Dual Opposed AV15H Subwoofer Build - Page 22 - AVS Forum
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post #631 of 802 Old 09-22-2010, 11:35 AM
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Originally Posted by penngray View Post

Thanks Scientist,

With that POV then a driver near a wall has the same effect as a driver near the floor, no?? That was the point Im trying to make with Bosso who posted there are advantages to having a up/down vs back/front.

I have always thought the subwoofer driver facing the wall does not have any reflection issues since the wavething is so large to start with. Well, there is boundary gain but I can not see how there is any increased cancellation issues. The room itself is going to have several cancellation issues already from any single sub setup. Hence multiple subs are always needed to smooth the response. That goes back to the dual sub or two sub appoarch and I would choose two subs if I can.

Except if they are top and bottom vs front and back, the distance to the LP would equal. Front to back they are unequal.

Quite true though that there are probably other room modes to be concerned with more than this.

I want to build my first sub, but I'm starting to think it's more complicated than building main speakers
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post #632 of 802 Old 09-22-2010, 11:35 AM
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Originally Posted by penngray View Post

Bosso, doesnt the floor interact similar to how the near wall interacts with the one driver?

Yes. In fact, the floor always has a parallel surface... the ceiling (except in the case of a vaulted or cathedral ceiling).

That fact is what led me to the stacking system. A typical 8' to 9' ceiling height will cause a problem from 60-70Hz.

With an up/down firing dual opposed sub, the upper driver lessens the floor to ceiling problem as the sub creates a single point source. When subs are stacked, the single point source becomes larger, presenting a different center point.

The monolith subwoofer (stacked modules) will create a virtual floor and ceiling height that's much farther apart than the actual ceiling to floor distance, eliminating the crossover region mountain/valley response.

That's the theory anyway... the results of testing that theory in my room will be posted in the Raven thread when all results are concluded.

The cool thing about the stackable system is that you can place one module, measure, stack a second, measure, stack another, measure and stack a fourth and measure, instantly comparing the 4 measurements to see what happens.

Bosso
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post #633 of 802 Old 09-22-2010, 11:40 AM
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By the way PBC, I think think this is great build you're doing here. I'm enjoying learning from it. Thank you for posting all about it. I don't mean to be negative, just trying to learn this new thing to me.
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post #634 of 802 Old 09-22-2010, 12:22 PM
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Originally Posted by tuxedocivic View Post

Except if they are top and bottom vs front and back, the distance to the LP would equal. Front to back they are unequal.

Quite true though that there are probably other room modes to be concerned with more than this.

I want to build my first sub, but I'm starting to think it's more complicated than building main speakers

yeah, I just do not see this issue on its own being important overall. Multiple sub environments are seldom equal distance to the LP either and the overall response is pretty smooth.

PBC can always place the sub with the drivers firing out the sides so that they are equal distance to LP, if he notices a difference (notice cancellations) then great. Again, This is all about large wavelengths and these possible small issues are just not audible enough to matter. I know a null exists in my room @ 47Hz but I can not hear the difference although I will spend $500 in having another sub just to fix the meaurement

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post #635 of 802 Old 09-22-2010, 08:56 PM
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Originally Posted by penngray View Post

yeah, I just do not see this issue on its own being important overall. Multiple sub environments are seldom equal distance to the LP either and the overall response is pretty smooth.

PBC can always place the sub with the drivers firing out the sides so that they are equal distance to LP, if he notices a difference (notice cancellations) then great. Again, This is all about large wavelengths and these possible small issues are just not audible enough to matter. I know a null exists in my room @ 47Hz but I can not hear the difference although I will spend $500 in having another sub just to fix the meaurement

There's enough theory and actual data to infer that it does make a difference. First, the out-of-phase sub definitely had some output, as dipole theory predicts. Secondly, the now in-phase sub has some cancellations at higher frequencies, just as dipole theory says it should.

