From normpeterson@earthlink.net Fri Sep 17 12:31:34 2004
Subject:Re: amps

Hey, great speaker info! Hadn't brushed up on my "ohmage and wattage" for a while.
Norm

----- Original Message -----
From:
To: CloneWheel@yahoogroups.com
Sent: 9/17/2004 12:16:12 PM
Subject: Re: [CWSG] amps

In a message dated 9/17/04 8:47:53 AM, swbeach@worldchat.com writes:

<< Is that what you mean by 'Fs'?
>>

Fs: The resonant frequency of a loudspeaker driver in free-air. This is the
highest peak, the frequency of the speaker that it was designed to be good if
you plugged it in and just let it operate without a box.

There's also Vas: The equivalent volume of air having the same compliance as
the suspension system of the driver. This is the internal volume of the box
you're putting the speaker in. You need to find that volume and then get a
speaker that was designed for that specific volume. If you don't dial this in,
you've wasted your time and money and you won't like the results. A cheap speaker
placed in the right box will sound better than an expensive one put in the
wrong box.

<< Would anyone care to guess what the crossover point might be for the
Roland KC-550? What frequency response would the woofer need to be capable of
sounding? Would 40hz - to 3.5k be adequate? >>

Assuming the 550 is built like a PA the xover point would likely be 800 khz
like a Leslie.

Your horn takes over where the speaker is forced to leave off by the xover.
You can overlap the two but by using the Fs figure, you can see where that
speaker is going to be good at. When you buy a speaker, it should say what those
specs are. If you don't know then find out. If you can't get a supplier who can
give you those params move on to someone else's speakers. Many speakers are
being made today that handle all types of jobs. Some speakers are made by a few
companies that makes everyone's speakers, they just supply the maker with
specs and put a brand on it.

And don't forget IMPEDANCE seen as OHMS-no not a mantra, Ohm's law. You need
to find a speaker that has the same impedance that your old speaker had.
8-ohms? 16-ohms like in a Leslie? Otherwise the xover which was designed for a
certain impedance will not know what to do with the odd impedance and it won't
match the horn. Neither will your amp. Changing impedances can work though, if
too low the amp may fry or in the least your sound will be harsh or mushy. Most
of the time there are piezos and those are multi ohm, "anything goes." But the
woofer is a specific impedance. If your amp wants to see 8 ohms and you get a
speaker that's 4 or 2, your amps going to have to work harder to supply that.
If you put a 16 ohm load on your amp wanting 8 or less, your amp will not be
as loud as before and you'll wonder why. It's like a flood gate on a dam. The
lower numerically the impedance number, the wider the amp wants to open. If it
can't handle it, you'll fry it. Hence some car stereo boomers buy
amps/speakers that go down to 1 ohm and more so they can squeeze all the power out of the
amp.

In essence you'll want to investigate Thiele-Small parameters: Thiele-Small
parameters are a set of data characterizing the electrical and mechanical
properties of a loudspeaker transducer. This data can be used to help design
enclosures and predict the driver performance within them.

You can see there's more here than just picking up a name brand speaker and
popping it in. Manufacturers research when making amps to get the right speaker
at the right price.

Goodluck.

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