Room Acoustics & Speakers - woz: Is15 inch overkill for music?????experts - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th March 2004, 12:15 AM   #1
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Room Acoustics & Speakers - woz: Is15 inch overkill for music?????experts

From:

http://groups.yahoo.com/group/Thunde...nical/files/TL Circuits/Ultracurve/Behringer target curves.html

=================
Now, the Beringer, just like the Derringer it is some pun wise compared to, is a specific tool for a specific job. Correctly applied the effect of either is mind-blowing. Used wrongly it can make a bad situation worse.

It is ESSENTIAL to understand a little about speakers in general and room acoustics, as well as understanding the specifics of your speakers. As a result this whole "little" article has to become quite long. Lets start at the beginning - the room.....

Part One: The room of doom - why listening to a stereo indoors is bad idea

For a room in which a speaker plays we find three predominant frequency ranges through which the room behaves dramatically different.

For frequencies in the midrange and treble, where the room dimensions are large, compared to the wavelength of the frequency reproduced the room behaves in general diffuse but consistent. We shall call this range the reverberant range, as this describes it's behaviour well. In this range we can think of sound to be similar to a ray of light and being reflected, diffused or absorbed by room surfaces.

Depending upon the directionality of the speaker and the reflectivity of surfaces in the room that sound is radiated towards the room will reflect (or not) and generate a reverberant field that merges with the direct sound of the speaker. If two or more speaker are used (stereo, multichannel) it is essential for correct reproduction that the acoustic environment around each speaker is as symmetrical and identical as possible.

Gross asymmetry (like heavy drapes on the left wall and a naked wall on the right side) MUST be avoided at all cost. Please also note that few absorbing materials are consistently absorbing over a wide frequency range. I personally prefer the use of diffusion as much as possible with some absorption behind and around the listening position to excessive damping, as the latter often leads to a "dead" and unnatural, lifeless and amusical sound.

Contrary to many claims made by manufacturers of digital room correction, there is NO WAY to effectively deal with the reflections in the reverberant range and the only real way to achieve a resolution of problems is physical, be in using controlled directivity speakers or absorptive/diffusive room treatment.

In most modern living quarters the reverberant range starts somewhere in the 200 - 300Hz range. The larger the room the lower extends the reverberant range, though usually the ceiling/floor distance is the limiting factor. The common 2.4m high ceilings will lead to a main mode at 143Hz and a strong second mode at 286Hz, demarking basically the reverberant frequency range.

Below the reverberant range the room transit into the modal range. Here the behaviour of sound in the room is dominated by resonances; in effect the room becomes a resonant system where both the position of sound source and sound receiver (ear) with respect to room boundaries becomes a determining factor in the resulting frequency response. In the modal range deviations from a flat response by more than 20db are common.

Very few effective ways exist to deal with the problem in a mechanical fashion (room treatment) and even the various "Bass Trap" products are contrary to their marketing NOT effective in combating these problems. In the modal range we will encounter both pressure maxima (resonant reinforcement) and pressure minima (resonant cancellation).

Certain effective speaker setup systems like Wilson Audio's WASP rely on optimising the speaker and listener position such that the number of frequencies at which the listener receives either a boosted or cancelled signal are minimised. However, again effectiveness is limited. As a rule, pressure maxima exist near all room boundaries and pressure minima are scattered like "black holes" across the room. In a pressure minima there is simply no sound pressure, thus no sound and deep notches occur. In a maxima there is a boost and thus at the room mode a strong peak.

While there is no way "to fill in" a "black hole" a number of solutions exist to allow peaks to be dealt with. As you are reading this in the context of using an equaliser that you will chose to equalise these peaks out. This usually requires parametric equalisers or dedicated room correction systems (like TACT), simple graphic equalisers are not able to help, as they offer to coarse a view of the spectrum.

Below the modal range our room behaves as more or less ideal pressure chamber. Room modes stop to exist at a frequency where 1/2 of Wavelength of the tone is longer than the longest room dimension. In my listening room this dimension is depending how you look at it 5.5m or very long (through the open door into the hall). For a 5.5m dimension the room becomes a pressure chamber (in my case a leaky one) below around 30Hz and here a notable bass boost is present helping to extend the bass of large speakers down as far as one wishes, assuming there is still SOME usable output.

