How to Choose a Loudspeaker -- What the Science Shows - Page 162 - AVS Forum | Home Theater Discussions And Reviews
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post #4831 of 5313 Old 09-10-2019, 09:37 AM
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Originally Posted by craig john View Post
You're calling things resonances that don't fit the "classical" definition of resonances.
Didn't he say as much a couple days ago?
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Originally Posted by Floyd Toole View Post
So, don't get hung up on semantics. Deviations from a linear frequency response are all describable as "resonances" if one chooses to.
Even put "resonances" in quotes.
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post #4832 of 5313 Old 09-10-2019, 10:21 AM
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Originally Posted by Soulburner View Post
I think these room correction processes are learning much more about the speakers and the room than meets the eye.
Your post is good advice. However, I question the above remark based on what I have experienced.

I have one of the most powerful and expensive multichannel processors on the market, widely praised for its processing power and complicated signal processing. It is enormously flexible, clearly designed by smart people in the math and DSP categories, but equally clearly these people did not understand the acoustics and psychoacoustics of loudspeakers and rooms - my speciality. The result is that, in its self-calibration mode it does things that should not be done.

I won't go into the details of my history with this unit, but it began with a setup procedure, using their proprietary microphone, spatial averaging with weighted mic locations, and allusions to combined IIR and FIR processing promising a very special result.

It was indeed special, because the superb sound of my Revel Salon2s was clearly degraded. Measurements I made with REW disagreed with the unit's displayed result, but agreed with my ears. With help from a product specialist, manual EQ overrides were able to restore the essence of good sound.

Some subsequent fiddles have taken it to the point that I can enjoy programs, but only by overriding or disabling some of the internal processes.

I know that there are other digital equalizers with problems. All originate with clever math/DSP engineers doing things that may make academic sense, but that pay insufficient attention to the peculiarities of human perception. At professional audio gatherings I have had extended discussions/arguments with some of their engineers. It has always come down to opinion, not fact, and the opinions are inclined to enhance the customers' perceived value in the product. It is part of a mighty struggle to be different or distinctive in a product that delivers something that nowadays many people can do for themselves with off-the-shelf DSP, free measurement software and a $100 mic.

None of these processes are supported by published double-blind subjective evaluations. Tell me if I am wrong.

The universal availability of "room EQ" is now a kind of "disease" in audio. People place trust in these devices that is misplaced. As I have stated several times, when the operating manual of the "calibration" device basically states that if the customer does not like the sound from the default target curve, then change the target curve. At this point it becomes a subjectively guided tone-control exercise, not a calibration. The "circle of confusion" for whatever program used during the tweaking is now permanently installed in the system.

All that said, equalization is part of the necessary treatment of room modes in bass. There is no escape from that, but even there, something that should be simple is sometimes compromised. Chapter 8 in the 3rd edition.

Toole, F. E. (2015). “The Measurement and Calibration of Sound Reproducing Systems”, J. Audio Eng. Soc., vol. 63, pp.512-541. This is an open-access paper available to non-members at www.aes.org http://www.aes.org/e-lib/browse.cfm?elib=17839
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post #4833 of 5313 Old 09-10-2019, 10:22 AM
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Originally Posted by sdurani View Post
Didn't he say as much a couple days ago? Even put "resonances" in quotes.
I'm one of the least technical people reading this thread and even I got Dr. Toole's definition of "resonances" as applied to speaker performance from his To Resonate or not to Resonate, That is the Question? post.
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post #4834 of 5313 Old 09-10-2019, 10:43 AM
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Didn't he say as much a couple days ago? Even put "resonances" in quotes.
Indeed, he definitely did. That anybody might have been confused about it afterwards is super weird.

And for the 3rd or 4th time, when a loudspeaker is considered as a system, what does it even mean for it to have a "classical" resonance? What is its "natural resonant frequency"?

A speaker is made up of many mechanical, physical, and electrical components that interact with each other in such complicated ways that we can't even simulate them perfectly with modern computational fluid dynamics software. What does it even mean for such a system to have a natural resonant frequency, the same way a spring does?

If we see a bump in the frequency response plot for a speaker, that seems like as good an indication as any that it has a resonant frequency there, even if we can't point to any one constituent part that has a "classical" resonance at that frequency that we can understand.

