Salk SongTower QWT Floorstanding Speaker Review

[admin]

You may not have heard of Salk Sound, but if you have, you were probably intrigued. Their speakers just look so darn good. But looks aren't everything - what really matters is how they sound. Utilizing a MTM (mid-tweeter-mid) configuration and a Quarter Wavelength Transmission Line design geared toward optimizing bass, the SongTowers sound great on paper. The question is how will they sound in your room?


Discuss "Salk SongTower QWT Floorstanding Speaker Review" here. Read the article.

[jamie2112]

Thanks for the review Tom. Thats funny you used a Rusted Root disc...I mixed Rusted Root live for about a year. They are hard on Any speaker.....

[Swerd]

It was a nice surprise to see this review. I'm glad to see your positive comments about it's detailed sound and it's bass. The SongTower is an exceptional speaker.

Too bad you didn't like the spikes. I have had no trouble with mine in the year I've had them.

I also compared the bass on the RBHs to the Salks and found that I honestly thought they sounded remarkably similar. The RBHs seemed a little boomy at times but the Salks seemed a little weak at others. I kept scratching out my notes and adding new ones just to change my mind the next moment. I did think that the linearity of the Salks was better and their bass detail was better at lower volumes...

The SongTowers did well with this material presenting a good amount of bass extension while keeping a richness to the sound that was quite evident. At first I thought the RBH's beat out of the Salk speakers in extension but decided that I was hearing more boom and not lower notes. The Salk speakers seemed more natural in their bass notes than did the RBH TKs.

It seems like the STs may have been the first properly designed transmission line speaker that you've heard. Your words reminded me of my own experience as I first listened to mine. The bass sounds different from any sealed or reflex design I had heard before, and defied my own expectations as to how reproduced bass sounds. I struggled to describe it in words.

By the way, the SongTowers are a mass-loaded quarter-wave transmission line design, as defined by Martin King. In this case, mass-loaded means that the cabinet opening is somewhat smaller in area than the cross sectional area of the whole line. The port that you see on the rear of the cabinet is also much shallower in depth than a typical reflex. Finally, there is no requirement that a transmission line have a folded labrynth inside the cabinet as long as the length of the line is ¼ the length of the tuning wavelength.

[MJK]

This is the second time today I have provided more info on the ML TL style of design. I guess things come in streaks. Below is a slightly better description from the Lowther ML TL page on my site.

I have been asked many times about the difference between a ML TL design and a simple bass reflex enclosure. From the outside the two look very similar and performance wise there is not a large difference. I think that the principle difference is the way the air volume in the cabinet is used to provide the spring that interacts with the mass of air in the port to form a resonant system.

In a bass reflex cabinet, the air in the box is compressed to a uniform pressure to form an air spring. Typically no damping material is added to the inside of the box so that the Q of the box remains high and the effective volume of air is predictable from the internal dimensions of the box. The shape of the bass reflex box is not that critical, only the internal volume matters. A bass reflex enclosure can be represented as a lumped mass hanging on a spring. If you displace the mass the entire spring stretches. When you let go, the mass oscillates at a predictable frequency that is a function of the springrate and the mass of air in the port. The key point is that the entire spring stretches linearly. This is a simple one degree of freedom mechanical system.

In my opinion, one of the negative attributes of a bass reflex enclosure is that any strong standing wave resonances in the enclosure will not be sufficiently damped. The lack of fiber in the center of the air volume allows energy from the back of the driver to potentially excite resonances and produce unwanted acoustic output that escapes through the port opening. Some people try and mitigate this problem by placing the port on the back of the enclosure. Placing the port on the back of the bass reflex enclosure may require more standoff from the rear wall and lead to room placement problems. The ML TL enclosure design requires stuffing in the internal volume of the enclosure. The presence of this stuffing is part of the design cycle and the amount and location is accounted for in the design process.

The ML TL enclosure can be thought of as a form of transmission line where quarter wavelength standing waves are used to provide the spring for the mass of air in the port. To physically model a straight uniform TL, clamp a yardstick to the edge of a counter or desk and pluck the free end so that it starts to vibrate. The vibration pattern is analogous to the air velocity in a TL. The TL's air velocity is zero at the closed end as is the yardstick's motion at the clamped end. The TL's air velocity is a maximum at the open end as is the yardstick's velocity at the free end.

