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post #241 of 431 Old 02-14-2020, 07:11 AM
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@a77cj7 : Outstanding work ! This has become one of the most documented Devs of them all, awsome !!

Cool that a pillow fixed the resonance, but to expand further: since two pillows seemed to much (no airflow), what if you tried to "stagger" them? Like first one pillow all the way to the frontwall inside the box, and then nr 2 a bit higher up and all the way to the back wall, so the there is airflow in a zig-zag kind of way ?

Also: plug a port

Otherwise: it seems the peak gets EQ down in most cases, so for a "revision" on this one, would it be desirable to tune it for less of a peak and excend its usable area past 120-130hz ? It seems that area between 80 and 120hz is a punchy one to have(as a77 also notes on the mini) If that’s possible

I mean, why tune it for something that gets EQ’ed away anyway? Headroom?

BTW, could you put up the pre-EQ vs post-EQ graphs?

Also: @Red Five : i believe you earlier put up graphs of what the front and rear chamber looked like separate? Could you show those two for this one?
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post #242 of 431 Old 02-14-2020, 07:14 AM
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Quote:
Originally Posted by Nalleh View Post
@a77cj7 : Outstanding work ! This has become one of the most documented Devs of them all, awsome !!

Cool that a pillow fixed the resonance, but to expand further: since two pillows seemed to much (no airflow), what if you tried to "stagger" them? Like first one pillow all the way to the frontwall inside the box, and then nr 2 a bit higher up and all the way to the back wall, so the there is airflow in a zig-zag kind of way ?

Also: plug a port

Otherwise: it seems the peak gets EQ down in most cases, so for a "revision" on this one, would it be desirable to tune it for less of a peak and excend its usable area past 120-130hz ? It seems that area between 80 and 120hz is a punchy one to have(as a77 also notes on the mini) If that’s possible

I mean, why tune it for something that gets EQ’ed away anyway? Headroom?

BTW, could you put up the pre-EQ vs post-EQ graphs?

Also: @Red Five : i believe you earlier put up graphs of what the front and rear chamber looked like separate? Could you show those two for this one?

The SPL graph for the front and rear separate?

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post #243 of 431 Old 02-14-2020, 07:16 AM
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Quote:
Originally Posted by Red Five View Post
The SPL graph for the front and rear separate?
Yes

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post #244 of 431 Old 02-14-2020, 07:19 AM
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Lightbulb

Quote:
Originally Posted by a77cj7 View Post
Now for the other experiment of the night, chasing resonances.

First, flip this heavy cab upright to make it easy to work on.

Lets take a baseline measurement to start things off. My mini tripod didn’t put the mic at the right level, so I had to customize a bit.


You’ve seen it before, but here’s the close-mic baseline anyways:


Now, for the additives. Two $5 Wally World pillows, the lowest-density they had at that price. Plus two additional braces to keep the pillows in place.


Remove the hatch. It sure seems like I’ve done this part before.


Screw on the braces:

If this works out, I’ll PL them in place.

Add a pillow:

Its sitting there loosely, plenty of space for air movement around it.

Seal it back up and take another sweep:


Well, would you look at that. It seems the resonance had been reduced to effectively nothing. Thats great news.

Since one pillow was good, maybe two will be better. Lets open it back up and find out.

Two pillows:

They’re very snug in there, no space for air movement.

Seal it and send it again:


The resonance is completely gone now! It looks like the bottom end output has dropped off sharply though. Apparently Helmholtz resonators need air movement to work. The more you know!

The bracing will be attached with PL3x, and the single pillow will be stapled or screwed to it. This turned out to be a very simple solution to a very nasty resonance.
Good call on that one John! @Red Five

This applies to all Devastators, not just the quad. I will be adding a pillow to any I build.
I will add some to the mini’s, since they also display a resonance at slightly higher frequency, due to the shorter cabinet.

Chris
The rear chamber bracing could be modified to catch 2 pillows and prevent port blockage.
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post #245 of 431 Old 02-14-2020, 07:20 AM
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It should look like this...





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post #246 of 431 Old 02-14-2020, 07:26 AM - Thread Starter
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EXPERIMENTAL Quad JBL Devastator Build

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Originally Posted by BP1Fanatic View Post
The rear chamber bracing could be modified to catch 2 pillows and prevent port blockage.


