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Sealed vs. Bass Reflex MEHs


Chris A

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This thread was created based on the discussion of the relative merits of bass reflex vs. sealed bass bin construction for multiple-entry horns (MEHs).  The genesis of this thread can be found here:

 

https://community.klipsch.com/index.php?/topic/161404-a-k-402-based-full-range-multiple-entry-horn/page/57/&tab=comments#comment-2634408

 

which is also repeated here for convenience:

 

Quote

Hi Chris...

 

...Thought I'd add a few thoughts re bass-reflex since I've used them at home (and for live sound).

For home, I've built sealed, bass-reflex, and push-pull slot load (PPSL) subs, all using the same 18" driver(s) for comparisons.

I chose the BMS 18n862 based off of Josh Ricci (data-bass) getting very good results using it, in both sealed and vented DIYs.

 

The sealed was certainly the easiest to build and get great results.  A no brainer really. 

Adding EQ to the bottom was a bit trickier than first appeared. I ended up using a Linkwitz transform ala the miniDSP route.

The tricky part was xmax  increased fast, given the gain it took to flatten response to as low as I wanted, 30Hz.

But as long as I keep the sealed at reasonable SPL, it is simply super. 

 

Then I built the bass-reflex.  Hornresp led me there, but it definitely still took some trial and error with  port area and length, to get to 30Hz and keep port velocity within bounds.

Must get right, takes work, but once accomplished, it rocks. Requires so much less amp power than the sealed, and sounds just as good to my ears.

 

Interestingly, I found the phase traces / group delay of the bass-reflex, and the sealed after the necessary EQ to get to the same f-3 response, were very similar.

Something we don't normally hear about.

 

Oh, i've never encountered anyone using a passive high-pass for a bass reflex to prevent it from overloading below tuning.  Come to think of it, I haven't heard of anyone using anything but active for bass-reflex....but I'm less in tune with home audio than live sound on this. Your post about folks using BR because they continue to use passives took me by big surprise.

 

I'll abbreviate any comments about the PPSL subs other than to say the motivation behind them was purely for cabinet vibration reduction, and the hope of needing less extensive internal  bracing.  Happy to say it worked awesomely!  Opposed subs is the only way I'll fly anymore. 

I've noticed the prelims on Danley Hyperion indicate dual opposed subs, covering 14-45Hz. 

It also appears he's probably going bass-reflex from the pict...as it looks like there's a hole in the bottom of the cabinet, hence the funky bottom plates and feet.

 

...and the ensuing discussion.

 

Chris

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Here is another comment from the other thread that I think can kick things off:

 

39 minutes ago, gnarly said:

If you want lower end extension with less amp power required, bass-reflex is the way to go.

 

Now we're discussing amplifier power required, when not too many pages before this in the K-402-MEH thread (and other related threads), it was noted that amplifier power isn't a factor in today's economic environment.  Why the shift towards this topic, but flipping the stance/position in this case?  It doesn't seem rational or relevant to MEHs.  It only seems argumentative.

 

Chris

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Hmm

16 hours ago, NBPK402 said:

What about using a pair of 15" passive radiators on a MEH?

Wouldn't that be kind of the same as bass-reflex? Maybe you could tune lower with heavier passive radiators, but you still have all the "bad" things from the bass-reflex!

 

I have contemplated making a big MEH with four 8" woofers (one each corner) covering maybe 100-300 Hz, supported by 4 times 15" woofers (one each corner) as kind of a build in sub with 1/4 wavelenght integration. In that way I could reduce the size of the off-axis ports near the compressiondriver, hoping that the extra bigger holes further out the horn for the 15's won't disturb the sound waves in the midrange so much, and gain more membrane-area in the sub! That would make a really big true point-source!

 

We'll see, if I ever build it. But I would prefer that approach to a design with passive woofers.

 

Steffen

Edited by Supersteff
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2 hours ago, NBPK402 said:

What about using a pair of 15" passive radiators on a MEH?

