Understanding subwoofers

[sigbergaudio]

Gee, why didn’t Revel, Perlisten, KEF, etc think of that concept?

It's harder to sell and market.

With regards to Perlisten they are quite home theater focused (an area of the market where subs are a given), so I would say they're pretty close to this approach.

 

[melomane13]

Really, ported speakers should plugged? Nonsense.

There are at least two good reasons to block the reflex port:
1) eliminate tube resonance in the midrange
2) facilitate crossover with the subwoofer

 

[EJ3]

There are at least two good reasons to block the reflex port:
1) eliminate tube resonance in the midrange
2) facilitate crossover with the subwoofer

In my opinion:
If you have issue 1: then the port was not done properly.
Thus being at least a partial cause of issue 2.

 

[Mark609]

In my opinion:
If you have issue 1: then the port was not done properly.
Thus being at least a partial cause of issue 2.

Not necessarily, as I explained here in post #955. https://forum.ascendacoustics.com/h...s-electronics/6638-introducing-the-elx/page64

The fact that Dave did a fine job tuning the ported ELX is not the issue with me.

 

[john61ct]

They very purposefully supply a plug, to give the owner a **choice**.

There are plenty of contexts where closing the port improves the sound of the system as a whole

 

[Mark609]

They very purposefully supply a plug, to give the owner a **choice**.

There are plenty of contexts where closing the port improves the sound of the system as a whole

Would good phase alignment between subs and mains be one of them?

I've also read that pairing ported speakers with sealed can be a problem regarding phase. Don't know if it's relevant but ported have a 24 dB slope while sealed is 12 dB.

 

[john61ct]

Yes exactly, can help make it easier.

 

[thcdru2k]

As a starting point, sealed speakers with sealed subs often integrate well with Linkwitz-Riley 24 dB/octave slopes because the rolloff and phase behavior tend to blend naturally. Ported speakers with sealed subs may benefit from Linkwitz-Riley 24 dB/octave or 48 dB/octave slopes depending on port tuning and crossover behavior, while ported speakers with ported subs can be more sensitive to overlap and phase interaction near tuning, making steeper slopes like Linkwitz-Riley 48 dB/octave worth experimenting with.

 

[EJ3]

Not necessarily, as I explained here in post #955. https://forum.ascendacoustics.com/h...s-electronics/6638-introducing-the-elx/page64

The fact that Dave did a fine job tuning the ported ELX is not the issue with me.

Well, not everything and not every application is cut and dry.
But, just because it is ported, doesn't mean that plugging the port is always the solution.
There are many factors in play.

 

[melomane13]

In my opinion:
If you have issue 1: then the port was not done properly.
Thus being at least a partial cause of issue 2.

Most, if not all, port reflex designs exhibit resonance.
Since it's a compromise to achieve some bass, and given that we'll be using subwoofers, we can close the port, which is no longer serving its primary function but still muddying the midrange, especially at high SPLs.

2) By closing it, the enclosure becomes sealed, which reduces group delay and makes it easier to integrate the subwoofer. This is true regardless of the port's perfection.

The bass reflex design is a fantastic invention, but poorly suited if the speaker needs to reproduce the midrange frequencies.

 

[EJ3]

Most, if not all, port reflex designs exhibit resonance.
Since it's a compromise to achieve some bass, and given that we'll be using subwoofers, we can close the port, which is no longer serving its primary function but still muddying the midrange, especially at high SPLs.

2) By closing it, the enclosure becomes sealed, which reduces group delay and makes it easier to integrate the subwoofer. This is true regardless of the port's perfection.

The bass reflex design is a fantastic invention, but poorly suited if the speaker needs to reproduce the midrange frequencies.

To me, the title: Understanding Subwoofers indicates frequencies below midrange or woofers (and is the way that my system is set up):
My mains have a very small bass-resonance peak (without any EQ of any type):
The close-miked woofer (and port) response of the mains: At the system resonance of 60 Hz, the output is only about 2 dB above its average level in the upper part of the woofer’s range, and even that minor output variation was spread over almost two octaves. When the bass curve was spliced to the room-response measurement, the resulting composite frequency response was flat within about ±2 dB from 26 to 20,000 Hz. The horizontal directivity of the tweeter was only discernible in the room measurement above 10,000 Hz.
At 90-dB SPL at 1 meter, the distortion is less than 1 percent from 100 Hz down to almost 60 Hz, the effective crossover to the port. Below that crossover the distortion rose to 5 percent at 45 Hz and 9 percent at 35 Hz. In high-power tests with single-cycle tone bursts, the woofer began to sound “hard” at about 350 watts into its 8.5-ohm impedance at 100 Hz. At higher frequencies the amplifier clipped—at outputs of 490 watts at 1.000 Hz and 1,380 watts at 10,000 Hz—before distortion became visible on the acoustic waveform.
Quasi-anechoic FFT measurements shows an overall group-delay variation of about 0.1 millisecond between 4,000 and 20,000 Hz and 0.5 ms between 1,000 and 20.000 Hz, convincing evidence of the attention paid to the phase characteristics of the Dahlquist M-905.
Each main and each sub have their own amp that can (if needed) put out over 1600 watts RMS.
My pair of passive sub-bass speakers (the raw driver) have a rated FR of 20Hz-80Hz.
I have the HP at 55Hz & the LP at 70Hz (coming out of the Pre-Amp [before going to the amps]), so I am pretty sure that the subs are not trying to do any midrange.

 

[john61ct]

Is that 55Hz your lowest HPF? If so, why so high?

Would you keep that as is for film soundtracks?

