Bipole Isobaric Tempest Sub?? (1 Viewer)

[Greg P]

This is the latest idea ive been tinkering with. A design like the pinacle digital 600 sub. If you read my post below I followed up with my goals of my $800 DIY sub.
1. Tight, percussive bass, very dynamic(I want it
to sounds like a servo 15 on roids)
2. 115-120db output in a medium sized room
3. extension to flat to 24-25hz at least with a
slight rolloff afterwards
- A sealed tempest down to the depths I want is
going to be to big, as I do have some size limits
Im new to DIY so the last week Ive been trying to learn all about T/S parmaeters. Im debating between a ported and a isobaric design right now. From what I gather an Isobaric only needs 1/2 the enclosure volume of a sealed sub to reach a given flat frequency, and with an extra driver (plus exta watts) you would gain another 6db of output. Would this Isobaric design have the same output as the ported? Ive also heard you can port the Isobaric design, is this work well how does it comare to the other 2 designs?
Thanks guys

 

[ThomasW]

Greg
Please read the sections on these websites about isobaric designs.
http://216.150.71.139/audioinnovation/theories.html http://www.snippets.org/ldsg/boxes.php3#ISOBARIC
[Edited last by ThomasW on July 25, 2001 at 10:25 PM]

 

[Scott Simonian]

All those preferences look like what I want too. Hope its cheap and easy for newbies like us to make. But I need cheap CHEAP!!!

 

[Kishu]

Thomas or other Gurus,
Going by Greg's top 3 requirements (which I believe many will have ) what are your recommendations for a great Sub for HT and music? I think I'm being a bit lazy and am looking for your recommendations
I'd prefer my sub however to roll off from 20Hz..
Cheers,
Kishore

 

[ThomasW]

Well what are you limitations? Money, size of sub, size of room, SAF?
It's really no big deal to get solid output to 20Hz.
I'm not a big proponent of HT focused subs. A low Qtc sub can easily do HT duties just by either raising the output a little or adding just a bit of bass boost from the processor.
I like dual Tempests in a big sealed tube, targeting a Qtc 0.50. That's a pretty big tube, around 18-20cu ft.
If that's too big and you want a smaller box, go with 2 Tempests mounted in an Isobaric config. Box size is cut in half, but you loose the +3db output by using the Isobaric driver configuration. Not a big deal if the room is small.
You won't get 115-120db out at 20Hz with either of these designs. But you probably don't really need that either. Most people fail to understand how loud that really is.... = beginnings of permanent ear damage after 20 minutes of exposure
[Edited last by ThomasW on July 27, 2001 at 11:42 PM]

 

[Tyson]

I have heard the Dual Tempest sealed sonosub that Tom built for Dennis here in Denver. Let me just say that if you need more bass than what these puppies can put out, then you are in need of serious help! Before hearing them, I don't think I ever had bass directly massage my intestines. . . .

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"Remember Sammy Jenkins"

 

[Greg Monfort]

>You won't get 115-120db out at 20Hz with either of these designs. But you probably don't really need that either. Most people fail to understand how loud that really is.... = beginnings of permanent ear damage after 20 minutes of exposure
====
Hearing damage is frequency dependent. Quoting from the Hearing Institute:
"Sound levels at or below 75dBA produce NO hearing loss what ever, at any frequency even at 4 kHz" (where damage is most easily done).
If you look at the Robinson-Dadson (update of Fletcher-Munsen) human hearing equal loudness curves, this equates to:
145 dB at 10 HZ
131 dB at 16 HZ
125 dB at 20 HZ
114 dB at 32 HZ
So while we may be literally 'rumbling our guts' or 'shaking the house down', we won't be doing any hearing damage from the SPL of any but the most extreme HT/music sub systems even if playing a continuous sinewave for extended periods. It's the high SPL average of a rock concert over several hours, working in a noisy plant 8hrs/day, or riding motorcycles without ear plugs on long trips, etc., that damages.
GM
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Loud is beautiful, if it's clean

 

[ThomasW]

When doing the initial testing of the big IB, I was running sine waves at 105db (nearfield) from 5Hz to 100Hz. And that messed up my ears for several days. After that I started using both the little foam plugs combined with high attenuation over the ear cups. That took care of the problem.
So anymore I don't trust the so called safe exposure levels regardless of frequency