This is actually an issue that I'm afraid we might run into Roy on, because his (now expired) patent on a bass reflex--horn loaded bass bin is not in principle different from a bass reflex-ported MEH or even a tapped horn (a patent that is still in force that's owned by DSL).  These are all different ways of looking at the same thing: a phase inverter on the back chamber of a horn-loaded set of woofers.  Roy seems to think that good things happen when you use a phase inverter in a bass horn (which he thus far has not discussed openly--in terms of which parameters get "better" and which get "worse" when you do that).  I have an idea of what happens, but no data on his particular new bass bin.  Here is the data for an SH-50, showing the effects of the bass reflex ports below 80 Hz:

 

TAD TD-4002 Jubilee vs. Danley SH-50 phase response.jpg

 

TAD TD-4002 Jubilee vs. Danley SH-50 group delay response.jpg

 

And the KPT-1802-HLS in a home environment (the purple/indigo trace that parallels the tapped horn sub trace):

 

Low Bass Phase Response of Several Bass Bins.jpg

 

You can see the sealed design K-402-MEH bass bin phase response in nominally half space in the bluish/cyan trace, above, which is much flatter (and therefore better in my estimation) than the internally ported 1802-HLS, the tapped horn, and the Cornwall (a conventional direct-radiating bass reflex woofer).  Steeper slopes are worse, flatter are typically better.  The current Jubilee bass bin shows the effects of an exponential horn expansion below 1/4 wave resonance (i.e., 40 Hz). 

 

So I'm a little hamstrung in answering this question.  Roy's initial invention had the "preferred embodiment" using passive radiators, which he shifted to using cardboard tube ports after the initial KPT1802-HLSs (and apparently the few 1502-HLSs that were built and sold) for home hi-fi duty.   The difference between cinema duty and home hi-fi duty appears to be that home hi-fi (home theaters) typically use the 10-30 Hz pass band as the operating frequency band of the subwoofer, while the commercial cinema use says "26-240 Hz" for the -3 dB passband.  He's now saying that the "new Jubilee" bass bin (internally ported with a single 12" woofer) is "better" than the current KPT-KHJ-LF bass bin with dual 12" woofers and no ports.  But he apparently declines to say why--in quantitative terms.  What engineering parameters improve, and which degrade?  My preference today, if asked, is still to not use an internal reflex (back chamber phase inverting) port. 

 

I use tapped horn subs, but the reason is form factor and their relative efficiency and lower compression distortion than direct radiators (especially ported direct radiating subs).  If I didn't use tapped horns, and I had the space for them, I'd probably use either a multiplicity of K-402-MEHs in boundary gain (i.e., five surround channels) as a first choice, or alternatively, a conventional front-loaded horn having a very long internal path length for efficiency and avoidance of compression distortion (i.e., more than one of these).  Since I don't have floor space for a conventional front-loaded horn, the MEH solution would be my preferred option.

 

Chris

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What this is basically saying is that the "back chamber phase inverter"--i.e., bass reflex or tapped horn--continuously moves its effective acoustic center away from the listener as the frequency decreases (or lobing increases the effective distance between the direct radiating woofer and/or port and the listener) below a certain break-point frequency where the phase inverter, i.e., port resonance, kicks in.  This seems to be the common denominator of these designs, and unfortunately, this isn't a desirable characteristic--in my experience...and the source that Toole cited in his book (referenced here in the K-402-MEH thread).

 

Chris

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Returning to the issues of bass extension and cone excursion from the other thread, I prepared a few graphics. I took the same BMS 18n862 driver in the same 171 liter vented box, resulting in a "QB3" (quasi-Butterworth 3rd-order) alignment. This alignment is very close to a 4th-order Butterworth alignment, with slightly better transient response at the expense of some loss of low-frequency extension.

 

Suppose that we want to equalize that 31.5 Hz response to be flat to 30 Hz. That's not much EQ, but I wanted to put everything on equal footing. The figures marked "Butterworth4" show this situation. The black trace in the left half is the natural response of the system, the blue trace is the desired 30 Hz response, and the red trace is the EQ required to get it there. The trace in the right half is the impulse (transient) response of this system.

