Author Topic: bass traps for corners  (Read 7013 times)

Offline Paul Spencer

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Re: bass traps for corners
« Reply #20 on: August 23, 2012, 10:14:51 PM »
T20 vs F20 ... F20 is a front loaded horn design with more chunky proportions, more volume and more efficient in material use, but its form factor makes it harder to hide. When made into that kind of size, it tends to be bandwidth limited like a tapped horn. Tapped horns are always bandwidth limited, but with a FLH you have a chance to get them to run over a wide bandwidth. Not that you need it here.

Now for a given size and extension, a tapped horn will tend to protect the driver from excursion to a lower point, but with no sealed cavity, you ideally need a rumble filter. T20 controls excursion to 20 Hz nicely. With F20, at 25 Hz the excursion jumps right up, but then reaches a point where the sealed rear air volume stops it going further. Still, excursion limits come in much sooner. So in terms of getting max SPL, the tapped horn wins. Both seem to occupy similar territory in terms of their sound. They are brutal, funky, tactile, forceful.

When I had them both in the same room, I didn't really compare them doing the same job. One was in the corner, the other plonked in the middle of the front wall. They are gigantic in any room, you can't really shift them easily. Although, I'm proud to say I managed to get my T20 from the workshop into the HT room on my own when I finished it at 11pm one night. Not bad when you consider it can't make it through the workshop door way without going on a very difficult angle, it's 2.35m tall!

The horns definitely have a different sound. If I could put it this way. Horns for rock, pop, bass heavy music and home theatre. Sealed for acoustic double bass and where you want accurate bass. But everyone should experience a bass horn with some time to spend with them, at least once. I will soon be using both, kind of a cake and eat it too setup.

tuyen

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Re: bass traps for corners
« Reply #21 on: August 24, 2012, 12:50:58 PM »
Hi Paul,

Any designs which uses just 1 bass driver?   Not really looking for crazy spls, as I listen to music at relatively low to medium volumes..

Also thoughts on stereo subs vs mono for my application (ie. <40hz)?


Offline Paul Spencer

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Re: bass traps for corners
« Reply #22 on: August 24, 2012, 01:08:45 PM »
F20 is originally meant for just one driver, I modified it for a pair of 10" woofers. Don't overlook the advantage of using two drivers dual opposed - they cancel vibration and you can pay less attention to the box if you are feeling lazy. If you don't want very high output then a pair of Peerless XLS drivers would probably do well in my T20, or even a pair of woofers.

Below 40 Hz - if you have two subs well it's not too difficult to make them stereo, but I wouldn't go out of my way to get it. It's not something I've tested carefully, but mostly I've had stereo bass all the way down, not due to any great conviction but just because it was no effort to get it. Now I'm moving towards mono below 40 Hz. The hearing mechanisms involved in stereo perception tend to break down at low frequencies. In the midrange and top end we easily pick image location due to the different time and intensity of the sound in each ear, as well as a few processing tricks in the system. When the wavelenths are longer than the dimensions of the room itself, the distance between each ear become pretty minor! Also the difference in intensity is less, becuase the wavelenths are so long the bass just wraps around your head with no acoustic shadowing. We count on things like harmonic distortion to locate the bass. Short answer - stereo sub bass won't hurt, go for it if convenient.


tuyen

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Re: bass traps for corners
« Reply #23 on: August 24, 2012, 01:45:25 PM »
Thanks heaps for the info Paul. 

Andrew (atilsey) said he is happy to build another tuba horn if I was interested..  will see what price he comes back with.. might just be easiest in my situation to go with something like that.     I'm not really into building/testing out different woofer cabinets..  not even sure how I would be able to bring the pieces of wood home from the shops, if I was keen to try!

Offline terry j

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Re: bass traps for corners
« Reply #24 on: August 24, 2012, 02:30:10 PM »
Corner loading includes floor and two walls, but if the mouth of the horn extends to the ceiling, then you are firing into an even more constrained space, I believe it's a step beyond corner loading. I'm not sure I can visualise what you are thinking ... top and bottom corners?

I prob misunderstood you. See if the following shows where I went off the rails.

A horn is completely bounded, either a real horn (circular) shape or simply four walls.

To go low means you gotta go big. You mentioned however the 'free' gain if rather than making the actual horn huge, instead we mount it in the room corner, and in effect the walls either side become the horn walls/boundaries. For those two sides we have not actually built the horn walls, rather we have the room walls serve that purpose.

