How to diagnose the need for room treatment?

Given that none of your dimensions are evenly divisible into any other: You're ahead of the game. Here's a possibility, as far as an available test that will help you in identifying problem areas- (http://www.acousticsciences.com/matt-test-flyer.pdf) The test is available on Stereophile's Test CD 2: (http://ssl.blueearth.net/primedia/home.php?cat=2) The other test CDs that they offer have some good listening room diagnostic tracks as well(that don't require any instrumentation, outside of your ears). ASC's site (http://www.asc-hifi.com/) offers much in the way of explanation, re: resonanaces, echo, reflections, reverb, comb filtering, etc., and ways to treat a room to combat/control them(click on, "Acoustic Basics"). Auralex(my fav) in it's many forms(and a number of other treatments) can be purchased very reasonably on eBay (http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=acoustic+foam&_sacat=See-All-Categories) (http://shop.ebay.com/items/?_nkw=acoustic+treatment&_sacat=0&_fromfsb=&_trksid=m270.l1313&_odkw=acoustic+foam&_osacat=0) Hopefully you'll find something in this short list of resources helpful to you.

Try playing something that should have lots of bass. If your system should be able to play deep bass and you can hear it, and are happy with it, you are probably be OK.

If the bass is lacking or muddled, you may need bass treatments in the corners of your room.

You've played with speaker position and you've dealt with the first reflection points (including floor bounce?) and in your opinion it sounds good. If that's the case, then don't go any further. It's not that you couldn't improve the sound quality, but go to the above websites graciously listed by Rodman and look at the products they offer. Then ask yourself whether you really want them in your living room? I suspect the answer will be self-evident.

I beg to differ with the last couple of responses. If you'd really like to get the best sound possible from your setup, you really need to make an attempt to gain a solid understanding of how your gear, room acoustics, speaker placement and seating placement are interacting.

Get a cheap spl meter from Radio Shack and a cd with test tones from either rives.com, a website or a Stereophile test cd. Place the meter on a camera tripod where your head is when you sit in the sweetspot. Measure the response using the test tones (search archives here on how to do this exactly), and graph them on the chart you can download from rives.com.

If you play with speaker and seating placement & remeasure, you will be able to significantly affect in room bass performance. Often you will have peaks at some frequencies and troughs at other frequencies. Offer, you have to live with tradeoffs to get the best overall balance. Bass traps in the corners behind the speakers offer the biggest improvement in most situations. the room acoustics forum on audioasylum is the best place I've read up on this topic.
Good room treatment doesn't have to cost tons or look like hell. Natural fibre rugs, velvet curtains, upholstery and bookshelves can all contribute to improved sonics if diy or commercial room treatments aren't in your budget or to your liking.
Don't let anybody fool you. The room is probably your most important component. Cheers,

Spencer

If you have a significant-other's-acceptance issue. There are very attractive alternatives to the pro-sound booth type traps/treatments. Some of which actually allow you to submit your own artwork/photographs for display, while still effectively controlling your room's acoustics: (http://www.asc-hifi.com/panel-trap.htm) (http://www.purewaveaudio.com/c=bdYyIFF0rsQhnkyyRIpP7ioV5/product/AUR-SPS23/Auralex_24x36x1_SonicPrint_Panel_Uses_Movie_Art_Image_from_Auralex.html) Of course- How far you pursue excellence in your listening room depends solely on how serious you are about your music.

Another option if you have a PC is Room EQ Wizard (for PC and free - a vry cheap solution) or Fuzzmeasure Pro 3 (for Mac $150) - you'll need a measurement microphone and a pre-amp like a Dual Art USB pre and off you go - measure to your hearts content.

I can't tell from your comments exactly how much actual speaker/sitting positioning work you have already done, or how you did it, so it is really hard to comment on what you should do next.

BUT, IMHO, you really can't get your sound to 'improve' until you can describe specifically what it is that you expect to improve by making any changes or use of 'room treatments'.

FWIW, it strikes me from your comment 'it sounds good to me' that you really haven't a focus on exactly what to expect, just that you think by adding something it might get better, when actually it not only might not, it might sound worse.

