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post #1 of 37 Old 03-25-2013, 05:23 PM - Thread Starter
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It’s been over a year since I completed my purpose built music and video room; and I have recently been persuaded by some forum members to post my experience.

Let me first of all say I am not a great fan of “pretty” home theater rooms, if you have the need, time and budget that is fine, but that is not what I was looking for nor did I want support for 3D. I wanted to put as much of my money, as I could, into the audio and video technology and acoustics of the room. Having my roots in both the professional music recording industry and secondly in broadcast video I wanted a room that gave me great audio performance for stereo and 5.1 audio with support for 2.4:1 video and 11.1 film sound.

Due to a complete remodel of my home, I had the opportunity to add “my own piece of heaven”. A dedicated music room that supported video. It had to meet many criteria, some of which were:

• Within budget – it was not elastic.
• Acoustically well controlled before the application of any electronic EQ.
• At least 60dB SRI to the main home, as I like it loud at night.
• NC level of 25dB or better with HVAC active.
• Flat RT of 0.2 secs. from at least 63Hz to 20KHz.
• No windows for total light control
• No secondary decay.
• Acoustically symmetrical for all audio modes; stereo, 5.1, 7.1, 9.1 and 11.1.
• Screen & projection system to support both 16:9 and 2.4:1 aspect ratios.
• Support vinyl playback.
• Seat three people.
• Technical systems to support:
o Separate 100 amp 120VAC single phase supply; straight of main 200 amp feeder to house.
o Separate safety ground from main house system.
o Isolated technical ground system.
o Balanced line levels to all active speakers.
o SD/HD SDI support for most hardware, I hate HDCP.
o Green pure sine wave UPS, only active upon power loss– not double conversion due to audible noise.

Well that was a start for now; I also had to deal with the realities of the various building code issues such as old underground pools, local streams and building lines that cut through where the room was to be built. These issues dictated the maximum room size if I was not to exceed the budget.

The room was to be part of the new renovation not a separate building. So it was designed as a fully isolated “box within a box” to reduce noise transmission and to have its own low velocity ducted HVAC system. The noisiest equipment, the projector, was to be installed inside the room, its NC rating was 27dB, but the room design supported its movement to an external placement if it became a noise intrusion.

The resulting available space provided for a room that had a finished size of 18’ 6” L x 12’ 8” W X 8’ H. These selected dimensions provide the most uniform spacing of all room modes and met a number (but not all) of well-known acoustics criteria. However, it restricted the placement of subs to either; two at the front 1/3 in from each side wall or four by adding one in each rear corner, (you will see why later). The other restriction that rapidly became apparent was that width speakers were never going to be possible so I deleted that requirement.

Although my goal was to design the room with acoustics similar to a recording studio control room, it was not practical/necessary to have the speakers raised above the floor as in a recording studio. This would have severally restricted the screen width and I did not want to use a perforated screen. Also due to space restrictions and access issues the door had to be almost in the center of a sidewall and the equipment rack needed to be located within the room on the same side as the door. This “rack room” was also to form a plenum chamber for 30% of the HVAC air entering the room besides cooling the equipment. The remainder of the air was fed through plenum chambers behind the front LHS/RHS speakers. The returns occurring from plenum chambers behind each of the larger rear surrounds.

So what equipment was to go into the room? I purposely chose the main five speakers to represent types that were frequently used in recording studios and cutting rooms and that had a THX PM3 rating. All the satellites needed to compliment and closely match their frequency response and power handling with the crossover frequencies to all HF units being the same. I already had a pair of subs that I liked and were a good match to the selected 11 satellite speaker system and had sufficient output to drive a 1900 cubic ft room. I say 11-satellite system, as there was to be two pairs of surrounds. The larger pair matched the front three for 5.1 music, the second smaller pair were for film surrounds. Each pair was appropriately positioned to meet their performance requirements.

A/V equipment List:

• 5 Genelec 1038’s for music and film
• 4 Genelec 8040’s for rear and side film surrounds
• 2 Genelec 8030’s for front heights
• 2 SVS PB12 NSD subs
• Audyssey XT 32 Sub EQ for primary sub equalization
• Denon AVP-A1HDCI with Audyssey XT32 upgrade + Pro kit.
• Denon DBP-A100 + SDI mod
• Denon DVD-3800BDCI + SDI mod
• Denon DVD-5900 + SDI mod
• Toshiba HD A35
• Thorens TD160S + Hadcock GH228 arm + Lentek Entre cartridge and head amp.
• iScan VP50 Pro with SDI
• BenQ W10000 with ISF calibration
• Panamorph UH380 lens with sled
• Da-Lite tensioned dual mask screen – 115” diagonal for 2.4:1.

So what did the room design end up looking like: see the attachment showing the various elevations.



In my next post I will review the room construction techniques selected, and why, and post some of the foundation, floor and framing pictures.

Pauls HT Room Model (1).pdf 166k .pdf file
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File Type: pdf Pauls HT Room Model (1).pdf (166.4 KB, 72 views)
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post #2 of 37 Old 03-25-2013, 06:46 PM
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Hi Paul...glad to see you took KBarne's advice and decided to post about your experience.  One thing you'll find is most forum members won't take the time to download attachments so be sure and post your pics "inline" (i.e. use the insert image icon instead of the paper clip).  If you don't have anything to convert files such as PDF, try using a snipping tool or some other screen capture program.  I took the liberty of converting your PDF to a jpg for you so others who might not download could comment.  Look forward to your pics!

 

Joe

 

EDIT:  Removed picture since it was added to original post

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post #3 of 37 Old 03-25-2013, 07:15 PM
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Awesome! Subscribed!


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post #4 of 37 Old 03-25-2013, 08:11 PM
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Same here!!! Looking forward to this build!

Ray

 

"Listen with an open heart and mind."

 

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post #5 of 37 Old 03-26-2013, 04:30 AM - Thread Starter
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Quote:
Originally Posted by jkasanic View Post

Hi Paul...glad to see you took KBarne's advice and decided to post about your experience.  One thing you'll find is most forum members won't take the time to download attachments so be sure and post your pics "inline" (i.e. use the insert image icon instead of the paper clip).  If you don't have anything to convert files such as PDF, try using a snipping tool or some other screen capture program.  I took the liberty of converting your PDF to a jpg for you so others who might not download could comment.  Look forward to your pics!

Joe



Thank you for the advice, will do.

I will post again tonight.

Paul

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post #6 of 37 Old 03-26-2013, 04:50 AM
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So looking forward to this thread!

Embedded photos are great, but they often disappear over time, while attachments are on the AVS.
This should be one informative thread, so I'd suggest embedded and attachments.
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post #7 of 37 Old 03-26-2013, 06:05 AM - Thread Starter
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Originally Posted by Tedd View Post

So looking forward to this thread!

Embedded photos are great, but they often disappear over time, while attachments are on the AVS.
This should be one informative thread, so I'd suggest embedded and attachments.

I have updated my starting post as requested. Sorry for the "beginners" errors, I have not uploaded images before to any great extent so I am new to this.