In this region the positioning of listener and speaker becomes completely irrelevant. It should be noted that the demarcation between all three of these ranges is somewhat fluid so it is a question more of abstract judgement where one starts and the other ends. However once we are in the modal region all sorts of proverbial hits the fan and live becomes VERY interesting. In the reverberant region things are interesting too, but primarily due to the stupidity of modern speaker designers. Only in the pressure region at very low frequencies is life easy and predictable. But usually not only do we have a lot of problems with the room; we often have as bad or worse problems with the speaker....
=================
  Reply With Quote
Old 6th March 2004, 12:17 AM   #2
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
From:

http://groups.yahoo.com/group/Thunde...nical/files/TL Circuits/Ultracurve/Behringer target curves.html

=================
Part Two: Friend or foe - the Loudspeaker designer and his products

Considering the extensive body of knowledge that exists on room acoustics, the "average room" and so on it comes again and again as a surprise to me how ill considered and conceived most so-called "High Fidelity" loudspeakers are, especially if one compares the situation to the sound reinforcement sector and serious studio monitors (meaning NOT the Yamaha NS-10 or BBC LS 3/5). Speakers interact with the room in various ways, both due their own behaviour and due to the different regions of the room discussed above.

The key to much of perceived tonality is the behaviour of room and speaker though the reverberant range, because in this range we find the fundamentals of most instruments and the human voice as well as all the harmonics. Above I commented that in reverberant range the speaker behaves a lot like a light source.

For a long time two specific types of speakers have been sold to the unsuspecting public that have by design severe behavioural problems in this range. One type is the Full Range Dipole and the full range omnipolar speaker. Neither type is found in serious Studio or sound reinforcement applications for exactly this reason.

Dipoles and Omnipolar Speakers create way more problems than they solve, by radiating energy over a very WIDE frequency range and also a very wide area. Think simply of a naked light bulb in a room. This is your omnipolar speaker and to a lesser degree your dipole. This makes the frequency response in room within the reverberant range maximally dependant on the room symmetry, absorption etc. and thus will require major efforts on room treatment to correct for the problem. Of course, a notable minority of listeners actually likes the presentation of Omniís and full range dipoles and they by all means are welcome to their preference.

Another major problem source are modern "conventional" Hifi Speakers. They misuse a semi omni directional HF unit (the dome tweeter was designed by Stu Hegeman for applications radiating upwards and giving omni directional hemispherical response) in combination with a cone unit that at higher frequencies coming up to the crossover frequency is actually quite directional and as a result the directionality changes strongly with frequency.

The use of non coincident sound sources also adds to the problem as now in at least one plane (lateral or vertical depending upon orientation) the radiation is turned into several "beams" going off on sides of the main (forward) one. All in one unholy mess and one that has done much to cause the rather unnatural, upper midrange emphasised sound of modern Hifi systems, by placing a depression in the upper fundamentals and a strong emphasis onto the lower harmonics for the response off axis, assuming a flat on axis response. Here you cannot really do anything with equalisation, as "fixing" the problem in the overall response will severely unbalance the on axis response and thus the first arrival of sound.

THAT SAID, if no other measures can be taken to address the problem, equalising the in room reverberant response flat will sound subjectively better. However, a better solution is to either switch to controlled dispersion loudspeakers or if a change of speakers is not possible at least all reasonable means should be employed to correct especially the excessively wide dispersion in the upper midrange of common dome tweeters. One of best solution are the type of diffraction control felt/foam rings embodied by the AIG "Imagers".

http://www.audio-ideas.com/tweaks.html

Room treatment of various sorts can be used effectively in this range to eliminate first reflection points (primary ceiling and floor) and an arrangement that places the speakers along the long room wall wide apart and strongly toed in can further help to reduce problems from non too ideal directivity of the speakers.

I generally advise against removing sidewall reflections with damping material, as the sidewall reflections somewhat match the behaviour of a concert hall and thus are more less similar to the natural behaviour of music and can in modest amounts enhance the naturalness of presentation, diffusion is preferable.

If full range dipole speakers are used (Maneplanars, ESL's etc...) it is essential that the rear wave is in some way diffused and damped, to avoid strong reflections. My preferred suggestion would be to place diffusers fairly close behind the Speaker, like for example variations on the Argent Room-Lense theme. Unlike with dynamic speakers, where a location close to rear walls is entirely possible and indeed even desirable (more later), dipoles require "room to breath". The area behind a dipole speaker should in addition be quite absorptive, after all we need to kill most of the rear output.