 

But, as we discussed, a vented box really needs a highpass filter to prevent overexcursion below the cutoff frequency. Most people just introduce some arbitrary highpass filter and hope for the best. Instead, I will mathematically change the 4th-order Butterworth response into a 5th-order Butterworth response. This accomplishes two things: it adds a 1st-order highpass filter to prevent overexcursion, and it maintains the desired 30 Hz cutoff frequency. This situation is shown in the figures marked "Butterworth5". Note that the EQ is cutting rather than boosting at very low frequencies. Note also that the transient response has degraded.

 

Now let's put that same 18n862 driver into a 96 liter closed box. This results in an optimal Qtc of 0.7071. And then let's EQ it for 2nd-order Butterworth response with cutoff frequency of 30 Hz, exactly as in the vented cases above. The figures marked "Butterworth2" show the necessary EQ to accomplish this, and the resulting transient response. The EQ adds about 9 dB of constant boost at low frequencies (undesirable), but the transient response is outstanding.

 

Finally, let's do the same thing to the 2nd-order closed box response that we did to the 4th-order vented box response -- add a highpass filter. The figures marked "Butterworth3" show that about 7 dB peak boost near 30 Hz does the job, while the EQ again cuts rather than boosts at low frequencies, to avoid overexcursion. And the transient response, while not as good as in Butterworth2, is still better than the original Butterworth4 of the vented box without the highpass filter, and far better than the Butterworth5 with the highpass filter.

 

Still concerned about overexcursion? Use two 18n862 drivers in a box that is only slightly larger than the vented box, and you cut excursion in half while picking-up 6 dB sensitivity, so that 7 dB peak boost is not so painful any more. The downside is the cost of two drivers.

 

B4.png

B5.png

B2.png

B3.png

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That's a great depiction of the discussion we were having. And the results mirror the simulations, as well as electrical filter transfer function measurements I've made.

The sealed BW3's impulse is a bit better than the vented BW5. Not a lot, but definitely better.

Here's a test i forgot i made a year ago, that also supports sealed being ultimately best.

Green is sealed with a Linkwitz transform in place, I forget exactly what hpf filter was used. Low pass was linear phase.

Blue is vented with a BW3 hpf. Not sure why i didn't lowpass it like the sealed, guess cause all i cared about was looking at the low end.

Oh, forget that Smaart says 'Phase' on top graph, it's Group Delay.  Smaart toggles back and forth, phase and GD, but panel title doesn't change.

482737652_sealedwithLTvsvented18n862.thumb.JPG.380ade864ef1efd066f600cd82b31d91.JPG

 

Clearly there's more GD with the vented, but a good part has to be the different hfp orders.  I'm sure it would look closer if I'd used a BW1 hp.

 

Those subs btw, are about 175L vented, and 110L sealed.  Have them running right now playing around with getting a B&C dcx/me464 setup working.

562402411_stackingdilemna.thumb.jpg.83b83bff2dedd370be8230ab5e954157.jpg

 

 

Honestly though, my ears aren't golden enough to hear the differences in the sims or measurements, between those two subs.

Heck, which one is sitting on the floor makes more difference, i think.

I do know the vented will play considerably louder before pushing my amp into clipping. 

I put each box on a channel of a QSC PL-380 amp, 1500W per channel @ 8 ohms. (Drivers are 8 ohm)

 

 

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On 5/14/2021 at 10:17 AM, Chris A said:

Here is another comment from the other thread that I think can kick things off:

 

 

Now we're discussing amplifier power required, when not too many pages before this in the K-402-MEH thread (and other related threads), it was noted that amplifier power isn't a factor in today's economic environment.  Why the shift towards this topic, but flipping the stance/position in this case?  It doesn't seem rational or relevant to MEHs.  It only seems argumentative.

 

Chris

 

That's simply not true...that amplifier power isn't a factor today.  In fact, a little math will show most home audio lacks sufficient amp peak power to fully reproduce subwoofer transients.

And please don't hold me (or anyone else) accountable for not having read all the K-402-MEH posts or other related threads.  Besides, whos to say those posts have to be agreed with 🙃

 

I don't see there was a topic shift.  The discussion was sealed vs vented subs, and how they compare.  Relative power requirements are often discussed in such comparisons.

And within the context liberty of having compared two drivers to one, it sure doesn't seem like a big topic switch to me.

