[Rclark]

I'm always good thanks. Part of me wants to let you try my amps but I think your bias dial might be stuck.

[James Romeyn]

Re. OTL driving GedLee Abbey: negative search for Abbey impedance graph.  Please post if anyone has such. 

[medium jim]

I'm always good thanks. Part of me wants to let you try my amps but I think your bias dial might be stuck.

Talk about calling the kettle black.

Jim

[brj]

Re. OTL driving GedLee Abbey: negative search for Abbey impedance graph.  Please post if anyone has such.

A Google image search on "gedlee abbey impedance" yields:

http://www.audiocircle.com/index.php?topic=87209.msg852984#msg852984

[James Romeyn]

A Google image search on "gedlee abbey impedance" yields:

http://www.audiocircle.com/index.php?topic=87209.msg852984#msg852984

I must miss something obvious.  How does 5 Ohm centered @ 150 Hz and 26 Ohm centered @ 1050 Hz = "8 Ohm above 100 Hz."

IMHO the 5 Ohm minimum in most or all the octave 100-200 Hz (where is considerable music energy) is not well suited to OTL, hence consistent with Jason's response to this pairing. 

In my experience OTL kicks butt on the right load, which stays above 8 Ohm above 100 Hz, is fairly flat above 100 Hz and appropriately high sensitivity.  Abbey looks like 1-5 ratio above 100 Hz, which is nowhere near "flat."   

[JohnLL]

Generally speaking it takes 2 tubes/transistors per pole to produce 25 watts/channel. As you start adding more devices the circuit gets more complicated. You may have noticed that the most highly regarded amps are simple class A SS or SETS. I suggest you take the Pano how much voltage do you need test here. When you finish square the voltage and you have watts.
http://www.diyaudio.com/forums/multi-way/204857-test-how-much-voltage-power-do-your-speakers-need.html

Speakers are driven by both voltage and current. There is no such thing as a power supply with too much current supply capability and it has nothing to do with voltage or amp “power” but dynamics are a different matter..

[neekomax]

I'm thinking of trying a 30 wpc Tripath amp. Currently I run a 100 wpc Class AB SS amp into my 6 ohm, 86-87 db sensitivity speakers, which are hipassed internally at 200 Hz, so the amp only has to drive the frequencies above that. I'm in a 12x11x9 ft room sitting about 8.5' from the speakers. I like it loud when I can, but I really don't know what decibel level that translates to at the LP (is there a decibel meter iPhone app or do you have to buy a special tool)? I listen to modern jazz and various and sundry pop/rock/electronic/soul/funk genres, most recorded in the last 15 years.

Anyway, any opinions about whether I'll have enough power at 30 wpc?

[Pete Schumacher]

I'm thinking of trying a 30 wpc Tripath amp. Currently I run a 100 wpc Class AB SS amp into my 6 ohm, 86-87 db sensitivity speakers, which are hipassed internally at 200 Hz, so the amp only has to drive the frequencies above that. I'm in a 12x11x9 ft room sitting about 8.5' from the speakers. I like it loud when I can, but I really don't know what decibel level that translates to at the LP (is there a decibel meter iPhone app or do you have to buy a special tool)? I listen to modern jazz and various and sundry pop/rock/electronic/soul/funk genres, most recorded in the last 15 years.

Anyway, any opinions about whether I'll have enough power at 30 wpc?

While your speakers may get high passed at 200Hz, the amp is still producing the full spectrum.  Unless you high pass the signal to the amp, you gain nothing, and in fact, will have less available output moving down to the 30W amp.

Amps are voltage sources, and when the voltage reaches the supply rail level, they will "clip."  It doesn't matter that they aren't sending any power to the load.  In fact, an amp can clip when delivering ZERO watts. 

Active setups work best when the crossover is set up between the source and the amp inputs.  Breaking up the music signal into a series of bands allows a smaller amp to deliver closer to its max rating without clipping.

For example, if a high quality recording has a 10:1 peak to average ratio (crest factor), that means for 1W of music power, the instantaneous power requirement is 10W.  If you break up the spectrum into 3 pieces, you can reduce that crest fact to 3.33:1.  Now, instead of needing a 10W peak output to deliver 1W RMS, you only need a 3.33W peak output to deliver 1W RMS.  But that has to be done before the amp input, not between the amp and speakers.

[neekomax]

While your speakers may get high passed at 200Hz, the amp is still producing the full spectrum.  Unless you high pass the signal to the amp, you gain nothing, and in fact, will have less available output moving down to the 30W amp.

Amps are voltage sources, and when the voltage reaches the supply rail level, they will "clip."  It doesn't matter that they aren't sending any power to the load.  In fact, an amp can clip when delivering ZERO watts. 

Active setups work best when the crossover is set up between the source and the amp inputs.  Breaking up the music signal into a series of bands allows a smaller amp to deliver closer to its max rating without clipping.

