# At reference, what should a subs response curve look like?

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At reference, what should a subs response curve look like?

Just trying to calculate or see if I am hitting the DB required.

On REW at 0db, I hit 85db running the sub cal frequency outside of right or left speaker which I know isi 10db hot.
I am flat 10hz to 80 pretty much.

But what db should each frequency be hitting? Where should I be hitting at say 20hz if I'm at reference on a response curve if I'm running flat 0db? Should it be 75?
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At reference, what should a subs response curve look like?

Just trying to calculate or see if I am hitting the DB required.

On REW at 0db, I hit 85db running the sub cal frequency outside of right or left speaker which I know isi 10db hot.
I am flat 10hz to 80 pretty much.

But what db should each frequency be hitting? Where should I be hitting at say 20hz if I'm at reference on a response curve if I'm running flat 0db? Should it be 75?

Hi,

You have actually asked a couple of different questions mixed together. The first question is: What are Reference volumes? And, the second question is: What is the lowest frequency where I want to be able to hit Reference volumes?

The first question is relatively simple. Dolby/THX Reference for 5.1 movie content is a nominal average volume of 85dB for the regular channels, with peak volumes of up to 105dB for the regular channels, and peak volumes of 115dB for the LFE (low-frequency effects) channel. The LFE channel is intended to be played by subwoofer. It is recorded +10dB louder than the regular channels, which are played by both the regular speakers and the subwoofers, with crossovers determining where the subs take over from the speakers.

People sometimes get confused by the test tones that our AVR's use when they calibrate our HT systems to Reference. The test tones are only 75dB, instead of the 85dB that we might expect them to be, because people found 85dB test tones too loud. So, the test tones were reduced to 75dB. But, our AVR's are programmed to automatically add another +10dB to those 75dB levels, so that at 0.0 MV (master volume) our regular channels will play 85dB with the potential peaks mentioned above. (They are only potential peaks because not every movie will have volume peaks that loud.)

Just because an HT system is calibrated to Reference though, doesn't mean that our speakers and subwoofers can actually play those volume levels, especially without distortion. That depends on the inherent capability of our transducers and their distance from our MLP (main listening position). Calibrating our systems to Reference simply gives us all a common starting point. (As a side note, 0.0 MV on a calibrated system is quite loud for most of us.)

As for the second question: whether your subwoofer(s) should be able to hit maximum volume levels of 115dB (peak LFE volumes) at 20Hz, that is a question which depends entirely on your own listening preferences and the inherent capabilities of your subwoofer(s). If you want to understand some of this better, both Dolby/THX Reference and what occurs during an Audyssey calibration, are explained in a great deal more detail in Section II of the Guide linked in my signature.

Regards,
Mike
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At reference, what should a subs response curve look like? ... what db should each frequency be hitting? Where should I be hitting at say 20hz if I'm at reference on a response curve if I'm running flat 0db? ...
AFAIK, a flat FR curve has a variance of +/-3dB - or 6dB down (-6dB) from peak (+0dB).

If you've got:
• a good sub with in-room extension to the mid-teens (or lower), at 20Hz your level of output should fall within that +/-3dB (or +0/-6dB) variance;
• a sub that struggles to get below 30Hz, at 20Hz your level of output will fall well outside of the variance.
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AFAIK, a flat FR curve has a variance of +/-3dB - or 6dB down (-6dB) from peak (+0dB).

If you've got:
• a good sub with in-room extension to the mid-teens (or lower), at 20Hz your level of output should fall within that +/-3dB (or +0/-6dB) variance;
• a sub that struggles to get below 30Hz, at 20Hz your level of output will fall well outside of the variance.
I will add that a published FR for a sub is generally performed at well below reference volume so a sub that may fall in that flat range on paper may not be able to achieve a flat response at reference volume or even be able to reach reference volume at any frequency.

Generally for subs, that 115 db peak standard applies to any frequency you wish to reach reference volume at. Therefore, if you want reference at 20 hz, you need to be able to produce 115 db peak at the listening positions. For 10 hz, if you want reference volume, you need to still reach 115 db peak. For a vast majority of people, trying to achieve reference at these ultra low frequencies is not really possible without a lot of really big subwoofers so its a matter do you want to pursue it or not, especially given cost and space requirements.

Sometimes, its a matter of saying "I can achieve reference from 30 hz on up and I still have sufficient output at 20 hz and below to still be usable even if not quite reference, and that's good enough." For others, they want to get reference as low as possible. This thread actually spends a lot of time detailing the pursuit of reference ULF to 10 hz for many posters. You may find it informative. Unfortunately, now a bit dated relative to how many new subs have come out in the interim.

