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Old 10th May 2005, 04:00 PM   #11
Dwiel is offline Dwiel  United States
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Thanks for all of the great info!

I definately have quite a bit of research to do before I should decide on one design, but this is a great help.

It looks like the FE206E speaker would be like $90 - 100 or so. (shipped) Is that about as cheap as they get, assuming the high SPL goes for a full range speaker?

Someone else mentioned using a 2W amplifier. I am not entirely sure how jokingly this was said... It seems that most amplifiers are at least 50W even in cars... Will a 2W amp really cover it or was he just being sarcastic? Assuming this is the case, I could probably use a nice OP AMP design... In the case that I do use opamps (I like this idea because the amplification is already packaged for me = easier) what would be a good low Iq?

Thanks for all the great help!
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Old 10th May 2005, 05:44 PM   #12
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He was not joking, 2W into a 96dB speaker is 99dB output,
into a typical 86dB effiecient speaker this takes 20W

(typical?? - well I it makes the math easy as there plenty of speakers around this value some less some more)

Then you could go with horns - 100 or 110dB efficient - 10W in and you are talking paaaaaaaain! (google for example Electrovoice MH4020A - about 110 dB 1W/1m - no idea what they sound like, designed for stadiums - you know there is that /1m in the spec and people in stadiums are many meters away)

I had a friend who had some electrovoice drivers connected to a homemade horn - had to pad them down to match some effiecient 15" bass drivers in big reflex(?) boxes - his 300B hardly had to work at all - nice sounding system, there seems to a certain 'ease' to effiecient systems and they can be very dynamic.

Rant mode - why do people think that adding more drivers can make a speaker more efficient? You don't get something for nothing. You can of course 'couple' it to the air more effieciently (horns for example) or 'beam it' (as in acoustic lens used on some horns) where the same sound power is concentrated in a smaller area and is therefore louder, or ... I'm probably missing something. AND talking about efficiencies but not using power as the reference!???!!! as in 92dB/2.82V/1m - yes that is 1W into 8 ohms but it is 2W into 4, and efficiency is about power! Of course it is easier to measure voltage and not worry about power - and ... this is going to get to long. end rant.

Bill
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Old 10th May 2005, 09:18 PM   #13
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by AndrewT
Hi ilimzn,
same driving voltage with double the series impedance gives half absorbed power.
You say the two speakers in series will give 3db more SPL at the same driving voltage. Can you clarify that?
Like you say above, same driving voltage with double the impedance (for two series connected speakers) gives half absorbed power but the same output SPL.
Similairly, two speakers in parallel absorb twice the power (3dB) but produce 6dB higher SPL.
Sounds strange but has to do with acoustic impedance matching - larger cone area is preferable to larger excursion, and with two membranes you get that preference.

Regarding zobels, you don't really get better efficiency by not using them unless we are talking current drive. If you are looking at a frequency response measured in a DIN baffle, it is done (for woofers) using voltage drive, so any impedance you would put in parallel with the speaker would change nothing. Obviously, this would be the default for a voltage driven full range speaker. The problem is when it's not voltage driven (i.e. large source impedance), a zobel will obviously gobble up power, but then, without it will get a rising frequency response. That being said, there are speakers speciffically designed for this kind of drive, and they indeed are usually full range.
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Old 10th May 2005, 09:31 PM   #14
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by B Cullingford
Rant mode - why do people think that adding more drivers can make a speaker more efficient? You don't get something for nothing... or ... I'm probably missing something.
Multiple drivers emulate larger cone area and this is precisely about coupling. How do you think arrays acieve such high efficiency
Of course, it is not something for nothing - you can only couple it so much so if for practical purposes area approaches 'infinite', the 'gain' from increasing it diminishes.

Quote:
AND talking about efficiencies but not using power as the reference!???!!! as in 92dB/2.82V/1m - yes that is 1W into 8 ohms but it is 2W into 4, and efficiency is about power! Of course it is easier to measure voltage and not worry about power - and ... this is going to get to long. end rant.
Bill [/B]
Actually, it would be better to express efficiency as driving voltage as the grand majority of speakers is intended for voltage drive (or at least the parameters are declared for this kind of driving mode). Otherwise, you would need to adjust driving voltage vs frequency to get constant power because the impedance changes with frequency. In other words, you need to have the impedance diagram at the very least.
In the vast majority of cases, howeber, when a manufacturer declares dB SPL/1m/1W the 1W is whatever voltage it takes to get 1W at the RATED impedance (This is actually the whole reason behind the rated impedance figure!). This is because most speakers are measured with constant voltage drive anyway. In order to calculate crossovers (as a first approximation well before tweaking by ear) you normally need to express sensitivity as XdB/1m/X Volts or it becomes extremely convoluted to calculate padding, especially if you are using zobels and different driver unit impedances.
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