tuyen Posted June 20, 2013 Posted June 20, 2013 Hi all, Anyone with experience with the Beyma Liberty-8 12" guitar driver? It is meant to be a replica of the famous JBL E-120 driver which unfortunately is discontinued model. Getting some rave reviews amongst the diy crowd. http://www.diyaudio.com/forums/multi-way/231551-beyma-12p80nd-tpl-150-a-13.html 102db sensitivity, flat between 400 and 3000. Should pair nicely with the Beyma TPL-150H AMT driver on top? Maybe a pair of JBL 2235H(15") or 2245H(18") in ported box underneath. Objective: to design a high fidelity, high spl system for family member. Something basic like this.. JBL 2245H (18") in ported box, JBL 8" in sealed box for mids and Beyma TPL-150 AMT driver in custom waveguide for highs. Active crossover, high power amps.
tuyen Posted June 20, 2013 Author Posted June 20, 2013 JBL 2245 (95db) + Beyma 8" mid 8m70V2 (95db), Beyma TPL-150 with custom waveguide (100db) 1
tuyen Posted June 21, 2013 Author Posted June 21, 2013 Nup. But am leaning towards similar lines. The guy is cncing me a pair of wave guides for the tpl150. Reckons it sorts out the small issues I found with the stock metal horn from beyma.
tuyen Posted June 21, 2013 Author Posted June 21, 2013 for people who are interested, check out the insides of the bass cab. To think this is all just a temp setup to test the drivers config! The guy is going to build more elegant cabs from walnut for the final build.
Gee Emm Posted June 21, 2013 Posted June 21, 2013 Interesting. What are peoples thoughts with that much filling inside a reflex enclosure? Graham
ArthurDent Posted June 21, 2013 Posted June 21, 2013 Interesting. What are peoples thoughts with that much filling inside a reflex enclosure? Graham It doesn't look like the really dense cotton wadding but even so I would have assumed it was taken into account when calculating Vb.
svenr Posted June 21, 2013 Posted June 21, 2013 (edited) Whether the filling is beneficial depends on the crossover frequency. I'd filter that 18" at about 200..30 Hz. The inside dimensions of the box are quite a bit smaller than this crossover wavelength, thus no modes will exists that need to be absorbed. The absence of mid frequencies will also prevent reflection through the ports and the membrane. The only thing the filling therefore does is lowering the efficiency of the system. Btw - I don't recommend anyone having such a waveguide built. Without a proper design of both the acoustic throat impedance and the directivity this will just be a pricey bit of wood with absolutely unknown acoustic properties. Edited June 21, 2013 by svenr 1
ArthurDent Posted June 21, 2013 Posted June 21, 2013 Perhaps the restricted flow to the ports, especially when the rest of the cotton wadding goes in (and is therefore between the driver and the ports, something you should never do) is part of the design?
tuyen Posted June 21, 2013 Author Posted June 21, 2013 Hi svenr, Could you possibly elaborate what you mean by 'proper design of acoustic throat impedance and directivity'? Is there some data I should be asking the guy for to be sure it is worthwhile? His words below (which having myself played with the Beyma TPL-150H for the past year in both stock horn and without horn, do tend to agree with him): "I built a few prototypes. The one on the pics is the best one yet. Very good imaging. Integration between between the mid is seemless. High extension above 10k is very good." "The beyma horn sounds too forward. Lacks clarity and extension above 10K. Does not image well." "I tried the horn version but it did not image well. It also sounded more like a pro audio speaker. The one without the wave guide did not blend well with the mid, lacked detail and dynamics which why I chose to make a custom wave guide. The custom wave guide images well and blends in with the mid. Its like they are one " "I tried the horn version TPL-150H but I did not like the sound for hifi. Sounds good for Pro sound. I was not happy with the TPL-150 with out the horn which is why I built a custom wave guide. It is a cut down version of the horn." As for the stuffing used: the guy's current test setup (his fav so far): Testing the 2118 in a MTM set up. Seemless integration with all the drivers. Sound stage is much taller. An improvement compared to a single 2118. It plays loud and clear at 100db efficiency. Crossover points for now are LR-24, 270, 1650.
