VMPS 626R Evaluation and upgrade

 

 

This evaluation and upgrade recommendation will be divided up into several categories.

First is a visual report.

Secondly will be measured parameters.

Thirdly will be a subjective analysis of how they sounded with references.

Lastly will be a report on an upgrade that will include physical changes, new measured parameters, and subjective assessment. It will also include pricing information.

The Visual report:

There were Red flags that popped up right away that just led to more and more Red flags.

The cabinet quality does not look good, and I'll leave it at that. The best thing VMPS has done to date is get MLS to build their enclosures for them. I am sure the quality of the enclosures have recently shot up several notches. Judging from the looks of this box it is clearly one of the older units.

Right away I noticed that these were not very heavy for a speaker this size, 33lbs each. By contrast our much smaller Diluceo speaker weighs 34lbs each.

A closer examination of the cabinet showed that the front baffle was an inch thick but the side walls were all only 5/8" think.

And for such a large box there was no bracing. Needless to say the enclosure was extremely resonant. A slight knuckle wrap to the side created quite a buzz. Can you say Buzzzzzz, Buzzzzzz, Buzzzzzz? This speaker can.

Adding some bracing or Blackhole 5 material to the inside of these speakers will go a long way towards immediate improvements.

The only speaker I have ever seen that was worse than this in all my years in audio was some speakers sold from the backs of White vans.

We have tested some of those too: See Dahlton's and Digital Audio.

These speakers were supposed to be coated with some type of sound coat material, but the inside was only coated with what looks like a creamy light Yellow paint. It didn't help.

 

Fit of the drivers was the next thing that stands out visually.

They didn't fit.

There was a large gap around the woofer and around the tweeter.

Painting the open area Black helped hide it some but this is not what I would expect from an expensive speaker.

The fit and finish on the White van speakers were better.

Then there was an odd looking Green tag on the from of the planar mid with a couple of bolts sticking out from it.

None of the driver mounting screws matched either.

Some were sheet rock screws and some were shiny steel pan head screws.

The giant white sticker on the back that was generic to all models was a bit unsightly as well.

The grills were made nicely and looked good, but smashed down over the foam strips that were placed on the tweeter when they were put on.

On to the enternals:

First scary thing was that the woofer was connected with spade connectors that were soldered on to the wire, but the wire was stripped back too far leaving un-tinned bare copper wire exposed that had already Oxidized.

If the connection is going to be soldered it should be soldered straight to the terminal without inserting a slip connect into the path.

Sealing it with heat shrink to prevent oxidation would have been nice too.

Scary thing number two was no dampening material. An empty box? Not really. I later discovered a small layer of it stuck against the top of the box.

The light creamy Yellow paint can also be seen in these shots.

Nice little .12mH inductor from Chokes Unlimited to the upper right looks like 16 gauge. Nothing fancy but nothing wrong with that. Inexpensive (about $2.00) but effective.

Variable L-pads look like they are from Solen.

The one on the left is a LP15W8 and is $2.03 each ordered in singles.

The one on the right is a LP100W8 and is $4.67 each ordered in singles.

Prices drop on 100 quantity packs.

I guess they are okay for car audio, but I would never use them in a speaker, especially not a high end speaker. Their effect on the signal is detrimental in more ways than one. Bad, bad, bad...

A closer look at the network reveals more of the same.

The Mid and woofer share a series network (very crafty).

Looks like an ERSE 16 gauge laminated I core and a 51uF Axon poly cap.

I retail the Axon caps for $10. 94 each.

They were by-passed with some small GE caps which certainly can't hurt. The speakers were different though in that one had a third by-pass cap that looked like a little polyester cap or something.

Did the caps in the pair of speakers have caps matched down to the third decimal place?

No they did not, but they were matched.

One was a 55.19uF and one was a 55.22uF Great QC there!

To bad one inductor was a 4.2mH and one was a 3.7mH. Not too close there and the response curves show it too.

The cost of those are in the $11. range depending on what value it is supposed to be and that is a retail price as well, not an OEM cost.

I can understand using a cheaper laminated I core inductor in this application for several reasons.

One, the woofer does not play very high to begin with (which masks some of the smearing effects that these coils can have). Still I would rather use an air core if at all possible.

Secondly it has a lower DCR than the air core which helps keep the woofer output level up. It needs it. The woofer only has 88db sensitivity.

Also in line with the Mid was the low pass first order .12mH inductor seen above.

What was really ugly was seeing the tweeter circuit. A second order configuration using a 1uf and a couple of by-pass caps along with an iron core inductor. An iron core inductor on the tweeter circuit? Ahhhhhhhh. Sure it only cost a dollar but speed an extra dollar or two and use an air core inductor here. It is a small value after all. Can you say smear? This speaker can.

Getting into some measurements:

First the woofer by itself.

Re - 7.0 ohms, Fs - 33Hz, Qms - 5.09, Qes - .30, Qts - .28, Sd - 126.67 sq cm, Dia - 12.7cm, Ms - 16.54 grams, Vas 31.49 liters, Cms - 1.41 mm/N, Le - 1.88mH, BL - 8.94, Z - 8 ohms, SPL - 88.3db,

Optimal ported enclosure is .279 cubic feet and it will be -3db down at 59.3Hz. Too bad it is not in an optimal ported enclosure.

It is in a much larger enclosure that is 1.146 cubic feet. That was deducting for the woofer and the Mid enclosure. Below is the predicted response in a box this size with the measured port size.

As seen the oversized box causes the woofers response to roll off early loosing 4 to 5db of output in the bottom end. This could explain some of the thinness that was noticed in the listening tests and lack of bottom end plus loosness in the bass region.

Measured impedance responses verify the predicted port tuning of 29Hz that Bass Box software calculated.

Altering the port from its 5.8125" length to a 2.6" length will re-tune the box to 39Hz and bring up the bottom end quite a bit. What a simple tweak, if you can get the old ports beat out. See below:

This will bring the bottom end up but it will still be pretty loose because the box size is still way too big. -3db will be 36Hz.

On to actual output measurements:

It was really difficult to get this response curve to look this good and get the two speakers finally adjusted with the L-pad adjusters on the back.

I took a lot of measurements of these up and down the vertical plane until a finally found a spot right on the tweeter axis that yielded minimum cancellations of the drivers.

For comparisons I have uploaded several measurements of pairs of Diluceo's that were sent out to our customers. See Diluceo response curves.