At what point your sub or mid-bass unit hums?

[ironbadge]

I purchased a VTF-2 MK4 and a MBM-12 MK2 few months ago. I did not notice they hum at that point. Recently I found the VTF-2 MK4 hums, with or without the RCA cable attached, from 9 o'clock volume level. The humming increases with the volume increasing. The MBM-12 MK2 exhibits the same humming at 11 o'clock volume level.

With the cable attached, the noise is a typical electronic hum; without the cable attached, the noise is more like a rumbling. I detached the cables completely, or detached them at the receiver end, they still hum. I unplugged the power plug and plugged it to the other outlet across the basement, the mid-bass still hums (I did not try this with the sub). To my knowledge, the previous homeowner did not have cable TV but they had Verizon FIOS like I do now. I do not use TV services. I use antennae. No other electronic or electric or any other equipment was operating at the times I observed the humming.

I talked to HSU tech support and I was told that is normal. The gentleman also told turning the units past the 12 o'clock level is too loud. He told me the volume knobs should be at 10-11 o'clock levels max. I have very limited knowledge about electronics but I took some electronics courses before. I was told if it hums, it's not good.

Here are my questions:
1. Is this normal? If not, how bad is it?
2. At what levels do your units start humming?
3. Can a power conditioner device help?
4. Any other solution can help?

I appreciate all your inputs all your helps!
Best,
ib.

[ironbadge]

Last night I had dinner with an electronics engineer and I asked him about the humming. He said some capacitors may be bad leading to some AC leaks hence the hums. He said there should be no hum at any volume level.

[D-Shark]

Ironbadge wrote:

With the cable attached, the noise is a typical electronic hum; without the cable attached, the noise is more like a rumbling. I detached the cables completely, or detached them at the receiver end, they still hum. I unplugged the power plug and plugged it to the other outlet across the basement, the mid-bass still hums (I did not try this with the sub). To my knowledge, the previous homeowner did not have cable TV but they had Verizon FIOS like I do now. I do not use TV services. I use antennae. No other electronic or electric or any other equipment was operating at the times I observed the humming.

I talked to HSU tech support and I was told that is normal. The gentleman also told turning the units past the 12 o'clock level is too loud. He told me the volume knobs should be at 10-11 o'clock levels max. I have very limited knowledge about electronics but I took some electronics courses before. I was told if it hums, it's not good.

I purchased twin Mid Bass Modules and twin ULS-15's about 3 years ago. Like you I had a hum very similar to what you describe. This morning I turned both up to Max Volume and they are dead quiet. Now it took me 3 years to figure out how to eliminate ground loops and AC noise that were creating the Hum.

First thing, if you have not checked then go to Lowe's and get a 120 volt outlet tester and confirm that all you wall outlets have proper continuity and earth ground.

Second thing, check to see if you have lighting dimmers, florescent lights with a ballast, a furnace or other items on the same AC circuit as your subs. These type of items on the same AC circuit can feed the AC circuit with noise and cause problems.

Third thing, Your Sub and MBM have 2-prong power cords which means the amps in both units are not grounded to Earth Ground at the wall outlet. What I did is attach a simple test lead (purchased at Radio Shack) from a toggle switch on the sub amp to the metal chassis of my surge protector (see black lead in photo). The surge protector chassis is bonded to Earth Ground via the power cord to the wall socket. The red test lead is clipped to my MBM. Doing this provided a proper Earth Ground from the Sub amp chassis to the power outlet earth ground and eliminated 80% of my hum due to what I think was a Ground Loop.

Last thing, I recently installed the Furman AC-215A Surge Protector / Power Conditioner shown in the photo. Without it I start to get some hum from the MBM with Volume set at 3:00 O'clock. With it I can turn the volume knob to Max and the MBM is dead quiet. The Furman seems to do a good job cleaning up noise in the incoming AC and eliminated the last 20% of sub hum I was getting. This is the best price I could find:

http://www.amazon.com/gp/product/B003PJ6NPO/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Currently I have my MBM and Sub volume knobs set at 1:00 O'clock and the Bass is full, even and wonderful. My system is 2-channel only and tuned for music listening. You might notice that I'm using Speaker Level connections to the Sub & MBM. I find this method provides a more seamless integration with the Mains. Hope this gives you some ideas to try, don't give up.

