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post #1 of 57 Old 01-29-2007, 11:34 AM - Thread Starter
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I just spent the last couple of days dialing in my Velodyne DD-15 sub with auto EQ with the rest of my system. My room is a dedicated Home Theater with a Paradigm 7.1 setup. I did treat the room walls up to ear level with Linacoustic on the side and back walls and the entire front (screen) wall). After the EQing the DD-15 I have noticed a definite improvement in the sound--especially the bass. Simple things like a car door slamming, etc that would have went un-noticed before, now have sharp and crisp sounding bass. Here is my room's response as graphed by the DD-15.




I had always planned on adding bass traps. However, this looks relatively flat. Does anyone think that adding bass traps to my room would result in better results that would be noticeable?? Is it possible that the design of my room doesn't call for bass traps?? Thanks - Andrew

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post #2 of 57 Old 01-29-2007, 02:22 PM
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Andrew,

> Is it possible that the design of my room doesn't call for bass traps?? <<br />
No.

Seriously, all rooms benefit from bass trapping. Generally, the more trapping the better. Understand that raw low frequency response is only half the story. Just as important is reducing modal ringing (excessing decay times) which is hidden in simple response graphs like the one you show.

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post #3 of 57 Old 01-29-2007, 02:58 PM
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Ethan is spot on.. The ringing in the room is going to give a "one note" bass sound. With bass traps you will get a clearity on the bass that sounds punchy and well defined.

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post #4 of 57 Old 01-29-2007, 09:07 PM
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And you won't know what is being added by the room in terms of ringing and boominess until you have the bass traps to get rid of it.


Also, your graph could still use a little smoothing. Plus, the deep extension doesn't seem to be getting very much boost. Do you have the sub in or near a corner? I would expect a DD-15 to have a lot of slam down low...
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post #5 of 57 Old 01-30-2007, 07:01 PM - Thread Starter
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Thanks for the responses.

I have a false screen wall (GOM in front of the speakers) about 6 feet from the true back wall. The sub is in the front corner of the theater, but one of the walls is a false wall...so it is really about 6 feet up on the side wall. I did try and place the DD-15 in the true front corner (behind the screen wall) but it shook the screen too much

What would deeper exetnsion down low look like on my response? Higher dbs?

Since I do have a false wall with about 3 feet on space in the middle and 6 feet on the sides, I definitely can easily place bass traps behind the screen wall. However, corner bass traps would be only a few feet from my L and R speakers. Is this enough room?
L&R Speakers are Paradigm Studio 100's V3 and they do port out the the back.

Is it worth placing bass traps directly behind the screen itself (it is not perforated) on the floor? I didn't know if the screen would hinder the performance of the bass traps. I was thinking on the floor behind the screen if it was going to help.

edit...here's a picture of the theater layout:


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post #6 of 57 Old 01-31-2007, 04:28 AM
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>Since I do have a false wall with about 3 feet on space in the middle and 6 feet on the sides, I definitely can easily place bass traps behind the screen wall. However, corner bass traps would be only a few feet from my L and R speakers. Is this enough room?<<br />
That should be fine. Just make sure the trap is not touching it.

>Is it worth placing bass traps directly behind the screen itself (it is not perforated) on the floor? I didn't know if the screen would hinder the performance of the bass traps. I was thinking on the floor behind the screen if it was going to help.<<br />
You can put some there, but it is always better to put bass traps in the corners.

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post #7 of 57 Old 01-31-2007, 04:53 AM - Thread Starter
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Glen,

What about the extra two corners that are located where the room extends out behind the screen (fireplace above). Would these be considered true corners as well?

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post #8 of 57 Old 01-31-2007, 08:52 AM
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Quote:
Originally Posted by barhoram View Post

I just spent the last couple of days dialing in my Velodyne DD-15 sub with auto EQ with the rest of my system. My room is a dedicated Home Theater with a Paradigm 7.1 setup. I did treat the room walls up to ear level with Linacoustic on the side and back walls and the entire front (screen) wall). After the EQing the DD-15 I have noticed a definite improvement in the sound--especially the bass. Simple things like a car door slamming, etc that would have went un-noticed before, now have sharp and crisp sounding bass. Here is my room's response as graphed by the DD-15.