Paul

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post #8 of 37 Old 03-26-2013, 08:14 AM
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Fantastic!
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post #9 of 37 Old 03-26-2013, 06:00 PM - Thread Starter
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The following drawing shows the construction techniques used to build all the walls and HVAC details etc.



Wall X Sections Model (1).pdf 108k .pdf file

So, starting with the foundations that were to support both the house extension and the new music room, I went with 8” concrete block with the three walls that supported the music room being filled with concrete to remove all voids and increase mass. These had a double row of J bolts to hold the two separated plates one for the outside and inside house walls and one for the music room plates. Building a second foundation wall just to support the A/V room was not an option due to budget nor would it have provided any significant improvement in my isolation. The mass of the void-less wall was more than sufficient to reduce any sound transmission between the isolated plates.


PIC 1358 the Foundation

The spacing between the plates was typically 1”-2” around the new perimeter while I positioned the room to provide at least a 4” spacing between the rear music room wall and our family room where my daughter & wife play a grand piano. The rear of the room was isolated from the main house by sitting that wall on a pair of joists that spanned the new outside wall to the new internal wall isolated plates.
The plate spacing isolated the music room floor from the house main structure and provided sufficient area to create a 2” space between the three remaining room internal and external walls and build the room to its correct dimensions.


PIC1414 Joists and Rim Joists

PIC1419 Isolated Plates

PIC 1437 The Final Floor With a 4" space at the rear and 1"-2" around the remaining perimeter

PIC 1729 Door Opening showing plate spacing and air gap between the finished framed walls


Impact and vibration tests on the A/V floor confirmed that the transmitted sound to both the family and breakfast room floors was inaudible.

What you cannot see from the above pictures is that all flooring to joist, to plate and rim joist etc. were all caulked both sides of the breakfast/music room foundation wall to close any open air gaps. This was really tedious and time consuming. It doesn’t take much of a penetration to significantly impact an NC rating. As I was striving for at least 60dB then nothing could be ignored. This requirement also affected any holes that needed to be punched through the music room walls to support back boxes and prohibited any sockets or light switches being mounted in the adjacent breakfast room wall. This meant that all power outlets along this adjacent breakfast wall were to be floor mounted, just as in the music room. The only light switch that was allowed in the external wall was the one next to the back door due to a framing issue.


PIC0895 Breakfast Room & Switch

The back box was mounted inside an airtight ¾” ply box that was later injected with hard polyurethane foam. This provided an acoustic performance similar to what would be achieved from the 2 layers of drywall. This technique was also used for all internal wall boxes that fed speakers, projector, utility socket and switches.


PIC0833 The Problem Switch

The outside framing was relatively conventional 16” OC except that the adjacent family and breakfast room walls were framed right up to the roof. This would allow me to acoustically seal of the music room volume from the rest of the house.





PIC1539/1540/1541/1546 External Wall studs

Once these walls were framed they were covered with two layers of 5/8” drywall; all joints were taped and staggered. This was again all caulked to seal any air holes between the construction/drywall and house framing. These walls would then be filled from the outside with 3” Roxsul to dampen them.


PIC0872 Dry Walled External Wall

I now had a sealed area and a fully isolated floor that I could frame the music room in. In order to reduce the chance of having the same resonance and coincidence wall frequencies and therefore significantly reducing the isolation at those frequencies the internal room studs were placed on 24” centers; all other studs being on 16” centers.




PIC1681/0877/0862 16” & 24” Music Room Studs & Blocking Looking towards the rear of the room.

Once this “free standing” frame was constructed it was in-filled with Roxsul. The wall framing (inside and out) had wire supports added to ensure that the Roxsul would not fall into the wall void and that it would press up against the drywall, thereby applying maximum damping. This technique was not necessary for the outside walls above the ceiling or in the family room as the Roxsul could be packed between the 16” studs from the outside.


PIC0897 Music Room Roxsul


PIC1725 Rack Room

Finally the two layers of taped and staggered 5/8” drywall wall added. Please note that ALL drywall associated with this rooms construction both inside and out, was put up using screws, nails were never going to be an option as they loosen with time. I expected significant SPL’s in the music room so the wall vibration would be an issue with nails. It is the drywall that is the ONLY thing that holds the internal shell square so its movement was not an option.



PIC0918/0931 Dry Wall Goes In

I am only posting a small sample of the photos that I have just to give an idea as to what was being built. If you have any specific construction questions after reading this I will try to answer them and include any relevant photos.

Next post; the doors, HVAC and electrical systems.
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File Type: pdf Wall X Sections Model (1).pdf (108.1 KB, 8 views)

Paul

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post #10 of 37 Old 03-26-2013, 06:27 PM
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Paul, Did you hire a specific home-theater company to do all the structural and acoustic design and layout?
thanks
Vik


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post #11 of 37 Old 03-26-2013, 07:04 PM - Thread Starter
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Quote:
Originally Posted by vikgrao View Post

Paul, Did you hire a specific home-theater company to do all the structural and acoustic design and layout?
thanks
Vik

No, I designed all the acoustics and electrical/electronic systems and acted as the General Contractor as the GC I hired went bankrupt very early on in the project.

I used to teach acoustics and electronic systems at a UK University so I have a significant academic background. I have also designed and built numerous radio station and recording studio complexes in the UK, so have a reasonable understanding of how to put that academic knowledge into practice and what does and does not work. However I am amazed at just how often things (acoustics) don't do what I expect them to. I had one of these experiences on this project as you will see if you follow my postings.

Paul

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post #12 of 37 Old 03-26-2013, 07:11 PM
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I have enjoyed and anticipate more. smile.gif

DIY Sound Group Volt 10 surround speaker build

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My Setup Thread

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post #13 of 37 Old 03-26-2013, 07:44 PM
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Thanks again for sharing! Its always great to see the room builds of persons who are experts in this field. Yes i will be following your postings!


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post #14 of 37 Old 03-27-2013, 06:13 AM - Thread Starter
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Originally Posted by vikgrao View Post

Thanks again for sharing! Its always great to see the room builds of persons who are experts in this field. Yes i will be following your postings!

Please remember that an "expert" is just a drip under pressure.smile.gif

Paul

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post #15 of 37 Old 03-27-2013, 12:25 PM
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Instead of being a drip under pressure, I'd rather just be a constant drip! smile.gif. A really annoying loud one!!

Shawn Byrne
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CEDIA Certified Professional EST II - HAA Level III Certified -THX Certified Professional


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post #16 of 37 Old 03-27-2013, 05:54 PM - Thread Starter
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The Doors

The wall construction should be capable of at least an SRI rating of 60+dB (STC 65dB class). So it is no use installing either a single door or just two standard doors. You need the door opening to perform as well as the walls. Otherwise there would be no purpose of going through all this construction only to be let down by poor door performance.