[ironbadge]

Originally Posted by D-Shark

First thing, if you have not checked then go to Lowe's and get a 120 volt outlet tester and confirm that all you wall outlets have proper continuity and earth ground.

Will do.

Originally Posted by D-Shark

Second thing, check to see if you have lighting dimmers, florescent lights with a ballast, a furnace or other items on the same AC circuit as your subs. These type of items on the same AC circuit can feed the AC circuit with noise and cause problems.

Yes my basement has all the things you mentioned. It appears I need a conditioner.

Originally Posted by D-Shark

What I did is attach a simple test lead (purchased at Radio Shack) from a toggle switch on the sub amp to the metal chassis of my surge protector (see black lead in photo). The surge protector chassis is bonded to Earth Ground via the power cord to the wall socket. The red test lead is clipped to my MBM. Doing this provided a proper Earth Ground from the Sub amp chassis to the power outlet earth ground and eliminated 80% of my hum due to what I think was a Ground Loop.

I wonder why this grounding stuff was not designed and integrated into the subs and MBM in the first place?
Now it appears this works. What is your permanent installation?

Originally Posted by D-Shark

Last thing, I recently installed the Furman AC-215A Surge Protector / Power Conditioner shown in the photo. Without it I start to get some hum from the MBM with Volume set at 3:00 O'clock. With it I can turn the volume knob to Max and the MBM is dead quiet. The Furman seems to do a good job cleaning up noise in the incoming AC and eliminated the last 20% of sub hum I was getting. This is the best price I could find:

http://www.amazon.com/gp/product/B003PJ6NPO/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

An AVS member directed me to this Mark Seaton's suggestion: a Monoprice unit. I have not ordered it, but like it as it has more outlets. I may need two of them because my audio tower is twenty feet away from the bass units. What do you think?

Originally Posted by D-Shark

Hope this gives you some ideas to try, don't give up.

I certainly will not give up. I am still waiting HSU's response to my email I sent two days ago. In the meantime, I will try all your suggestions. Thank you very much. I appreciate your help!
My last resolution will be asking the engineer, who happens to be my uncle, to fix them. However, I really want to see how HSU handles this issue. I am not settled with my audio stuff yet, so I really want to find and work with responsive providers.

[D-Shark]

I wonder why this grounding stuff was not designed and integrated into the subs and MBM in the first place?
Now it appears this works. What is your permanent installation?

In my case using the test lead to ground the sub chassis to earth ground at my surge protector eliminated the hum caused by a ground loop in my system. The test leads are my permanent solution since they can't be seen from front.

There are reasons why Hsu may have elected to use a 2-prong power cord instead of a 3-prong with Earth Ground. In some cases (but not all) this can minimize the chance of a ground loop. I could write pages here on Ground Loops, they can be tough to track down.

That being said each home environment is different and impossible for a manufacturer to anticipate all possible variables when it comes to subs. Short of coming to your home Hsu can only offer suggestions and not much more. Point being don't expect Hsu to respond with a simple fix. You are going to have to do a little work here to solve the problem.

Hsu makes a very good sub and you would likely have the exact same problems with another sub.

An AVS member directed me to this Mark Seaton's suggestion: a Monoprice unit. I have not ordered it, but like it as it has more outlets. I may need two of them because my audio tower is twenty feet away from the bass units. What do you think?

I'm not familiar with the Monoprice unit. In my case I needed two units each with only 2 outlets (one for my left Sub & MBM, one for my right Sub & MBM). What impressed me with the Furman AC215A were all the positive reviews from Guitar Players using them for their Guitar Amps and Pedal Boards. The Furman unit is of real solid construction and worth every penny for my needs. I had to have surge protection and the Filtration appears to really work unlike on some other devices I have tried.

The Furman unit really seems to do a good job of power conditioning in my system. On my subs it eliminated most of the Hum without attaching the Earth Ground. With the Earth Ground attached everything is Dead Quiet. My advice would be to order one of these units (Furman or Monoprice) from someone like amazon with a good return policy and see if it works. If not return it and try the other.

[D-Shark]

Ironbadge wrote:


I wonder why this grounding stuff was not designed and integrated into the subs and MBM in the first place?
Now it appears this works. What is your permanent installation?