If this issue were truly unimportant, then dipole subs shouldn't work at all, since they have both in-phase and out-of-phase output typically meeting in a couple feet... Linkwitz has tons of theory and measurement on this.

Unfortunately, PBC has stated he can't turn the subs sideways, prolly because they'd be too wide that way, but delaying the front drivers would kinda make up for it similarly.
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post #636 of 802 Old 09-23-2010, 04:26 AM - Thread Starter
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Originally Posted by tlag View Post

Unfortunately, PBC has stated he can't turn the subs sideways, prolly because they'd be too wide that way, but delaying the front drivers would kinda make up for it similarly.

True, but I guess I could for the sake of some measurements/theory. Just can't leave them in that position.

You've mentioned "delaying the front drivers" a couple times. But I'm still confused. How would I delay only the front drivers in this design?

 

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post #637 of 802 Old 09-23-2010, 06:00 AM
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Quote:
Originally Posted by tlag View Post

There's enough theory and actual data to infer that it does make a difference. First, the out-of-phase sub definitely had some output, as dipole theory predicts. Secondly, the now in-phase sub has some cancellations at higher frequencies, just as dipole theory says it should.

If this issue were truly unimportant, then dipole subs shouldn't work at all, since they have both in-phase and out-of-phase output typically meeting in a couple feet... Linkwitz has tons of theory and measurement on this.

Unfortunately, PBC has stated he can't turn the subs sideways, prolly because they'd be too wide that way, but delaying the front drivers would kinda make up for it similarly.


As I posted before, Im 100% agreeing with the data showing maybe some issues, no more then room issues though so fix the room and do not worry about the sub driver facing the wall. Im completely betting against any real listening differences if the test was done under controlled conditions.

Linkwitz dipole data isnt important here.

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post #638 of 802 Old 09-23-2010, 07:53 AM
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Im with penngray on this one. I think its a non issue.

Bosso,
I don't see up/ down firing doing anything different other than switching the driver distances from the front wall and back wall, or the 2 side walls to the floor and ceiling instead. Should be a wash basically. Unless the reflection from the wall you are facing is stronger than the others. Is that the case? If so you could just turn the sub sideways and fire into the side wall instead. Anyway you go about it there will be a difference in distance to one of the three main corner boundaries or another. I don't see what the big difference would be between any of the 3 other than the shorter distance typically between the floor and ceiling? Seems like the better solution is the 45 degree firing angle like in the pic you posted. That arrangement has the drivers equal distance from the floor and ceiling, the corner and are equally spaced relative to their own wall and each others wall. The difference in distance would come from the other boundaries on the opposite side of the room and should have less effect. I just don't think this is a big worry on the radar. I would love to see some actual investigation data on it though.

All of this talk of delaying the front drivers is pointless imho. Not to mention that it won't work with his enclosures. Any time that you get that far into time alignment tweaking its gone off of the deep end a bit. You can only ever match things perfectly at one point in space. As soon as you move anywhere else in room your careful tweaking of that would degrade. I guess if your the sort of person who sits in the same exact sweet spot everytime and is alone then it might be worth the effort.
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post #639 of 802 Old 09-23-2010, 09:00 AM
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Quote:
Originally Posted by Ricci View Post

Im with penngray on this one. I think its a non issue.

Bosso,
I don't see up/ down firing doing anything different other than switching the driver distances from the front wall and back wall, or the 2 side walls to the floor and ceiling instead. Should be a wash basically. Unless the reflection from the wall you are facing is stronger than the others. Is that the case? If so you could just turn the sub sideways and fire into the side wall instead. Anyway you go about it there will be a difference in distance to one of the three main corner boundaries or another. I don't see what the big difference would be between any of the 3 other than the shorter distance typically between the floor and ceiling? Seems like the better solution is the 45 degree firing angle like in the pic you posted. That arrangement has the drivers equal distance from the floor and ceiling, the corner and are equally spaced relative to their own wall and each others wall. The difference in distance would come from the other boundaries on the opposite side of the room and should have less effect. I just don't think this is a big worry on the radar. I would love to see some actual investigation data on it though.

