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ADS L990
Loudspeaker (1987-1988)
© 2013 KenRockwell.com. All rights reserved.

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ADS L990 (Sealed-box 3-way tower speaker, Dieter Rams styled with perforated metal front grille, 35 " x 11" x 11" with 10" woofer, 1.5" dome midrange and 0.75" dome tweeter, 65 pounds.) This free website's biggest source of support is when you use these links, especially this link to ADS speakers at eBay where they sell for about $250 the pair (see How to Win at eBay) when you get anything, regardless of the country in which you live. Thanks! Ken.

May 2013   Audio Reviews   All Reviews

ADS L400 Review



The ADS L990 is a small tower loudspeaker with a 10" woofer, 1-1/2" dome midrange and 3/4" dome tweeter — all made in Boston, Massachusetts, USA.

It measures 35 " x 11" x 11" and sits on a short plinth. Connectores are laboratory-standard 3/4" spaced binding posts pointing straight down. You can then run the wires out a slot in the rear of the plinth for neat installation.

It's rated 8 Ω, for amplifiers with rated outputs from 15 W to 200 W peak. It has a tweeter overload protector — but none for its dome midrange or woofer.

It's rated 40 - 25,000 Hz ±3 dB with 88 dB SPL sensitivity at 1 watt at 1 meter.

Its crossover frequencies are 700 Hz and 3 kHz. The high woofer crossover (700 Hz as oppused to 300 Hz) is to limit power to the 1.5" dome midrange.

List price was $2,000 the pair, corrected for inflation in 2013. (That was $975 in 1987 dollars.)



Sound is extraordinary because of the dome midrange. The dome midrange means that all except the bass is coming from domes, not cones. Cones are subject to all sorts or breakup and resonamces, especially from the sound going into the box and coming out again mutilated.

With the dome midrange, there is far less accoustic energy storage and therefore far less potential for temporal colouration.

Balance wise, the L990 is much more neutral than most other ADS speakers. ADS speakers price themselves on their neutrality, but tend to err on the side of bright tweeters.

The L990 has no peaks, it's all quite neutral.

Honestly, for symphonic and vocal music most suseptible to degraadation by speaker midrange resonances, I like these L990 about as much as my B&W 801 and Quad ESL63.

The bass is quite good, with more power handing than you'd expect. The tower packs a lot of box volume in very little floor space. Bass is unboomy and with quite a low Fc; about 40 cps.

The 10" woofer is almost as wide as the speaker itself; ADS was very clever in the mechaical and grille design.

The midrange and tweeters are offset from center to distribute the effects of diffraction.


Bass Measurements

In August of 1995 I measured this response with a Radio Shack classic sound-level meter, C-weighted:

+3 dB @ 90 Hz

0 dB @ 55 Hz

-3 dB @ 40 Hz

-10 dB @ 30 Hz


Measuring its impedance versus frequency, I came up with these parameters for a second-order high-pass filter for simulation purposes in the next step:

Left f=39.23 Hz , Q=0.825

Right f=36.10 Hz, Q=0.676

I'm unsure how I came up with these, since I also determined that the Q was a little above 1.


Bass Equalization Network

In 1988, I designed and built an active low-level equalizer to compensate for the L990's phase and frequency response.

This network lowers the speaker's low-frequency response by one full octave and smothes-out its slight resonance around 67 cps.

This network, based on the work published by Ralph Greiner in the JAES of March, 1983, replaces the L990's low-frequency response with one of a second-order high-pass filted with an Fc of 20 cps and a Qtc of 0.7.

For sanity's sake, I also added an 18 dB/octave low-cut filter at 20 Hz to keep from blowing-out the woofer with any signal below 20 cps.

The completed system works great, with solid respionse to 20 cps, tighter transient response and no more slight boom in the mid-bass.

Here are 2013 measurements on my 1988 circuit, made on the Rohde & Schwarz UPL:


Frequency Response

ADS L990

Frequency Response, 200 mV input.


ADS L990

Frequency Response, marker at peak response, 200 mV input.

ADS L990

Frequency Response, marker at 37 Hz, 200 mV input.


ADS L990

Frequency Response, marker at 68 Hz, 200 mV input.


Maximum Output Levels (MOL)

ADS L990

MOL at 0.1% THD at 1 kc: 9.662 V RMS, 200 kΩ load.


ADS L990

MOL at 0.1% THD at 21 cps: 9.03 V RMS, 200 kΩ load, 1.761 V RMS input.


Maximum input level at 68 cps is in excess of 10 V RMS.



These are pure THD only, not including noise.

ADS L990

THD with 200 mV RMS input, 200 kΩ load.


ADS L990

THD with 1 V RMS input, 200 kΩ load.

Output noise levels

With input shorted with 5Ω: -98.25 dBV unweighted (22 kc bandwidth), -101.82 dBV A-weighted.


Without 20 Hz high-pass filter

If I bypass the 20 Hz HPF, here are my measurements.

Now it inverts polarity. THD is the same, or a bit less.

Here are the frequency response measurements:


Response, 5 ~ 1,000 cps. (+18.06 dB, or a gain of 8, at DC.)



Response, 16 ~ 100 cps.



Response, 40 ~ 200 cps.

Network Response
801 predicted
801 measured C/flat
1 kc
0.0 dB reference
100 cps
-1.875 dB
0 dB
0 dB
70-75 cps
+0.2 dB
+1.5 dB
68.1 cps
-3.00 dB
60 cps
(-2.7 dB)
-0.8 dB
-0.8 dB / 0 dB
47.2 cps
0.0 dB
45 cps
(+1.0 dB)
-0.1 dB
-3 dB
40 cps
+3.05 dB
+0.2 dB
-4.7 dB / -2.7 dB
35 cps
(+5.6 dB)
+1.4 dB / +4.4 dB
-6 dB / -3 dB
32 cps
(+7.5 dB)
+2.3 dB / +5.3 dB
-7 dB / -4 dB
30 cps
(+8.5 dB)
+1.9 dB/ +6 dB
-8.5 dB / -4.5 dB
25 cps
+11.4 dB
+1.8 dB / + 6.3 dB
-11.5 dB / -7 dB
20 cps
+14.1 dB
0 dB / +5.5 dB
-16 dB / -10.5 dB
18 cps
+15.2 dB
-2.9 dB / +5.1 dB
-20 dB / -12 dB
16 cps
+16.0 dB
-7.1 dB / +1.9 dB
-25 dB / -16 dB
15 cps
+16.4 dB
12.5 cps
+17.1 dB
10 cps
+17.6 dB
5 cps
+18.1 dB
+18.1 dB
DC gain
8.04 x

Cursor (read from graph)


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Mr. & Mrs. Ken Rockwell, Ryan and Katie.


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