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Is it the monitors or the room?
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Nonlinear
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#1
23rd January 2013
Old 23rd January 2013
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Is it the monitors or the room?

If you run a frequency/time response test of your room and find peaks, dips and ringing - how do you know if it's caused by the room or the monitors (or both)?

We assume that the monitor manufacturer gave us truthful response charts for their monitors but that might be a bad assumption.

So how do you nail this down and fix it?
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23rd January 2013
Old 23rd January 2013
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Quote:
Originally Posted by Nonlinear View Post
If you run a frequency/time response test of your room and find peaks, dips and ringing - how do you know if it's caused by the room or the monitors (or both)?

We assume that the monitor manufacturer gave us truthful response charts for their monitors but that might be a bad assumption.

So how do you nail this down and fix it?
Test the monitor outside, on top of a ladder. That will give you a pretty good idea of what the monitor does by itself. In the room, well, welcome to the world of small room acousitcs!

Andre
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23rd January 2013
Old 23rd January 2013
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Quote:
Originally Posted by avare View Post
Test the monitor outside, on top of a ladder. That will give you a pretty good idea of what the monitor does by itself. In the room, well, welcome to the world of small room acousitcs!

Andre
+1

Better add:- you need a hi-vis jacket, safety harness, hard hat and safety specs for the health and safety department.
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23rd January 2013
Old 23rd January 2013
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Quote:
find peaks, dips and ringing -
Because speakers alone can't do that. But if the speakers are not placed right in the room it can cause SBIR.
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23rd January 2013
Old 23rd January 2013
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Quote:
Originally Posted by Glenn Kuras View Post
Because speakers alone can't do that.
They sure can!

Speakers are transducers mounted in a box. There is no such thing as a perfectly flat speaker with zero time domain resonances. They all have their own peculiarities which is why they all SOUND different.

Speaker manufacturers have many of the same challenges getting sound out of their boxes as we do setting up the speakers in our boxes (rooms).
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23rd January 2013
Old 23rd January 2013
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Quote:
Originally Posted by Nonlinear View Post
They sure can!

Speakers are transducers mounted in a box. There is no such thing as a perfectly flat speaker with zero time domain resonances. They all have their own peculiarities which is why they all SOUND different.

Speaker manufacturers have many of the same challenges getting sound out of their boxes as we do setting up the speakers in our boxes (rooms).
Yeah but you will never find (i hope) speaker which have a -45dB null in their frequency response, when measured in freefield / anechoic chamber !
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23rd January 2013
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Quote:
Originally Posted by Cubic Spline View Post
Yeah but you will never find (i hope) speaker which have a -45dB null in their frequency response, when measured in freefield / anechoic chamber !
Yes, you can find it. When tweeter is out of phase with midrange driver, you will get something similar to that at their crossover frequency.
(yes, this loudspeaker must be internally wrongly wired to do that, but this is possible)


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Better control room needs:
-a much smaller desk
-speaker stands
-best possible position for loudspeakers and yourself
-a broader and thicker cloud
-a broader and thicker wall panels
-more super chunks in all corners
-a binary diffuser slats over proposed treatment
-to not expect "sensational" response
-good luck!
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23rd January 2013
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Quote:
Originally Posted by boggy View Post
Yes, you can find it. When tweeter is out of phase with midrange driver, you will get something similar to that at crossover frequency.
(yes, this loudspeaker must be internally wrongly wired to do that, but this is possible)


Yes of course it is "possible", but who sells speakers with wrongly wired drivers ?!
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23rd January 2013
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Quote:
Originally Posted by Cubic Spline View Post
Yes of course it is "possible", but who sells speakers with wrongly wired drivers ?!
I can' resist. Old (as opposed to what, new?) Henny Youngman joke:

I went to the airport and told them I would like to fly to Miami and send my luggage to Chicago. The airline person said "Sorry but we can not do that." I said "Why? You did it last year."

I have had American Airlilnes fly me to Tucson and my luggage to Los Angeles.

Andre
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23rd January 2013
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Quote:
Originally Posted by Nonlinear View Post
They sure can!

.
Sure no speaker is totally flat but when you test your room the major nulls and peaks are the room (or like I said SBIR) unless the speaker is broken. But no speaker will cause ringing.
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24th January 2013
Old 24th January 2013
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Quote:
Originally Posted by Glenn Kuras View Post
But no speaker will cause ringing.
"Waterfall" plots of any speaker I have seen all show some degree of ringing, usually greatest in the low ranges (especially on bass reflex and passive radiator designs).
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24th January 2013
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Decay time is caused from the room. Think of this like reverb.
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24th January 2013
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Quote:
Originally Posted by Glenn Kuras View Post
Decay time is caused from the room. Think of this like reverb.
Bass reflex, transmission line, passive radiator loudspeaker constructions may have pretty long decay time at their "natural" resonant (low) frequency (design dependent), when measured in anechoic chamber, so this one may not be a room issue.
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24th January 2013
Old 24th January 2013
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Quote:
Originally Posted by boggy View Post
Bass reflex, transmission line, passive radiator loudspeaker constructions may have pretty long decay time at their "natural" resonant (low) frequency (design dependent), when measured in anechoic chamber, so this one may not be a room issue.

