mwmkravchenko

Yep. And you have some great SPL numbers there. A true horn for two of those drivers would be enormous. It would have to be built into a theater rider like I've designed for a few clients. But get you even greater output. Impressive bit of work. I appreciate your level of detail in the files.

Interesting.

Master Ricci, has anyone pointed out that this is a bandpass box. Not a horn? I like the output capabilities. But this is not a horn. You have two drivers in two separate chambers couples on both sides of the drivers to vents. Nice classic bandpass enclosure. Awesome bit of design work at any rate.

Those curves look vaguely familiar...

Great results for all your hard work Brian.

2 hours ago, SME said:

FWIW, I've heard a system calibrated to the Synthesis curve, and while the bass certainly benefited by the suppression of ugly room resonances, pretty much everything above 200 Hz sounded better without the room EQ.  The corrected version was much too rolled off in the upper mid and high frequencies, which suppressed a substantial amount of detail.  I'm also quite convinced that their curve would give inferior results compared to what I use on my system.  My speakers have rather different directivity vs. frequency than theirs, and they are placed against the front wall, so this should be expected.

Agreed.

I'm very much not a fan of one curve fits all and auto generated room EQ.  All you have to do is move about the room a little bit and your wonderful EQ is out the window..

We are basically agreeing on the room timing measurements.  My unstated reasoning is that an accurate measurement cannot be made without a stimulus that actually excites all the room modes.  In most cases this precludes the MLS types of signals.  You need chirps and or discrete gated sine wave stimulus to really excite what can happen below around 200 hertz.

DFT gating is also very important to be chosen correctly as you have pointed out. And the correct type of math Math on the DFT.  Choose wisely or suffer the consequences

I'm guessing that this Audyssey EQ is a sliding dynamic loudness contour.  That does have application when you are listening  at levels below 70 to 75db averaged.

Simple comment on room measurements.  They are very dependent on the stimulus made to take the measurement and the type of math applied to perform the measurement.  The errors multiply rather rapidly depending on the choices made.

I know of no professional who works in acoustics that looks at averaged measurements and gives them any worth.  Raw measurements are where the real information lies.

Lastly.  I may have not posted the links to all the Sean Olive Papers and may be remembering What I was reading in the JAES papers freely available and also on the JAES website.  But I know for a fact that the reference speakers were in a standardized listening room and that the panel of trained listeners preferred the sound characteristics associated with a standardized semi-reverberant room.  Not an anechoic reproduction also called diffuse field EQ that was the norm for a few years back. 

6 hours ago, lowerFE said:

There is a WORLD of difference between accurate reproduction on a headphone vs on a loudspeaker. There is zero crosstalk on headphones, which dramatically changes how imaging is perceived. There is no concept of direct vs reflected sound on headphones since it is all direct sound. There is no concept of directivity on headphones either. The amount of bass is dependent on the seal and fit of the headphone. Correlations between headphones do not necessarily apply to speakers. 

The writers of those articles would have a very healthy argument that you are incorrect.

And so would I I often use a high quality pair of headphones as a reference when working on loudspeakers.  The entire basis of the articles I cited are the relationships between the sound of an accurate pair of speakers and an accurate pair of headphones.  Don't allow what you have in a headphone sway your decision.  There are some headphones that have been designed with this type of carefully crafted contour.  The data for this type of EQ matching loudspeakers is widely available in  many reports and there is even standards that are in the works to define an accurate headphone response.

They all use a well setup loudspeaker as a reference. 

http://seanolive.blogspot.ca/2014/01/the-perception-and-measurement-of.html

http://read.uberflip.com/i/324330-lis-2014/22

http://seanolive.blogspot.ca/2008/12/loudspeaker-preferences-of-trained.html

A lot larger pool of people than I have ever had the chance to work with agree that listener preferences are universally agreed upon regardless of age.

Good sound is simply put, the right sound.  Right in the sense that it accurately reproduces the sound of a live acoustic event.  Caveat being that when you set up a loudspeaker system in this way many recordings are exposed for a series of poor choices.  And poorer outcome in reproduced sound.

One last note.  There should be no difference between accurate reproduction on a loudspeaker and accurate reproduction on a headphone.  That is the anchor of this series of research articles.  After all you are using the same set of ears for both types of listening aren't you?

