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Author Topic: JTR releases new 2x18 Subwoofers - info here  (Read 7200 times)

Caleb Dueck

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #40 on: May 09, 2019, 08:43:16 am »

I think we donít we are necessarily making the correct distinctions.  Bass ďhornsĒ are for all intents and purposes a fallacy as regards what we use in pro audio.  True horns need extreme mouth areas to reproduce very low frequency, hence why horns stacked in multiples do improve extension.  The reality of all practical horns we use are that they are deriving their bass from the horn length, effectively making them a 1/4 wave design.  Tapped horns, scoops, rear loaded, front loaded are all only variants of the same physical phenomena.  True bass horns, as I understand, require a reasonably gentle expansion rate, therefore they would exhibit significant delay rendering them of no practical use for live systems.

True, "horn" is not a universal, defined term.  I was thinking specifically of the Danley DBH218 used in multiples, vs various other brands of ported subs. 

I prefer the sound of a sealed rear chamber front horn 😉 vs a tapped horn (TH118 in this case).  I'm biased slightly toward horns like the DBH218 vs tapped, but would need other non-tapped models to hear and compare.  IE a dual 15" folded horn to compare with TH115 and BC415, and ported like the TS215, and a folded 4x12 folded horn to compare with TH412 and BC414. 

Even if that were possible, it then highlights other differences.  IE, -3 cutoff frequency and how that changes the perceived tonal differences, and things like volume vs EQ on ported to make them sound "tighter" or more "sloppy". 

Ivan has a good point.  If we need X dB at 20Hz, and we are willing to EQ down the upper frequencies - we can calculate quantity and cubic volume of various sub models.  If I were sitting around bored I'd compare a few for fun.  Not counting power compression, and 4, or 5, or is it 6 dB SPL increase in the real world when doubling subs? 😉
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Roland Clarke

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #41 on: May 09, 2019, 10:03:02 am »

Obviously Ivanís point is totally correct, but in practical terms we are almost always looking at being able to get, within reason, as much spl in the 50-100 hz range.  In this respect, Danley and any other manufacturer are not so different when looking at live sound reinforcement.  It also has to be born in mind that with the exception of outdoor use, many bass speakers are going to be compromised in the small and medium spaces that a lot of music concerts happen in.  The BC series speakers Danley make look interesting in that they use 1/4 wave design to produce insane spl.  Sure they are large, but Iíve seen videos of gigs with thousands of people at where the bass end was being handled by just 2 cabs.

I canít comment on the TH 118 as Iíve never heard one in the flesh, however, I have a couple of tapped horns I built which are based on the xoc 1 th18 design, but with some modifications and these are v good.  There are some double 18Ē I personally quite like, the KS28, J sub, HP700, etc.  I should also make the point that there are also a whole lot of terrible designs out there, trying to be different, but just flying in the face of all the physics we know.
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Mark Wilkinson

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #42 on: May 09, 2019, 11:08:01 am »

Multiple bass horns do not provide as much "extension" as people would like to think that they do.

The short horns (the ones used in PA applications) are made that size to enable a practical size.

This can cause ripples in the response down on the bottom, because the horn is not providing enough loading to the driver.

What really happens when you use multiples is that that the larger mouth starts to fill in the ripples.  So the overall "low end response" may appear louder (because it is smoother), but it really doesn't get much lower.

YES, the lower freq will be louder, but so will the rest of the response (due to the additional cabinets), but the actual -3dB point will not change much.


I see what you're saying. 
I think I've been one of those who's sometimes let the less rippled, smoother response of multiple labhorns vs a single, turn in to the illusion of a deeper low corner.
But in my defense lol, it is pretty commonly accepted that low end extension occurs with multiple front loaded horns...I mean even your DBH218 main page says so..

I've read that the horn's high pass frequency lowers as horn length increases and with a shallower flare rare.
Is that correct ?, and do those become the the main reasons that putting more boxes together doesn't lower the corner so much ? ?
 
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Roland Clarke

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #43 on: May 09, 2019, 11:36:54 am »

I think that itís exactly that.  However, as the length increases you are effectively changing the 1/4 wave length which is what lowers the running.  My understanding is that to exhibit genuine horn characteristics the mouth of the horn would have to several metres wide and as the flare rate has to be gradual, many meters long, I suspect delay would be in terms of 30ms plus.  I think the directional nature of some of the Danley subs is particularly interesting when we are all having that discussion about directionality.
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Ivan Beaver

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #44 on: May 09, 2019, 12:14:35 pm »

I think that itís exactly that.  However, as the length increases you are effectively changing the 1/4 wave length which is what lowers the running.  My understanding is that to exhibit genuine horn characteristics the mouth of the horn would have to several metres wide and as the flare rate has to be gradual, many meters long, I suspect delay would be in terms of 30ms plus.  I think the directional nature of some of the Danley subs is particularly interesting when we are all having that discussion about directionality.
Multiple cabinets will not change the length of the horn.  It is the length of the horn that is the biggest determining factor of the low freq extension.

Long horns=lower freq.  Yes there are other factors as well.