Based on that assumption, I would suggest that you save your money for a while and try to improve the sounds in your room (assuming you are not restricted by WAF) simply by carefully tweeking placement/toe/listening chair positiong until your set up produces tonal smoothness from bass thru highs (you can use a SPL meter and a disc with test tones) and clarity of tone, a set up which produces this clarity in the context of a soundstage which is wide and deep (and if possible, but it is more equipment dependent, high).

Room treatments are good when you have identified specific problems in identified frequencies and select the treatments that are designed to do it. There is no 'one size fits all' solutions, and some things are unobtainable at any realistic price or visual acceptance to many.

FWIW, I've been able to set up a modest sized room with fairly flat/smooth frequency response +/- about 3db except for a 5db boost at 32hz (not tameable) and a 40/50 hz 5db suckout (room dimension created and not tameable either) without using any acoustic materiels other than normal domestic furnishings. It only took a couple of years to do it all. Lots of small changes and patient listening to speaker/listening seat tweaking. :-)

If you want some down and dirty recommendations, I would suggest that you post your rooms dimensions, identify present locations of speakers and listening chair, along with a description of and location of room openings (windows and doors), and stuff placed on/near walls.

Also a description of your equipment, especially your speakers, and if possible what you would like to improve, sonically.

Fundmentally I agree with Sbank - I would only like to reinforce the fact that speaker/room set up, assuming you have already done some of the preliminary work, and if you have high expectations, is not a short term project with quick fixes. It is a slow methodical process with a lot of small changes and patient listening.

Hope that helps a bit.........

Although I don't have the room optimization experience that most of the others have had, I'd like to offer one small but I think significant point.

Particularly once you get above bass frequencies, tuning the room for flat frequency response using a test cd, microphone, etc., is not necessarily going to get you the best sound, and in fact probably won't. The microphone is not going to discriminate very well, if at all, between early arrival sound (the direct path from the speakers to the listening position) and later arriving sound (reflected off of walls, ceiling, etc). But your ears will!

I believe that some of the more sophisticated (and expensive) equipment that does this sort of thing can help to take arrival time into account, in a meaningful manner, but a Radio Shack sound level meter used with test tones from a cd will not. Although I think you will get meaningful results that way in the deep bass region, because of the long period and wavelength of the tones, and the consequent lack of timing sensitivity and directionality of our hearing at low frequencies.

Regards,
-- Al

Recommended reading for setting up your system for better sound: "Get Better Sound" by Jim Smith. Smith is a professional sound consultant whose setups have won several "best of the show" awards. His book walks the reader through a systematic method of getter better sound from your system including room treatments, if needed. The book has received several raves on boards and ezines. I found it very helpful.

Guys,

Thank you very much. Really. I have a fair amount of reading ahead of me + getting acquainted with test CDs & SPL meters. I'm not looking for quick fixes, so getting a good understanding of how my room/system behave together and how to improve the sound sounds like fun.

I hope you don't mind me asking back again for further guidance in a while. Will check out the room accoustics forum too.

A lot of good info/advice. Thank you!
Horacio

Al said, "I believe that some of the MORE SOPHISTICATED ( AND EXPENSIVE) equipment that does this sort of thing can help to take arrival time into account, in a meaningful manner,"

I take exception to those statements. The REW (Room EQ Wizard available at the Home Theater Shack) is sophisticated and does time domains. It is for FREE FREE FREE FREE FREE

Bob

Al wrote: "Particularly once you get above bass frequencies, tuning the room for flat frequency response using a test cd, microphone, etc., is not necessarily going to get you the best sound, and in fact probably won't. The microphone is not going to discriminate very well, if at all, between early arrival sound (the direct path from the speakers to the listening position) and later arriving sound (reflected off of walls, ceiling, etc). But your ears will!"

I think your comments apply better to the bass frequencies, not above bass frequencies. In the bass, the arrival/decay times are more easily measured and corrected whereas at higher frequencies room mode interactions approach randomness. Thus, at those higher frequencies, only FR adjustments are feasible.

