Speaker IV – In-Cabinet Speaker Padding

I finally got around to a final modification to the “built-in” speakers of the entertainment center (AKA Speaker IV).  The way the speakers sit in the cabinet leaves a gap of about an inch between the baffle and the door.  That gap is an acoustic mass that has to interact with the speaker output, creating resonances.

Solution: add some acoustic foam around the front of the speaker to seal the gap.  So the foam cut-outs for the drivers are something of a hatchet job.  It works.  Well.  The mid-range, such as voices, are so much clearer, more intelligible.  Little details that were masked before are now discernible.

2016-01-18 17.25.57Drivers are a 2″ G2Si ribbon tweeter and Peerless 6.5″ HDS series mid-bass.  Cross-over is acoustic 4th order LR at 2.5 kHz.  The mid-bass is in a sealed cabinet tuned to 80 Hz.  Why so high?  The intention is for these to be crossed over to a subwoofer at 80 Hz as “small” speakers.

Response tested sitting about 32″ off the floor – pre foam.  (I’ll do an update when I do a post-foam test.)  Test level is 1 watt, measurement distance 18″.  Measurement window is about 3.5 msec, so the response is smoothed.

S4 right zoomedThe distortion levels are respectable.  The distortion above 1 kHz is mostly 3rd harmonic (green) which suggests the ribbon tweeters would sound best crossed over above 4 kHz, as well as the mid-bass could be crossed over lower as part of a 3-way design.  (Will have to confirm with additional measurements of the individual drivers.)  Alas, not a big enough opening in the entertainment center for 3 drivers.

S4 Right Distortion

NHT Classic 2 Center Channel

On occasion I buy speakers because I can’t make them for the price.  A good example is the NHT Classic 2 center channel.  I purchased a pair of these to act as the left/right speakers in the living room during the NHT holiday sales.  Price was $299 each.  The NHT Classic line, particularly the Classic 3, have received a lot of very positive magazine reviews.  The family lineage caries over to the Classic 2 center channel.  I really like these speakers, recommend them in general, and on value.  You can spend a lot more money and get a lot less speaker.

2016-02-27 17.26.28Yes, you read right.  I’m using a true center channel for a left and right speaker.  Here’s my reasoning.  The TV in the living room is above the fireplace, leaving just less than 8″ of height for speakers below it.  I looked at several loudspeaker bars and really did not like most of them.  The crossovers are too high, and the mid-bass units too small to really go down to 80 Hz.  Not all, just the vast majority.  The few audiophile quality designs I liked were quite pricey.

2016-02-27 17.26.58

The NHT Classic 2 is a 3-way design.  A tweeter, a small mid-range, and a pair of mid-bass units.  The advantage of the small mid-range is the cross-over to the mid-bass units can be low enough that a horizontal layout doesn’t beam in the upper mid-range.  And the Classic 2 is short enough to fit underneath the living room TV.

First up, the frequency response.  Measurement conditions are on a box 32″ off the ground, mic at about 18″, in the front third of a 14′ x 17′ room.  the measurement window is only 3.5 msec, so the response is limited to 220 Hz on the low frequency end.  3 dBW was required to reach 90 dB at 1 meter.  The response is reasonaby flat up to 10 kHz.

NHT Classic2 FreqWhat I am really happy with is the distortion levels at 90 dB.  0.4% or less at frequencies over 1 kHz.  Distortion falls to 0.2% between 300 – 800 Hz.  This is excellent, beating anything else I own or have built !!!  Distortion is also mostly second order, the nice distortion, except the 300 – 800 Hz range, where the third harmonic rises.

NHT Classic2 DistortionThe sound is very detailed, even with cable TV.  Vocals are so clear.  I watched the movie The Man from Uncle and was blown away.  This movie has several parts where the movie plays music – just an amazing, immersive experience.  I attribute this sound quality to the very even distortion characteristics.

My First Home Theatre Setup


The main loudspeakers are Speaker I, and the surrounds (not visible) are my own dipoles. No center channel at this time, nor side speakers.  The love seat is for the theatre, the main couch is for the Apogee Scintilla setup on the opposite wall.  The bass was quite good in the corner like this, and the imaging benefitted from only one reflection from the right wall.


Just a quick snapshot of my rack. Amplifiers are Parasound 750A for the surrounds, Adcom 5500 for the bass modules, and an Aragon 4004 mkII for the satellites. The surround processor is a Lexicon CP-3 with “+” software. The electronic x-over is a Marchand XM-9. The crossover frequency is 250 Hz. The source is a Pioneer DVL-909 which is a combination compact disc, laser disc, and DVD player.

Apogee Scintilla


This is an Apogee Scintilla, probably made in 1986 or 1987. (Texas size, 18 pound cat named “Chester” added for scale.) The diaphrams are Kapton film with aluminum foil conductors. The tweeters (4 of them, 2 front, 2 rear) and mid-range are suspended between a 2″ wide by 1.5″ deep by 54″ tall magnet gap composed of 2 double rows of magnets. The woofer ribbon diaphram is in front of a perforrated sheet of steel onto which are attached rows of magnets. The magnets alternate polarity so as to provided the same direction of force to the aluminum trace which “snakes” down the Kapton film. All of those magnets make the system very heavy: 140 pounds per speaker!