I thought thats exactly what I did?


Chris
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post #247 of 431 Old 02-14-2020, 07:26 AM
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You could also try standing up the 2 pillows instead of laying them flat.

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post #248 of 431 Old 02-14-2020, 07:36 AM - Thread Starter
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Quote:
Originally Posted by Nalleh View Post



Cool that a pillow fixed the resonance, but to expand further: since two pillows seemed to much (no airflow), what if you tried to "stagger" them? Like first one pillow all the way to the frontwall inside the box, and then nr 2 a bit higher up and all the way to the back wall, so the there is airflow in a zig-zag kind of way ?
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You could also try standing up the 2 pillows instead of laying them flat.

I’m not really sure what you’re chasing here, since one works quite effectively.

But this is a thread for measurements, and its not much effort to pull the hatch. I’ll go try it.

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Also: plug a port
Yeah, yeah, that one too.

Chris
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post #249 of 431 Old 02-14-2020, 07:44 AM
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Quote:
Originally Posted by a77cj7 View Post
I thought thats exactly what I did?


Chris
Not enough to prevent port blockage.

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post #250 of 431 Old 02-14-2020, 07:47 AM - Thread Starter
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Quote:
Originally Posted by BP1Fanatic View Post
Not enough to prevent port blockage.


The pillows are 10” or so off the port, or are you just referring to blocking the whole bottom half of the chamber?

Chris
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post #251 of 431 Old 02-14-2020, 07:47 AM
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Correct!

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post #252 of 431 Old 02-14-2020, 08:19 AM - Thread Starter
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Quote:
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Correct!


Yeah, that was intentional, to show that just stuffing in pillows isn’t the best idea.

Chris
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post #253 of 431 Old 02-14-2020, 08:28 AM
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I will have the same with 2x 21DS 18hz, and build 2 dev´s... wondering... would it be worth to put all 21" in 4 dev boxes?
As you say it´s not even close...
Ok... let's see if I can clear this up...... build 2 DEVs then A/B them with your ported 21" to get an idea of their different tones.

YES... they DO sound different...... since you will have 2 of each, this allows you to blend the 2 to get the exact tone you prefer in your space. You may come to the conclusion that you vastly prefer the tone of the DEVs..... ok build two more... DONE.

The point is to have the OPTION to shape the tone you like..... listen to 2 before you build 4 because you already have the other ported boxes. Either way, DEVs will be a part of your life.... the question is how many...

Now for the "not even close" part..... this is referring to the midbass slam....2 ported 21" are no match for 2 DEVs in that range. 21s will give you a nice kick.... BUT DEVs feel like they could break your ribs.....


Hope this helps....

Juju
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EXPERIMENTAL Quad JBL Devastator Build

Quote:
Originally Posted by Nalleh View Post
Cool that a pillow fixed the resonance, but to expand further: since two pillows seemed to much (no airflow), what if you tried to "stagger" them? Like first one pillow all the way to the frontwall inside the box, and then nr 2 a bit higher up and all the way to the back wall, so the there is airflow in a zig-zag kind of way ?
Quote:
Originally Posted by BP1Fanatic View Post
You could also try standing up the 2 pillows instead of laying them flat.
Ok, various pillow configuration testing, as requested.

Pillows standing up:


Sweep:


Pillows staggered:


Sweep:


All sweeps:


I’ll admit to being surprised by this one. Looks like standing pillows don’t lose any low end compared to the single pillow, but do completely kill the resonance.

Chris
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post #255 of 431 Old 02-14-2020, 08:38 AM - Thread Starter
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Also: plug a port
Quick and dirty plugged port testing.


The HPF was disabled. The staggered pillows are still in the rear chamber.


To pursue this concept further, I’ll have to model it and see what HPF is needed. Also need to see how port velocity looks(I assume fine in this one), and how far power is limited due to excursion. I expect excursion to be an issue.

Chris
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It looks like stapling pillows onto the side walls is a very viable option. Does it change the subjective sound signature at all? The Minis have a little ring to them, this has me thinking...
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Quote:
Originally Posted by a77cj7 View Post
Quick and dirty plugged port testing.


