pros and cons of dual 8s

[cerwinmad]

Hi guys, i have a cerwin vega VE-28s sub. it is two 8 inch drivers arranged vertically, with a rear facing port.I am very interested to know the pros and cons of this design. i have it crossover at 60Hz, and to me sounds great, very deep and accurate. I had a DB Dynamics 12 and it outdoes it in every way.

 

[TLS Guy]

Hi guys, i have a cerwin vega VE-28s sub. it is two 8 inch drivers arranged vertically, with a rear facing port.I am very interested to know the pros and cons of this design. i have it crossover at 60Hz, and to me sounds great, very deep and accurate. I had a DB Dynamics 12 and it outdoes it in every way.

I think you have this common misunderstanding that larger diameter cones equals deeper bass. Not so! Nowhere is the diameter of the speaker cone part of an equation that determines the lowest reach of a speaker.

Think of a speaker as a spring driven by a motor, which it is. Now the slower the frequency at which the spring will move the weight up and down is determined by how heavy the weight on the end of the spring is (the heavier the slower/deeper bass) and the stiffness of the spring, compliance, (the looser or softer the slower/deeper bass). Now the moving mass and motor force interact to make a parameter known as the equivalent volume of the driver (VAS), which determines optimal box size and tuning.

Now the rate at which the speaker (spring vibrates on free air) is called the free air resonance of the driver Fs. The effective lowest reach of the driver is usually a little higher than that number. The stiffness of the driver helps determine a parameter known has the Q of the driver, which relates to the parameters of the stiffness of the spring, which is determined by the looseness or stiffness of the driver suspension.

So we now come to a ratio referred to as the efficiency bandwidth ratio (EBR) which is Fs/Qt. The lower that ratio the lower the potential low frequency cut off of the driver. It does not tell us anything about the enclosure volume required. That is a product related to the the moving mass and motor force which determine Vas as stated above.

So you are pleased with your sub, because these numbers line up to produce a satisfactory end product.

I don't know your sub, but usually the smaller the cone the lighter. However you can make small heavy cones. I general however the smaller lighter cone has to have a looser suspension for equivalent Fs. That can make the speaker less robust.

 

[Exit]

A subwoofer is about moving air. The piston areas of two 8” woofers (pi r squared) x 2 = 3.14 x 16 x 2 = 100.48 sq in. The piston area of a 12” woofer is 3.14 x 36 = 113.04 sq in. So the piston areas are about equal. The piston volumes are what really count but they are harder to calculate because you have to know more about the technical design of the speakers (i.e. cone excursion, etc.). and from there it gets much more technical into the speaker design. A real technical discussion is not requried since there are so many variables in subwoofer design. The point being, it is credible for the double eights to sound better than the single 12 or vice versa as far as filling a room with sound. It all depends on how well the designers and manufacturers did their jobs, which is generally reflected in the prices of the subwoofers. There are bound to be sound quality differences between a subwoofer that is priced a few hundred dollars greater than the other. There generally is a quality vs price relationship as you move up the model and cost ladder.

 

[TLS Guy]

A subwoofer is about moving air. The piston areas of two 8” woofers (pi r squared) x 2 = 3.14 x 16 x 2 = 100.48 sq in. The piston area of a 12” woofer is 3.14 x 36 = 113.04 sq in. So the piston areas are about equal. The piston volumes are what really count but they are harder to calculate because you have to know more about the technical design of the speakers (i.e. cone excursion, etc.). and from there it gets much more technical into the speaker design. A real technical discussion is not requried since there are so many variables in subwoofer design. The point being, it is credible for the double eights to sound better than the single 12 or vice versa as far as filling a room with sound. It all depends on how well the designers and manufacturers did their jobs, which is generally reflected in the prices of the subwoofers. There are bound to be sound quality differences between a subwoofer that is priced a few hundred dollars greater than the other. There generally is a quality vs price relationship as you move up the model and cost ladder.

Piston size and volumes have nothing to whether a sub is any good or how low it will go. Everything that matters is in my post.

 

[Exit]

"Everything that matters is in my post"

How modest. Whatever you say. Try filling up an 8500 cu ft room to acceptable sound pressure levels with an 8" subwoofer and you will see piston area (speaker diameter(s)) matter.

 

[TLS Guy]

"Everything that matters is in my post"

How modest. Whatever you say. Try filling up an 8500 cu ft room with an 8" subwoofer and you will see piston area (speaker diameter(s)) matter.

I probably should not have put it that way, but what I mean is deep comes down to mass and compliance with correct loading. As far as filling the room it would come down to the spl of the driver wouldn't it? So this is a function of xmax and area. He has a cone area with his two 8 inch woofers the same as one 12.

Really the point of it all, is that you can get good bass depth from smaller drivers. Spl will depend on cone excursion and how many drivers you use. There is an advantage to using more drivers, as each driver has its own motor, and thermal dynamic compression will be decreased with multiples.

The questioner likes his subs, but has a feeling, I think, he would do better with a driver/drivers of larger diameter. Well that does not follow. He is happy with his sub, and I have explained why smaller drivers properly designed and loaded can do a good job, which his sub apparently does. So he needs to enjoy his sub. Bigger drivers don't of themselves guarantee deeper bass.

 

[cerwinmad]

thanks guys that helps alot, i am very happy with the sub, and yeah i was always under the impression bigger was better! cheers.

