Help With Setup

[nxs450]

Hello Matt what do you think about a B&K 200.7 amplifier? Also you recommended Emotiva amps. Are the gen 1's okay like the XPA-3?

 

[Matthew J Poes]

Thanks Matt

So as per REW 101 the peaks above -20 should be addressed. All 3 of my front speakers exhibit almost the same peaks. I'm not seeing very many above -20, in the measurement that I posted, am I correct about that? I actually did the string trick last night and it worked. The peak around 16ms is on the back wall beside my equipment rack, I treated my side walls with 2" OC 703 but did not do the back. When I put a 2'x4' piece of acoustic material in the spot, the peak went away. Same with the peaks around 6ms to 8ms, which ended up on the ceiling above front row seating.

What about the peaks right at 0ms to 2ms, is that something that needs addressed?

Alan

Anything under 2ms is going to be a result of the speaker itself and the immediate area around it. It just depends on what your area around your speaker look like and what kind of speakers you have.

Remember that your goal is not to create an anechoic environment. As long as they are controlled and smooth, reflections are a good thing. They help with our perception of space and imaging.

For example Toole suggests not treating first reflection points. I think his view has merit, especially since it's a very scientifically informed view. However his view is also based on certain assumptions about the speakers that aren't true for everyone. For example, he expects the speakers to have controlled directivity. Very few speakers do have this property. If the off axis response is not smooth then the reflection is like a sound source with a crummy response. All you can do is absorb it.

In the first 5ms or so you deal with things like diffraction effects from the speaker cabinet and anything immediately around it. What if your speakers are near a wall with a TV inches from the cabinet. Maybe some absorption around that area is good then to absorb some of these diffraction effects. When Dr Geddes started talking on other forums about the technical issues of cabinet diffraction effects we started joking about the creation of a speaker condom. Wrapping cabinets in acoustic foam. My setup had a lot of diffraction surfaces and he had joked I needed to wrap all of my front wall with foam. When I built my theater I paid attention to this and avoided diffraction surfaces to the extent possible.

https://www.stereophile.com/content/measuring-loudspeakers-part-two-page-2 Atkinson explains this stuff in this article.

 

[Matthew J Poes]

Hello Matt what do you think about a B&K 200.7 amplifier? Also you recommended Emotiva amps. Are the gen 1's okay like the XPA-3?

All good. I believe the B&K's were actually made by ATI who makes great amps.

The only issue with used amps would be condition. Are the caps still good. Anything less than 15 years old should be ok as long as the parts used were of good quality. Both of these brands fall into this category.

I know some Emotiva amps have had some reliability problems, but I don't think the XPA series falls into that category. I've heard nothing but good things. I've had hands on experience with the Gen 1 and 2. I don't have any reason to believe they would be bad. They certainly measure really well.

 

[Talley]

Do your self a favor.... Use a mirror on the floor... sit where the mic is at and have someone move the mirror until you can see your tweeter/midrange in it. Close enough at least. Then throw a large blanket bundled up in that spot and measure that speaker... then throw something like a book down and measure again. You'll see the difference it makes. Hard reflections are just that.

I'll have to open my notes because it's been a year since did this in depth but from what I remember your ears can only perceive reflections down to a certain point and at various times... first 5ms is the critical where you want nothing within -10db or -12db of original signal... then up to 10ms it's something like -14 or so then at 10-20ms it's -20db and aver that you it won't matter because the reflections will give the sense of space/ambiance to the room

This is why throwing up nothing but absorption panels is the worst thing you can do... you kill that ambiance. Sucks the room dry. You want to eliminate the 1st, 2nd, possibly 3rd reflection points and the rest don't worry about

It's all in the master handbook of acoustics. My book w/ my notes are at home I'll have to dig it up.

 

[Talley]

This is also why my uncle treats the floor... Something nobody thinks about at all but it makes a huge difference. Something as simple as bricks/baskets will work. I know it's not "engineered" but nor is using bookshelves w/ books... that works great too.