The HPF was disabled. The staggered pillows are still in the rear chamber.


To pursue this concept further, I’ll have to model it and see what HPF is needed. Also need to see how port velocity looks(I assume fine in this one), and how far power is limited due to excursion. I expect excursion to be an issue.

Chris
You are doing great work Sir..... thank you for your dedication....


Juju

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Quote:
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It looks like stapling pillows onto the side walls is a very viable option. Does it change the subjective sound signature at all? The Minis have a little ring to them, this has me thinking...
The LFE does as well... BUT only when stoopid loud.... I think that I will change out the poly fill on the hatch and put 2 pillows in the LFE.



Juju

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post #259 of 431 Old 02-14-2020, 09:08 AM - Thread Starter
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Quote:
Originally Posted by Red Five View Post
It looks like stapling pillows onto the side walls is a very viable option. Does it change the subjective sound signature at all? The Minis have a little ring to them, this has me thinking...


I’ll have to work on that one. It will probably be hard to say without the ability to instantly switch back and forth.

Chris
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Quote:
Originally Posted by jujuman200 View Post
The LFE does as well... BUT only when stoopid loud.... I think that I will change out the poly fill on the hatch and put 2 pillows in the LFE.



Juju


Might need more than two in that rear chamber. Measurements should tell you though.

Chris
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post #261 of 431 Old 02-14-2020, 09:24 AM
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Chris: Not to sound like a broken record, but ONCE AGAIN you amaze me with your efforts and the knowledge gained! I am absolutely honored to be a part of this by nothing more than buying a pair of drivers, smiling to myself as I enjoy the process. In my own cynicism, I tend to view most research grants (which is actually what this has been) as being more about profit and/or power than simply seeking after knowledge.


Chris, Red Five, et al: I would like a little more elaboration on the point made above about the exaggerated midbass response, flattening it when this is what is cited as such a benefit of these Devs, the 'slam' that people perceive. By eq-ing it flat (and yes, you have a DIFFICULT room, Chris!) aren't you suppressing this? And so what are the issues with designing a flatter response?


I started to write (as I think!) about wavelength and such ... but clearly there is much about these horns I don't really understand. So I am fine with others do the designing, but please help me understand a little about the compromises in the Devastator lineage.
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Quote:
Originally Posted by jujuman200 View Post
Ok... let's see if I can clear this up...... build 2 DEVs then A/B them with your ported 21" to get an idea of their different tones.

YES... they DO sound different...... since you will have 2 of each, this allows you to blend the 2 to get the exact tone you prefer in your space. You may come to the conclusion that you vastly prefer the tone of the DEVs..... ok build two more... DONE.

The point is to have the OPTION to shape the tone you like..... listen to 2 before you build 4 because you already have the other ported boxes. Either way, DEVs will be a part of your life.... the question is how many...

Now for the "not even close" part..... this is referring to the midbass slam....2 ported 21" are no match for 2 DEVs in that range. 21s will give you a nice kick.... BUT DEVs feel like they could break your ribs.....


Hope this helps....

Juju
Thanks, I want the feeling that my ribs are close to being broken
As soon as my new house is ready I start building Dev´s!
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post #263 of 431 Old 02-14-2020, 10:21 AM
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Quote:
Originally Posted by a77cj7 View Post
Might need more than two in that rear chamber. Measurements should tell you though.

Chris
I agree measurements should tell....


Juju

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Quote:
Originally Posted by MTBDOC View Post
Chris, Red Five, et al: I would like a little more elaboration on the point made above about the exaggerated midbass response, flattening it when this is what is cited as such a benefit of these Devs, the 'slam' that people perceive. By eq-ing it flat (and yes, you have a DIFFICULT room, Chris!) aren't you suppressing this? And so what are the issues with designing a flatter response?
Well, with the jbl’s (and many of the pro drivers), a flatter response could be achieved by avoiding the quarter wave resonator completely and using a traditional ported direct-radiator design.

The additional midbass headroom can be useful to combat room issues. For example, my testing:

Close-mic:


MLP:


In my room, the dip from 35-70hz would be even worse and harder to correct without the additional headroom.

Also, this is just taking into account the response of the Devastator.
I’m using a variety of subs to get the overall response I want. The mini’s higher peak works very well to supply the mid-bass response for the combined system, and their positioning between the mains makes the directionality work.

