbea
16-11-2014, 06:06 AM
I have a similar question, but reversed, so I thought I'd use this thread called "Harbeth speakers and shielding".

I have a 27" DELL LED(not CRT) computer monitor two feet in front of me. Flanking that is a pair of P3ESR. Each is very close to the edge of the monitor, maybe an inch and a half of air separates the side of one speaker to the corresponding edge of the computer monitor.

Here's the thing: I can sometimes hear buzzing in the speakers that correspond to visual activity on the LED monitor. For example, while "scrolling" in a web browser window, I hear a "bzzz" in the speakers while I scroll, and stop when I stop scrolling. Or if I have a game on screen that has a lot of shifting color action, I can hear shifting buzzing on the speakers.

Additionally, the sound that I use for the PC with the LED monitor is completely separate from the amp that drives the Harbeth speakers, as confusing as that may be.

My question is this: can my LED monitor cause harm to my Harbeth speakers? Is that buzzing that the monitor seems to be imparting to the P3ESRs, does that indicate some underlying condition that could cause damage to the P3ESRs over time?

willem
16-11-2014, 11:03 AM
I experience the same, and have assumed the route it takes is through my amplifier rather then directly to the speakers (LS3/5a's in my case). However, that still leaves the question about the origin: is it the monitor or the videocard in the computer? I am currently away from home, so I cannot experiment.

A.S.
16-11-2014, 11:23 AM
Does the buzz change in loudness if you relocate the speakers, even a little? How about if you re-route the speaker cables?

It's certainly nothing inherently to do with the speakers.

Stephen PG
16-11-2014, 11:39 AM
Turn off the monitor, does the noise go away?

Jeff_C
16-11-2014, 11:49 AM
My guess would be that the speakers or their position near the monitor has nothing to do with this noise problem. I monitor sound on my computer with headphones and I used to get buzzing noises when the mouse was moved around the screen. I bought a cheap USB soundcard/headphone amp and the problem was cured.

I think the analogue sound circuity in the computer must have been be too close to other circuitry causing interference. Once the pure digital signal can be converted to analogue outside of the computer the problem goes away.

willem
16-11-2014, 12:41 PM
I recently added the dirt cheap Behringer UCA 202 external DAC to my desktop computer, but I cannot remember if this solved the problem.

It did improve the sound quality compared to the inbuilt sound card. I am afraid I am away from home, and not back for a few weeks, so I cannot check if the buzz has gone.

Crantzbea
23-11-2014, 02:04 AM
Thanks for all of your thoughts. I now have tried moving the speakers, lifting the cables, turning off the monitor even, to no change (still buzzes). So I am thinking that Jeff_C may be on the right track. The difference between his situation and mine is that the sound system that i'm listening to (with the Harbeths) has *nothing* to do with the PC that is clearly causing the problem, apart from the speakers' proximity to that PC and monitor.

I think i've established now that it is not the video monitor. It *does* seem to be linked to some sort of activity on the video card, or perhaps the digital bus on which the video card sits.

Could noise generated on one computer travel through the mains to affect a separate soundsystem plugged into the same wall outlet?

willem
23-11-2014, 11:03 AM
I would be surprised if it is the mains. Are you using the sound card inside the computer or on the mother board to convert the digital signal into analogue?

I ask because I am still a bit unclear about the precise composition of your system.

Jeff_C
23-11-2014, 11:08 AM
Thanks for all of your thoughts. I now have tried moving the speakers, lifting the cables, turning off the monitor even, to no change (still buzzes). So I am thinking that Jeff_C may be on the right track. The difference between his situation and mine is that the sound system that i'm listening to (with the Harbeths) has *nothing* to do with the PC that is clearly causing the problem, apart from the speakers' proximity to that PC and monitor.

I think i've established now that it is not the video monitor. It *does* seem to be linked to some sort of activity on the video card, or perhaps the digital bus on which the video card sits.

Could noise generated on one computer travel through the mains to affect a separate soundsystem plugged into the same wall outlet?

I did not realise that your speakers sound were not sourced from the computer. On the basis that the sound is generated from a completely separate audio source other than the computer, I would try and isolate anything in the audio chain like the amplifier, CD player/radio from the computer main box. Try and get them as far apart as you can. Presumably this "buzzing" is not present when the computer and monitor is switched off, so it must be something to do with proximity of computer and audio electronics.