[monte]

Is there any more talk about a 8 " subwoofer build? I have seen what rak 313 was building, so cool.Does Rythmic or GR have plans in the works?

[Danny Richie]

Is there any more talk about a 8 " subwoofer build? I have seen what rak 313 was building, so cool.Does Rythmic or GR have plans in the works?

I have the SW-08-16FR woofers available right now: http://gr-research.com/sw-12-08-1.aspx

They can be used in any infinite baffle or open baffle applications using H, W, or U frame types. I have not drawn up any cabinet plans as the application that they will be used in really needs to be part of the design from the beginning.

[corndog71]

It might not be a bad idea to have H, W, and U box plans available.  If anything it gives the DIY person a roadmap vs having to scour the forum for ideas.

[Danny Richie]

It might not be a bad idea to have H, W, and U box plans available.  If anything it gives the DIY person a roadmap vs having to scour the forum for ideas.

Adding it to my list...

[Roger A. Modjeski]

Hi,


I have made a few subs myself. I prefer closed box systems because it eliminates back wave cancellation. Would someone please explain to me why anyone would want an open baffle woofer where the back wave cancels so much that the excursion is out of this world to get any deep bass. Granted one can EQ the system to flatness but the excursion has to go up. What is the slope of the required EQ?

Question 2. How can an open baffle cause a pressure change in the room as that is what makes good bass in my opinion?

[monte]

I only ask about 8's because of waf and a 15 x14 room.I have a sunfire  jr in there now .How low can they get down to or how many would I need?

[gab]

Hi,


I have made a few subs myself. I prefer closed box systems because it eliminates back wave cancellation. Would someone please explain to me why anyone would want an open baffle woofer where the back wave cancels so much that the excursion is out of this world to get any deep bass. Granted one can EQ the system to flatness but the excursion has to go up. What is the slope of the required EQ?

Question 2. How can an open baffle cause a pressure change in the room as that is what makes good bass in my opinion?

Hi Roger. Some of the best technical info on OB bass is available here:

www.linkwitzlabs.com and

www.musicanddesign.com

Check out the excursion capabilities of the Seas driver that Linkwitz uses in his LX521 design!

gab

[ebag4]

Hi,


I have made a few subs myself. I prefer closed box systems because it eliminates back wave cancellation. Would someone please explain to me why anyone would want an open baffle woofer where the back wave cancels so much that the excursion is out of this world to get any deep bass. Granted one can EQ the system to flatness but the excursion has to go up. What is the slope of the required EQ?

Question 2. How can an open baffle cause a pressure change in the room as that is what makes good bass in my opinion?

Hi Roger,
I don't know the technical reasons it all works, but if you haven't heard a good OB bass system you owe it to yourself to seek one out for a listen.  I have the GR Research 12" servo pairs per channel and it is the best bass I have ever heard.  For comparison I also have an excellent 4x15" infinite baffle bass in my HT system (driven by 2400 watts), but I like the OB  bass in my 2 channel system better.  The total lack of boom along with the clean articulate bass of the servo system makes me smile every time I listen.

Best,
Ed

[Early B.]

Hi,


I have made a few subs myself. I prefer closed box systems because it eliminates back wave cancellation. Would someone please explain to me why anyone would want an open baffle woofer where the back wave cancels so much that the excursion is out of this world to get any deep bass. Granted one can EQ the system to flatness but the excursion has to go up. What is the slope of the required EQ?

Question 2. How can an open baffle cause a pressure change in the room as that is what makes good bass in my opinion?

There are plenty of people who can give you a technical response, but I'll offer a simple one -- with any box sub, the bass will sound like it's in a box, whereas a properly designed OB sub will sound open, just like in reality.

Oh, and my OB servo sub pressurizes my 13' x 20' room better than any box sub I've ever owned. That's what makes it sound so good.

[AKLegal]

I built two H-frames for the 8 inch subs.  I just scaled down the plans for the 12 inch sub H-frame. 