Chris
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post #265 of 431 Old 02-14-2020, 10:35 AM
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Quote:
Originally Posted by a77cj7 View Post
Well, with the jbl’s (and many of the pro drivers), a flatter response could be achieved by avoiding the quarter wave resonator completely and using a traditional ported direct-radiator design.

The additional midbass headroom can be useful to combat room issues. For example, my testing:


... snip ...


In my room, the dip from 35-70hz would be even worse and harder to correct without the additional headroom.

Also, this is just taking into account the response of the Devastator.
I’m using a variety of subs to get the overall response I want. The mini’s higher peak works very well to supply the mid-bass response for the combined system, and their positioning between the mains makes the directionality work.

Chris

Thanks, that makes sense. What this REALLY demonstrates is the need to have some sort of room measurements BEFORE building too much! I have a umik & minidsp-hd but haven't started using it yet. Then again, most everyone seems to like the midbass SLAM from the Devs, so it suggests that a flat response isn't actually the subjective preference of everyone.
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post #266 of 431 Old 02-14-2020, 10:38 AM - Thread Starter
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Originally Posted by MTBDOC View Post
Thanks, that makes sense. What this REALLY demonstrates is the need to have some sort of room measurements BEFORE building too much! I have a umik & minidsp-hd but haven't started using it yet. Then again, most everyone seems to like the midbass SLAM from the Devs, so it suggests that a flat response isn't actually the subjective preference of everyone.


I forgot to add the last part of that post...

The flat response I’m using for testing isn’t necessarily the desired response. It was just the most-fair way for me to compare the two without excessive time spent on the eq.

Chris
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post #267 of 431 Old 02-14-2020, 10:44 AM
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Originally Posted by a77cj7 View Post
I forgot to add the last part of that post...

The flat response I’m using for testing isn’t necessarily the desired response. It was just the most-fair way for me to compare the two without excessive time spent on the eq.

Chris
Flat response is the only way to judge speakers on a level playing field..... in practice, a system with a ruler flat response generally sounds like A$$ to put it mildly....


Juju

Sub List: 1- Red Five Mini V1 Devastator 18" w/PA460, 1- Red Five Devastator LFE 21", 1- Red Five Devastator 21" Finalizer V2 DF , 1- BOSS platform [The Hideaway Theater], 2- 18" "Full Marty" tuned to 17Hz w/RSS460HO
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post #268 of 431 Old 02-14-2020, 11:10 AM
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You are doing great work Sir..... thank you for your dedication....


Juju
Ditto!

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post #269 of 431 Old 02-14-2020, 11:31 AM
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Originally Posted by MTBDOC View Post
I started to write (as I think!) about wavelength and such ... but clearly there is much about these horns I don't really understand. So I am fine with others do the designing, but please help me understand a little about the compromises in the Devastator lineage.
Devastators are parallel tuned BP6's....each chamber ports to the outside of the enclosure.

A series tuned BP6 is the rear chamber ports into the front chamber and the front chamber ports to the outside of the enclosure.

Horns have positive flare ports...FLH, RLH, and TH.

A tapped horn is basically a series tuned BP6 where the whole enclosure is 1 big positive flare port.

A front loaded horn is a BP4 with a positive flare port.

When Chris laid the 2 pillows flat and blocked the ports, he changed the enclosure from a BP6 to a BP4, hence the low end response went away on the graph.
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post #270 of 431 Old 02-14-2020, 11:38 AM
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Originally Posted by a77cj7 View Post
Well, with the jbl’s (and many of the pro drivers), a flatter response could be achieved by avoiding the quarter wave resonator completely and using a traditional ported direct-radiator design.

The additional midbass headroom can be useful to combat room issues. For example, my testing:

Close-mic:


MLP:


In my room, the dip from 35-70hz would be even worse and harder to correct without the additional headroom.

Also, this is just taking into account the response of the Devastator.
I’m using a variety of subs to get the overall response I want. The mini’s higher peak works very well to supply the mid-bass response for the combined system, and their positioning between the mains makes the directionality work.

Chris
Omg Chris, the PA folks over on diyaudio.com are not getting this concept.

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