Open baffle speaker pitfalls

[test1223]

It would certainly be interesting to simulate how different speaker concepts excite a sample room if the speaker position in the room is always identical, but that's not the goal of the thread.

Yes. The spinorama data lack of important insides in the bass behavior of a loudspeaker. Even if you have a look at simpler monopole speakers you can't see much with these measurements. For example take the superior behavior of a stand mount speaker with a bass near the floor vs. a book shelf speaker on a stand. The floor bounce phase offset can't anywhere be found in the spinorama data but will be present with almost any bookshelf speaker placement in a real room.

Now with dipol speakers the complexity is take to another level. As you might have noticed the frequencies where the resonances are will slightly change if you add a solid floor and to place the speaker on a floor is very likely. So should the simulation contain a floor? I would say of cause it should.

The question is where does the speaker end and where does the room beginn and with bass frequencies I would argue that the whole room is the speaker.

It is simply not possible to create a simulation or measurement for every listening room in the world.

A big problem yes. But what did you get from using free field conditions to evaluate speaker designs in the bass frequencies? For monopoles I would say you get some inside but you have to have knowledge about room interaction with monopole speakers. For dipols there isn't much research about the room interaction so your claim

If free field measurements or simulations in the bass-midrange show you errors in the radiation and directivity, then the probability that this speaker will cause problems in your listening room (and measure less well) is much higher than a speaker without design flaws.

has to be evaluated in the first place. I would argue that even for monopol designs the design goal of a flat frequency response in the bass doesn't deliver the highest possibility of a good in room response. A lot of listening rooms are more similar for a speaker class (size) and some assumed room gain is beneficial (have a look at the KEFs bass tuning). So I would claim that for dipole designs there might be much more unexpected behavior which is on average better but doesn't look that good if you have a look at the free field response only.

When we use simulations we are pretty powerful. I think you restrict yourself to established types of presenting data here. But in this context you don't get much from the advantage that you can compare these data to other free field data, since it doesn't tell much without taking the room or at least the floor into account anyways.

 

[yourmando]

@ctrl Thanks a bunch for doing these simulations. This is very helpful!

+1 this is dope

 

[Richard G]

Yes. The spinorama data lack of important insides in the bass behavior of a loudspeaker. Even if you have a look at simpler monopole speakers you can't see much with these measurements. For example take the superior behavior of a stand mount speaker with a bass near the floor vs. a book shelf speaker on a stand. The floor bounce phase offset can't anywhere be found in the spinorama data but will be present with almost any bookshelf speaker placement in a real room.

Now with dipol speakers the complexity is take to another level. As you might have noticed the frequencies where the resonances are will slightly change if you add a solid floor and to place the speaker on a floor is very likely. So should the simulation contain a floor? I would say of cause it should.

The question is where does the speaker end and where does the room beginn and with bass frequencies I would argue that the whole room is the speaker.

A big problem yes. But what did you get from using free field conditions to evaluate speaker designs in the bass frequencies? For monopoles I would say you get some inside but you have to have knowledge about room interaction with monopole speakers. For dipols there isn't much research about the room interaction so your claim

has to be evaluated in the first place. I would argue that even for monopol designs the design goal of a flat frequency response in the bass doesn't deliver the highest possibility of a good in room response. A lot of listening rooms are more similar for a speaker class (size) and some assumed room gain is beneficial (have a look at the KEFs bass tuning). So I would claim that for dipole designs there might be much more unexpected behavior which is on average better but doesn't look that good if you have a look at the free field response only.

When we use simulations we are pretty powerful. I think you restrict yourself to established types of presenting data here. But in this context you don't get much from the advantage that you can compare these data to other free field data, since it doesn't tell much without taking the room or at least the floor into account anyways.

There is some good analysis on the effects of the room on dipoles, including placement of the driver relative to the floor and walls, reflections etc at http://www.dipolplus.de/thema5.html

 

[charlielaub]

There is some good analysis on the effects of the room on dipoles, including placement of the driver relative to the floor and walls, reflections etc at http://www.dipolplus.de/thema5.html

Unfortunately, apart from the first analysis of floor gain due to the proximity of the woofer to the floor, most of the rest is wrong. This is because when boundary reflections reach the listener at least 6msec after the direct sound the brain suppresses them for several tens of milliseconds. This is how we are able to make sense of sounds in a reflective environment such as an indoor space. So you cannot sum the source and its reflection and produce a frequency response showing an interference pattern - that is just not how the human hearing process works and is incorrect/misleading.