It's overly simplistic to think that you might get rid of the resonances of all the components of the system (drivers, port, cabinet, crossover) and thus end up with a neutral speaker, if you're not going to also consider the interactions between all of these components.
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post #4835 of 5313 Old 09-10-2019, 10:43 AM
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Originally Posted by Floyd Toole View Post
It is enormously flexible, clearly designed by smart people in the math and DSP categories, but equally clearly these people did not understand the acoustics and psychoacoustics of loudspeakers and rooms - my speciality.
Indeed, connect multiple subs and each one will be calibrated/equalized as though the others don't exist. How did they miss something so basic about small room acoustics?
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As I have stated several times, when the operating manual of the "calibration" device basically states that if the customer does not like the sound from the default target curve, then change the target curve. At this point it becomes a subjectively guided tone-control exercise, not a calibration.
Sure, but if automated room correction can smooth out the frequency response (fewer/smaller peaks & dips), then I don't mind having to rely on personal preference when it comes to adjusting the target curve (i.e., I won't fault the algorithm for not knowing what I like).

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post #4836 of 5313 Old 09-10-2019, 11:03 AM
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The point is that above a certain cycle point, many of the peaks and dips that can be seen (as measured), are not what we perceive. Sure, using time-gating can help - but at the expense of resolution. It's easier, and a lot more reliable, to simply get a decent loudspeaker and leave it as-is. Or as pointed out, buy a $100 microphone, spend some time learning to use free software and how to get reliable measurements, and do it yourself.

I installed a sound system for a gymnasium recently. They did not have a big budget. We bought inexpensive passive loudspeakers with good directivity traits, bought some inexpensive amplifiers with DSP - spent a couple of hours measuring speakers (making quasi-anechoic measurements in a large empty gymnasium) and making a filter to provide a flat (+/- 1.5dB) listening window. A sub in each of the 4 corners provides an even low across the floor. Everyone is happy with the performance, for less than $2k including 8 speakers, 4 subs, 2 amps and a mixer. The science works.
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post #4837 of 5313 Old 09-10-2019, 11:08 AM
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Originally Posted by Floyd Toole View Post


People place trust in these devices that is misplaced.
Sad but true.

Most folks think they are plug and play when in reality they often do things that muddle the sound; they definitely need some "informed" tweaking and problems often arise from microphone placement but even with "perfect" microphone placement tweaking is still required in my personal experience.

The "tweaking" can have dramatic positive effects as many of us know well.

But I'd venture that most just plug and play.

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post #4838 of 5313 Old 09-10-2019, 11:23 AM
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Originally Posted by TimVG View Post
The point is that above a certain cycle point, many of the peaks and dips that can be seen (as measured), are not what we perceive. Sure, using time-gating can help - but at the expense of resolution. It's easier, and a lot more reliable, to simply get a decent loudspeaker and leave it as-is. Or as pointed out, buy a $100 microphone, spend some time learning to use free software and how to get reliable measurements, and do it yourself.

I installed a sound system for a gymnasium recently. They did not have a big budget. We bought inexpensive passive loudspeakers with good directivity traits, bought some inexpensive amplifiers with DSP - spent a couple of hours measuring speakers (making quasi-anechoic measurements in a large empty gymnasium) and making a filter to provide a flat (+/- 1.5dB) listening window. A sub in each of the 4 corners provides an even low across the floor. Everyone is happy with the performance, for less than $2k including 8 speakers, 4 subs, 2 amps and a mixer. The science works.

Wow, that's a low budget system for that amount of equipment in a gymnasium. With 8 main speakers I assume you have good coverage. I wish more venues would use four subs, one in each corner. Question is, how big is the gym and how loud can the system play? Is the PA for voice only or does it have to play music too?
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post #4839 of 5313 Old 09-10-2019, 11:45 AM
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Wow, that's a low budget system for that amount of equipment in a gymnasium. With 8 main speakers I assume you have good coverage. I wish more venues would use four subs, one in each corner. Question is, how big is the gym and how loud can the system play? Is the PA for voice only or does it have to play music too?
It's 8 satelites with a 6" mid/woofer and a 1" dome on a waveguide crossed at 80Hz to four ported 15" subs. It's mostly for music since it's for modern dance practice. I'll have have to take some dimensions next time I'm there. Here's a newspaper picture while we were installing.



