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Chris A

A K-402-Based Full-Range Multiple-Entry Horn

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How do I know if I need to use any stuffing, and or pyramid foam (for reflections) with my cabinet? My external dimensions are 25" wide (front), 17" deep with it being 13" wide in the rear, and 47" high. I am using 2 Emminence 15" Kappa C woofers with the EV DH1A compression driver (which is huge). The cabinet is 3/4" thick except for the front baffle which is 1 1/2" thick.

 

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My walls are also 3/4 inches thick so they will get excited by the woofers.

 

From what I have read DYNAMAT is very effective but really expensive and tuned for use with sheet metal so it seems that multiple layers wold be required for plywood.

 

I had read someone saying that the recycled tire rubber floor matting you see in gyms would make a good damper.  I have some of it here so I will try this first.  It is about 3/8 inch in thickness and is very heavy as if I want to add more weight to the cabinet.

 

Since my baffles are like sails in the wind I am attaching thick wool felt.  Again to placate me wondering if I shouldn't have done it if I don't.

 

For stuffing I am going to use the long fiber wool that has been used in all of my speakers for thirty years when I thought the transmission line was the answer.  There is no question (in my mind, at least) it is the best compromise stuffing.  I will not STUFF the cabinet.  I agree with Chris A that the back volume is not critical along with what is done with the volume; assuming that because of the small entry ports the reflected sounds we attempt to guard against with conventional speakers simply do not find their way into the output to any significant degree.  Speaking conceptually since I have no real idea.  

 

With a combination of some kind of heavy damper followed by THICK soft felt would probably be ideal taking care of wall damping and absorption without the use of stuffing but that much wool felt will cost lots of money so I am going to hope the wool, by itself, is plenty.

 

Luckily there are many ways to skin the cat and still have the skinned cat you always wanted.

 

RYTHMIK boxes assembled and attaching glue blocks for the 402 cabinets with the hope of having them assembled middle of next week. 

 

 

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My walls are also 3/4 inches thick so they will get excited by the woofers.   From what I have read DYNAMAT is very effective but really expensive and tuned for use with sheet metal so it seems that multiple layers wold be required for plywood.  

I had read someone saying that the recycled tire rubber floor matting you see in gyms would make a good damper.  I have some of it here so I will try this first.  It is about 3/8 inch in thickness and is very heavy as if I want to add more weight to the cabinet.

 

Since my baffles are like sails in the wind I am attaching thick wool felt.  Again to placate me wondering if I shouldn't have done it if I don't.

 

For stuffing I am going to use the long fiber wool that has been used in all of my speakers for thirty years when I thought the transmission line was the answer.  There is no question (in my mind, at least) it is the best compromise stuffing.  I will not STUFF the cabinet.  I agree with Chris A that the back volume is not critical along with what is done with the volume; assuming that because of the small entry ports the reflected sounds we attempt to guard against with conventional speakers simply do not find their way into the output to any significant degree.  Speaking conceptually since I have no real idea.  

 

With a combination of some kind of heavy damper followed by THICK soft felt would probably be ideal taking care of wall damping and absorption without the use of stuffing but that much wool felt will cost lots of money so I am going to hope the wool, by itself, is plenty.

 

Luckily there are many ways to skin the cat and still have the skinned cat you always wanted.

 

RYTHMIK boxes assembled and attaching glue blocks for the 402 cabinets with the hope of having them assembled middle of next week. 

 

 

 

 

 

The stuff I got was from Amazon, and it cost me about $120 to do 2 layers of each type for the full cabinet..  https://www.amazon.com/dp/B00URUIKAK/ref=cm_sw_r_cp_apa_i_cwfhFbT5NXHX9

 

https://www.amazon.com/dp/B07TKXMPH7/ref=cm_sw_r_cp_apa_i_qxfhFb33DCFAB

 

I hear you on the weight... I think mine are around 200+ lbs each.

 

 

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I figured yours would be of similar weight.  Having a removable back makes the box much easier to deal with.  

 

That material is similar to what I applied to the horn.  It made a dig difference there and I only used a little bit since it was an experiment. 

 

So you really hear less resonance with this on the walls of your box?  Sure would make things easy in comparison to any other method I can think of.

 

Have one box assembled and get to see how everything fits inside today.  I had to make my boxes wider for the woofers to fit.  I think I will have to do some manipulation to get the assembly though the hole in the box.  I think the magnets are going to be closer to the walls than I had thought.  This will make it easier to use them as a brace but tricky to get in the box.

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I figured yours would be of similar weight.  Having a removable back makes the box much easier to deal with.    

That material is similar to what I applied to the horn.  It made a dig difference there and I only used a little bit since it was an experiment. 

 

So you really hear less resonance with this on the walls of your box?  Sure would make things easy in comparison to any other method I can think of.

 

Have one box assembled and get to see how everything fits inside today.  I had to make my boxes wider for the woofers to fit.  I think I will have to do some manipulation to get the assembly though the hole in the box.  I think the magnets are going to be closer to the walls than I had thought.  This will make it easier to use them as a brace but tricky to get in the box.

 

The carpenter missunderstood me, and that is why I ended up with a one piece cabinet. I think the way he did it was easier for applying the veneer though. I have not used any measuring equipment yet. I hope to have my new amp done soon so I can get Chris to tune ot for me. I think the bass I have with a cabinet is more than I have with the left and right without a cabinet. I will most likely have him do it the same way for the others,but I will have the rear panel access a little wider so I can get the woofers inside easier.  

