ISOBARIC sealed enclosure... Any experiences ? Any advantages ?
In a project of a quite large 4-ways sealed enclosure, I wonder if going for the isobaric principle for the woofer setion would offer advantages... 🤔
The goal is not to reduce volume, but improve bass extension in frequency response, transient and step response, distortion, by using a tandem of speakers, like this - but larger about the back volume
According to many expert authors, combining two identical speakers in that way offers an equivalence of :
If the enclosure volume remains the same (the common chamber is not counted) for one sealed speaker, or two isobaric speakers, as a consequence the result is a lowering of the QTC, so a better transient, earlier bass cutoff start but smoother and longer slope, potentially giving a better bass extrension.
Any advice or experience in that field ?
Thank you Guys !
T
In a project of a quite large 4-ways sealed enclosure, I wonder if going for the isobaric principle for the woofer setion would offer advantages... 🤔
The goal is not to reduce volume, but improve bass extension in frequency response, transient and step response, distortion, by using a tandem of speakers, like this - but larger about the back volume
According to many expert authors, combining two identical speakers in that way offers an equivalence of :
- Z / 2 (connected in //)
- VAS / 2
- QTS unchanged
- FS unchanged
If the enclosure volume remains the same (the common chamber is not counted) for one sealed speaker, or two isobaric speakers, as a consequence the result is a lowering of the QTC, so a better transient, earlier bass cutoff start but smoother and longer slope, potentially giving a better bass extrension.
Any advice or experience in that field ?
Thank you Guys !
T
Better turn one woofer and use clamshell (face to face) like arrangement. It reduces distortion too.
Linn did this with their Keltik speaker in the early 90s. 3 way with two oval/racetrack 6x9" woffers in isobarik for the bass. Sounded amazing in a relatively small box. Nice fast tight deep bass.
Totem's Mani2 speaker did this as well. The bass that little stand-mount put out was amazing! Made it a little current hungry, so choose your amp wisely, but no problem with the deep solid bass!
You could just buy a dsp and eq the entire speaker instead of cashing out 2xcash for the extra woofers.
Will give you higher total sq.
Or just half the volume for each woofer and not do isobaric will lower thd in the upper bandpass and have about the same in the lower and a higher max spl, or you can traslate this to lower -f3(about 1/2 octave lower)without compromising max spl compared to isobaric
Or just buy better woofers for the same cost?
I opted for dsp and half the volume instead of isobaric.
Will give you higher total sq.
Or just half the volume for each woofer and not do isobaric will lower thd in the upper bandpass and have about the same in the lower and a higher max spl, or you can traslate this to lower -f3(about 1/2 octave lower)without compromising max spl compared to isobaric
Or just buy better woofers for the same cost?
I opted for dsp and half the volume instead of isobaric.
The disadvantage of reducing the displacement of two drivers to that of one (-6dB output potential) outweighs any possible advantages in a large enclosure.
none of that is attributed as a benefit of isobaric
Second order distortion. Not always a good thing.
Isobarik brings an approximate halving of the box volume. That is pretty much it. Today, with much wider driver choice one can just oick a more appropriate driver for the box size yoiu are targeting.
There may be somethign to be said about the isolation of stuff coming thru the driver fronm the cabinet.
It does not increase bass extention. Twice the cost, twice the power reequired (*often from just wiring the drivers in parallel), a more compicated box all for the same output as a single driver in a box twice as big.
An Isobarik also limits the HF extention.
I have built moire than 1 set of isobariks. They were a bit of a mystery until i took a woofer out of the Linn Isobariks.
dave
Let's take an example using the Dayton E150HEs. They need 4-5 liters sealed for a Q around 0.65 while not becoming limited by power handling. What if you want to cram them into 2.5 liters net? A single driver is just about on par in output with isobarik between 20-50Hz, but has a Q of .8 (iso being .64). The isobarik also uses a third less power per driver. Doubling up the single driver gives a boost of 1-2dB, but a Q of 1.