[Guy 13]

Hi Roger.
I have H frame OB sub woofer with two 12" woofers on each channel
and they sound great.
I also have the same, but with two 12" GR Research servo drivers,
also in OB frame, they also sound great, different, but very good.
I also did a U frame variation of Danny's 12" servo drivers
and it also sounded great, they look terrible and crocked,
but sound was good.
I also own two F12G sealed servo woofers
and they are gattering dust.
I do prefer the Open Baffle configuration,
even if they need more room to do their job.
The sound is like other AC members wrote.
If you have already some 8, 10, 12 or even 15" woofers,
try the U frame configuration with two drivers on each channel,
it's easy and cheap to built.
I did it myself, me with my two hands full of tumbs.

Guy 13

[mlundy57]

What dimensions would you use for the baffles of a three driver W frame with the 8" servo drivers?

Mike

[Roger A. Modjeski]

Hi Roger. Some of the best technical info on OB bass is available here:

www.linkwitzlabs.com and

www.musicanddesign.com

Check out the excursion capabilities of the Seas driver that Linkwitz uses in his LX521 design!

gab

I went to both sites for a quick look. Could you please give me some links to specific articles about EQ, Response, etc. The Linkwitz site has so many topics. All I see there are links to ads. Where is that driver you want me to look at?

I want to get a quick feel for what is going on. The acoustical physics do not look good for an open baffle but the listeners like them. Let's see what is going on.

Anyone giving this some thought will see that you cannot change the pressure in the room with an open baffle. I am not saying you cannot create a wave to some extent. I want to see what is required.

I spend a lot of time on my Music Reference site explaining things to people about amplifiers which are my specialty. I would like to have someone in this camp educate me. Here is my school.   http://www.audiocircle.com/index.php?board=124.0

[Danny Richie]

Roger,

The H frame is typically 13 to 14 inches deep. So it does separate the front wave from the back wave quite a bit and does load the drivers.

Still there is a low end roll off associated with any OB driver set just like there is for a sealed box. However, the servo system is a different story. It works to maintain a linear response down to the extension filter that you choose. So there is no roll off like a typical woofer.

With the servo system there is also a minimizing of overshoot of the woofer. Mass of the cone in motion has an inertia that that wants to continue on. With a typical woofer only the suspension brings it back to center. So there is some overshoot of the cone movement that is not under power. With the servo system the woofer is electrically stopped preventing the overshoot. So the whole stroke is under power. This allows for greater SPL, control and accuracy.

And I have in room response measurements in a pretty good sized room showing pretty serious SPL levels. One day during some testing I played some music with low note hits to it and in in my room (pretty good sized) I was hitting 113db peaks at 25Hz with a pair of Super-V's.

[gab]

I went to both sites for a quick look. Could you please give me some links to specific articles about EQ, Response, etc. The Linkwitz site has so many topics. All I see there are links to ads. Where is that driver you want me to look at?

Roger - I would start here: http://www.linkwitzlab.com/frontiers.htm

The driver he uses in the LX521 (his reference speaker) is this one (2 per side):

http://www.seas.no/index.php?option=com_content&view=article&id=398:d1004-04-l26ro4y&catid=94:design-by-seas-woofers&Itemid=506

gab

[geowak]

Hi Roger.
I have H frame OB sub woofer with two 12" woofers on each channel
and they sound great.
I also have the same, but with two 12" GR Research servo drivers,
also in OB frame, they also sound great, different, but very good.
I also did a U frame variation of Danny's 12" servo drivers
and it also sounded great, they look terrible and crocked,
but sound was good.
I also own two F12G sealed servo woofers
and they are gattering dust.
I do prefer the Open Baffle configuration,
even if they need more room to do their job.
The sound is like other AC members wrote.
If you have already some 8, 10, 12 or even 15" woofers,
try the U frame configuration with two drivers on each channel,
it's easy and cheap to built.
I did it myself, me with my two hands full of tumbs.

Guy 13

Guy
Interesting comments on the OB implementation of woofers. Also the fact that you have two F12Gs gathering dust, when many others are raving about the benefits of sealed boxes when using subs!! I have seen your setup... cool stuff.

[Roger A. Modjeski]

Roger - I would start here: http://www.linkwitzlab.com/frontiers.htm

The driver he uses in the LX521 (his reference speaker) is this one (2 per side):

http://www.seas.no/index.php?option=com_content&view=article&id=398:d1004-04-l26ro4y&catid=94:design-by-seas-woofers&Itemid=506

gab

Thanks very much for a great link. It really helps when someone who has searched the topic can give a direct link to what he liked. Otherwise the new person (me) has to dig around too much.

