Can I use a single channel amp with REW

[Hermit]

As much as it hurts - I've been thinking again...

I would like to test each speaker in my system, and Im a bit concerned I might damage my AV receiver, swapping wiring around. I believe I can use a single channel amp to power each speaker individually - can't I ?

Thanks... Hermit... peace and happiness

[brucek]

I believe I can use a single channel amp to power each speaker individually - can't I ?

I don't see why not...............................

brucek

[jerome]

I don't see either why you should not be able to do that. Many people use monoblock amplifiers or multiple channel amplifiers (bunch of single channel amp located into one box) and it works fine.

Now one problem will be that you won't get the same results in REW with your receiver and your one channel amp.

[Hermit]

... and that's what worries me Jerome...

The whole point to REW is tuning HT systems, but even using a direct receiver signal, I wonder how poor the acoustic match will be, to a stand-alone amp.

I ask the question because I have been wondering if REW's test tone generation, would mimimize the apparent difference, since it is looking at the consistant frequency of its test tone?

The idea of a portable REW test system intrigues me and I'm just wondering if it would provide reasonably good results? I think it would be cool to carry a single suitcase of gear to someones house, and provide them with a decent analysis of their acoustics, without having to mess with their equipment much.

If the only way to get accurate REW results is to use the main HT receiver/amp - I will drop the idea of a stand-alone amp for REW testing.

Thanks... Hermit

p.s... I still haven't done a real REW test. Everything I am asking could be totally meaningless because I know so little. I am just having so much fun getting set up to do some real acoustic analysis, and my engineering/geeky nature sometimes overwhelmes my common-sense...

ADD: Decided I would enjoy figuring out my own answers. Will be buying a Dayton APA150 amp and a pair of small audiophile speakers (also will use them for small office tv upgrade). Then Im going to run REW tests with the seperate amp and speakers (stand alone), using the Dayton thru my existing HT speakers, and using REW and my receiver in the normal manner. I'll compare the results and to try to figure out how I can use the stand alone set up to make reasonable decisions about room acoustics. I hope to create a test system I can use to test my friends acoustics, without them having to have their high-end equipment. Hope to help them make choices for acoustic treatments, and equipment buying, "before" they spend their dollars... maybe Ill be able to help them spend their money more effectively... ???

[jerome]

Hermit wrote:

The whole point to REW is tuning HT systems, but even using a direct receiver signal, I wonder how poor the acoustic match will be, to a stand-alone amp.

The whole point of using REW is to test and calibrate the system to be used to listen to music and/or watch movies. I don't see any point in testing a different system instead of the real system. Quality of the receiver does not matter anymore at this point because what you want to achieve is the best calibration for your entire system, not just for one speaker at a time.

Hermit wrote:

I ask the question because I have been wondering if REW's test tone generation, would minimize the apparent difference, since it is looking at the consistant frequency of its test tone?

The quality of the test tone generation does not matter. What's important here is level of each frequency seen from the microphone. I don't think that REW check the consistency of its test tone, but only the levels. It's a very good tool if you're interested in calibrating your speakers (and sub), checking/modifying the room acoustic characteristics (room treatment), ... but a bad tool if you want to discover how good your system sounds.

Hermit wrote:

The idea of a portable REW test system intrigues me and I'm just wondering if it would provide reasonably good results? I think it would be cool to carry a single suitcase of gear to someones house, and provide them with a decent analysis of their acoustics, without having to mess with their equipment much.

Yes for checking the room response. No to test how your friend's system will perform in the room.
It's important for you to know that different speakers and amplifiers will respond in a different way in the same room. For instance, two different subs in the same room may need completely different location, gain and/or phase settings. Personal taste is an important factor too: some people like lots of bass, others a wide sound stage, etc
I know some people who do just that: carry a bag full of equipment and help people calibrate their system. But they only bring a mic, a PC with REW, an external sound card, test CDs, etc. No speakers, no receiver, no amplifier.

Hermit wrote:

I still haven't done a real REW test. Everything I am asking could be totally meaningless because I know so little. I am just having so much fun getting set up to do some real acoustic analysis, and my engineering/geeky nature sometimes overwhelmes my common-sense...

