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Old 19th December 2003, 09:21 PM   #1
amo is offline amo  United States
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Default The "sound" of high acceleration factor

When a naive diy begginer, such as myself, attempts to design a first system, the options seem endless - so many drivers, so little time.... But then constraints begin to take place, and the options quickly dissapear. Two such constrains, seem to be especially tough together. If you want an all-sealed design, with Qb between .5 and .7, and at the same time one that can reproduce respectable SPL, and at the same time must be driven by a half dozen alephs, non of which are to exceed a specific size to reduce heat dissipation..... I thought these were reasonable parameters, untill I began modeling the system for power requirements using Mr. Linkwitz's formular (or rather formulas found on his site...). The vast majority of high quality drivers, when placed in a sealed box of the above mentioned Qb, require MASSIVE ammounts of power to be driven to decen SPL. In some cases, multiples of drivers must be used, also encreasing power requirements.... What to do......

I keep coming back to the same solution, which seems to be the most reasonable, although very expensive. This solution will have one large driver reproducing the midbass, from maybe 60 Hz to 800 Hz, and probably 1 Khz if we factor in after-XO responce. What bothers me, however, is that this driver has an exceleration factor of 175, and I need some reasurance that this is ok, even all the way up to 1 Khz, before I commit to this expensive solution. So if anyone has comments, I would love to hear them. Thanks!
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Old 19th December 2003, 11:44 PM   #2
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Peak Current = Force x Bl... Does this mean that acceleration factor (being Bl/Mms) has little to do with the "sound", and -ONLY-SPL is effected by quantety of current available? In other words, low Bl and high Mms are ok, as long as you have enough power to drive the speaker????? Is my logic correct?
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Old 19th December 2003, 11:50 PM   #3
Nielsio is offline Nielsio  Netherlands
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What kind of noise-levels do you want to make?

I don't really see the problem. If you see the fact that going low-efficiency multiway is a problem for, in example, amplification, then go high-efficiency!?
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Old 19th December 2003, 11:56 PM   #4
GM is offline GM  United States
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Hmm, I get 177.78 for 60-800Hz, and 277.78 for 60-1kHz, but it's not relevant per se since either the driver has the necessary BW at the desired Q, etc. for the app., or it doesn't.

GM
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Old 20th December 2003, 12:47 AM   #5
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What spl's are you trying to reach ?

What is the power of your 6 (stereo?) alephs?

I'm in the middle of a sealed 3-way project....

Cheers

Rob
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Old 20th December 2003, 01:00 AM   #6
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This is one of those things where figures and measurements don't tell the whole story...

Yes, a high acceleration factor is a good thing, but it needs to be coupled with a lack of cone breakup, colouration, and many other factors besides, as with all these things, a driver can measure really well, but have a sound that usually tends towards the sterile. There is no substitute for listening, or if that is impossible, using others opinions. However, as with all web based stuff, you also need to filter responses and opinions...
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Old 20th December 2003, 02:54 AM   #7
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Quote:
Originally posted by pinkmouse
This is one of those things where figures and measurements don't tell the whole story...

Yes, a high acceleration factor is a good thing, but it needs to be coupled with a lack of cone breakup, colouration, and many other factors besides, as with all these things, a driver can measure really well, but have a sound that usually tends towards the sterile. There is no substitute for listening, or if that is impossible, using others opinions. However, as with all web based stuff, you also need to filter responses and opinions...
Agreed on all accounts. However, i have been relying on people's openions for far too long, and these also tell 50% of the story. So finally I decided to go for the second half, and crunch some numbers. I can tall you that it has been an eye opening experience.
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Old 20th December 2003, 03:04 AM   #8
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Quote:
Originally posted by RobWells
What spl's are you trying to reach ?

What is the power of your 6 (stereo?) alephs?

I'm in the middle of a sealed 3-way project....

Cheers

Rob
The Alephs are still in the "awaiting PCBs" stage, I am afraid.... But, four of them will be 30 watts each (6 channels by the way, not 12). These 4 x 30 will drive a pair of tweeters (94 dB efficiency), and a pair of dome midranges (also 94 dB). I have decided to use a dome midrange for several reasons. First, construction is much simpler, and there is no "box interaction", aside from half space radiation.... The other reason is efficiency. I think 30 watts will push these drivers hard enouph, especially if the baffle step is factored in.

The remaining 2 channels are up in the air, untill I can establish power requirements exactly. The driver is 97 dB efficient, but I am not too sure how it will combine with the other two. I know for sure that for now the woofers will be pushed by a pair of P3A amps, as I can not in any way deal with that much heat. I hope that in a year or so, when I get a new place, I will be able to move the woofers to a pair of Alephs, and use the P3As for a pair of sealed subs (45 Hz and lower?)

I have analyzed several drivers for bass duty, that will not take much power, and still deliver UP TO, 110 dB peak. I am not sure I need so much SPL, but its always good to have a little extra.
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Old 20th December 2003, 03:05 AM   #9
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Quote:
Originally posted by GM
Hmm, I get 177.78 for 60-800Hz, and 277.78 for 60-1kHz, but it's not relevant per se since either the driver has the necessary BW at the desired Q, etc. for the app., or it doesn't.

GM

How are you calculating that?
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Old 20th December 2003, 03:07 AM   #10
amo is offline amo  United States
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Quote:
Originally posted by Nielsio
What kind of noise-levels do you want to make?

I don't really see the problem. If you see the fact that going low-efficiency multiway is a problem for, in example, amplification, then go high-efficiency!?
High efficiency is exactly what I am trying to get, but it appears to be hard to achieve in a sealed box...


I guess what I am trying to understand, is if the Acceleration Factor is just another measure of efficiency, where more power solves any inedequecy (sp?), or does it add to the sound (other things equal) reguardless of power levels.
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