Quote

What is the exception? I've found that this is not true for people with substantial hearing loss, i.e. a lot of old people. This is the group that heavily favours a very rolled off treble sound. For some reason I don't yet know, these people seem to think treble is the devil. I would think with hearing loss, you would want MORE treble to compensate for their reduced high frequency hearing. However, it seems like people with hearing loss genuinely hate treble because for some reason it greatly irritates them. I brought these to the Burning Amp, where most of the attendees are well over 50. I ran a long 20 second frequency response sweep, which meant there were 10 seconds or so where the sweep is in the treble region. I noticed several people covering their ears during the sweep, and some looked like they're in pain. I got much less positive reception there, which is understandable because most of the speakers that were presented had, in my opinion, essentially no treble. And of course, these "treble-less" speakers got huge positive receptions, which is not surprising at all if hearing high frequency causes these people to contort their facial expressions.

 

Some how I don't quite agree with that summation.

True some people like little or no treble.

But that is not really attributable to age.  I have clients and colleagues that are long in the tooth but really appreciate an extended top end response.

I do agree that your idea of a generally accepted loudspeaker response is best described as subjectively flat.  Most systems that I have listened to that were dead flat were very bright on the top end.  My personal work aims for a combined listening position that is down a few db beyond 10 khertz.  Down about 1.5 to 2 db in the last octave.

Welcome to my world has been ringing in my head after reading your post Brian.  You are ironing out many of the problems, and discovering new ones.  It is what engineering actually consists of.

Happy to hear you have attained your goals. Now the real fun begins.  Listening to music!

Nice work!

Ground plane. Get friendly with some pieces of plywood and duct tape. Place them on the pavement and tape the joints. Two sheets will allow you a 2 meter measurement distance all around your box.

I have done a fair bit of design work for directional control of tweeters.  I also have done horn design since 1994.  So I nit pick when I hear waveguide and horn.  There is so little difference that I have come up with this as a qualifying factor for one versus the other.  If there is an efficiency gain in the output of the driver in the new mounting then it is a horn.  If there is no gain in efficiency then it is a waveguide.

The trick in that definition is that there is always some change in the efficiency of the driver when mounted in a constraining coupling area from smaller to larger.  So waveguide is basically a marketing name that tried to distance the concept from terrible sounding horns.

And for sure you will get me to agree that there are a lot of terrible sounding horns.  There are also some really great sounding horns.

If I remember correctly Genelec has one of the few smaller format monitors that claims to have a very controlled dispersion pattern.  I have seen the enclosure but not worked through it's design in any detail.  But it uses a combination of time delay that is naturally occurring through the cabinet design and the driver mounting coupled with some DSP correction.

DSP is not magic.  If your speakers sounds crappy to begin with you will only make it marginal with the most brute force correctional you can buy.  That I have witnessed from one of the top DSP designers in the world.  It is impressive to hear many of the warts fade.  But they are still there.  DSP cannot correct for poor driver design.  And if there are serious resonance distortions in the drivers cone surround or spider.  Those types of flawes in design will dominate the sound no matter what you do.

You can only get constant directivity using a few methods.  And the directivity control is frequency dependent.  So each few octaves of response need another of controlling the directivity.  Correctly designed horns is the only broad band method that really works.  But that is a difficult task.  A good horn only covers a few octaves of frequency response before it looses it's effective directivity.  And as you go lower in frequency the horns must get larger.  Can be done.  And I have done design work for it.  But it is not a small system.  Think 4 horns where the largest is almost 5 feet square to control directivity down to about 64 hertz.

A simple suggestion.  Finish what you are working on.  It will be great.

Thank you for the suggestion. I did consider it, but I can't fit this woofer. The speaker would need to be 1" bigger length and width wise and 2" deeper and that increased the speaker size by over 50%, which was too much. Would need 1000W to make use of all that excursion in such a small speaker as well, which is obviously impractical. 

 

But I am curious, could you go in a little detail why you think this is an extremely well designed woofer?

A kilowatt is no big deal in terms of power availability.  Enclosure size is cast in stone it looks like.  You are indeed doing a nice job on your enclosure.  

The driver has all the quality of the Scandinavian drivers.  With a cost that is about $18 over landed cost.  The only improvements I could make is a smaller stronger motor and a larger coil.  Add to that a custom surround and spider and you have tapped out the possible improvements.That is in fact what I have done on my 7 inch.  A little more X-max and a little more refinement on the cone surround interface.  But I'll tell you that blindfolded in front of two of them I doubt that I could tell them apart.  Under controlled conditions with a set of each in a two way speaker configuration my guess would be I probably could tell them apart.  Basically because I paid a little more attention to the cone.  And I have a larger cone.  An attempt at getting the most from the least.  I know that Stereo Integrity makes a very high quality shallow 6.5.  And it has comparable build quality.

