Please explain "house curve" - AVS Forum
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post #1 of 50 Old 08-05-2005, 10:51 AM - Thread Starter
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I've been reading in this forum about using the BFD to fine tune my subwoofer set-up. "House curve" is mentioned a lot, so I did a search on this forum, but no luck -everyone is using this term, but I don't see anyone defining it or explaining how to get a house curve. Anyone care to enlighten me? Much appreciated.
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post #2 of 50 Old 08-05-2005, 11:09 AM
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Well, the "perfect" setup will be absolutely flat.

However, some people prefer a little more oomph down low and purposefully EQ their sub to be a little hot at lower frequencies. The resulting frequency response is referred to as a house curve. Nothing fancy. It would look like the sub has a slight downhill tilt to it from 20 Hz up to the crossover, rather than being flat.

Hope that helps.

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post #3 of 50 Old 08-05-2005, 11:14 AM
 
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Quote:
Originally Posted by RTracey
I've been reading in this forum about using the BFD to fine tune my subwoofer set-up. "House curve" is mentioned a lot, so I did a search on this forum, but no luck -everyone is using this term, but I don't see anyone defining it or explaining how to get a house curve. Anyone care to enlighten me? Much appreciated.
http://www.hometheaterforum.com/htfo...?s=&forumid=46

Search HTF for "house curve" and you'll get many hundred hits.

Basically you EQ your sub to match its frequency response with equal loudness curve (AKA Fletcher-Munson curve). You can do it with BFD by adding a one filter or many small ones. Actually I don't recommend house curve, since often it creates a boomy sound. Maybe a small curve, something like +3-4 dB rise from 80 Hz to 20 Hz is ok, but not more than that.
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post #4 of 50 Old 08-05-2005, 11:17 AM
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Ilkka, isn't that the point of using a C-weighting?

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post #5 of 50 Old 08-05-2005, 11:20 AM
 
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Originally Posted by TrojanHorse
Ilkka, isn't that the point of using a C-weighting?
Yes and house curve too. Actually nobody knows the absolute origin of the house curve, but the phenomenon it tries to correct is the equal loudness curve.

You can use your C-weighted SPL meter to create a house curve. Just EQ it flat, but don't use any correction factors. You'll end up with a nice house curve.
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post #6 of 50 Old 08-05-2005, 11:37 AM
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Shoot... now i'm confused. i took my measurements w/ an RS meter w/ c-weighting selected. So, in essence, by equalizing my response to be flat, I'm actually creating a slight tilt? My ignorance stems from not knowing what c weighting is, I guess.

I haven't actually input my filters yet, but I spent a lot of time w/ the Room EQ program making a nice looking house curve that I was going to try. Was this all for naught?
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post #7 of 50 Old 08-05-2005, 12:07 PM
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A house curve is GREAT for movies but it isn't the best for music in my opinion.

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post #8 of 50 Old 08-05-2005, 12:21 PM
 
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Quote:
Originally Posted by kurt12
Shoot... now i'm confused. i took my measurements w/ an RS meter w/ c-weighting selected. So, in essence, by equalizing my response to be flat, I'm actually creating a slight tilt? My ignorance stems from not knowing what c weighting is, I guess.

I haven't actually input my filters yet, but I spent a lot of time w/ the Room EQ program making a nice looking house curve that I was going to try. Was this all for naught?
You might want to check Google for "C-weighting"? :)

You have to add some correction factors to your readings, since RS meter is C-weighted. If you don't do that, you will get a house curve (or a double house curve in your case).
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post #9 of 50 Old 08-05-2005, 01:09 PM
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Quote:
Originally Posted by UNICRON-WMD
A house curve is GREAT for movies but it isn't the best for music in my opinion.

The "audiophile" group will disagree with you on that one. However, usually they are in the 90% music / 10% HT "audiophile" group.


For HT use, a house curve is great for low frequency sound effects. As long as you do not over do it, a house curve is great for music also!


Some high end processors have a bass boost (loudness) that varies with the master volume. This bass response follows the FM loudness curves, so perhaps the "audiophile" group ASSumes that everyone has that variable loudness function.


You know what they say about people who ASSumes things like that!!!
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post #10 of 50 Old 08-05-2005, 01:29 PM
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From a film sound perspective, a "house curve" is a specific frequency response which has a slope that somewhat attenuates the high frequencies. It originates from a psycho-acoustic phenomenon which makes a flat frequency response sound too bright in a large space like a movie theater.

