When do you need to go below 40hz

medium jim · « **Reply #41 on:** 15 Jun 2012, 09:14 pm »

Dear Opnly Bafld:

I respectfully hope they do use it as a point of reference!

Jim

opnly bafld · « **Reply #42 on:** 15 Jun 2012, 09:19 pm »

medium jim · « **Reply #43 on:** 15 Jun 2012, 09:21 pm »

OB:

Is it wrong? Please enlighten all of us?

Point of clarification, I'm not talking about the physical size so much as the amount of energy created.

Jim

opnly bafld · « **Reply #44 on:** 15 Jun 2012, 09:24 pm »

srb · « **Reply #45 on:** 15 Jun 2012, 09:28 pm »

It's too simplistic and generalized.

The effective circular cone areas need to be computed and compared and this will differ quite a bit depending on the widths of the mounting flange and the surround. When you then factor in motor strength, voice coil current capacity and XMAX excursion, its possible to find 2 x 8" drivers that can produce greater output than 1 x 12" driver, just as its possible to find 1 x 12" driver that can better the output of 4 x 8" drivers.

Steve

medium jim · « **Reply #46 on:** 15 Jun 2012, 09:34 pm »

srb:

Correct, I'm generalizing. Different speaker designs do vary greatly, not to mention their efficiency. I still feel that when choosing subs, it is a good reference tool.

Jim

opnly bafld · « **Reply #47 on:** 15 Jun 2012, 09:35 pm »

*Scotty* · « **Reply #48 on:** 15 Jun 2012, 09:39 pm »

If you go to the Madisound website and look at the cone area of 8in.,10in.,12in.and 15in.
woofers you will find that a rough rule of thumb has two 8in. woofers approximately equal to one 12in.
The numbers don't work out neatly. The average 8in. has about 235 sq. cm. of area,the 10in. 350sq.cm.,the 12in. at 500sq.cm. and the 15in. has 850 sq.cm. of area.
I have had good luck using the two 8in. for one 12in. and two 12in. for one 15in. for a working approximation. I have never had an occasion to deal with 8in.vs 10in.vs 12in.
I use these approximations for guesstimating the air-coupling efficiency between woofers in a room. This rough approximation has proven quite useful to me. YMMV
Scotty

medium jim · « **Reply #49 on:** 15 Jun 2012, 09:45 pm »

OB:

You do understand what a reference point is? I'm in agreement with srb as well. Sorry, I don't see it as a case of apples vs apples.

I did think your jethro math comment was funny though and wished you left it intact.

Jim

medium jim · « **Reply #50 on:** 15 Jun 2012, 11:07 pm »

Scotty:

I agree in principle with your read on it if only the math side of it. I should have initially noted my reference was to how they created energy. Do two 8" subs equal the energy of one 12" or one 10"? Does two 10" subs equal one 15" or one 12"?

As srb noted, there are too many variables to neatly fit it into a nice package as I attempted to.

Jim

opnly bafld · « **Reply #51 on:** 15 Jun 2012, 11:36 pm »

*Scotty* · « **Reply #52 on:** 16 Jun 2012, 12:12 am »

The four 8s might be the equivalent of a 16in. if the volumetric displacement of air is also the same, but only if the 8s are all in the same location or enclosure. If they are spread about the room they will couple to the air as single 8in. woofers, when they share the same baffle they gain efficiency due to the fact that they are sharing a mutual air-load and radiating into the same space.
Scotty

medium jim · « **Reply #53 on:** 16 Jun 2012, 12:24 am »

OB:

Sorry if you felt my question was condensending, wasn't my intent.

Again, Scotty understands what I'm referring to i.e., how subs interact in a room, or fill the room with energy.

I'm sorry that I hit a nerve with you and hopefully we can move on and get the thread back to the subject line.

Jim

opnly bafld · « **Reply #54 on:** 16 Jun 2012, 12:26 am »

fredgarvin · « **Reply #55 on:** 16 Jun 2012, 12:27 am »

Quote from: opnly bafld on 15 Jun 2012, 11:36 pm

Sure if you compare an overbuilt $$$ 12" with a 1000 watts to 4 $30 cheapo 8" drivers with 100 watts between them SRB has a point (apples to oranges), but if you compare drivers with similar build quality and amount of wattage the 4 ~ 8"s will destroy the single 12", in other words apples to apples.

So if say we use drivers from the same manufacturers line two 8" = @ 11" ~ four 8" = @ 16"

As far as your condescending question as to whether I understand what a reference point is, I do and I think your example is seriously flawed based on my experience of having a friend that owned a car stereo shop (with a staggering number of trophies) where he built and measured hundreds and hundreds of sub boxes using all sizes and multiples of drivers. Of course my home audio experience tells me the same.

Maybe your friend could chime in, since you can't support your statement.

opnly bafld · « **Reply #56 on:** 16 Jun 2012, 12:27 am »

opnly bafld · « **Reply #57 on:** 16 Jun 2012, 12:29 am »

fredgarvin · « **Reply #58 on:** 16 Jun 2012, 12:33 am »

Me, I want it solid at least to 30hz. In my near-field desk system I let that slide, but in my main system if I don't have that available I get underfill with a sub. I want to feel it as well as hear it. I don't seem to have a room mode problem until about 15ft. from the source, where it gets boomy. I listen at about 8 to 10' generally. I am thinking of a second sub, for experimentation as much as anything. I'm getting down to about 28hz at this point.

opnly bafld · « **Reply #59 on:** 16 Jun 2012, 12:43 am »

Quote from: fredgarvin on 16 Jun 2012, 12:33 am

Me, I want it solid at least to 30hz.

That is my sweet spot also in my main system in the larger room, in my smaller room it all depends on what I'm listening to and my mood.