 

Honestly, you seem to be the argumentative one.... i hope you can see your comment sure has riled me up !

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2 hours ago, gnarly said:

That's simply not true...that amplifier power isn't a factor today.  In fact, a little math will show most home audio lacks sufficient amp peak power to fully reproduce subwoofer transients.

This is fair, but note that full front-loaded horn subwoofers typically are typically more efficient than direct radiating subwoofers, and are much less affected by compression distortion (including voice coil heating) than direct radiators.  I often have a trouble keeping separate those that prefer more amplifier/required driving power from those that seem to approach from the other direction to the argument, especially when we are not talking about "subwoofers" (which I wasn't talking about--at least those subwoofers not on the same aperture of the MEH, not using a separate box for the subwoofer). 

 

Those that prefer more power are typically not nearly as verbose as those that argue for very low power amplifiers everywhere with horn-loaded loudspeakers/subwoofers (like tubes...especially SETs).  For woofers reproducing bass (i.e., above subwoofer frequencies, perhaps defined as above 30-40 Hz), power isn't an issue unless using something like very low power tube amplifiers (and that particularly includes SETs, which typically don't use global feedback because of their lack of forward loop gain).  So I'm really talking about full-range MEHs that include bass reflex ports on their apertures (i.e., again, we're back to the definition of "full range MEHs" vis-à-vis just "MEHs" which you apparent assume to mean a separate bass bin.  That's really not the subject of this thread.  I set this one up to talk about bass reflex ports on the MEH horn aperture.

 

2 hours ago, gnarly said:

The discussion was sealed vs vented subs, and how they compare. 

This is actually not true, either the last thread (K-402-MEH) or in this one.  I was actually referring to woofers on MEHs, and why I don't support the idea of bass reflex ports on the MEH aperture for their woofers, for the reasons I stated.

 

______________________________________________________________

 

If you want to argue bass reflex vs. sealed (not including MEHs), then that's probably another thread that can be opened up to the larger K-forum community that doesn't deal with MEHs--because that topic will probably eventually degrade into a moderator-locked thread (...if I read my tea leaves correctly...).  I restricted the applicability of bass reflex here to MEHs (on the same aperture) to keep that from occurring.  It's very similar situation to arguing "objectivity vs. subjectivity in audio" in my experience, and some people apparently just want to argue instead of just understanding one another and agreeing to disagree.  I prefer not to be the OP on that thread, by the way.  Someone else can open up that thread, if you don't mind.

______________________________________________________________
 

2 hours ago, gnarly said:

 

562402411_stackingdilemna.thumb.jpg.83b83bff2dedd370be8230ab5e954157.jpg

Just so you know, the above pictures of separate HF horn from bass bins/subwoofers really isn't the subject of this thread (for clarification). 

_______________________________________________________________________

 

2 hours ago, gnarly said:

And please don't hold me (or anyone else) accountable for not having read all the K-402-MEH posts...

 

I actually consider it to be discourteous to say what you did here (quoted just above), but I guess it's the norm on other audio forums to say this. It says that you don't care what anyone else (or everyone else) is saying, and I don't believe that's really the case in this instance. 

 

Nowadays, I really do try to keep the threads that I create (i.e., as "OP") to be shorter such that these kind of statements really can't be justified.  That's why I tend to move certain subjects off of some threads (as the "OP") when it appears it's going to devolve into a long discussion that is really departing from the central theme of the thread.

 

Chris

  

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4 minutes ago, Chris A said:

I was actually referring to woofers on MEHs, and why I don't support the idea of bass reflex ports on the MEH aperture for their woofers, for the reasons I stated.

 

FWIW, I try to keep my posts generic with regard to implementation (i.e., the frequency response, transient response, enclosure volume, and cone excursion comparisons should hold generally true whether in a direct radiator or in a MEH, with the understanding that MEH-loaded bass will likely reduce excursion). My main concern is with the transient response. @Chris A, as you have indicated several times, your main concern is deleterious effects of phase growth in the bass. They are interrelated.

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6 minutes ago, Edgar said:

with the understanding that MEH-loaded bass will likely reduce excursion). My main concern is with the transient response. @Chris A, as you have indicated several times, your main concern is deleterious effects of phase growth in the bass. They are interrelated.

