Do I need 8" woofers in my speakers if I'm going to have 2 subwoofers?

[PashkaTLT]

Hello,

I'm choosing future speakers, perhaps for my home theater or perhaps for my music system (if new speakers beat my current KRK Rokit 10-3).
My HT will have 2 x 12" subwoofers and my music system has 2 x 18" subwoofers.

I will be getting some really good 3-way speakers (looking at KEF R3 currently) and my question is: do I need to get speakers with large (~8") woofers or having 5-6.5" woofers will be absolutely enough provided I will have subwoofers?

 

[Alice of Old Vincennes]

6.5 are enough

 

[Power Pop 23]

Hello,

I'm choosing future speakers, perhaps for my home theater or perhaps for my music system (if new speakers beat my current KRK Rokit 10-3).
My HT will have 2 x 12" subwoofers and my music system has 2 x 18" subwoofers.

I will be getting some really good 3-way speakers (looking at KEF R3 currently) and my question is: do I need to get speakers with large (~8") woofers or having 5-6.5" woofers will be absolutely enough provided I will have subwoofers?

Probably not

The frequencies allocated to a larger woofer may play with less distortion at higher sound pressure levels.

 

[Ellebob]

SImple answer for most, probably not needed.

However, it depends on volume desired. As a generalization, if you are looking at speakers that have a 5 or 6" driver and a version with an 8" driver, the 8" will be better in few ways.

1. It will go lower. Probably not needed with subs.
2. It will play louder.
3. Its noticeable distortion won't start until louder levels.

Listening space (smaller vs bigger room), seating distance and volume desired are the big factors. At moderate volumes it will be fine going with the smaller speaker.

 

[PashkaTLT]

6.5 are enough

What about 5" ?

 

[tomtoo]

Its all about how loud you want to go

 

[Alice of Old Vincennes]

What about 5" ?

Prefer 6.5. 5’s harder to blend with subs

 

[terryforsythe]

Hello,

I'm choosing future speakers, perhaps for my home theater or perhaps for my music system (if new speakers beat my current KRK Rokit 10-3).
My HT will have 2 x 12" subwoofers and my music system has 2 x 18" subwoofers.

I will be getting some really good 3-way speakers (looking at KEF R3 currently) and my question is: do I need to get speakers with large (~8") woofers or having 5-6.5" woofers will be absolutely enough provided I will have subwoofers?

It depends on the speakers, the sub/speaker crossover frequency, the SPL at which you will be listening, and how much harmonic distortion is acceptable to you.

At 86dB SPL @ 1m, the KEF R3 total harmonic distortion (THD) is below -40dB (1%) down to about 62Hz, and below -30dB (3.16%) down to about 38Hz. For the volume at which I listen, the KEF 6.5" woofer is more than sufficient. But, not all manufacturers use woofers that good, so do your homework on whatever speaker you end up choosing.

 

[DWPress]

Definitely a case where the spinorama can give you valuable information about choosing speakers. As @terryforsythe mentions, take into consideration your desired SPL and acceptable THD in the system mains as they crossover to subs. Amir isn't the only one with a Klipple, there's a website that amalgamates various sources which is an excellent reference.

 

[mglobe]

Hello,

I'm choosing future speakers, perhaps for my home theater or perhaps for my music system (if new speakers beat my current KRK Rokit 10-3).
My HT will have 2 x 12" subwoofers and my music system has 2 x 18" subwoofers.

I will be getting some really good 3-way speakers (looking at KEF R3 currently) and my question is: do I need to get speakers with large (~8") woofers or having 5-6.5" woofers will be absolutely enough provided I will have subwoofers?

From my experience, the R3’s work really well with subs. You may want to consider the 12” with the music system and the 18’s with HT.

 

[levimax]

The more full range the mains the easier / better sub integration will be.

 

[Bruce Morgen]

Even when high-passed at the usual 80Hz, an 8" woofer will generally* be less distorted than a smaller one, but that difference is very small compared with a 6.5" counterpart all things being equal**. Smaller than that and we're getting into fairly audible differences IMO -- that's why my Kali IN-5 is assigned to center channel duty and my main L+R pair are IN-8v2s.

