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

[Digital_Thor]

Also, your room.
My room has 'soft' floors and walls, making it absorb bass easier, which require me to use larger woofers to get soldid deep bass. Speakers like KEF R3 sounds 'thin' and lacking bass in my living room.... Whereas in others with brick walls, it sounds way fuller.
LS50 Meta sounded absolutely bass-less in my room, as an example.

 

[terryforsythe]

My room has 'soft' floors and walls, making it absorb bass easier, which require me to use larger woofers to get soldid deep bass.

Are you using a subwoofer?

 

[Digby]

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.

Is it really as simple as using this calculation or do differing 6" drivers have different distortion profiles that make them more or less pleasant to listen to at 97db and, correct me if I'm reading you wrong, but isn't xmax the absolute limit of excursion before damage is to the driver, therefore usable range (non-destructive & acceptable distortion for listening) will likely be rather below this 97db per channel at 4m in this scenario?

 

[Digital_Thor]

Are you using a subwoofer?

I do, because even 4 x Satori WO24P can't produce that deep physicaly felt 'bump' that I like.
Further, while the Satori go to around 60Hz, my subwoofers go up to around 100Hz, because I use the principle ala Earl Geddes where by this, you gain additional bass sources and a smoother bass response over a larger listening area.

 

[JohnnyNG]

You want as much capability at 80Hz and below (assuming that crossover) as possible. -3dB point doesn't tell much. Even great 6.5" 2-ways can get in a bit of trouble there at high levels and it doesn't matter how many 18" subs you have at that point.

 

[EJ3]

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.

Very good to know. Thank you. (Even looking: just because is fun)!

 

[NTK]

Is it really as simple as using this calculation or do differing 6" drivers have different distortion profiles that make them more or less pleasant to listen to at 97db and, correct me if I'm reading you wrong, but isn't xmax the absolute limit of excursion before damage is to the driver, therefore usable range (non-destructive & acceptable distortion for listening) will likely be rather below this 97db per channel at 4m in this scenario?

You can find more background technical info on this method by the late Siegfried Linkwitz at:

Loudspeaker system design

Unfortunately, there is no standard definition for xmax. Linkwitz measured his drivers himself using shaped tone bursts using his own max distortions criteria. I cross compared the xmax number of the SB woofer with the Purifi 6.5 inch one. Purifi gave two numbers — linear excursion and mechanical excursion. Purifi may be probably more conservative with their rating of ±5.9 mm linear excursion than SB. Since the numbers are comparable I used the xmax SB specified.

We are talking about maximum SPL capability, which hopefully we don't need to reach very often. As with most other devices, things tend to go bad really fast when at the linearity limit. A just noticeable 1 dB SPL increase requires a 12% increase in cone travel. At the limit, a 12% increase in travel can cause a very significant increase in degradation in performance.

So it requires some personal judgement as to what is the required max level and what is tolerable performance at max level. If what you want is "unconstrained dynamics", then there is no other way than huge speakers that can deliver PA level SPL.

[Edit] Forgot to include the Purifi spec sheet

 

[Heinrich]

Hello,

... (looking at KEF R3 currently) and my question is: do I need to get speakers with large (~8") woofers or ...

The R3s are quite well equipped, top sophisticated motor, well designed surround, reasonable tuning, not just cost effective as is often seen. And foremost, it is a three-way. Don't know which two way w/ an 8" would surpass that, besides of all the other goodies the R3s offer.

Speaking of loud, there's always the temptation to test the limits when the arrangement is new. But nearly guaranteed that won't be sustaninable w/ the R3s, because of your ears.