We are talking about a working room.. I know I know it is fun to just disagree.
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24th January 2013
Old 24th January 2013
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Quote:
Originally Posted by avare View Post
I can' resist. Old (as opposed to what, new?) Henny Youngman joke:

I went to the airport and told them I would like to fly to Miami and send my luggage to Chicago. The airline person said "Sorry but we can not do that." I said "Why? You did it last year."

I have had American Airlilnes fly me to Tucson and my luggage to Los Angeles.

Andre
The perfect quote for this thread and the answers.
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24th January 2013
Old 24th January 2013
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Quote:
Originally Posted by Glenn Kuras View Post
The perfect quote for this thread and the answers.
If you want to believe that speakers are perfect and everything can be fixed with "GIK" treatments - good luck to you!

In the mean time you might want to read this: MONITORS versus HI-FI SPEAKERS

I would try Avare's suggestion unfortunately I am in a noisy area (Los Angeles) and getting a decent reading outdoors is nearly impossible. I guess the next best thing would be to surround the speaker with absorbers and take a measurement (i.e., DIY anechoic chamber).
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24th January 2013
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Quote:
Originally Posted by Nonlinear View Post
If you want to believe that speakers are perfect and everything can be fixed with "GIK" treatments - good luck to you!
Glenn is a gentleman. Your remark is uncalled for.

Quote:
I would try Avare's suggestion unfortunately I am in a noisy area (Los Angeles) and getting a decent reading outdoors is nearly impossible. I guess the next best thing would be to surround the speaker with absorbers and take a measurement (i.e., DIY anechoic chamber).
Do you want to resolve your question or be obstructive? You can use MLSSA based software to get good results up to 10 dB below the ambient noise floor. Some have claimed up to 20 dB below the noise floor.

Andre
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24th January 2013
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Quote:
If you want to believe that speakers are perfect and everything can be fixed with "GIK" treatments - good luck to you!
I never said any of that.. Well I should say that GIK treatment fixes room problems but that was not the question.

Peace
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24th January 2013
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Originally Posted by avare View Post
Glenn is a gentleman. Your remark is uncalled for.

Do you want to resolve your question or be obstructive? You can use MLSSA based software to get good results up to 10 dB below the ambient noise floor. Some have claimed up to 20 dB below the noise floor.

Andre
You don't live in a vacuum - you could (also) go elsewhere to do the test..... the middle (or edge, etc.) of the city is not the only place this test can be performed....

Rod
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24th January 2013
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Originally Posted by Nonlinear View Post
"Waterfall" plots of any speaker I have seen all show some degree of ringing, usually greatest in the low ranges (especially on bass reflex and passive radiator designs).
Correct. Though speakers usually have a single resonance at the port tuning frequency, where a room has many resonant frequencies.

--Ethan

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24th January 2013
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Quote:
Originally Posted by Rod Gervais View Post
You don't live in a vacuum - you could (also) go elsewhere to do the test..... the middle (or edge, etc.) of the city is not the only place this test can be performed....

Rod
+1. The first place that ran through my mind after the OP's post regarding location is Griffith Park. There are a couple of acres of open land there. Plus it is IN Los Angeles.

Andre
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24th January 2013
Old 24th January 2013
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Resonance

Newell shows Watefall plots of many well know monitor speakers in his Recording Studio Design book.
Most are quite broad lumps of decay, many over 100mS long.
I am told Eq can have IR also.
Worth considering the last two sentences in tandem IMO.

DD
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25th January 2013
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Quote:
Originally Posted by Ethan Winer View Post
Correct. Though speakers usually have a single resonance at the port tuning frequency,

--Ethan
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What is the longest decay times you have seen with a 60db range from the port? Interesting and thanks for chiming in.
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25th January 2013
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Lots of interesting discussion. Don't lose track of a few things... Reducing cabinet resonance is a huge part of the picture for designers that aspire to make great monitors. The old school method of rapping your knuckle all around the cabinet exterior is illuminating. Another aspect that is overlooked by many is the crossover network. The common misconception is that the crossover simply sends appropriately EQ'ed bands to the corresponding driver and that all is well and perfect but in truth, there are compromises to be made and some phase anomalies seen in test data are due to cost-cutting in the design of the crossover. Jim Thiel has given excellent presentations on design compromises over the years, as have others.