 

[Greg Monfort]

Yes, we each have to make judgment calls based on what we know (or think we know), but based on my own experiences and what I've read published by Institutes that spend their time studying this subject; if you have average/healthy ears, then while they may 'mess up' for a short period of time, no permanent damage is done. Considering the number of times this has happened to me over the years (especially when I was racing two-strokes), I would be stone deaf by now if it wasn't true.
As always though, YMMV.
GM
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Loud is beautiful, if it's clean

 

[Greg P]

Can you guys tell me the sonic benefits of an Isobaric ported sub vs. a regular ported. Th Isobaric ported would be more muscial and have more characteristics of a sealed sub? I think Im gonna email Dan Wiggins about this project and the parameters. ported designs dont use Qtc. Right? What is a good value to change to determine how the sub will sound. I know ported subs are more complicated to find the proper formula.
"If that's too big and you want a smaller box, go with 2 Tempests mounted in an Isobaric config. Box size is cut in half, but you loose the +3db output by using the Isobaric driver configuration. Not a big deal if the room is small.
You won't get 115-120db out at 20Hz with either of these designs"
I hope your just talking about right at 20hz, because my SVS was recorded to hit 110db across the board from 25hz and up in a 7500sq ft room. An Isobaric ported Tempest should damn well be able to blow the SVS away. I would presume though if I tuned the Tempest down to 20hz I should be able to at least get 115db at 20hz in most rooms. The Adire audio web site claims a ported tempest can reach levels of 120db in most rooms.

 

[Jack Gilvey]

An isobaric merely cuts the box size in half for a given vented alignment or sealed Qtc. The sensitivity and output is the same as for a single driver. It can be applied to sealed or vented. It has nothing to do with the "musicality" of a sub.

 

[ThomasW]

Greg P
My statement about not getting 115-120db out was in reference to continuous output. Yes, you could certainly hit peaks that high.
You might want to bookmark the following site. It tells what the T/S parameters are. Understand they apply to all speaker designs, sealed, ported, PR, IB, bandpass, etc.... Link Removed
There is no sonic benefit to a ported isobaric design vs regular ported. The only benefit to any isobaric design is using a box 1/2 the size as the non-isobaric.

 

[Greg P]

Ok,
On my own sub Im shooting for a Qtc of around 5.777 (I believe this is the Bessel alignment(even group delay)) and .60 . What do you guys think of this? I calculated the F3 for a sealed Tempest and at .6 and it came out to 35.8hz . Did I calculate this right? Using the DIysubwoofers.org page. ( this would be in a 164 liter enclosure) Oh yah, does anyone know the conversion of cubic inches to liters?

 

[Julian Data]

Greg,
I hope you meant for a Qtc of .577. Not 5.777. Talk about a one hertz box!
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[Jack Gilvey]

One thing about an isobaric reflex design. In a half-size cabinet, the port would need to be a lot longer for a given tuning and diameter than it would in the same alignment with a single driver/twice the Vb. This could conceivably degrade the sound, or not even fit in the cabinet. You've got to fit twice the port in half the cabinet.

 

[JohanK]

Greg, I believe dividing liters by 28.3 will give you cubic feet. There are 1728 cubic inches in a cubic foot.
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http://www.hometheaterforum.com/bbs/equipment/28687.html
Link Removed

 

[ThomasW]

Gerg P
Why not grab a free copy of LspCAD from the Adire site? It comes preloaded with the parameters of the Adire drivers. There is a great help section. Use the "Yankee Tool" to convert to metric.
Also if you haven't already done so get the Tempest application papers from Adire. I believe they already have done the calculations for a Qtc 0.577 box
[Edited last by ThomasW on July 29, 2001 at 10:03 PM]

 

[Jack Gilvey]

I calculated the F3 for a sealed Tempest and at .6 and it came out to 35.8hz . Did I calculate this right? Using the DIysubwoofers.org page. ( this would be in a 164 liter enclosure)

That sounds about right. Realize, though, that if you're running the sub with a standard receiver crossover, like a 12db/oct. low-pass @ 80Hz, the actual f3 would be about 29Hz. In-room, you're talking low-20's extension...serious stuff.
Download LspCAD for the Adire drivers from Adire.com.