The same of course applies also to Omnis, but things are much worse there, because while dipoles have at least a "null" (an area with no sound radiation) on their sides Omniís radiate to everywhere, while really radiation is only desirable into the direction of the listener. All the extra radiation needs to be diffused and damped.

From the above it should be clear that before you attempt to equalise your speaker flat throughout the reverberant range (or before you use other digital room correction products) you need to address as much of the directionality problems of your speakers as possible.

Of course, some of us do not have such problems, this includes people with 12" - 15" Coaxial speakers, larger fullrange speakers (especially if additionally loaded into a front horn). I'll come back to this in the section on the modal region - but the old Hartley Concert Master Speaker (22" Dipole Woofer and 10" sealed box fullrange speaker) is surprisingly close to an ideal domestic speaker.
=================
  Reply With Quote
Old 6th March 2004, 12:40 AM   #3
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
From:

http://groups.yahoo.com/group/Thund...hnical/files/TL Circuits/Ultracurve/Behringer target curves.html

=================
Part Three: Forever onwards.....

Now in to the meatier chunks. Above I said that in the modal range the room becomes resonant. One possible option is of course to locate speakers and listeners in pressure maxima, that is near walls. So if you move your listening position as close to one of the long walls, centered and place the speakers along the other long wall, strongly toed in and (if neccesary) Imagered, you will have sorted many of the problems for the reverant range and you will have coupled yourself (listener) and the speakers maximally to room modes. Of course, the bass is gonna sound hugely boomy, but we have an equaliser for that.

The one problem we will have is the floor/ceiling mode where we, due to a seated hight of around 90cm - 1m are precariously close to at least one pressure minimae. This usually falls around the 100 - 150Hz range and not much can be done about this, it will fall whichever way it will. in the context of the other main modes hoever both speakers and listener are well placed.

As a further freebie placing speakers and listener close to the walls will both extend and increase their bass output, which after equalising the resulting system will have less actual power input at low frequencies and thus less distortion, so in the bass the system will player lower and louder without strain.

Of course, such an approach only makes sense if a suitable equaliser or room compensator is in the system, it effectivley becomes an absolute requirement.

There is of course another trick here which we have so far missed. While all normal enclosed dynamic speakers operate in the modal region effectively as omnidirectional radiator (regardless of being a domestic foreshortened LF Horn, Reflex or sealed box). Using a DIPOLE to cover the modal range will actually result in a rather well behaved LF behaviour. The way the dipole interacts with room modes will result in a much more even LF response.

What follows from this is of course that 99% of ALL HiFi speaker designers got it all *** forward. They make hybrid Electrostatic or ribbon dipole speakers that are dipoles where they should directional monopoles (midrange/treble) and that omni directional where they SHOULD be dipolar (bass). Normal Box speakers really can only take refuge to special room setups or equalisation.

It seems in the last 70 or so years of sound reproduction only three or four companies ever "GOT IT" (or at least got it to some degree), namely the earlier mentioned Hartley, Celestion with their SL-600 & dipole Subwoofer combo, Gradient in Finland and the now defunked Audio Artistry headed up by Sigfried Linkwitz (added later - and Siegfried Linkwitz's new commercial speaker, the Orion, as well as the most recent versions of the classic MEG Studio Monitors from Germany).

Finally, below the modal range our best choice (should we wish to extend our response that low) is a simple monopole subwoofer, either sealed, passive radiator or vented with a suitably low cutoff and SPL capability at low frequencies.

I hope this somewhat exhaustive coverage of room and speaker acoustics has helped a little to understand what can be done and what not.
======================
  Reply With Quote
Old 6th March 2004, 01:16 AM   #4
diyAudio Member
 
Bill Fitzpatrick's Avatar
 
Join Date: Jun 2001
Location: Eugene, OR
Well, I was going to give you due credit until I went to your website and suffered through all those ad pop-ups. Pretty disgusting.
  Reply With Quote
Old 6th March 2004, 02:13 AM   #5
7V is offline 7V  United Kingdom
diyAudio Member
 
7V's Avatar
 
Join Date: Feb 2003
Location: North London
For what it's worth, I'd like to make some additional points on this question.

Firstly, the best position for placing a speaker for stereo imagery and frequency response in the reverberant range is invariably not the best for bass interaction with the room.

It might therefore be a good idea to separate the speakers for bass and the rest of the range. Keeping the bass speakers below 150Hz will help make them undetectable (in terms of direction). Using two bass speakers will make them even less detectable and gives additional options in cancelling each other's room modes.

