Blending sub and speakers, sealed vs. ported and other factors? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 16 Old 09-19-2017, 01:35 PM - Thread Starter
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Blending sub and speakers, sealed vs. ported and other factors?

For background, I’ve been playing around with an inexpensive, secondary 2.1 system in the gym area of the unfinished portion of our basement.

I also have a pair of Klipsch Forte in this area. They are wired to the main system, which is in the finished “media room” part of the basement. I don’t want my son to have to mess with the main system when he’s working out (this sometimes requires making speaker wire swaps), so I set up this 2.1 system for him to use. The 2.1 system also provides a venue to evaluate various bookshelf speakers I come across.

The system consists of the following:
AVR: Pioneer VSX-517 (low end pre-HDMI model found at thrift store for $20)
Sub: JBL 550P (currently on Amazon for $189)
Speakers: Polk S20 ($159/pr refurbs), NHT SB3 ($125/pr Craigslist). I also have a couple other pairs that I have not yet evaluated in this system.

I evaluated both the Polks and the NHTs. Both were set to small, calibrated with a SPL meter, and evaluated with 80Hz and 100Hz crossovers. BTW, the Polks are 4 dB more efficient, based on the calibration settings.

What I’ve noticed is that the NHTs seem to have a more coherent or seamless blend with the sub. The overall bass presentation seems more detailed too. With the Polks, I could always tell that I was listening to a 2.1 system, which is a bit distracting. With the NHTs, I am pretty impressed by what this inexpensive little system can do. The sealed NHTs and sealed JBL sub sound pretty good together, even with a lowly AVR.

So now I am curious about which speaker attributes aid in blending with a sub. Is there something to sealed vs. ported, or is it more to do with the frequency response of the speakers?

Anecdotally, my first 5.1 system was 4 NHT Super Ones, a Super Center, and a Velodyne 1210. I always felt that this system had a coherent sound with good sub integration. Maybe I’m having good luck with NHT and sub blending.

Last edited by adam2434; 09-19-2017 at 07:02 PM.
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post #2 of 16 Old 09-19-2017, 02:19 PM
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Originally Posted by adam2434 View Post
For background, I’ve been playing around with an inexpensive, secondary 2.1 system in the gym area of the unfinished portion of our basement.

I also have a pair of Klipsch Forte in this area. They are wired to the main system, which is in the finished “media room” part of the basement. I don’t want my son to have to mess with the main system when he’s working out (this sometimes requires making speaker wire swaps), so I set up this 2.1 system for him to use. The 2.1 system also provides a venue to evaluate various bookshelf speakers I come across.

The system consists of the following:
AVR: Pioneer VSX-517 (low end pre-HDMI model found at thrift store for $20)
Sub: JBL 550P (currently on Amazon for $189)
Speakers: Polk S20 ($159/pr refurbs), NHT SB3 ($125/pr Craigslist). I also have a couple other pairs that I have not yet evaluated in this system.

I evaluated both the Polks and the NHTs. Both were set to small, calibrated with a SPL meter, and evaluated with 80Hz and 100Hz crossovers. BTW, the Polks are 4 dB more efficient, based on the calibration settings.

What I’ve noticed is that the NHTs seem to have a more coherent or seamless blend with the sub. The overall bass presentation seems more detailed too. With the Polks, I could always tell that I was listening to a 2.1 system, which is a bit distracting. With the NHTs, I am pretty impressed by what this inexpensive little system can do. The sealed NHTs and sealed JBL sub sound pretty good together, even with a lowly AVR.

So now I am curious about which speaker attributes aid in blending with a sub. Is there something to sealed vs. ported, or is it more to do with the frequency response of the speakers.

Anecdotally, my first 5.1 system was 4 NHT Super Ones, a Super Center, and a Velodyne 1210. I always felt that this system had a coherent sound with good sub integration. Maybe I’m having good luck with NHT and sub blending.
My first HT system had a sealed Velodyne ULD15 servo sub and sealed B&W CM1 Concept 90s and blended beautifully.

My AVR had no EQ and neither did the sub.

My current HT system has a sealed Velodyne DD15 servo sub and ported Usher V602 mains and blend beautifully.

Mind you the DD15 has built in sub EQ and the AVR has EQ for the speakers only so not sure if that is a major factor but that's all I've got for you!

