John Mulcahy - Creator of REW!


Leonard Caillouet

An AV NIRVANA VIP is John Mulcahy. We want to highlight John because for the AV NIRVANA community, which consists largely of audio and video hobbyists and DIYers, the advent of the ability to do our own analysis of the behavior of our systems in our actual rooms really changed things. When inexpensive tools for room acoustics measurements became available, we no longer had to guess or work with manual tones and measurements or RTA, but could gather and analyze large amounts of data efficiently. REW, the software that John developed and continues to improve, is easily the most significant tool for many of us. The fact that John has provided it for free and continues to support and expand and improve it represents an impact that is hard to estimate.

We asked John for a little history on the development of REW and this is what he had to say:
"Room EQ Wizard was inspired by the "TMREQ Wizard", a Java application that I wrote as a little spare time activity whilst I was Technical Director of TAG McLaren Audio (TMA). Its aim was to assist owners of TMA AV processors in setting up those units' TAG McLaren Room EQualisation (TMREQ) filters.

Following the sale of TAG McLaren Audio early in 2004 I decided to write a new application that would combine equaliser filter response visualisation and adjustment with audio measurement, as I wasn't that happy with the 3rd party packages I had been using for measurement at the time and thought an integrated solution would be easier to use. That was the birth of Room EQ Wizard.

I added support for the BFD1124P, popular for subwoofer EQ at the time, and came to meet Sonnie. Sonnie had authored the "BFD Guide", a comprehensive manual on how to manually measure an audio system and adjust a BFD to improve the response. Sonnie started using REW, and in 2006 we founded Home Theater Shack.

Over the years the range of equalisers supported by REW has grown, but the EQ side has been outstripped by the measurement capabilities - these days REW is primarily a measurement system. 13 years after starting work on REW I still enjoy adding new features and capabilities to it and the ToDo list is longer than ever! "

But John is an interesting individual not only because of his excellent software and his constant personal support of users. John, as one might expect, has a rich history in the industry and credentials that confirm that he is a pretty smart and hard working guy. John graduated with 1st Class Honors from University College Cork in Ireland in Electrical Engineering. He has since accumulated an impressive resume in the electronics industry.

John has more than 25 years’ experience in the development of high technology products and the management of technology companies, in sectors ranging from avionics and automotive electronics to high end audio and broadcast. In the audio arena John was the Technical Director of TAG McLaren Audio, with responsibility for the development of McLaren’s award-winning range of Home Theater components. He is also the author of REW (Room EQ Wizard), a comprehensive acoustic measurement and analysis package.

Much like the rest of us, John loves audio. When asked about his history in audio and equipment this is what he gave us:
"HiFi became an interest after I started my first job, in the 80's. I blame a colleague at work, Darrell, for infecting me with the HiFi bug. He had a set of Meridian M10's driven from a Pink Triangle turntable, it sounded incredible. I was hooked and worked my way through a wide variety of equipment over the years. A few items I remember fondly include the Musical Fidelity A1 integrated amp (class A with a top plate that could double as a grill!) and my PT Too turntable with Rega RB300 arm (I still have it, but been more than a few years since I played anything on it). For a few years I had a Wadia 16 feeding a Primare 928 system (preamp and monobloc power amps) driving Martin Logan electrostatics. Headphones became a bit of an obsession for a while, culminating in Stax Lambda Signatures driven by the SRM-T1 tube energiser. Wish I still had them, though I have a set of Audeze LCD-2 driven by a Wadia 121. After TAG McLaren Audio was set up I had a full set of TMA equipment, I still have the AV192R processor and 250MR monoblocs though they are driving a pair of ATC SCM40 nowadays."

More than anyone else, John exemplifies the kind of person we expect will find of interest. He is a tinkerer, always trying to find a better way to get a little more out of a system, and he happily shares his knowledge and experience. He has certainly affected most of our lives for the better and has inspired many DIYers to experiment and tweak their systems in ways that would not have been practical without his software and guidance.

Thank you, John, from the AV NIRVANA community.
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Active Member
Apr 17, 2017
My AV System  
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Emotiva XMC-2
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Emotiva XPA-5
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McCormack DNA-1 Custom Monoblocks (On Standby)
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Woo Audio WA6se w/ Audeze LCD-2
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Oppo BDP-95
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Revel Voice
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Thank you for acknowledging John's credentials and longstanding contributions in such complete detail. I'm grateful for his personal guidance on more than one occasion, and take great interest in following his solutions for others. Before discovering REW, my DIY efforts were discouraged by manual data collection. Now I enthusiastically approach a calibration session. The on-line manual offers plenty of insight into the required measurements, and web support is plentiful. That's a pretty amazing accomplishment which deserves a round of applause!


Senior Admin
Staff member
Apr 2, 2017
My AV System  
Preamp, Processor or Receiver
Monolith HTP-1 Processor (Movies and Surround)
Main Amp
Benchmark Media AHB2 Monoblocks
Additional Amp
Emotiva XPA-Eleven
Computer Audio
Intel NUC w/ Roon ROCK
miniDSP SHD (Two-Channel Music Only)
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Panasonic UB9000 4K UHD Player (for movies only)
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MartinLogan Renaissance ESL 15A
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MartinLogan Focus C-18
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MartinLogan EFX Surrounds
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MartinLogan ElectroMotion ESL
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MartinLogan EM-IC
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MartinLogan EM-IC
SVS SB16-Ultra x4 (music) + PB16-Ultra x2 (movies)
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Elite 128" Screen
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Universal MX-890
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Roku Ultra
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Lifetime Roon Subscription
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Dish Joey 4K
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Kaleidescape Strato S 12TB
An amazing guy he is... and we certainly appreciate all that he has done for the industry in a way that has basically been a continual charitable event. I am honored to have been his partner for 8 years in a different venture. It was a pleasure working with John... and we look forward to working with him here at AV NIRVANA.


Feb 22, 2018
Hello everyone,
I am from Taiwan and using REW to do DRC study. Thanks John's contribution in DRC. Thank you very much.


Sep 27, 2017
John Mulcahy is not only generous, I think he is a genius, and deserves the Nobel prize(as well as the money that goes with it).....nothing less.

Hopefully one day I'll be able to describe how far reaching his contribution has been to me.

Simon Curran

Apr 22, 2018
I've been using this software... at first for fun... now to try to start a product. As an Electrical Engineer myself I was blow away by how much functionality has been added to the software and I kept wondering who this John guy was and what motivated him. Thanks for this little write-up.


New Member
Jun 14, 2019
I started to recently use REW. It's an incredible product and John is a gifted individual. Thank you so much for sharing your talents and being so generous. There is so much the product can do that I can't imagine what goes into developing it. As a Mechanical Engineer, Business owner with more than 30 years in 3D engineering software use and sales I'm impressed.
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