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Add a Subwoofer into your standard Medallion Cabinet

Suggested by a client, there is 1.5 cubic feet of space in the bottom of the Medallion cabinets.  The trick is to find a subwoofer that will work in this space.

I have tried and very much like the DIY Cable woofer.  (this woofer is out of production, and a new woofer will be substituted in a few months.  You may wish to try other woofers, but I cannot say if they will be compatible.  The Eminence LAB 12 should work, but I have not tried it.  If you try it let me know how it works please ).

When properly dialed in it creates a the effect of deeper bass without any additional nasty affects.  Just be sure to recognize that there is both a phase reversal and time delay in the Medallion bass, as it comes off the rear of the cone and then travels down the horn.  It is necessary to properly adjust the phase angle on the plate amp to correct for this. Luckily, the plate amp specified has a variable phase control.   I find that 180 degrees of phase sounded best in my set-up.

 


Art Dudley's ears

Art Dudley designed these “ears” to fit in his Medallion II cabinets when using his 2A3 drivers.  They increase the low end extension and help fill in a hole in the mid-bass response that occurs if the chamber is not properly sized.

Tony Glynn, my predecessor, indicates that this should work well for a pair of PM2C’s also, and should be a little larger if you are using PM5A’s  They are not required if you are using PM7A’s or PM6A’s. 

You can make these by gluing plywood sheets together.  They should be 8” high by 4-3/4 inches wide.  Use 2 pieces of ¾ inch plywood, and one piece ½ thick.  Mark along the lines and cut with a band saw or a scroll saw.  The exact shape is not all that important, so don’t worry if you wander off the lines slightly.  When you are done cutting you will have 2 pieces, one for each upper corner of the compression chamber. 

Drill 2 holes in the ear to secure to the sides of your cabinet.  The lower hole should be about an inch from the bottom, the upper hole should be about 2-1/2 inches from the top.  Take some time to size these properly so you do not put a screw all the way through the cabinet.  The cabinet sides are ¾ inch thick, so do not allow the screw to extend into the cabinets more than ½ inch. 

I have used similar sized ears for DX4’s, and they work very well in that usage.  But please feel free to adjust these up or down in size and report back as to what sounds best.

If you cannot read the print, here are the dimensions:

2-1/16 inch thick, 8" tall, 3-3/16 wide at top

Center portion is 2-/12 inches wide, bottom is 1-1/2" wide

Top and bottom angle sections are 2-1/8" tall

Inserts and Bolts

One of the challenges in mounting Lowthers is keeping any magnetic material away from the cone. Little specks of material get into the voice coil, causing a grating and rubbing sound. OUCH! It becomes necessary to disassemble the driver and get the metal out - time consuming if you have experience and very dangerous if you do not.

So I recommend brass knife inserts and non-magnetic stainless steel bolts to attach the drivers to your box. The only magnetic material is the allen wrench you use to drive the bolts in, and I know you will be careful with that. Insertion is a little tough, but use wax (never soap) as a lubricant after drilling a ¼" hole.

Some customers have had difficulty getting these, so I am offering them free with the purchase of drivers, and $15 per set of eight otherwise.


The Gizmo

Designed and sold by Decware, the Gizmo is advertised as an impedance and phase correction module for Lowther drivers. A short history. Steve Deckert purchased a pair of DX55 drivers from me to do some development work on. This is a neodymium magnet-based 5" driver. He used it in a corner horn of his own design, the details of which are shown on his web site.

The final speaker showed some promise and interesting capabilities, but overall was not satisfying. Steve then put together his first Gizmo in an attempt to relieve some of the problems. He felt that they were totally successful, and that the end result was a great speaker. Steve likes to call this "the device that saved Lowthers ass."

My initial belief was this device was specific to the combination DX55 and his horn until I got an e-mail from Alan Hendler. He purchased a pair for his PM2A/Medallion II combination, and thought the end result was extremely impressive. Alan is an ex-recording engineer, and his ears are to be trusted. So a pair was purchased for my study.

Plugging them into the system at first resulted in an obvious improvement in terms of frequency response. It was extended up and down, and what remains of the midrange peak sounded pretty well flattened out. Most enjoyable. The downside was a very slow attack and significant reduction in dynamics.

Steve told me to wait until they broke in before making my final assessment, and to back off on the variable resistor. He was right on both counts. The combination resulted in a system that is quick, but much more realistic in it's sound. I feel that there is still a slight reduction in dynamic contrast and a slight rounding of the leading edges of the music. But overall the improvement greatly outweighs the minor drawbacks and they are staying with my system.

