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Old 16th October 2012, 11:56 AM   #441
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Quote:
Originally Posted by Elias View Post
My initial thought when starting this thread was to explore bass reproduction with monopoles and dipoles in a small room with rigid walls and without any absorption other than normal living room furnitures. This is living reality for many.

Let's keep it that way. Discussion requiring heavy room treatments do not really belong in this thread.


- Elias
I have just finished building a set of slot loaded open baffles, comprising of 10 x 15" drivers pr. side - these are up and playng in my 400 sq.ft.++ (40m2) regular basement room, concrete floor/walls insulated and panelled just like a regular living room. NO room treatments of any kind, just sensible placement of necessary furniture, and equippment. The room is a dedicated music room though, so care have been taken to have symmetry on everything from the speakers rear wall to well behind the ears of the listener...

This is my third large format OB bass system, and it is WAY better than anything else I have ever heard.

Top class bass for playing regular music (ridiculous surround-style foundation shakin' "bass" is of no interest) is definitely possible with OB, it is just a question of scale, quality of drivers and enough space around the speakers (and a couple of other clever tricks)

And slot-loading DEFINITELY has quite a lot of directivity at least at a certain distance; the amount of energy hitting you in the sweet spot is downright scary.
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Last edited by pengesluk; 16th October 2012 at 11:58 AM.
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Old 16th October 2012, 12:29 PM   #442
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Originally Posted by StigErik View Post
To my ears, dipole bass is difficult to integrate with monopole subwoofers. I've tried it many times, and every time the monopole sounded "different" than the dipoles. Hard to describe, but its a different type of sound.

Dipole subwoofers are as efficient as wood-fired steam engines... that's why we don't see them too often I guess.
There are several reasons for monopoles/dipoles etc. not gaining momentum in popularity;

1. These are very difficult to establish as commercially viable products, for obvious reasons...

2. As a result of # 1. the very same commercial market is not particularily interested in PROMOTING such solutions

3. Lots of myths and half-*** negative science around OB's and dipoles

4. Most enthusiasts building such creations have seldom taken it to the max and/or explored the combination of unorthodox techniques and components.

I can appreciate and understand all of this, but please do not write off OB/dipoles as "proper" solutions for world class bass; the more extreme and esoteric variants DO actually work, contrary to many "minimum solution" excecutions of the same theme(s). Remember the Bumble Bee's inability to fly...??

Last edited by pengesluk; 16th October 2012 at 12:32 PM.
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Old 16th October 2012, 12:38 PM   #443
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Not to go off topic but this slot loaded woofer thing has really gotten out of hand. Slot loading at low frequency does very little if anything in the free field. Increased directionality is not there. Certainly if you move closer to the woofer you will hear increased bass, but this is true of any dipole system because the closer you get the stronger the front source gets compared to the rear source whioch due to the differences in propagation distance. See Nelson Pass Slot loaded OB for a documented discussion of a scaled, slot loaded woofer system with many measurements.
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Old 16th October 2012, 12:51 PM   #444
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JohnK and Dr. Gedlee:

Yes, I agree that monopole and dipole in domestic listening rooms differ mainly in EQ needed to make responses same at listening position:

Monopole Raw response:

Click the image to open in full size.

Dipole raw response:

Click the image to open in full size.

Cardioid system as Monopole and Dipole driving together:

Click the image to open in full size.

Equalization is generated for Monopole, Dipole, and Cardioid. Equalization is applied to test sweep for each setup and run. Results are:

Monopole:

Click the image to open in full size.

Dipole:

Click the image to open in full size.

Cardioid:

Click the image to open in full size.

Similar results are obtained with differing speaker and microphone placements. This work was done with microphone at 44 inches. It is quite clear that room response dominates, and may be equalized.

Raw Impulse responses Monopole top, Dipole bottom:

Click the image to open in full size.

Impulse Responses with correction filters: Monopole top, Dipole bottom:

Click the image to open in full size.

For given driver, monopole produces more output with less driver excursion, and excursion related distortions. Dipole doesn't excite walls, floor, and ceiling in null plane.

Listening impressions for equalized conditions are virtually identical: Fantastic.

