Ripol cavity resonance vs cross over design

[Heinrich]

Linkwitz was one of the few people to not play fast and loose with the term "subwoofer."

I didn‘t say that, only to be clear. The dipole (sub) woofer is a dead end, that’s what I said.

The ‚ripole‘ the more so. In my book it realizes all the downs to the max, and bearly the anyway faint ups of open baffle. As to support my detailed argumentation I linked to the Linkwitz site.

 

[Bending]

I tied to find distortion measurements of any dipole design (Ripol or slot loaded) but the only one I found is on Linkwitz page including crossover and midrange.
As dipole woofers require more travel it requires woofer which are designed for it, mechanically and magnetic motor too. I could imagine that there are not many (sub)woofers which have low distortion with larger travel.
This one is specifically designed for Dipole: https://audioxpress.com/article/test-bench-the-uf295fas-thin-profile-dipole-10-woofer-from-neotera
but not yet in production

 

[Heinrich]

I tied to find distortion measurements of any dipole design (Ripol or slot loaded) but the only one I found is on Linkwitz page including crossover and midrange.
As dipole woofers require more travel it requires woofer which are designed for it, mechanically and magnetic motor too. I could imagine that there are not many (sub)woofers which have low distortion with larger travel.
This one is specifically designed for Dipole: https://audioxpress.com/article/test-bench-the-uf295fas-thin-profile-dipole-10-woofer-from-neotera
but not yet in production

Hi @bendig, I‘m absolutely convinced that you‘ll find a proper solution. I‘m looking forward to your kind report. As curious as I am, I still would propose to plan for a prototype with inexpensive drivers to look out for potential problems.

 

[Heinrich]

Yes. Please read about slot-loaded open baffle, for example here: https://www.firstwatt.com/wp-content/uploads/2023/12/art_slob.pdf

I stated my strong opinion, that the pdf linked in here is misleading by being just wrong. Nobody to pick up my criticism, no correction in one or the other direction? It's a pitty, indeed.

 

[KSTR]

I stated my strong opinion, that the pdf linked in here is misleading by being just wrong. Nobody to pick up my criticism, no correction in one or the other direction? It's a pitty, indeed.

I think you might be overreacting here.
The reason I linked this PDF is because it shows with a simple illustration that several smaller dipole woofers with reduced cavity depth can be stacked on top of each other for a suwoofer with enough output, nothing less and nothing more, responding to the original question:

Most Ripol designs are based on 12" drivers and have the cavity resonances often around 300Hz or a little lower. Would a design with smaller woofers and therefore smaller cavities significantly increase the cavity resonance frequency?

 

[goryu]

Check this out:

The XSD Speaker

This is a thread dedicated to the eXtremely Sexy Dipole (XSD) speaker that originated as a cardboard prototype 8 years ago in this thread. I built it 8 years ago using cheap $5 woofers and cardboard. It sounded so good, I made a note to myself that I must revisit this one day as a proper...

www.diyaudio.com

 

[M240i]

I stated my strong opinion, that the pdf linked in here is misleading by being just wrong. Nobody to pick up my criticism, no correction in one or the other direction? It's a pitty, indeed.

I haven't listened to those particular speakers. But, Nelson Pass opined "They sound really good. They measure well."
Since he's a fairly well respected audio guy, how are we to take that?

 

[Heinrich]

I think you might be overreacting here.
The reason I linked this PDF is because it shows with a simple illustration that several smaller dipole woofers with reduced cavity depth can be stacked on top of each other for a suwoofer with enough output, nothing less and nothing more, responding to the original question:

There's 99% misleading stuff in that pdf. It was neither discussed by you nor any other, not even as a sidenote. I wonder if someone needing an illustration on how a box could be stacked would identify the balloney contained there.

Again, 9dB of a gain for nothing, plausible?! Why is it that the industry refuses to take an 8-fold advantage, that Mr. Nelson Pass proclaims? Following his 'reasoning' it should be readily at hand with even closed boxes. And the wonders could be enhanced with even smaller 'slits', no limits!

