How many here have measured their frequency response?

targa02 · « **Reply #20 on:** 12 Sep 2012, 05:01 am »

Sure. I live in a 2-story loft condo with a very understanding wife. My system is on the first floor against the long wall. I sit approximately 10 feet from each speaker and they are 8 feet apart (center to center). I have room treatments (4 inch thick x 24 inch wide x 60 inch tall) behind each speaker and in two corners. The other corners are not really a problem due to the strange room set up. Ceiling is 19 feet tall. I have a big window to my left approximately 8 feet from the speaker. To my right the room opens to the dining room/kitchen/loft. Speakers are pulled about 30 inches out from the wall pointed just over my shoulders. The SBH is to my left (close to the back corner) against the wall.

I am running Spatial/Pure Music thru 2010 Mac Mini feeding a fully loaded Empirical Offramp 4 which I then run AES to a MSB Platinum DAC 3 with volume control. The MSB drives ATC SCM 50ASLs. I use Pi Audio RevB, LessLoss power cables and a mixture of Blue Jeans, Wyred4Sound and Spatial cables.

It is hard to explain how the SBH affects my system. As I stated before, most of the time I forget about it. I will say this: before SBH there were some songs that I could not listen to because the bass was overwhelming. I was overloading the room. Since installing the SBH I no longer have to skip songs because of overloading. I simply sit back and enjoy.

I wish I had measurements from pre-SBH to post. Maybe I will contact Clayton to see if he will help me set it up.

targa02 · « **Reply #21 on:** 12 Sep 2012, 05:04 am »

Hi Scotty,

No, I have not tried moving my speakers closer to the wall. I assumed (it sounds like incorrectly) that I would make my bass problem worse. I will certainly give it a try. Thanks!

*Scotty* · « **Reply #22 on:** 12 Sep 2012, 05:27 am »

Also no guarantees, but the SBH might be more effective if it was directly behind you on the wall instead of in the corner.
The graphic below shows the before condition and the results after standing wave cancellation has take place in a simulated room.
The speakers in the front generate a planer wave which minimally excites room resonant modes other than one associated with rooms longest dimension.

When this condition has been satisfied then the generation of an out of phase planer wave from the rear of the room results in a cancellation of the bass wave from the front of the room before it hits the rear wall and causes a standing wave problem. The SBH is trying to do the same thing, launch a counter wave at the correct time to cancel out the bass wave from the front before it causes a problem. The fewer room modes that are excited by non symmetrically placed woofers in the room the less work the SBH subwoofer has to do.
Scotty

JohnR · « **Reply #23 on:** 12 Sep 2012, 06:50 am »

Quote from: *Scotty* on 12 Sep 2012, 03:35 am

I just haven't worried about exactly how the system measures, because beyond a very crude graphic equalizer program that resides on my Linux computer, computer based equalization is not a viable option. The good thing about putting an extra sub-woofer at the rear of the room is that by itself it is an effective tool for controlling the bass resonant behavior in the listening room which is the primary cause of the response irregularities in the first place.

Ah. But that's why you could benefit from using a better measurement program

If you measure the decay, you know where you are and then what measures you might take to control it and/or how effective they are.

How to measure decay: http://www.hifizine.com/2011/06/bass-integration-guide-part-1/ (towards the end e.g. see Figure 13)

Strategies to help improve low-frequency decay time:

* Modify the room envelope
* "Nearfield" positioning of subs
* Dipoles with specific positioning
* Acoustic absorption/damping
* Tuned resonators
* CABS/DBA
* Black-hole

JLM · « **Reply #24 on:** 12 Sep 2012, 08:53 am »

targa02,

Thanks so much for user feedback on the Black Hole Active Absorber. Ever since I found it, I've been a fanboy but have never listened to it. Being a poor boy out in the north woods I don't get out much and have to rely on what seems right. Seems that it is doing exactly what it's supposed to. And I like that it requires no testing/computers (like Clayton's higher frequency software) or signal cables running from front to back of the room. IMO the Black Hole Active Absorber would be the star performer in Clayton's (and most anyone else's) arsenal of frequency correction methods. (Not to say that swam wouldn't be great for a monitor based system, just lots of cabinets/cables for a domestic environment.)

Without separate (main) subs, you're pretty much stuck optimising speaker location for higher frequencies. Glad you're happy with the overall effect.

*Scotty* · « **Reply #25 on:** 13 Sep 2012, 12:41 am »

Here is an image of my listening room's layout showing main speakers and sub-woofer locations.

Scotty

JLM · « **Reply #26 on:** 13 Sep 2012, 01:26 am »

Scotty,

What are your main speakers (and how deep do they go on their own)?

*Scotty* · « **Reply #27 on:** 13 Sep 2012, 01:51 am »

They are flat to at least 20hz and may have usable output to 15hz. Sensitivity is 95dB here's a picture.