For a properly designed dipole loudspeaker that has identical front and rear frequency response and in a room with walls that can reflect all frequencies equally, the room reflections that occur sufficiently after the direct sound are actually beneficial and increase the apparent soundstage. IMO this is poorly understood and only applies to dipole systems. It is also why many audiophiles feel the need to resort to "room treatment" for their boxed loduspeakers, which have very position and frequency dependent acoustic radiation (e.g. for angles away from the direct, on-axis sound). For monopole radiators the room reflections are much more detrimental to the sound stage, etc.

 

[Richard G]

You’ve reminded me of Linkwitz’ article on the delay between reflected signal and the direct signal reaching the listener, and room reverberation time https://www.linkwitzlab.com/listening_room.htm and

 

[deanznz]

You’ve reminded me of Linkwitz’ article on the delay between reflected signal and the direct signal reaching the listener, and room reverberation time https://www.linkwitzlab.com/listening_room.htm

Interesting.. thank you. After reading that someone may like this idea that is abbreviated in this post:

I think I get it. You are using moderately narrow directivity L and R speakers crossed in front of the listening position (LP), plus one Distributed Mode Loudspeaker(DML) fed L+R edge-on to the listening position (LP), so the LP and the front wall are in the DML's dipole nulls and side wall reflections are largely from the DML. Clever.

the thread is here:

DML And Waveguided Speaker Combined?

See graphics below: The loudspeakers AC and DC have relatively narrow dispersion of constant directivity 90° by 60° nominal from about 800Hz on. Otherwise I would consider them ‘perfect’ in regards of available extension, spl, HD, IM, no resonances etc. Nice cousins to JBL’s M2 maybe. When...

www.audiosciencereview.com

For anyone who has an exciter or 2 and a panel or 2, I highly recommend people try this out, it sounds wonderful. Even mono music has more life to it. Being able to vary the volume between the Main speakers and the DML is an important option. If anyone thinks their system is pretty nice, but finds they are still chasing..... something then try this.

Dean.

 

[yourmando]

9. U-frame resonance side effects
How difficult it is to "avoid" the U-frame resonance should have been mentioned in the opening post, as it was one of the reasons to start this thread. This means that even drivers that are not directly in the U-frame but, for example, a little above it, of course still excite the resonance.

For this purpose we will look at the simulation of a loudspeaker with an angled U-frame.
In the lower part of the baffle there are normally two 15'' woofers, which were omitted for the simulation. As we know, the crossover frequency for these woofers in the U-frame has to be chosen very low - mostly at 60-100Hz (below the occurring cabinet resonance / short transmission line resonance).
View attachment 298465View attachment 298463 View attachment 298464
…

Unfortunately, this is not the real problem. The problem is the collapse of the dipole radiation in the area around the fundamental resonance and the uneven radiation caused by the harmonics.
View attachment 298480 View attachment 298481

I’ve been thinking back on this thread because I’m about to design a dipole and I’m trying to decide if it’s worth it to add small angled U frame baffles mainly as support stands. I would lean toward making the triangles hollow to sidestep the issue (and add subwoofers for low low bass).

I’d be also be interested to hear @perrymarshall ‘s take on the tradeoff of the between lower bass vs pattern control ripples at due to the resonance.

 

[RayDunzl]

Audio buddy's brother-on-law recently bought some OB's.

Duet15 - PureAudioProject

pureaudioproject.com

I'll hear them someday, I suppose.

Haven't found any measurements.

 

[Richard G]

Slot loading: the result of some empirical work by a imo clever designer
(It’s been a while since I read about the nine(?) bass alignments looked. I can’t recall if it includes slot loading)

This design with slot loading of the woofers which looks like a derivative - and refinement - of ripole bass
i believe that for this project keeping costs low was a key objective, so he used small cheap woofers
Even though he partly offsets their very small volume displacement by using eight woofers per side - they do not go low. I’d want to supplement them with a decent sized

All that said, I share this for anyone interested in slot loading. Because I gather he experimented with the ratio of the slot to (was it?) driver displacement and shares a ratio that performs better than a ballpark design … so could be applied to any slot design. And where space is limited it’s a good way to go.
https://www.diyaudio.com/community/threads/the-xsd-speaker.385717/