The system powering them in Oct ’00:

  • (Top-Left) This amp-sized item is not an amplifier, but a Theta Digital Data II combination Laser Disc / CD transport (1995 vintage).
  • (Bottom-Left) A Theta ProProgeny A DAC to match the transport. Actually, it a bit newer than the transport (1999 vintage). I selected this DAC based on reputation, but also because the output voltage is better than 4 volts for full swing.
  • (Bottom-Right) The pre-amp, a McCormack TLC-1 was rated stereophile class A for its pair of unity gain outputs: one passive, and one buffered. No pre-amp gain meant selecting a DAC with higher than normal output voltage.
  • (Top-Right) Amplification is via an Adcom 5500 that used to be on subwoofer duty in the home theatre. The Adcom does have some turn-on thump that I don’t like, but IMHO it is the most heavy duty of the regular offerings (the 5802 and HCA-2200 don’t count as regular) of Parasound, Adcom, and Rotel. I had originally tried to get a Parasound HCA-2200 II (it is rated to run bridged into 4 ohms, very rare), but the deal fell through.

However, as pictured above, the sound wasn’t the best. The sound was very laid back. The Scintillas sounded as if the upper vocal registers and the mid-range up to 1-2 kHz were supressed. Since I was not the only one that has heard this sound characteristic, I did not think anything was terribly wrong. Not so! The correct placement is to put the mid-range / tweeter ribbons on the inside:


After getting the setup right, I was an order of magnitude happier with the Scintilla sound. The ribbons are truly the jems of the speaker and it will take some serious comparison testing to the Martin Logan CLSIIz to decide if any one is better. The sound is stunningly detailed and smooth in the operating range of the mid-range and tweeter with no hint of a cross-over transition. Imaging is very good; before flip-flopping there was sound stage in the center, and to the extreme left/right, but no where else.

I’m still experimenting with the Scintilla’s position which greatly affects how strong the bass output is. Originally I had them 2′ from the wall which produced overpowering bass in the 30-40 Hz region. Since them I have moved them out to 4.5′ from the walls, but the amount of 30-40 Hz bass is still slightly unnatural. Getting the mid-range / tweeters in the right position helped the bass balance even more. The strategy appears to be to position the speakers in one of the listening room’s bass nulls to cancel some of the bass. The result, done properly, should be amazingly flat bass response throughout a whole room. I have yet to play any music loud enough to make the bass panels move except for a Telarc disc where a T-rex eats you for a snack. No subwoofer I have heard has been this good. After all, the bass radiating area is the same as eight 12″ woofers (or just a litte more than five 15″ woofers, or a little less than four 18″ woofers)!

Something to keep in mind is that these speakers are 13-14 years old (at time of my purchase). Inductors have come a long way since then, and capacitors even more so. Plus, my experience is capacitors do degrade over time (especially electrolitics), and the Scintilla’s capacitors would be large and have been getting a good workout over the years. Some replacement of these parts is probably in order. More important is tensioning of the bass membrane. There is some breakup buzzing in the 200-300 Hz range which is audible on male voices and with 1/3 octave pink noise tests.

I also need to try some more powerful amplifiers. The 5500 clips on deep bass notes when the sound is moderate (sorry, my Radio Shack SPL meter is broken). It just doesn’t have the output transistor count for driving so much current all of the time. Below is the impedance curve – 1 ohm in the bass, with a rise to almost 2 ohms at the cross-over between the bass panels and mid-range.  The 5500 never shut down mind you – I just didn’t perceive the bass quality I was expecting.



Martin Logan CLS IIz


This is what a CLS IIz looks like with the black finish. (5’10” author added for scale.) The diaphragms are transparent which is not easily discerned due to the camera flash. For much more information you should visit their site.


The system powering them in Nov ’99. The large, amp-sized item on the top left is not an amplifier. It is a Theta Digital Data II combination Laser Disc / CD transport. To the right is a Rotel RDD-980 transport which I originally bought for my CLS II system. The DAC is a Theta ProProgeny A (left 1st shelf). This DAC impressed me so immensely with its construction quality that I decided to replace the Rotel transport with a Theta transport. The pre-amp is a McCormack TLC-1 (right 1st shelf), and amplification is a pair of ’91 vintage PS Audio Delta 250 monoblock amplifiers (left and right bottom shelf). Later I upgraded to an Aragon 4004 (below).


This purchase was not initially stress free.  The frame split on one of the two panels during shipping.  I ended up repairing it myself.

DamageFront1 DamageFront2

You may have heard that the impedance of electrostatic speakers is very low at high frequencies.  I took some measurements of the undamaged speaker, with and without the power applied.  That’s under 2 ohms at 20 kHz !!!