Sorry, I had to Chuckle a Bit since a few years back I had one of Velodyne's better 18" Subs that had a low level HUM. Tech support at Velodyne advised me to try a "Cheater Plug", an adapter that converts the power cord from a 3-prong (with Earth Ground) to a 2-prong (without Earth Ground). Lifting the Earth Ground did not improve the situation in this case.

I think a lot people live with Sub Hum because they are told this is normal. In more recent years as I have learned more about proper grounding & AC noise suppression I have been able to eliminate Sub Hum in most cases. It takes effort and some trial & error.

[ironbadge]

I will get some alligator clips to test the grounding as you did. My sub's plate would look a bit funny because mine is facing out so I can adjust the volume easily but I don't really care as long as the sound comes out right. I just received a pair of Belkin surge protectors and will try the coax connection as suggested by Mark Seaton. I will certainly get a pair of power conditioners because I need one for the audio tower and one for the bass units.
I tried to attach a picture was not allowed. Strange.

[ironbadge]

Originally Posted by D-Shark

Point being don't expect Hsu to respond with a simple fix. You are going to have to do a little work here to solve the problem.

I got a response from HSU. Just some questions to clarify something. It appears I am on my own.

Originally Posted by D-Shark

My advice would be to order one of these units (Furman or Monoprice) from someone like amazon with a good return policy and see if it works. If not return it and try the other.

I may get both of them: one for the audio tower and one for the bass units. ChromeJob suggests using a UPS. Have you ever tried a UPS?

[D-Shark]

ironbadge,

Did you have an luck with the noise isolation devices for the coax cables? My guess is you may have noise entering your system from more than one source?

I do not have experience with a UPS in an Audio System. Trouble is all these devices (surge protectors, power conditioners, uninterruptable power supplies, etc.) make claims yet I have found big differences in how effective they are.

I don't think a UPS necessarily provides better power conditioning. I go back to the Furman AC-215a that I purchased, I have been impressed with it's power conditioning capability. Furman has other products with more outlets you might want to consider.

This might be of interest: http://www.musicplayers.com/reviews/...rmanAC215a.php

[ironbadge]

Originally Posted by D-Shark

ironbadge,

Did you have an luck with the noise isolation devices for the coax cables? My guess is you may have noise entering your system from more than one source?

I will try it this weekend. I will need a longer TV coax cable though.

Originally Posted by D-Shark

I do not have experience with a UPS in an Audio System. Trouble is all these devices (surge protectors, power conditioners, uninterruptable power supplies, etc.) make claims yet I have found big differences in how effective they are.

On the other hand, one or some of them may be effective for some reasons (!) so I may have to try them all.

Originally Posted by D-Shark

I don't think a UPS necessarily provides better power conditioning. I go back to the Furman AC-215a that I purchased, I have been impressed with it's power conditioning capability. Furman has other products with more outlets you might want to consider.

This might be of interest: http://www.musicplayers.com/reviews/...rmanAC215a.php

I am a bit skeptical about the UPS but ChromeJob's experience was good. Again, if it works then I will go for it.

[ironbadge]

Originally Posted by D-Shark

Currently I have my MBM and Sub volume knobs set at 1:00 O'clock and the Bass is full, even and wonderful.

The HSU technician I spoke with said the volume past 11 o'clock is too loud (!). I am comfortable with the VTF-2 MK volume at 10-11 o'clock and the MBM-12 MK2 volume at 12 o'clock. Few of my CDs require a little higher volume. Your volume level at 1 o'clock is even higher than mine, meaning my volume levels are not that high, so I'm surprised when I heard the tech's comment.

[Dr_Hsu]

Originally Posted by ironbadge

The HSU technician I spoke with said the volume past 11 o'clock is too loud (!). I am comfortable with the VTF-2 MK volume at 10-11 o'clock and the MBM-12 MK2 volume at 12 o'clock. Few of my CDs require a little higher volume. Your volume level at 1 o'clock is even higher than mine, meaning my volume levels are not that high, so I'm surprised when I heard the tech's comment.

Note that the VTF-2 MK4 amp has much higher gain than the ULS. Hence most customers find 9 o'clock is plenty high, especially when connected to a receiver's sub out. On two channel systems, it can be a different story. It then depends on the gain of the power amp driving the main speakers, and the sensitivity of the main speakers. If you are using a tube amp with very high gain and a high sensitivity speaker (say a Klipschorn with 104 dB sensitivity), then the volume setting on the sub need to be much higher. Another factor is the room. If you sit in a bass shy location, like in the middle of the room, again you may need high volume settings on the sub.