Guest Peter the Greek Posted June 21, 2013 Posted June 21, 2013 (edited) Whether the filling is beneficial depends on the crossover frequency. I'd filter that 18" at about 200..30 Hz. The inside dimensions of the box are quite a bit smaller than this crossover wavelength, thus no modes will exists that need to be absorbed. The absence of mid frequencies will also prevent reflection through the ports and the membrane. The only thing the filling therefore does is lowering the efficiency of the system. So for subs or "bass bins - lets say everything below 300hz there is no need to add absorption to the box? interesting, thanks (I'd been mulling over this recently) That being said, what about damping? say lining the inside of the box with another layer of material (say mdf) over a damping compound such as greenglue in between to reduce internal cabinet resonance? Edit: I have a short memory....thread here Edited June 21, 2013 by Peter the Greek
tuyen Posted June 21, 2013 Author Posted June 21, 2013 Are we saying that the insulation is not providing any benefits in his case as he is crossing between 200-300hz? He is actually just lowering the efficiency of the driver, this actually losing SQ?? Should I advise him to try remove all the insulation out and as a result, he will gain efficiency and performance?
Once was an audiophile Posted June 21, 2013 Posted June 21, 2013 Nup. But am leaning towards similar lines. The guy is cncing me a pair of wave guides for the tpl150. Reckons it sorts out the small issues I found with the stock metal horn from beyma. Tuyen you need a girlfriend
lovetube Posted June 21, 2013 Posted June 21, 2013 Tuyen you need a girlfriend you want him get killed or what Mario ?
davewantsmoore Posted June 21, 2013 Posted June 21, 2013 So for subs or "bass bins - lets say everything below 300hz there is no need to add absorption to the box? Depends on box size
Guest Peter the Greek Posted June 22, 2013 Posted June 22, 2013 Depends on box size Can you please expand on that?
tuyen Posted June 22, 2013 Author Posted June 22, 2013 I'm curious to hear the response for this too. My rythmik audio sub kit (direct servo amp + GR research 12" servo-enabled paper cone driver) came with dampening material to fit around the insides too. The design is meant to be a small box sealed box and users are assuming to cross at no higher than 80hz?
ArthurDent Posted June 22, 2013 Posted June 22, 2013 (edited) I'm curious to hear the response for this too. My rythmik audio sub kit (direct servo amp + GR research 12" servo-enabled paper cone driver) came with dampening material to fit around the insides too. The design is meant to be a small box sealed box and users are assuming to cross at no higher than 80hz? Sealed boxes are different to ported in that they are designed to be filled with damping material. Lining the internal surfaces of a small sealed or ported box for that matter designed to only go to 80hz and then probably with 4th or 8th order filtering. Assuming that the largest internal dimension is less than 1/4 wavelength of the usable passband. Complete waste of time. Edit: Unless the damping material was designed to damp the panels and not standing waves. Edited June 22, 2013 by KenTripp
tuyen Posted June 22, 2013 Author Posted June 22, 2013 Sealed boxes are different to ported in that they are designed to be filled with damping material. Lining the internal surfaces of a small sealed or ported box for that matter designed to only go to 80hz and then probably with 4th or 8th order filtering. Assuming that the largest internal dimension is less than 1/4 wavelength of the usable passband. Complete waste of time. Sorry Ken, slightly confused by your post. Are you talking 'in theory' here, or do you mean the example of the bass cab the guy above is using? Can you confirm that if all the insulation material was removed from his bass cab, he will just gain efficiency without any sq issues?
ArthurDent Posted June 22, 2013 Posted June 22, 2013 Sorry Ken, slightly confused by your post. Are you talking 'in theory' here, or do you mean the example of the bass cab the guy above is using? Can you confirm that if all the insulation material was removed from his bass cab, he will just gain efficiency without any sq issues? Well I was responding to your post about a small sealed sub so comments are applicable to that. As for the ported box, the amount of fill and it's placement is unusual. Efficiency and SQ issues with and without the fill? Measurements and listening will answer that question.