I had always planned on adding bass traps. However, this looks relatively flat. Does anyone think that adding bass traps to my room would result in better results that would be noticeable?? Is it possible that the design of my room doesn't call for bass traps?? Thanks - Andrew

the auto-EQ of the SMS-1 is not sufficient to get a flat FR, all it does is adjust gain of the original filters. you should be using the manual EQ and properly set FR, gain , and Q.
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post #9 of 57 Old 02-01-2007, 05:16 AM
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Quote:
Originally Posted by barhoram View Post

Glen,

What about the extra two corners that are located where the room extends out behind the screen (fireplace above). Would these be considered true corners as well?

On my first post I did not notice the fireplace behind the screen. Yes that would be a great place for bass trapping also. In fact I would stuff the hole fireplace with fluffy fiberglass.

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post #10 of 57 Old 02-01-2007, 05:33 AM - Thread Starter
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Plincoln,
Thanks for the reply. Do you know anywhere online that outlines how to use the manual EQ to adjust those parameters. The user's manual doesn't go into too much detail in those areas.

Glenn,
I have several left over bags of Roxul Safe N' Sound (mineral wool) from building the theater. Would I be ok stacking them in their plastic bags in the fireplace cutout?? Or would I need to open them up? Should I leave any space on the sides or back of the mineral wool?

For the corners, would one of your standard traps placed at an angle be as effective as the corner model? Since it will be behind a false wall, the looks of a angled trap won't matter. Or do the corner models perform that much better?

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post #11 of 57 Old 02-01-2007, 06:17 AM
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Quote:
Originally Posted by barhoram View Post

Plincoln,
Thanks for the reply. Do you know anywhere online that outlines how to use the manual EQ to adjust those parameters. The user's manual doesn't go into too much detail in those areas.

http://pdf.outlawaudio.com/outlaw/docs/sms1guide.pdf

That's a great guide to read through...starting on page 16 is what you are after, but I would go ahead and just start at the beginning...some of it will be old news for you, but it can't hurt.
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post #12 of 57 Old 02-01-2007, 09:12 AM
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Quote:
Originally Posted by barhoram View Post

I had always planned on adding bass traps. However, this looks relatively flat. Does anyone think that adding bass traps to my room would result in better results that would be noticeable?? Is it possible that the design of my room doesn't call for bass traps?? Thanks - Andrew

Bass traps are not very effective in the subwoofer range. EQ is your best bet at these very low frequencies. The bass trap sellers will of course tell you otherwise. After EQ to balance the levels, ringing (even 2 seconds duration) is not perceptible below 100 Hz. See Karjalainen et al., "Perception of temporal decay of low-frequency room modes," AES 116th Convention, 2004.

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post #13 of 57 Old 02-01-2007, 07:51 PM
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Originally Posted by Terry Montlick View Post

Bass traps are not very effective in the subwoofer range. EQ is your best bet at these very low frequencies. The bass trap sellers will of course tell you otherwise. After EQ to balance the levels, ringing (even 2 seconds duration) is not perceptible below 100 Hz. See Karjalainen et al., "Perception of temporal decay of low-frequency room modes," AES 116th Convention, 2004.

- Terry

Interesting.... Do you think something like the GIK 244 sound panel is worth it for frequencies above 100hz? Or is the equalizer the best thing here too?
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post #14 of 57 Old 02-02-2007, 06:21 AM
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Interesting.... Do you think something like the GIK 244 sound panel is worth it for frequencies above 100hz? Or is the equalizer the best thing here too?

Conventional porous bass traps, of the type sold by Glenn and Ethan, can be quite effective above 100 Hz when their area is a good fraction of the room surface. At subwoofer frequencies (below 80 Hz), do not expect much. The laws of physics are against you.

Equalization above 100 Hz is not very effective in dealing with individual room modes. There are simply too many of them, and our modal decay time discrimination is more sensitive at these higher frequencies. Acoustic treatment is the way to go for these frequencies.

