I went to the Bristol hifi show at the weekend.
The only speaker that stood out to me was this open baffle speaker.
But as I was looking at it and listening, I thought, it could be so much better if the baffle was replaced with a DML panel.
Steve.
Attachments
JohnnoG says he is going to send me some larger round flueted proplex panels 2x4ft.
I will have to use more 10watt exciters or find a larger more powerful exciter to drive this heavy panel.
It will weigh about 1.8kg 🤔
I want to see how the performance changes with a larger panel, or if the 2ft x 2ft is more the optimum size ?
The flutes will go down the panel, but we were talking about the flutes going across as well ?
We will see.
No stifling of inspiration here.
Steve.
I will have to use more 10watt exciters or find a larger more powerful exciter to drive this heavy panel.
It will weigh about 1.8kg 🤔
I want to see how the performance changes with a larger panel, or if the 2ft x 2ft is more the optimum size ?
The flutes will go down the panel, but we were talking about the flutes going across as well ?
We will see.
No stifling of inspiration here.
Steve.
I will also be carrying on testing the film passive diaphragm on the proplex panels.
I will probably use a thicker film as cling film is a pain in the neck, especially when you have a bunch of bananas for fingers 😃
I Just need to get the spacing off of the panel just right .
I was talking to my friend at the audio show, he was the one that said he preferred the sound of his DML wharfdale picture panels, with the picture in place.
This was about ten years ago.
He said " you took your time" 🤣
Although I am not using paper this time.
Steve.
I will probably use a thicker film as cling film is a pain in the neck, especially when you have a bunch of bananas for fingers 😃
I Just need to get the spacing off of the panel just right .
I was talking to my friend at the audio show, he was the one that said he preferred the sound of his DML wharfdale picture panels, with the picture in place.
This was about ten years ago.
He said " you took your time" 🤣
Although I am not using paper this time.
Steve.
I agree. I think there's no real reason why a (properly terminated and supported) DML woofer can't sound as good as a 15" OP woofer.
Andre.
I was talking about the baffle on top of the box ,and replacing it with a dml panel.
Some panels can get down to 40hz with my exciter as long as you do not want to listen to loud pounding electronic low frequencies.
There are design ideas for flat panel low frequency panels, but I don't know how much dml activity is going on below 40hz unless the panel is very massive, like a wall.
Steve.
I was talking about the baffle on top of the box ,and replacing it with a dml panel.
Some panels can get down to 40hz with my exciter as long as you do not want to listen to loud pounding electronic low frequencies.
There are design ideas for flat panel low frequency panels, but I don't know how much dml activity is going on below 40hz unless the panel is very massive, like a wall.
Steve.
The general (>300hz) advantages of DML's over pistons are omnidirectionality and phase coherence, but these advantages disappear below 300hz (more or less.) Subs are omnidirectional unless you have a massive horn.
I was working on improving the Pure Audio OB design when I discovered DML. I initially used DML panels of the same
dimensions as the open baffles that I was testing, and just left the Alpha 15 woofers in the panel because I thought the DML panels would need extra bass. They actually didn't. The panels sounded just as good without the woofers and without LF rolloff.
It's all to do with surface area and excursion. The size of the panel I was using could move the same volume of air as 2 x 15"woofers could.
But as far as DML activity goes at those low frequencies, I would say it's a moot point: There's no DML advantage to be had over pistonic activity at those frequencies. In fact, I suspect one would lose punch, transient response and efficiency in DML compared to a piston. A panel working so low would have to be as floppy as soggy spaghetti in order to generate a bending wave.
I'd suggest the panel rather be made stiff, with its edges properly terminated, and the driver well supported in order to generate a wholly pistonic action.
The advantage is of course, that a very large panel can have multiple exciters and thence obviate the need for large excursion AND retain punch and transient response.
Hello Eric,
Maybe 2 aspects to explore from your experience :
- if you remember, some posts ago (many?) I suggested the possibility of a limit in dimensions for DML; a consequence of the dimensions being the time to stop the oscillations in comparison to what the hearing system can tolerate. Have you checked spectrograms of those panels?
- You had the possibility to test low, medium and high density EPS. Have you observed using the same exciter the HF extension ?
After the boiled egg opener in in #4429, the use of egg white as grain filler, the egg shape dome, it is time to discovered the ring for egg! I didn't know this accessory!
Joke aside, good you shared (remind) your experience Pete.
25kg/m³ seems a good basis for EPS testing.
Christian
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All + @Andre Bellwood , @Veleric, @pway
I made some additional impedance measurements
1/ The second exciter I have shows about the same characteristics as its brother. Not far from the specifications
2/ As it is what I have currently, I measured the impedance of my canvas panels and added a FR measured outdoor about one year ago.
The impedance scale is on the right, SPL on the left. Both impedance curves are similar (don't consider the sharp spikes which are a problem in the test set up, 50Hz harmonics). The peaks in the impedance curves reflect the damping of the membrane. There is probably unused information behind.
When I will be back in the location I have plywood panel, I'll post the impedance curve.
I made some additional impedance measurements
1/ The second exciter I have shows about the same characteristics as its brother. Not far from the specifications
The impedance scale is on the right, SPL on the left. Both impedance curves are similar (don't consider the sharp spikes which are a problem in the test set up, 50Hz harmonics). The peaks in the impedance curves reflect the damping of the membrane. There is probably unused information behind.
When I will be back in the location I have plywood panel, I'll post the impedance curve.
Hi Christian,
Even with a bit of interference, those measurements are very nice. Do you know if your sound card is DC-coupled? (it certainly looks like it is!)