I glanced throught it. Typicall Linkwitz, a lot of math, but he writes well and knows his stuff. I especially like his last comment on this link.

What you hear is not the air pressure variation in itself
but what has drawn your attention
in the two streams of superimposed air pressure variations at your eardrums

This explains why a OB woofer sounds so different than a closed box as the closed box is making a pressure variation in the room.

Has anyone tried combining two systems, OB and a good (not boomy) closed box? At very low frequencies the baffel has to be very large to prevent the wash around but a closed box could take over there. He even states

The observed audible difference between monopole and dipole for bass below fs is:

Less boom and droning of specific notes with a dipole,
A higher degree of articulation and resolution of complex musical bass lines,
A sense of air, spaciousness, and very natural reproduction of acoustic bass,
Less physical impact,
Less absolute bottom foundation below the lowest room mode frequency.

As I read it the first 3 are virtues of the monopole and the last 2 are its weakness which could be improved by a closed box.

I did construct a electrostatic OB woofer. It was 4 x 4 feet of diaphragm. It did have an interesting character though could not go as low as my closed box. This is something I hope to explore when I get the school running in Berkeley. It would be a great project for a student. Anyone interested? The link to the school is here.  http://www.audiocircle.com/index.php?topic=125987.0

[Danny Richie]

Less physical impact,
Less absolute bottom foundation below the lowest room mode frequency.

As I read it the first 3 are virtues of the monopole and the last 2 are its weakness which could be improved by a closed box.

Only true for uncontrolled OB subs. The servo controlled OB subs maintain physical impact and play as low as the sealed box versions.

I have a room that is 23 feet by 17 feet and with 9 foot ceilings. It is also open to another room in the back end with a very wide opening. So there is a lot of air space. I had a pair of Super-V's set up in the listening position. I wired them to my Clio measuring system and started sending them narrow bean test tones. See below.



As frequency increases you start loosing the ability to accurate measure a mono signal from a pair of speakers. When the wavelengths get shorter they start cancelling each other out and won't give you real numbers.

I also did some time frame captures during some music playback with low bass notes and was seeing peaks in the 113 to 115db range. Here is one of them.



I am sure I could hits some higher numbers but saw no need to push them any harder.

Again, the OB servo subs will play flat to 20Hz and -3db in the teens with no problem.

[bdp24]

     Hi Roger. Do you recall the British (or is it German?) company Gradient? In the '80's they made an OB sub specifically for the Quad 63 speaker. It was similar to Danny's GR Research OB sub, with two 12" woofers facing in opposing directions---180 degrees apart---in an H-frame (which also served as a stand for the 63), but of course did not have the advantage of the Rythmik Servo-Feedback controlled system and amplifier (closed-loop). They were very popular with 63 owners, who had been dis-satisfied with all other 63-sub combinations they had tried. The listeners who most prefer OB subs are owners of any and all Dipole speakers (Quad, Soundlab, Magneplanar, Eminent Technology), speakers notorious for being hard to integrate a subwoofer with. One reason for that, it has been argued, is the completely different radiation characteristics of dipole speakers (figure-of-eight) and monopole woofers (their relative SPL fall-off rates diverge as the listening distance and frequency changes. The balance between speaker and sub can be correctly balanced at only one listening distance and frequency). I haven't yet heard your ESL's and subs, but I'm sure that was a design consideration and objective. The GR Research/Rythmik Servo OB Sub system is currently the one preferred by discriminating Dipole users everywhere! There are still old-timers who swear by the Magneplanar Tympani T-IV bass panels as woofers for their dipole speakers. I hedged my bet and have both. Actually, I have all three---Tympani T-IV bass panels, GR Research/Rythmik Servo OB subs, and the sealed box version of the Servo subs. I don't have them all set up and running in the same room, but I'm working on getting a bigger room! I will be comparing the T-IV panels against the OB's, and trying the sealed subs at perhaps 40Hz down with both. We shall see. This is with both Quad 57's (single or stacked) and ET LFT-8b's. I've been working towards this system my whole adult life!
     By the way, everyone---I am using Roger's fantastic Music Reference RM-200 MK.II amplifier to power my speakers. You should all try to hear one.

[monte]

After reading and looking at a ton of pictures, I am not thinking about 8's. The 12's in a h or w frame is what I am after, what do you think?