What Dr. Oskar Heil of AMT fame forgot is the acoustic impedance, and it goes on and on. A bit upset I got, to be honest. But it's over now.

Should we believe in authorities and their listening experiences? Better not, me thinks.

Yes. Please read about slot-loaded open baffle, ...

With this notion, putting the term in italics you opened the door into a net of wishfull thinking.

I haven't listened to those particular speakers. But, Nelson Pass opined "They sound really good. They measure well."
Since he's a fairly well respected audio guy, how are we to take that?

Mr. Nelson Pass has some followship, but in between engineers his designs, amps mostly, to my humble knowledge, aren't as much respected, as you may think.

 

[M240i]

Acoustical impedance is reflected in the acoustical measurements, yes?

There's not a free lunch there. Nor is one claimed.

 

[Heinrich]

Acoustical impedance is reflected in the acoustical measurements, yes?

There's not a free lunch there. Nor is one claimed.

No, actually. It would be like telling that quantum mechanics is reflected in measuring the moon's distance to Chicago. In short, the relation is missing.

I was not talking about lunch. There is none, not even in its metaphorical sense. Nothing to digest, except lukewarm, polluted air.

I'm not going to explain acoustical impedance lost in translation from academia to the hobbyist's imagination. Mr. Pass claims that the energy goes with velocity squared (correct), that there is a proportional velocity increase by reducing the slot's area (incorrect) and henceforth there is an increase in output (incorrect), and he claims he has measurement that confirms (incorrect), making it all worthwhile (incorrect). All this chain reaction of poorly performed reasoning might originate in misunderstanding academia's use of 'velocity' which in acoustics implicates acceleration, which is force, in radiation terms weighted by area, pressure finally. Rethink, more velocity by smaller area, what drives the molecules to their velocity, pressure maybe, again over a smaller area, and how many of that molecules in a compressible gas of what volume?

While the attempt of Mr. Pass is debunked by sheer thinking in basic terms, what about an experiment. Wait, plausibility: not anybody uses it, except DIYers of a certain type. It would be so so so easy to restrict the opening of an arbitrary woofer below the cone's area, doesn't have to be a slot actually, if the argumentation would hold ... ... .

The experiment now: push a closed box closer and closer to a rigid wall. Measure the increase in output, 9dB should be achievable, EXPLODING once the remaining slot's area would be less than a 10th of the cone area.

Take care, don't demolish your house, I do not take any responsibility!

Another word of caution: Look up "Demon Core" in the wiki, and see how crazy dangerous it is a) to tinker around and b) especially when exploring SLOB ideas

 

[phr33ksho]

There is a velocity increase, however there is also a proportional decrease in the effective radiating area with slot loading - the surface that bounds the air at increased velocity is proportionally smaller. What you do get is more cardioid type dispersion, and a small gain in efficiency (over a small dimensioned completely open baffle) because the acoustic impedance is more closely matched, so you get slightly more output from the front, and the nulls are pushed further back than 90 degrees - https://lautsprechershop.de/pdf/ripol/ridtahler.pdf

One needs to accept low efficiency and the need for large surface area and/or excursion to get bass from an open baffle of any kind. That being said I feel the strongest point in favor of this configuration is the reaction force cancellation - open baffles tend to not be particularly rigid, so are excited by the reaction force of the motor - if the panel has resonance nodes in the woofers output range it can lead to large amounts of spurious output. I've built a ripole woofer unit similar in design to the one proposed by linkwitz on the bottom of this page - https://www.linkwitzlab.com/woofer3.htm - I'm using a DSP and crossing over at 100hz with an lr4 low pass, and no high pass. I've got it tuned with a corner frequency of about 14hz and with 4 12 inch drivers, having about 11mm usable x-max it has enough output for my normal listening levels. There is an objective and subjective difference to the quality of open baffle vs sealed bass, which I think largely derives from the fact that dipoles don't excite the rooms DC mode, however the ETCs also look fairly different with the lengths being similar but dipols having a quicker energy dropoff. I don't think people should be discourage from experimenting but expectations should be kept realistic - a good rule of thumb is you need 4x the surface area for open baffle low bass that you would with sealed. For some electronic music I find it sounds better, for others worse it kind of depends on how the producer is using the bass frequencies. For acoustic stuff however I personally find it an improvement