What does change with multiple cabinets is the impedance or radiation resistance that occurs where the cabinet mouth meets the air.

This impedance will affect the overall freq response.

Most PA horns are made to short, in order to make them transportable, so there is not as smooth a transition to the air as we would like.  Multiple cabinets help this transition.

It is all a matter of compromise
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Chris Grimshaw

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #45 on: May 09, 2019, 02:29:30 pm »

Multiple cabinets will not change the length of the horn.  It is the length of the horn that is the biggest determining factor of the low freq extension.

Ivan,

A large stack of horns will have a longer effective path length:

Consider a large stack of horn loaded subs. Those at the bottom of the stack will effectively have their output constrained by the cabinets around them.
You could imagine positioning some plywood such that the sum of the applied pressure would be zero, and the plywood wouldn't vibrate in sympathy with the bass.
That bit of plywood would represent the extended horn path that's a result of the stack of horns.

Simulating stacks of front-loaded horns compared to single cabinets also shows a decrease in the lower cutoff.

Chris
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Ivan Beaver

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #46 on: May 09, 2019, 02:54:33 pm »

Ivan,

A large stack of horns will have a longer effective path length:

Consider a large stack of horn loaded subs. Those at the bottom of the stack will effectively have their output constrained by the cabinets around them.
You could imagine positioning some plywood such that the sum of the applied pressure would be zero, and the plywood wouldn't vibrate in sympathy with the bass.
That bit of plywood would represent the extended horn path that's a result of the stack of horns.

Simulating stacks of front-loaded horns compared to single cabinets also shows a decrease in the lower cutoff.

Chris
When people say "a lower cutoff", it really depends on how much?

I have measured a couple of stacks of different brands of horn subs, a couple of Hz is the most I have seen.

I would not get excited about a couple of Hz, untill you get below 20Hz or so.

Is the difference between 38 and 36Hz really enough to talk about?  38 and 30 yes.  36, not so much.

It is all a matter of magnitude.

I can go pee in the local lake and the lake level will rise.  Not enough to matter to anybody, but it DID rise.   Technically.

It comes down to "how much".  Just like saying that a 1200 watt amp has more headroom than a 1000 watt amp.  Technically that is true, but does it really matter and can anybody tell a difference?

Just sayin'------------
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Roland Clarke

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #47 on: May 09, 2019, 03:39:08 pm »

Multiple cabinets will not change the length of the horn.  It is the length of the horn that is the biggest determining factor of the low freq extension.

Long horns=lower freq.  Yes there are other factors as well.

What does change with multiple cabinets is the impedance or radiation resistance that occurs where the cabinet mouth meets the air.

This impedance will affect the overall freq response.

Most PA horns are made to short, in order to make them transportable, so there is not as smooth a transition to the air as we would like.  Multiple cabinets help this transition.

It is all a matter of compromise

Iím totally agree with you, but the point I was making that at those frequencies apart from some gain, they arenít exhibiting any true horn characteristics because they would need to be much longer with a much larger exit.  What they are exhibiting is 1/4 wave behaviour.  This point was discussed with Martin King, who expressed the view that most of these cabinets, tapped horns and all are effectively transmission lines.  Iím inclined to agree with this interpretation.
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Chris Grimshaw

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #48 on: May 09, 2019, 05:25:13 pm »

The nomenclature around subwoofer cabinets can get very confusing. The tapped horn cabinets work as quarter-wave resonators for the bottom tuning frequency (I guess that's where the "transmission line" would come in), but there are other effects higher up.


Ivan, I see your point about small changes not being worth bothering about. I do, however, believe that the effective path length of a front-loaded horn will increase in large stacks, and the low corner will decrease in frequency. The simulations I have done back me up. Here's what I think is going on:

- When a single cabinet is used, the radiation becomes spherical in shape shortly after exiting the mouth of the horn.
- When we stack a load of subwoofer cabinets (assuming a square stack), we effectively create a plane source with dimensions of the order of metres, maybe 10s of metres.
- At some distance away from the stack, the wavefront tends towards spherical again*. I suspect that extra distance is the additional path length which appears to lower the LF cutoff.

FWIW, my simulations show dramatic changes in the low corner when 16x cabinets are used - from 52Hz to 34Hz.

* This would go some way to explaining the observation that large horn subwoofer stacks "throw" the sound a long way, with lower-than-expected levels near the stacks.

Chris
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Ivan Beaver

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Re: JTR releases new 2x18 Subwoofers - info here
« Reply #49 on: May 09, 2019, 06:45:50 pm »

  This point was discussed with Martin King, who expressed the view that most of these cabinets, tapped horns and all are effectively transmission lines.  Iím inclined to agree with this interpretation.
The first 2 versions of the Tapped horn were just basically "tapped transmission lines"

The transmission line turned into a horn after that, and he started to pickup more gain.
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Ivan Beaver
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ProSoundWeb Community

Re: JTR releases new 2x18 Subwoofers - info here
¬ę Reply #49 on: May 09, 2019, 06:45:50 pm ¬Ľ


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