I think that you should try to play with REW with your system in your room to see how it really works.

[Hermit]

Hi Jerome...

I understand and will comply... .

I realize Im not coordinating my personal goals and public questions very well. Not only do I want to calibrate existing systems, I also want to help make well informed decisions, "before" the money is spent. I am a "mad scientist" by nature, and I am hoping to put together a standardized test set up that will let me compare acoustics, in different settings. I think that using a common amp and speakers, will provide insight for me into differing room acoustics. Since the search for knowledge and understanding is so much fun for me, I don't mind buying a little extra equipment. Not to mention I will use the amp and speakers for my office tv, so its a no lose situation.

My friends can't afford their high-end equipment now... but I hope to use REW to figure out a good direction for their upgrades... not to mention I just love testing out my theories and ideas.

Everyones help has been very useful for me to figure out what I want to buy up front. I seem a little off the mark because I am trying to do 2 things at the same time - perform the normal calibration for my system - and develope a way to do some "outside-of-the-box" testing...

Wish me luck... the scientist: Hermit von Audiostein... eh eh eh !!!

[jerome]

I think that what you want to achieve sounds very respectable. I wish I would have had the same idea when I built my home theater room in my basement, that would have saved me a lot of extra work ...

Go ahead and let us know what you discover along the way !

[Hermit]

Thanks Jerome... always wondering "what if", I am...

Being so solitary, with decent resources, I constantly play with everything, just so I don't get bored and lazy. Afraid its a bit of the ADHD - never diagnosed but I know I have a touch of manic, a splash of obsessive, a bit of antisocial, a smattering of idiot savant, and a major dose of reclusive depression - but other than that Im pretty normal...

Im holding off on REW while I finish my acoustics which is taking me a long time because I keep "adding" more to it. Dont really want to show it until its done and tested. And with the delivery for my new mains delayed until late January, I am spending way to much time just working with imagination and theory. Unbelivably, I find this mental exercise to be such a big part of the fun, I get carried away - I greatly love learning to do stuff with visualization and study, before I actually put "hands on".

Will report in... a long report if some success... a very short one, if I fail to make sense of the experimental testing. The last of my electronics is on its way. The glue is drying on the last of my panels. Just have to build a window treatment and interior airlock entrance door (and install ventilation, and build/mount swiveling corner absorbers, and... etc...)... I am insane... ... Hermit

[DrWho]

Btw, REW works just fine with portable measurement rigs. In fact, I put together a portable/shippable unit for senior design last semester:
http://courses.ece.uiuc.edu/ece445/?...07&proj=18#a18


For what it's worth, the room is absolutely going to dominate every measurement you do in the room...as such, there is absolutely some merit to measuring each speaker individually with the same amp.

However, an easier approach would probably be to put your receiver into its multichannel external input mode and then move the RCA cable to the speaker you want to measure. Most every receiver has multichannel inputs on the back, but not all. It's nice because you've already got the speaker wires run.

[Hermit]

Hello Doc.... this is excellent news....

Sorry... but Im going to try to talk "engineer", even though I don't know how - so please try to read between my mistakes. I'll look the fool by using the wrong words - but this is to to wait until I know more.

In the end, I only have one real question from this very long winded post. In your experience, "Do you think it is "likely" these efforts can bring me enough understanding, to justify the time spent?"

Also, most of my information here is just description - Im not actually asking for analysis. Its to complex for an internet analysis, at least until I get some specific test results. Im just asking to be judged if my general direction and theory is headed in a good direction, or am I being a "nutter"?

I've studied enough to see the intellectual page you are on, but a lot of the print is still to fine for me to make out clearly. I have fair knowledge of sound wave dynamics, room size & structure, effects of materials & their placement, speaker positioning, and hardware performance - per the concepts in the Master Handbook of Acoustics and several hundred online articles. I came to believe, during my studies, that physical room acoustics are so important, they "have" to be understood and improved first thing, because they color everything else so much. Since you've done this kind of work for real, and I am just a novice "wanna-be", I believe you can correct me if I am off target.