Kal

Bob wrote: "I take exception to those statements. The REW (Room EQ Wizard available at the Home Theater Shack) is sophisticated and does time domains. It is for FREE FREE FREE FREE FREE"

Yes, yes, yes...................but REW is a measurement tool, only. It cannot implement a correction even if it defines it. One needs an additional tool to use the results.

Kal

In the bass, the arrival/decay times are more easily measured and corrected whereas at higher frequencies room mode interactions approach randomness. Thus, at those higher frequencies, only FR adjustments are feasible.

Yes, at higher frequencies only FR adjustments are feasible, but the point I was trying to convey is that making those FR adjustments on the basis of measured flat frequency response, in response to continuous tones monitored only in the frequency domain, will not provide best results. Listening to music provides the last (and most important) word in that part of the spectrum, it seems to me.

Arrival times in the deep bass assume importance particularly because of reinforcement and standing wave issues, as everyone probably realizes. Which causes the measured (and heard) amplitude of deep bass to vary as a function of frequency and location in the room, and which can be more easily corrected on the basis of measurement, as you indicated.

Regards,
-- Al

Hi KR4, That is true. But first one has to identify the problems. How you correct it and how much you wish to achieve is up to each audiophile.

The problem I see is that, very few know what they are dealing with, as far as in room response is concerned.

Bob

FWIW, in my post I referred to 'smooth FR' but I purposefully did not say 'flat FR'. Flat suggests to me hearing all frequencies at the same SPL, and when I have heard sounds in a room that were measurable as flat (especially from speakers which allegedly had a flat FR) the result was too much upper-mid and high frequency energy, where as a 'smooth' albeit tilted FR could be much more realistic for most installations.

Personally I really detest peaky mid-range and upper midrange FR, and it is easy thru measurements to determine whether this is attributibutibe to the speaker or the room (or both) by doing both near field and listen position measurements. Am I wrong, or am I missing the point?

Newbee -- I don't think you are missing the point, you are just making some additional points.

To re-state my basic point, room effects at mid and high frequencies are heard differently by microphones + sound level meters than by the human hearing mechanism. The human hearing mechanism tends to some degree to "latch on" to the leading edges of transient waveforms, and give them greater emphasis than what may follow a few milliseconds later. I think that is pretty well recognized. But a microphone + sound level meter monitoring a continuous frequency sweep, or a series of tones covering the different parts of the spectrum, will not do that -- the late arriving sounds at any given frequency will be taken into account, so to speak, simply based on their amplitude. Therefore, whatever the desired tilt of the fr may be, tuning the room or the system to provide it on the basis of that measurement technique will not give the desired result when listened to by a human.

Regards,
-- Al

How about a dumb question :)

I am going to try Room EQ wizard with a good microphone placed at ear level where I normally sit. Do I aim the microphone at the front of the room (HDTV) or do I aim it at the ceiling?

I will be trying to analyze (and perhaps improve) my 5:1 theater system.

The ceiling.

Hi Ghstaudio, I assume you are using the Radio Shack microphone/Spl meter (although you did say a good microphone so its probably not Radio Shack). But If you are buying a microphone and you need a SPL meter, just buy the Radio Shack unit. It is more than adequate and the freq correction is done by the REW set up. Also many/most use this combination, myself included, and help in setup is freely available.

Point it straight ahead. It mut be on a tripod at where your head is.

When you get your Freq response graph, waterfall and RT60, please post them here for interpertation. That will be interesting.
Bob

If you are trying to assess room acoustics based on system throughput, aiming the mic forward, or at any speaker, biases the results to the performance of that speaker. Pointing it upwards makes for the least biased results. Also, averaging more than one mic position helps.

Kal

Make sure you have a measurement microphone - an omnidirectional condenser type. For example the Behringer ECM-8000. An ordinary microphone is not suitable

I will first use the RS microphone. I was going to try an AKG CK-32 cartridge (good omnidirectional mike). Finally, I have a rane RA-27 with a measuring microphone that I could try (requires me to build a small interface).

Most likely, I'll never get past the RS.

