Ported vs OB 8" sub question

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mlundy57

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Ported vs OB 8" sub question
« on: 21 Oct 2014, 04:56 pm »
How would the performance of two OB H-frame subs, each with two 8" servo drivers and an HX300 amp (one for each channel), compare with one ported sub (both channels summed to a single input) with a single 8" non-servo driver and a 300W Amp that is -3@ 28Hz?

Mike

Early B.

Re: Ported vs OB 8" sub question
« Reply #1 on: 21 Oct 2014, 05:13 pm »
Apples and oranges. As you know, an OB servo sub has a completely different sound characteristic than any box sub, ported or not. A better question would be the performance difference between one OB servo sub vs. two of them.

Tyson

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Re: Ported vs OB 8" sub question
« Reply #2 on: 21 Oct 2014, 07:17 pm »
If you can avoid using a box for bass, then do it.  OB's are just an inherently better fit in a typical room than a box sub.  And that goes double if you have a "difficult" room. 

Folsom

Re: Ported vs OB 8" sub question
« Reply #3 on: 21 Oct 2014, 07:54 pm »
Danny's new speaker stand shows strengths of good OB implementation. He's taking advantage of cancellation techniques that don't work through box as far as I know; and understood it correctly.


mlundy57

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Re: Ported vs OB 8" sub question
« Reply #4 on: 21 Oct 2014, 07:59 pm »
What I'm trying to get a handle on is the difference in output. I realize a ported sub will play louder than an OB sub. {The single driver ported sub I am currently using has enough output to suit me for music in this room.} I'm wondering if having four drivers on two amps in an OB configuration will have the same output as one driver in a ported enclosure.

The reason is that I'm still up in the air about whether to use 8" or 12" drivers for the H-frames to go with the LGK Wedges. I understand that the 12's will outperform the 8's but I have space limitations to deal with. On the short wall, I do not have enough room to have the Wedges on stands plus two H-frames. The wedges have to sit on top of the H-frames and based on some recent posts it sounds like the Wedges will not perform well directly on top of the H-frames.

An H-frame with 12" drivers will put the center of the tweeter 1 1/2" - 2" above ear height if I don't have to put any isolation material between the Wedges and the H-Frame. If I do have to put isolation material between the two, the tweeter will end up 3"-5" above ear height. I assume this would not be a desirable position. With 8" drivers I would lose out on overall performance vs the 12's but the H-frames would be short enough that even with isolation material on top the tweeters would be at ear level. That way everything would fit in the available space and I wouldn't lose any of the Wedge's magic.

Another option would be to rearrange the room and place everything on the long wall. If I did this I would have the room for both stand mounted Wedges and H-frames with 12" drivers. However, what I have been reading about room acoustics says to never place the speakers on the long wall.

(short wall - Wedges 5ft apart, LP up to 10ft away / long wall - Wedges 7ft apart, LP 6-7ft away)

So my options boil down to:

on the short wall:
1) 12" drivers with Wedges on top with damping material in between - tweeter 3-5 inches above ear level

2) 8" drivers with wedges on top with damping material in between - tweeter at ear height  or

3) on long wall - Wedges on stands and H-frames with 12" drivers separate

The ideal situation, Wedges on stands, 12" H-frames separate, on the short wall, will not work in this room so I have to compromise somewhere. The issue is which compromise to make?

Mike

Tyson

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Re: Ported vs OB 8" sub question
« Reply #5 on: 21 Oct 2014, 08:03 pm »
I think the 8 inch is the way to go - they will play a bit higher and blend a bit more seamlessly since they are smaller than the 12 inch drivers.  Using 2 per speaker will give you more than enough output. 

Danny Richie

Re: Ported vs OB 8" sub question
« Reply #6 on: 21 Oct 2014, 10:56 pm »
I am going to be trying several of those configurations myself.

mlundy57

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Re: Ported vs OB 8" sub question
« Reply #7 on: 21 Oct 2014, 11:02 pm »
I am going to be trying several of those configurations myself.

Since I will probably only be able to afford to build one set, (either the 8's or the 12's) I'll try to be patient and see how your tests turn out.

Mike

Captainhemo

Re: Ported vs OB 8" sub question
« Reply #8 on: 22 Oct 2014, 12:42 am »
Mike,
What about the 12's in a "W" frame like you talked about  earlier  ?   That would shrten things up a bit.  My 12's in an H-frame are only 1.75" taller than Danny's new  stands/subs ( mine are 29.75" before  spikes  , that's with a  double layered top and bottom plate,  and if I had  offset the  middle braces,  it would shrink that by .75").

-jay

bdp24

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Re: Ported vs OB 8" sub question
« Reply #9 on: 22 Oct 2014, 01:25 am »
What I'm trying to get a handle on is the difference in output. I realize a ported sub will play louder than an OB sub. {The single driver ported sub I am currently using has enough output to suit me for music in this room.} I'm wondering if having four drivers on two amps in an OB configuration will have the same output as one driver in a ported enclosure.