 

[ajar]

Slot loading: the result of some empirical work by a imo clever designer
(It’s been a while since I read about the nine(?) bass alignments looked. I can’t recall if it includes slot loading)

This design with slot loading of the woofers which looks like a derivative - and refinement - of ripole bass
i believe that for this project keeping costs low was a key objective, so he used small cheap woofers
Even though he partly offsets their very small volume displacement by using eight woofers per side - they do not go low. I’d want to supplement them with a decent sized

All that said, I share this for anyone interested in slot loading. Because I gather he experimented with the ratio of the slot to (was it?) driver displacement and shares a ratio that performs better than a ballpark design … so could be applied to any slot design. And where space is limited it’s a good way to go.
https://www.diyaudio.com/community/threads/the-xsd-speaker.385717/

Ripol is a derivative of slot loading theory.

 

[ctrl]

I’ve been thinking back on this thread because I’m about to design a dipole and I’m trying to decide if it’s worth it to add small angled U frame baffles mainly as support stands. I would lean toward making the triangles hollow to sidestep the issue (and add subwoofers for low low bass).

If the U-frames are only used for baffle support and are "open/hollow" at the sides, then there should hardly be any effect at low frequencies. So, radiation should be very similar to classic OB speaker.
With lower level SPL at low frequencies for the flat baffle version. Here is a comparison of example 2 U-frame with four drivers and example 4 flat baffle version:

At 100Hz the SPL difference is 3.6 dB.

From the upper mid-range and higher, it will probably be better if the sound emitted from the rear of the driver does not hit any additional reflective edges.

 

[Richard G]

Ripol is a derivative of slot loading theory.

Ah, the other way around … thank you.

ctrl,
Although I believe the primary attraction is compactness, rather than some attribute of sound quality - have you ever modeled them, or considered doing it in this thread for completeness?

My hunch is you’d need more driver displacement to get similar low end extension. But that’s just a WAG

Maybe the differences in sonic attributes aren’t that significant … so it’s a valid option if you’re not after the ultimate SQ, if close is acceptable where the constraints are WAF or simply limited space.

 

[ctrl]

ctrl,
Although I believe the primary attraction is compactness, rather than some attribute of sound quality - have you ever modeled them, or considered doing it in this thread for completeness?

At the moment, other projects and simulations have priority for me. Systems with a high quality factor Q have, for physical reasons, long attack and decay times, which is what resonance-based low-frequency extensions like ripols are - I'm not a fan of that (only my personal opinion). That's why I do not have the motivation for ripol simulations at the moment... sorry...

 

[Richard G]

At the moment, other projects and simulations have priority for me. Systems with a high quality factor Q have, for physical reasons, long attack and decay times, which is what resonance-based low-frequency extensions like ripols are - I'm not a fan of that (only my personal opinion). That's why I do not have the motivation for ripol simulations at the moment... sorry...

No apology needed…

Thank you for pointing out the basic: high Q, so long attack and decay times. That kills my interest, too

Cheers

 

[Scgorg]

I am not Ctrl, but I did recently play around with ripoles in AKABAK. Posting here since there seems to be interest.
This was a ripole using 2 12-inch woofers, in what I would consider a cabinet that is pretty typical size for such a speaker. The front and rear chambers may be a little larger than what is ideal (as can bee seen by the relatively low frequency of the cavity resonance), but the overall conclusions shouldn't change much. First image is front slot, second image is back slots. This image does not show the interfaces between the slots and the open air, to make the image easier to interpret. For the LE part of the simulation I have used T/S parameters from the Peerless SLS-P830669, except the diaphragm area used for the simulation is a little larger (about 15%).


First, normalized horisontal radiation pattern 20-600Hz:

As expected a slightly front-radiating bias can be seen as compared to a normal dipole. It transitions from cardioid directivity towards dipole at higher frequencies before becoming chaotic around 200Hz. The frequency where this occurs would go higher if the slots were made smaller. A reasonable best case scenario I would think is around 300Hz.

Here is the on-axis frequency response. because dipoles to a larger degree than other loudspeakers will have some distance dependence I have simulated both at 100 meter distance and at 1 meter distance:

The strong resonance and low-pass filter effect of the slots can be clearly seen. With some help from the room it would not be surprising to see this subwoofer go flat to around 30-40Hz in a room. It is no surprise, but I would highly recommend an aggressive low-pass to avoid the cavity resonance of the subwoofer.

