Repost from the recent past...
Last Sunday, Paul (Miney) packed up his B&W CDM 7NT floor standing speakers and drove from Reading, PA to my house in Gaithersburg, MD, about 150 miles away. Paul's goal was to decide whether to add a subwoofer to his B&W CDM 7NT floor standing speakers (used in a 2-channel music system) or to replace the B&Ws with something new. He came to my house to compare his B&Ws with my Salk SongTowers.
His B&Ws are a 2½-way floor standing speaker that he bought in 2001. They measure 37.5" high, nearly 9" wide, and a little over 11" deep. An
archived brochure can be seen here. Paul's speakers were finished in a deep-red cherry. It appeared to me that the top, front and rear of the cabinet were veneered, while the sides looked like there were covered with solid hardwood slabs. The overall appearance was very nice.
The CDM 7NT is a 2½-way design. On the sloped top of the tower is a 1" tube-loaded alloy-dome tweeter. The tube behind the tweeter diaphragm is said to absorb unwanted radiation from the rear of the diaphragm. The upper midwoofer, a woven 6.5" Kevlar driver with its bullet-shaped phase cone that appears instead of a dustcap, is a familiar face in the B&W family. The lower 6.5" woofer has a large dustcap that's bonded directly to the voice coil. Bonding dustcap to the voice coil and the cone is said to make the whole assembly more rigid. The two woofers are mounted in separate compartments of the cabinet, and each compartment comes with it own reflex port. The port for the lower woofer appears in front, and the port for the upper midwoofer is on the rear side. Both reflex ports are tuned to about 40 Hz. The lower woofer is rolled off at about 150 Hz, and the upper midwoofer is crossed over to the tweeter at 4000 Hz.
In contrast to B&Ws, the SongTower is a MTM 2-way design with two 5¼" SEAS coated paper midwoofers and a ¾" Hiquophon silk dome tweeter. The midwoofers are wired in parallel to each other are crossed over to the tweeter at 2500 Hz. The SongTower cabinet is about 10" taller than the B&W because it is a transmission line design whose length is one quarter the wavelength of its tuning frequency.
According to
this published review, on-axis response of the CDM 7NT measures ±2.3 dB from 200 Hz to 10 kHz. The -3 dB point is at 54 Hz, and the -6 dB point is at 43 Hz. Impedance reaches a minimum of 4.8 ohms at 9.9 kHz. Sensitivity averages 88.5 dB from 500 Hz to 2 kHz. The SongTower sensitivity is said to be about 88 dB. At my house, the B&Ws were slightly louder than the SongTowers when the volume settings were unchanged. We used my old Denon AVR-1800 as a preamp and a B&K EX4420 amplifier (200 wpc at 8 ohms and 350 at 4 ohms).
The most noticeable first impression I had of the B&Ws sound was their strong sounding bass. It was large and satisfying. I did not think these speakers need a subwoofer for music reproduction. In comparison, SongTower bass sounded cleaner but at the same time different. At first I thought the CDM 7NT's bass was deeper, but close comparison showed that the SongTower went just as deep.
If you characterize bass sound on a "muddy-to-tight scale" where muddy sound is on one extreme and clear tight bass is on the other, neither speaker would be near the undesirable muddy extreme, but the CDM 7NTs were definitely less tight sounding than the SongTowers. Please note, I would not say the CDM 7NT sounded muddy. Only in direct comparison to the SongTower was it less tight sounding.
During our listening session, the NTs were about 7' apart, and rather close (no more than 10"?) to the front of my entertainment center. At Paul's house, they're at least 12' apart and about 18" from the wall behind them. Could that have caused some of the apparent "muddiness"? Certainly. We didn't have enough space or wire length to try different locations for the B&Ws. This may also highlight the flexibility that SongTowers are known to have with regard to bass response.
Jim Salk had a number of comments earlier in this thread about
the subtle nature of bass from a transmission line (TL) cabinet, scroll down to where he said: As for your comments on bass extension, here are a few thoughts
I won't repeat all the comments from Jim's post, but I think it bears rereading it in light of the comparison of the bass sound of these two speakers. Most people, including myself, had never listened to a TL speaker before. To all those who are accustomed to hearing either sealed or reflex designs, a TL sounds unexpectedly different. Its sound is difficult for me to describe, but the more I listen to it, the more I prefer it over the other designs. I think Paul had his first experience with that the other day at my house.
I have previously heard B&W 602s, a 2-way bookshelf design that looked like it shared the same midwoofer and tweeter as the CDM 7NT (I am only judging by outward appearances). That 602 speaker had a problem in the upper midrange/lower treble range. There was noticeable edginess or excessive detail to its sound. It varied depending on the music we played. At first, it seemed to add detail over and above what is actually in the recording, but it easily became irritating and fatiguing with more time. On one song, a passage with loud trumpets this problem stood out, and we went back and forth between the STs and the 602s to compare how they did.
I expected to hear something similar with the CDM 7NT as I had heard with the 602. But it wasn't there. I don't know whether B&W modified the Kevlar midwoofer itself or used a different crossover design that attenuates it better, but the harsh high-frequency noise was not noticeable. Note that the crossover frequency between the midwoofer and tweeter was
raised from 3500 Hz in the 602 to 4000 Hz in the CDM 7NT. On brass instruments and female voices, I still think the SongTowers had greater "you are there" clarity, without any edgy harshness and with very wide dispersion. In the CDM 7NTs, brass instruments and female voices were clear sounding, but lacked the benefit of the SongTower's greater dispersion. I thought I noticed (for lack of a better term) a megaphone-like quality to these sounds from the CDM 7NT that were absent in the SongTower. I remind you of my earlier comments about placement of the B&W speakers. We did not experiment with different room locations, and that may or may not have influenced my impressions on their imaging and dispersion.
To sum up, I thought these two speakers were overall pretty close. I gave the edge (big surprise here) to the SongTowers - but I freely admit that I might be biased (
read why here). The CDM 7NTs sounded nice and are balanced overall. The SongTowers midrange clarity and dispersion won out, and their transmission line bass held it's own against the very good bass response of the CDM 7NT. It's easy for me to say that, but I'm glad I don't have to make the much more difficult choice before Paul - to keep the CDM 7NTs or sell them and buy SongTowers.
Paul later commented to me that " I really liked the SongTowers - everything about them. If I were looking to spend about $2k on new speakers, I probably would have ordered a pair from Jim on Sunday evening. As such I can highly recommend them to anyone. However, I do not think that the differences justify a change (or $$$ outlay) for me at this time. Part of me now wants to hear the HT2s and V3s, but not urgently, because one of the other outcomes of the experience was validation that I still like my CDM 7NTs very much."
Paul, I enjoyed your company and I'd do it all over again in a heartbeat. And thanks for that nice bottle of wine.
Note: In response to this post, there was some talk about how the CDM 7NT is no longer made (Miney bought his in 2001) and that the B&W 704 looks similar but doesn't sound the same.
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