The reason is that I'm still up in the air about whether to use 8" or 12" drivers for the H-frames to go with the LGK Wedges. I understand that the 12's will outperform the 8's but I have space limitations to deal with. On the short wall, I do not have enough room to have the Wedges on stands plus two H-frames. The wedges have to sit on top of the H-frames and based on some recent posts it sounds like the Wedges will not perform well directly on top of the H-frames.

An H-frame with 12" drivers will put the center of the tweeter 1 1/2" - 2" above ear height if I don't have to put any isolation material between the Wedges and the H-Frame. If I do have to put isolation material between the two, the tweeter will end up 3"-5" above ear height. I assume this would not be a desirable position. With 8" drivers I would lose out on overall performance vs the 12's but the H-frames would be short enough that even with isolation material on top the tweeters would be at ear level. That way everything would fit in the available space and I wouldn't lose any of the Wedge's magic.

Another option would be to rearrange the room and place everything on the long wall. If I did this I would have the room for both stand mounted Wedges and H-frames with 12" drivers. However, what I have been reading about room acoustics says to never place the speakers on the long wall.

(short wall - Wedges 5ft apart, LP up to 10ft away / long wall - Wedges 7ft apart, LP 6-7ft away)

So my options boil down to:

on the short wall:
1) 12" drivers with Wedges on top with damping material in between - tweeter 3-5 inches above ear level

2) 8" drivers with wedges on top with damping material in between - tweeter at ear height  or

3) on long wall - Wedges on stands and H-frames with 12" drivers separate

The ideal situation, Wedges on stands, 12" H-frames separate, on the short wall, will not work in this room so I have to compromise somewhere. The issue is which compromise to make?

Mike

Mike, you can raise the back of the wedges to make its tweeter point at your ears, rather than have it at ear level. As to the potential speaker locations your room affords, having them 5 ft apart and 10 feet from the LP is not enough separation of the speakers for them to image very well. I don't know where you read that the long wall is not good for putting speakers on---that's a gross over-simplification. I'll bet the speakers 7 ft apart on that wall and 7 ft from the LP will be the better option. Worth trying, anyway. The main reason for short wall placement is to get the speakers far enough away from the wall behind them. A way around that is to put the speakers on the long wall, and bring them out far enough that you can point them at the LP---the resulting angle of the enclosures will increase the effective distance the speakers are from the wall, relative to what it would be if the speakers weren't angled in as much. If that makes any sense! Then you can use absorption or diffraction on the wall behind the speakers, to take care of the delayed reflections. When I heard Michael Greens (Room Tune) set-up at CES years ago, he had the speakers much further apart than normal, and much closer to the LP. The resulting imaging was excellent.

mlundy57

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Re: Ported vs OB 8" sub question
« Reply #10 on: 22 Oct 2014, 01:44 am »
Mike,
What about the 12's in a "W" frame like you talked about  earlier  ?   That would shrten things up a bit.  My 12's in an H-frame are only 1.75" taller than Danny's new  stands/subs ( mine are 29.75" before  spikes  , that's with a  double layered top and bottom plate,  and if I had  offset the  middle braces,  it would shrink that by .75").

-jay

Jay,

29.75" before spikes would be at least 30.75 with spikes. Add 2" for isolation between the sub and the Wedge and the bottom of the Wedge would be at 32.75". The center of the tweeter is 11" up so that would make it 43.75".  Ear height at my listening position is 39". That makes the center of the tweeter 4.75" above ear height. I don't know how that translates into vertical degrees off axis but it is definitely not on axis.

I need 28" with spikes if I don't need to isolate the two pieces and 26" with spikes if I do need to isolate them which I'm pretty sure I do. There may be something shorter than 2" that would effectively isolate the two pieces. Then there would be a little more height to work with.

The W frame would work for height. It's 23.5" tall with a 3/4" top and bottom. A double layer top and bottom would make it 25" then 1" spikes would make the overall size 26". However, I recall some discussion about the W frame being inferior to the H frame in both strength and performance which is why I backed away from the W design.

Another factor is that the front subs won't have to reproduce the LFE channel for movies. There will be a sealed servo sub in the system for that.

Mike

mlundy57

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Re: Ported vs OB 8" sub question
« Reply #11 on: 22 Oct 2014, 02:06 am »
Mike

Mike, you can raise the back of the wedges to make its tweeter point at your ears, rather than have it at ear level. As to the potential speaker locations your room affords, having them 5 ft apart and 10 feet from the LP is not enough separation of the speakers for them to image very well. I don't know where you read that the long wall is not good for putting speakers on---that's a gross over-simplification. I'll bet the speakers 7 ft apart on that wall and 7 ft from the LP will be the better option. Worth trying, anyway. The main reason for short wall placement is to get the speakers far enough away from the wall behind them. A way around that is to put the speakers on the long wall, and bring them out far enough that you can point them at the LP---the resulting angle of the enclosures will increase the effective distance the speakers are from the wall, relative to what it would be if the speakers weren't angled in as much. If that makes any sense! Then you can use absorption or diffraction on the wall behind the speakers, to take care of the delayed reflections. When I heard Michael Greens (Room Tune) set-up at CES years ago, he had the speakers much further apart than normal, and much closer to the LP. The resulting imaging was excellent.