Coverage and subjective SQ is more than decent if you stay about 2m away from walls, which is not a problem for its purpose.
I haven't taken it to any absurd SPL levels, although some testing after calibration revealed ample headroom and most importantly - good sound quality. I'll post the steady-state average tomorrow - no EQ apart from the 'anechoic correction' and 2 or 3 sub filters.
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post #4840 of 5313 Old 09-10-2019, 07:19 PM
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Originally Posted by TimVG View Post
What if that ripple is caused by a reflection between the microphone capsule and the stand? Or the microphone and the seat of a chair? Or between the seat and the back of the chair? Even the supposedly 'advanced' systems such as Dirac require the user to intervene in several ways as it 'corrects' matters that absolutely do not need correcting. Can we still call this a calibration? I'm not against using these systems in a restricted capacity, but if EQ above the transition of the room is implemented, it should be done so based on anechoic or as-close-to-as-possible data.
That is the point, though - those reflections, at least caused by seats and other items in the room, are also going to reach your ears and be audible. I say this as I sit in a high-back leather chair.

Also, we're painting a broad brush here, as all algorithms are different - but the more sophisticated ones have thresholds and do not correct the smallest ripples for the very reasons you and Floyd state. They also take into account not just averages of multiple measurements, but compare what is common and not common between them. This is not to say they are perfect, but there is some level of sophistication at this point in the game.

It is always going to be best to get your placement and room right first to avoid having to attempt to correct these issues by modifying the output, but it's made for those who have imperfect speakers and rooms. And for that, many people hear improvements.

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post #4841 of 5313 Old 09-11-2019, 12:07 AM
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The question is: what will degrade the sound more - correcting a possibly (very) local effect for one listener that may or may not be audible, or adjusting the (hopefully correct) direct sound -the first sound to arrive at anyone's ears-.

There is actually a section about this in Sound Reproduction and multiple references throughout the book.
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post #4842 of 5313 Old 09-11-2019, 02:52 AM
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I'll post the steady-state average tomorrow - no EQ apart from the 'anechoic correction' and 2 or 3 sub filters.
And one filter at around 400Hz for some slight boundary interference caused by on-wall mounting. This is the average of the L/R channels at 9 points across the 'listening area'.

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post #4843 of 5313 Old 09-11-2019, 04:12 AM
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And one filter at around 400Hz for some slight boundary interference caused by on-wall mounting. This is the average of the L/R channels at 9 points across the 'listening area'.

If I had speakers that measured like that, I wouldn't do much even if there is too much of a slope for my tastes.

I would be tempted to nudge the dip at 3K if it was consistent though.

And I'd check the calibration file for the top end.
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post #4844 of 5313 Old 09-11-2019, 06:24 AM
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If I had speakers that measured like that, I wouldn't do much even if there is too much of a slope for my tastes.

I would be tempted to nudge the dip at 3K if it was consistent though.

And I'd check the calibration file for the top end.
This was measured as an average in a very large open space (see above). The slope is the result of neutral loudspeakers measured at a distance in a large room. The 3k dip is normal as it is a dip in the sound power response courtesy of it being a two way, with vertical reflections also taken into account. Correcting it would degrade the direct sound, making the speaker worse.
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post #4845 of 5313 Old 09-11-2019, 07:11 AM
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Indeed. The dip is an issue with most two ways around the crossover, but being 'normal' doesn't make it right.

On the other hand it is probably not an audible problem. Many speakers have such a dip designed into their response because people like it.
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post #4846 of 5313 Old 09-11-2019, 07:23 AM
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Perhaps I wasn’t clear. The dip is not there in the listening window response, or even the horizontal off-axis response. The measurement you see is steady-state, meaning it also captures all sorts of reflections, including vertical ones (hence the dip being normal, unavoidable even in vertically oriented multi-driver loudspeaker). The drop-off after 10Khz: the tweeter becomes highly directional – since this is avery large space, the curve you see should quite closely follow the sound power response. Again normal behavior under these conditions.
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post #4847 of 5313 Old 09-11-2019, 10:24 AM
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Originally Posted by TimVG View Post
Perhaps I wasn’t clear. The dip is not there in the listening window response, or even the horizontal off-axis response. The measurement you see is steady-state, meaning it also captures all sorts of reflections, including vertical ones (hence the dip being normal, unavoidable even in vertically oriented multi-driver loudspeaker). The drop-off after 10Khz: the tweeter becomes highly directional – since this is avery large space, the curve you see should quite closely follow the sound power response. Again normal behavior under these conditions.
I've never set up a system in a large space like a gymnasium so I don't know much about it. Your FR graph looks quite good. Nonetheless, I have some questions:

You have 8 speakers and your measurements are of 2 speakers, correct? What signal is sent to the other 6 speakers? Are you using "stereo" with 4 "Lefts" and 4 "Rights", or some sort of 8-channel, "surround sound" system, or are the same, mono, signals sent to all speakers? If all the speakers get the same signal, why not measure all the speakers at once?