Steve sells these in an expensive box for $200, and without a box and connectors for $100. Best of all they have a money back guarantee, so if you do not like them your money can come back.

This becomes a no-brainer. Try these out, and let me know what you guys think. I will try to post some of the replies to give everyone a little bit more information.

Decware: 309-671-2428


Back compression chamber sizing

In a bass horn loaded system, such as the Medallion, Big Fun Horn, or Hedlund Horn designs, the back of the driver loads a chamber, commonly referred to as the compression chamber.  This chamber has air that is compressed or expanded by the movement of the driver cone.  When this occurs, the change in pressure results in movement of air in or out of the horn throat, that part of the horn that opens up into the compression chamber.  This is how the horn is loaded, or driven.

The size of that back chamber is dependent on the size and strength of the magnet used for the driver, as well as other factors dealing with the horn design.  The Medallion cabinet has it’s compression chamber sized for a PM6A driver, so putting in a smaller magnet, such as any of the DX or EX series drivers, or using a more powerful magnet, such as the PM2A, will require that the compression chamber be reduced in size.  If you fail to do this, the horn will not be properly loaded, resulting in bass response that is incorrect.

As an example, when putting a PM2A into a Medallion, it is recommended that a sheet a full sheet of Deflex Wrap be installed into the back of the compression chamber.  This acts to reduce the size of the compression chamber to the correct size, and in addition absorbs some of the midrange waves coming of the back of the cone, preventing them from bouncing off the rear of the compression chamber and back into the cone.  Unfortunately there is no strict formula that can be used to determine proper size of the compression chamber; it is often dependent upon the room and placement of the cabinets within the room.  So experiment with this until you get the best bass response from your system.  

Do not use a compressible material, such as foam, as that defeats the purpose.  Never place any material near the throat, as it can affect clear airflow to the throat.  The throat must not only be clear, but it cannot have any fuzz, sharp edges, or other disturbances that will keep the air from flowing smoothly.  Think of aerodynamics in this area.

This is an area where it is necessary to be able to reverse any changes you make.  Use of double sided carpeting tape, found in most hardware stores, is a great way to try things out before making a permanent change.

TECHNICAL STUFF

The size of the compression chamber affects the highest frequency at which the horn will work.  Back loaded horns are loaded out of phase with the front of the speaker, and then there is a time delay as the wave goes through the horn path.  If the compression chamber is not properly sized, the signal from the horn arrives out of phase with the signal from the driver front, and they cancel each other out.  This produces a dip in the mid-bass response at around 300 to 350 hertz in the Medallion cabinet.

You should add more material into the compression chamber until the mid-bass response is correct.  If too much material is placed into the compression chamber the mid-bass will suffer, and the upper bass and lower midrange information will start to go through the horn where it does not belong.

Some designs, like the Big Fun Horn, have very large compression chambers.  I have had correspondence with users who tell me that they had to fill a very large amount of the Big Fun Horn compression chamber, all the way to the bottom edge of the driver when using a DX4, to make it sound right. 


Compression Chamber Dampening

The compression chamber will have midrange frequencies injected into it by the back of the cone, unless you are using a EX model driver which has a dampening module on the back to prevent this.  In cases where the back wall of the compression chamber is in the same plane as the front face of the cabinets, it may result in a direct reflection of the sound back into the cone.  This will cause the sound from the driver to have excessive frequency response peaks and valleys, as well as some muddying of the sound.  For this reason the chamber should have some sound dampening material applied, especially to the back wall.  Felt material and Deflex wrap are two of the most popular.

Felt can be applied on all surfaces of the compression chamber that are not within a few inches of the throat.  It can easily be applied with white glue, rubber cement, and other common adhesives.  You can staple it into place if you wish to try it out, but do not leave it in that condition as it may dampen airflow in those areas where it is bowed off of the chamber walls.

If using Deflex, use Deflex wrap with straight ribs, rather than the pad that has round ribs.  Place this in the back of the compression chamber making sure to keep the ribs running in the same direction that air will flow to the throat.  Keep the pad away from the throat as much as possible, no closer than 1” and 1-1/2” is preferred.   Construction adhesive, such as liquid nails, works well to attach it.

For some driver/compression chamber combinations it will be necessary to put a hole in the Deflex panel to accommodate the magnet.  An example of this is the PM2A in the Medallion cabinet.