I got the information regarding the long wall from a tutorial on the website of one of the companies that does acoustical room treatments. I don't remember which one.

As for absorption behind the speakers, I thought the whole idea of open baffle was to have the sound waves reflect off the front wall and the timing of those reflections was why the speakers needed to be at least 3ft off the wall. It seems that if absorption was placed behind them it would defeat the purpose.

Narrow speaker placement is why I have never been able to get a good soundstage, until the Wedges. These things image like crazy even though they are only 5ft apart. I can try an experiment on the long wall. All it will take is a couple of 20ft pieces of speaker cable.

Mike

Danny Richie

Re: Ported vs OB 8" sub question
« Reply #12 on: 22 Oct 2014, 02:29 am »
Just an FYI deal.

I still have the huge line sources from Mockingbird Audio set up in my listening room.

http://mockingbirddistribution.com/mockingbird-audio-lsx-speaker-system/

So I played the little LGK's on stands setting well out into the room and about two feet out in front of and just to the insides of the big line sources. And I played the triple 12" woofers along with them. I had to turn the gain down several clicks but didn't change anything else.

Dang that was impressive.  :thumb:

Captainhemo

Re: Ported vs OB 8" sub question
« Reply #13 on: 22 Oct 2014, 02:30 am »
I think  part of the issue with using the long wall  is it usually   puts the LP right up against the  rear wall which is not  desireable.   You'd really be wanting to  diffuse/absorb there if you're up against it

Mike, my tweeters on the  OB7's are high  (40" before base & spikes !!) so close to the same #'s as you mention.  When I'm  in  my  computer chair (right behind  my  couch)   I'm pretty close to level.  when  I'm on the couch I'm definitely  too low  but the difference in sound is  slight, it's there but  not dramatic.  I've often considered  tilting them forward,   just  have never done it  , will have to try it one of these days.

-jay

bdp24

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Re: Ported vs OB 8" sub question
« Reply #14 on: 24 Oct 2014, 10:10 am »
I got the information regarding the long wall from a tutorial on the website of one of the companies that does acoustical room treatments. I don't remember which one.

As for absorption behind the speakers, I thought the whole idea of open baffle was to have the sound waves reflect off the front wall and the timing of those reflections was why the speakers needed to be at least 3ft off the wall. It seems that if absorption was placed behind them it would defeat the purpose.

Narrow speaker placement is why I have never been able to get a good soundstage, until the Wedges. These things image like crazy even though they are only 5ft apart. I can try an experiment on the long wall. All it will take is a couple of 20ft pieces of speaker cable.

Mike
Absorption WILL remove the rear ambience an OB speaker produces, so if you want the ambience you can instead use diffraction. That is accomplished by "breaking up" the rear output with diffusers on the wall behind the speakers. They are made by a few companies, originally RPG. They are somewhat expensive, so people started making their own (you can find DIY plans on the WWW). It is a frame about 2' wide X 4' tall X 6" deep, with different depth cavities. The idea is to scatter the rear wave of the speaker, so that is isn't reflected straight off the wall and sent back into the room delayed in time from the sound from the front of the speakers. Works great, and is a good option for speakers that have to be close to the wall behind them.

bdp24

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Re: Ported vs OB 8" sub question
« Reply #15 on: 24 Oct 2014, 10:32 am »
I think  part of the issue with using the long wall  is it usually   puts the LP right up against the  rear wall which is not  desireable.   You'd really be wanting to  diffuse/absorb there if you're up against it

Mike, my tweeters on the  OB7's are high  (40" before base & spikes !!) so close to the same #'s as you mention.  When I'm  in  my  computer chair (right behind  my  couch)   I'm pretty close to level.  when  I'm on the couch I'm definitely  too low  but the difference in sound is  slight, it's there but  not dramatic.  I've often considered  tilting them forward,   just  have never done it  , will have to try it one of these days.

-jay
Check out the review of the Focal Aria speakers in the November issue of Stereophile. In a sidebar, the reviewer (Robert Deutsch) discusses his listening room remodel, and the room is pictured. He has the Aria's on the long wall (his room is too narrow to place speakers on the width wall) and his listening chair right up against the wall behind it. It is rather surprising to see a professional reviewer with such a mediocre listening room! In a case like this, the wall behind the listening position HAS to have sound-absorbing material. The Aria's are set-up as I suggested, wide apart with fairly severe toe-in, to keep the rear wave (the speakers are sealed, but even they produce sound that bounces off the wall behind them) from coming right back at the listener.