One of the first assignments given to me by my mentor years ago was to build four seemingly identical cabinets - one from 3/4" MDF, one from 3/4 plywood, one from laminated 3/8" MDF and 3/8" plywood and one from 3/4" thick concrete, all with identical dimensions and internal bracing. The drivers and crossover were then swapped between the cabinets and the testing commenced. The differences were NOT subtle! It's not really surprising that cabinet resonances are significant (and I am not talking about a tuned port or transmission line resonance - I'm talking about unwanted cabinet resonances) when you think that a monitor is a domain transfer device - voltage in, vibration out. The input can easily vary over 5 orders of magnitude with a broad frequency range and broad dynamic range.

And, but, also, consider the physics associated with delivering a music signal to an individual driver like a woofer. Due to aspects such as the mass of the magnet and the interaction of the cone with the internal and external air, etc., the movement of a speaker cone does not exactly mirror the signal that drives it. Speaker driver assemblies have their own set of physical characteristics that modify the composite output and the best designers live in that space between the driver and what the crossover provides to the driver plus the constraints placed on the whole by the cabinet.
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25th January 2013
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Interesting

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25th January 2013
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Quote:
Originally Posted by Glenn Kuras View Post
What is the longest decay times you have seen with a 60db range from the port?
I haven't tested this, but Newell's book Recording Studio Design that Dan mentioned shows waterfalls for 36 different speakers measured in an anechoic chamber. However, many of the resonances are at very low frequencies, and most anechoic chambers are valid down to only 100 Hz, with a few good down to 80 Hz. So if a speaker shows a resonance at 40 or 50 Hz, it's hard to know if it's the speaker or the chamber. This seems evident in those waterfalls, at least for the speakers that play down to 60 Hz or lower.

--Ethan
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25th January 2013
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Quote:
Originally Posted by Ethan Winer View Post
I haven't tested this, but Newell's book Recording Studio Design that Dan mentioned shows waterfalls for 36 different speakers measured in an anechoic chamber. However, many of the resonances are at very low frequencies, and most anechoic chambers are valid down to only 100 Hz, with a few good down to 80 Hz. So if a speaker shows a resonance at 40 or 50 Hz, it's hard to know if it's the speaker or the chamber. This seems evident in those waterfalls, at least for the speakers that play down to 60 Hz or lower.

--Ethan
And from looking at Dan's link (sorry read it pretty fast) it seems around 6 ms.. Yes that is not a typo that I just typed.
I think I am going to have my customers worry about the room ringing (more like 800ms or more) way before.
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25th January 2013
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Originally Posted by avare View Post
I have had American Airlilnes fly me to Tucson and my luggage to Los Angeles.

Andre
I was going to ask what brought you to Arizona, but then realized all you Canadians invade during the Winter. Andre, you'll have to let me know the next time you're in Arizona!

Quote:
Originally Posted by Ethan Winer View Post
I haven't tested this, but Newell's book Recording Studio Design that Dan mentioned shows waterfalls for 36 different speakers measured in an anechoic chamber. However, many of the resonances are at very low frequencies, and most anechoic chambers are valid down to only 100 Hz, with a few good down to 80 Hz. So if a speaker shows a resonance at 40 or 50 Hz, it's hard to know if it's the speaker or the chamber. This seems evident in those waterfalls, at least for the speakers that play down to 60 Hz or lower.

--Ethan
Ethan, I find this intriguing. I've always heard about port resonance and experienced it myself with my Rokits, however, this account confuses me.

How would you get port resonance under 100 Hz from a porthole? These holes are much smaller in surface area than say a Helmholtz resonator tuned to such frequencies. Most portholes are roughly 2"-3" in diameter which would suggest port resonance happens much higher in frequency like a couple hundred Hz or something.

I do hear strong gusts of air coming from ports when monitors play low frequencies like 50, 60 Hz as it needs a lot of air to move the speaker - is this actually what is referred to as port resonance? I don't really see how this can be "resonating" - it stops the second the sound stops.
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25th January 2013
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Quote:
Originally Posted by Glenn Kuras View Post
And from looking at Dan's link (sorry read it pretty fast) it seems around 6 ms.. Yes that is not a typo that I just typed.
I think I am going to have my customers worry about the room ringing (more like 800ms or more) way before.
I've generated data of woofers ringing well beyond that in ported cabinets. And for sure, if you go put an accelerometer on inexpensive PA cabinets, they will ring a while after a short signal burst. Off the top of my head I'd guess that the worst case I've seen on a prototype lightweight cabinet was in the high 200ms range. Part of the problem with cabinet resonance is that it can project in a different frequency range than the incident energy so in a worst case scenario it hangs out in space as a linked background that's not part of the instrument(s) that caused it to happen. And it consists of a combination of reproducible frequency signatures so it adds a homogenized boxey sound.
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26th January 2013
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I guess I have to take you word for it but glad it is a prototype.
Interesting subject.
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