My plan is to develope a good feel for the effects of various equipment/acoustic treatment arrangements, so I can fairly "guess" how to design/build/improve a super audio/HT experience. I plan to perform dozens of tests, comparing the differences in graphed responses of these three equipment/test set ups:
1 - Use a Dayton portable 75w RMS x2/bridgeable amp powering either a small pair of high quality speakers or single 10" sub (using the amp's 50 t0 150 Hz low-pass filter).... to determine test-unit performance for various speaker placements/configurations.
2 - Use this same amp to power my HT's speakers individually and as subsets - mains, center, surrounds, right side, left side.... hoping to see how typical speaker placement and design effect the graphs.
3 - Perform a normal REW analysis of my personal HT equipment and configure my system for best performance. This will give me an endpoint standard for comparison, and let me hear "all my system can be"...

Unfortunately, I will be learning in my 1300 cu ft room, which I have probably overkilled with 2020 watts (7.1 ch x 110w, 2x integrated 350w "mains" amps, and 550w SVS sub amp) and all speakers are "large room" designed (maxed out Onix "Rockets" and Axiom surrounds). Might be a bit "heavy"?... I'll see, ahh hear... when I get the new Rockets.

On the bright side I am very single, so there is no "Wife Approval Factor", and I have built dozens of acoustic panels, for everything, but the carpeted floor. The panels are meant to mitigate exaggerated bass response and calculated room modes. Im using thicknesses of solid #703 fiberglass up to 16", with a rough "mean average" around 6". Half of the panels are either smaller domed "clouds", large and trianguler front "corners", or a few ovals and irregulars for "spot" work. The other nineteen panels (4@24" plus 15@6") are freestanding, rectangular, and 4" thick, with a full absorption face and mildly refective side. While my room volume is low, it does have good dimensions (15'2 x 11' x 7'10), and I can adjust both % of panel coverage and panel placement, to tune the space.

OK... enough is enough... for one post.

You had to work hard to get the "Designers Award", and I'll bet you went thru much the same thing I am planning. Do you think this will be some valuable research/experience? and do you think it might help me to become more "wizardly", in an acoustic design sense?... after all, my goal is to get MUCH better at this stuff. By the way, what does "this device will be RAAD" mean?... although Im sure it is...

Thanks for you patience and insights and hope you are having some good holidays... Hermit...

[jerome]

Hermit wrote:

Unfortunately, I will be learning in my 1300 cu ft room, which I have probably overkilled with 2020 watts (7.1 ch x 110w, 2x integrated 350w "mains" amps, and 550w SVS sub amp) and all speakers are "large room" designed (maxed out Onix "Rockets" and Axiom surrounds). Might be a bit "heavy"?... I'll see, ahh hear... when I get the new Rockets.

You have to read the power specs carefully because it's not how many watts you have on the specs which is important. The first watt is the most important one !

For instance, most of the receiver specs are way overrated. Manufacturers plays with the specs to sell more. Take a look on the backside of your receiver to see the max power rating. As far as I know, none of the receivers are 100% efficient, they will be able to output 75-80% of this power (if it's equipped with a class-D amplifier). Then divide it by how many channels you are going to use and you will get a ruff idea of how much power you REALLY have. Lower than the advertised 7ch x 110w ?
In surround mode, your speakers are probably going to be setup in small mode and the sub will take care of the low frequencies. Then your receiver and main amp won't need more than a couple of watts to drive all your speakers, even at high volume (yes, I know it's really low but that's true )

350w for your fronts may not be so much if you want very good bass control (in stereo), have low sensitivity speakers and/or if you like to play very loud music. Or if it's 350W@4Ohms and you're speakers are 8Ohms then you have 175W max at the end ...

Really off topic, sorry

[Hermit]

Jerome... I very much appreciate anything anyone has to say, anytime...

I throw in a lot of info, hoping to get feedback like this. I read several other threads and was surprised how much mismatching the speakers to the room could hurt performance. In the "house curve" sticky I saw the steep curve described for a small room, and I am concerned I might have messed up, and bought equipment that will make matters worse for me.

I mentioned it to DrWho because he might tell me my testing is invalid, due to environmental limitations.

My habit is always to "up"grade, when in doubt... so I bought the best I could afford... at the highest price I could afford. It did not occur to me that the higher cost was due to increased capacity, in relation to room volume. I sure hope my speaker choice does not go from "my bad" to "my stupid".