It's all about breaking the sound up. Engineered panels just does it efficiently and controlled.

 

[nxs450]

This is also why my uncle treats the floor... Something nobody thinks about at all but it makes a huge difference. Something as simple as bricks/baskets will work. I know it's not "engineered" but nor is using bookshelves w/ books... that works great too.

It's all about breaking the sound up. Engineered panels just does it efficiently and controlled.

View attachment 5920

Little to high tech for me, lol.

 

[Matthew J Poes]

Do your self a favor.... Use a mirror on the floor... sit where the mic is at and have someone move the mirror until you can see your tweeter/midrange in it. Close enough at least. Then throw a large blanket bundled up in that spot and measure that speaker... then throw something like a book down and measure again. You'll see the difference it makes. Hard reflections are just that.

I'll have to open my notes because it's been a year since did this in depth but from what I remember your ears can only perceive reflections down to a certain point and at various times... first 5ms is the critical where you want nothing within -10db or -12db of original signal... then up to 10ms it's something like -14 or so then at 10-20ms it's -20db and aver that you it won't matter because the reflections will give the sense of space/ambiance to the room

This is why throwing up nothing but absorption panels is the worst thing you can do... you kill that ambiance. Sucks the room dry. You want to eliminate the 1st, 2nd, possibly 3rd reflection points and the rest don't worry about

It's all in the master handbook of acoustics. My book w/ my notes are at home I'll have to dig it up.

I really suggest folks read the books by Geddes and Toole over Everest. Everest based his suggestions on what was known 50+ years ago. The science today is many times more advanced and what we know is vastly different than what he knew. Many of his suggestions have been abandoned and even shown to be wrong. Live end-dead end is largely abandoned and the treatment of first reflections is handled differently and for different reasons. As I said, Toole doesn't even think you should treat them and he bases that on true experiments.

He shows this measurement of a reflection off an acoustic panel as an example of why blindly treating first reflections can make things werse.

 

[nxs450]

Well I think I am going to pull the trigger on a new Emotiva XPA-3. I didn't realize the gen 3's were rated at 275 watts per channel and are upgradable to at least 7 channels if not more down the road. Do you know of any better deals on these?
https://emotiva.com/product/xpa-3-gen3/
Alan

 

[Talley]

Best deal new unless you look for a gen 2. Just understand that the more modules you add the lower per channel watts you get.

 

[nxs450]

Best deal new unless you look for a gen 2. Just understand that the more modules you add the lower per channel watts you get.

Yeah I read that, and I don't know if I ever will but nice to know you can. I like the looks of it, and think it will drive my 3 HTM's quite well! Like Matt said they can handle big power.

 

[Matthew J Poes]

Yeah I read that, and I don't know if I ever will but nice to know you can. I like the looks of it, and think it will drive my 3 HTM's quite well! Like Matt said they can handle big power.

Yeah the deal is really that Emotiva offers better value than many other brands. They indicated not offering sales or discounts anymore on such products.

The XPA amps are fairly efficient Class H modules I believe and the power supply is a 3000 watt switchmode supply. Under most conditions an amp is never asked to produce peak power simultaneously. Just the front channels typically would take the brunt of that. This of course is changing as we move toward full range surrounds.

The dynamic peaks for surrounds in cinemas is 102dbs. I've not heard a number for homes, but assume a similar remix is used on home video releases. That 3db difference means half as much power would be needed for the surrounds.

All that to say that I think high powered and efficient speakers mixed with beefy amps will work well and be unlikely to really ever exceed what the XPA can do even if you did load it with more channels. Of course if you did need more power you could always add another amp chassis, but you would potentially need another dedicated circuit.