Geoff A. J., California
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post #3 of 16 Old 09-20-2017, 08:15 AM - Thread Starter
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This article from Rythmik gets a bit into the differences in blending sealed vs. ported mains, as well as differences in mains woofer size.

I skimmed through it, but will need to read it again carefully to grasp it better.

http://www.rythmikaudio.com/phase1.html
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post #4 of 16 Old 09-20-2017, 08:37 AM
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Sealed speakers generally blend better with a sub because they have a natural 2nd order rolloff in the bass frequencies, when combined with your 2nd order high pass from your receiver you get a 4th order summed high pass along with a 4th order low pass filter on the sub, this is why it sounds more seamless. The only other option which I have done is buy a receiver or processor that allows you to use 4th order slopes on the high pass as well so that you can blend ported speakers with a sub much easier. Measuring with REW helps a lot too when trying to choose the best crossover frequency.
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post #5 of 16 Old 09-20-2017, 10:24 AM
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Quote:
Originally Posted by adam2434 View Post
This article from Rythmik gets a bit into the differences in blending sealed vs. ported mains, as well as differences in mains woofer size.

I skimmed through it, but will need to read it again carefully to grasp it better.

http://www.rythmikaudio.com/phase1.html
It seems that they are recommending setting the sub crossover point to the same as that in the AVR when using ported main speakers.

Normally subs are set at their maximum crossover point with the AVR handling those duties on its own.

Learned something new.

Geoff A. J., California
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post #6 of 16 Old 09-20-2017, 01:04 PM
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Originally Posted by gajCA View Post
It seems that they are recommending setting the sub crossover point to the same as that in the AVR when using ported main speakers.

Normally subs are set at their maximum crossover point with the AVR handling those duties on its own.

Learned something new.
Typically that is what you want to do, I didn't read the article but you don't want to cascade your low pass crossover from the AVR and your sub, you either want to set it to max or ideally the sub would have an input that bypasses its internal crossover altogether.
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post #7 of 16 Old 09-20-2017, 02:45 PM
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Originally Posted by aarons915 View Post
Typically that is what you want to do, I didn't read the article but you don't want to cascade your low pass crossover from the AVR and your sub, you either want to set it to max or ideally the sub would have an input that bypasses its internal crossover altogether.
Yep, that's what I've always done but this is what their logic is:

"Consider the example of an 80 Hz crossover point. If the main speakers have a sealed box which are -3db at 80 Hz, the acoustic roll-off will be 2nd order. When this speaker is set to "small," in the receiver settings, it will have a 2nd order high pass filter at the crossover point of 80 Hz. The summed roll-off is therefore 4th order. The subwoofer should then have its crossover set to 80 Hz and use a 4th order low pass filter. This will yield a correctly implemented 4th order crossover. At 80 Hz, the response of the subwoofer and the mains will each be -6db."

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post #8 of 16 Old 09-20-2017, 02:59 PM
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Most AVRs apply a 4th order low pass to the sub channel. So, according to the way their recommendations read ("the subwoofer should then have its crossover set to 80Hz") , you would have two overlapping low-passes at the sub channel; one 4th order and one (probably) 4th order. But I don't think they are recommending setting the sub's own low-pass at 80Hz. It's a bit poorly worded.

They are simply pointing out why sealed speakers with an 80Hz roll-off are better for sub integration with an AVR. But not all sealed speakers have a roll-off at 80Hz.

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Originally Posted by gajCA View Post
Yep, that's what I've always done but this is what their logic is:

"Consider the example of an 80 Hz crossover point. If the main speakers have a sealed box which are -3db at 80 Hz, the acoustic roll-off will be 2nd order. When this speaker is set to "small," in the receiver settings, it will have a 2nd order high pass filter at the crossover point of 80 Hz. The summed roll-off is therefore 4th order. The subwoofer should then have its crossover set to 80 Hz and use a 4th order low pass filter. This will yield a correctly implemented 4th order crossover. At 80 Hz, the response of the subwoofer and the mains will each be -6db."
I would put the AVR crossover point above the -3dB point of the main speaker. That way you would not be combining speaker roll off with AVR roll off.