The door blanks that I used were purpose made by Prime Craft and are composed of two ¾” high-density MDF blanks bonded together to make a 1.5” door. Each weighed in at 200lbs. Supporting this is no mean feat so I ensured that my carpenter who was to hang them new exactly what was required and that the framed opening was almost a perfect fit to the door liners so there would be minimal air spaces from shimming that needed to be filled with foam. I elected to work with Zero of NY who specializes in acoustic doors and sealing systems. They provided the hinge assemblies and all door and threshold seals.


PIC Door X-sections Design & Installation
Door X Sections Model (1).pdf 628k .pdf file

AppleMark

The door liners would be set to leave a 1/8” gap between the inner and outer walls that was left un-caulked, then 1” rigid fiber glass was used to line the resulting opening to deaden the space between the doors and absorb any sound leakage.

The doors were to be kept closed using pressure handles but I was unable to get any that met the required access/building codes. In desperation I installed conventional latch locks and added appropriate caulking and fillers to offset the effects of boring holes into the doors; sacrilege.


HVAC

A separate acoustically isolated ducted system was installed under the room using oversized lined ducts and provided a 10% fresh air bleed as the room was effectively air-tight. Installing it above the room was never to be an option due to access, leaks and vibration issues. The sends and returns fed oversized plenum chambers to absorb much of the air noise. These chambers were formed by the rack room and the front and rear LHS/RHS lined spaces behind the main speakers. The power to this system was fed from the house main board in order to reduce any problems with noise and voltage drop.


PIC 0879 HVAC - missing front ducts

This is a relatively small room so I did not require a large volume of air exchange. The maximum heat load for the room would require just under 1TON of cooling. This requires approximately 300CFM to ensure that the air handler doesn’t ice up. Unfortunately for reasons I will not go into now, the HVAC Company installed a 1.5 TON unit; luckily I still managed to get the air handler to operate without icing at 380CFM. This gave me an air velocity at each inlet of approximately 2 ft /sec, a little higher than I wanted but with all the large plenum chambers and method of room dispersal, did not pose a noise problem. Well, only one, the room cools down too fast. This issue will be rectified at a later date.

All the ducts are fully lined and oversized so the final room air noise after feeding the three plenum chambers was just on the threshold of NR25 at the MLP. This can be improved if I manage to get the air velocity down to about 1.0 - 1.5 ft/sec; a future project. It will also help with the room cool rate.

With the HVAC off and no equipment fans running I am unable to measure the rooms noise floor as it is below what my equipment can measure (lowest NR25)

The Electrical System

In my mind, next to acoustics, this is the next most important consideration for the room. It is of prime importance that:

• Any electrical interference from the house, HVAC systems, fridges etc. does not get into the grounding system for the room or it will appear as a signal on the A/V circuits.
• The grounding system impedance is virtually zero ohms or again any interference that gets into the A/V circuitry will appear as noise on any signals.
• The room only uses a SINGLE phase supply or there is a potential to have 220 VAC between devices. This is not only dangerous but can lead to some horrible hum problems.

All these issues were solved by providing the room with its own single phase 100amp 120VAC supply straight of the incoming 200amp house supply. An oversized copper feeder to ensure absolutely minimal voltage drop at peak currents provided this supply. The new breaker box had its own safety ground associated with it and was isolated from the main house safety ground. The rack power strips were all isolated ground type, and a new low impedance technical ground was installed to support all the audio and video grounding requirements. Fortunately most modern A/V equipment is double insulated so does not require a safety ground. This made laying out the grounding system much easier and an isolated technical ground bus bar was added to the rack to which appropriate connections from the equipment were made. This provided the single bonding point for both the safety and technical grounds reducing the effects of any potential ground loops.

The breaker board provides ten 20 amp circuits to drive the rack and powered speakers to ensure that during high current demand voltage drops are kept to a minimum.


PIC 2349 100amp Breaker Box

All speakers are active and they need to be turned on and off when not in use. This was achieved using the X10 series 20amp switched outlets with an IR controller.

When I say this system is quiet…I mean it is quiet at ANY volume with no measurable hum and just the expected very low white noise from the audio chain.

Two UPS/anti-surge units are provided one for the projector (simulated sine wave) to protect the bulb and one for the AVP (pure sine wave) to protect the electronics.

So now I have a room with power, lighting and HVAC. Next post I will comment on the rooms’ un-treated initial acoustic tests, SRI rating and how it was to be setup and acoustically treated.
Attached Files
File Type: pdf Door X Sections Model (1).pdf (627.6 KB, 6 views)

Paul

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post #17 of 37 Old 03-27-2013, 07:18 PM
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Quote:
Originally Posted by Digione View Post

The Doors
The Electrical System

In my mind, next to acoustics, this is the next most important consideration for the room. It is of prime importance that:

• Any electrical interference from the house, HVAC systems, fridges etc. does not get into the grounding system for the room or it will appear as a signal on the A/V circuits.
• The grounding system impedance is virtually zero ohms or again any interference that gets into the A/V circuitry will appear as noise on any signals.
• The room only uses a SINGLE phase supply or there is a potential to have 220 VAC between devices. This is not only dangerous but can lead to some horrible hum problems.

All these issues were solved by providing the room with its own single phase 100amp 120VAC supply straight of the incoming 200amp house supply. An oversized copper feeder to ensure absolutely minimal voltage drop at peak currents provided this supply. The new breaker box had its own safety ground associated with it and was isolated from the main house safety ground. The rack power strips were all isolated ground type, and a new low impedance technical ground was installed to support all the audio and video grounding requirements. Fortunately most modern A/V equipment is double insulated so does not require a safety ground. This made laying out the grounding system much easier and an isolated technical ground bus bar was added to the rack to which appropriate connections from the equipment were made. This provided the single bonding point for both the safety and technical grounds reducing the effects of any potential ground loops.

I'm sure that you've already looked into this, but I recall reading a few NEC references with "gotchas" with regarding to having a sub-panel that doesn't tie into the same grounding electrode as the main panel.

For example:
http://www.naplia.com/homeinspectors/Resources/Sub-Panel%20GroundingFinal.pdf

One final grounding issue: We are often asked if sub panels added at spas and wells can be fed with a three-conductor feeder (two hots and one neutral) and then “grounded” by adding a grounding electrode (grounding rod).

There are four reasons why this grounding method is not acceptable:
1)The primary purpose of a grounding rod is to provide lightning protection. A rod is required for separate buildings with subpanels, but not as a substitute ground fault path for the system.
2)A metal rod driven into the dirt does not provide a low resistance path back to the service equipment and transformer to clear ground faults. In order to clear a ground fault,the equipment ground must be separate from the neutral and be continuous back to the service equipment, as stated at the beginning of this article.
3)Dirt is not a good conductor of electricity, especially when it is dry.
4)Four-conductor feeders are required for all sub panels (even in detached buildings and structures) since the 2008 NEC.

I was just curious.. The more I read the NEC about bonding, grounding and isolated grounds the less I know!