Excursion of the woofers look like this, which is pretty much the same as the woofer in free air at the same driving level. At lower frequencies there is quite a bit of excursion for the output level you get.

To conclude: I don't think ripoles make much sense unless you have a need for a small, directional sub. A similarly sized sealed sub would yield you more output in almost every case, with a wider range of possible upper crossovers to boot.

 

[Richard G]

Good work

i think both small and directional are desirable … outweighed by the advantages of small and sealed

Linkwitz used to say that for those who wanted to extend the depth of his dipole Phoenix and Orion he developed the Thor (from memory) a modest ~ 45 litres and sealed … with a “Linkwitz Transform” to optimise the bass below ~30/ 35 Hz

 

[eddantes]

Too science-y for this smooth-brain...

But I can share some direct experience. I owned Hawethorne Silver Iris..es on a basic 2 x 3 open baffle, and I still own and listen to 12" phillips norelco bicones in a fridge sized (somewhat dampened) U frame. Apart from the fact that the FR is definetly odd on both of these, and the beaming on the 12" full range is something to behold - both have qualities that I found valuable. Silver Iris open baffles had an almost eire effect of casting reflections that would make sounds appear all around me - it is surely not "the artist's intent" - but it was a lot of fun, and occasionally sent shivers and chills down my back during listening sessions late at night. The Uframe offer a dynamicism that is just intoxicating - sure you can't move your head even an inch and the FR has dips and peaks that even someone like me can identify, but no other speaker I've listened to puts sound inside my head like that one - from the tiniest whisper to the loudest boom - it's nearly like wearing headphones.

So - on a purely subjective basis - while it's clear that neither of these are anywhere near where "good" speakers (like my Revels) ought to be - they still bring party tricks, that I think are worthy of experience. And a part of me kinda feels like we're breeding out these "surprises" with the efforts here, and that's kinda sad, though I suppose, inevitable.

 

[Nwickliff]

Too science-y for this smooth-brain...

But I can share some direct experience. I owned Hawethorne Silver Iris..es on a basic 2 x 3 open baffle, and I still own and listen to 12" phillips norelco bicones in a fridge sized (somewhat dampened) U frame. Apart from the fact that the FR is definetly odd on both of these, and the beaming on the 12" full range is something to behold - both have qualities that I found valuable. Silver Iris open baffles had an almost eire effect of casting reflections that would make sounds appear all around me - it is surely not "the artist's intent" - but it was a lot of fun, and occasionally sent shivers and chills down my back during listening sessions late at night. The Uframe offer a dynamicism that is just intoxicating - sure you can't move your head even an inch and the FR has dips and peaks that even someone like me can identify, but no other speaker I've listened to puts sound inside my head like that one - from the tiniest whisper to the loudest boom - it's nearly like wearing headphones.

So - on a purely subjective basis - while it's clear that neither of these are anywhere near where "good" speakers (like my Revels) ought to be - they still bring party tricks, that I think are worthy of experience. And a part of me kinda feels like we're breeding out these "surprises" with the efforts here, and that's kinda sad, though I suppose, inevitable.

Love this. Makes me think of the entire audio journey I have taken starting with Klipsch RF82's and then Klipsch Hersey, Forte, Chorus, then, learning about measurements and resonance and then hearing the BOX from ALL the Klipsch speakers, then moving to Full range OB Lii audio 15" (exact same thing you said about that really other worldly audio experience but head in a vice situation) and Finally to flat DIY open baffle with Kef q100 driver as mid and tweeter with two 15" GRS drivers. Audio bliss, but there was something really fun about those head in a vice OB speakers and something really fun about the Klipsch Heritage speakers with their wavy frequency response and just a crazy directivity. They were fun and made me do double takes. Someday I'll grab another pair for the party tricks they performed. Accuracy isn't everything.

 

[ajar]

Is your comment about beaming positive or negative?

 

[Nwickliff]

Is your comment about beaming positive or negative?

I'm guessing just a reality. Not necessarily negative (if you keep your head still in the sweet spot) but oh man if you move it WILL be noticeable. Maybe it's just me but I think that beaming also helped mitigate reflections off sidewalls which increased incredible pinpoint imaging. It's been a long time for me so I could be romanticizing the experience at this point.