The human hearing mechanism tends to some degree to "latch on" to the leading edges of transient waveforms, and give them greater emphasis than what may follow a few milliseconds later.

Re my earlier comments on this issue, in a post in a different current thread Shadorne referenced a Wikipedia writeup on the "Haas Effect," which is what I was referring to without knowing its name:

http://en.wikipedia.org/wiki/Haas_effect

A brief excerpt from that article:

When two identical sounds (i.e., identical sound waves of the same perceived intensity) originate from two sources at different distances from the listener, the sound created at the closest location is heard (arrives) first. To the listener, this creates the impression that the sound comes from that location alone due to a phenomenon that might be described as "involuntary sensory inhibition" in that one's perception of later arrivals is suppressed.

The Haas effect occurs when arrival times of the sounds differ by up to 30–40 ms. As the arrival time (in respect to the listener) of the two audio sources increasingly differ beyond 40 ms, the sounds will begin to be heard as distinct.

Thanks, Shadorne!

Regards,
-- Al

Good point about the Haas effect. One should also note that there is a lower limit to time interval needed for distinguishing direct from reflected/delayed signals. If the arrival interval is on the order of 5msec +/-, the signals are not distinguished and the perceived source location is intermediate between the original source and the phantom source related to the reflection.

Kal

Good info, Kal, thanks!

To put all this in perspective, we should keep in mind that as a rough approximation sound propagates through air at around 1 foot per millisecond, varying somewhat with temperature, altitude, and other factors.

Regards,
-- Al

Thank you all again for the useful input.

I got my Radio Shack SPL meter (analog), a Stereophile Test CD 2, and got the RS SPL correction curves from Rives. All set! Today I had fun measuring and would very much appreciate your help in making sense out of the readings. For the record, I followed Rives' instructions and set up the meter in a tripod exactly where I sit, mic facing ahead and right in between the speakers, and adjusted the volume so that a 1kHz signal would be read at 0 dB. BTW speakers are 6.6 feet apart and I sit at 11.6 ft from either one of them. Both speakers are 5 feet away from the side walls and about 15 feet away from the back wall (yes, 15 ft; not a typo).

I can't find a way to post a graph here, so I'm posting a table of the measurements after the correction had been made (sorry it's so painful to read):
Hz -------- dB
<20.........no test tracks available
20..........-6.5
25..........-1.0
31.5........ 5.0
40.......... 2.5
50..........-2.5
63.......... 2.0
80.......... 3.5
100.........-0.8
125.........-2.5
160.........-1.5
200.........-2.7
250.........-4.5
315.........-3.0
400.........-3.5
500.........-2.0
630.........-1.0
800......... 1.0
1000........-0.5
1250........-1.0
1600........-1.5
2000........-4.5
2500........-5.5
3150........-6.5
4000........-5.0
5000........-0.5
6300........ 1.0
8000........-2.0
10000.......-9.0
12500.......-17.5
16000.......-20.0
20000.......-21.0

First thing that caught my attention is the huge drop above 10kHz. Maybe the system can't deliver? BTW system is made of B&W 804s + McIntosh MC275 + Rotel pre + Rotel CD player.

The low point at 20 Hz isn't surprising, as the 804s can't deliver that kind of bass. I'm looking at getting a sub, but that's a different story.

The 804s have their crossover frequencies at 350 Hz and 4 kHz, so I guess the troughs near those points are not to worry much about...I guess. However the one on the higher frequencies starts around 2 kHz and extends all the way to 4 kHz, so I'm second guessing if I should worry about it or not.

It seems to me I should focus on the peaks at 31.5 and 80 Hz. Should I worry about what's going on at 800 Hz or 6.3 kHz?

What am I missing? How should I move forward?

This is fun, even though now I’m officially a freak (my wife came by today when I was playing the warble tones and said ”yeap…you ARE an audio freak”. Oh well…it’s fun nonetheless!

Thank you!!
Horacio

Nice work, freak!

