In room response

Chad,
Did you ever get the 40Hz dip figured out?
John

Hi Goatwuss, I believe the REW would be higher resolution than what you are using , but I am not familiar with it just the one graph you posted. You need finer resolution than that.
I like to look at the graphs in several ways. No smoothing shows the most accurate response and therefore the real story of comb filtering, just how severe peaks or dip are within very narrow freq bands. 1/12 smoothing for general viewing and posting graps is preferred. 1 octave smoothing shows the energy levels loss or peaks over the octave levels.

Regarding the testing of preamps, I would not have assumed too much of a variation between preamps, unless one was broken, or so "colored" by design. And Iwold still have assumed that the in room response would overshadow that.

Bob

Hi Bob,

Thanks for your reply. I was using the Hifi news test LP.

Can you explain how exactly REW is a more accurate analyzer? I'm not challenging your assertion in the least, I just don't know.

I have used REW before, and I'm familiar with it. When I get a chance, I'll take another measurement with REW and post it on this thread. What type of smoothing should I use in REW? 1/3 smoothing still gives me quite a bit of comb filtering. Do you find 1/1 smoothing still gives accurate enough results?

Regarding comparing the phono preamps - Actually I did see quite a big difference. My supratek phono had some major response problems in the bass. I heard weak bass from it, and that is why I borrowed the Sim piece from my dealer, to run comparative RTA tests. Supratek has acknowledged that there is a problem with my preamp, and there are some parts now in transit to me that I will install in the phono circuit to hopefully fix the bass response problem.

Hi Goatwus, Nice of you to post. Which test record LP are you using? While I think it is very important to use a test LP, I think you need to go to a more accurate analyzer. A -4db at 30hz would be a very good in room response for those speakers and perhaps you can get a better response with more bass trapping and speaker placement if they are not yet optimized. You should try to use the REW, though there are other free software this one is very good. It will give you much better detail than the current software you are using and it is free.

I don,t believe you will "see" much comparing preamps at least in regard to their freq response in room. For that you would need specialized equipment to measure freq response, distortion etc right from the preamp. But one could very well sound better to your ears!

Bob

Hi Bob and others,

To see my room response, click the following link:

http://cgim.audiogon.com/i/vs/i/f/1209579742.jpg

That was measured with JDFT which is free RTA software. That was actually measured from my turntable(Vpi scoutmaster, jmw9sig, shelter 901), with a pink noise vinyl test track. I was in the process of testing the response of some phono pre's. (comparing the sim LP5.3 to the one built in my Supratek.)

Using the microphone and mic pre found on the ETF (now rplusD) site.

The speakers are Merlins vsm mxe's, and you'll see that I'm getting down to 30hz or so maybe -4db. Not bad for a 2 way with a single 6.5 mid/bass driver! This is an all tube system, with the Supratek Syrah pre, and Cary sixpac EL34 triode amps.

The scale on the left is not accurate as I didn't set a reference DB, but I did the measurements at about 75db on the SPL meter.

The room is 13ft by 14.5 ft, the speakers on the 14.5 wall, pulled about 3 feet out. There is no right side wall as it opens to the kitchen. I have GIK corner traps in the left corners, and fiberglass acoustic panels on the front and back walls.

There is a 50" plasma TV, and the left wall is a sliding glass door, and I've got nothing to address the 1st order reflections on the glass wall at this point, other than some shades.

Hi Raul, el gato got your tongue?

Bob

Hi Raul, I have a question for you and I need your help. I am looking to design my first $25,000 phono preamp. I have a few problems in the design stage but I think I got it sounding pretty good. The problem is the freq response. You can see the responses I get from several different changes in design. I like the deep blue line it sounds the best to me. The problem is it is the worst looking response. What should I do?
Also, is this a flat enough response plus 9db and minus 40db for a $25,000 preamp? You did do measurements, didn,t you? You should know and you should know the reason why.

Another thing I would like to know is why would you need a flat response in a phono preamp any way? Just what does it matter if the freq response is off like that, I mean if it sounds good right, who cares? Tell me what it means to not have a good freq response? What does it do to your music? If it does nothing, don't worry about it. But if it does something its probably something to worry about. And it does not matter if it is in the phono preamp, cartridge, amps, speakers or ROOM. If it does not measure good it can't sound good. And the reason why is because when you are missing freq you are missing music, when you are boosting freq you are coloring the music. It does not matter where those freq are boosted or decreased in your system it is freq error and plus/minus 9-35db is unacceptable!

Are you testing your equipment that you are designing with an amp that has a 9-35db freq response aberation? I hope not! Are you testing your equipment with an in room response of 9-35db? I hope not! So just how do you know you have a great room or a great $25,000 phono preamp unless you measure it. Because it sounds good? How can it sound good if it doesn't measure good? How can you be so worried about IMD and completly forget about freq response its only more part of the puzzle. Tell me how to fix IMD. And in the meantime I will tell you how to fix your freq response and clean up your IMD at the same time. That sounds like a good deal to me.