* "All generalizations are intrinsically false to one extent or another -- including this one!"

** "Concerning `all things': They're never actually equal."

 

[NTK]

You can estimate the max SPL based on driver diameter and linear xmax using this calculator.

For example, a SB Acoustics SB17CAC35-8 6" woofer has Sd (effective piston area) = 118 cm^2 and peak-to-peak xmax (linear coil travel) = 11 mm. Assume a 80 Hz cross-over to sub(s):

• Select "solve for dB"
• Sd = 118 cm^2 ⇒ Effective driver diameter = √(4 Sd / π) = 12.26 cm = 4.8 inch
• The calculator uses one-way peak Xmax, therefore, for this calculator, Xmax = 11/2 = 5.5 mm
• Result: 1 m free field SPL at 80 Hz = 97 dB
• At the cross-over frequency both the sub and main speaker contribute equal amounts of SPL, therefore the total SPL is 97 + 6 = 103 dB, free field
• Add another 6 dB for boundary gain, we've got 109 dB SPL per channel
• At 4 m listening distance, subtract 12 dB and you should be able to get clean 97 dB SPL per channel.

 

[skankhobag]

Since you’re not big on specifics, I’ll keep it general.

• Regardless of the size of the woofer in the main speakers, you’re going to want to cross over to the subs, one octave above the -3dB point of the loudspeakers frequency response. Generally speaking, all loudspeakers produce the most distortion as they start to dip down into the first octave that they can reproduce. It never hurts to crossover to the subwoofers much higher than very low bass frequencies so long as you’re running the subs in stereo.

• There is a common myth that humans cannot hear low bass (below 200 Hz) in stereo. If the room you’re listening in has really terrible acoustics, that will be true. On the other hand, if you have a very well treated and good sounding room, you will easily hear stereo all the way down to the lowest octave.

• The less low bass that your main speakers produce, the cleaner they will sound because low frequencies are not rattling the cabinet or any of the drivers around

• For both your subs and mains, use the steepest crossover slope that you possibly can with your system.

• You’re going to get the best sound with sealed subwoofers. It’s not that ported subwoofers sound bad, but their temporal response is poor the lower you go. Being a bassist, I love playing my instrument through my home theater in surround. I play with a lot of effects so scaling them up to surround is truly magnificent. The reason I mention this is because I can hear the difference that ported and sealed subwoofers make to the sound of my instrument. You have to make the decision as to what’s more important for you in the particular installation that you are creating. Sealed subs offer better phase response than ported designs and the cabinets are more compact. They can also be equalized to give response below their -3 dB point and do it cleanly. Ported subs offer higher efficiency down to their F3, but can’t go below that without a lot of distortion as well as the fact that their cabinets have to be about 50% larger.

For music, I would absolutely go for sealed cabinets, but, for home theater, it’s less important unless you watch a lot of live music concerts.

That’s my two cents. Do with it as you may.

 

[terryforsythe]

• Regardless of the size of the woofer in the main speakers, you’re going to want to cross over to the subs, one octave above the -3dB point of the loudspeakers frequency response. Generally speaking, all loudspeakers produce the most distortion as they start to dip down into the first octave that they can reproduce. It never hurts to crossover to the subwoofers much higher than very low bass frequencies so long as you’re running the subs in stereo.

Another "it depends". Specifically, it depends on the crossover slope.

If you are using a relatively shallow crossover slope, then yes, one octave above the -3dB frequency is a good rule of thumb. But, if you are using a relatively shallow crossover slope, then you want to cross it over very low or place a subwoofer right next to each speaker.

As an example, I inherited a SVS subwoofer and decided to try it with my KEF LS60 speakers in my office, letting the KEF app control the subwoofer integration. I don't know what is the crossover slope, but it probably is something like 2nd or 3rd order. I tried 80Hz, and I could hear where the subwoofer was located. It degraded the imaging. I kept dropping the crossover frequency in 10Hz increments until I no longer was audibly aware of the subwoofer location. I ended up at 40Hz.

