Geometry, surface and depth. The eight Capitol Studios echo chambers sit about 30 feet beneath the parking lot of the Capitol Records Tower at 1750 Vine Street. Each is a trapezoidal concrete room with no parallel surfaces and a hard lacquered finish, around 2,000 cubic feet, fed by a speaker at the narrow end and picked up by two microphones toward the wide end. Natural decay runs from about five seconds to 9.5 in the longest. All of it is expensive to copy, which is why the rooms are still in use seventy years on.
Where exactly are they, and how far is that from Burbank?
Under the tower just north of Hollywood Boulevard on Vine Street. The Capitol Records Tower was designed in 1953 by Louis Naidorf, then 24, of Welton Becket Associates, and completed in April 1956 as the first circular office building in the world (Sound On Sound). Hollywood itself is a neighbourhood of the City of Los Angeles. Burbank, where I work, is a separate city about nine miles north; the drive down Barham Boulevard and through the Cahuenga Pass takes 20 to 25 minutes outside rush hour and closer to 45 inside it. Parking follows the usual Hollywood arithmetic: metered street spaces around Vine and Yucca are short-term, so a full session day means a paid lot or the Metro B Line, whose Hollywood/Vine station is a block south.
Who built them, and when?
Chambers 1 through 4 were part of the original reinforced concrete construction in 1956. In 1969 part of the parking lot was excavated and chambers 5 through 8 went in (Mix). The two trade sources differ on authorship: Mix credits Les Paul with the design of the first four, while Sound On Sound names the acoustician Mike Rettinger, who built on the reverb experiments of Les Paul and Bill Putnam. Both agree on the construction: concrete, a reflective lacquer of the kind used on pipe organs, trapezoidal plans and irregular ceilings, each room slightly different in volume, about a storey underground in the words of Capitol engineer Nick Rives.
Why no parallel walls, and why the lacquer?
Because both decide the decay. Sabine's formula gives reverberation time as 0.161 times volume divided by total absorption, in metric units. A 2,000 cubic foot room is about 57 cubic metres with roughly 90 square metres of surface. To ring for five seconds, its total absorption has to be near 1.8 square metres, which means the surfaces return about 98 percent of the energy that hits them. Lacquered concrete does that. Painted drywall does not, which is why an empty spare bedroom never sounds like Chamber 4.
The trapezoid solves a different problem. Two parallel walls 12 feet apart return a slap every 21 milliseconds, a flutter at roughly 47 repeats per second that reads as a buzz on top of the tail. Angled walls and a sloped ceiling scatter those paths so the decay is dense and smooth instead of a picket fence. Small volume brings its own cost: the lowest mode of a 16 foot room sits near 35 Hz and the bass rings unevenly, which is why sends into a chamber are high-passed before they get there. The modelled version keeps a 6 dB per octave filter in the send path, adjustable from 80 to 750 Hz, for exactly that reason.
What is in the room besides concrete?
The speakers were Altec Voice of the Theatre A7s or 604e monitors, driven in mono, and they still are. The original return microphones were RCA 44 ribbons, later a pair of Altec 21D omnidirectional tube condensers for stereo returns. Today most of the chambers use Shure SM80 omnis, Chamber 6 keeps two RCA 44s, and Chamber 5 runs a pair of Sony C37A cardioid tube condensers (Mix). Moving the microphones deeper into the wide end lengthens the arrival and spreads the stereo image. Chamber 4 is the one engineers call classic; Chamber 7, with its speakers placed for a longer path, has the longest tail.
What did engineers do to the signal before and after the chamber?
Delay it on the way in and colour it on the way back. At Columbia's 30th Street studio Frank Laico, on advice from Les Paul, ran the send through a tape machine at 15 inches per second before it reached the chamber, which put a fixed gap between the dry word and the start of the tail and kept lyrics legible in front of a long decay (Sound On Sound). At Western Recorders, Chuck Britz drove the chamber speakers far harder than convention allowed and printed the echo during tracking rather than adding it in the mix. The modern equivalents are a pre-delay control, 0 to 250 ms in the Capitol model, and a three-band return equaliser at 125 Hz, 500 Hz and 5 kHz.
Who else got to use them?
Half of Hollywood, over the phone. Capitol leased chamber time to other studios through high-quality audio lines, to the Village, to Western Recorders (now EastWest) and to United Recording, until the mid-1990s. The neighbours also built their own. Western's chamber was a 10 by 12 foot cinder-block room off a loading dock. Gold Star poured two trapezoidal chambers about 18 feet long and 12 feet high in a proprietary plaster laid in two-inch coats, then cut the slab around them and filled the gap with tar so the building could not shake them. When Gold Star closed, David Gold had them destroyed rather than copied.
What threatens a chamber under a parking lot?
Neighbours with excavators. In 2008 a developer planned a condominium with underground parking 20 feet from the chambers. Capitol took the case to City Hall, and the agreement that came out of it restricted the loudest construction within 20 feet of the property line to 7 to 10 in the morning, before sessions start, with the Los Angeles City Council enforcing it (CBS News). The physics is the same one that runs under Hollywood Boulevard a block south, where the Metro B Line passes: ground-borne vibration enters through the slab and re-radiates from the walls. My note on checking a Hollywood room for subway vibration covers how to test for it before signing a lease.
What does a Burbank room do about it?
A residential room on North Catalina Street has no basement and no chamber, and none of this is a claim of a session at Capitol. The first option is a modelled chamber: the Universal Audio version reproduces chambers 2, 4, 6 and 7 with the microphone choices above and lets the decay be shortened from its natural value down to one second (Mix). The second is the 1940s method: a tiled bathroom, one speaker, one omnidirectional microphone, which is how Bill Putnam gave the Harmonicats a number one in 1947 from a washroom at Universal Recording in Chicago. The working settings are the same either way: high-pass the send near 150 to 200 Hz, set 30 to 60 ms of pre-delay on a lead vocal, pull 500 Hz on the return if the room honks, and narrow the width for a solo voice. Full credit list with sources at /credits.
Frequently asked
How deep are the Capitol Studios echo chambers? About 30 feet below the parking lot of the Capitol Records Tower at 1750 Vine Street, which a Capitol engineer describes as roughly a storey underground. Four were built with the tower in 1956 and four more were dug in 1969.
How long is the decay in a Capitol chamber? Sound On Sound gives a maximum of about five seconds for the roughly 2,000 cubic foot rooms. Mix, reviewing the modelled versions of chambers 2, 4, 6 and 7, measured natural decay times between 5 and 9.5 seconds.
Is Hollywood a separate city? No. Hollywood is a neighbourhood of the City of Los Angeles. Burbank, about nine miles north, is an incorporated city with its own government.
If a mix needs a chamber sound this week
Send the dry vocal or the stem and a reference for the length of tail you want. I will return two versions, one through a modelled chamber and one through a short real room, so the track can decide which one it takes. Background and contact at /about.