The GLOW Audio Sub One and Voice One speaker combination
"Tube amps require special speakers that tend to be very expensive."
The truth is, many commercially available speakers work well with GLOW tube amplifiers. This page is intended to provide general information regarding compatibility of the GLOW amps with various types of speakers, as well as more specific information regarding various makes and models of loudspeakers.
So, just how loud can I expect a 5 watt single ended tube amp to play?
The volume you get depends in large part on how "sensitive" your speakers are. Some refer to this as the "efficiency" of the loudspeaker. "Sensitivity" is measured by determining the decibel (dB) level of a speaker when 1 watt of power is applied, measured from 1 meter away. So for example, a loudspeaker with a sensitivity rating of "90 dB SPL" can create a sound pressure level ("SPL") of 90 decibels with 1 watt of power measured 1 meter from the speaker.
A speaker's sensitivity rating can be found in the owner's manual, sometimes on the back of the speaker, and often on the company's website. The sensitivity of speakers varies greatly, depending on the design and the materials used.
Single Ended Tube Amplifiers like our GLOW Amp One typically produce low power in exchange for high resolution. Single ended amps have a famously smooth and non-fatiguing sound because they do not produce third order harmonic distortion. The trade off to using only two gain stages is low power output. To assure adequate volume while using our amplifier, GLOW recommends as a general rule of thumb using speakers rated at 90 dB SPL 1W/1M sensitivity or higher (there are exceptions as discussed below).
The general rule is that, to INCREASE speaker sound output by 3 decibels, the amplifier power must be DOUBLED. Therefore, a speaker rated at 90 dB SPL 1W/1M would need 2 watts of power to play at 93 dB SPL. And to play at 96 dB SPL, the same speaker would need double the power that it required to play at 93 dB SPL, or 4 watts. This means that, with the GLOW Amp One, using speakers rated at 90 dB SPL, you will likely achieve maximum volume of about 96 to 98 dB SPL 1W/1M.
If you need higher volume levels, simply choose more sensitive speakers. For instance, if your speaker is rated at 96 dB SPL 1W/1M, it will play as loudly with 1 watt of power as a speaker rated at 90 db SPL would play with 4 watts. With the GLOW Amp One, a speaker with a sensitivity rating of 96 dB SPL will play in excess of 103 dB SPL.
The importance of sensitivity ratings should not be overlooked. Here is how stark the difference can be. If a speaker is rated at 83 dB SPL, then to reach a peak of 104 dB SPL the speakers would need an amplifier capable of producing in excess of 125 watts per channel. But, if a speaker is rated at 98 dB SPL, to reach the same SPL of 104 dB would require only 4 watts.
What this math means is that, if you match the GLOW Amp One with more sensitive speakers, you will find the GLOW Amp One quite capable of high volume levels, while offering incredible resolution and clarity.
A speaker with a high minimum impedance is also recommended; tube amps like a resistive load. Be careful not to mistake "minimum" impedance with "nominal" impedance; a speaker's "nominal" 6 ohms rating can mask a drop in minimum impedance to under 2 ohms along the audible frequency range, in reality creating a difficult load for any amplifier, despite what the nominal 6 ohm rating would suggest. Our GLOW Voice One has a minimum impedance of 6 ohms, making it easy to drive. To provide another example, a customer has informed us that he gets plenty of volume from his 83 dB rated Rogers LS3/5a speakers. The reason, we surmise, is that the speakers have a 15 ohm nominal impedance with a high minimum impedance, and are thus an easy load for our 5 watt Amp One amplifiers to drive.
There is a quiet revolution going on in the stodgy audio world.... more and more audiophiles are discovering that matching high sensitivity and/or high impedance loudspeakers with low power, high resolution tube amplifiers creates a dynamic combination that sounds head and shoulders above the usual high power amplifier/low sensitivity speaker combinations.
