Having a larger volume within the box enables better bass response, but it comes at the expense of requiring more wood for the box making it heavier and increasing the visual impact. Larger loudspeaker boxes may also not fit into every situation. As with any design there is a balance between the different factors to provide the optimum performance within the requirements for any given situation. The infinite baffle or sealed baffle loudspeaker can be represented by a series of electrical equivalent components.
This representation of the infinite baffle or sealed baffle speaker helps understand how the different elements relate and how the performance can be optimised. The diagrams shows the mechanical and electrical equivalent circuit for a woofer loudspeaker in a closed cabinet..
The resistor R ab represents the box losses and R al represents the leakage losses. The loudspeaker cone is represented by the transformer as it converts between the electrical and mechanical domains. The transformer has a turns ratio of 1 : S d where S d is the cone area. This converts the mechanical force to pressure and velocity u to volume velocity U.
The input force comes from the loudspeaker voice coil. The physical mass of the speaker cone behaves like an inductor on the acoustic domain, but in the electrical domain it appears as a capacitor. The result of the combined inductance and capacitance is a damped resonant circuit. As the box or closed baffle increases the stiffness on which the moving mass resonates, this increases the resonant frequency. When using a small box, it is necessary to have a very compliant suspension on the speaker to keep the resonant frequency low.
If this is too high, then the total electrical Q for the speaker becomes too low and the damping becomes too great. The efficiency is higher, but this is at the expense of good bass response.
Conversely a BL product which is too low gives rise to higher bass response , but the transient response becomes poor and the bass may tend to boom and sound dull. The overall Q of a speaker system, i. Values of Q tc above unity tend to have boomy bass, whilst values below critical damping which has a value of 0.
The critical damping gives a sound pressure level of -6dB at resonance. Often the value of 0. Apart from the resonance of the bass speaker cone, the box or cabinet will have internal resonances.
It is normal to damp these as much as possible by the use of sound absorbent material within the cabinet. Nearfield response suggests a quite linear response down to 50 Hz - not bad at all when you add the port response. These speakers should do well below 40 Hz.
The very simple series crossover shown in the pdf file was constructed for the MT and a ruler flat response was measured from to Hz - the upper limit of the CLIO system. After having found the subjectively best point of crossover between the bass and mid from using a 24 dB electronic crossover, I constructed a similar passive set-up. Not that easy as the mid is a 4 ohm driver and I don't want the impedance to drop below that.
Eventually things worked out and a 3rd order electrical crossover was in place and all drivers could be connected with positive polarity. My expectations to sensitivity were very high Tannoys still fresh in memory and I was initially a little disappointed from this until I realised how high I was playing. This speaker can play loud without apparent distortion and it takes an act of will to turn the volume knob down to normal listening level because the level of transparency is so good that you have to hear all the details on every piece of music.
This speaker does not have the absolute neutrality of the Acapella SE and the ability to portray any piece of music with the same grace and fidelity, but it has some more speed and sparkle that may suit some musical genres.
Un-treated paper cones are rarely neutral and the SS 15M mid-driver and 10" paper cone bass are no exception from this rule, but the agility and transient attach is something that coated magnesium cones comes short of and something that the home constructor has to be very much aware of before deciding on drivers for a new project. These speakers handle female vocals very well.
Sometimes paper cones and valves go hand in hand and this appear to be the case for the Acapella WB. I'm hesitant to coat the middriver. I know it will take some edginess, but also some vividness and well, colouration if you like. It's remarkable that paper cones have survived until this very day despite numerous alternatives with much better physical properties. But well produced paper cones have a "thing" that any other cone material hasn't.
In my small workshop the bass initially seemed a little low in level and extension, but it is not often you can hear anything from a 31 Hz warble tone, but this one can tell you it's there.
And getting the speakers into the much larger living room certainly opened the bass and there was the level and extension. The transient attach of the bass could be better kick drum and I have to experiment with a smaller cabinet size and possibly a higher vent tuning before I look for other drivers. The 4 ohms driver could almost provide the same sensitivity as the 8 ohms paper cone drivers but with low impedance in the bass region and the alu drivers provided some 3 dB reduction in sensitivity.
For the time being I'm staying with the paper cone although the alu cone appeared to work very well. First time living room set-up. Fresh coffee and a stack of CDs and LPs. Seen above is a range of drivers suggesting quite some confusion. And a 12" JBL bass driver! There's always a honeymoon with speakers. You may instantly recognise strengths and weaknesses from a new set-up, but it can take days, sometimes weeks to find out whether you can live with the sound from a driver and the way this particular driver will colour the sound, because all drivers do.
The 10" paper cone bass drivers did great and the tweeter also, but the 15MK00 driver will drive you nuts in the long run. Scan-Speak has done a fine job in elimination major break-up patterns usually associated wit paper cones but this does not mean this driver doesn't have some residual "paper" honky quality to its sound. This driver is phenomenal in accentuating sh Actually the glue used for refoaming drivers.
This material is well suited for coating paper cones and leaves a nice, non-sticky, flexible surface if done properly. This treatment did not change the frequency response and it improved the sound considerably. For some days I thought this was the cure, but something just kept these drivers from having a neutral presentation.
One very noticeable thing is when a high piano note is played and the 15M will smack in your face, but the note doesn't stop fast enough. It's like the 15M is ringing. Does the combination of a high mechanical Q, the kapton voice coil and the paper cone produce this effect?
Is a middriver with better damping what's needed? Tweeter attenuation was tested thoroughly and a new parallel crossover for the MT was constructed but this didn't perform better than the former series crossover. Seriously, a 25 year old el-cheapo driver! This driver has a coated paper cone and I removed the terrible plastic dust cap and inserted a phase plug from an old SEAS driver. Again, some very enjoyable midrange and good vocal performance. Replacing the 15M with these new drivers took some extensive crossover modifications every time.
There's no plug and play in this business Sorry, not my cup of tea. So it was time to reconsider the whole project. A pair of JBL A drivers in mint condition caught my attention at eBay and I've always wanted a pair of these and so I had - for a reasonable amount of money. I knew these bass drivers would have a relatively high Qt and probably would perform best in litres closed cabs and they might be worth a try in the Acapella WB.
JBL A Signature. What of the infinite goodness of God in teaching the grub of the ichneumon-fly to eat up the cabbage caterpillar alive? I see no infinite goodness here, but only the infinite foolishness of sentimental superstition. There were infinite possibilities for "the greaser" to pocket a goodly share of the profits, and "cover up his tracks. He took infinite pains with everything and his enthusiasm knew no bounds. New Word List Word List. Save This Word!
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