I am a little relieved that you don't think I have necessarily overdone it. Speaker efficiency is 91db, but I hope that driving the bad boys is not to much for my room. I have always thought more was better, because it was less work for the equipment... and now I find out this is only true to a point.

Oh well... will live and learn. Just have to wait until Feb to do tests to find out.

Thanks... Hermit

[DrWho]

The effects of the room totally swamp anything that the electronics might do, so you'll be just fine trying to quantify the effects of your room with a separate amplifier.

If you want to do this systematically, I would start by stripping down all the acoustic panels and then find the best speaker and listening positions...once you figure it out, you should start by looking at the ETC and get an idea of how the sound is bouncing around the room. Although there are some levels where this is just intuitive, it is going to depend highly on the power response of your speakers. The polar response at any frequency is going to be different which means different reflections are going to contain different frequency content. Generally speaking, you're going to see wider polars at the lower passband of each driver and narrowed polars at the higher pass band of each driver. For instance, a 12" woofer is gonna start beaming at 500Hz and be really obvious by 1kHz, while a 4" mid is going to be really wide at 1kHz and start beaming around 3kHz (and be really obvious by 6kHz).

Anyways, since you're probably not going to get accurate polar data from your speaker manufacturer and really you're only interested in the real reflections (not predicted ones), you can directly see what is happening by looking at the ETC. After that, it's pretty "simple"...you want to find ways to remove early reflections, but you also want to find ways to add more late arriving reflections so that you end up with a dense reverberant field instead of a few sporadic specular reflections. Early arriving reflections would be defined as reflections happening inside the Haas window, which is a minimum amount of time that needs to pass in order for two sounds to be heard as two separate and distinct sounds. Two sounds that happen within the Haas window are perceived as a single mushed up sound. In this case, you have the direct sound of the speaker (traveling the shortest path to your ears) and then you have the reflections (traveling a longer distance and thus arriving later).

If you just absorb the early reflections, then you have no more energy to bring back after the Haas window. This is why most acoustical treatment regiments involve a lot of diffusion and diffraction instead of absorption. In a small room you'll be limited by what you can accomplish, in which case you want to make sure that once the first reflection happens, that you try to maintain a dense and linearly decaying reverberant field. The next most important thing here will be to make sure that you don't have any strong late arriving reflections (which will show up as spikes rising higher than the reverberant field).

Btw, I probably should have mentioned it earlier, but you'll want to treat the bass first (bass traps, helmholtz resonators and all that shnazz)...the biggest reason is because they're harder to treat and will "inadvertantly" affect the MF/HF as well...it wouldn't hurt to think about the possible advantages to the MF/HF while you're treating the LF.

Anyways, as you add panels (do one at a time), you should see changes in the ETC. If you don't, then the location of your panel isn't doing anything, which means you've probably got the panel in the wrong location. The important thing here is being able to keep track of which reflections are because the mic is close to your listening position, or because the speakers are close to a wall ("early reflections" will show up in both places).

Btw, since it sounds like you've already got a bunch of treatment, you might just start by measuring the room in its current state and see how close to the ideal you are.

Page 2 in this pdf has a great picture of the ETC's before and after treatment:
http://www.rpginc.com/cgi-bin/bytese...ary/HT_AcD.pdf
It also labels and describes some of the terms I'm using too.

[Hermit]

Mike... many thanks... got an ear-to-ear grin out of this...

You have described testing quite similar to what I was thinking, BUT, I had absolutely no idea what to expect, how to deal with it, or how I could even explain it. I was just going to post graphs so others could tell me what I needed to understand. You just covered that really well, gave me a framework, and helped me tremendously. What you said was very clear.

There is an effect I don't know any word for - best description is hearing slices of the reverberent field. My musician buddy and I learned to "hear" individual acoustic treatments by having one person sit in the prime listening position, while the other carried various panels around and focused the panels effect on the listener.The "effect" is, we perceive acoustic panels like they are chunks of the sound field, that we can move and manipulate using the position and construction of the panel. Over the last 2 years we have worked to assemble these sound field chunks into a fairly smoothe and balanced auditory envelope. And now we can't perceive which subtle changes are improvements. .. all depends on what we are listening to. So here I am... learning about REW and targeted parametric equalization, so that we can refine our efforts.

