Speaker Related Projects

   2-Way Ribbon Tweeter Speakers
(Vifa and Pioneer. May-2020)

   Transmission Line Speakers
(Aborted attempt at a TL. September-2012)

   Acoustic Research AR-4x Rehab
(Rehab of a garage sale find. January-2016)

   Infinity RS-4000 Rehab
(Rehab of a garage sale find. June-2015)

(A tall, thin, upwards firing omnidirectional speaker. May-2010)

(A powered subwoofer using a 12" driver and 15" passive radiator. Jan-2010)

(A computer speaker; redux. December-2005)

(A computer speaker in a light canister. Jan-2005)

(10" vented subwoofer in a cardboard tube, powered by a Parapix amp. May-1999)

   MTM Center Channel Speaker
(A Madisound design. Nov-1997)

   2-way Surround Speakers
(5" woofer and 1" tweeter. July 1997)

   3-piece mini system
(6" DVC bass module mated to 4" car speaker. June 1997)

   3-way Vented Floorstanding Speaker
(vented 10" woofer, 5" mid and 1" tweeter in a 4 ft tower. Summer 1995)

   NHT1259 Subwoofer
(A 12" woofer in a sealed architectural pedestal. Winter 1994-95)

   Inexpensive Speaker Stands
(Particle board, sand and spray paint. Fall 1994)

   2-way satellite
(6.5" woofer and 1" tweeter. Summer/Fall 1994)

Audio Electronics Related Projects

  900 MHz Audio Receiver
(Better use for bad headphones. Jan-2008)

  Buster - A Simple Guitar Amp
(Perfect for the beginner. Jan-2010)

  A PC-based Audio Console
(Use a PC to play tunes. Jan-2010)

  LM-12 Amp
(Bridged LM-12 opamps. Aug-2003)

(A CD player and FM tuner from spare computer parts. Oct-2002)

   Quad 2000 4-Channel Amp
(Premade modules by Marantz. May-1998)

   Zen Amp and Bride of Zen Preamp
(by Nelson Pass. Apr-1997)


  Using Wood in Speakers FAQ
(Work in progress)

   MDF FAQ for speaker builders

   Woodworking Tools for the DYIer
(HomeTheaterHiFi.com Oct-1998)

  Some Thoughts on Cabinet Finished for DIY Speakers

   Large Grills Made Easy

   Some Parts Suppliers

Other Useful Stuff

   DIY Audio Related URLs

  Veneering Primer
(by Keith Lahteine)

   How to get a Black Piano Finish
(by DYI Loudspeaker List members)

   Sonotube FAQ
(by Gordon McGill)

   Excerpts from the Bass List
(Oldies but Goodies)

DIY Loudspeaker List

  DIY Loudspeaker List Archives


This is version 0.2 of the PRELIMINARY, unofficial NHT 1259 list of Frequently Asked Questions. The accuracy of data in this FAQ is unconfirmed and this FAQ is not sanctioned by NHT, the bass mailing list, or any other person(s). Mr. Ken Kantor of NHT has seen this document and corrected one error, but is not vouching for accuracy.

This document is now many years old. Some of the details such as driver availability may no longer be correct. However technical details for the NHT1259 driver itself should still be valid.

What is the 1259?

In brief, the 1259 is a cast-frame 12" woofer with a polypropylene cone, large vented voice coil, large magnet structure, rubber surround, and extremely long linear throw. The 1259 is a 6 ohm speaker with a single voice coil.

The 1259 is a custom woofer designed by Bill Bush, NHT Chief Engineer, for use in NHT products and made for them by Tonegen of Japan. NHT has made the driver available to builders through a retailer called A & S Speakers (Also known as Just Speakers).

							A & S Speakers
							4075 Sprig Drive
							Concord CA 94520 USA
							Voice 510-685-6400
							FAX 510-603-2724

As of January, 1996, if you mention the internet, you get a special price of $115 each for this driver from A & S. The regular price is $149 each. Madisound also sells the 1259 for $149.

What are its characteristics?