Here too you could just take a Purifi instead (6.5 has a Q of .7 in 2,4 liters) but I would then be curious of cramming it into 1 liter 🙂
I guess the main question is whether Q means anything once you equalize the response. Though I love DSP and use it extensively with MSO and Dirac, I do feel like the speaker that's "naturally" closer to the preferred response will sound better, but there are, of course, many confounders here
Here too you could just take a Purifi instead (6.5 has a Q of .7 in 2,4 liters) but I would then be curious of cramming it into 1 liter 🙂
I guess the main question is whether Q means anything once you equalize the response. Though I love DSP and use it extensively with MSO and Dirac, I do feel like the speaker that's "naturally" closer to the preferred response will sound better, but there are, of course, many confounders here
There is zero point in building such a small isobarik. The material overhead means the end enclosure is likely swamp the bixsize gains with isobarik, likley larger than a single driver box odf thw same alignment.
dave
dave
If you use EQ you need more power, more excursion, distortion increases, greater cost. So they are not equivalent.
dave
Not exactly, excursion is the same for a single driver and isobaric. As I mentioned, power per driver is reduced in isobaric
^ this...
... But if you already have drivers or some other circumstances isobaric can make sense. But again, "makes sense" only means being able to use a smaller enclosure.
Not according to WinISD. And the total power is quite irrelevant in terms of performance.
Of course, no one is denying that. I'm talking about a fixed, undersized box for normal configuration
Thank you Guys !
Here's what would look the project on paper :
Filling / Stuffing at 100% with Cotton Wool / Sealed enclosure / Isobaric tandem of 2X BEYMA 12BR70 Woofers.
BEYMA 12BR70-8 specs - I have several brand new or barely used sample of this reliable and ruggered speaker in stock, hence my choice :
Comparative simulations of Isobaric and non-Isobaric :
1 - The Isobaric project, as described in the pictures above. Discard the red curves, which shows obviously that the combination is unsuitable in BR (220L !)...
2 - Non-isobaric version, with only one 12BR70 in sealed 100% stuffed enclosure, of same external dimensions (hence the increrase from 75 to 86L of internal volume) . In other words : he internal 12BR70, its chamber and matching panels are deleted here. Again, discard red and black curves.
Conclusion :
For the two combinations having the same external cabinet size :
* The Isobaric offers a better step response and better group delay vs. the non-Isobaric single woofer.
* We can also expect a slightly extended very low end extension for the Isobaric, but with an earlier frequency drop start at 100Hz vs. 70Hz for the non-Isobaric single woofer.
Without real surprise, this is due to the QTC=0.70 of the Isobaric instead of the QTC=0.81 for the non-isobaric single woofer.
T
Here's what would look the project on paper :
Filling / Stuffing at 100% with Cotton Wool / Sealed enclosure / Isobaric tandem of 2X BEYMA 12BR70 Woofers.
BEYMA 12BR70-8 specs - I have several brand new or barely used sample of this reliable and ruggered speaker in stock, hence my choice :
Comparative simulations of Isobaric and non-Isobaric :
1 - The Isobaric project, as described in the pictures above. Discard the red curves, which shows obviously that the combination is unsuitable in BR (220L !)...
2 - Non-isobaric version, with only one 12BR70 in sealed 100% stuffed enclosure, of same external dimensions (hence the increrase from 75 to 86L of internal volume) . In other words : he internal 12BR70, its chamber and matching panels are deleted here. Again, discard red and black curves.
Conclusion :
For the two combinations having the same external cabinet size :
* The Isobaric offers a better step response and better group delay vs. the non-Isobaric single woofer.
* We can also expect a slightly extended very low end extension for the Isobaric, but with an earlier frequency drop start at 100Hz vs. 70Hz for the non-Isobaric single woofer.
Without real surprise, this is due to the QTC=0.70 of the Isobaric instead of the QTC=0.81 for the non-isobaric single woofer.
T
Then i expect winISD is wrong. Quality of amp often is related to its size. Smaller often performing better.
dave
Last edited:
No, you need more power for the same cone travel.
And that may lead to higher distortion for the same spl.
Thats the prize you pay
Tubeelectron: but q is irrelevant once you eq the response.
Put woofer no2 on the back high up instead.
You couldshrink the chamnber a bit more, smaller the better, the triangle is a nice touch.
dave
dave