Our brain knows that we are in a large space with a relatively far-off sound source, and it expects to hear the high-frequency losses that are present due to air absorption. So when that high frequency loss is absent, we overcompensate and hear the sound as too bright.

For all but the hugest home theaters, however, a flat response is the desirable "house curve."

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post #11 of 50 Old 08-05-2005, 01:55 PM
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Quote:
Originally Posted by Terry Montlick

For all but the hugest home theaters, however, a flat response is the desirable "house curve."

Regards,
Terry

I will bite on that one.

How flat is "flat?

You have a baseline SPL level in the room, so plus or minus how many dB is "flat"?

I prefer a DEEP bass boost of about 6dBspl over baseline. So, I guess I could define "flat" as plus or minus 6dBspl and get away with it!!!

By the same token, I could cut DEEP bass by 6dBspl over baseline and still be in that plus or minus 6dBspl "flat" specification.

So, DEEP bass could vary by 12dBspl, and I could say my system response is "flat" using the same specifications!

Just how flat does flat have to be to be called "flat", and does "flat" really have a useful meaning? Obviously, the 12dBspl difference in DEEP bass in the above "flat" response specification will sound different in major ways!!!
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post #12 of 50 Old 08-05-2005, 02:14 PM
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The tolerance limit for "flat" is typically defined as +/- 3 dB, measured over standard 1/3-octave band filters.

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post #13 of 50 Old 08-05-2005, 03:12 PM
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How much of a no-no is it to add boost filters in addition to those that are taming peaks? I know it's not ideal because of the extra demand on the amp, but I'm having a hard time getting a flat curve w/o them.
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post #14 of 50 Old 08-05-2005, 03:22 PM
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I think you can safely add a small boost, but go easy. Better to use a broader reduction filter and just boost the over all volume with the sub amp.

Bottom line, these discussions of house curves are nice, but you also have to consider what sounds good (to you) and if you need a slight boost to the low bass to be happy, dont' worry about what is technically correct.

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post #15 of 50 Old 08-05-2005, 03:44 PM
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So I'm guessing a 9 dB boost at 67.2 Hz would not be considered "taking it easy".
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post #16 of 50 Old 08-05-2005, 04:09 PM
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Quote:
Originally Posted by Terry Montlick
The tolerance limit for "flat" is typically defined as +/- 3 dB, measured over standard 1/3-octave band filters.

- Terry

Heck, that is the tolerance of my speakers.


http://www.nhthifi.com/products/2point9.html


I would never attempt to get my room response that flat.


However, you did use a 1/3 octave measurement scheme. A balance of plus or minus 3dB 1/3 octave to 1/3 octave is much easier to obtain than with a plus or minus 3db tolerance over a 1/12 octave scale.


I will have to check out my system (or is it room) using your definition of "flat".
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post #17 of 50 Old 08-05-2005, 04:17 PM
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Quote:
Originally Posted by TrojanHorse
I think you can safely add a small boost, but go easy. Better to use a broader reduction filter and just boost the over all volume with the sub amp.

Bottom line, these discussions of house curves are nice, but you also have to consider what sounds good (to you) and if you need a slight boost to the low bass to be happy, dont' worry about what is technically correct.


I think that knowing what "flat" is defined as is a good starting point.

Flat as defined by Terry may not be as flat as you think if you look at the sound in finer detail.

I think that Terry's point was, you want the general balance of sound to be flat. 1/3 octave is a pretty broad measurement. Deep bass could be on the high side and still be in spec of plus or minus 3dB 1/3 octave scale.
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post #18 of 50 Old 08-05-2005, 04:30 PM
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I personally think the 1/3 octave is useless if you are trying to EQ your sub whether you use that as a definition of flat or not. 1/3 octave will hide some serious peaks and nulls (we're talking about < 80 Hz here)

I think the program I used has a 0.7 Hz resolution between tones.

I think I see a different definition of what you "need" to do to measure flat on a daily basis too. The meter is weighted, the meter is inaccurate at certain frequencies and you have the Fletcher Munson business. Is flat the unweighted, corrected value, or the weighted, corrected value?

I went with weighted, uncorrected because quite frankly, the peaks are quite obvious anyway.