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post #15 of 57 Old 02-03-2007, 10:40 AM
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Terry,

> The bass trap sellers will of course tell you otherwise. <<br />
Not me, and I've stated many times that I use the one-band cut-only EQ on my big SVS subwoofer to tame the most prominent length mode in my room around 40 Hz. And I know you agree that EQ is not useful for bass nulls, and those are at least as big a problem as bass peaks and modal ringing.

But to say that porous traps are not effective below 100 Hz isn't accurate either. The demo video on my company's site show eight bass traps making a real improvement all the way down to the 40 Hz lower limit we tested. You are correct that most of the improvement is in the mid bass range and up, but there can still be a big improvement down to fairly low frequencies.

Just to be clear on what's possible with "porous" bass traps, the ETF waterfall plot below shows the response and ringing in my living room using only that type of trap. Okay, I have a lot of traps. But there's still less total surface coverage than in many pro-designed rooms. And you can see the response is very uniform, with little ringing, at all but the very lowest frequencies.

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post #16 of 57 Old 02-03-2007, 11:10 AM
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Originally Posted by Ethan Winer View Post

But to say that porous traps are not effective below 100 Hz isn't accurate either.

I did not say that. I said, "Bass traps are not very effective in the subwoofer range," and "At subwoofer frequencies (below 80 Hz), do not expect much."

As for ringing below 100 Hz, even if bass traps could substantially effect it, this is not a perception issue to begin with (see above cited paper).

You don't really want to bring up the subject of bass trap subwoofer frequency effectiveness, do you? In the tests we did together, just bass traps (even filling the room to the rafters with them) failed miserably in flattening the uneven subwoofer frequency response. This was the conclusion of the simplest possible objective flatness test -- a standard deviation calculation. This analysis is freely available to anyone on the Realtraps web site.

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post #17 of 57 Old 02-03-2007, 11:51 AM
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Originally Posted by barhoram View Post

I have several left over bags of Roxul Safe N' Sound (mineral wool) from building the theater. Would I be ok stacking them in their plastic bags in the fireplace cutout?? Or would I need to open them up? Should I leave any space on the sides or back of the mineral wool?

I'd put as many of those leftover bags as you could behind your false wall. If need be get more bags. Fill it, the more the better. You can leave them wrapped in plastic, bass doesn't care about a thin layer of plastic - it will go right through.

Everything I say here is my opinion. It is not my employers opinion, it is not my wife's opinion, it is not my neighbors opinion, it is My Opinion.
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post #18 of 57 Old 02-05-2007, 01:41 PM
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Terry,

> I did not say that. I said, "Bass traps are not very effective in the subwoofer range," and "At subwoofer frequencies (below 80 Hz), do not expect much." <<br />
Which is exactly why I posted the response and ringing for my living room. You can clearly see that all the way down to ~45 Hz the response and ringing are quite exceptional.

> As for ringing below 100 Hz, even if bass traps could substantially effect it, this is not a perception issue to begin with (see above cited paper). <<br />
I disagree with that research based on my own experience. Let me guess, the tests were not done in a domestic size room, yes? Just like the "research" that says it's okay for a room to have a long reverb time at low frequencies.

Of course I'm not dissing research, but a lot of research in the past did not consider that small rooms behave very differently from large rooms. Also, just because something appeared in the AES Journal does not make it so.

> You don't really want to bring up the subject of bass trap subwoofer frequency effectiveness, do you? <<br />
Sure I do!

> In the tests we did together, just bass traps (even filling the room to the rafters with them) failed miserably in flattening the uneven subwoofer frequency response. <<br />
Or put another way, In the tests we did together, just EQ (even using all 12 bands) failed miserably in flattening the uneven subwoofer frequency response.

So now where does that leave us?

Seriously, as we both know, it's impossible to make any room perfectly flat with no excess ringing. It's not even possible to get close to flat. So we do the best we can, using all of the tools at our disposal, and hopefully eventually can ignore all the tech nonsense and start enjoying the music.

I'll still take my room with 40 traps over any other room in a house I've ever heard.

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post #19 of 57 Old 02-05-2007, 02:15 PM
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Quote:
Originally Posted by Ethan Winer View Post

Terry,

> I did not say that. I said, "Bass traps are not very effective in the subwoofer range," and "At subwoofer frequencies (below 80 Hz), do not expect much." <

Which is exactly why I posted the response and ringing for my living room. You can clearly see that all the way down to ~45 Hz the response and ringing are quite exceptional.