All of this talk of delaying the front drivers is pointless imho. Not to mention that it won't work with his enclosures. Any time that you get that far into time alignment tweaking its gone off of the deep end a bit. You can only ever match things perfectly at one point in space. As soon as you move anywhere else in room your careful tweaking of that would degrade. I guess if your the sort of person who sits in the same exact sweet spot everytime and is alone then it might be worth the effort.



This is a subject that I've not only given a lot of thought, I've done the placement/measurements thing hundreds of times. If there were no merit to it, I probably would not be mentioning it this far into my experiences.

The bottom line should be results. Mine are pretty good, averaged over all LPs. I try to pass along the reasons for my good results to save others the headaches I went through.

In the sense that what others choose to do has no effect on my results, yes, Penn is correct, it's a non issue.

Bosso
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post #640 of 802 Old 09-23-2010, 10:26 AM
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Originally Posted by bossobass View Post


I try to pass along the reasons for my good results to save others the headaches I went through.

Bosso

Thanks

I think all room modes are equally important. If it can be avoided, it should be. For PCB maybe this is the only option. For me when I get around to my first build, I'll be looking to remove any added headaches.
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post #641 of 802 Old 09-23-2010, 10:39 AM - Thread Starter
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Quote:
Originally Posted by Ricci View Post

All of this talk of delaying the front drivers is pointless imho. Not to mention that it won't work with his enclosures. Any time that you get that far into time alignment tweaking its gone off of the deep end a bit. You can only ever match things perfectly at one point in space. As soon as you move anywhere else in room your careful tweaking of that would degrade. I guess if your the sort of person who sits in the same exact sweet spot everytime and is alone then it might be worth the effort.

I'm not even sure how one would go about delaying the front drivers vs the back?

If I get time tomorrow, I'll move the driver positions (point them side to side vs back to front) and measure the un-EQ'd FR. I can't leave them like that, but it'll be interesting to see how the FR changes.

 

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post #642 of 802 Old 09-23-2010, 10:46 AM
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I'm not even sure how one would go about delaying the front drivers vs the back?

.

If you had separate amps with phase adjustment I think you could.
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post #643 of 802 Old 09-23-2010, 10:54 AM
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Quote:
Originally Posted by tuxedocivic View Post

If you had separate amps with phase adjustment I think you could.

We tend to use a DSP like the DCX or similar to control everything the sub does. The amps used in DIY tend to be very powerful pro audio amps no DSPs in them.

When he is fine tuning his setup each driver can be controlled by a channel on the DCX and he can change phase all he wants then and its still a moot point where the driver is pointing.

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post #644 of 802 Old 09-23-2010, 11:22 AM
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Originally Posted by Ricci View Post

Seems like the better solution is the 45 degree firing angle like in the pic you posted. That arrangement has the drivers equal distance from the floor and ceiling, the corner and are equally spaced relative to their own wall and each others wall.

Don't think it will work here, but in general you might even be able to take that one step further: with the addition of a few carefully placed boards, I'd bet you could get a configuration where you had at least some approximation to horn loading?

This makes me want to do a hyperbolic horn with opposed drivers. Cabinet width would probably be too narrow to get any decent sized drivers directly opposed to each other, you'd likely have to do one above the other, swinging half the interior throat above the other half, but still might be pretty effective? However, I don't have any placement that would work in the current house (sigh)....
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post #645 of 802 Old 09-23-2010, 11:41 AM - Thread Starter
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Originally Posted by tuxedocivic View Post

If you had separate amps with phase adjustment I think you could.

I "assuming" he meant delay the front driver versus the back driver in each box, hence my confusion. I.e., that would mean, I think, that I would need a 4 separate phase/delay adjustments, 1 per driver.