Following forum advice on materials, methods, and priorities I have been slowly building an array of 23 freestanding, rectangular wall panels (17 @ 6" x 48", 6 @ 24" x 48" for first reflections) , 2 floor-to-ceiling, freestanding front corners (actually 4 half-height stackable units), 31 small dome-shaped ceiling panels (to improve diffusion), and a couple of ovals (for front and rear wall). Sounds like a lot, however, I intentionally built many on a "very" small scale, to provide a more even acoustic distribution. An acoustic engineer told me he had great luck with lots of smaller panels (6' x 48 "), distributed all the way around the room. We found he was right and I am using the small scale idea to "assemble" the sound field, with carefully placed treatments, on every surface, but the carpeted floor (where Im playing with chairs, foot rests, and tables to manipulate effect).

This fits in quite well to acheive your suggestion of controlling the reflections to generate a smoothe Haas field and tune the frequency effects - if I can figure out where to place the panels to grab the unwanted reflections, and aim the desirable ones. Another nice thing is we were unknowingly practicing exactly the kind of manipulations you suggest for creating the dense field. Ahh Hah !!... theres the word for my "effect" in your post... "specular" sound field. My "chunks" of sound are the specular effects of the panels, and our "auditory envelope" is the Haas field... woo hoo!!!... if Im not misunderstanding? Sure do wish I had a great memory, because I'll bet I have read a lot of this, but forgot or didn't understand at the time.

Lastly, I was also concerned about killing the room with to much absorption. So I used soft plastic sheeting, duct tape, fabrics, and wood framing to replace some of the absorption surface, with diffusion. By building and covering the thinner, rounded profiles with reflective materials I feel I have tuned the panels to stay lively, while controlling much of the bass response. Since everything is either freestanding or simply moved, I can very easily rearrange the treatments, to sculpte the sound field. Also, I have been sure to build a few extra panels/treatments, so I know I have enough building blocks to finish the job... and can quickly add and subtract effect as needed.

A quick question... Do you enjoy this sort of "long" post with a student... or have you done it so much its sort of boring? I'd like to know so I can tailor my posts.

I have already scheduled to get together with my audio cohort, in a week, so we can assemble and try out the equipment. He has a bit of experience from years ago, and we tend to get more done together, than seperately. I read instructions on graph resolutions and info transfer, and I hope to have some "real" work done in a couple of weeks.

With great appreciation , and lots of loud hoots and excited hollers ... Bye... Don...

[DrWho]

One thing you might consider researching is the usable bandwidth for the panels you've made. For instance, absorption is only effective when it is thicker than 1/4 the wavelength (when mounted on the wall). So at 1kHz you have a 1 foot wavelength which means you need a 3" panel (or thicker).

The 1/4 wavelength rule shows up with diffusion and lots of other stuff too...

[Hermit]

Thanks... Will do this, again... Only better...

Truth is I started this project over 4 years ago. I have hundreds of pages printed from forums, several books, and dozens of pages of thinking on paper = sabin calculations, axial mode & pressure plots, standing wave projections, absorbtion coefficients, poly & flat panel designs, my solutions, etc...

Bad news is I've forgotten the details, although I have great records. Good news is once I had designs it was mostly a matter of building stuff. Take a year out for my medical treatment and here I am 3 years later, getting near the end. With everyones help I am getting back up to speed quickly, and am relieved I haven't found any glaring problems... yet!

Great news is every time I review the early work, I remember the details quick and easy, and it looks like a did a decent job. I remember most of the details of why I think what I do, and did what I did, and it is fitting in with your instructions very well.

I tried to upload pictures, but I failed again. I have to figure out how to meet forum file criteria and how to get the reduced files onto the thread. The photos will bridge my writings to the real world and show what I can't say well enough. Also, my project is complete enough to do some "valid" REW testing, over the next couple of weeks. I expect to have much clearer and more professional feedback very soon. I'll do my best to have concise calculations, estimates, photos, and t