They will probably meet the CABS requirements for the generation of a planer wavefront from the front of the room if they are placed close enough to the front wall, which I have attempted to do.
What is not shown in the drawing is the 15ft. wall of thermopane windows partially shown in the above image, they may be helping to keep me from overloading the room. The floor and the ceiling of the condo are constructed of concrete.
The room is L shaped like the example in the Adrian Celestino's doctoral thesis but I am missing part of the boundary behind my listening position due to the opening to the foyer and the hallway leading to the bedrooms.
Scotty

Rclark · « **Reply #28 on:** 13 Sep 2012, 01:59 am »

That's an interesting layout, and a very non-intuitive positioning of the subs. Just goes to show how valuable true measurements are, rather than winging it by ear or using a crude meter. I can't wait to get into this.

*Scotty* · « **Reply #29 on:** 13 Sep 2012, 02:07 am »

Actually measurements had nothing to do with the placement of the subs. I started with CABS recommendations for a L shaped room and then modified the placement to help kill the bass somewhat before it travels through the wall between my living room and my next door neighbors.
Measurements suggest that I need to relocate the sub behind me 3ft. closer to the corner on the wall behind the listening position.
Scotty

medium jim · « **Reply #30 on:** 13 Sep 2012, 02:12 am »

Quote from: Rclark on 13 Sep 2012, 01:59 am

That's an interesting layout, and a very non-intuitive positioning of the subs. Just goes to show how valuable true measurements are, rather than winging it by ear or using a crude meter. I can't wait to get into this.

Please don't start anything here, okay....

Jim

Rclark · « **Reply #31 on:** 13 Sep 2012, 02:13 am »

Scotty, what are CABS? Can you point me to a paper?

*Scotty* · « **Reply #32 on:** 13 Sep 2012, 02:25 am »

Here is the link to Adrian Celestino's doctoral thesis. The L shaped room simulations are at the bottom of the pdf doc. The L shaped room might be one of the worst case scenarios and because of missing room boundaries, mine might be even worse.
Physics is frequently non-intuitive, the fact of which has often held back advancements in physics.
http://vbn.aau.dk/files/12831869/AC-phd.pdf
The graphics alone are worth a thousand words in this paper.
Scotty

Rclark · « **Reply #33 on:** 13 Sep 2012, 02:29 am »

Excellent, I'll put that into my reading list. Thank you.

*Scotty* · « **Reply #34 on:** 13 Sep 2012, 02:33 am »

Rclark, Don't put it off, it may be the single most powerful approach to leveraging flat response in the listening room to come along in the last 25 years.
Scotty

Rclark · « **Reply #35 on:** 13 Sep 2012, 02:39 am »

I'll read it Scotty. I'm looking forward to getting as close to sota as I can.

*Scotty* · « **Reply #36 on:** 13 Sep 2012, 03:28 am »

Rclark, a simple Rat Shack meter and a set of comprehensive test tones is a good place to start learning about what is happening frequency response wise in your listening room. It's a cheap and effective tool for finding out the awful truth. Once you find out that all is not well in the listening room you may be moved to do something about it. More advanced approaches to measurement will give you more information to base a decision on but they also demand a higher commitment of time and money to do them correctly.
If you are going to use room treatments and non-symmetric placement of multiple subs to control the bass reverberation behavior in your listening room they can be very useful in providing you with information about whether you are making any progress or just chasing your own tail.
Scotty

Rclark · « **Reply #37 on:** 13 Sep 2012, 03:36 am »

No, I want to skip right over "rat shack meter" phase. There's no point in wasting money on one of those when I'm getting a measurement system.

I am going to use room treatments, etc, I'm going full bore on this system, was the whole point from the beginning, not reaching a half way point and calling it good. I expect to lean on you quite a bit for advice.

*Scotty* · « **Reply #38 on:** 13 Sep 2012, 03:51 am »

You never know, halfway measures may get you all the way there. Is your room square to rectangular in shape? If it is, then start with multiple subs symmetrically placed at each end of the listening room as per the graphic shown in message #49 in this sister thread. http://www.audiocircle.com/index.php?topic=109579.msg1130506#msg1130506
The advanced measurements may show that just the addition of one sub out of phase at the rear of the listening room may solve most of your bass response problems.
You may be able to save money on room treatments for the bass spectrum if you try multiple subs first.
Scotty

medium jim · « **Reply #39 on:** 13 Sep 2012, 03:54 am »

Quote from: Rclark on 13 Sep 2012, 03:36 am

No, I want to skip right over "rat shack meter" phase. There's no point in wasting money on one of those when I'm getting a measurement system.

I am going to use room treatments, etc, I'm going full bore on this system, was the whole point from the beginning, not reaching a half way point and calling it good. I expect to lean on you quite a bit for advice.

Spending $50.00 on a Radio Shack Digital SPL meter was one of the best investments I've made as it isn't just about taking measurements, even if you can with it. It will save your hearing if you like to listen for extended periods of time.

The notion of using it and being half assed is funny. I'm with Steve Ford who also set up his systems with his ears and common sense. He indicated that his systems measured just fine and have no doubt that mine would as well....I guess Steve and I will just have to survive with our backwoods set ups.

Jim

P.S. if after measuring and moving things around and still having issues, I would have employed a computer based system and highly recommend the same to anyone.