If he simply means delay one sub differently from the other, I think I can do that. Although as I explained somewhere above, I don't know why, but using the phase adjustment on Output 1 made differences in the FR, but adjusting it in for the other Output (when I had two outputs from the DCX that is) made zero difference. As if the phase adjustment wasn't doing anything at all for the second sub. Odd, as every other control seemed to change each sub separately (PEQs, gains, etc), but not phase.

 

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post #646 of 802 Old 09-23-2010, 11:42 AM
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Quote:
Originally Posted by penngray View Post

We tend to use a DSP like the DCX or similar to control everything the sub does. The amps used in DIY tend to be very powerful pro audio amps no DSPs in them.

When he is fine tuning his setup each driver can be controlled by a channel on the DCX and he can change phase all he wants then and its still a moot point where the driver is pointing.

We're talking about 2 different things here.

Phase adjustment has no bearing on reflections.

Bosso
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post #647 of 802 Old 09-23-2010, 11:51 AM
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Originally Posted by bossobass View Post

Phase adjustment has no bearing on reflections.

Sure it could; reflection could make the effective path length longer, putting the signal from a driver being reflected out of phase from one that is not reflected...
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Sure it could; reflection could make the effective path length longer, putting the signal from a driver being reflected out of phase from one that is not reflected...

I'm not talking about time alignment of waves from separate point sources.

The reflection of a wave is either constructive or destructive unto itself. Phase adjustment will not change that fact, only the drivers orientation to the reflective surfaces will.

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post #649 of 802 Old 09-23-2010, 11:59 AM
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Originally Posted by bossobass View Post

I'm not talking about time alignment of waves from separate point sources.

The reflection of a wave is either constructive or destructive unto itself. Phase adjustment will not change that fact, only the drivers orientation to the reflective surfaces will.

Fair enough, but for bass frequencies the reflection WRT to the individual driver should be negligible (certainly true as long as you're dealing with lengths smaller than the smallest reproduced wavelength) compared to the difference in path lengths for the two different drivers.... For the situation described in this thread the relative phase of the two drivers will be a bigger issue (although I have little idea how much so).
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post #650 of 802 Old 09-23-2010, 12:03 PM
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Originally Posted by bossobass View Post

We're talking about 2 different things here.

Phase adjustment has no bearing on reflections.

Bosso

Never said they did but we only have EQing and Phase adjustments.

Reflections change the arrival time of any sound wave, changing the phase can adjust arrival time of the sound wave. No?

The reflection stuff goes back to the original question about a sub reflecting off walls (your post with that cool picture).

This is where the "splitting hairs" stuff starts. debating words and phrases instead of looking at what the real world problem is and solving it with the tools avaliable and we only have EQing and phase adjustment.

When setting up a room with multiple subs no one is going to be debating anything about the length between the drivers in a dual driver subwoofer design. They are simply going to place that sub in room (knowing position compromises ) Then they are going to use the tools available to them to smooth out the in room response. If they have something like the DCX then they can play with the phase of each driver and EQ what they can until the room has a nice response curve.

The discussion gets off topic with fun theory, etc.

I would want to just know where is PBC at with enjoying his new dual sub.

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post #651 of 802 Old 09-23-2010, 12:05 PM - Thread Starter
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I'm too busy trying to get as flat a response as possible, then I'll start to try and enjoy them!

 

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post #652 of 802 Old 09-23-2010, 12:09 PM
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lmao, you might want to have more subs and room treatments before you attempt that.

Do not stress to much over it all

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post #653 of 802 Old 09-23-2010, 12:21 PM
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I'm too busy trying to get as flat a response as possible, then I'll start to try and enjoy them!

Make sure you enjoy how it sounds first instead of relying on graphs to base your enjoyment. I was really happy with the response I got at my LP but during listening tests it sucked and other seats gave me a headache with so much bass. It wasn't until I experimented with placement and phase using listening tests did I then go back and make corrections to the graph via EQ.

Speakers are a piece of cake to set-up for mids and highs, bass is the most difficult by far.