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This looks to be a superb driver for a 2 way system. Stating the obvious but i couldn't help it.

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On 8/13/2020 at 1:04 PM, rickmcinnis said:

Well, listened to one of them yesterday.

 

Did not want to open both boxes if I did not like what I heard with the one.

 

First impressions are very good.  If anything these are less resonant than the Truextent/2441s - less stridency on massed strings not as if the JBL were strident in any way, nowhere close, of course.  But after hearing the titanium diaphragm in the KLIPSCH supplied driver I was concerned.

 

CELESTION has tamed titanium.  With less EQ than was required before I get response to 22K - within a dB or so - I do not really want them flat up there.  I could have a rise if I wanted it.  Less EQ is required in general though the hump in the 1000 hz region is more pronounced but easier to quell. Nice shape.  One would think these drivers and the K-402 are very compatible.  One wonders if this is the driver Mr. Delgado will choose for his update of the JUBILEE?  He could not go wrong.

 

They really do go down to 300,  in fact real close to 200 - one could EQ them flat from 200 to 22k - but one worries if that would put stress on the driver and is not needed.  I like the idea of having a smooth slope instead of a cliff which is what the cutoff would be at 200 hz.

................

...............

...................

And to find a buyer for the JBLs ...

 If you are interested selling the Truextent diaphragms please shoot me a PM at your leisure (with their history,  model number and a price)

BTW, (and I do not mean to pollute the original thread), you might very well be crossing this driver too low. Also, did you have the diaphragms professionally installed or use a tone sweep when they were installed (many of those drivers of that era are not self centering and may need to be evenly torqued and shimmed - in spite of what some others may claim).

-Tom

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2 hours ago, rickmcinnis said:

I have a surprising second order distortion peak (based on REW and I am not sure how much to trust those distortion measurements) in the mid 400 hz range.  I wonder if I have too little capacitance and the distortion is due to the level being boosted there?

 

I do have a dip in the region which is being corrected.

I've found that the degree of overlap of the crossover frequencies in MEHs is much, much different than traditional multi-horn loudspeakers.  I would recommend playing with that overlap and greatly increase it (there are no drawbacks like there are with multi-horn loudspeakers like lobing, etc.).  Just EQ the resulting on-axis flat again.  I do recommend that you also do some off-axis polar measurements for grins.  I recommend taking a measurement at 10 degree intervals (horizontal, then vertical).

 

Here is a distortion plot (in percent of the fundamental) of my center K-402-MEH with dual diaphragm BMS 4592ND as an example, on axis, nominally at 80 dB at 1m:

 

1448478832_K-402-MEHHarmonicDistortion().thumb.PNG.1aaa85f964f3697af50e7969c8c92b9f.PNG

 

The top harmonic is actually THD, not second harmonic. The second harmonic is the red trace.  All the harmonics are below the noise floor of the room in this plot.

 

Chris

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Chris, in your experience, what is a good crossover frequency for the MEH design? (2inch compression driver mated with a pair of 12 or 15 inch woofers). I get wary of running the compression driver too low. 

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Well, the answer may surprise you...

 

I run the natural response of the woofers and then compression driver, after flattening the SPL response of both sections individually.  Then I look at the natural crossing point of the two.  In the case of the BMS 4592ND, I believe that was 550-600 Hz. 

 

I use first-order crossover filters (effectively) to take out the 90 degree lead of the woofers to the compression driver.  Voila! Time alignment.  When I did this (and stopped trying to tell the compression driver and the woofers where to cross using the crossover and PEQs), all the performance measurements got better and it sounded better.  I simply trim off the response of drivers that is not needed using attenuating PEQs in order to keep the crossover interference band SPL response flat. 

 

Chris

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2 hours ago, rickmcinnis said:

I am not yet in MEH NIRVANA so my experience is purely with two separate horns.  With both the CELESTION and the JBL by themselves there would be a distortion peak somewhere in that range - even with the mic one meter from the horn.  Not a BIG peak but enough to stand out.  I thought it could be my amplifiers or something inherent to the horn.  I am using the First Watt SIT1 to drive the compression drivers and these have an output impedance of 4 ohms.  I wondered if that was the cause.  These amplifiers are capacitance coupled, one stage amplifiers so i have used the output capacitance as part of the high pass filter.  BUT I have found trying to use that as THE high pass filter does not work as well as instinct would suggest.  It is much better to use much more capacitance than the filter would call for.  There is much less distortion.  I know there is a best value but I have yet to find it.  At the moment I am using about 140 uF.  (edit: AND PEQs) When I would use 30 uF there was a surprising amount of distortion.  So much for my instincts.

I have never lost a compression driver due to overload, much less one that was damaged via a SS amplifier (especially one with 10 w output like your SIT-1).  I recommend removing the excess reactance and bi-amping using a DSP crossover.  The entire reason for using direct coupled drivers to amplifiers is to remove all the electrical reactance that can be removed.  If you are using passive crossovers or "safety blocking" capacitors in line, I recommend instead using DSP crossover and direct coupling--unless you're using a low-reliability tube type amplifier that tends to fail with voltage on the outputs.

 

2 hours ago, rickmcinnis said:

Now that I have discovered these things will go much lower than the JBLs i am wondering if I should not re-think my port locations? 

Did you include a picture or drawing of your ports?  The ports that I have detailed in the prototype K-402-MEH are more than sufficient to do the job without any added gnashing of teeth or wringing of hands 😉  I recommend using those first and foremost.

 

Chris

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