Full Range Single Drivers: In many cases, these "low power" adherents prefer full range speakers, without crossovers, to avoid the midrange coloration that often results from use of crossovers. We at GLOW agree that a high quality full range driver matched with a GLOW amplifier creates a stunningly realistic and detailed sound that many high power systems cannot replicate.
Horn loaded speakers: Please note that many compression horn loaded speakers, such as certain models built by ALTEC, KLIPSCH and CERWIN VEGA, are rated at 96 dB SPL 1W/1M or higher. Also note that, while horn loaded speakers have a reputation for sounding forward and even harsh, we think this is primarilyy due to transistor "hash" and is not necessarily the fault of the speaker. In fact we have found, when coupled with a Single Ended tube amplifier like the GLOW Amp One, horn loaded speakers can sound very smooth and silky indeed.
KLIPSCH makes a number of high sensitivity speakers, including the la Scala, which with 1 watt will produce 104 dB SPL! WIth 4-5 watts, the la Scala can play at rock concert volumes. While most speakers are nowhere near as sensitive as these KLIPSCH models, there are other high sensitivity speakers readily available on the mass market, made by companies such as TANNOY, JBL, CERWIN VEGA, ALTEC LANSING and others, including companies specializing in studio and monitor type speakers, and manufacturers of raw drivers such as FOSTEX and LOWTHER.
We have one customer who powers his KLIPSCH Heresy III speakers with our diminutive amp, and reports that he has no problems hosting high volume dance parties in a very large room. How is this possible? Because the KLIPSCH are rated at 99 dB SPL 1W/1M, so with a mere 4 watts, the speakers can pump out 105 dB SPL 1W/1M. There is a cavernous fitness center in Pinole, California (FitVERSE), with 30 foot ceilings and over 5,000 square feet of space, that uses a 5 watt GLOW Amp One matched with efficient Klipsch B-20 bookshelf speakers and a 15" subwoofer to FILL THE ENTIRE SPACE with loud, bass heavy work out music for its fitness patrons.
Ribbon drivers: Speakers with ribbon type tweeters can be quite efficient. An example of one such offering is the Martin Logan Motion LX 16. This small bookshelf speaker is rated at 92 db SPL.
Please keep in mind that the suitability of a loudspeaker also depends on the crossover type used. Typically, a full range loudspeaker powered by a tube amplifier will play louder than a multi-driver loudspeaker even when the sensitivity ratings are comparable. This is because the crossover, especially if poorly designed, can create phase and impedance anomalies that make the speaker a difficult load to drive.
"But my speakers require a minimum power of 20 watts." Many speakers state in their manuals that they require a MINIMUM amplifier power rating of 15 or 20 or 30 watts for their speakers. Does this preclude use of a 5 watt or 15 watt GLOW amplifier? No. These minimum ratings are to protect the speaker's tweeters from being blown by a transistor amp that is driven past its power rating, causing it to CLIP. When a transistor amp clips, it sends a square wave to your speaker, causing catastrophic distortion that can damage or destroy your tweeters. This does not happen with a well designed tube amp. A tube amp will "soft clip" meaning it will simply reach an output limit and tail off... no square wave and no clipping. Thus you do not run the risk of damaging your tweeters with a low power tube amp, as you would with an underpowered transistor amp.
(Note: Some transistor amplifier manufacturers such as Proton and NAD have attempted to replicate the "soft clip" feature of tube amplifiers by building in a circuit that mimics the performance of tube amplifiers when they reach their power threshold. But the predominant method of dealing with this problem has been for transistor amplifier manufacturers to design amps to produce as much power as possible to avoid clippping. Because transistors will overheat and self destruct (thermal runaway) if driven to their limits, more power output necessitates stringing together a series of transistor gain stages and the use of massive amounts of negative feedback to control distortion as the signal travels from one gain stage to the next and finally to your speakers. Many audio amplifiers have 9 or more gain stages. This may be good for increasing power output, but it is bad for musicality and transparency.