The peaks @ 31.5hz & 80hz are probably the biggest concerns I see. In room high frequency plots tend to drop off steeply as you see, so not as surprising(at highest frequencies) as you might expect. However your overall picture of bass all + and treble all - doesn't seem like it would sound very natural. Do you get the sense that your "bass is turned up, and treble down?" Speaker placement & seating changes could affect this greatly. Since you are already far out from back wall, I'm guessing that current placement is exciting some room nodes. Experiment in small increments(i.e. 6in).
Lastly, not a big problem, but by definition, shouldn't 1000hz = 0? Cheers,
Spencer

SPL meter readings could be a LOT worse - a few observations.....

1)5db bump at 32 hz will add just a little sense of deep bottom end, not a bad thing actually for many.
2)3.5 db boots at 85db will add to the sense of bass, again not a bad thing, and the 2.0 db boost at 60hz will reinforce it. BUT...

3)Then you have a broad gently dip in the upper bass, lower midrange. Not a bad thing in itself, but might serve to over emphasize the appearance of the 'boosted' bass, and make it sound heavier than it actuall is.

4) After a normal 1 1/3d octave centering at 1000hz you have a broad and very audible dip in the mid/upper mid/highsrange which is going to make your speakers very 'forgiving', especially when using digital sources, but many might think the sound is dullish.

5)most speajers display the sharp roll off in the highs abouve 10K. I think mostly because you are comparing your 'in room specs' with anechoic measurements made by the manufacturer either 1 or 2 meters from the speakers.

I agree with Sbank about the effect of speaker placement, but what I think of when I see your comments about listening distance from speaker to speaker and speaker to listening chair, is not so much making a major correction to the SPL levels you mentioned because I don't see that so much a big deal. Some changes might be made in the bass, but the broad nature of the dips in the mids and highs suggest to me that the speakers are the cause, or the room surfaces are over damped.

What I do think you can do (if your wife and situation allows) is to get some space between your speakers. For example, I typically listen to dynamic speakers that are about one foot+/- closer together than they are apart. In your case that would be about 10 feet. If you thin that they are too close to the side walls you can simply try toeing the speaker in towards your seat, even substantially past it, to control 1st sidewall reflections. What you should get by doing this is getting a vastly improved since of sound stage in all dimensions.

FWIW.

SPL meter readings could be a LOT worse - a few observations.....

No kidding. The bass response is superb - almost to the point of being suspicious - hardly any room is ever that good without being treated.The broad dip in the midrange is probably just "midrange scoop" - most speakers are weak off axis in the upper midrange and your ears and SPL meter will sense this.

Since you have positioned your speakers in the middle of the room (15 feet out) they will not excite the room length mode nor its harmonics - as the speakers sit at a pressure null. I think this is the principal reason you are getting such good bass - as usual "acoustic physics" dictates how it will sound...

Good stuff!

Looking at the room dimensions and its modes I found f1 for length is 34 Hz and f0 for width is 36 Hz. Close enough to 31.5 Hz?
Also f3 for length is 69 Hz and f4 is 86 Hz, plus f1 for width is 72 Hz and f0 for height is 78 Hz. Might be a good shot at the 63 & 80 Hz bump?

Further comments following yur comments:
- room is not overdamped. If anything, it's underdamped. Hard stone floors with no rugs (for now). Brick walls. No drapes (for now).
- Cannot spread the speakers further apart. Room circulaion happens at the side of each speaker and it would be unpractical to change that (unless I change the whole setup, that is).
- I swear, no treatments are in place other than a bookcase and a sofa on the side first reflection points.
- to me it doesn't sound dull...but maybe it's me being used to it.

Will try playing around with positioning again next weekend.
Keep the good ideas flowing!

Cheers,
Horacio

most speakers display the sharp roll off in the highs above 10K. I think mostly because you are comparing your 'in room specs' with anechoic measurements made by the manufacturer either 1 or 2 meters from the speakers.

I wonder if treble beaming could be a factor as well, assuming the tweeters are pointed straight ahead. Should be easy enough to check, by toeing the speakers in a little, and re-measuring.

I had looked at the specs for the speakers, and they specify a horizontal dispersion covering a 60 degree arc (meaning +/- 30 degrees from straight ahead). Which would make toe-in especially important were they to be moved further apart.