Effective cone diam.        D:     20.00 cm            7.87 in.
Maximum linear excursion Xmax:      1.50 cm            0.59 in.
Bl product                 Bl:      7.50 N/A 
Voice coil dc resistance   Re:      3.40 Ohms
Mechanical mass            Md:     32.00 gm
Mechanical compliance     Cms:      1.52 e-3 m/N
Mechanical losses         Rms:      1.55 kg/s

Nominal impedance     6 ohms
Maximum music power   300 watts
Frequency range       19-1000 Hz        
Sensitivity           90 dB SPL @ 2.83 VRMS @ 1 meter
Voice coil inductance 1.2 mH
Voice coil diameter   50 mm
Voice coil height     34 mm
Air gap height        8 mm
Magnet weight         59 oz
Effective cone diameter     d:     20.00 cm
Maximum linear excursion Xmax:      1.30 cm
Resonant frequency         F0:     19.00 Hz
Equivalent volume         Vas:    190.00 L             6.71 cu. ft
Mechanical Q              Qms:      2.60  
Electrical Q              Qes:      0.56  
Total Q                   Qts:      0.46  
Reference efficiency       n0:      0.22 %
Output level<             SPL:     85.52 dB SPL
Effective area             Sd:    507.00 sq. cm
Maximum displacement       Vd:    408.41 cu. cm
                          Krm:     28.89
                          Kxm:     26.67
                          Erm:       .584
                          Exm:       .647
Enclosure volume           Vb:     88.62    299.21 L 
-3dB frequency             F3:     32.43     15.56 Hz
Peak response ripple       Rh:      0.00      0.04 dB
Maximum acoustic output   Par:      0.15      0.03 W
Maximum SPL               SPL:    100.88     94.14 dB SPL
Maximum electrical input  Per:     68.57     14.52 W

Intervals per octave   6.0
Starting frequency  
15.9    -12.66     -2.21 dB
17.8    -10.78     -0.77 dB
20.0     -8.99     -0.27 dB
22.4     -7.29     -0.13 dB
25.2     -5.73     -0.09 dB
28.3     -4.36     -0.07 dB
31.7     -3.20     -0.05 dB
35.6     -2.27     -0.03 dB
40.0     -1.56     -0.02 dB
44.9     -1.05     -0.01 dB
50.4     -0.69     -0.00 dB
56.6     -0.45      0.00 dB

Desired system Q         Qtc:      0.71
Recommended box volume    Vb:     88.62 L             3.13 cu. ft
Enclosure damping                 3.00 (0 - 5)
Tuning ratio               a:      1.91 
System resonance          Fc:     32.43 Hz
Actual system Q          Qtc:      0.71 

-3dB frequency            F3:     32.43 Hz
Peak response ripple      Rh:      0.00 dB
Maximum acoustic output  Par:      0.15 W 
Maximum SPL                      100.88 dB
Maximum input power      Par:     68.57 W

Recommended box volume    Vb:    299.21 L            10.57 cu. ft
Tuning ratio               a:      0.64 
Enclosure resonance       Fb:     16.50 Hz
Recommended vent diameter Dv:     20.05 cm            7.89 in.
Desired vent diameter     Dv:      5.08 cm            2.00 in.
Vent length               Lv:      3.73 cm            1.47 in.
-3dB Frequency            F3:     15.56 Hz
Peak response ripple      Rh:      0.04 dB
Max. acoustic output     Par:      0.03 W 
Maximum SPL                       94.14 dB SPL
Maximum input power      Per:     14.52 W

How can I use it?

The 1259 works best in a sealed enclosure of approximately 3 cubic feet (85 liters), stuffed with approximately 3 pounds of acoustic polyester fiber or fiberglass insulation.

In the NHT 3.3, the first speaker design in which the 1259 was incorporated, the internal volume used is 2.7 cubic feet (76.44 liters). In addition, the NHT 3.3 makes use of a sub-divided enclosure with resistive damping between sections to achieve an even lower 3dB rolloff frequency (called F3).

One of the best material for speaker cabinets is 1" MDF (Medium Density Fibreboard). It is more expensive than particle board, but much better damped. Some have used 3/4" MDF successfully, and have made up for the thinness with extra braces. MDF is hard to find, but many lumber yards can special order it from their normal distributors. Often, the lumber yard doesn't even know that they can get it, because so few people ask for it.

When calculating volume, allow for the space taken up by the speaker itself and all internal braces. Use lots of braces spaced irregularly. They will not hurt and will probably help. Use cleats at the joints, shelf braces, cross braces, and even battens across the larger panels. Box L vs W vs H is not critical at all (nor in any other closed box in which the shortest wavelengths to be reproduced are appreciably longer than the shortest box dimension).

Exact enclosure volume is not critical, and stuffing can be added or subtracted to fine tune the response. Mr. Ken Kantor recommends adjusting the stuffing by monitoring the impedance versus frequency of the sealed box system. Add stuffing to lower the frequency where the impedance is highest. When that impedance peak starts to rise in frequency, you have added too much.