I think the neoterra driver would be an interesting midwoofer in an open baffle speaker, however it doesn't have the size or x-max to act as a subwoofer in an open baffle - for that you really want a 12+ inch with a healthy x-max. That being said it doesn't make sense to get some uber sub with 3inch p-p travel and 3k watt rms as your excursion becomes limited by aerodynamic noise produced by the frame and spider. The neoterra design would be great for removing this issue, however I suspect it is not capable of the high excursion levels where the advantage would be apparent in its current state

 

[M240i]

@phr33ksho
Thanks for posting. It's good to hear from someone with actual experience.
My own system is similar to yours with four 12" woofers per side in a dipole (not ripole) configuration.
I haven't experienced better bass performance in many decades of listening to various audio systems.

It's too bad dipole woofer systems are a dead end.

 

[phr33ksho]

I'll post some photos when I'm done with the build, it's definitely very unique - I plan on building a second unit and using them in conjunction with the upper baffle portion of the lx521.4

I've also got a couple ideas I'd like to experiment with, including a concept to increase the chamber resonance frequency, as well as adding some resistive screens to the rear to make it a true cardioid (although the main motivation is just to increase the output at listening position).

 

[Heinrich]

@phr33ksho
Thanks for posting. It's good to hear from someone with actual experience.

Don't see my contribution as experience based? You may miss out.

My own system is similar to yours with four 12" woofers per side in a dipole (not ripole) configuration.
I haven't experienced better bass performance in many decades of listening to various audio systems.

Congratulation, seems you've found the best for you after so many decades of variations!

It's too bad dipole woofer systems are a dead end.

Look, with in total 8 pieces of quite competent 12" woofers I would rock my community down the street.

Anyway, think of having, actually, a dipole with two speakers in anti-phase. Ported type, closed, whatever, just anti-phase makes a dipole. Integrate that into a room. Adjust for optimal response, and sooner or later the relative phase is going to be changed in order to optimize, position is altered. And then successively the plan will change from dipole to something else with more power using the same speakers, but with a more intelligent use of them.

Let me recap. There is missing experience in general, you are very much satisfied with your belongings, so much so, that you feel nothing but confidence, not willing to discuss your results. The Mr. Nelson Pass "slot", debunked as nonsense, is pushed out of the way, anyway.

 

[BrianKjeldsen]

With all due respect, great achievements!! This shouldn‘t hinder me to comment on your referring project. Regarding the gas state equation pV = nkT, it is nonlinear. Only that its contribution is nelegable compred to the motor‘s. I recently built a successful box comprising a 7“ woofer in 8 liters going down to 20Hz in-room.

Regardless of my huge respect for S.Linkwitz, the dipole sub is a dead end, and even more so the so called ripole. Distortion gets out of hand, always. Better to have several sealed boxes, positioned reasonably in the room, and equalize to taste.

Regarding line level equalizing, I thought, for my own use, of combining real tiny inductors combined with capacitors very much like ‚solderdude‘ does for headphone equalization. Didn‘t try yet.

It would be interesting to see the 7" subwoofer in detail. I guess sensitivity and max spl is significantly reduced, and only works for a multiple subwoofer set-up. Multi subwoofers is definitely the way to go, if it's practically possible. For me and many others it's not possible. Visually I find OB's appealing, and since you can make them sound great, within their limitations, then it's still one way to get good hifi loudspeakers.