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post #19 of 50 Old 08-05-2005, 05:03 PM
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Quote:
Originally Posted by J_Palmer_Cass
...
I think that Terry's point was, you want the general balance of sound to be flat. 1/3 octave is a pretty broad measurement. Deep bass could be on the high side and still be in spec of plus or minus 3dB 1/3 octave scale.
Correct. The specification I gave is not my own, but that of the European Broadcasting Union (EBU). It is given in their 1998 technical recommendation 3276. More specifically, it applies to on-axis seating (+/- 10 degrees from the main angle), and the frequency range 40 hz to 16 kHz.

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post #20 of 50 Old 08-05-2005, 05:09 PM
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Quote:
Originally Posted by TrojanHorse
I personally think the 1/3 octave is useless if you are trying to EQ your sub whether you use that as a definition of flat or not. 1/3 octave will hide some serious peaks and nulls (we're talking about < 80 Hz here)

I think the program I used has a 0.7 Hz resolution between tones.

I think I see a different definition of what you "need" to do to measure flat on a daily basis too. The meter is weighted, the meter is inaccurate at certain frequencies and you have the Fletcher Munson business. Is flat the unweighted, corrected value, or the weighted, corrected value?

I went with weighted, uncorrected because quite frankly, the peaks are quite obvious anyway.


Terry is talking about measuring with an RTA or similar equipment with a pretty accurate microphone.

FM is the reason I like to "see" the bass boosted a bit at the low end. I am not sure how "flat" that measures with an 1/3 octave RTA setting.

Terry might be (is) right. Your ears may not be as sensitive as your eyes looking at a chart, so perhaps flat plus or minus 3dB on an 1/3 octave scale is technically correct for the sound to be right. Terry is a pretty bright guy on these issues!
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post #21 of 50 Old 08-05-2005, 05:22 PM
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Quote:
Originally Posted by Terry Montlick
Correct. The specification I gave is not my own, but that of the European Broadcasting Union (EBU). It is given in their 1998 technical recommendation 3276. More specifically, it applies to on-axis seating (+/- 10 degrees from the main angle), and the frequency range 40 hz to 16 kHz.

Regards,
Terry

Excellent.

So balance 40 to 16kHz, use a 1/3 octave scale. Plus or minus 3dB is considered flat.

Funny thing about that is, I have checked a few CD's on my RTA. Most all CD's rolloff at 40Hz at the low end, and roll off at around 15kHz at the high end.

So I guess the intent is to make the sonic balance of the room flat over the majority of the recording range.
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post #22 of 50 Old 08-05-2005, 07:13 PM
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Quote:
Originally Posted by J_Palmer_Cass
Excellent.

So balance 40 to 16kHz, use a 1/3 octave scale. Plus or minus 3dB is considered flat.
...
Yup. And if you are within this range, you are doing pretty well!

There was a 2001 journal paper by engineers at Genelec which studied 164 professional monitoring rooms throughout Europe. This level of "flatness" for the room response (the third-octave smoothed magnitude response, in technical terms) was achieved by more than 50% of the rooms, but only above 130 Hz. This percentage rose to 90% if you only looked at the sound above 400 Hz.

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post #23 of 50 Old 08-05-2005, 07:30 PM - Thread Starter
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Thanks to everyone for responding to my question - very helpful! Looks like a great discussion going on.

Ross
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post #24 of 50 Old 08-07-2005, 04:51 PM
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Quote:
You can use your C-weighted SPL meter to create a house curve. Just EQ it flat, but don't use any correction factors. You'll end up with a nice house curve.
Well, the RS meter doesn’t start with drastic deviations until about 40 Hz. Above that point it’s pretty consistently off only a dB or two. If your house curve doesn’t start until 40, it will indeed sound boomy and inaccurate.
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It originates from a psycho-acoustic phenomenon which makes a flat frequency response sound too bright in a large space like a movie theater.
Actually, that’s 100% backwards. Larger rooms need flatter response than small rooms in order to sound correct. I found this out the first time I RTA’d a large church and right off the bat tried to dial in the same house cure I had at home. It was extremely bass heavy.