The push for more watts has had a corresponding effect on loudspeaker design. Many loudspeakers are designed with ever more robust components to handle the massive power that the transistor amps pump out. The result is use of polypropylene and metal drivers, ferro-fluid cooling, more mass in the drivers, and more complex crossovers to marry drivers designed to handle high power, but that don't otherwise match well. This makes the speaker less prone to being overdriven, but all the engineering put in to the speaker to increase its power handling capabilities does not always make the speaker sound better. All this nonsense, just to avoid the effects of a transistor amp clipping!
To summarize, don't let the relatively low power rating of our little amplifiers fool you.... when matched with the right speakers, the GLOW amps will play as loud as you need!
SPEAKER RATINGS CHART
Below is a partial list of speakers that will work well with our GLOW amplifiers. Our own speakers, introduced in North America in 2009, are specifically designed to match our amplifiers, and although rated at only 88 dB SPL 1W/1M, without using a power sapping crossover can play quite loud enough for most small to medium sized rooms in most circumstances.
THE FOLLOWING LIST IS INTENDED TO PROVIDE AN EXAMPLE OF SPEAKER SENSITIVITY RATINGS AND IS NOT AN ENDORSEMENT OF ANY PARTICULAR BRAND OR TYPE OF LOUDSPEAKER. We do indicate with an asterisk speakers we have personally auditioned and can recommend.
102 dB and higher SPL with 1 watt input:
114: ORIS Horn www.bd-design.nl
107: AVANTGARDE ACOUSTIC www.avantgarde-acoustic.de/
104: KLIPSCH La Scala* www.klipsch.com
102: PI Speakers rated from 95 - 102 dB SPL www.pispeakers.com
98-101 dB SPL with 1 watt input:
101: ZU Loudspeakers* http://www.zuaudio.com/loudspeakers
99: KLIPSCH Heresy III*
See also other classic as well as newer KLIPSCH models, with sensitivity ratings typically above 93 dB SPL.
TANNOY loudspeakers.* Some models rated 99 dB SPL and up. http://www.tannoy-speakers.com
(Note: we use a pair of massive 15" Tannoy dual concentric studio monitors to voice our amps)
ROYAL (Italy) loudspeakers ranging from 93 - 99 dB SPL www.royaldevice.com/donna.htm
98: BEAUHORN Loudspeakers. www.beauhorn.com
LOWTHER - Full range drivers rated at 98 dB SPL and up. www.lowther-america.com
94-97 dB SPL with 1 watt input:
CERWIN VEGA Loudspeakers - Various models rated from 92 to 97 dB SPL http://www.cerwinvega.com/
OMEGA Loudspeakers* - Various models rated from 93 to 96 dB SPL www.omegaloudspeakers.com
SONIST Loudspeakers* - www.sonist.com
FOSTEX full range drivers. http://www.fostexspeakers.com/
Coincident - Several models including Triumph rated at 94 db and higher
90-93 dB SPL with 1 watt input:
There are many loudspeakers that fall within this output range, too many to list here, so what you see is simply a small sampling of what is available.
TEKTON loudspeakers (various full range models) http://www.tektondesign.com/model41.htm
Hornshoppe Horns - www.thehornshoppe.com
Martin Logan LX16 at 92 db SPL
Monitor Audio Bronze at 90 db SPL
PSB Alpha B1 at 91 db SPL
Definitive Technology 45 at 91 db SPL
Many KEF, B&W, JBL, Definitive Technology, and other bookshelf models fall within this range.
ADS L420, L520, and L620 at 92 db SPL, 6 ohms nominal and 4 ohms minimum SPL.
Below 90 dB SPL with 1 watt input (normally too low for our Amp One, but because these speakers are either full range or present a minimum impedance load above 4 ohms, they still work well with our amp!) :
87: GLOW Audio Voice One http://www.glow-audio.com
ROLE Sampans http://www.roleaudio.com/sampan.html
John Blue JB3 http://www.audio-magus.com/product_p/sjb3.htm
88: BLUMENSTEIN Orca* www.blumensteinaudio.com