In a large, "echo-y" space like a gym, with all hard reflective surfaces, I would think the time-gated response would be quite different than the un-gated response, no? Was this a gated or un-gated measurement?

What smoothing did you use in the measurement?

How do you "time" the subwoofers relative to the speakers so as to avoid phase errors around the crossovers at different listening positions? Does the response around the speaker/subwoofer crossover look the same at multiple measurement points, or does using 4 displaced subwoofers eliminate that from consideration? Was the same, mono, signal sent to all the subs, or was each sub "timed" independently? I presume you EQ'd the subs as one combined sub, correct?

Sorry for all the questions, but I'm just trying to understand how to set up and optimize a system like this. Clearly, it's different than a small room HT. Thanks.

Craig

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post #4848 of 5313 Old 09-11-2019, 10:40 AM
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Originally Posted by craig john View Post
I've never set up a system in a large space like a gymnasium so I don't know much about it. Your FR graph looks quite good. Nonetheless, I have some questions:

You have 8 speakers and your measurements are of 2 speakers, correct? What signal is sent to the other 6 speakers? Are you using "stereo" with 4 "Lefts" and 4 "Rights", or some sort of 8-channel, "surround sound" system, or are the same, mono, signals sent to all speakers? If all the speakers get the same signal, why not measure all the speakers at once?

In a large, "echo-y" space like a gym, with all hard reflective surfaces, I would think the time-gated response would be quite different than the un-gated response, no? Was this a gated or un-gated measurement?

What smoothing did you use in the measurement?

How do you "time" the subwoofers relative to the speakers so as to avoid phase errors around the crossovers at different listening positions? Does the response around the speaker/subwoofer crossover look the same at multiple measurement points, or does using 4 displaced subwoofers eliminate that from consideration? Was the same, mono, signal sent to all the subs, or was each sub "timed" independently? I presume you EQ'd the subs as one combined sub, correct?

Sorry for all the questions, but I'm just trying to understand how to set up and optimize a system like this. Clearly, it's different than a small room HT. Thanks.

Craig

Hi Craig
1) each position was measured using 4 speakers simultaneously. For 8 speakers this makes 2 measurements per position (L/R). They were later all averaged into this single curve.

2) This is an average of 18 steady-state measurements (2*9) - there is no gating involved - making gated measurements in this capacity seems pointless to me. The listening window was corrected in advance in a series of quasi-anechoic measurements. Using gated measurements can be useful up to a certain point in this respect, as are nearfield measurements. The large, open-space with plenty of room away from boundaries can help though.

3) 1/12 octave smoothing for this steady-state measurement. I used 1/24th when making a correction filter to optimise the listening window response.

4) I didn't - no delay is being applied. I have to be hones, I had no idea what to expect before I was actually in the process of measuring, but the 'one sub per corner' approach seem to work pretty darn well. There are some dips and bumps as one moves across the floor, but I've heard way worse from way more expensive setups. The subs are receiving a mono signal comprised of the L/R summation. The subs were EQ'd as one indeed. Since this room is practically a perfect rectangle - I just followed the Welti papers. It worked out surprisingly well considering the size of the room.
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post #4849 of 5313 Old 09-11-2019, 10:43 AM
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Sad but true.

Most folks think they are plug and play when in reality they often do things that muddle the sound; they definitely need some "informed" tweaking and problems often arise from microphone placement but even with "perfect" microphone placement tweaking is still required in my personal experience.

The "tweaking" can have dramatic positive effects as many of us know well.

But I'd venture that most just plug and play.
Well, if you are not going to plug and play, then why bother with all those solutions at all?
At the point you have enough knowledge to not PnP you more likely than not have enough knowledge to just use a PEQ or a convolution engine and do it all by yourself.
Multiple subwoofer management might be complicated all by yourself though, probably needs some math modeling to get it right, unless you are willing to experiment a lot.