[SME]

I run my two MBMs along with two subs off a MiniDSP 2x4 with unbalanced outputs. Unfortunately, the MiniDSP taps out at about 0.9 V, which is a lot less than most receivers. So to ensure I have enough headroom I have to run my MBMs with gain at around 1 oclock.

At that gain level, I have a bit of hum, but it's not audible unless the room is dead quiet or I put my head up to it. My guess is that most of the hum comes from the long unbalanced signal cables that run under the floor and that I could eliminate it by using XLR cables and transformers to convert to unbalanced at each MBM.

[ironbadge]

Originally Posted by Dr_Hsu

Note that the VTF-2 MK4 amp has much higher gain than the ULS. Hence most customers find 9 o'clock is plenty high, especially when connected to a receiver's sub out. On two channel systems, it can be a different story. It then depends on the gain of the power amp driving the main speakers, and the sensitivity of the main speakers. If you are using a tube amp with very high gain and a high sensitivity speaker (say a Klipschorn with 104 dB sensitivity), then the volume setting on the sub need to be much higher. Another factor is the room. If you sit in a bass shy location, like in the middle of the room, again you may need high volume settings on the sub.

Thank you very much for your response, Dr. Hsu. I am honored and grateful. Please forgive my ignorance and treat me like a student. I am a 25+ year accountant/auditor/financial analyst but just a novice in audio. I hope our discussion is similar to classroom exercises. If at any point you think I may have made an inappropriate comment, please understand I never intend to do so and please let me know. Thank you in advance.

I do not have a lot of money. In fact, I have very little money, but I save to buy good stuff, and I baby them. As you can see under my signature, that is a lot for a poor guy, but my wife is well cared and happy and my son is about to enter a college (that I pay), and I am very proud. Another secret is, I let only two of my friends touch my audio video equipment.

I am an Asian. Half of my life is a long journey traveling through "time and space," 23 years and from the other side of the Earth to be exact, from the land of the red and home of the slave to the land of the free and home of the brave recently. Ten years ago I spoke a little English and now just a little better English so please also forgive my accent. I held off my love for music and sound for that long. Now I am slowly but steadily boarding the train of the magic of the sound.

All I want is to make sure my bass units (the VTF-2 and MBM) are in good health and working as they are supposed to. Like I said, the audio engineer, who also happens to be my uncle, said the hum is not normal and that irritates me. I understand nothing is perfect but if something is wrong it needs to be fixed. I do not care much about the power, but I care a lot about the fineness of the equipment. It is difficult for me to admit to someone that "it is a HSU unit and it hums." It hurts. Really.

One thing I do not understand is, if the amp will start humming if the volume is set past 11 or 12 o'clock, then why don't we just limit it at that point? Or, if we need to have that much gain, then why don't we have some fixes to eliminate the hum completely? I think the hum adds noises to the sound and that will distort the sound and decrease the performance of the whole system.

My "listening area" is actually a cave in the basement and there is only one spot I can sit. I need to perform sub crawlings to determine the good sub spots but I can only do it in a week or two. I will post some pics to share with HSU's members

At this point, as a beginner, I start with some simple stuff. In the very near future, I will be working with my uncle to revive his tube amp inventory. Then I will be slowly going back to the two-channel land. With tube amps. I need to save some money for that.

I understand that working with audio experts, more like artists, like you, is not like working with numbers, like me. It requires a lot of compassion, a lot of "like," and lot of in common, and a lot of patience. I know it because I watched my uncle fixing and modifying speakers, amps, pre-amps, TVs, cassette tape players, and things I was unsure what they are long time ago. For some reasons, I believe the audio people are not too much about money

I will try all I can and I will report the result. I believe we here at HSU will find the truth and have a result. If the result is not very favorable, please let me know if other HSU units can have lower humming effects. I would try that option, too.

[ironbadge]

Originally Posted by SME

So to ensure I have enough headroom I have to run my MBMs with gain at around 1 oclock.

At that gain level, I have a bit of hum, but it's not audible unless the room is dead quiet or I put my head up to it.

As you can see, I only use an AVR. My MBM starts humming at 11-ish with or without the cable. Same symptom with my sub but at lower level, past 9. Yes, with both, I need to place my ear next to them and the "cave" is dead quiet.