I agree and actually see them as more than just "interrelated", but actually different aspects of the same phenomenon, so I'm also just as concerned (actually more concerned) with transient response.  That's where the phase growth is actually heard--during transients (per Griesinger's article on the subject where the phase shift results in a time domain distortion of the peaks of transient response, [see slide 17 for the punch line] which is what the ear is actually listening for).

 

Chris

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3 minutes ago, Chris A said:

I agree and actually see them as more than just "interrelated", but actually different aspects of the same phenomenon, so I'm also just as concerned (actually more concerned) with transient response. 

 

I agree that they represent the same phenomenon, but you and I may cordially disagree on how to mitigate its effects. I generally strive for minimum phase, while I get the impression that you prefer something closer to linear phase. The main difference is in the pre-ring. 

 

Either one, however is preferable to phase that wanders all over the place, even if magnitude response is flat.

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28 minutes ago, Edgar said:

I generally strive for minimum phase, while I get the impression that you prefer something closer to linear phase.

I'm generally aimed at just eliminating the non-minimum-phase portions of the loudspeaker response (i.e., all pass), but note that bass reflex might be considered by others as "minimum phase".  I don't accept that...kind of phase growth.

 

Chris

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10 minutes ago, Chris A said:

note that bass reflex might be considered by others as "minimum phase".  I don't accept that.

 

That's a really good point. I need to find a better definition.

 

EDIT: How about "minimum phase plus smallest RMS Duration possible"? At the very least, I like your stated goal of removing excess phase.

Edited by Edgar
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23 hours ago, Chris A said:

  He's now saying that the "new Jubilee" bass bin (internally ported with a single 12" woofer) is "better" than the current KPT-KHJ-LF bass bin with dual 12" woofers and no ports.  But he apparently declines to say why--in quantitative terms.  What engineering parameters improve, and which degrade?  My preference today, if asked, is still to not use an internal reflex (back chamber phase inverting) port. 

Chris

I generally avoid the subs discussions,

but this one bleeds over to Klipsch's Flagship for the Home, the Jub.

I salute K for not putting out a $100K speaker, but the eye needs to stay on audible performance and declining marginal returns.

 

The question is:

What were, are, the Design Goals for both systems

and how did they perform to Specs.

 

Is the change to a single driver to meet a cost target at the expense of performance,  and or adaptability  to different environments ?

 

What are the performance metrics, and how tight are the tolerances.

 

What is - are the test track for woofers ?

 

Kick drum measured on the line in to the amp vs the measured 1W 1M with a microphone. aka a square wave like  test ?

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1 hour ago, Bubo said:

What were, are, the Design Goals for both systems [i.e., full-range MEHs vs. the "new Jubilee", I believe you're talking about here...] and how did they perform to Specs.

As I might have indicated earlier, really nothing has been released on the "new Jubilee" ("new Jub"), but it was revealed that Roy's now expired patent is one of the contributing technologies to the new Jub bass bins (complete with "airflow animations" of the bass bin with a single 12" woofer and bass reflex ports embedded within the horn itself).  So anything we talk about here is mostly conjecture, and I've learned over time that Roy likes to do "drive by's" on those sort of comments and speculation.  I really don't blame him for picking at the speculation before the product specifications have been released. 

 

However, in the past, Klipsch doesn't release a lot of detailed information on most of its loudspeaker models--much like their competitors.  Fortunately, Roy has, over the years, shared some aspects of the current Jubilee performance (the two-way version using the KPT-KHJ-LF bass bin--apparently now discontinued according to Roy himself).  So I really can't comment on the "new Jub", and if pressed, I would have a difficult time recreating the exact requirements that Roy, et al. used during the creation of the K-402 horn. The KPT-KHJ-LF bass bin  has a JAES article on that effort that outlines the requirements quite clearly.  Unfortunately, that's the part of the Jubilee that Roy has chosen to change in terms of its design details.  I assume that the design requirements have also changed (but I expect he'll let us all know if that's true or not).

 

I suppose everyone can say that they have their "druthers" in terms of loudspeaker design. 