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post #10 of 16 Old 09-20-2017, 03:02 PM
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What that article has wrong is that the receiver already applies a 4th order low pass at the selected crossover frequency. Maybe they're talking about a system that only high passes the mains but I don't know of any receivers that would do that. What they're suggesting would basically give you an 8th order low pass on the sub which would be down like 12 db at 80hz and roll off at 48 decibels per octave instead of 24. This is the graphical representation of how a 4th order crossover works, you can see the sum of the frequencies is flat.
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post #11 of 16 Old 09-20-2017, 03:17 PM
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Originally Posted by aarons915 View Post
What that article has wrong is that the receiver already applies a 4th order low pass at the selected crossover frequency. Maybe they're talking about a system that only high passes the mains but I don't know of any receivers that would do that. What they're suggesting would basically give you an 8th order low pass on the sub which would be down like 12 db at 80hz and roll off at 48 decibels per octave instead of 24. This is the graphical representation of how a 4th order crossover works, you can see the sum of the frequencies is flat.
Most AVRs do apply a 4th order low-pass at their selected crossover frequency.

I thought that is what you were saying in post#4, no?


EDIT: Sorry, I think we are saying the same thing. I read your 1st sentence differently from what you meant.
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Originally Posted by sivadselim View Post
Most AVRs do apply a 4th order low-pass at their selected crossover frequency.

I thought that is what you were saying in post#4, no?


EDIT: Sorry, I think we are saying the same thing. I read your 1st sentence differently from what you meant.
Yes receivers do apply the low pass to your sub already so that's why I was saying you wouldn't want to basically double up on the low pass and use your subs as well.
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post #13 of 16 Old 09-20-2017, 04:27 PM
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Yes receivers do apply the low pass to your sub already so that's why I was saying you wouldn't want to basically double up on the low pass and use your subs as well.

Right, I misinterpreted what you said in the 1st sentence. I initially thought you were saying that THEY were wrong to say that the AVR applies a 4th order low pass.

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What that article has wrong is that the receiver already applies a 4th order low pass at the selected crossover frequency.

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post #14 of 16 Old 09-20-2017, 07:35 PM - Thread Starter
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I will have to read the article again, but I did not get the impression that they were suggesting to set the on-sub crossover to 80 Hz, but rather that an AVR's crossover set to 80 Hz would yield a 4th order 80 Hz lowpass filter. Point being that the AVR's highpass is 2nd order and is better suited for sealed speakers with an inherent 2nd order rolloff.

However, I'm not clear whether the sealed speaker order-matching benefit would apply at a higher frequency than where the natural 2nd order rolloff occurs. For example, if a sealed speaker starts a 2nd order rolloff at 50 Hz, does the order-matching benefit exist at 80 Hz?
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post #15 of 16 Old 09-20-2017, 07:39 PM
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However, I'm not clear whether the sealed speaker order-matching benefit would apply at a higher frequency than where the natural 2nd rolloff order occurs. For example, if a sealed speaker starts a 2nd order rolloff at 50 Hz, does the order-matching benefit exist at 80 Hz?
No.

The original THX spec specified sealed speakers with 2nd order rolloff @ 80Hz with a 2nd order high-pass @ 80Hz in the AVR + 4th order low pass @ 80Hz in the AVR.

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post #16 of 16 Old 09-21-2017, 08:36 AM - Thread Starter
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No.

The original THX spec specified sealed speakers with 2nd order rolloff @ 80Hz with a 2nd order high-pass @ 80Hz in the AVR + 4th order low pass @ 80Hz in the AVR.
However, the Rythmik article states the following:

One rule of thumb is that if we use 6-1/2" woofer based front speakers in a sealed box, they can be comfortably crossed over at 80 Hz without much phase/delay time adjustment (the SB2 without delay time adjustment is already quite good). For anything equal to 4-1/2" for smaller, crossover at 100 Hz may cause localization. Placement becomes important. For vented box front speakers, large delay time adjustment may be needed.

Coincidently, Rythmik is using the NHT SB3 (sealed with 6.5” woofer), so the same sealed speaker I am using. They also use the NHT SB2, which also has a 6.5” woofer, but is incorrectly described as having a 5” woofer in the article.

I would expect that the NHT SB3 natural 2nd order rolloff would start lower than 80 Hz. Maybe more around 50-60 Hz? Not sure.

The Rythmik article shows that the SB3/SB2 and sub need minimal phase adjustment to achieve a pretty flat frequency response in the 80 Hz crossover region. It would have been interesting if they had included a ported speaker with 6.5” woofer.
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