 

[nxs450]

I just did this 20 amp service with commercial/hospital grade outlets to my equipment. It is in the bsmt and not hard to run more if ever needed. lol

 

[Matthew J Poes]

I just did this 20 amp service with commercial/hospital grade outlets to my equipment. It is in the bsmt and not hard to run more if ever needed. lol

I'm sure you will be good for a while, haha.

How many circuits is that?

I ended up running three 20 amp circuits into my equipment closet and two more into the main theater. I also have everything run and ready to go for a 240 line, but ran into code issues that prevented me from having it hooked up. Not that I need it in my system.

 

[Talley]

Good job peeps.

Now to add the 15kva isolation transformer

 

[Matthew J Poes]

Good job peeps.

Now to add the 15kva isolation transformer

Hah I would have such a thing if I was a master electrician. Since I have to pay other people to do it, no so much. I do have a whole home surge arrestor, but no isolator.

 

[Talley]

Hah I would have such a thing if I was a master electrician. Since I have to pay other people to do it, no so much. I do have a whole home surge arrestor, but no isolator.

I could put a unit together bring it up in June

 

[nxs450]

I'm sure you will be good for a while, haha.

How many circuits is that?

I ended up running three 20 amp circuits into my equipment closet and two more into the main theater. I also have everything run and ready to go for a 240 line, but ran into code issues that prevented me from having it hooked up. Not that I need it in my system.

Just one 20 amp breaker for the 12 outlets, but like a say know problem to add more if needed. I wouldn't even mess with inspection for running your 240. The way I feel is it is none of there business what I do in my own home!

 

[Matthew J Poes]

Just one 20 amp breaker for the 12 outlets, but like a say know problem to add more if needed. I wouldn't even mess with inspection for running your 240. The way I feel is it is none of there business what I do in my own home!

I would normally agree with you but we had a bunch of reasons why we had to. First, the guy in charge of that process lives in my neighborhood. Second, we run a business out of our house that requires special insurance, when we finished the basement we needed to submit proof of inspection. At this point I could have it run and not inspected, but I would have to undo it before selling the house as they require an inspection when the house is sold and that would likely fail if they noticed it. Honestly, the only reason I've not done it at this point is that I only own one amplifier that can make use of 240 and I don't really need the extra current right now. I have 7,200 watts of continuous output and much more momentary output capability. I have speakers which all have a rated sensitivity of 95db's at 1 watt or higher. Even my subs are more than 90db at 1 watt for the most part. If I need more than 7200 continuous watts, I think I probably need my hearing checked.

 

[Talley]

Never hurts to have more headroom

 

[Todd Anderson]

I agree with that 100% Talley. I have 6 circuits running to my HT. Matt... you had mentioned a "Star Ground"? Can you elaborate on that?

 

[nxs450]

I would normally agree with you but we had a bunch of reasons why we had to. First, the guy in charge of that process lives in my neighborhood. Second, we run a business out of our house that requires special insurance, when we finished the basement we needed to submit proof of inspection. At this point I could have it run and not inspected, but I would have to undo it before selling the house as they require an inspection when the house is sold and that would likely fail if they noticed it. Honestly, the only reason I've not done it at this point is that I only own one amplifier that can make use of 240 and I don't really need the extra current right now. I have 7,200 watts of continuous output and much more momentary output capability. I have speakers which all have a rated sensitivity of 95db's at 1 watt or higher. Even my subs are more than 90db at 1 watt for the most part. If I need more than 7200 continuous watts, I think I probably need my hearing checked.

Yeah under your circumstances I 100% agree.

 

[nxs450]

Good job peeps.

Now to add the 15kva isolation transformer

So I did minimal research after seeing the $ for these. So are they mainly for noise, popping, etc.? I noticed you are a Master electrician, I know enough to get me in trouble, lol. Do you have instructions for building and installing one of these, and is it something I could do? I have seen some transformers on ebay.
https://www.ebay.com/sch/i.html?_nkw=plitron
What is a cost effective way (cheap) for surge protection, for either whole house, or at equipment location?