svenr Posted June 23, 2013 Posted June 23, 2013 Beyma Liberty-8 as a midrange driver - I won't recommend using any instrument driver in a serious reproduction system. The metal dustcap is designed to resonate strongly to add 'sparkle' and 'excitement' to guitar sounds. The dustcap produces high frequency noise not related to the spectral or temporal properties of the input signal - it intentionally adds high frequency components to the sound. This is a fantastic thing for a jazz guitar amp such as the Roland Jazz Chorus 50 - fantastic bright and transparent sound. However, this mechanism of colouration is not at all desirable in sound reproduction.As for the Beyma TPL-150H - have a look at the original datasheet with Beyma's horn (http://profesional.beyma.com/ingles/pdf/TPL150H.pdf).%C2'>If your guy cuts the horn short, the horizontal directivity will get much worse with increased beaming towards higher frequencies. Vertical directivity probably doesn't get any worse - but it's very bad already for a single driver use. The guy's horn on a single TPL-150H will give you an unknown on-axis response with potential resonances due to the shortened horn and improper impedance termination of the throat. Because of the increasing directivity, your diffuse soundfield will comprise very little high frequency energy, rendering the sound dull and the apparent stage width too small. ALso, the impedance plot of the TPL-150H with the original Beyma horn shows the resonance at about 1.4kHz. With the short horn this resonance probably increases to something like 1.5..1.6kHz. The minimum useful crossover frequency is therfore at 2.0..2.2 kHz unless you want to risk excessive diaphragm excursion and high distortion.I recommend using a horn suitable for single use. The best horns available for DIY are the oblate spheroidal designs by 18Sound (XT120 and XT1086 for 1" bolt-on throat drivers). Have a look at the datasheets - perfect directivity on both horizontal and vertical direction. Based on my impedance measurements, but horns are free of acoustic resonances above their effective cut-off frequencies (2kHz for XT120 and 1.7kHz for XT1086). I'd recommend using a proven driver such as the Beyma CP380/M with either of these horns.Filling the cabinet with fibrous absorbent is only useful if one wants to absorb energy to dampen modal resoinances inside the cabinet. However, if the cabinet's dimensins are smaller than half the wavelength of the upper crossover frequency, no modal resonance will be excited and there's mnothing to dampen. The fibrous filling does also increase the compliance of the cabinet, i.e. make it acoustically bigger, but at the expense of abrobing energy which would otherwise have been returned to the membrane. Thus the lower efficiency after the introduction of fibrous filling. Just because there are commercial products filled with stuff and cut-off at 80 Hz doesn't mean that the dude who "designed" them actually knows anything about its effects.Don't confuse acoustic cabinet modes with mechanical cabinet modes. Mechanical modes (i.e. resonance of individual cabinet panels) will radiate energy into the room when excited. The best option is to shift mechanical resonances out of the driver pass band by increasing the panel stiffness such that the lowest eigenmode of the panel is well above the upper cut-off. If this doesn't work for say mid frequency cabinets, adding damping to lower the amount of radiation is the way to go. 1
davewantsmoore Posted June 23, 2013 Posted June 23, 2013 The design is meant to be a small box sealed box and users are assuming to cross at no higher than 80hz? My small sealed subwoofers have no stuffing, or lining, anything. Empty box. Putting anything inside the box will not improve performance. 14 litres (Approximately 25cm cube internal dimensions) Walls = 36mm (3x12mm) MDF LPF = 24dB/oct @ -6dB = 80hz
davewantsmoore Posted June 23, 2013 Posted June 23, 2013 (edited) Svenr has got it on the horn. The termination/throat design is extremely sensitive in how it affects the impedance.... and obviously the rast of the horn shape affects the pattern. You need more than a few measurements of both to understand that you are doing the right thing. I began 'playing' with waveguides on dome tweeters a long time now (yes, I know you can't polish a sows ear, or something like that, heh) .... and it took 5 years to fully realise just how difficult it was to design. It been a long road but the latest designs are getting moulded from ABS plastic nicely. https://lh3.googleusercontent.com/-6k6_5OdfNxo/UHX5syXm0nI/AAAAAAAAIs8/ua4HyUbOS04/s512/Group%2520Pic2.jpg Edited June 23, 2013 by davewantsmoore
tuyen Posted June 23, 2013 Author Posted June 23, 2013 (edited) thanks for the reply svenr. Question though, if shortening the horn has negative effects, what about if you remove the horn completely? Wouldn't that be even worse than shortening the horn version of the driver? Why would Beyma sell the TPL150 AMT driver in a 'hornless' version and publish that it is suitable to cross at 1khz? hornless version: http://www.usspeaker.com/beyma%20tpl150-1.htm horn version: http://www.usspeaker.com/beyma%20tpl150h-1.htm I've briefly heard the Beyma CP380M in a small spherical tractix horn. I would say the TPL150 is in a different league to the CP380M in terms of SQ (level of refinement or 'naturalness'). The CP380M was less directional though, which was the upside. Cheers for the tips on the bass driver cabs. Will experiment when doing my build. Any recommendations on suitable mid driver that I can use between the JBL 2245H 18" bass and Beyma TPL150H AMT tweeter? MTM setup? The guy with the DIY setup above is currently in process of testing some PHL 6.5" mids in MTM. Edited June 23, 2013 by tuyen
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