Eminence does the Alpha 15 specifically for OB applications.
https://eminence.com/products/alpha_15a#specifications
Also have a look at the BIANCO-105B-350. It's substantially more substantial than the Alpha15.
https://www.sbaudience.com/index.php/products/open-baffle-drivers/bianco-15ob350/
I built 2 panels, 460x770mm x 20mm EPS/paper-skin for experimental purposes and was going to use a 15" Alpha for the bottom end. However, that size panel was large enough that the addition of the Alpha15 did not necessarily sound as good as the panel by itself. I suspect that a (passive) cross-over (2nd-order 200Hz LPF) does stuff around with transients and dynamics in the upper bass range, and destroys the attack of snares, toms, slap-bass and brass instruments. It also interferes with the fundamental harmonic of the male voice. So, IMHO, I thought that the woofer was unnecessary IF The panel was large enough.
But the HF bugged me...
In the end I got a very nice response by placing a Tectonic driver onto an over-sized kind of "puck"— a 100mm dia disc of 6mm Twinwall polycarb in a hole in the EPS.
However! This does reduce efficiency. The disc does not necessarily give a better or "louder"(?) response at HF, so I suspect that it simply reduces the resonances at panel frequencies while matching the disc response with the panel material.
One of the problems these days... 🙂
You need another person to help with the cling film. Best sound comes, when the film is tightly pulled fully around the panel, all edges closed, even on the untreated 20mm EPS sheet. Kitchen aluminium sheet gives a nicer sound, but you have to fix it permanently later on. Before that you'd have to 'iron' it on somehow. Adding an adhesive would make any panel treated. Any cover film, more or less as in #8,552
You might be able to incorporate both HF and LF sections on the same panel as shown in Fig. 18 of the famous NXT patent
or, make an additional panel for bass, or a separate subwoofer with a panel and a cone woofer. To get a better result, the DM panel must be framed and suspended along the perimeter.
or, make an additional panel for bass, or a separate subwoofer with a panel and a cone woofer. To get a better result, the DM panel must be framed and suspended along the perimeter.
??????.
If I had known you had already done all these experiments I would not have wasted my time doing them myself.
Is there anything else I should know.
Steve.
What was it about the HF that bugged you ?
I noticed you had the 10k dip with the hump afterwards, this is caused by the exciter ring area.
The plot says paper eps ?
Steve.
I suggested that here, #8,484 and here #8,512 for others to try, which also means that I too would try that. 🙂 Sure, it is quite hard to attach cling film by yourself. If the wife helps, something positive comes out of it, even the experiment fails. 🙂
Also, I like to read documents/patents the old fashioned way, by copy-pasting important sections/paragraphs and images in a MS Word online doc. That way, I read the document twice, plus a copy is left for later reading, Like here, #8,264 and here #8,405. That way, I can stop reading unnecessary docs half way.
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I was not getting as much HF as what I was getting mids, and I was trying (many!) different ways to introduce a higher-efficiency mechanical "tweeter" for want of a better word, i.e. a single driver but covering different frequencies via physical connections to different sized radiators. The 100mm polycarb disc seemed to decrease mid-range efficiency and thus brought it down to the level of the sagging HF performance.
I suppose this would be the same as using an EQ to drop the mids instead of boosting the tops (as a professional live sound engineer would...)
Possibly, but I couldn't get rid of it. I tried different size rings, I put felts and weights and holes into the rings... After many days of head-scratching I eventually did a (very) nearfield measurement of the exciter, and found that the dip came from the exciter hisself... grr...
Yup, EPS with kraft paper skins.
20mm EPS, 17kg/m3 density. I think 20mm is way too thick, and is also contributing to the sagging top end.
The EPS is stiffened with 64gsm Kraft paper. I used diluted cold glue as adhesive. The cured weight of the paper/glue/EPS composite does make a difference to the response as you can see from the different FR curves.
There's more detail here:
https://www.diyaudio.com/community/threads/dml-pa-systems.390363/page-3#post-7135522
But I probably won't be building this system in the future—I'm going for high-power, high-efficiency PA speakers with a high WAF (she has to help carry them at gigs 😍 )
I've progressed to 1,000 x 350 x 10mm EPS with Kevlar skins. I can get the weight down to 200g per panel before adding 4 x Dayton DAEX 32QMB-4's. This gives me 160WRMS power handling at an estimated 96dBSPL/W>4r per panel. It's still midrange-heavy. But with a good sub, and a bit of a tweek in the HF I've got a VERY nice pair of PA speakers.
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Andre bellwood.
On page 226 post 4502 I mention my method of a very small hole with very light damping , which fills the dip at 10k and flattens the response above.
I use this only on neat eps , I'm not sure of the effect with paper though ?
This reduces the harshness of the sound in the 10k and above, which can hurt sometimes
I watch the response in real time as I adjust the foam damping as it is crucial to get it right.
It takes a lot of care and attention.
This only affects the output within the coil area, mostly.
I know from experience that paper will heavily damp eps ,as you have found.
Steve.
On page 226 post 4502 I mention my method of a very small hole with very light damping , which fills the dip at 10k and flattens the response above.