I'm not sure I understood the 220 issue as well. The only way you'll get 220 is with 2 hots........ which shouldn't happen accidentally. I don't think that using 220 (preferred by high current amps) should cause more hum. Am I wrong here? I always thought that ground loops was the issue, not using 2 legs of a single phase service. (220 is still single phase, it's 2 legs, technically split phase, I believe)
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post #18 of 37 Old 03-28-2013, 12:42 PM - Thread Starter
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Quote:
Originally Posted by homeav View Post

I'm sure that you've already looked into this, but I recall reading a few NEC references with "gotchas" with regarding to having a sub-panel that doesn't tie into the same grounding electrode as the main panel.

For example:
http://www.naplia.com/homeinspectors/Resources/Sub-Panel%20GroundingFinal.pdf

One final grounding issue: We are often asked if sub panels added at spas and wells can be fed with a three-conductor feeder (two hots and one neutral) and then “grounded” by adding a grounding electrode (grounding rod).

There are four reasons why this grounding method is not acceptable:1)The primary purpose of a grounding rod is to provide lightning protection. A rod is required for separate buildings with subpanels, but not as a substitute ground fault path for the system.
2)A metal rod driven into the dirt does not provide a low resistance path back to the service equipment and transformer to clear ground faults. In order to clear a ground fault,the equipment ground must be separate from the neutral and be continuous back to the service equipment, as stated at the beginning of this article.
3)Dirt is not a good conductor of electricity, especially when it is dry.
4)Four-conductor feeders are required for all sub panels (even in detached buildings and structures) since the 2008 NEC.

I was just curious.. The more I read the NEC about bonding, grounding and isolated grounds the less I know!

I'm not sure I understood the 220 issue as well. The only way you'll get 220 is with 2 hots........ which shouldn't happen accidentally. I don't think that using 220 (preferred by high current amps) should cause more hum. Am I wrong here? I always thought that ground loops was the issue, not using 2 legs of a single phase service. (220 is still single phase, it's 2 legs, technically split phase, I believe)

I have considerable experience in specifying isolated Safety grounds and Technical grounds as I design recording, radio and TV broadcast facilities. These facilities must meet all electrical codes.

The safety ground issue that you mention is taken care of by bonding the HT room safety ground (inside the new breaker box where it is isolated from neutral bond by removing the screw) to the house safety ground rod at ground level through its own low impedance ground wire connection. So yes they are connected at one point. Actually this safety bond point is the racks isolated ground strip not inside the box. The neutral to ground bond is still present inside the main distribution box only.

My technical ground is NOT a rod driven into the ground it is formed using 648 sqft on welded steel meshing buried under the HT room floor. This Is bonded to several 6 foot copper stakes and the steel reinforcement in the foundations. I can assure you that the ground it is buried in is always damp and its impedance will be far less than the safety ground. Typically a technical ground would be 0.2 - 0.1 ohms.

I have come across rooms where the 120VAC power to the room is actually fed from each phase. A potential for 220VAC then exists between the outlets on different phases. The phase angle difference can induce different ground potentials between any interconnected hardware and as a consequence induce ground currents and hence hum. A problem that I have met on several occasions. It is less of a problem with switched mode supplies but can be very notable with equipment that uses conventional analog supplies.


The NEC electrical codes can ONLY be applied by the local electrical building inspector to new construction that is permitted. Once these inspections are complete the homeowner can do whatever they want at their own peril. smile.gif

Paul

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I have considerable experience in specifying isolated Safety grounds and Technical grounds as I design recording, radio and TV broadcast facilities. These facilities must meet all electrical codes.

The safety ground issue that you mention is taken care of by bonding the HT room safety ground (inside the new breaker box where it is isolated from neutral bond by removing the screw) to the house safety ground rod at the ground level through its own low impedance ground wire connection. So yes they are connected at one point.

My technical ground is NOT a rod driven into the ground it is formed using 648 sqft on welded steel meshing buried under the HT room floor. This Is bonded to several 6 foot copper stakes and the steel reinforcement in the foundations. I can assure you that the ground it is buried in is always damp and its impedance will be far less than the safety ground. Typically a technical ground would be 0.2 - 0.1 ohms.

I have come across rooms where the 120VAC power to the room is actually fed from each phase. A potential for 220VAC then exists between the outlets on different phases. The phase angle difference can induce different ground potentials between any interconnected hardware and as a consequence induce ground currents and hence hum. A problem that I have met on several occasions. It is less of a problem with switched mode supplies but can be very notable with equipment that uses conventional analog supplies.


The NEC electrical codes can ONLY be applied by the local electrical building inspector to new construction that is permitted. Once these inspections are complete the homeowner can do whatever they want at their own peril. smile.gif

Hi Paul,
Thanks for the explanation, I'm jealous of your setup!

I love that you have a technical ground - never mind the fact that you have a really effective grounding system. I didn't realize that the measured impedance of a technical ground is THAT low. Wow.

The phase angle difference is interesting, I bet that was all sorts of fun to diagnose. I thought that generally the split phase service was from the same transformer, so it's weird that the phase angle could be an issue. Interesting. That makes me want to look at the phase angles of my power the next time I hook up my ION power meter.

Your understanding of safety and technical grounds puts you in a fairly small group!

Have you ever measured your safety ground, just for fun? I know that the impedance of many safety grounds is way too high (enough to justify installing additional rods).
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Hi Paul,
Thanks for the explanation, I'm jealous of your setup!

I love that you have a technical ground - never mind the fact that you have a really effective grounding system. I didn't realize that the measured impedance of a technical ground is THAT low. Wow.

The phase angle difference is interesting, I bet that was all sorts of fun to diagnose. I thought that generally the split phase service was from the same transformer, so it's weird that the phase angle could be an issue. Interesting. That makes me want to look at the phase angles of my power the next time I hook up my ION power meter.

Your understanding of safety and technical grounds puts you in a fairly small group!

Have you ever measured your safety ground, just for fun? I know that the impedance of many safety grounds is way too high (enough to justify installing additional rods).

I have not measured the impedance of mine, nor shall I as all is well, but I am required to for some of my designs. When required it is always done by the electrical contractor not me as I am not a certified electrician. The construction techniques for mine were no different to what I specify for a professional system. These typically measure 0.2 - 0.4 ohms. However they are generally much larger in area and often use up to three naughts cables, or in environments were there is a lot of RF noise from switched mode supplies, IP data or RF equipment the ground bonds are made from either flat copper or flat braided copper. The increased surface area significantly reduces the impedance of the ground ties.

Besides having a good technical ground the only thing to remember is that the safety ground, neutral and technical ground are only bonded together at ONE point. No loops must be present such as, left in breaker box bonding screws, or shorts from racks to floor metalwork or HVAC systems.

Lightning arresting systems is a whole different issue that I get involved in. As far as the building is concerned the idea is to make the PD across any technical areas to be as low as possible and prevent the ingress of any strikes into the buildings high or low voltage systems. This is a whole different set of requirements and involves, in my opinion, quite a lot of "black magic" as lighting is very unpredictable. I stay on the fringe of this topic.

Paul

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Besides having a good technical ground the only thing to remember is that the safety ground, neutral and technical ground are only bonded together at ONE point. No loops must be present such as, left in breaker box bonding screws, or shorts from racks to floor metalwork or HVAC systems.