In contrast, in my family room I have small bookshelf speakers crossed over to a subwoofer that is even further from the speakers than in my office. In my family room I am crossed over at 100Hz using 8th order crossover slopes, and I can't hear where the subwoofer is located. The steep crossover slopes really help get the subwoofer response to roll off quickly, which helps to audibly mask its location.

Another issue is that some ported speakers are easier to integrate with a subwoofer when their ports are plugged, though it is not always the case. In my family room plugging the ports definitely helped smooth the transition frequency range around the crossover frequency. But, the speakers' bass response does not extend as low, which for me is not a problem given my 100Hz crossover frequency.

 

[dlaloum]

A couple of things to keep in mind...

The Dolby Theatre standards only require the LFE channel to go down to 32Hz...

For your mains, for music / stereo purposes a speaker that goes down to 40Hz is considered "full range" - yes you can find speakers with a response down to 20Hz, but they tend to be pretty big (and frequently subject to WAF issues... ).

In terms of Music - there are plenty of full range speakers out there with 6.5" woofers... those that reach down lower mostly use multiple woofers to do that, as woofer total surface area will drive the SPL limitations in the very low end.

My full range main speakers have a 10" sealed woofer (Gallo ref 3.2) and my surround speakers, also full range, achieve the same result with 4 x 5" bass reflex woofers (B&O Penta) - the mains are, according to specs, capable of 24Hz, and the surrounds 35Hz.

I don't find that I "NEED" a subwoofer - but I do run a sub for the LFE channel, and it does extend the lower end and provide additional SPL - if bass managed properly... - I use a 10" sealed sub.

Having full range main and surrounds should provide optimal results with Dirac ART in the near future.

 

[terryforsythe]

For music, I would absolutely go for sealed cabinets

I agree. I like the sound of sealed subwoofers better than vented. Same goes for speakers, though the design of some speakers allow for the ports to be plugged, which worked well in my case.

 

[PashkaTLT]

Another "it depends". Specifically, it depends on the crossover slope.

If you are using a relatively shallow crossover slope, then yes, one octave above the -3dB frequency is a good rule of thumb. But, if you are using a relatively shallow crossover slope, then you want to cross it over very low or place a subwoofer right next to each speaker.

What's good rule of thumb on choosing the crossover frequency on the speakers if I have a very steep (Butterworth 48db/octave) filter?

 

[levimax]

What'a good rule of thumb on choosing the crossover frequency on the speakers if I have a very steep (Butterworth 48db/octave) filter?

Cross where both drivers are operating "flat" (not rolling off) and behaving minimum phase, look at group delay and find zones where both drivers don't have rapid changes.

 

[terryforsythe]

What's good rule of thumb on choosing the crossover frequency on the speakers if I have a very steep (Butterworth 48db/octave) filter?

It depends on how close the subwoofers are to the speakers, the room acoustics, etc. If the subwoofers are not right next to the speakers, I would start with 70Hz. If you can hear where the subwoofers are located with your eyes closed, then lower the frequency. If not, try a little higher. Also, much depends on how well you can get the subwoofers and speakers time aligned. If you cross over too close to the speaker's lower resonant frequency, keeping them phased aligned can be challenging due to the group delay.

As a side note, I tuned my friends system with a single subwoofer and speakers. Due to a huge dip in his room response at 150Hz, we opted to run the subwoofer beyond that to help the speakers to fill in the dip, and adjusted the time delay to get them in phase. We could hear the subwoofer's location, of course, but sometimes you need to take the lesser of two evils. We moved the subwoofer between the speakers and that helped out the soundstage quite a bit. Given his room, his system, and the fact he was not about to spend more money on an additional subwoofer, it probably was the best compromise. We both agreed that configuration sounded best from all of the options we tried. Unfortunately he has since passed, which is how I inherited the subwoofer.