The phenomenon is explained in the “Large room equalization†section of most Ashly equalizer manuals: “As sound travels long distances through the air, high frequencies are attenuated more [rapidly] than low frequencies. In general large rooms benefit from some low frequency roll-off [and] high frequency boost...â€
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How much of a no-no is it to add boost filters in addition to those that are taming peaks? I know it's not ideal because of the extra demand on the amp, but I'm having a hard time getting a flat curve w/o them.
That “don’t boost†thing is one of those myths that just won’t die. For EQing subs, boosting or cutting is largely academic.

For instance, let’s say you have a couple of considerable dips in your response, down 10 dB or more at 22 and 63 Hz. If you followed the “cut only†rule, equalizing, your overall gain will down a substantial 10-12 dB or more. Of course, you will have to recover probably that full 10-12 dB to get the output back up to where you had it.

So you have to boost the sub right back up. Thus it would appear that you are now driving your sub as hard as before, right? Nope. The situation now is that you have much flatter response. This means the frequencies that were underrepresented before ( ~22Hz and 63Hz in your case) are now being driven harder than they were before equalizing. That’s right – you’ve succeeded in boosting those low areas, whether you intended to or not.

So – anyway you cut it, subwoofer equalizing places increased demands on the amp and driver. It’s unavoidable, so you just have to make sure you have enough headroom going in. So don’t worry about setting filters for boost if it’s a more efficient way to flatten your response (i.e., using fewer filters).

The only thing to look out for is a true null. Not all under-represented areas in the response curve are nulls. A true null you can’t boost – it won’t respond to equalization. So it’s best not to try to boost a null. No sense “burning†headroom when you don’t get anything in return.

Ross,
Quote:
but I don't see anyone defining it or explaining how to get a house curve. Anyone care to enlighten me? Much appreciated
Basically a house curve is perceived flat response as opposed to measured flat response. As noted earlier in this post, small rooms don’t typically sound good with measured flat response – they generally sound overly bright with anemic bass. Thus a house curve will have response gradually rising as it descends to the lower frequencies.

Dialing in the right curve is the tricky part. Rooms of different sizes need different slopes; smaller rooms need steeper slopes than larger rooms. A bedroom theater set-up compared to one set up in a family room open to other areas in the house is a couple of typical small vs. large home scenarios.

Here’s a method that worked well for me in the place I used to live (haven’t had time to tweak my system yet in our new place). It was very musical (i.e, sounded balanced and accurate) yet gave enough impact for movies to vibrate the sofa. :D Other people have told me they like this method, too. Try it and see if works for you.

What you need do is first get your sub response reasonably flat. Then play a couple of sine wave test tones, one at 100 Hz, the other at 32 Hz. With measured flat response, the 100 Hz tone will sound louder than 32 Hz. Boost the 32 Hz tone until it sounds like it’s the same volume level as the 100 Hz tone. Then as much as possible, EQ for a straight line between the two. I prefer to shelve response below 32 Hz. I tried keeping the slope going below that point, but everything sounded unnaturally boomy.

It’s not a bad idea to take the Fletcher-Munson phenomenon into consideration, in that you want to dial in your house curve at your usual listening volume. If you set it for a higher volume than you normally listen too, then it will probably sound bass-shy when you turn things down. The inverse is true if you house-curve for too low a level.

Good luck!

Regards,
Wayne A. Pflughaupt
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post #25 of 50 Old 08-07-2005, 05:04 PM
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Quote:
Originally Posted by Wayne A. Pflughaupt
Actually, that’s 100% backwards. Larger rooms need flatter response than small rooms in order to sound correct. I found this out the first time I RTA’d a large church and right off the bat tried to dial in the same house cure I had at home. It was extremely bass heavy.

The phenomenon is explained in the “Large room equalization†section of most Ashly equalizer manuals: “As sound travels long distances through the air, high frequencies are attenuated more [rapidly] than low frequencies. In general large rooms benefit from some low frequency roll-off [and] high frequency boost...â€
High-frequency roll-off is a well-established principle in movie sound reproduction. Do some research on the X-curve, Wayne. It is specified in ISO 2969, "Cinematography, B-chain electro-acoustic response of motion-picture control rooms and indoor theatres. Specifications and measurements." It calls for a 3 dB/octave roll-off above 2 kHz. It's implementation is absolutely standard in every commercial movie theater.