You said, "here is where exist that IM/HD that gives heavy distortions in what we hear ( there is no perfect driver: moving coil, electrostatic, ribbon, etc.. The speaker designers has to choose the best " trade offs ", but the distortions are there. ): less clarity, less resolution, less precision, less natural balance, less pitch, les, less, less......., and this is what we are really hearing: LESS MUSIC."

YES you are hearing LESS MUSIC if your freq response is plus/minus 9-35db. A freq error is distortion and one we can minimize. If your freq response is off at any point it is undesirable And I say within plus or minus max 2.5db. And as you get closer you do get to realise there is no perfect component or perhaps there is. But at least you are hearing all that your system has got, perhaps even for better or for worse.

And you also said, "I already point it out that IMHO the most important improvement that we can/could have adding a pair of true stereo way subwoofers is to lower the intermodulation distortion on the main spekaers, in this way you don't only have ( for the first time ) true undistorted low bass response ( that when you hear it for the first time it will be extremly hard to live with out it. ) but you clean up all the whole system frequency response: mid bass, midrange and high frequencies, that give to us several advantages : lower distortion response, lower coloration, higher accuracy response, better dynamics, improve over all the sounstage/imagin/focus, improve on inner detail perception, etc, etc that at the " end of the day " can(could take us nearer to the recording and nearer to the live event."

Raul, YES EXACTLY!!! That is what a flatter freq response gives you. lower distortion because you are not overdriving speakers (OH believe me, we can get into that later), lower coloration there are no peaks to obscure other freq or dips to hide details, those are colorations, improve overall soundstage, image, focus etc this is obtained when you room has a good decay time, just another benefit to bass traps, improve dynamics and inner detail sure how can you have inner detail and dynamics when half of the music is missing and the other half is obscuing detail by overpowering music that is 60db below it. When your system is plus/minus9-35 db, it does not matter where the problem is and if its in the room you have got to fix the room. The good thing is you can fix the biggest detriment to great sound.

Yea, The Emperor Wears No Clothes.

Bob

Hi Strabo, excellent response (pun intended) and it is exactly as I would describe my experience with the REW. Of course the REW does not tell you how to fix your room response so experimenting with speaker placement, crossover points and levels along with proper room treatment etc..are essential. Good for you optimizing the use of acoustic treatment using the REW.

Bob

Bob,
Yes, the changes definately cleaned up bass issues. Based on my original graph I had two note bass. Now it is much more even.

I wouldn't have even attempted this without the software. I did adjust my sub (used only for HT) manually once. It was a PIA and I never moved onto the mains. My first move with the software was to find an optimal speaker position within the reasonable options of my room.

The software quickly pinpointed problem frequencies. Next I used the tone generator to find the exact locations in my room of the problems and started treating those spots.

I have 7 major problem areas that I have attacked with fiberglass panels and one helmholtz resonator. There is an eighth problem area that is into the room a bit so I left it, but the rest were either in a corner, mid-wall, or quarter-wall. Some were at the floor, some were at the ceiling. None were floor to ceiling, and not all corners, mids, or quarters needed work.

I still have plans for more work on the seven areas. The forecast is for crappy weather for the next 4 days which may give me a chance at new measurements soon.

Hi Holeneck, Thanks for posting! I have a few questions. You are using TruRTA which is obviously differnt from the REW software. My question is that your reference level seems quite low, if you look at the 1000hz freq it is at at approx 52db, which is very low. Is it possible to redo the level so you are measuring at a higher level such as the recommended 75 db as recommended by the REW? Otherwise it looks very good.
Thanks,
Bob

http://cgim.audiogon.com/i/vs/i/f/1209053544.jpg

the above response is taken with a USB microphone that is not accurate above 10k.

another big issue with good system setup is properly integrating a sub. Proper Phase adjustment is cruical.

http://cgim.audiogon.com/i/vs/i/f/1209053544.jpg

here is my in-room response

Hi Strabo, I see the pictures of your before and after in room response. I believe there is a substantial change for the better. You mention room treatment and speaker positioning as the two changes you made to get a better graph. Did you hear a change for the better? And do you think you could have made these changes (for the better) without using the REW?

Bob

As to follow up my previous post, is there a target RT30 or RT60 time?

What made me ask is we have a small auditorium at work that seems like it was built using the classic LEDE approach and it is D E A D. IMO, it is overkill and boarderline difficult to listen in. I know I don't want my listening room to sound this dead. Is there an optimum measurement to shoot for?

04-23-08: Holenneck, not sure how to post my in-room response, but it is pretty snazzy, especially since i am incorporating Anthem's new room control.

I'm curious, since you have the tools to look into this, how does "room control" affect the waterfall graphs or RT60 decay?

Can you post before and after pic's of the RT60 with the room control?