"Half the world is looking for Jesus, and the other half is looking for more bass..."
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post #654 of 802 Old 09-23-2010, 05:48 PM
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I was playing in the ripple tank running sims for other reasons and I decided to run pbc's sims as well.

Of course, this is not a conclusive exercise by any means. There is no ceiling in the tank and the waves are simple plane waves. Also, there is only the corner drawn and the reflections from opposing walls are taken out so that we can see only what effect the boundaries and placement have.

Standing waves from parallel walls (or floor to ceiling) are not of interest here. The next step would be to install walls roughly to scale with openings, etc., to approximate the actual room, which is actually quite informative, IMO.

The illustrations are self explanatory. One is the current placement, then turning the subs sideways, then stacking the subs in the corner in 3 variations:


I took the 2 best placements from above and increased the frequency:


Again, the ceiling to floor is the wild card, but the sims fairly follow my actual tests of various similar placements/stacking I've done in my room over the years regarding a corner and crossover region frequencies.

Ingvar Ohman wrote an article about sub placement that I read 8 years ago, as well as his paper on system Q preferences and both influenced me early on. I still reference some of his stuff now and again.

The main concern here is, despite the posts to the contrary, pbc has put a lot of fine effort and hard earned cash into a very good system and he is looking at a rather wide -12dB (with 1/6 octave smoothing) ditch through cross and has clocked -5dB less total SPL for several scenes than the Ultra gave,

I would certainly not see that as a trivial matter and the drop in output is certainly not optimal performance for his system. I've built and tested a very similar system and got much better results without post EQ and, IMO, all the heavy lifting and tweaking was well worth it.

Bosso
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post #655 of 802 Old 09-23-2010, 11:07 PM
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Bosso, what frequency are the waves in the tank sims? They look short compared to room dimensions and so might not be applicable to subs.
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post #656 of 802 Old 09-23-2010, 11:59 PM
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Quote:
Originally Posted by A9X-308 View Post

Bosso, what frequency are the waves in the tank sims? They look short compared to room dimensions and so might not be applicable to subs.

That applet does not allow for frequency to be pulled. It is just a slider.

It also doesn't allow for multiple creation points at different heights, so the stacked shots are just a single point source. In an actual room it would look similar to the others.

Here is a link to it. http://www.falstad.com/ripple/

The program isn't the best thing in the world to draw conclusions from. Case in point, add boarders, and then use a single point source near the corner. Draw in an enclosure, and try it out with the "driver" pointed at different directions in relations to the walls. Why does the output go down to nothing with the driver facing the corner at the lowest frequency setting? .
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post #657 of 802 Old 09-24-2010, 05:55 AM
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Bosso, that is very cool!! I would still question the audible difference but it still cool stuff

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post #658 of 802 Old 09-24-2010, 07:47 AM
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Yeah soho, that was the Java app I was thinking of, but couldn't remember the name of it.
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post #659 of 802 Old 09-24-2010, 01:25 PM
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I also don't believe any conclusion can be drawn from the simulation simply because the boundaries representing the floor and ceiling are absent.
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post #660 of 802 Old 09-24-2010, 02:25 PM - Thread Starter
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Well, reran some measurements. The 3808 I'm borrowing from my brother definitely has an issue with test tones. The subwoofer tone is about 5db too hot (confirmed this with my HD Basics DVE disc). In any event, ran Audyssey in a single position, then played with the Distance control on the AVR which fixed quite a bit.

Also likely explains the chuffing I was getting on the PB13, it was being well over driven (didn't think in my small room it would chuff).

Of course, I'll have to redo this once I move the AV15 that's sitting on top of the PB13 back to the floor.

Before adjusting distance:



After adjusting distance:


LL
LL

 

My DIY Subs ... http://www.avsforum.com/avs-vb/showthread.php?t=1233892

Quote:

J Dunlavy:.. if you stop to think about it, no loudspeaker can sound more accurate than it measures.

 

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