For example, if a high quality recording has a 10:1 peak to average ratio (crest factor), that means for 1W of music power, the instantaneous power requirement is 10W.  If you break up the spectrum into 3 pieces, you can reduce that crest fact to 3.33:1.  Now, instead of needing a 10W peak output to deliver 1W RMS, you only need a 3.33W peak output to deliver 1W RMS.  But that has to be done before the amp input, not between the amp and speakers.

aHA! Of course, seems obvious now that you mention that my amp is sending the full frequency range regardless of what the crossover at my speakers is doing. 

Thanks for that.

Are those numbers that you spoke of accurate - as in the 1:10 continuous to peak power ratio- , and if so wouldn't that mean that an amp should be capable of delivering at least 100 wpc peak (plus headroom, I assume)? Is the amp likely being pushed to 10 watts of continuous power in my situation?

[Rclark]

Which Tripath were you thinking of? You're welcome to try my Virtue if you want. Should blend well with your speakers as they are high passed. It's about 55 watts at 8ohm.

[neekomax]

Which Tripath were you thinking of? You're welcome to try my Virtue if you want. Should blend well with your speakers as they are high passed. It's about 55 watts at 8ohm.

Thanks, but unless the high pass filter is (easily) defeatable, I don't think it will work. Pete pointed out that the amp still needs to send the full freq. spectrum to the binding posts, as the crossover sends the bass to the BASH amps in the speakers only after that point. Unless I'm missing something, which is quite possible.

I'm looking at the Red Wine Audio Signature 30. My current amp is a bit noisy and I'm curious to hear what battery power would do for my system, but I just read an user review  that said that it didn't quite cut it with the guy's 86 db speakers, so I'm not sure...

[Pete Schumacher]

Are those numbers that you spoke of accurate - as in the 1:10 continuous to peak power ratio- , and if so wouldn't that mean that an amp should be capable of delivering at least 100 wpc peak (plus headroom, I assume)? Is the amp likely being pushed to 10 watts of continuous power in my situation?

It all depends on the source recording.  Modern pop, rock, etc, is usually compressed to death, leaving you maybe 5:1 peak to average ratio.  That means your 100W amp will deliver about 20W music power before the amp is clipping on the peaks.  With better recordings that don't compress, you'll get 10:1, even up to 100:1 peak to average ratios.  I've heard a few orchestral recordings that featured such dynamic range.  The 1812 overture with a real cannon comes to mind.

Then of course is your listening volume and listening distance.  The theory is that speakers lose about 6dB for distance doubling, but in a room, that's not the case since the room reflects quite a bit of energy.  If your speakers run 88dB, and you sit 12' away, you're likely getting around 90dB at your listening position with about 5W going into each of your speakers.  If you like to listen at louder average levels, it's likely that even your 100W amp will clip on the peaks, creating a grating, harsh sound even if the clipping isn't obvious.

[AJinFLA]

My current amp is a bit noisy

The Peachtree?

[neekomax]

The Peachtree?

No, the Acurus DIA-100. I use the Peachtree as a preamp.

[Tone Depth]

duplicate post

[Tone Depth]

I've got a reasonably powered amp (225 wpc) and a 3,000 cf family room open at back to a 1,000 cf kitchen. I'm considering new bookshelf speakers. What minimum speaker efficiency should I be considering? I previously saw a formula I could probably use to reframe the calculation, but I haven't been successful relocating it.

[Pete Schumacher]

I've got a reasonably powered amp (225 wpc) and a 3,000 cf family room open at back to a 1,000 cf kitchen. I'm considering new bookshelf speakers. What minimum speaker efficiency should I be considering? I previously saw a formula I could probably use to reframe the calculation, but I haven't been successful relocating it.

There are so many unknowns here.  How loud do you like to listen?  How low in frequency do you want them to reach?  What is the largest footprint they can occupy?  How close do you sit and where are the speakers going to be relative to the walls?

If you like really good recordings, and don't want the amp clipping, you'll be delivering between 20 and 40 Watts of average music power.  So if you sit about 12' away from the speakers and they have mid 80dB sensitivity, you will be getting mid to upper 90dB at 1m.  You'd probably be able to get 90d-92B overall at the listening position.  If you want to be able to hit 102dB at your seat, then you'll need much more sensitivity.  Compression tweeters, high powered planars, and pro woofers would be required.

[srb]

You should be able to hit peaks of 105dB with 90dB speakers, given your amplifier power and listening distance.  If you assume 85dB as your average loud listening level, that would give you ~20dB for peaks which would encompass the majority of music although there are a smaller number of recordings with higher dynamic range.

So I would use 90dB as a starting point, and higher if your listening habits are louder and/or you listen to recordings with higher dynamic range.  There are speakers in the 88dB to 91dB range that use conventional audiophile woofers and non-compression dome or ribbon tweeters, although they usually use dual midbass or woofers to achieve it.

Then of course, the speakers themselves have to be able to achieve your maximum target SPL without hitting thermal or mechanical limits.

You can play around with this SPL calculator to see how changes in variables affect SPL.
http://myhometheater.homestead.com/splcalculator.html

If your 225wpc amplifier is an 8 ohm rating, and your speakers are lower impedance, then the possible additional available power (depending on the specific amplifier) might expand your possible speaker choices.

Steve

[Tone Depth]

Thanks for your comments.