It's unfortunate, though, that it's impractical to move them further apart; I agree with Newbee that it would be likely to improve imaging considerably.

Regards,
-- Al

I wonder if treble beaming could be a factor as well, assuming the tweeters are pointed straight ahead. Should be easy enough to check, by toeing the speakers in a little, and re-measuring.

Only very high up (at 10 Khz and above), however,the 804S is a typical B&W with the "midrange scoop" - they run the excessively large midrange up to 4 Khz and the tweeter has no waveguide. This means you get beaming on the midrange and which causes the mids to lose energy between 1khz and 4Khz when in a room. Above 4Khz the energy returns as the tweeter takes over with its typical wide dispersion pattern in the absence of a waveguide.The power response would show a "scoop" in the midrange and a stereophile horizontal dispersion plot would show this hole at 60 degrees off axis. Perceptively this sounds laid back in the mids but with plenty of presence detail - it creates a very nice sound with emphasis on articulation that B&W is known for.

The only B&W's I know that do not exhibit this "midrange scoop" are the B&W silver signature, the B&W 805N (Nautilus and not the "S" version) and their top of the line 4 way Nautilus. It is actually not uncommon for most two ways with large 6 inch midranges and a tweeter crossed over high to sound this way.

The in room HF roll off is quite typical anyway - that would be completely normal for a room that size.

Here is a useful chart to explain how the speaker will sound. You can see why B&W would choose to voice it this particular way: bass string pluck, drum and guitar attack and vocal presence will all be increased- giving the impression of more detail compared to a flat power response.

Of course some people believe that measurements are like the zodiac and reading the position of planets ....i.e. "completely meaningless" ....just don't tell that to the engineers mixing/mastering your music. They use many rules of thumb based on measurements - a good engineer will know exactly what to do to create a desired effect and so will a speaker designer....

Shadorne -- Thanks for the good explanation and the good reference!

Regards,
-- Al

Shadrone/Almarg - Good point about beaming in HF and the effect of tinkering with toe-in. But with speakers 11 ft away, and with only a six ft spread, you really are not that far off axis to begin with.

Shadrone, "The bass response is superb...". Obviously I agree, but let me say that I never thought it was suspicious. It actually resembled my bass frequencies before I tweeked the set up a bit (without using any acoustic crutches, which I still do not need). For fun, and for illustration of the benefits of position tweaking for Lewinskih.

My set up is as follows, in a 13.5x19.5x9 ft room with the speakers 58" from the wall behind them, 9' apart and the listening spot (ear location) at either 52" or 36" from the back wall.

........52"....36"
1000 0db db0
200hz 0db 0 db
160 -1db 0 db
125 +2db +3db
100 +1db -2db
80 0db -2db
60 -2db -1db
50 -5db -4db
40 -4db -3db
32 +1db +4db

One might think that the bass response at 36 inches would be better because it is smoother and it has some beneficial (I think) boost at 32hz, like the poster. But to my ears, any linearity one might loose, the gain in imaging by moving the listening position forward 16 inches was huge.

Shadrone, I want to thank you for bringing to my attention something (some time ago in another post) about the creation of a null on the center line of the room. I've since moved my listening position and speakers off center line and it has helped in getting a more balanced frequency response whereas nulls had previously been a problem.

IMHO, of course, just a mid-day stream of (un)consciousness. :-)

Nice.

Newbee: thanks for sharing your experience in your room. Your freq response does resemble indeed the shape of mine!BTW, how far is the listening position from the speakers?

Al: the speakers are indeed facing straight ahead. I gather beaming refers to high freq, right? Shadorne's [very interesting] explanation seems to suggest beaming in the mids. I have no clue what the dispersion of the mids driver is. Anyway, as Newbee said, at 11 ft away it would seem dispersion would be wide enough, right?

Bottom line, what I'm taking away is:
a) frequency response looks "good enough". No need to get into bass traps, resonators, diffusors, etc.
b) imaging is likely to be improved by moving speakers further apart (will try it for fun)
c) playing with speaker location might improve things some, particularly if they are exciting a room mode

Are these fair takeaways?