Lightning arresting systems is a whole different issue that I get involved in. As far as the building is concerned the idea is to make the PD across any technical areas to be as low as possible and prevent the ingress of any strikes into the buildings high or low voltage systems. This is a whole different set of requirements and involves, in my opinion, quite a lot of "black magic" as lighting is very unpredictable. I stay on the fringe of this topic.

I'm glad you mentioned about being bonded together at ONE point (at least for my own intellectual curiosity). I forgot that everything is bonded together ONCE. I've read some about isolated grounds and how when not done right, there is either no gain -- or it's worse. So it's cool that you have the background with regards to designing it for commercial spaces -- to get the benefit that it's intended for.

Lightning arresting is too much black magic. Ever since I read a study about a lightning rod with a blunt end was more effective than one with a tip, it seems like there is too much that's counter-intuitive about lightning protection!
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Lightning arresting is too much black magic. Ever since I read a study about a lightning rod with a blunt end was more effective than one with a tip, it seems like there is too much that's counter-intuitive about lightning protection!

Agreed, especailly when you start to use isotopes atop of poles to attract the lightning.eek.gif

Paul

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The Initial Tests

Unfortunately during many of my tests I did not record the results to a file so much of what follows is based upon my memory and paperwork.

• Floor impact tests (a hammer) resulted in zero detectable sound transmission to the two adjacent rooms. Ear on the floor test.
• Using a generator, SVS subs, SPL meters etc. the sweep tone tests resulted in all the expected standing waves below 200Hz spaced as expected; EG: 30,44,60,70,89,92,120,133 etc. (rounded values)
• Walls and ceiling were checked for resonances using a velocity transducer. I was unable to excite a resonance into any of the side walls at the SPL’s I could generate or using a simple impact. However the ceiling was a different matter. It was a large damped flexible membrane and flexed from about 8Hz to 15Hz. Peaking at about 10HZ with almost 1/8” movement (remember my comment about drywall screws!). However, it was very heavily damped so removing the stimulus resulted in it coming to rest “instantly”. This, as I discovered, can show up on certain projected images, they move, during certain extreme LF sound effects; but not TRON.smile.gif
• The major disadvantage of having walls that have high mass is that as I found out, they don’t flex very much and start to behave as concrete walls providing very little absorption to LF; one of the usual benefits of drywall walls.
• The room mode spacing and density was reasonable with little bunching and was as predicted from the room dimension ratios and acoustics criteria that I had chosen.

Many of the original room calculations were performed using Modecalc; the following graphs are reproduced using the JBL & Room Mode calculator application just for this post.


PIC Axial Mode Spacing

PIC All Room Modes

PIC Axial Standing Waves

The room length axial standing wave pattern in conjunction with the minimum seating distance away from the rear diffuser resulted in an MLP at approximately 5’ from the rear wall. This kept the MLP in a well diffused sound field from the rear diffuser and minimized any length node or antinodes. Height and width position cannot really be adjusted so acoustic treatment was needed to deal with those frequencies.

• The preverbal hand clap test sounded like a really smooth, but bright, reverb chamber with approximately a 2 second decay. Surprisingly there was no audible slap echo between any surfaces.
• Creating a white noise signal of 100dB 3’ feet away from the door inside the room resulted in a mid-band 33dB signal being picked up at a distance of 3 feet from the music door in the breakfast room. So my SRI of 60+dB seemed to have been achieved.
Note that this is mid band and is significantly reduced for low frequencies as this is really mass limited.
• HVAC noise measurements at this point were pointless as there were no plenum chambers or acoustical absorption.

Treatment & Layout (see PDF1 post 1)



This is really a highly abridged version of what happened over a 6 month process.

The MLP was effectively set, see above, so all speakers were placed at the optimum positions/angles relative to it. I did ensure that the two sets of surrounds were exactly the same distance from the MLP, you will see why later. Genelec recommends that the acoustic axis of the relevant speakers is directed to the listener. All surrounds were angled and placed according to current recommendations and practices. The subs were then located 1/3 in from each wall as there was no other suitable location. However I did reserve space for two smaller subs under the rear corner large surrounds. Correct placement of height speakers is often an issue for most home environments, even a custom one, so they were placed as high as possible and angled appropriately.

The screen and projector placement was based upon zoom capacity and the largest 2.4:1 screen that I could install. This was a 115” Da-Lite tensioned electric dual mask screen that also supported a smaller 16:9 ratio.

I wanted an analytical room with a relatively short flat RT time of 0.25 secs down to at least 63Hz (hopeful as always), however, I choose to go for 0.2 secs due to a hearing issue that I suffer from. This is a short RT time so in order to create a pleasant diffuse sound field at the MLP I used a 6” deep QRD (sequence +1,+1,-1, +1) on the rear wall to handle the front speakers (and to some extent the rears) and 3” deep QRD (sequence +1, +1)on the side walls to handle the side film surrounds. QRD orientation was to set to achieve the spread desired.

Initially I designed resonant panel/membrane absorbers for the primary modes. However, while they did exactly what I expected them to do their absorption values were far too low and only managed to reduce peaks or troughs by about 3-4dB. They also posed more absorption construction problems for the middle and higher frequencies. This work was a terrific waste of time and money…but I continue to learn.smile.gif


PIC 1229 Rear Panel/Membrane damping

PIC 1231 Front Panel/Membrane damping

PIC 1241 Rear Panel/membranes installed

PIC 1244 front Panel/Membranes installed

The panel/membrane absorbers were removed after numerous tests and replaced with broad band LF traps/absorbers in all corner locations, across the entire front of the room (floor to ceiling), part of the rear wall and broad band absorption at the ceiling wall interface. This gave me sufficient absorption all the way down to 30Hz due to the depth and design of the traps and effectively controlled all room modes. I do not use deep sold “wads” of absorption as it provides high flow resistance and a poor surface area for absorption. What was required for good LF absorption were deep traps with a high surface area (ever been in an anechoic chamber?). Once all this Roxsul was added it brought the peaks and troughs to a range that I believed Audyssey EQ could handle, and it did.

The addition of all the internal woodwork had made the walls very rigid and LF absorption from the walls flexing seemed to be almost nonexistent and now seemed to be behaving as thin concrete walls.

The flat surface under the screen had most of its area removed providing acoustic access to the absorption below to prevent any secondary decays and the rack room was lined with 1” rigid fiberglass with a ceiling bass trap. This treatment served three purposes:
1. It absorbed any fan noise from the players
2. It ensured no secondary decays
3. It provides the sound absorption required to turn it into a plenum chamber

Each room corner area was treated with a mix of 1” rigid fiber glass and 3” Roxsul to create the required plenum chambers.



AppleMark

PIC 2331/1585/1584 Front Absorption



PIC 1587/1589 Rear LF Traps

The remaining untreated side walls and door were treated with broad band absorbers to reduce the predominant modes and remove all flutter echo, which had now become very apparent. This occurred as the masking effects of the all the higher order room modes were now gone. Absorbers were then placed at the primary first point of reflection for the front LHS & RHS speakers.