There is a double bass array that seems to not require modeling (it requires a special room though).

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post #4850 of 5313 Old 09-11-2019, 10:56 AM
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Well, if you are not going to plug and play, then why bother with all those solutions at all?
At the point you have enough knowledge to not PnP you more likely than not have enough knowledge to just use a PEQ or a convolution engine and do it all by yourself.
Multiple subwoofer management might be complicated all by yourself though, probably needs some math modeling to get it right, unless you are willing to experiment a lot.

There is a double bass array that seems to not require modeling (it requires a special room though).
I used REW and Umik in my secondary room to dial in dual subs using a MiniDSP as the subwoofer crossover/eq as my 30 year old NAD stereo receiver, obviously, lacked any built in eq.

Used mostly for music in 2.2 and once in a while in quasi 3.2 with the center powered by a separate amp in mono, (hence the "quasi").

Couldn't be bothered to use it in my main 5.1 HT room as my "tweaking" of Audyssey produced satisfactory results.

I'm not OCD enough to double check the measurements in that room using REW and Umik despite having that ability.
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Sad but true.

Most folks think they are plug and play when in reality they often do things that muddle the sound; they definitely need some "informed" tweaking and problems often arise from microphone placement but even with "perfect" microphone placement tweaking is still required in my personal experience.

The "tweaking" can have dramatic positive effects as many of us know well.

But I'd venture that most just plug and play.
I agree Geoff. None of these systems is as simple as "Plug 'n Play." They all require measurements and tweaking to be used optimally. They also benefit from measurement and tweaking BEFORE they are run.
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post #4852 of 5313 Old 09-11-2019, 01:50 PM
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Thanks for the explanations...

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Hi Craig
1) each position was measured using 4 speakers simultaneously. For 8 speakers this makes 2 measurements per position (L/R). They were later all averaged into this single curve.
Is that how the system will be used... as L/R stereo?

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2) This is an average of 18 steady-state measurements (2*9) - there is no gating involved - making gated measurements in this capacity seems pointless to me. The listening window was corrected in advance in a series of quasi-anechoic measurements. Using gated measurements can be useful up to a certain point in this respect, as are nearfield measurements. The large, open-space with plenty of room away from boundaries can help though.
This is surprising to me. I've never set up an audio system in a gymnasium, but I've been in a few. They're all reverberant spaces, which I thought would contaminate the response with reflections. It's amazing that the graph is so flat if it includes all the reflected energy. But, hey, that's why I asked.

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3) 1/12 octave smoothing for this steady-state measurement. I used 1/24th when making a correction filter to optimise the listening window response.
Very nice!

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4) I didn't - no delay is being applied. I have to be hones, I had no idea what to expect before I was actually in the process of measuring, but the 'one sub per corner' approach seem to work pretty darn well. There are some dips and bumps as one moves across the floor, but I've heard way worse from way more expensive setups. The subs are receiving a mono signal comprised of the L/R summation. The subs were EQ'd as one indeed. Since this room is practically a perfect rectangle - I just followed the Welti papers. It worked out surprisingly well considering the size of the room.
Again... very nice! Your results are far better than I would have expected given the environment you're working with.

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"Perfection is not attainable, but if we chase perfection we can catch excellence."

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post #4853 of 5313 Old 09-11-2019, 02:00 PM
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The larger the better for the "uniformity" of the curve.
Really small rooms/apartments are the worst.
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post #4854 of 5313 Old 09-11-2019, 02:05 PM
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Hey @TimVG ,

I'm curious how you set up the 8 main speakers in that room. 4 on each long wall? 2 on each wall? Stereo (L/R) or mono? Got a drawing or photo you could show us?
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post #4855 of 5313 Old 09-11-2019, 02:16 PM
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Quote:
Originally Posted by sdurani View Post
if automated room correction can smooth out the frequency response (fewer/smaller peaks & dips), then I don't mind having to rely on personal preference when it comes to adjusting the target curve (i.e., I won't fault the algorithm for not knowing what I like).
E-r-r-r-r, have we not been saying that the small peaks and dips in room curves are likely to be caused by non-minimum phase phenomena, most likely caused by reflections and cannot be equalized. To two ears and a brain they are innocuous spaciousness, not coloration. It is attempts to "correct" such fluctuations that lead to degradation of well designed loudspeakers. So, above the transition frequency, small details in steady-state room curves should be ignored because unless you have comprehensive anechoic data on the loudspeakers you don't know what caused them.