Thank you!!

Re distance - 10 ft from the plane of the speakers (10 1/2' from each speaker itself).

Re takaways - IMHO, yes.

Al: the speakers are indeed facing straight ahead. I gather beaming refers to high freq, right? Shadorne's [very interesting] explanation seems to suggest beaming in the mids. I have no clue what the dispersion of the mids driver is. Anyway, as Newbee said, at 11 ft away it would seem dispersion would be wide enough, right?

My understanding is that a driver will tend to beam as its diameter approaches or exceeds the wavelength of the sound it is radiating. According to a quick calculation I did, the one inch diameter of your dome tweeter corresponds roughly to the wavelength of a 12 kHz note. So at or near that frequency, and higher, it could be expected that the tweeter's dispersion would narrow considerably, and progressively with higher frequency.

The speaker is spec'd for +/- 30 degrees dispersion, which your listening position clearly satisfies, but we have no way of knowing how rigorously that spec was defined, e.g., if it was intended to cover all frequencies up to 20kHz.

In principle, a similar concern could exist with respect to the mid-range driver, given its 6 inch diameter and 4kHz upper crossover frequency. But I would have higher confidence that the manufacturer's spec for dispersion would be accurate for the mid-range frequencies, than for say 15 to 20kHz which most people can't hear anyway.

So that is the background on why I raised the question, but I think that Shadorne's good response pretty much puts the issue to bed.

Regards,
-- Al

Al,

That is roughly correct but beaming starts a little earlier. If you look at figure 3 you will see that the prototypical 6" woofer and combined midrange should not really be used above 1.8 Khz - like was done in the famous Energy Pro 22 speaker.

So why do we see so many speakers with 6 inch woofer/mids and a tweeter with a crossover much higher than 2 Khz?

Cost is the answer - unfortunately few tweeters can handle SPL requirements at that low crossover point - not without distortion and risk of failure. However to avoid having to add another driver (increased cost/complexity) the designers make do with beaming in the midrange...odd really in what is ostensibly an audiophile design and given we have known about the physics of loudspeakers for donkeys years and considering this frequency region is where our hearing is the most acute and discerning.

Al, Shadorne,

Very informative answers. I wasn't aware of beaming.

Thanks all three for your input. If you don't mind checking back on Sunday, I will try to make time and play with all of the above and post back results. I trust your input will help me make sense of what I measure/hear.

Thanks again for all your valuable input.

Regards,
Horacio

I am in India. It looks like it is not possible to get fiberglass panels over here. Is it possible to use EGG TRAYS which are made of THICK paper to back and the side walls. Thickness of the egg tray could range from 1/10 in to 1/4 of an inch.

EGG TRAY is 1ft by 1ft in dimension has corrugations such that it can fit eggs. It am not sure it works as a absorber or diffuser.

Let me know your opinion.

Paper egg trays are, fundamentally, useless.

Kal

Sandhya,

Thanks for bringing up this thread of mine again. A year and a half has gone by and I've done a fair amount of further reading and experimentation and things have improved, and I'm still working on improving things further. This might be the second most interesting aspect to being an oddiophile (ja!), following the enjoyment of music itself, of course.

I'm surprised you cant't find fiberglass panels in India. Where are you looking for them, may I ask? I say this because I'm in Argentina and I can find them at construction supply stores. Both the panel and the fiberglass wool are used as insulation for construction and industrial applications.

Horacio

Horacio,
Congrats on last nights win by argentina into q/f.

Last since I posted, after further reading I came to know that this is the same thing which is used for A/C Insulation. We do find it over here.

I have more questions.

1. What is the amount of insulation we need to do. 1 in or 2 inch. How do we determine.

2. I suppose we need to make wooden frames, fit the fiberglass wool and then what do we need to cover it with. Fabric is the only choice.

3. How much of % of walls do we need to cover it with. Is there a possibility that the room would become not lively or dead.

You say you are experimenting. How are you doing it.

Can you let me know few examples.