Did I follow you correctly to this point?

Hence my question, I started from the idea that a horn has four boundaries, well at least fully bounded. Two walls either side are only two boundaries, what about the top and bottom? Hence my question about floor and ceiling, thinking that they are analogous to the two 'missing' boundaries.


Offline vitavoxdude

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Re: bass traps for corners
« Reply #25 on: August 24, 2012, 02:49:25 PM »
Hi Paul,

Any designs which uses just 1 bass driver?   Not really looking for crazy spls, as I listen to music at relatively low to medium volumes..

Also thoughts on stereo subs vs mono for my application (ie. <40hz)?


IMV 2 subs are always better than one as long as they do not upset the room too much.  2 subs = half the driver excursion = faster more realistic bass. ;D  Until you get down to beneath 18Hz you can still tell where the sound is coming from so unless a single is placed between the speakers then it will not sound quite right. :-X  If my deep bass drivers did not weigh so much I'd bring them round but 2 strong men do not cut it as they are >100Kg each with the built in amps. :'(
V
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Offline Paul Spencer

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Re: bass traps for corners
« Reply #26 on: September 11, 2012, 12:21:42 AM »
Corner loading includes floor and two walls, but if the mouth of the horn extends to the ceiling, then you are firing into an even more constrained space, I believe it's a step beyond corner loading. I'm not sure I can visualise what you are thinking ... top and bottom corners?

I prob misunderstood you. See if the following shows where I went off the rails.

A horn is completely bounded, either a real horn (circular) shape or simply four walls.

To go low means you gotta go big. You mentioned however the 'free' gain if rather than making the actual horn huge, instead we mount it in the room corner, and in effect the walls either side become the horn walls/boundaries. For those two sides we have not actually built the horn walls, rather we have the room walls serve that purpose.

Did I follow you correctly to this point?

Hence my question, I started from the idea that a horn has four boundaries, well at least fully bounded. Two walls either side are only two boundaries, what about the top and bottom? Hence my question about floor and ceiling, thinking that they are analogous to the two 'missing' boundaries.



In order to use the floor, ceiling and walls as boundaries, you need the horn mouth to equal the size of the front wall!

Let's take a step back. First, we have free space, a speaker radiating as it it would if suspended up in the air. Now we put it on the ground - half space. That is what we estimate with speaker modelling usually. Next step is quarter space, we add the rear wall. To get this with a horn, the mouth needs to be near the floor and rear wall. Often it is not even this constrained, with horns sticking out into the room so they see only half space loading. Such a horn has to be big!

The length of the horn is related to tuning, the size of the mouth is related to the loading (half space, etc). Each time you jump down to a more constrained "space" then you can halve the mouth size.

Next step is a corner, so we now add the side wall and we have 3 boundaries. We can realistically achieve this kind of loading by firing the mouth into the corner. The next step is to extend the mouth up to the ceiling, using modules most likely. We now have a more constrained loading, but I don't know what we would call it. One step further, and this is as far as we can go, is to make the entire front wall the mouth of the horn. In that case the entire room becomes a horn, and the listening position is now nearfield for the bass, as you are sitting in the mouth of the horn. You launch a plane wave into the room, and all room modes are gone with the exception of the depth mode, which would now be excited very strongly.

In your room Terry, what would be interesting is a double bass array, because you could actually make it work. Most rooms aren't big enough.

Offline terry j

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Re: bass traps for corners
« Reply #27 on: September 11, 2012, 03:18:19 PM »


In your room Terry, what would be interesting is a double bass array, because you could actually make it work. Most rooms aren't big enough.

cept for the 'crazy' orientation in the room. And that, after more than a few experiments, is non negotiable!

Offline kajak12

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Re: bass traps for corners
« Reply #28 on: September 11, 2012, 08:23:17 PM »


In your room Terry, what would be interesting is a double bass array, because you could actually make it work. Most rooms aren't big enough.

cept for the 'crazy' orientation in the room. And that, after more than a few experiments, is non negotiable!
how are you going tj????????????
still discovering the link between electronics and audio reproduction.so much to learn and so little time

Offline Paul Spencer

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Re: bass traps for corners
« Reply #29 on: September 12, 2012, 01:51:12 AM »


In your room Terry, what would be interesting is a double bass array, because you could actually make it work. Most rooms aren't big enough.

cept for the 'crazy' orientation in the room. And that, after more than a few experiments, is non negotiable!