Setting up a system according to personal preferences in spectral balance includes the circle of confusion and therefore generalization to all programs is not possible. Depending on the shortcomings in your loudspeakers and room results can vary. Better to have easily accessible tone controls that can be instantly adapted to your personal preference - for any program.

I don't have them, and miss them, so I, like you, arrived at a compromise setting that suits some programs better than others. Funny that so many elaborate, expensive, high-end audio products have no easily accessible tone controls. I can only assume that people don't care that much about realistic spectral balance or don't notice when it is absent . . . So much for the high-end "ethic".

I think I'm grumpy today
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post #4856 of 5313 Old 09-11-2019, 02:41 PM
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Originally Posted by TimVG View Post
Everyone is happy with the performance, for less than $2k including 8 speakers, 4 subs, 2 amps and a mixer. The science works.
I know I am! Definitely my kind of system!

Sony XBR65x900e / STR-DN1080 / original PS4 / WOW! Ultra TV / Quantum Access Mini PC Stick w/Windows 10 / 8 x Rockville SPG88 8“ DJ PA Speakers / Dayton Audio SA1000 / Kicker 08S15L74 in a Tapped-Tapered Quarter Wave Tube (negative flare tapped horn).
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post #4857 of 5313 Old 09-11-2019, 03:01 PM
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Originally Posted by Rex Anderson View Post
Hey @TimVG ,

I'm curious how you set up the 8 main speakers in that room. 4 on each long wall? 2 on each wall? Stereo (L/R) or mono? Got a drawing or photo you could show us?
2 on each wall / stereo. If you were to face one wall, the four speakers to your left would be L and the four to the right R. As said this will be mainly used for modern dance practice.

edit: I tried to make a little layout in text, but it doesn't seem to show as it should here

I could have gone mono, but opted for stereo for the satelites. To be completely honest. I have no background in audio apart from a healthy interest.
This project came into my hands because there was little money left for sound, and I said I would be able to get good sound in that room for the available budget if they let me handle it. Honestly, it came out as good as I could have hoped for. I just followed the guidelines as portrayed in Sound Reproduction.

Most of the discussions about the subject here are what I consider nitpicking. But the fact is that simply 'following the book' plus learning how to get decent measurements out of a loudspeaker, and understanding what can be corrected, provided a very nice result.
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post #4858 of 5313 Old 09-11-2019, 03:10 PM
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Thanks for the explanations...


Is that how the system will be used... as L/R stereo?


This is surprising to me. I've never set up an audio system in a gymnasium, but I've been in a few. They're all reverberant spaces, which I thought would contaminate the response with reflections. It's amazing that the graph is so flat if it includes all the reflected energy. But, hey, that's why I asked.

.

-Yes, if you face the main (mirrored!) wall from the center, everything to your left would be L and everything to your right R. I guess I could have gone mono.. But I opted for stereo.

-Well I deliberately chose a model loudspeaker with good directivity. It's the one thing I wouldn't be able to fix with (quasi-anechoic) EQ so that needed to be right. The fact that the steady-state curve is smooth, without any post-installation EQ (apart from one 400Hz dip caused by wall mounting) shows that everything, including what is reflected, is well-behaved.
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post #4859 of 5313 Old 09-11-2019, 03:15 PM
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Originally Posted by Floyd Toole View Post
I think I'm grumpy today
If it's any comfort, your book (and posts) helped me provide good, instead of likely terrible sound, for our school gymnasium on a limited budget. It's no home theater, but the science seems to apply well in other spaces too.
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post #4860 of 5313 Old 09-11-2019, 04:11 PM
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Quote:
Originally Posted by TimVG View Post
If it's any comfort, your book (and posts) helped me provide good, instead of likely terrible sound, for our school gymnasium on a limited budget. It's no home theater, but the science seems to apply well in other spaces too.
I personally find it a bit comical that anyone is questioning that setup, it appears to measure better than most of our "Hifi" setups. I think for the cost and size of the room you've done a superb job and I'm sure no one is going to complain about that sound during gym class...
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