I started out making speakers using the best of the Scandinavian stuff.

  http://www.kravchenko-audio.com/blog

Old pictures taken with a box camera. ( remember those?)

Have you considered this driver:

http://www.diysoundgroup.com/anarchy-woofer.html

I design and produce drivers for a living.  And I have used this driver.  It is extremely well engineered and is of equal or better build quality to what you have chosen. 

I have no relationship with this driver or the link to the website.  It simply is a very well made driver.  And it sounds great. 

Kyle makes a good point. We often simulate airspeeds under a worst case scenario with a full power sine wave at the airspeed maximum, but that's very rare. most of the time we aren't running the speaker wide open for all it's got and the content is almost always much more transient, wide bandwidth and complex. In a way it's sort of similar to the reason that I now prefer very low qts drivers for their higher efficiency. With complex, wide bandwidth material the power requirements are lower and it leaves more effective headroom in the amplifier on those types of signals. Also less thermal demands on the voice coils.

Probably the best selling point on a high efficiency driver is the correlation between where they are efficient and where the bulk of what is considered "bass" is centered. 60 hertz is where the money is. And many pro drivers will get you higher spl for a given size versus a conventional subwoofer with much less power input. Last point. Amp power never makes up for the nearly 10 dB of greater efficiency. Do the math and ask a very simple power compression question. You will find the answer!

Some of the best work done in this field is by people wanting to simulate musical instruments.  And this video is of a mitered organ pipe.  Or a rectangular organ pipe that has a 90 degree bend.  Sometimes they even have a 180 degree bend.  I have a boat load of thesis papers and other studies that get to the number crunching but it's nice to see something rather than read about it.

 

One could write a phd thesis on modeling flow of a fluid -- this simply comes down to FEA, and any other modeling is just an approximation. But lets face it, this is not rocket science, its just a speaker

 

I will say there was only one subwoofer I have seen that did not have port issues and it was a twin 18" box with a single 18" port - no curves. Very low velocity, extremely capable. When you see ports with high air velocity then that's normally an indication of being undersized. There are reasons to do this (extension, size etc) but it does mean the port it exhibiting its limits.

 

Hello Kyle.  I have heard about you from Josh but never had the pleasure of talking with you.  I guess this is a close second.

I think quite a few people have written their PHD on that subject!

Just a speaker  

Don't get me started on that one.  The truth of the matter is at very few times are we going to tax the port compression on a properly designed subwoofer.  And the times when that does happen we usually have program material that masks the effect in the first place.

And the difference between no problems from a port at any time is the difference between a realistic enclosure size and a not so realistic enclosure size.

Twin 18 with an 18 inch diameter port.  Wow.  A genuine phallic idol to the vent gods if there ever was one!

Hey Mark,

 

 Welcome.

 

I'd agree with your last sentence but the caveat is that it is basically impossible with any type of serviceable design using modern high power drivers. By the time the vents are made that large, the overall size is completely out of control, or the pipe resonances are bad, or you are faced with a large system with little useable output compared with the size of the device, or a combination of all of the above.

Thanks Josh.

I found this forum by accident.  And most of the posts I have read are by very thoughtful people.  I'll hang around from time to time and see what's interesting.

You are very right in that statement.  And I have no answer other than design to the goals that you are seeking.  A clean sounding bass from say a properly damped sealed enclosure with a low distortion woofer, or a well designed front loaded horn set the standards as to what is clean sounding.  The job of a proper design is to get you there or as close as you can.  Designing a port has always been a set of compromises.  And there are ways to get a decent sound out of a vented enclosure that have not been discussed such as the power port type of vented enclosure.  It has pretty much the lowest turbulence for a given diameter of enclosure.

Calculating this kind of thing is a job for a FEA program.  

One thing I noticed in the comments above by SME.  You are applying fluid flow calculations to air flow calculations.  There are some similarities between the two mediums.  Where the differences begin is that a fluid is pretty much non-compressible.  Whereas a gas is.  And that is where we run into problems when we want to do some useful calculations in the junctions of the interior of a container with a port and the the end of the port.  Much has to be taken into account in order to make any useful calculations.  And that makes the calculations a real pain in the but.

From lurking around on some of the threads I see that some of you guys are pretty handy with Hornresp.  A few years back I asked David McBean to include particle velocity measurements in Hornresp to use in some very high SPL type of cabinets.  It is not a full around every corner, nook and so on calculation.  But it does get you somewhere in a hurry.

The keeping it below 10 meters/second rule of thumb goes a long way into making a serviceable port.