Bookshelf Speakers for tube amp?

[limelight76]

After reading PWR RYD's thread on his KT88 SE amp build and seeing his DIY version of Oddwatt's KT88 Octal Monoblocks, I have been wanting to start a similar monoblock DIY project. At 25wpc, I am wondering what possible 2-way bookshelf speaker designs might be a good match? I have a 12' x 16' listening room and typical music is classic rock, blues, adult contemporary. Bookshelf designs typically have lower sensitivity (<85dB/2.83v/1m) e.g. Speedsters, etc.. Given the room and listening preferences, any thoughts on current bookshelf designs working? I would love to build a highly efficient 3-way or full-range horn but don't have the space in the current set up.

[kevin007]

Re: Bookshelf Speakers for tube amp?

I would seriously consider these: http://www.diysoundgroup.com/wavegui...ries-kits.html

Kevin

[limelight76]

Re: Bookshelf Speakers for tube amp?

Kevin,

Thanks for suggestion. After reading some threads and write-ups by Jeff, it does sound like the Tempest might be a good option.

[kevin007]

Re: Bookshelf Speakers for tube amp?

I haven't built one yet but from what I have read they should make a great speaker for a tube amp setup. Some of them are upwards of 95 db sensitivity!

Kevin

[limelight76]

Re: Bookshelf Speakers for tube amp?

They look very interesting. It looks like they are getting a lot of attention as excellent LCR speakers for home theater. I may plan on eventually turning this into more of a "media room" so these might be a good first step.

For now this is what I am thinking in terms of the setup:

[PWR RYD]

Re: Bookshelf Speakers for tube amp?

A pair of 25 watt push-pull KT88 amps, with effecient speakers like the Tempest, in your size room would flat out ROCK! I would recommend you add an appropriate sized sub to fill in the very bottom end.

[kevin007]

Re: Bookshelf Speakers for tube amp?

A pair of 25 watt push-pull KT88 amps, with effecient speakers like the Tempest, in your size room would flat out ROCK! I would recommend you add an appropriate sized sub to fill in the very bottom end.

+1

[zobsky]

Re: Bookshelf Speakers for tube amp?

Sensitivity is a factor, but what is equally important is the phase angle and impedance. Here's an article that explained it beautifully but is now lost. I kinda recovered it via the wayback machine.
http://web.archive.org/web/200903281...efriendly.html . In short, you want speakers that have simple or no crossovers (tending towards a less capacitive load)

[Wolf]

Re: Bookshelf Speakers for tube amp?

Sensitivity is a factor, but what is equally important is the phase angle and impedance. Here's an article that explained it beautifully but is now lost. I kinda recovered it via the wayback machine.
http://web.archive.org/web/200903281...efriendly.html . In short, you want speakers that have simple or no crossovers (tending towards a less capacitive load)

You can have complex xovers and not have a very capacitive load. The impedance phase shows inductive and capacitive swings. + angle is inductive, and - is capacitive. Just keep the phase as flat as possible and you should be good. Most of the designers try to keep them between the +/-40 deg mark, but less variance is better when able. Toobs may require minimizing that swing more than normal.

Later,
Wolf

[limelight76]

Re: Bookshelf Speakers for tube amp?

Zobsky, Wolf,

Thank you for the great information. Referencing the following: " If phase angles must be capacitive, impedance should be high. The lower the impedance, the flatter it must be, and the less capacitive the phase angles must be. All three variables (slope of impedance, value of impedance, value of phase angle) together determine how good a match a speaker will be for a tube amp."

I have not been able to find an impedance plot for the Tempest but I did find this in a write-up by Jeff which would lend itself to the idea that this speaker might still be a good candidate "The system is nominally an 8 ohm load, and like the Zephyr, impedance is actually higher than 8 ohms over most of the range, making this a very easy load to drive. "

I was able to find the article you reference regarding impendance and phase angle (with actual graphs that the wayback machine stripped out) here: http://www.dhtrob.com/overige/tubefriendly_lsp_en.php

[limelight76]

Re: Bookshelf Speakers for tube amp?

For those interested, below are two impedance graphs (referenced in the article) that show different speaker designs deemed excellence for tube amplifier applications. You can clearly see how these speakers both generally stay above 8 Ohms and when they do occasionally fall below that level, they generally have near flat or good inductance (+ phase angle). In addition, when they are most capacitive (-phase angles), their impedance is well above nominal.

Tube Friendly Speaker 1


Tube Friendly Speaker 2


While I have not found an impedance plot for the Fusion Tempest, Jeff mentioned in his write-up that it achieves greater then 8 Ohm impedance across most of the range - similar to the Zephyr design. I was able to find an impedance plot of the Zephyr – shown below. It shows the area of most concern is around 90Hz where there is the most capacitive phase angle (-60). However, at this point the impedance is close to 20 Ohms. As the impedance approaches 8 Ohms, the phase angle is already starting to flatten. Based on the article, this appears to be acceptable for tube amp applications.

Zephyr


The impedance for the Tempest would likely be slightly different, however if the overall impedance “character” of the Tempest is similar to the Zephyr as Jeff suggests, I would gather the Tempest would in fact make an excellent tube speaker given the impedance, phase, and sensitivity (98dB/2.83V/1m) characteristics.

Maybe someone on here may have the actual impedance plot of the Tempest?

[limelight76]

Re: Bookshelf Speakers for tube amp?

Jeff was able to supply the impedance info for the Tempest. It is essentially identical.