Those spikes seem to line up with 50Hz mains hums and their harmonics. Silly question, but are you using shielded cables? A single common earth through the whole system? Are you measuring the devices on your table-top, and is there a fan or a computer on the table-top which vibrates it slightly? umm... l lights...some kinds of lights cause all kinds of mains interference.
Long time ago that I haven't considered the performance of this card. It is an old soundblaster Audigy 2NX. The RMAA tests I found say -0.6dB @40hz. Where I am sure is that I ran the 3 calibrations steps of REW (no load, short circuit, known resistance)
Yes spikes are mains related by some way. The quality of the cables might be a question as I use those jack to RCA cables available in any supermarket. A circulation of current through the parasitic or physical capacitors of the mains to DC power supplies is a possibility.
The only possible fan is the one from the laptop. All the devices are on a wood table.
I will run additional tests tomorrow to sort among all those possibilities.
Thank you
Christian
Christian the cheap shielded RCA cables are fine as long as they are shielded.
In any case, looking closer, those harmonics go too deep for it to be caused by straight mains interference. And there are no even-order spikes, they're odd -order, which implies 50Hz square-waves, or badly-smoothed power supplies?
I also found that mounting my drivers (with sticky stuff) on the work-table with the computer on it definitely picked up fan vibrations, as well as any other loud noises in the background when doing impedance measurements. I was surprised.
Does anyone have learnt experiences on the type of paint to use over XPS foam ?
The only XPS panel i can get in Australian "Big box" stores is a bit porous , The options would be water based so it doesn't break down the foam like a solvent based paint , latex style paints may be too soft and could damp out waves.
I looked at some paints which are claimed to be "non - stick - dirt shedding coatings which i wont use in case the VHB tape unsticks itself.
So i am thinking of exterior house paint because it dries a little harder than an interior paint would and may possibly give sharper cleaner waveform reflection
I also have a choice of satin sheen which is like a matt coating but that may also act a little dull compared to a gloss reflective surface.
There is also Gloss which might sound too tinny so i will probably start with semi-gloss as a starting point .
Edited ** I will use a circle of epoxy (araldite) to mount the exciter on to before i paint the panel , i will sand the front only and recoat if neccessary.
Do people think the 50/50 PVA is still a better sealer for its hardness over water based exterior paint ?
The only XPS panel i can get in Australian "Big box" stores is a bit porous , The options would be water based so it doesn't break down the foam like a solvent based paint , latex style paints may be too soft and could damp out waves.
I looked at some paints which are claimed to be "non - stick - dirt shedding coatings which i wont use in case the VHB tape unsticks itself.
So i am thinking of exterior house paint because it dries a little harder than an interior paint would and may possibly give sharper cleaner waveform reflection
I also have a choice of satin sheen which is like a matt coating but that may also act a little dull compared to a gloss reflective surface.
There is also Gloss which might sound too tinny so i will probably start with semi-gloss as a starting point .
Edited ** I will use a circle of epoxy (araldite) to mount the exciter on to before i paint the panel , i will sand the front only and recoat if neccessary.
Do people think the 50/50 PVA is still a better sealer for its hardness over water based exterior paint ?
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Hi Steve,
Interesting question. The easy answer is 100Hz - 4khz or so. Of course that's only a fraction of the answer. If you've ever heard a guitar, electric or acoustic, playing through any wide-band, flat-response speakers, then you know it sounds bad. Very bad.
Basically acoustic and electrics both have audible information below 100hz and well over 5kHz, but their aural fingerprints have completely different 'shapes.'
The nitty-gritty... Electric and acoustic guitars are generally tuned the same, and they play the same notes, and they generally have the same length fretboards, and the same number of frets. Generally. But they sound vastly different, they have different spectra, and are played differently to each other. A Gibson will not sound the same as a Fender Strat will not sound the same as a Telecaster. And they're all electric. And they all "like" different amplifiers—A Vox AC30 sounds completely different to a Fender Twin Reverb sounds different to a Marshall stack even if you stick (the holy-frail) Celestion GK12 speakers into all of them.
Say nothing of acoustic guitars where a steel-string acoustic is as different to an electric guitar as it is to a nylon-string guitar.
I was surprised when I saw the DML guitar speaker.
The problem is that a DML panel has no break-up nodes. Or maybe it's ALL break-up below co-incidence. I dunno. If one uses DML for acoustic guitar, then that should be fine because one does not normally over-drive an acoustic guitar amplifier (the guitar itself feeds back too easily and too low in frequency.)
But electric guitar speakers are made to over-drive. Classic rock guitar speakers, like the Celestion GK12-100, have cones which are designed to break up progressively under high wattage drive.
But maybe a DML can be used for electric guitar IF all of the over-drive comes from the pedals or from the amp itself (if it has a carefully-designed output stage that delivers the correct type of distortion.)
Having said all that, maybe there is a place for DML guitar speakers. The DML limited-bandwidth issue is not a problem, and actually fits nicely with acoustic OR electric guitars. You don't need flat response, and in fact, different types of colour in the speaker sound might make it attractive to different styles and players. The only thing a DML might need is a smooth, low-Q presence peak in the response say, 6db up between 1,5khz - 3.5khz or so. Electric and acoustic will both benefit from this.
Other than that, the amp has to have decent tone controls -- bass, mid & treble -- for the player to get his own sound easily. I'm not sure how DML panels will respond to being over-driven. Maybe that's something worth checking.
Here's the Celestion G-12K guitar speaker response. They are mostly in open-backed cabinets, so that's probably what you would hear firing at you from the stage.
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Thanks André. Paul pointed the same square waves possibility. Next step is to have a look with the spectrum analyzer.
About the mechanichal coupling, REW help warns also about it. Good to know it is a reallity. There is a filter available to make a noise reduction (see below)