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post #26 of 50 Old 08-07-2005, 08:04 PM
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Terry,

I greatly respect your opinions, but I don’t think we’re on the same page here - the thread is about house curve, not X curve. The X curve’s intentional rollout of the higher frequencies is specific to the film industry, primarily for the benefit of speech intelligibility rather than accuracy or high fidelity. No one outside of the film industry has any use for the X-curve; it’s probably the reason why music reproduction sounds so poor in movie theaters. Certainly, no serious home theater buff aspiring to accurate, high fidelity reproduction wants a system that has a 12 dB drop between 2-20 kHz.

That aside, you have to keep in mind that when Ashly talks about “large rooms†they mean large churches, concert halls, sports arenas, etc. – in other words, a venue seating between roughly 4-10,000 people. By comparison...
Quote:
From a film sound perspective, a "house curve" ... originates from a psycho-acoustic phenomenon which makes a flat frequency response sound too bright in a large space like a movie theater.
...film industry professionals may think their little movie theaters that seat a few hundred people are “big rooms,†but they really aren’t, not in the grand scheme of things. However, a theater is small enough that ruler flat response indeed sounds bright, so some compensation is certainly needed. So they got that right, even if they “missed it†on the reason.

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post #27 of 50 Old 08-07-2005, 08:54 PM
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Hi Wayne,

The term "house curve" comes from the film industry, so that is what I'm talking about. The "house" being referred to is the movie house. The X-Curve and "house curve" are one in the same. Perhaps there is another meaning, but I'm not aware of it. It has nothing to do with speech intelligibility -- only perceived "brighness" at high frequencies.

This is from SMPTE 202M-1998, the official US film industry document describing the X-Curve.

Quote:
All published experimenters have found that in a large room, a flat response near-field loudspeaker is subjectively best matched by a distant loudspeaker having a rolled-off high-frequency response in steady-state measurements.
The first of the experimenters being referenced are acousticians C.P. Boner and C.R. Boner, who defined the need for a revised "house curve" for movie theaters back in the 60's. Since then, the perceived high-frequency "brightness" of large room when flat source material is played has become a well excepted fact, culminating in the issuance of ISO 2969 in the mid 1970's. Here, "large room" is defined as one of 150 cubic meters or larger. Since psychoacoustic brightness phenomenon is room size dependent, smaller movie theaters are advised to use a 1.5 dB/octave roll-off, rather than 3 dB/octave of SMPTE 202M-1998 and ISO 2969.

A home theater, because it is a much smaller space, does not require any roll-off -- the same as near-field monitor conditions. Its response should be flat at high frequencies. The X-curve/house curve does not apply to home theaters.

Regards,
Terry

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post #28 of 50 Old 08-07-2005, 09:55 PM
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It is clear that this will only be settled by a gentleman's duel with calibrated microphones at 40 paces...

If you think this post was dumb, you really should read my blog=> http://bumpedhishead.blogspot.com/
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post #29 of 50 Old 08-07-2005, 10:03 PM
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Originally Posted by billybob_jcv
It is clear that this will only be settled by a gentleman's duel with calibrated microphones at 40 paces...
Fortunately, Wayne and I are both gentlemen. I respect him and he respects me. :)

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post #30 of 50 Old 08-08-2005, 08:48 AM
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Quote:
Originally Posted by Wayne A. Pflughaupt
For instance, let’s say you have a couple of considerable dips in your response, down 10 dB or more at 22 and 63 Hz. If you followed the “cut only†rule, equalizing, your overall gain will down a substantial 10-12 dB or more. Of course, you will have to recover probably that full 10-12 dB to get the output back up to where you had it.

So you have to boost the sub right back up. Thus it would appear that you are now driving your sub as hard as before, right? Nope. The situation now is that you have much flatter response. This means the frequencies that were underrepresented before ( ~22Hz and 63Hz in your case) are now being driven harder than they were before equalizing. That’s right – you’ve succeeded in boosting those low areas, whether you intended to or not.

So – anyway you cut it, subwoofer equalizing places increased demands on the amp and driver. It’s unavoidable, so you just have to make sure you have enough headroom going in. So don’t worry about setting filters for boost if it’s a more efficient way to flatten your response (i.e., using fewer filters).


Regards,
Wayne A. Pflughaupt


Well, how many people have the extra 10dB of headroom available from their subwoofer(s) to give them that 10dB boost?

As a general rule, I would say that boosting bass in the manner that you described would be a bad procedure for the AVERAGE home system.
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