Regards,

Andrew
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Old 16th October 2012, 01:00 PM   #445
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JohnK;
Did you ever build this kind of construction in this scale yourself? I have all the mentioned systems here, and there is a very marked difference in the directivity between those regular OB's and the slot loaded version. No question. This is also usually the first comment from other listeners - some 10-12 seasoned audio friends happened to mention this particular feature. Move a foot to the left or right and it changes caracter. Listening distance is about 10 ft. right now - I can relate to your theory when we increase the listening distance but at 10' I have to relate to our EXPERIENCE rather than theory.

Mind you, this particular "concentrated energy field" was not on my mind when designing the whole concept - we just discovered it during the first listening session.

If doing SLOBS is wrong I don't wanna be right.

Last edited by pengesluk; 16th October 2012 at 01:05 PM.
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Old 16th October 2012, 01:38 PM   #446
Rudolf is offline Rudolf  Germany
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Originally Posted by Barleywater View Post
Dipole doesn't excite walls, floor, and ceiling in null plane.

Listening impressions for equalized conditions are virtually identical: Fantastic.
Impressive data, Andrew. But your final remark keeps me curious: Do you say that with the frequency response of all 3 versions equalized to the same target the dipole-non-excitement in the null plane doesn't make a difference in listening?

Rudolf
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Old 16th October 2012, 01:55 PM   #447
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If one would do equalized or normalized comparisons, then time-domain ringing would be the only (possibly) remaining difference between the three source types, right? It would be interesting to see if there would be any significant difference in ringing (because of 'less' or 'fewer' mode excitation).
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Old 16th October 2012, 02:17 PM   #448
Rudolf is offline Rudolf  Germany
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I’m still riding my hobby horse … the dipole woofer directivity.
It is obvious that we don’t see a figure-8 pattern below the Schroeder frequency. But the excitation of individual modes can change dramatically when the dipole source is rotated.

Measurements were taken in a 4 x 5 m room with “hard” walls except the front wall, which is a slanted ceiling in the upper half and a knee wall below. The H frame is 1.30 m from the front wall and 1.10 m from the side wall. The microphone was on the 45° axis, about 1.30 m from the H frame. 0° is along the 5 m length, 90° along the 4 m width of the room:

FR left 0 45 90 degree.gif

You can probably imagine why I choose the 45° alignment. I have processed those three impulse responses through Elias’ Bark wavelet analysis.

Bark left 0 45 90 degree.gif

It is up to everybody to see for himself if it does make any difference in the time domain "ringing".

Rudolf
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Old 16th October 2012, 03:19 PM   #449
gedlee is offline gedlee  United States
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Originally Posted by 6.283 View Post
But wasn't exactly that one point Earl was mentioning that there is virtually no directivity in small rooms at LFs ?
One always has to consider the bandwidth that is being talked about. In the modal region directivity cannot exist, but above the Schroeder frequency it can. If the bandwidth is such that it encompases both regions - as it almost always does for dipole speaker systems - then one cannot easily determine if the sound quality difference is due to the range below fs or above. So lets say that a dipole system is deemed to "sound better" (and I for one am not ready to accept that premise as unconditional) then it could be the differences in the "directional possible" region or it could be the other region. We just do not have any data (that I have seen) to make that determination.

I have said that, on paper, a dipole has an advantage from 125 Hz up to about 500 Hz, but dipoles also have disadvantages as well. I consider these two octave to be just about the least important perceptually so it becomes a real mixed bag as far as a dipole being the ideal. From the examples that I have heard, the dipoles did seem to be very good in this region, but thir poor performance elsewhere left them lacking IMO. (And no I won't point out the specific dipoles that I have heard - they were well regarded however.)
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Old 16th October 2012, 03:32 PM   #450
6.283 is offline 6.283  Germany
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Originally Posted by Rudolf View Post
I’m still riding my hobby horse … the dipole woofer directivity.
It is obvious that we don’t see a figure-8 pattern below the Schroeder frequency. But the excitation of individual modes can change dramatically when the dipole source is rotated.
But to me that means that there are leftovers from directivity, no ?

Quote:
Originally Posted by gedlee View Post
One always has to consider the bandwidth that is being talked about.
Yes, I was quoting you with <125Hz in mind.


And thanks to John for the measurements and time time you have invested !
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Last edited by 6.283; 16th October 2012 at 03:37 PM.
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