Doesn't matter at all with a DBA, because you are creating a plane wave. Both plane wave arrays are time aligned, the rear one inverted in polarity to yield an anechoic response completely free from room interaction. You know the arrangement I'm talking about right?

Offline terry j

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Re: bass traps for corners
« Reply #30 on: September 12, 2012, 03:56:09 PM »

how are you going tj????????????

You talkin to me mario?? If so, thanks for the interest! We seem to have a funny relationship..'at each others throats' one minute, the next not so much :D

Cept for my bloody back when I blew it doing some jackhammering, pretty good thanks. Seein as how the bathurst bgtg is coming up soon, at least I can get my tweeter back into the system and ready. However, that also means man handling these speakers which weigh, dunno, 100+ kgs each? so with my back right now even that is iffy.

So just hobbling around the house atm.

You still up for that long promised visit when you're over this way? If not, things always get in the way, maybe we'll at least meet at the hi fi show depending on days etc.

Offline terry j

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Re: bass traps for corners
« Reply #31 on: September 12, 2012, 04:00:31 PM »


Doesn't matter at all with a DBA, because you are creating a plane wave. Both plane wave arrays are time aligned, the rear one inverted in polarity to yield an anechoic response completely free from room interaction. You know the arrangement I'm talking about right?

Sure, I know the arrangement. That big thread on avs I think it was.

Guess you're right when I think about it, as long as the two planar waves meet at the LP, and depending on xover point, the result should be the same.

Still, given the crazy layout and what walls the drivers could be mounted on it still seems problematic to me. Heh, we can look at it theoretically when I see you and the layout is before the both of us.

Still, I must confess to not feeling I have any great need for better or improved bass. Still, these things are always comparative so who knows ultimately..

Offline Paul Spencer

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Re: bass traps for corners
« Reply #32 on: September 12, 2012, 04:18:23 PM »
Terry, the real problem is pragmatic - mounting subs on the walls, especially with your 50m high ceiling. The real bummer about a DBA is that you use 8 subs but get the output of about 2. In other words, buy 6 more identical subs, and another power amp and you get an anechoic version of your current subs. The result could be "wow, the bass is even better" or it could be "ho hum, I wasted all that money and effort and it's no better." Someone is selling four on DTV, so you (almost) have the chance, someone on SNA is selling a single as well. But actually I know a driver you could get that is good value.

Offline terry j

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Re: bass traps for corners
« Reply #33 on: September 12, 2012, 05:52:15 PM »
Terry, the real problem is pragmatic - mounting subs on the walls, especially with your 50m high ceiling. The real bummer about a DBA is that you use 8 subs but get the output of about 2. In other words, buy 6 more identical subs, and another power amp and you get an anechoic version of your current subs. The result could be "wow, the bass is even better" or it could be "ho hum, I wasted all that money and effort and it's no better." Someone is selling four on DTV, so you (almost) have the chance, someone on SNA is selling a single as well. But actually I know a driver you could get that is good value.

yeah, that 50 m high ceiling is a bitch!  ;D You can change the light bulb for me next time.

Your other point is more valid, it's funny cause basically I never have to worry about WAF, as you may have noticed, yet there is no damned way I would ever touch the fabric of the house given what it is (and the work being put into it) so the mounting issue you raised, not ever having thought about it rules it out straight away. Even with my bass traps, I have to be wary of how I mount them as well as not going all the way up. no point in covering the cornice in the room seein as it is an architectural feature.

I take it you mean maelstroms on dtv? See, all I'd ever do is two more sealed subs, forget the DBA. Do I need two more subs with the amps required and how to control it? Nah.

well maybe nah :D

Offline kajak12

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Re: bass traps for corners
« Reply #34 on: September 12, 2012, 09:50:14 PM »

how are you going tj????????????

You talkin to me mario?? If so, thanks for the interest! We seem to have a funny relationship..'at each others throats' one minute, the next not so much :D

Cept for my bloody back when I blew it doing some jackhammering, pretty good thanks. Seein as how the bathurst bgtg is coming up soon, at least I can get my tweeter back into the system and ready. However, that also means man handling these speakers which weigh, dunno, 100+ kgs each? so with my back right now even that is iffy.