There are two ways of changing the frequency of vibration for the yardstick. If you shorten the length cantilevered off the counter, the frequency of vibration will increase. Make the length longer and the frequency decreases. This is how straight TL's have traditionally been tuned by adjusting the length. The second way of tuning the frequency of the yardstick is to add a lump of mass to the free end. Put a piece of modeling clay on the free end and watch the frequency decrease. What I have done to the classic TL is put a lump of mass at the terminus end using a restrictive port. For a given frequency, I can shorten the TL (make it stiffer) increasing the tuning frequency and then add mass (air in a port) to pull the frequency back down and get a similar tuned result. One other benefit of having a lump of mass at the terminus is a rolled off port output above the first quarter wavelength resonance. This result is similar to a bass reflex port's response. I did this first with the ML TQWT and then with a straight TL. If you try the yardstick analogy, I think by changing the length and adding mass to the end you can demonstrate to yourself exactly what I am doing in my MathCad computer models.

If you plot the pressure and volume velocity profile inside the enclosure, you will see the transmission line standing wave behavior. The air in the enclosure behaves differently from the air in a classic bass reflex design. The elongated height of some floor standing speakers allow this to occur, some people/designers get the benefit of this action without even realizing it is happening. There is not sharp line between bass reflex and ML TL, it is a gradual transition.

Hope that helps,

Martin

[Nuance AH]

Tom -

Fantastic review man! I thoroughly enjoyed it, plus you made me laugh out loud a few times attracting the attention of the people around me (they looked at me like "what's he laughing about").

Thanks for taking the time to do this write-up.

[gene]

By the way, the SongTowers are a mass-loaded quarter-wave transmission line design, as defined by Martin King. In this case, mass-loaded means that the cabinet opening is somewhat smaller in area than the cross sectional area of the whole line. The port that you see on the rear of the cabinet is also much shallower in depth than a typical reflex. Finally, there is no requirement that a transmission line have a folded labrynth inside the cabinet as long as the length of the line is ¼ the length of the tuning wavelength

Sorry but I am not buying it. Since this design employs dual woofers, they either need dual lines or have a single entry point with an exit equidistant from the "woofers". This is not apparent in this design and the claims that their design can extend bass below what a ported design can do are dubious at best. In order to reach down in the 40Hz range, the path length would have to be 7 feet long!

Also looking over the impedance plot, you can see a saddle point right at the tuning frequency. I would expect a flatter impedance curve for a true TL design. At the very best it is appears to be an under stuffed TL design or a hybrid/quasi TL design that also incorporates a tuned vent

Regardless, what I gather from Tom is that they are great sounding speakers that look as good as they sound. Hats off to the design team at Salk for making a product Tom didn't trash

[Swerd]

Sorry but I am not buying it. Since this design employs dual woofers, they either need dual lines or have a single entry point with an exit equidistant from the "woofers". This is not apparent in this design and the claims that their design can extend bass below what a ported design can do are dubious at best. In order to reach down in the 40Hz range, the path length would have to be 7 feet long!

Also looking over the impedance plot, you can see a saddle point right at the tuning frequency. I would expect a flatter impedance curve for a true TL design. At the very best it is appears to be an under stuffed TL design or a hybrid/quasi TL design that also incorporates a tuned vent

I am much less qualified to discuss this than Martin King himself, who just posted above as MJK. I suggest spending some time browsing and reading at his web site. He has articles that specifically deal with mass loading and with dual woofers as in a MTM design.

Regardless, what I gather from Tom is that they are great sounding speakers that look as good as they sound. Hats off to the design team at Salk for making a product Tom didn't trash

Agreed .

Hat's off to Jim Salk (owner & chief sawdust maker of Salk Sound), Dennis Murphy (crossover designer), Paul Kittenger (who designed the cabinet using Martin King's math models), and Martin J. King (who developed the ability to precisely model TL designs by computer). They all had roles in the design and development of these speakers.

[Nuance AH]

Hats off to the design team at Salk for making a product Tom didn't trash

LOL - too funny.

[Tom Andry]

Hats off to the design team at Salk for making a product Tom didn't trash

Geesh, you're going to give me a rep as a tough reviewer. Then people will only want to send me their best stuff... wait, that's not such a bad thing.

Thanks to all. Martin, I agonized over the TL/non-TL thing. Like I said in the review, call it a cheese sandwich design. I don't care 'cause it sounds good to me!

[bigspur1984]

It was a nice surprise to see this review. I'm glad to see your positive comments about it's detailed sound and it's bass. The SongTower is an exceptional speaker.

Too bad you didn't like the spikes. I have had no trouble with mine in the year I've had them.

I am about to put my deposit down on a pair of SoundTowers, after reading this review I was wondering if I needed to order the sharp spikes instead of the standard. You say that you have had no trouble with yours, are they on carpet? Mine will be but I do not have very thick carpet.