In order to maintain the maximum possible room symmetry at ear level a dome diffuser was placed opposite the rack, now both walls had hard diffusing surfaces. Absorption was placed above this diffuser to reduce flutter echo and help absorb reflections coming of the rack opposite.

This just left the ceiling treatment and me getting tired and short on funds. I decided that I would leave the ceiling treatment until after the room was complete and I had put down the extra thick high density carpet underlay, the carpet and placed the chairs. These would all significantly impact the floor to ceiling mode absorption so I wanted to see what might need to be added after I got the room measured and equalized and actually listened to some music.

So this is what the room now looked like.


PIC 1882 Front With Cloth Panels

PIC 1879 Side QRD’s with Covered Dome diffusers behind

PIC 2332 Rear with Cloth Panels

Next time, the hardware and cabling.

Paul

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Wow, this thread is very informative and awesome! Thanks!!!

Ray

 

"Listen with an open heart and mind."

 

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Wow, this thread is very informative and awesome! Thanks!!!

+1 thanks Paul for doing this thread!
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Paul, your efforts here are awesome. The thread is very much appreciated. I don't want to derail your narrative, but I would think it would be informative for me and several others if you could describe your efforts in using panel traps; in particular, what were the design goals, the build techniques, and in ways were they inadequate? Did you identify particular limitations that would be generalizable to other installations?

Fred


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Paul, your efforts here are awesome. The thread is very much appreciated. I don't want to derail your narrative, but I would think it would be informative for me and several others if you could describe your efforts in using panel traps; in particular, what were the design goals, the build techniques, and in ways were they inadequate? Did you identify particular limitations that would be generalizable to other installations?

Fred

Thank you.

I will be happy to share those limited experiences as soon as I can get a little extra time. I am trying to get all the all the "main posts" completed in between getting ready for the Broadcasters Convention, NAB, in LV in a week.

So please be patient juts for a while. Also I will not be posting during the NAB week beginning April 7th.

Just for the record almost all the music recording control rooms that I have built use large (passive) bass traps. It was not unusual to assign 40-50% of the volume of the room just to broad band bass traps. Usually, due to limited space, all the radio control room and performance areas were based upon my companies unique design of a wall panel that integrated the panel/membrane absorbers within them. The walls in these rooms were the resonant absorbers having a series of absorbers built in that formed the entire surface of the wall. The IBA (International Broadcast Authority) in the UK would only grant licenses if the rooms met fairly tight RT and secondary decay limits together with the noise and distortion performance of the equipment. They actually came out and measured them all before awarding the license. I have not worked in the UK since 1999 so I do not know whether the old licensing requirements still exists for Independent Radio Facilities. I was "shocked" when I started working in the States that no such "legal" requirements existed for any broadcast facilities and it was just left up to the architects acoustic consultant to fit it in the available budget.

Paul

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post #28 of 37 Old 03-29-2013, 03:39 PM - Thread Starter
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Equipment

A list of hardware that the room supports is included with my signature, so view away. I also covered the major items in the opening post. It does not include any of the displays that I use for monitoring.

AppleMark
PIC 2335 Rack View

So why did I choose the Genelec speaker solution? Firstly I wanted a professionally accepted speaker whose acoustic design was an integral part of the amplifiers design and the required crossovers. The 1038 are tri-amp with tailored electronic crossovers and lots of power and hence headroom to spare and they are THX and PM3 rated. They have good HL & VL dispersion angles, very low distortion at high acoustic levels and a +- 2.5dB anechoic response on axis from 35Hz to 20KHz. These monitors, like most other large monitors should be and were, flush mounted to minimize corner edge diffraction effects.

All speakers were mounted on rubber and felt pads to isolate them from the surrounding woodwork/floor and reduce/eliminate any structure born sound transmission that would cause early sound issues.

The 8040 and 8030 have a similar sound to the 1038, are bi-amped with active compensated crossovers and match the HF crossover frequency for the 1038’s. They also work well when non-flush mounted due to their design. Sure, for the money there are many other speakers to choose from but they are not used in professional rooms for reference listening. I had worked with Genelec’s in several professional rooms and was aware of their capabilities or lack thereof. The main issue for me is that they have a predominant upper mid-range; even when voiced flat. This issue became even more predominant in my final listening tests and is yet to be resolved totally to my satisfaction through EQ.





PIC 2231/1589/1588/1587 Genelecs & Subs in Position


Unfortunately I have no pictures of the height Genelecs as I forgot to take them before fastening the (difficult to remove) covers. You will need to look at the room layout PDF to see where they are mounted.

For its price there is no other Pre amp that provides the range of flexibility, processing and technical performance as the Denon AVP –A1HDCI. Particularly after its recent XT32, 3D and audio processing upgrade. Due to the “limited” number of balanced line outputs from the AVP, especially since the upgrade removed the equalized second set of pre-outs for the surround B’s my setup had to be configured differently to support all the speakers.
I use the external Audyssey Sub EQ to pre EQ the two subs as it contains Sub EQ HT something the upgraded AVP was not supposed to have. Even if it did contain it I cannot use it as I use sub 2 & 3 to drive the second set of smaller film surrounds. This leaves only sub 1 to drive all the subs be it two or four.

I mentioned earlier that the two pairs of surrounds are deliberately set to be at the same distance from the MLP. Their sensitivity is set to ensure that both sets of surrounds speakers require the same signal level to create equal SPL’s. Luckily Audyssey selects the same LF crossover for both sets of speakers and they both use the same HF crossover frequency. All this allows me to use the Audyssey EQ for the 1038‘s to drive the smaller 8040 surrounds. I can load the Audyssey files for either pair (when being really anal) but I am unable to hear the difference using the 1038 EQ on the 8040’s. However, using the 8040 EQ on the 1038’s for music is not a good match. This arrangement allows me to easily switch between music and film surrounds using the X10 powered outlets to activate the pair I need to use as both are driven simultaneously from the AVP.

The system runs 1080P24 for all video sources SD or HD. The projector frame rate doubles that to P48 using the HDMI input. All players except the A35 are SDI modified so I have the option of either watching the HDMI with HDCP output or the SD/HD SDI output via the DVDO VP50PRO with no HDCP. Audio is always processed by the AVP either from the HDMI connection, the DL4 link or optical connections.

You can see the difference between the SDI out and HDMI outs, especially for SD, I have my own believe as to why this is so as both carry effectively exactly the same digital data. I think that it may be related to increased data jitter from the HDCP “processing” that occurs within the HDMI hardware link; just as audio clock jitter audibly effects any audio link; hence the advantage of DL4 for BluRay audio. I wouldn’t be surprised if my previous comment starts a “war”. One which I will not be drawn into, all I know is that I can see a small difference; is it important to me not really; it was more of an academic exercise as I dislike the issues that arise from using HDCP. Unfortunately the data for the SDI hardware is taken from two different locations inside the players. One is the actual output of the MPEG decoder the other is the input to the HDMI chip. In the latter case the data actually has to pass through the scaling hardware so I have no idea what that it is doing to the signal even though it is not scaling it.
For audio comparison purposes, the AVP has copper stereo connections to both the A100 and 3800 for analog CD playback using the AVP both the balanced and unbalanced stereo CD inputs. Looking at the AVP schematics there is no significant electronic design differences between these two inputs, that in my opinion, would be audible.