Actually, the frequency response of this room is not very good at all. More than 12 dB range from 20-200 Hz? I wouldn't be showing that graph around very much if I were you.

Quote:


> As for ringing below 100 Hz, even if bass traps could substantially effect it, this is not a perception issue to begin with (see above cited paper). <

I disagree with that research based on my own experience. Let me guess, the tests were not done in a domestic size room, yes?

Wrong as usual, Ethan.

Your lip service to the scientific method, and yet your disdain for the science of acoustics and ignorance of the acoustic literature would be entertaining if it wasn't so sad.

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post #20 of 57 Old 02-06-2007, 12:06 PM
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Terry,

There's no need for that sort of tone. I don't insult you, and I see no reason for you to insult me.

> Actually, the frequency response of this room is not very good at all. More than 12 dB range from 20-200 Hz? I wouldn't be showing that graph around very much if I were you. <<br />
That's preposterous and I'm sure you know it. Some months ago you and another regular here tried to dismiss my claim that with bass trapping you can never have too much. At that time I asked you both at least three or four times to show me some hi-res waterfall graphs for rooms you've done. You never did. So I'll ask you now, yet again, to please show me results of rooms you've been hired to improve.

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post #21 of 57 Old 02-06-2007, 12:33 PM
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Originally Posted by Ethan Winer View Post

Terry,

There's no need for that sort of tone. I don't insult you, and I see no reason for you to insult me.

Sorry, but that was not an insult. It was a sad statement of fact. As far as I can tell, you are not at all versed in the professional literature, even that on bass absorption. I once tried to explain the key results of Mechel's important 1988 paper to you, but was unsuccessful.

Quote:


> Actually, the frequency response of this room is not very good at all. More than 12 dB range from 20-200 Hz? I wouldn't be showing that graph around very much if I were you. <

That's preposterous and I'm sure you know it.

If you knew how to read a waterfall graph, you would see this uneven frequency response quite clearly.

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post #22 of 57 Old 02-06-2007, 01:47 PM
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Quit it guys...

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post #23 of 57 Old 02-06-2007, 02:43 PM
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Quote:
Originally Posted by Terry Montlick View Post

Actually, the frequency response of this room is not very good at all. More than 12 dB range from 20-200 Hz? I wouldn't be showing that graph around very much if I were you.

- Terry

To me that doesn't look bad at all. I wish my living room measured that well.

I have a few questions:
Ethan, why do you think you have that broad peak around 160hz. Without that you'd be +- 10db (which I think is pretty darn good).

Ethan, what happens above 200hz? Is that the bottom of your hole? My room has a frustrating dip in the same general area. I probably need more bass traps, more positional tweaks, more time, more money, more sex, more something.

Terry,
Specifically what don't you like about Ethan's waterfall. There is some weird stuff going on below 80hz, but I don't think it is too bad. In fact, I don't think I've seen anything better (except in a specially built room with TACT room correction on all channels). What do you think is wrong with his setup. What would you do to make it better (using lower resolution measurements doesn't count)?

Terry, I assume you provide your customers with before and after treatment plots. Do the after treatment plots typically look better than Ethan's? If so I better start saving up, I'd like you to come over and visit ;-)

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post #24 of 57 Old 02-06-2007, 04:13 PM
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Originally Posted by dknightd View Post

Terry, I assume you provide your customers with before and after treatment plots. Do the after treatment plots typically look better than Ethan's? If so I better start saving up, I'd like you to come over and visit ;-)

OK, start saving now.

Here's a waterfall plot (same 200 ms window size, ~30 dB amplitude range, and 20-200 Hz frequency range as Ethan's) of a typical theater we did:



Notice the flatness of the frequency response (the uniformity of the horizontal "mountain peaks" at t=0). We would have hammered down that resonance at around 20 Hz via EQ, but it gave the room a little extra visceral "oomph"!

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post #25 of 57 Old 02-06-2007, 06:06 PM
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Terry, looks nice !

