# Termination Peak Bandwidth



## jim1961 (Apr 8, 2011)

In reference to the LEDE / RFZ modeling applied to a home listening room, if one is embedding a specular reflection to get a termination peak of -8db, how critical is the bandwidth?

My ISD Gap = 24ms









Purple = 4.2k
Green = 2.1k
Yellow = 1.6k
Orange = 1k

The above are 200us smoothed 1 octave bandwidth ETC sine sweeps. 










The above is my unsmoothed ETC response (right channel only)

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Any conversation related to ETC measurements and room models/goals is welcome here


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## Gregr (Nov 2, 2010)

jim1961 said:


> In reference to the LEDE / RFZ modeling applied to a home
> listening room, if one is embedding a specular reflection to get a termination peak
> of -8db, how critical is the bandwidth?
> 
> ...




Hi Jim,
I wish I had an answer. Honestly, I would love to listen in on this conversation as it 
progressed. 

HTS I guess is first a Home Theater forum and conversations are about Video and audio 
as this relates to dynamic sound presence, not so much about sound isolation as you will
find in a well engineered sound room for recording of the type material one would listen 
to in a Home Theater. 

I am not attempting to speak for Home Theater, these are my observations only. It is 
my understanding the LEDE, RFZ, Haas Kicker, ISD Gap are Trademark of Sound Room 
Acoustical Treatments at least Registered as such many years ago. Today you will find 
these term used in a HT along with other Acoustic Treatments. The Live end and Dead 
end are used with additional considerations for Bass absorption/diffusion in the corners 
and soffit only as indicated thru testing and/or experience. But even the live end is minimal
I think... the hand clap test is a diffused sound. But I am not an expert at all. You could
take your question to GIK I am sure there are several Sound Engineers there who will 
appreciate your question. 

That said..., I think an ISD Gap of 20ms is the magic number. Your termination number
of -8db is beyond my pay grade but if you are using a reflective panel to trigger your 
termination number I only wonder about adjustment in the Kicker? My understanding 
of frequency adjustment is to quiet a resonant frequency in this instance I would say 
bandwidth/freq is absolutely critical to achieve a neutral RFZ I cannot say an -8db is 
acceptable. 

I apologize to ask more questions in a reply than was asked in the original Post. I am 
interested in a real answer to your question. I want to recommend a site where you 
can join and repost your question. Because of the name of this site I have to 
send a private message.


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## jim1961 (Apr 8, 2011)

Gregr said:


> Hi Jim,
> I wish I had an answer. Honestly, I would love to listen in on this conversation as it
> progressed.
> 
> ...


Keep in mind, the -8db refers to the termination strength at 24ms, not the RFZ. 

Here is a link to a paper by Don Davis where he specifies a termination strength of -5 to -10db.
http://jgbouska.tripod.com/audio/d_davis_lede_audio_1987_p1.pdf

Here is one by Dr. Peter D'Antonio suggesting -10db 
http://www.docstoc.com/docs/111150235/Audio-Project-Studios

Both good reads if your interested in the subject.

Toole has said in many writings that the termination strength should not be less than -12db

So I am not sure what you find odd about -8db as a termination strength.


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## Gregr (Nov 2, 2010)

Jim, 

Please remember I am no expert by any stretch..., I believed I was trying to respond 
to Bandwidth(frequency) imbedded in attempts to achieve the -8db termination. 

I am thinking of the RFZ as a neutral zone achieved when first reflections are controlled
and your -8db measurement was a RFZ boundry measurement.

I think I better read your references before I say anymore and waste your time 
thinking I might have a point.

Thank you for your kind and informative response. I am very interested in acoustics.
If I ever have an answer for you 
reather than a question I'll send it out to you.
Thanks again


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## jim1961 (Apr 8, 2011)

Gregr said:


> Jim,
> 
> Please remember I am no expert by any stretch..., I believed I was trying to respond
> to Bandwidth(frequency) imbedded in attempts to achieve the -8db termination.
> ...


We all learned somehow from someone 

I think your confusing the specifications for the RFZ (ISD Gap) with those of the terminator. In the RFZ, you want the reflective energies within it to be -20db or better below the direct signal. At the of of the ISD gap, if you terminate, you want ideally peaks in the -12 to -5db (depending on who you read), followed by an exponentially following "tail" of decreasing peaks. The following pic shows these features.


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## HopefulFred (Jan 20, 2011)

Hey Jim. I'm no position at all to speak about this with any sort of authority, but it would seem to me that you could try out a few simple adjustments to your room and give it a listen - as well as a measurement.

It sounds like your space is a pretty carefully constructed mixing room, right? Have you installed a specific reflector to generate the kicker? I wonder about the size of that reflective surface and its influence on the spectrum of the reflection.

Since 1kHz is a wave just over a foot long, the margins of your surface may refract a significant portion of those longer wavelengths away from the LP - depending on how it's set up (size, adjacent surfaces, etc.) - at least I think so.

Of course the other way to look at the trend in your kicker spectrum is that it's too strong in the higher bands. If that's the way you see it, maybe you could add some thin fabrics and measure for a decrease in the strength of the high end.

My point is, can you change the size (or surface) of the reflector and see what kind of influence that may have on the spectrum of the kicker? It'd be interesting to see if changing the size could influence the spectrum, and actually answer your question for you if you could measure the difference but not hear it.

Fred


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## jim1961 (Apr 8, 2011)

HopefulFred said:


> Hey Jim. I'm no position at all to speak about this with any sort of authority, but it would seem to me that you could try out a few simple adjustments to your room and give it a listen - as well as a measurement.


The adjustment to handle lower frequencies wouldnt be a simple one im afraid.



HopefulFred said:


> It sounds like your space is a pretty carefully constructed mixing room, right? Have you installed a specific reflector to generate the kicker? I wonder about the size of that reflective surface and its influence on the spectrum of the reflection.


My space is a dedicated listening room. I do have a specific panel dedicated for the kicker, yes. The size does play into the bandwidth.



HopefulFred said:


> Since 1kHz is a wave just over a foot long, the margins of your surface may refract a significant portion of those longer wavelengths away from the LP - depending on how it's set up (size, adjacent surfaces, etc.) - at least I think so.


This is basically right.



HopefulFred said:


> Of course the other way to look at the trend in your kicker spectrum is that it's too strong in the higher bands. If that's the way you see it, maybe you could add some thin fabrics and measure for a decrease in the strength of the high end.


Its basically flat from about 2k-20k, then rolling off significantly below 1500hz. So if I am to go further, increasing the low end would be the way to go. Lessening the highs would compromise the termination strength.



HopefulFred said:


> My point is, can you change the size (or surface) of the reflector and see what kind of influence that may have on the spectrum of the kicker? It'd be interesting to see if changing the size could influence the spectrum, and actually answer your question for you if you could measure the difference but not hear it.
> 
> Fred


Yes, I can make the kicker respond lower. But I was hoping to find the answer via those who have data or experience in the matter for making this kind of change would constitute a MAJOR redesign. I dont want to go there unless I become convinced of its necessity or advantage first. 

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In the Don Davis paper linked earlier in the thread, it was pointed out that its in the higher frequencies (above 2k) primarily that our direction queues in the human ear come into play. 

I have also read that the Haas effect in this case is a trigger, brought into being by the ISD termination. And that trigger and the psycho-acoustic effects it creates is what I am trying to understand better. 

Generally speaking, you want your reflections to be a mirror in bandwidth to your direct signal. This is stated time and time again in various papers. But I am singling out only the termination peak in this thread / discussion and trying to determine if it also must be broadband.


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