 

[Alice of Old Vincennes]

Marketing. To integrate subs properly, you need to be able to take and interpret measurements. Then you need some DSP to get the subs to work with the mains. That's a huge barrier to sales. Maybe people don't want to go through that effort. Maybe they have misgivings about DSP. Maybe they don't believe in measurements. Better to go the REL route and say "just plug your amplifier output into this sub, don't bother with DSP, don't bother with high-pass, it will just work", and you will get more sales.

Remember: we are in it for the sound quality. Manufacturers are in it for money. The two motivations are not necessarily aligned.

Conspiracy. I wonder when Rhythmic, SVS, Revel, etc will join?

 

[Mark609]

Is that 55Hz your lowest HPF? If so, why so high?

Would you keep that as is for film soundtracks?

55 Hz is high? Nah. 155 is high, not 55.

 

[EJ3]

Is that 55Hz your lowest HPF? If so, why so high?

Would you keep that as is for film soundtracks?

I do not know, I haven't had a TV/Projector or anything to watch a film on since 2007.
In general, I don't listen to film soundtracks.
I have been collecting just a few concert Blue Rays & 4Ks (with the occasional movie) to eventually play on my Oppo 205 UDP,
when I eventually get a large screen or projector.
Since 2018 there has been no digital source (CD, DVD, Blue Ray, 4K, 8K), etc happening in my system.
My current sources are LP's, FM, Cassettes and Reel to Reel.
This has sort of been chosen by location (and very limited, erratic) bandwidth. When cell phone sort of functions, sometimes but mostly not, then not much digital is going to happen (unless I physically bring it in). I am at the end of the power grid and have two 15 amp circuits to run a home on. It's a different than average lifestyle here.
This 1st picture is taken from the very back of the inside of my home, diagonally toward the front of the home. Picture 2 is diagonally toward the back (where I was standing when I took picture one. Picture 3 is diagonally across the front deck and picture 4 is across the front yard (before the roof was put over the deck). My nearest neighbor is more than 1/4 mile away. Life is at a different, less hectic, more relaxed, pace out here. Next, the menu from one of the local restaurants.

 

[thcdru2k]

It would be nice if there were more studies and guides on integrating identical vs non-identical subs, or symmetrical vs asymmetrical rooms where each sub loads the room differently. A lot of real-world setups aren’t perfectly symmetrical.

 

[Keith_W]

Conspiracy. I wonder when Rhythmic, SVS, Revel, etc will join?

You will notice that none of them will tell you that you need additional DSP upstream of the subs and speakers to get the subs to integrate. They don't say you have to learn to take and read measurements. Instead, they talk about their subs. Or if their subs are DSP enabled, they will talk about the benefits of subwoofer DSP. It's not so much a conspiracy, it's a bunch of people who have all independently reached the same conclusion: if you really educate the consumer about what is needed, it will turn many people off.

 

[DY2]

Hi Keith, thanks for your perspective.
I have a few questions regarding subwoofer integration that I would love to get your take on.
Why is a DSP considered absolutely necessary for proper subwoofer integration, and what specific room acoustics or phase alignment issues make it indispensable in your view?
Also, how can one integrate subwoofers as effectively as possible without relying on a DSP, and what are the best practices regarding physical placement, phase toggles, or crossover settings on the subs themselves?
Finally, when analyzing room measurements like those in REW, what exactly should we be looking for, and which specific graphs or metrics like frequency response, decay times, or phase are the most critical to pay attention to?
I appreciate your insights on this.

Just to clarify, as you can see in my signature, I am currently using a DBX PA2 for my main multi-sub setup. I spent a massive amount of time and effort moving these subs around the room, trying to find the absolute best physical placement and getting them aligned as close to perfect as possible before letting the processing take over.
I am asking these questions because I am genuinely curious about your philosophy and approach to this process. I also want to better understand the deeper theory behind manual integration versus digital correction, especially since I am planning a secondary, purely analog stereo system where a DSP might not be an option. I wanted to see how much of a great integration can be achieved purely through physical placement and manual settings based on your experience.

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[Keith_W]

Hello @DY2,

Please take a look at the eBook in my signature about REW measurements.

As for the rest of your subwoofer DSP questions, I am currently working on another eBook on subwoofer integration. It is specific to Acourate, but the principles apply universally. In fact, you could simply take the workflow and apply it in REW or in any other DSP. Just be aware that many other DSP packages aren't as full featured as Acourate and some things may be either impossible or very difficult to do (depending on what you are using). You can read the draft here. There is a lot to say, I am only halfway there, and it's 20 pages already.

Re: integrating subs without DSP. It will be much more difficult. With DSP, you do everything you can to avoid dips in the frequency response - reposition subs, adjust timing, etc. This is because the peaks can simply be chopped off. Very simple. But WITHOUT DSP, you have to do everything you can to avoid peaks in the frequency response, since those are far more audible than dips. And you will never get a nice and smooth curve, unless you have a lot of subwoofers.

 

[DY2]

Hi Keith,
Thank you so much for the detailed explanation and for sharing those links. I will definitely dive into your REW eBook and check out the draft for your new guide on subwoofer integration. Your ability to break down these complex topics is highly appreciated.
What you mentioned about the multi-sub exception is actually what led me here. As you can see from the attached REW graph, I managed to get some surprisingly good results through purely manual alignment, positioning, and manual settings before introducing any digital processing. Even though I was quite happy with how it sounded at that stage, I eventually transitioned to a DSP (the DBX PA2) because I wanted to squeeze every last ounce of performance out of my 6-subwoofer setup.
I’ve been actively looking to connect with other enthusiasts who have gone down a similar multi-sub path to exchange experiences, and your posts stood out immediately especially given how thoroughly you explain the underlying theory in your writing.
Thanks again for your insights, and I look forward to reading more of your work!