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post #26 of 57 Old 02-07-2007, 10:58 AM
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Looks better - largely because of the scale used. It's down to about 6db (which is very good) if you ignore the 20Hz - but...

while I agree that EQ can help with ringing:
-IF you get the center exactly correct
-IF you get the Q exactly correct
-IF you're only worried about one seat

Taking the same measurements in a different seat in that room without changing the EQ would have the ringing right back again - as happened during your and Ethan's experiment and the center frequency wasn't spot on. The FR would also vary I strongly suspect.

As to whether or not subwoofer range ringing is detrimental, I don't know that a single paper that you cited is enough to get me to ignore 2 second decay times fom 80Hz down.

I'll agree that for frequency abberations that are consistent across seats and peaks in nature, EQ is the way to go - after you've done what you can with treatment.

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post #27 of 57 Old 02-07-2007, 11:36 AM
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Quote:
Originally Posted by dknightd View Post

Ethan, why do you think you have that broad peak around 160hz. Without that you'd be +- 10db (which I think is pretty darn good).

Actually, the span is 10 dB - each division is 3 dB.

The response at any given location in the room is the sum of the direct sound from the loudspeakers plus many competing reflections from the floor, ceiling, and all the walls. If you move the microphone even one inch the response changes dramatically. Even at very low frequencies, and especially if there are no bass traps.

In a room the size of my living room - 25 by 16 by 11 feet high at the center peak - this is as good as it gets. Well, okay, I could put in another 40 traps and make it even better. But as it is now this room sounds fabulous. Better than a lot of very expensive professional studio control rooms the same size.

> what happens above 200hz? Is that the bottom of your hole? My room has a frustrating dip in the same general area. I probably need more bass traps, more positional tweaks, more time, more money, more sex, more something. <<br />
Again, what "happens" above 200 Hz depends on where I measure. Most of the bass problems in most rooms are at the lowest three or four octaves.

> Specifically what don't you like about Ethan's waterfall. <<br />
It's not my waterfall plots, it's me personally. Though I have no idea why he takes that attitude! Especially the personal insults. You should ask Terry the size of the room in his graph, where the measuring microphone was placed, if he used any EQ, and how many bands of EQ.

--Ethan

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post #28 of 57 Old 02-07-2007, 11:40 AM
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Hi Bryan,

Found another measurement where we had leveled off that LF peak:



I have scale this more tightly to the 30 dB range to be directly comparable to Ethan's graph.

Actually, there was no EQ above 80 Hz. It was just used for the subwoofers. And because of the long wavelengths of the subwoofer EQ, it was quite robust with respect to listening position.

Above 80 Hz, you are seeing the result of a whole lot of acoustic treatment!

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post #29 of 57 Old 02-07-2007, 11:52 AM
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Bryan,

> Looks better - largely because of the scale used. <<br />
Yes that, and there's no time span or anything else on the graph.

> while I agree that EQ can help with ringing:
> -IF you get the center exactly correct
> -IF you get the Q exactly correct
> -IF you're only worried about one seat

I'm working now on a brief article that will put this to bed for once and for all. Empirical evidence trumps theory every time, and I now have bullet-proof empirical evidence.

> As to whether or not subwoofer range ringing is detrimental, I don't know that a single paper that you cited is enough to get me to ignore 2 second decay times fom 80Hz down. <<br />
Of course I agree. There's research and then there's research. I've seen a few howlers in the AES journal over the years. Even if the research Terry cited is valid for one room, how well does it apply to my room and to your room?

One huge thing missing from a lot of the "expert" opinions I see are they rely too much on reading stuff someone else wrote, and not enough on first hand practical experience. I've been playing with pro studio gear for 40 years now. I know exactly what 1 second of reverb added to a bass track sounds like, and it's not a pretty story. I also know what a 12 dB boost with a Q of 0.9 sounds like. And so forth. I have all of these tools available in front of me as I write this. So I can test almost anything in 10 seconds on my very accurate home studio system.

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post #30 of 57 Old 02-07-2007, 12:04 PM
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Terry,

> Above 80 Hz, you are seeing the result of a whole lot of acoustic treatment! <<br />
Obviously! I'm glad to have had such a large influence on you!

So please tell us more about this room. How big, how much treatment, where the treatment is placed, how thick it is, and so forth.

--Ethan

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