I couldnt find a cable I needed that I thought I had so it will be tomorrow before I can get my mini male to female stereo RCA adaptor.

not sure how to post my in-room response, but it is pretty snazzy, especially since i am incorporating Anthem's new room control.

Wow, A phone call from Acoustat6 to help you out, What a guy :) Chadnliz my graph is better then what is was. Basicly you was as a flat line as possible with some exceptions. Just remenber you can't boost a dip with a eq or turning up the amp on the sub, etc. If you in a null your not going to hear it no matter how loud you make it.
By moving your speakers, trapping, and moving your listening position are the options. It is hard to do. I have a large peak at 34Hz from my room - the first mode in the length.
I just have to live with it. Its hard to trap a wave that big. I could move my subs but it screws up other frequencies

Hi Holenneck, you said "If you have a well engineered speaker and a treated room, exceptional sound can be achieved."

Well you ain't just whistling Dixie with that! Truer words were never spoken.
Thanks, do you have a graph of your room?

Hi JPV, thanks for posting and keep up the good work. Keep us posted if you achieve a better response and let us know how it improves the sound or other observations.

Hi Chad, thanks I am happy that I could help you out. You are now firmly on the right track.
Bob

I think this a great idea for a thread, it is amazing to me that more people do not realize the effect a room has on the overall sound of a system.
If you have a well engineered speaker and a treated room, exceptional sound can be achieved.

I saw your graph Jpv and I have alot to learn about how to make sense of what I am looking at. I would like to add Acoustat6 spent alot of time with me on phone helping me understand all my questions, very helpful!
I am going to try to run some measurements tomorrow if I have all cables I believe are out in my barn.....should be fun and likely very beneficial.

here is my room from 4/19. As you can see I need more traps

http://i36.photobucket.com/albums/e43/jpv1988/419response.jpg

The sound card in your PC will be fine. If your pc can run Vista, REW will be no problem for it. I have been using this for about 4 months now and the changes it has brought about are amazing. You really can't do it by ear, as well as this can. (start the flames)You may like the way it sounds but it may not be correct. There are house curves but until you know you have that dip or peak caused by the room and speaker position and tried to correct it don't get discouraged with your system.

Wow Bob thanks for the explanation! Do I need any special sound card or are most internal laptop cards good enough (newer computer with Windows Vista).

Hi Chandliz, It is actually quite simplie, even if I did have to ask for assistance from my brother!

You dont need the Behringer unit to do this, so just put that to the side for now along with the test disc as the REW provides its own test signals.

You dont need the micropone either at this point but later on it can be used if you so desire, you know upgrading and all that.

Do you have a radio shack or other sound level meter? If so, that is used for its microphone capabilities as well as the SLP meter.

The first thing to do is download the REW software (for FREE, its for free, I love that!) current version is V4.11


The second thing you need to do is calibrate your sound card on your computer. You need a cable to go from the speaker or headphone out to the mic in, you are running a loop out and then back in to your computer to calibrate the soundcard. The software put out tones and then it runs back into the computer and compares the output to the input and corrects for any level problems on the soundcard.

Now you have the free software loaded and the sound card of your computer calibrated for the software. You need a cable from the speaker or headphone out of your computer and run it into an aux input of your preamp. So it is most likely a 1/8" jack to RCA cable.

You are almost ready to make a measurement but first you have to calibrate the Radioshack SPL meter. Again you need a 1/8"cable at the input of you computer mic in and a single RCA to the input of the Radioshack SPL meter. There are controls at the top where it says calibrate and run the test to obtain 75db reference level (or one close to that as you may need to adjust up or down depending on the the steps in your stepped attenuators if you have them such as I do.) You then need to mark the volume control position as every test is taken from the exact same level for obvious reasons.


Then run the test and post it here.

Bob

I would like to do this but dont really understand it all, I have a Behringer unit, Mic and test discs but I dont know if I have the right unit to do this and help on HT Shak was sorta vague and inconclusive...thos there is alot of nice folks over there trying to help.

Hi Jylee, Thanks for posting, yes the EQ Wizard is a great tool and one that is quite revealing.

Hi Strabo, This very well could be a fun thread, thanks for saying so. It also can be very informative. Great to see the change in your freq response, in the before and after. Good idea and I should post mine to also show the changes from speaker placement, bass traps etc.. It also would be great to see your most recent measurements.

Bob

This could be a fun thread. Your rooms are much better than mine.

Here is my before graph. This was my initial FR measurement before doing any room treatments or changing speaker placement.
[URL=http://cgim.audiogon.com/i/vs/s/f/1208799876.jpg]Original[/URL]

After moving the speakers and fixing quite a few trouble spots.
[URL=http://cgim.audiogon.com/i/vs/s/f/1208799877.jpg
]Current[/URL]
I've actually made a few changes since this measurement and need to get a new graph and waterfall.

I've played with Room EQ Wizard a few years back. It is a very useful and powerful tool. Here's one measurement I have taken previously.

Revel M20

The system back then was Revel M20 and Classe CAP-151 combo.