So just hobbling around the house atm.

You still up for that long promised visit when you're over this way? If not, things always get in the way, maybe we'll at least meet at the hi fi show depending on days etc.
I will be at steves in october,if i can get to your house i will
still discovering the link between electronics and audio reproduction.so much to learn and so little time

Offline terry j

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Re: bass traps for corners
« Reply #35 on: September 13, 2012, 08:15:19 AM »

I will be at steves in october,if i can get to your house i will

Well, as I have always said, you'd be welcome. It is about an hour or so away, maybe hour and a half or thereabouts. Still, TBH, you'd just be better off enjoying meeting your mates I'd guess. I'm still undecided if I'll bother going to the show, may as well I guess, so at least we can have a coffee if we go on the same day.

Or a beer!

Offline stevenvalve

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Re: bass traps for corners
« Reply #36 on: September 13, 2012, 02:33:18 PM »

I will be at steves in october,if i can get to your house i will

Well, as I have always said, you'd be welcome. It is about an hour or so away, maybe hour and a half or thereabouts. Still, TBH, you'd just be better off enjoying meeting your mates I'd guess. I'm still undecided if I'll bother going to the show, may as well I guess, so at least we can have a coffee if we go on the same day.

Or a beer!
Terry. You will meet fellow mountain audio heads, you can listen to their good mountain systems, then the show, it is important to come, make the time. The show will disappear new friends will not. There is a lot for everyone to learn.

Offline terry j

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Re: bass traps for corners
« Reply #37 on: September 13, 2012, 02:54:37 PM »
steven, again given our 'track' your response is more than gracious.

Ahh, the mountains, gotta love it. Went to school just up from you, lived a decade at lawson. Beautiful area, cept for the traffic nowadays I suspect!

Spose you're right about making the effort for the show, they'll prob disappear again..anyone know if last years was deemed a success? Seems a few missing this year, eg SGR. Earle I know is too busy and does not need more work, but woulda thought sgr would be there (unless I simply missed them on the list)

I presume lenehan will be there?? Another brand with a rep I'd like to have a listen to.

Another that intrigues me, those 80k two ways, name escapes me as I type, guru sells them, big wig name, as soon as I hit post I'll no doubt remember...anyways that much for a two way? Audio note is it?

Re the systems in the mountains, sounds like a good idea for a travelling circus! Must be a few there now worth a round trip visit. Bit like the open garden set up :D A smorgasboard if you will.

In any case, if I go I intend to do a bit of syd catch up with mates, so for me personally looking at sat with the mates on sun. Drive home yada yada. Not for a second did I think I'd put my hand up for your gtg, I doubt I fit that particular group profile audio wise, so no doubt would be an awkward guest in more ways than one.

BUT, a quick drop in to shake your hand for your magnanimousness and a quick meet and greet (if we don't cross at the show) does sound worthwhile.

tuyen

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Re: bass traps for corners
« Reply #38 on: November 16, 2012, 09:48:25 AM »
Been using a few wide band absorber panels for awhile now. Nice improvement overall. Just makes me want to turn the volume up.

The main ones that gave most benefit were the side panels to block first reflection points.



Page about the effects that I could understand:
http://www.facstaff.bucknell.edu/esantane/movies/Acoustic.html

Offline Paul Spencer

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Re: bass traps for corners
« Reply #39 on: November 16, 2012, 10:30:23 AM »
Treating first reflection points is slighly controversial. I hear generally that most people who try it like the result, however, there is some research indicating that it's not the thing to do, that as far as reflections are concerned, the ones off the side wall are the ones that add most to the sense of body. Floyd Toole is the champion of that viewpoint. So the question is, and it's one not easily answered for certain, 'why do you like it?' Is it because the first reflection points are doing harm? Or is it because those points are the places where your speakers are directing a more fullrange sound, hence panels there have the most effect in bringing down the reverb in general. If you put panels further off axis, then there isn't as much treble for example, so they will have less effect.

Here's my little theory. Unproven, just a bit of a hunch really. You want to have a certain amount of general absorption in a room to get the reverb time down to a certain range, so there is a nice balance of sound direct from the speakers mixed with sound from the room. If you can get your RT to measure flat across all frequencies, and somewhere around 0.3 - 0.4 seconds and then plenty of bass absorption, as indicated by the in-room decay plots, then you can have a pretty good canvas to paint with.