Finally there is a Darblet attached immediately to the rear of the projector using a male to male HDMI adapter just to add that little something extra, it is set to HD50% and never touched.


PIC 2379 Projector & Darblet

In order to reduce vibration, my turntable sits upon an isolated 25lb granite slab that in turn is isolated and sits on a pull-out drawer. The pre-amp is then situated inside the slab at the front. This keeps all my phono cables as short as possible. I still feel that there are a lot of vinyl albums that can give CD’s a real “run for their money”. I have many of the original Sheffield Lab recordings and enjoy the sonic excellence of performances from, to mention just a few, Harry James, Amanda McBroom and Jim Keltner. However, having said that, these days some of the SACD’s and high bit rate DVDA’s provides stunning stereo and 5.1 performance.

Cabling

This is always a hot topic so I will keep my comments short and simple. I make all my own copper cables except HDMI. All audio cables are made from multi-strand plain copper and do not contain any twisting or wrapping of strands at a soldered joints. All connectors are by Neutrik and gold plated to reduce any oxidization effects. I employ balanced connectivity wherever possible. The phono cables are silver multi-stranded low noise cables that use an insulated central conductor that is then wrapped with a carbon impregnated plastic and then the screen.

Besides the two pairs of copper cables that take stereo analog feeds from the A100 and 3800 DVD players to the AVP the only other cables are the speaker connections; all at line level.
1. The Genelecs all use balanced Star-Quad cabling to ensure the highest possible interference rejection as they are up to 25 feet long. These cables are again plain copper multi-strand and are located well away from any magnetic sources or power cables.
2. The Audyssey Sub EQ and subs require unbalanced line level signals. These interconnects are created using multi-strand plain copper balanced cabling. The hot and cold carry the unbalanced signals while the screen is ONLY connected at the source end to the cold ground connection. Again all cabling is run as far away as possible from any AC power or magnetic sources.

So the next update will review the Studio 6 AudioTools and Audyssey measurements, sorry no REW graphs.

Paul

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Overview

How I based my measurements.

I have never spent large amounts of time creating frequency and time domain plots, as I have tended to just rely on my ears. This approach came about after spending years working with experienced studio owners and then designing and working in professional recording studio environments continually comparing what I heard in different rooms. By experimentation I eventually started to think that I understood what I had to do to a room to make it sound “right”.

Most of my measurements were centered round reverberation times (RT60) and early decays in the main listening area. Back then this focus on having responses to be flat all the way down to “DC” was not really that important. I worked in a music environment not film production and the Foley stage. I generally didn’t care what happened much below 30Hz provide that most the energy down there got absorbed. I well remember all the “hoopla” for the first control room in the UK that was designed to be flat down to 20Hz.

After the RT was determined as being acceptable, EQ was often applied using 1/3rd octave analog equalizers, such as the White, and then often just by ear. Modern day sophisticated room analysis that requires significant processing power, was either too expensive, not available or deemed as not being necessary I.E. we can make it sound good. Remembering that when a mix left your studio it must not only sound good in that studio and the next one, but also on Radio and at home.

So I still tend to rely upon my ears and memory (even at my age) and my classically trained wife and daughter pianists to determine if something sounds right. On occasions I even use a Microtech Gefell M930 to mic up our grand piano (mono) and listen to it on my system.

Currently I rely upon my Studio Six Audio Tools applications, Audyssey and occasionally my SVS-1 for room measurements. REW is an amazing free piece of software for room analysis but I do not yet own a calibrated mic/USB interface to drive it.

For this room most, if not everything I hear and measured, correlates well with what the software I use shows me, what I expected from the room treatment (or lack thereof) and the speakers. Furthermore I am not a “fiddler”, if it sounds good I have no desire to ferret out a problem that I may not be able to fix. This would then drive me nuts as I have type A personality and I am very anal.

The Measurements

SMS-1

I only have two measurements that I kept from this hardware the first, shown below, was the response of the untreated room; the second was of the room after the Audyssey XT32 Pro EQ, which is shown later.


PIC SMS-1 LF Room Sweep – No acoustic treatment.

Based upon the selected MLP you can see the frequency of peaks and troughs correlate well with the various axial room mode shown in my last posting. It is clear that there is very little LF absorption from the drywall as it now seems to be behaving as a rigid wall. I could never detect any resonances or flexing except for the ceiling as mentioned earlier.

STUDIOSIX

I mostly use the Impulse Response (IR) application together with the calibrated iAudioInterface and associated mic. for room analysis. This application supports various methods of analysis from impulse to swept sinewave. Unfortunately its response is only 63Hz to 10Khz so I had to rely upon Audyssey and the SVS-1 to see what was going on in upper and lower octaves, and of course my ears.

The first and simplest test performed was an impulse test created by bursting a large balloon at the front center speaker position.


PIC Energy Time Curve

The decay characteristic from this test indicates that the room has an average RT a little less than 0.2 secs. With no apparent nasty reflections or obvious secondary decay characteristics.


PIC Schroeder decays

The main two decay markers that provide clues to the perceived RT60 time, EDT and T30 both confirm a close to designed RT time of 0.2 secs. The graph below -50dB indicates a potential for secondary decay. However, this is not the case it is the iTouch noise floor impacting the decay rate.


PIC Early Decay Time

This shows the decay time per third octave within the first 10mS and correlates with perceived RT60 time. Again ideally all should be equal to 0.2 secs but show a faster decay of approximately 0.17secs. This is upheld by close examination of the initial Schroeder decay. I have not yet determined why there is a significant increase in the RT times around 200Hz and a spike at 2000Hz. However these only occur during the first 10mS and do not appear to effect the overall RT60 decay time. NOTE: It was later discovered to be some woodwork and rack hardware were “ringing” just for this initial period.


PIC Early Reflections

This provides a closer look at the reflections that occur at the MLP within the first 200 milliseconds. It is useful to look for echoes and repeating decay patterns or non-linear decays.


PIC Third Octave RT60 Analysis

This provides a closer insight into the actual decay times per one third octave. Ideally these should either all be the same and will normally begin to rise below 63Hz. Within the accuracy of this hardware, they all approximate to the design goal of 0.2 secs decay, starting to gradually rise as expected below 63Hz.


PIC Definition - Vocal Perception Analysis

This provides a good indication of how clear a voice will be perceived within the room. This is often used to measure public speaking areas but I use it as an indication as to how well vocals and the center channel speech will be perceived.

The following graphs were all created using a 3 second sine wave sweep fed via the AVP to the front L/R 1038’s and both subs. No Audyssey EQ was engaged in the AVP but was engaged in the external Sub EQ. All levels, distances and EQ had been set using Audyssey Pro.