When you do this, the Deflex also acts to reduce the compression chamber size, so be careful.  Once again, as an example the PM2A in the Medallion cabinet wants a full sheet of Deflex in each chamber to sound it’s best, at least in my room.  Others seem to agree with this formula.  However, in my prior set-up, only ½ sheet of Deflex was used in each chamber.

The felt has little effect on the compression chamber size.  For experimenters I suggest the use of double sided tape, commonly found in hardware stores as carpet tape, to hold the felt or Deflex panel in place.  Use glue only when you find the one that works best for you.


Whizzer Dampening

Without going into the technical mumbo-jumbo, one of the things that occurs with the old style Lowther cones is that the whizzer resonated at about 2 KHz, creating what many referred to as the Lowther shout.  This has been addressed by the new cone design, but since few of you have the new cone design, lets talk about what can be done.

The easiest thing to do is to turn the drivers so that they face 15 to 20 degrees away from your listening position. 

I personally tried and liked the effect of Marc Wauters 98 cent fix.  This consists of placing a lightweight piece of foam between the outer edge of the whizzer and the middle of the main cone.  As a result, it drastically reduced the resonance peak of the whizzer.  Sadly, Marc has recently removed his site.

Another approach is to take 2 cotton balls for each driver.  Pull them out, and then twist lightly so that you get a 2 or 3 inch long cylinder.  Then place this between the whizzer and main cone.  It is not as effective as the Marc Wauters fix, but does create a noticeable drop in the upper midrange peak.

You can purchase the new style phase plug without upgrading the cone.  It does make the highs very directional, so that you must listen with the speakers aimed directly in line with your ears.


Humidity

For a couple of reasons, the Lowther cones sound better with moderate to high humidity.  They are hydroscopic, meaning that the paper cones do absorb water.  This will make the cones slightly more flexible, and a little heavier. You may wish to add a humidifier to your listening room.

Extremely high humidity may result in rotting of the cones, so that extremes should be prevented.


Swamping Resistors

At the resonance frequency of 37 Hertz, Lowther driver have a large peak in impedance.  This occurs in the same range that many output transformers see a peak in their reactance.  The combined effect causes poor power transfer to the speakers because the impedance is too high.  Often a high quality 50 ohm resistor in parallel with the drive may lower the speaker impedance in the resonance range sufficiently to allow better power transfer.  I suggest you use a Mills non-inductive wire wound resistor.

Just put the resistor across the two speaker terminals.  If bass response gets better, leave it in.


Phase Plugs

There are a variety of different phase plugs that can be fitted into your Lowther.  The old standard plug, referred to as the bullet plug, was designed to prevent certain high frequencies from canceling each other. 

An extended version of the bullet plug is used by Oris for their horns.  These are extended to the approximate location of the front of the horn, once again to avoid phase cancellation.  They are available from Welborne Labs.

The new standard plug, called the Phase Equalizer plug, but commonly called the holey doorknob or showerhead plug, is designed to load the whizzer cone in addition to preventing cancellation of certain tones.  It has the effect of flattening frequency response, but does make the highs very directional.  So you must point the speakers at your ears when you listen when using these plugs.

A variety of “lightbulb” phase plugs are available.  These are usually used to horn load the whizzer for those designs that horn load the front of the driver.  Different lengths and diameters are used for different front horns.  Lowther sells 1 size for their cabinet designs, and Beauhorn has 2 different sizes for sale also.

Several people prefer the sound with no phase plug.  It increases the “air” from various instruments played through the drivers.  In theory it produces a “ragged” high frequency response, with dips and lifts in the upper octaves.  My ears heard the extra air, but not any frequency response aberrations.  Someday, I will actually get around to measuring what is actually going on. 


C37 on the Cones

This is just a bad idea.  The cones are already coated.  Putting C37 on the cones stiffens them, which has roughly the same effect as the cones as making them new.  In other words, if you liked the sound of your drivers before they broke in, this is for you.  It makes the midrange and highs more prominent, and decreases bass output.  Just say no.


Subwoofers

These are difficult to integrate with Lowthers due to the speed and low distortion presented by the bass horn.  I have heard the Sunfire subwoofer integrate pretty well with PM2A’s in Medallions.  Others have reported good results with Hsu subwoofers.  Crossover from the Lowthers to the subwoofers at the lowest possible frequency.   I would be interested in what others have found in this regard.

My personal favorite after listening to several systems is the Alon Thunderbolt subwoofer.  Fast, musical, and powerful.  Not cheap, but mates very well with our speakers.


Other Stuff

Please write to me with your favorite tweaks and information.  I will try to include those items which several people have tried and have reported the same results, or those which I have personally tried and confirmed.