From organtec@charter.net Sat Sep 10 06:53:38 2011
Subject:Re: Leslie woofers 16-ohm

Some of your info is ok but not all rules apply to all amp designs.

One error….using a higher impedance speaker than called for by the amp draws less on the amp, NOT more.

Conversely, using a speaker of lower impedance than that specified by the amp has a greater power draw on the amp, remember E=IR. Using a speaker of less impedance won’t usually damage the speaker but the damage will be done to the amp trying to deliver more power than it is capable.

Any amp, tube or solid state is much more tolerate of impedance mis-match if it has an output transformer, or in McIntoshes design, an autoformer in the output.

In a solid state direct coupled amp, as the impedance halves the amp will try to double it’s output, which only some can do and only to a certain extent beyond which the amp overheats and shuts down, or worse, destroys it self.

There ARE certain woofers we have used that are 8 ohms which will work very well in a Leslie amp which is designed for 16 ohms. These are few. They play louder, have a much less reactive back emf to the amp. Most will NOT work properly.

There are some amps which are rated at a 2 ohm load. Deceptive advertising which gives greater power output figures and makes it look more powerful. Yes, the amp will probably work at that load impedance as it was built to do so. But as far real power rating, the STANDARD impedance for ratings is for 8 ohms. So an amp rated @ 400 watts into 2 ohms is just that. Into 4 ohms it will deliver half or 200 watts. Into 8 ohms, 100 watts. Not so impressive now, is it?

Using an 8 ohm speaker in a Leslie with an 8 ohm resistor is pure foolishness. You are dissipating ½ the audio power into heat in the resistor, the balance making audio.

As in any audio situation there are many factors to consider such as//

Impedance

Frequency response with tolerance percentage

EFFICENCY//db per watt

Resonant frequency

Power handling, not much of an issue as a Leslie is only 40 watts. There were days when this was a healthy output, not any more in this time of megawatt amps.

There are many more items for a speaker nut to know

Ex.

Diaphragm/voice coil mass or weifgt

Voice coil gap flux density

Under/over hung voice coil

Various materials used in speaker construction etc.



From: CloneWheel@yahoogroups.com [mailto:CloneWheel@yahoogroups.com] On Behalf Of rafael2pop
Sent: Friday, September 09, 2011 10:58 AM
To: CloneWheel
Subject: [CWSG] Re: Leslie woofers 16-ohm





Goff and Everyone,

Just a reminder, as rule of thumb "it shouldn't be used a loudspeaker of less impedance than rated on the spec label for the amp".

No problem is the speaker is designed for greater impedance

Conversely NEVER use less ohms on the speaker side than required by the amp ohms.

Notice: if the amp tells " 8 ohm" it even will tolerate 16 ohm charge but if so that loudspeaker will drain extra RMS power from the amp.

OTOH , should same amp (8 ohm SPK output ) wired to a 4 ohm car-audio speaker, loudspeakers will be at risk for sure.

ANOTHER SCENARIO AMP: 16 ohm tube amps:

Having a 16 ohm output amp, and anybody think to put there a 8 ohm loudspeaker, it will be the same risk as mentioned about a 4 ohm car audio wired to a 8 ohm rack style power amp.

On a Leslie amp no problem if it's wired with a 16 or 32 ohm loudspeaker, but NOT lesser impedances, except this option:

A solution " ala McGyver " would be to use to use a 8 ohm loudspeaker BUT with extra resistors , let's say of 20/30W (in serie at the output ) so getting 16 ohm impedance to match the intended output amp (Leslie amp with 16 ohm)

Obviously , the resistors will drain part of the charge and energy will be got as dissipated heat instead of speaker power, but still it can be used without risk.

For the purpose a digital multimeter DMM or analog Ohmmeter will be needed for safer measurement of 16 Ohm on the speaker side (combined with resistors)

As alwayws what count is the rated power of the amp, that in case of Leslie amps are not so big ( < dissipated power of two 6550 tubes) this is under 65Watt RMS ).

That is quite far of the average loudspeaker by today standards for on stage use.

So can be understand that extra power for Leslies can be obtained from hybrid approach of tube pre or tube amp (as AMA from SpeakEasy) mixed with a solidstate amp of 150W RMS and above, to get enough sound to make a "guerrilla" with guitar amps on stage

What would be interesting to know the opinion from the experimenters/ connoiseurs (and/or compulsive testers) how a hybrid amp sounds on stage regarging it has both power tubes (6550, EL34 , 6L6, 6L6GC, etc.) AND solid state transistor power

In other words how an hybrid amp stacks against the "old good 147s or 122s " those vintage gems , barely holding a pair of 6550 power tubes.

Best,

Raff

Posted by: "Goff Macaraeg" goffmac747@aol.com goff747
Thu Sep 8, 2011 10:29 pm (PDT)

I know we've discussed this before. Wondered if there have been any updates in aftermarket 100 watt woofers, video/sound clips for regular Leslie use?

What 15 inch 16-ohm gets the correct "wooh-wooh" ramp tone?

Goff

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