Everyone's cut off in the pursuit of bass is different. There is no set standard that specifies what the cut-off low frequency is to achieve "reference" per se, although THX does in fact state certain minimum spl at frequencies for subs to receive their certification. They won't publically reveal what that is to my knowledge. I am certain they spec down to 20 hz, but probably not below that. If they do go any lower, I am pretty sure they don't address anything lower than about 16 hz based on the subs that have received the certification.
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Room acoustics can limit your output , some rooms are terrible and low bass causes everything to rattle , . I have no way to adjust the curve and no dsp.
Essentially relying on audysee.
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AFAIK, a flat FR curve has a variance of +/-3dB - or 6dB down (-6dB) from peak (+0dB).

If you've got:
• a good sub with in-room extension to the mid-teens (or lower), at 20Hz your level of output should fall within that +/-3dB (or +0/-6dB) variance;
• a sub that struggles to get below 30Hz, at 20Hz your level of output will fall well outside of the variance.
I meant what DB should it hit on a sweep.

e.g. thats mine at reference.
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Basically, at reference, what should an REW sweep look like.
Well, to know that you would need to know what "reference" was. Do you google? Have you ever googled? Can I interest you in a years subscription to google? If you get 1 year, Ill match it with another year for free!

I meant what DB should it hit on a sweep.

View attachment 3141686

e.g. thats mine at reference.
Basically, at reference, what should an REW sweep look like.

You actually don't even have to use Google, since I answered your question about what Reference is in Post #2. 85dB is a nominal average volume for 5.1 movies, but depending on the movie, peaks can reach 115dB for the LFE channel. If you want to hit "Reference" at 20Hz, that means that you would be able to measure 115dB for that frequency at your MLP.

Regards,
Mike

Edit: Please read Post # 2. There is no difference between Dolby/THX Reference for cinema and for HT. "Reference" is a nominal average SPL of 85dB when a calibrated AVR is playing 0.0 master volume. As stated earlier, 85dB test tones are too loud for most people, so the AVR uses 75dB test tones during calibration and then automatically adds +10dB afterwards, so that at a master volume of 0.0, the AVR will play 85dB. Peaks for the regular channels can be 105dB at that volume, and peaks for the LFE channel can be 115dB. You need to start by understanding that part!

(If this keeps up, I'll accept the nomination! )
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You actually don't even have to use Google, since I answered your question about what Reference is in Post #2. 85dB is a nominal average volume for 5.1 movies, but depending on the movie, peaks can reach 115dB for the LFE channel. If you want to hit "Reference" at 20Hz, that means that you would be able to measure 115dB for that frequency at your MLP.

Regards,
Mike

So is an REW sweep comparable to a peak measurement at a given frequency?

I can RTA and see I hit 115db peaks when watching a film but it doesn't answer my question re: what should an REW sweep curve look like at reference re: LFE channel.

I'm not asking what reference is. Reference is 85db in a cinema, and 75db in a home cinema as per nominal standards adopted my AVR manufacturers. I'm also not asking about peaks in a film; I know this already and I'm also aware some films go insane with peaks (aka Dark Knight) and push the boundaries further.

For an REW sweep at reference volume (for a home cinema, aka 75db, the most common reference point used on this forum), what should the REW sweep look like? Should it be hitting 115db at every frequency at 75db (calibrated matched speaker volume)?
A sweep is not "reference" unless done at "reference" and even then it wont show the PEAKS.

"Should it be hitting 115db at every frequency at 75db (calibrated matched speaker volume)?"

No. thats borderline insane to expect. Reference is 85dB not including peaks and the sub channel. SO if reference is 85dB, what should your sweep look like? And did you run it at reference?

You are asking what speed should my car show at 60 KPH, and then showing it running 47KPH and asking what it should look like at 60.

Excuse me whille I go get the broom. I have a pile of hair that just appeared behind me on the floor.

Mike, how do you do it?!! Im nominating you for sainthood!
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A sweep is not "reference" unless done at "reference" and even then it wont show the PEAKS.

"Should it be hitting 115db at every frequency at 75db (calibrated matched speaker volume)?"

No. thats borderline insane to expect. Reference is 85dB not including peaks and the sub channel. SO if reference is 85dB, what should your sweep look like? And did you run it at reference?

You are asking what speed should my car show at 60 KPH, and then showing it running 47KPH and asking what it should look like at 60.

Excuse me whille I go get the broom. I have a pile of hair that just appeared behind me on the floor.

Mike, how do you do it?!! Im nominating you for sainthood!
Common sense...or lack thereof...at it's finest.