 

[buton6]

If it sounds, good it has to be good. I am guilty of the same thing, I have good stuff at home but keep looking for something else (hope my wife doesn't read this)

 

[cerwinmad]

Ha Ha yeah this home theatre business is a hunger thats hard to satisfy!! but then again if perfection was easy to obtain, what would we do with ourselves!!!

 

[blacksquid]

A subwoofer is about moving air. The piston areas of two 8” woofers (pi r squared) x 2 = 3.14 x 16 x 2 = 100.48 sq in. The piston area of a 12” woofer is 3.14 x 36 = 113.04 sq in. So the piston areas are about equal. The piston volumes are what really count but they are harder to calculate because you have to know more about the technical design of the speakers (i.e. cone excursion, etc.). and from there it gets much more technical into the speaker design. A real technical discussion is not requried since there are so many variables in subwoofer design. The point being, it is credible for the double eights to sound better than the single 12 or vice versa as far as filling a room with sound. It all depends on how well the designers and manufacturers did their jobs, which is generally reflected in the prices of the subwoofers. There are bound to be sound quality differences between a subwoofer that is priced a few hundred dollars greater than the other. There generally is a quality vs price relationship as you move up the model and cost ladder.

Agreed! I've got a B&W PV1 which has dual 8s mounted back-to-back (looks like a silver bowling ball). I find the sub to be very accurate and it goes down pretty low. The surprising thing is that the unit has no vibration when operating! Great sub for me.

 

[mike c]

Agreed! I've got a B&W PV1 which has dual 8s mounted back-to-back (looks like a silver bowling ball). I find the sub to be very accurate and it goes down pretty low. The surprising thing is that the unit has no vibration when operating! Great sub for me.

defining "goes low" is relative ...

http://www.avtalk.co.uk/forum/index.php?t=msg&th=20041&start=0&rid=7164&SQ=1204159022

http://www.hometheatershack.com/forums/subwoofer-tests/5749-b-w-pv1.html

+/-3dB points: 41.26Hz -> 106.7Hz

+/- 3 dB points: 35 Hz - 110 Hz

 

[blacksquid]

defining "goes low" is relative ...

http://www.avtalk.co.uk/forum/index.php?t=msg&th=20041&start=0&rid=7164&SQ=1204159022

http://www.hometheatershack.com/forums/subwoofer-tests/5749-b-w-pv1.html

Thanks for the link! This information was not available when I went searching for info on the PV1. In any case, I find the sub to be very pleasing musically , more than adequate for the types of movies that I watch, and it works well in my relatively small space. The WAF is way up there too!

 

[mike c]

Thanks for the link! This information was not available when I went searching for info on the PV1. In any case, I find the sub to be very pleasing musically , more than adequate for the types of movies that I watch, and it works well in my relatively small space. The WAF is way up there too!

i agree. WAF on the PV1 is hands down the best on any sub.

and for music, the PV1's should be sufficient ... it's just that for HT, there's a new trend to go even lower.

 

[annunaki]

i agree. WAF on the PV1 is hands down the best on any sub.

and for music, the PV1's should be sufficient ... it's just that for HT, there's a new trend to go even lower.

I would not say it is new for all of us Mike.

 

[mike c]

I would not say it is new for all of us Mike.

wanted to lay it on him softly

 

[cerwinmad]

yeah i agree! low bass is good bass!! i have the CV VE-12s and the twelves definitely reinforce the bass. very good excursion in my opinion, especially watching movies. not sure if you guys have any experience with these speakers. posssibly below your refined tastes!!!

 

[Exit]

Those B&W PV1 silver balls look really cool. I bet they would go good with Orb or Gallo spherical speakers. At a price of 995 pounds, with a pound worth about two US dollars, those are about $2000 US. That’s pretty expensive for the US market compared with other alternatives available.

 

[TLS Guy]

yeah i agree! low bass is good bass!! i have the CV VE-12s and the twelves definitely reinforce the bass. very good excursion in my opinion, especially watching movies. not sure if you guys have any experience with these speakers. posssibly below your refined tastes!!!

As I pointed out, you don't have to have a 12 or 15 inch speaker to get deep bass.

I actually don't use a sub, these speakers don't need one. Four 10 inch equals two 15 inch, but I have four voice coils instead of two and less dynamic compression. I have still captured the LFE for movies. You have to be careful with these speakers not to demolish the room, because they could! Yes, they are refined, but deliver all the goods when required.

http://mdcarter.smugmug.com/gallery/2424008_RKGvb#127077096

 

[mike c]

As I pointed out, you don't have to have a 12 or 15 inch speaker to get deep bass.

are you talking about one on one: say 10" vs. 15"
or are you talking about triple 10"ers vs. a single 15"er?

 

[TLS Guy]

are you talking about one on one: say 10" vs. 15"
or are you talking about triple 10"ers vs. a single 15"er?

In terms of depth the answer is that the F3 point is not related to driver diameter. However to achieve equivalent spl you will likely need multiples unless you build a driver with very large xmax. In other words two 8s to get the spl of a 12 and two 10s to get the spl of a 15. However one 8 can have the same F3 as a 15. F3 is determined by Fs and compliance with correct loading. No where does the speaker diameter enter into the equation for the lowest note a speaker can produce. I have never been fond of 15 drivers and I will always opt to design for two 10 inch over one 15 inch.