 

My preferences include the ability to minimize phase and group delay growth, thus improving the impulse (a.k.a., transient) performance to as low levels as is possible--along with all the other things that the Jubilee does well.  I've also found that putting the woofers on the same aperture as the HF driver on the K-402 Horn in the MEH design that I've documented (K-402-MEH thread) actually improves performance in some areas, and trading away some areas of performance that I personally value less (but as it turns out--this isn't very much--the trade is a very good one--in my estimation). 

 

I try to highlight the requirements that I design to, and their rationale.  Oftentimes, this information is largely omitted from other DIY efforts, and particularly manufacturer's information about their loudspeaker designs.  Roy has done a good job in communicating his design requirements (in general) for the current Jubilee over time--perhaps not all requirements, but many of the major ones.

 

So, over time, I also try to reveal my requirements for the K-402-MEH and all other related MEHs that I design.  In general, here are the requirements categories that I designed to (with discussion of some requirements thresholds in some areas):

 

 

I think it's worthwhile to point out that there are actually many requirements, and each has its own threshold value related to the exact loudspeaker design that's chosen.  So it's difficult to relate all requirements without handing you a full specification (which I could do if I spent many months developing--which I'm not really interested in doing currently). 

 

However, if someone did start to document full specifications (like the military requires for its developing major products) virtually everyone would benefit. 

 

Chris

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5 hours ago, Chris A said:

As I might have indicated earlier, really nothing has been released on the "new Jubilee" ("new Jub"), but it was revealed that Roy's now expired patent is one of the contributing technologies to the new Jub bass bins (complete with "airflow animations" of the bass bin with a single 12" woofer and bass reflex ports embedded within the horn itself).  So anything we talk about here is mostly conjecture, and I've learned over time that Roy likes to do "drive by's" on those sort of comments and speculation.  I really don't blame him for picking at the speculation before the product specifications have been released. 

 

However, in the past, Klipsch doesn't release a lot of detailed information on most of its loudspeaker models--much like their competitors.  Fortunately, Roy has, over the years, shared some aspects of the current Jubilee performance (the two-way version using the KPT-KHJ-LF bass bin--apparently now discontinued according to Roy himself).  So I really can't comment on the "new Jub", and if pressed, I would have a difficult time recreating the exact requirements that Roy, et al. used during the creation of the K-402 horn. The KPT-KHJ-LF bass bin  has a JAES article on that effort that outlines the requirements quite clearly.  Unfortunately, that's the part of the Jubilee that Roy has chosen to change in terms of its design details.  I assume that the design requirements have also changed (but I expect he'll let us all know if that's true or not).

 

I suppose everyone can say that they have their "druthers" in terms of loudspeaker design. 

 

My preferences include the ability to minimize phase and group delay growth, thus improving the impulse (a.k.a., transient) performance to as low levels as is possible--along with all the other things that the Jubilee does well.  I've also found that putting the woofers on the same aperture as the HF driver on the K-402 Horn in the MEH design that I've documented (K-402-MEH thread) actually improves performance in some areas, and trading away some areas of performance that I personally value less (but as it turns out--this isn't very much--the trade is a very good one--in my estimation). 

 

I try to highlight the requirements that I design to, and their rationale.  Oftentimes, this information is largely omitted from other DIY efforts, and particularly manufacturer's information about their loudspeaker designs.  Roy has done a good job in communicating his design requirements (in general) for the current Jubilee over time--perhaps not all requirements, but many of the major ones.

 

So, over time, I also try to reveal my requirements for the K-402-MEH and all other related MEHs that I design.  In general, here are the requirements categories that I designed to (with discussion of some requirements thresholds in some areas):

 

 

I think it's worthwhile to point out that there are actually many requirements, and each has its own threshold value related to the exact loudspeaker design that's chosen.  So it's difficult to relate all requirements without handing you a full specification (which I could do if I spent many months developing--which I'm not really interested in doing currently). 

 

However, if someone did start to document full specifications (like the military requires for its developing major products) virtually everyone would benefit. 

 

Chris

Hi Chris 

 

Please check your PM

 

Cheers 

Deano 

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