I use this only on neat eps , I'm not sure of the effect with paper though ?
This reduces the harshness of the sound in the 10k and above, which can hurt sometimes
I watch the response in real time as I adjust the foam damping as it is crucial to get it right.
It takes a lot of care and attention.
This only affects the output within the coil area, mostly.
I know from experience that paper will heavily damp eps ,as you have found.
Steve.
Ja, I tried this initially when I started working with DML's. And I suppose that if I was going for a studio-monitor response or a custom-built home hi-fi then I wouldn't mind spending individual time per system to get little details 'just right.' But I'm going for robust systems that need to be assembled without tweaking. At all. Therefore I need robust solutions that will produce units that can get chucked around and that work and measure and sound pukka even if the assembly process is not followed 110% to the letter.
The second thing is that anything over 10kHz is probably not going to make any difference to most males over the age of 40 or so, or to most females over the age of about 50. It also does not make much difference to live PA systems. That glassy harshness comes more from the 6-8kHz region and makes your eyes water if it's out of kilter.
Absolutely! Paper does damp the EPS very nicely indeed! And with the polycarb disc and the resultant flat response it's good for a "pretty" Hi-Fi sound. But it sounds rather muffled and dead in a live PA application.
Cheers,
A.
EPS/Kevlar panels with 4 x DAEX32QMB-4 per panel mounted onto Twinwall polycarb discs.
Use headphones. Of course, no microphone recording will ever give you a faithful impression of a live sound system... but the general idea is there.
Use headphones. Of course, no microphone recording will ever give you a faithful impression of a live sound system... but the general idea is there.
I usually spot sibilance in the 10k region.
there is also the coil cavity resonance that shows up on some panel materials somewhere in the 3k area depending on materials and coil size.
6mm proplex which is designed to be robust is well damped and has a very flat frequency response up to 20k.
all I have done is attached an exciter.
with 4 powerful exciters I'm sure proplex would be fine for PA work.
Steve.
there is also the coil cavity resonance that shows up on some panel materials somewhere in the 3k area depending on materials and coil size.
6mm proplex which is designed to be robust is well damped and has a very flat frequency response up to 20k.
all I have done is attached an exciter.
with 4 powerful exciters I'm sure proplex would be fine for PA work.
Steve.
Two persons, who has better hearing than I, said that proplex/polypropylene has a gloomy sound, after hearing such sheets. What do you think?
So chdsl.... It would be helpful at this point to know what DML builds you have made.
Thanks
Eucy
You'd have to go back a month or so to find out what I've been experimenting with. For example, you can start from here #7,016 or here #7,261 or here #7,321. I've been digging up lot of info since then, whatever relevant I posted here in this thread for everyone. Still time to build one, sometime later in the late spring or summer. Too cold in the unheated shed in the garden.
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Very interesting. In studio mastering we usually catch male sibilance at 4-6k, and female sibilance at 5-7k. I don't think I recall anybody ever notching their de-essing compressors to 10k.
Proplex? Is that what we call Twinwall Polycarbonate down here? If it is, then I have tested it indeed. Yes, high frequencies are good, but it's a heavy material man—around 190kg/m3. Its areal mass comes out to around 1kg/m2 as opposed to, say an EPS/Kevlar composite which is half of that. And that means at least 4db less sensitivity, and that means I need a 5,000W amp for Twinwall as opposed to a 1,000W amp for EPS/Kevlar for the same dbSPL delivery.
Of course I have to take Young's Modulus and stiffness into account as well. But the bottom line is indeed that high Fc suffers for high sensitivity.
Next step is to dig around the issue of Fc and whether it's really so important....
@Eucyblues99
I am also interested in trying this #7,601 out this summer, somewhat modified, and the ideas of Lee De Forrest #7,970. All of them are DM panels, with an exciter or some other motor.Andre bellwood.
Your plot shows your peak at 15k and the dip at 10k for the single exciter.
My exciter usually peaks (depending on the material) about 10k with dips either side similar to your plots.
Female vocals usually set this peak off.
How many watts were you using in your Video?
Steve.
Your plot shows your peak at 15k and the dip at 10k for the single exciter.
My exciter usually peaks (depending on the material) about 10k with dips either side similar to your plots.
Female vocals usually set this peak off.
How many watts were you using in your Video?
Steve.
Andre bellwood.
Proplex is a heavy duty floor protector and able to withstand high impact.
I think it is polypropylene ,the sample was sent to me by JohnnoG after it had been used to protect his flooring.
There are a few dents in it but it still works fine.
I have also made recordings of these panels with my 10watt exciters.
Steve.
Proplex is a heavy duty floor protector and able to withstand high impact.
I think it is polypropylene ,the sample was sent to me by JohnnoG after it had been used to protect his flooring.
There are a few dents in it but it still works fine.
I have also made recordings of these panels with my 10watt exciters.
Steve.
I was using a 2 x 150WRMS amp of which I might have peaked at 40W at the most raucous times during the party. The clipping indicators didn't wake up at all, and the signal input indicators were only-just idling. That sound check was idling... probably running between 5 & 15W.