Thanks
Sandhya

Sandhya,

Thanks for the compliments. It's a big deal in this part of the World!

To me it has been worthwhile learning about this. The two books I have are Alton Everest's master Handbook of Acoustics and Floyd Toole's Sound Reproduction. Both very good and they complement each other nicely.
I've been reading a lot over the internet too. Examples: Real Traps website, as well as the other websites mentioned obove on this thread.

As far as your question about fiberglass thickness and how much and placement. It depends!!
Treating some of the first reflection points is important, and for that you can use 2" fibeglass panels of 50 kg/m3 placed against the wall.
For bass absorption you'll be better off with a fair amount of space between the panel and the wall, at least 4" space, and a 4"-thick panel.
Check out Audio Asylum for Jon Risch's panel recepies. same for bass tube traps.
For covering the fiberglass I use polyester batting (cheap insulator used for mild-cold weather jackets).

My way of experimenting has been listening and taking measurements with a Radio Shack SPL meter when changing speaker and listening positions, building 2 large bass tube traps, building 2 3"-thick panels for front wall first reflection points, and building two 4"-thick self-standing panels, and adding a thick wool carpet on the floor first reflection points. I'm now building a larger panel for a specific place where I suspect it will be very beneficial.

This takes time and effort, though, and is oftentimes frustrating. So be aware of it before going in. It pays off, though!!

Sorry for the long post.

Horacio

Listnening priorities : 70 Music vs 30 Movies.
Last few weeks I have been studying about Room treatment.

Few Decisions I have made.

Currently my room is 17' 4" X 12' 3" X 9'. Initially thought of increasing the size to 22' ft in length. Gave up the idea as it involved more civil work, more expenditure etc. Also I thought 17 ft is not too bad of a size of a room. Also Will be creating Acoustic panels such that they can be removable.

Acoustic treatment design will consist of two parts

1. Broadband absorbers which will be positioned on the side, back and front walls.
2. 3 Superchunk(right triangle rockwool from floor to roof) bass absorbers.4th one I cant use as there is entrance door situated there.

All the acoustic panels will be 4 inches thick. Will be using 96 Kg/cu.m Rockwool.

My side walls will contain 6 ft width X 4.5 ft Height panels. There will be three panels each of 2 X 4.5. These will be positioned based on the first reflection points. These will be hung 2 inches away from the wall. To hang them away from the wall I will be using a A nut bolt method where the screw will be embedded into the back part of the panel. The front part of the screw with the head will be inserted into the frame hanger which is fixed into the wall. This is like frame being hung on to the wall but the nail is on the frame not on the wall. Another advantage with this method is I can remove them and change the spacing between wall and panel by rotating the screw to 0,1,2 or 3 inches. I will be using 4 inch nut bolts.

My Back wall is pretty close to my seating position I will have a 6ft by 4.0 ft panels. I dont have too much space so I am planning to stick them to the wall leaving no space between the wall and panel.

My front wall where I hang my projector screen will be covered with absorbtion panels about 8ft X 5 ft. It will starting at 32 to 34 inches from the bottom and reaching up till the roof. My 32 inches from the floor will be covered by my new HT rack. Same with my front panels, I will stick them to the wall leaving no space between wall and panel.

Question : My Projector screen will be hanging over this absorbtion. The screen will always be pulled down. The spring action which the screen had is all gone. Will this be a problem for absorbtion not happenning. If so I might need to fix my screen such that It will go up as and when required.

My Front two corners will contain two super chunk corner bass absorbers. The dimensions of each being 17X 17X24 inches. I can only use one back super chunk corner bass absorbers of size 15 X 15 X 21 inches. On the other corner I have the entrance door situated.

I might treat my center of my ceiling with 4ft by 12ft with 12 ft being parallel to the speaker line and 4ft being the width. Not decided yet. Currently my room's fall ceiling is already done. Dont want to disturb it. If at at all I do it it would be such that I will run two Iron rails parallel to the Speaker line. Then hang the absorbers to the two rail lines. Before I commit to this I will test it without the ceiling absorbers and then decide about it.

Let me know your opinions.