I believe that you could use even more bass speakers than two to cancel more of the room modes but I haven't yet tried this extensively.

The point about crossovers and their effect on the dispersion characteristics (in the reverberant range) as one switches from a directional mid-band to an omni-directional tweeter is well made and, like you, I believe that a good solution is to dispense with them.

In the reverberant range, keeping the speakers away from the walls and toed in a little helps to remove the room from the equation and, if these speakers can be excused deep bass duty, little is lost in terms of the room reinforcement of the bass.

The use of a line array configuration will go a long way to minimising early reflections from the ceiling and floor, although with some designs (like mine) you may have to do your serious listening while seated - stand and you can lose the highs.

I believe that it is also true, again in the reverberant range, that the human brain performs its own equalization, thus allowing us to have intelligible conversations even while walking from kitchen to bathroom to living room to garden (although clearly not about hi-fi ). This 'psycho-equalization' will filter out subtle effects but may not be adequate where there are coarser reflections and 'bathroom-like' reverberations.

The 'mirror method' is effective in the reverberant range for improving and balancing reflections without killing the room. You simply get a friend to hold a mirror against the wall while you sit in your listening position. Wherever you can see the speakers in the mirror is where you add the padding, damping or whatever.

Sayonara KYW. Long time no speak.
  Reply With Quote
Old 6th March 2004, 11:41 AM   #6
diyAudio Member
 
slowmotion's Avatar
 
Join Date: Nov 2002
Location: Norge
Quote:
Originally posted by Bill Fitzpatrick
Well, I was going to give you due credit until I went to your website and suffered through all those ad pop-ups. Pretty disgusting.
Just use a proper browser,
then you'll have no problems with pop-ups

cheers
__________________
- Jan -
  Reply With Quote
Old 6th March 2004, 01:22 PM   #7
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by Bill Fitzpatrick
Well, I was going to give you due credit until I went to your website and suffered through all those ad pop-ups. Pretty disgusting.
No-one asked you to visit, all relevant material was placed here in the posts. Also, with as basic a combo as google toolbar and MSIE6 I experience NO popups.

Sayonara
  Reply With Quote
Old 6th March 2004, 03:10 PM   #8
fedde is offline fedde  Netherlands
diyAudio Member
 
Join Date: Jul 2002
Location: Eindhoven, the Netherlands
Send a message via ICQ to fedde
Quote:
Originally posted by Kuei Yang Wang
It seems in the last 70 or so years of sound reproduction only three or four companies ever "GOT IT" (or at least got it to some degree), namely the earlier mentioned Hartley, Celestion with their SL-600 & dipole Subwoofer combo, Gradient in Finland and the now defunked Audio Artistry headed up by Sigfried Linkwitz (added later - and Siegfried Linkwitz's new commercial speaker, the Orion, as well as the most recent versions of the classic MEG Studio Monitors from Germany).
What about Tannoy... ?
I know one problem is the not ideal (in other words: moving) horn mouth around the tweeter.

And what about the full-range open baffle system you use now; doesn't have that the same HF dipole problems !?

For the rest, thank you for the good information!

Fedde
__________________
http://www.fedde.nu, gainclone and non-oversampling DAC audio projects and kits...
  Reply With Quote
Old 6th March 2004, 03:52 PM   #9
SimontY is offline SimontY  United Kingdom
diyAudio Member
 
SimontY's Avatar
 
Join Date: May 2003
Location: Sheffield, North England
Send a message via MSN to SimontY
Quote:
Originally posted by Kuei Yang Wang

No-one asked you to visit, all relevant material was placed here in the posts. Also, with as basic a combo as google toolbar and MSIE6 I experience NO popups.
Yup, or even better: use Opera, in which you can set popups to open only when you click a link.

Nice reading material KYW, thanks.
  Reply With Quote
Old 6th March 2004, 06:37 PM   #10
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by fedde
What about Tannoy... ?
Tannoys are good Midrange/Treble systems, but at low frequencies require acoustic loading which in effect means at low frequencies they are subject to room modes like all other speakers. At least above a few 100Hz Tannoys have well behaved dispersion, which helps no end.

I give tannoy coaxials 9/10 in the reverbrant range, 3/10 in the modal range. Average HiFi speakers don't maneage > 3/10 in any category....

Sayonara
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Is15 inch overkill for music?????experts Andre Baptiste Multi-Way 164 17th March 2004 10:59 AM


New To Site? Need Help?

All times are GMT. The time now is 03:11 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2