The 1259 is built to be mounted facing outwards. Do not use it facing downward or upward. The suspension is not suitable for this use and distortion and/or damage will result from the sagging cone.

Is there a dual voice coil version available?

No. Some people use two 1259 subwoofers for stereo and claim that the performance is superb. There are many advantages to dual subwoofers, such as better stereo image, fewer problems with room interactions, and of course, more bass. Others only use one 1259. If you use just one, you should get a separate power amplifier just for the 1259 and use that amplifier to mix stereo down to mono.

How low will this driver go?

In an optimum cabinet, it will go flat to 30 Hz, and will generate appreciable energy down to 20 Hz, thanks to the more 6 db/octave rolloff of an acoustic suspension cabinet (versus the 12 db/octave rolloff of a tuned port enclosure). Depending on the shape and dimensions of the listening room (i.e., the combination of room gain and room modes), a proper 1259 subwoofer can produce satisfying response well down towards 20 Hz. The 1259 is designed to work well in a near cubical enclosure placed flush against the wall with the driver pointed out into the room.

How high will the 1259 go?

The woofer will operate effectively up to 1 kHz, but the signal applied to the 1259 should be down by at least 12 dB at 1 kHz. Optimum crossover frequencies range from 100 to 250 Hz.

What about a crossover for it?

In the NHT 3.3, the 1259 is driven through the following low-pass filter: This filter has a cutoff frequency of approximately 100 Hz.

       12 mH
       Iron    |       |
       Core    C1      |
             200uF     |
              Non     NHT
             Polar    1259
            Electro-   |
             lytic     |
               |       |

Is this woofer really great?

This is a very good woofer. It is tailored to excellent home audio in a reasonably sized sealed box, and at a fair price. In addition, the NHT Company puts extremely high demands on Tonegen, the speaker manufacturer, for consistancy and accuracy in the driver. NHT tests each 1259 to 10% nominal Vas, Mms, and Qts, and +/- 1 dB response, at their factory before shipping to A & S. This is much tighter tolerance than home builders get in other drivers, and has many benefits.

You can spend more money and get a larger woofer, a bigger magnet, etc. Such a driver may be more suitablet for specific applications, like theater sound or outdoor sound, but may actually be inferior for home use. Large magnets improve efficiency, but reduce the low-frequency radiation of woofers by acting as a brake on the counter-voltage the voice coil generates as it cuts through the flux of the magnet. Larger woofers suffer from cone breakup and distortion for large excursions. Finally, more expensive woofers may require larger or more complex enclosures.

To our knowledge, the NHT 1259 is one of the most effective deep-bass woofers that have been offered to the DIY constructor. The 1259 has been designed specifically for a small sealed box (acoustic suspension). Used in a vented box, the 1259 might produce more bass, but at the expense of some combination of increased distortion, looser bass, less even frequency response, less maximum output, and at the risk of damage. Vented boxes are not recommended for the NHT 1259. The NHT 1259 is a very high compliance woofer which relies on the air in a sealed enclosure to provide back pressure that linearizes cone motion and protects the driver from damage or destruction by excessive excursion below the frequencies at which a vented box loads the woofer cone.

One additional attribute of the NHT 1259 is that a key developer of the driver, Mr. Ken Kantor, has helped members of the bass list use the driver to its full potentials, offered candid advice, and even revealed some NHT proprietary details for using the driver. This level of support for a DIY driver is unheard of today.

Are there any other great woofers available for DIY subwoofing?

Several manufacturers offer excellent woofers, including Eton, Peerless, JBL, McCauley, Madisound, and Dynaudio. Members of the bass/DIY loudspeaker list often discuss their experiences with other woofers. More than a hundred members of the list have bought the NHT 1259, some who appreciate its unique balance between reasonable price and superb performance, and others who went by its reputation.

Where can I learn more?

Buy and read the Loudspeaker Design Cookbook by Vance Dickason. This is the best treatise on DIY speakers that is friendly and readable, yet technical and accurate.

   The Loudspeaker Design Cookbook, by Vance Dickason ISBN 1-882580-10-9

   Old Colony Sound Lab
   PO Box 243
   Peterborough NH 03458-0243 USA

   8608 University Green; Box 4283
   Madison WI 53711 USA

Who wrote this FAQ?

Credit goes to many people, including:

  • Paul Close
  • Ken Kantor
  • Dan Hildebrand
  • Doug Purl

and many other members of the bass mailing list, may it live on forever.


Note: The contents in these pages are provided without any guarantee, written or implied. Readers are free to use them at their own risk, for personal use only. No commercial use is allowed without prior written consent from the author.