Not the sharpest bowl in the bowl drawer...
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Common sense...or lack thereof...at it's finest.

Not the sharpest bowl in the bowl drawer...
LMAO!
Well, shes not bad to look at is the saving grace. You nailed it however!
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A sweep is not "reference" unless done at "reference" and even then it wont show the PEAKS.

"Should it be hitting 115db at every frequency at 75db (calibrated matched speaker volume)?"

No. thats borderline insane to expect. Reference is 85dB not including peaks and the sub channel. SO if reference is 85dB, what should your sweep look like? And did you run it at reference?

You are asking what speed should my car show at 60 KPH, and then showing it running 47KPH and asking what it should look like at 60.

Excuse me whille I go get the broom. I have a pile of hair that just appeared behind me on the floor.

Mike, how do you do it?!! Im nominating you for sainthood!
To rephrase question, what should a perfect REW sweep for the LFE look like for a setup calibrated to 75db for speaker cal (pink noise) in REW volume with the sweep done at 75db and the sub calibrated at the same level to 85db?

I ask because I see people posting sweeps showing 100+db frequencies on their sweeps. I'm wondering what level in the world they're listening at, either +db hot on their sub or master volume/above reference.

A lot of the room shaking bass REW curves I see on the forum posted by users look.. 'too high' from my experience hwihc is why I was wondering.
At reference level (AVR set to 0) a perfect sweep with disabled LPF should look like this.

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To rephrase question, what should a perfect REW sweep for the LFE look like for a setup calibrated to 75db for speaker cal (pink noise) in REW volume with the sweep done at 75db and the sub calibrated at the same level to 85db?

I ask because I see people posting sweeps showing 100+db frequencies on their sweeps. I'm wondering what level in the world they're listening at, either +db hot on their sub or master volume/above reference.

A lot of the room shaking bass REW curves I see on the forum posted by users look.. 'too high' from my experience hwihc is why I was wondering.
Do you understand the definition of insanity?

There is no “perfect” sweep...or whatever the hell it is that you’re looking for. There is only going to be sweeps between 85-115dB at any particular LFE (0-120Hz?) frequency...period.

This is not rocket surgery! If you would just listen to what you’re being told you would probably (maybe?) understand that. Instead, you continue to overthink the **** out of it and asking the same dumbass questions, expecting a different answer (definition of insanity).
To rephrase question, what should a perfect REW sweep for the LFE look like for a setup calibrated to 75db for speaker cal (pink noise) in REW volume with the sweep done at 75db and the sub calibrated at the same level to 85db?

I ask because I see people posting sweeps showing 100+db frequencies on their sweeps. I'm wondering what level in the world they're listening at, either +db hot on their sub or master volume/above reference.

A lot of the room shaking bass REW curves I see on the forum posted by users look.. 'too high' from my experience hwihc is why I was wondering.
Many run their subs hot by just bumping the sub some or using a miniDSP(or similar) to make a more gradual boost curve. Thats why you see those 100dB+ bass graphs. Dont go looking for (theoretical) perfection, that just doesnt exist with speakers(and rooms) today. Try a few different things and find out for yourself what you like.

Sent from my iPad using Tapatalk
Your reference curve should look like a base sweep or you have compression taking place and it needs to be turned down. Don't worry about what the DB readings look like in other peoples sweeps. 80% of the time they are not correct.

This is why I preach to do compression sweeps.

Then take another sweep at -15db, followed by -10. Overlay the graphs...if the responses all look similar and increase in volume by the full +5db db, then take another sweep @ -5, then -2, and finally 0. Stop and compare sweeps after each increase looking for signs of compression.

If the response shows signs of compression before you get to 0(meaning the response of your loudest sweep no longer looks similar to the base sweep and does not show a linear increase in volume), then you have found the limits of your subs. Turn the volume down a couple DB and that is your systems clean output capability.
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At reference level (AVR set to 0) a perfect sweep with disabled LPF should look like this.

View attachment 3141748
Here you go @aoaaron . perfect reference sweep
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To rephrase question, what should a perfect REW sweep for the LFE look like for a setup calibrated to 75db for speaker cal (pink noise) in REW volume with the sweep done at 75db and the sub calibrated at the same level to 85db?

I ask because I see people posting sweeps showing 100+db frequencies on their sweeps. I'm wondering what level in the world they're listening at, either +db hot on their sub or master volume/above reference.

A lot of the room shaking bass REW curves I see on the forum posted by users look.. 'too high' from my experience hwihc is why I was wondering.
The point of louder sweeps is to find the limit or compression points. It doesn't have anything to do with reference. It is all about how loud can the subs go before the curve changes.
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