PIC Energy Time Curve


PIC Schroeder decays


PIC Early Decay Time


PIC Early Reflections


PIC Third Octave RT60 Analysis


PIC Definition - Vocal Perception Analysis

Overall these graphs confirm the response seen by the simple impulse test. The differences mostly resulting from the increased wideband energy available from the sine sweep as opposed to the narrow band energy of the impulse test.

AUDYSSEY

I use both Audyssey XT32 in the AVP for all channel EQ and additional XT32 EQ in my external Audyssey Sub Equaliser. This was on the direct advice of Chris at Audyssey as the upgraded AVP does not contain SubEQHT. The double ADC conversion was determined to be neither audible nor measurable but the equivalent XT64 EQ gives me a very flexible approach to getting a well-integrated flat LF response. Just the subs are first calibrated with the Sub EQ then the AVP EQ is run on top of that. The small improvements can clearly be seen in the following graphs.


PIC Audyssey Sub XT32 Pro EQ



PIC AVP Audyssey XT32 Pro EQ

The most obvious points to note are that:

• All pairs of speakers have acoustically identically responses before and after EQ – within the limits of these measurements.
• The final Audyssey response of all satellite speakers is virtually identical above the selected LF crossover.
• That the frequencies of the peaks and troughs of the non-equalized responses correspond to the earlier predicted L, W, H axial mode values.
• The corresponding LF peaks and trough level changes are as would be expected from the placement of the speaker relative to the walls and ceiling.
• Relative to the MLP the values of distance are exact for all pairs of satellites and their level match is good. Level match could be made exact by adjusting the gain controls on the rear of each satellite but +- 0.5dB is more than close enough.

What is interesting, to me, is that I expected the lower modes to be slightly better controlled before EQ, based upon the amount of LF trapping and broadband absorption that was calculated and used. I assume that this is partially as a result of the walls, ceiling and floor apparently not contributing much, if anything, to the absorption at these room axial frequencies.

AppleMark
PIC SVS-1 EQ Graph

As can be seen from this simple sinewave sweep, using the SVS-1 at the MLP, that no room axial modes seem to be creating any problems and that Audyssey did what it was supposed to do.

Conclusions

Overall I am reasonably happy with the acoustic performance of the room. Imaging and depth perspective is outstanding. The bass integration is excellent and the LF response for either music or film is excellent, with plenty of extension, “slam” and is outstandingly tight and clean.

The room acoustic isolation from the main house is very good; as measured earlier, and could not have been improved without significant additional construction expense.

My equipment is unable to measure below NC25/26 so the final room NC rating is not known. However, the projector alone will prevent it going below NC25 and would need to be either re-located outside the room, put in a sound absorbing enclosure or replaced with something quieter.


PIC NC Equipment Noise Floor - HVAC active

In my last contribution I will review those things I could have done “better” or at least differently, and what issues I am having with the room that I will need to correct.

Paul

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Originally Posted by HopefulFred View Post

Paul, your efforts here are awesome. The thread is very much appreciated. I don't want to derail your narrative, but I would think it would be informative for me and several others if you could describe your efforts in using panel traps; in particular, what were the design goals, the build techniques, and in ways were they inadequate? Did you identify particular limitations that would be generalizable to other installations?

Fred

All my design experience was based upon a modular acoustics system that I developed and deployed for twelve of the first Independent Radio Stations that were built when radio became de-regulated in the UK. Getting a license required that all performance areas met very specific IBA Acoustic and electrical characteristics. These were actually measured by IBA technicians prior to the issuance of the license.

It had been my experience while working at the BBC that getting sufficient LF absorption requires either most of the wall area to become panel absorbers or to use extremely large passive bass traps. The former required a lot of wall space - actually all of it, the later required the volume of the room to be almost double what the useful space ended up.

As space was not usually a premium for any of the recording studios that I built I always employed huge passive LF traps in the walls and ceilings. Many of these traps were over 4 feet deep and used fiber glass lined sections in which hung a series half inch fiber board lined both sides with 2" of soft fiber glass spaced 6" apart. It is almost impossible to design in too much absorption below 60Hz and required far less effort. Achieving large values of Sabins absorption at low frequencies is just very challenging.

The Radio Station designs were always within confined areas so I deployed tuned panel absorbers that were an integral part of the wall structure. The modular wall sections were made from 8" lumber on 16" centers. The outer skins formed the mass isolation layer to meet the NC ratings while the 8" air space was a series of pairs of classic panel absorbers. There was NO absorption behind the membranes as the material used, Revac, was a lead loaded bitumen compound that was self damping and came in a wide range of masses/sqft. This allowed me to make the entire surface of each wall into a series of tuned panel absorbers to match each rooms axial modes. Several of these panels were replaced with Helmholtz (peg board) resonators to absorb frequencies around 120-240 HZ with higher frequencies being controlled by varying amounts of thin fiberglass absorption placed inside the wall cloth cover frames.

Design of the membrane absorbers was straightforward but getting the required absorption and RT60 time always required full wall and much of the ceiling coverage.

Using just the classic formula for calculating the membranes resonance, then provided that your traps are perfectly airtight and the membrane is appropriately damped, I have never had a problem with their design. I cannot stress though that you need a lot of area as their Sabins absorption values are not very large. This was clearly noted when I created the membranes for my room. I had over 100 sqft of membranes but it only reduced the levels by about 3 to 4dB at the lowest three L & W axial modes. I still have a mild height axial mode issue in my room, but that will be addressed later using shallow (4") tuned membrane absorbers placed on the ceiling. These will be made from a mixture of 1/4" drywall and 1/8" ply, covering approximately 100 sqft. Remember that they are designed to only absorb a fairly narrow band of frequencies. Damping them to broaden this range or placing them across corners only reduces their absorption at the desired center frequency. So dealing with a large range of axial modes below say 250 Hz is very difficult using membrane absorbers. They are only suitable for the lower main axial modes, require very flexible damped membranes and deep cavities. Heavy membranes, that are consequently not very flexible, are no substitute for deep cavities. The heaviest material I have successfully used in 1/4" drywall on 3' wide panels. The panels stiffness is very important so putting drywall on something much narrower won't allow it to easily vibrate. That is why panels are often made from 1/8" plywood or "roofing style" materials.

So given the volume I would always resort to large passive bass traps; and I did on this occasion to. Most of us don't have enough available wall area or a wife that would allow us to line all the walls/ceilings with the membranes. Just take a look at many of the earlier BBC treatments you will see that virtually every available area is covered with their modular absorber system. Just because the room is small does not mean that you do not need lots of LF absorption. The mere fact that the room will not support a 16/32HZ axial standing waves doesn't mean that you cannot generate that frequency within the room. Once you generate it you have to absorb the energy, the only way is as heat and that means lots of LF absorption that has a low flow resistance.

In the end it depends what your goals are and issues like WAF, budget and available space. Small areas of membranes work well for mild control of the lower axial modes but they won't give you really short LF RT times without large areas. Unfortunately neither will passive bass traps unless you have lots of volume to give up. I gave up 25% of the volume of my small room just for LF absorption.

Paul

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