Upskirt PMC speaker porn!

[Tenson]

Alright so I was listening to some music today (Track 3 of Nitin Sawhney's Prophesy album) and at 3:10 there was a note that made a pretty loud vibrating noise. I had heard this the past few days just here and there and I kept moving things in the room about trying to stop whatever was making the noise. On this track it must have hit the resonant frequency exactly. It was the 'acoustic lens' (tweeter grill to most people!). My speakers are PMC AML1's. When I held it the vibrating pretty much disappeared. I tried some blobs of blue-tack but it didn't help.

Damn… now I could either glue the tweeter cover to the front baffle (it attaches behind it) or make the effort to take the speaker apart! I went for the second and after a lot of messing about trying to get a screwdriver that fitted… I got it open.

I have actually taken the tweeter cover off completely as it seems to revile more detail and also smoothes out the frequency response! I can't notice much difference in the dispersion pattern either, which is what the 'acoustic lens' was supposed to improve.

Anyway, some pictures! I am amazed at the drivers in these things, the tweeters magnets are as big as some woofers and the woofers are so heavy I can't hold it in one hand for more than a few seconds.

Before I did anything!

I took the baffle off with a lot of effort… I think they look pretty cool like this!

Took the tweeter out, what big magnets you have!

Took the 'acoustic lens' off. Finally I can clean the fluff off the tweeter!

I tried omni-directional speakers for a little while but I didn't like them very much…

Now I know how they make such small speaker go down to 27Hz The woofer seems to be made of a interesting material that looks like very thick corrugated card.. hmmm..

The frequency response before removing the 'acoustic lens'

Notice improvements in the circled areas….

Anyway there we go! I am sorry for the poor image quality but I have a crap camera.

I also got to see how the transmission line is folded so I might make a DIY pair some time

 

[Tenson]

Oh, comments?!

 

[mosfet]

I'd think removing the acoustic lens from the tweeters has removed some comb-filtering effects caused by the lens hence the smoother HF response.

Perhaps you're familiar with the 'tissue paper' tweak often applied to Yamaha NS10 monitors Tenson? The same applies here where a couple of sheets of tissue paper are used to purposefully introduce comb-filtering to attenuate the HF output on the Yamaha's. I remember seeing an article somewhere on the web with measurements for various types and brands of tissue paper!

 

[Tenson]

Perhaps, I have had to turn down the treble a tad since removing them. I am hearing a lot more detail though

I thought the tissue paper was just used to absorb some of the output, not introduce comb filtering?

Funny really because when Thorsten saw the AML1's the first thing he did was suggest removing the acoustic lens!

ooh.. back to stargate!

 

[mosfet]

I thought the tissue paper was just used to absorb some of the output, not introduce comb filtering?

I suppose some absorption would take place but not a great deal (given the one quarter wavelength at 20kHz is a little less than 5mm). Here's the article I referred to above the conclusion of which reads:

As a result, it would appear that the tissue creates the one thing that studio designers around the world try to avoid, fearing it most in their control rooms: Comb Filtering. The paper filters are not absorbing the high frequencies, but simply reflecting them back into the tweeter, thereby causing cancellation through comb filtering.

http://www.bobhodas.com/tissue.html

I'd be inclined to agree with Thorsten (gritted teeth!)

 

[Lefty]

Just googled that speaker - costs about £3000 What's the rest of your kit?

Lefty

 

[Tenson]

Thanks Mosfet, that should make for some interesting reading.

Lefty, they were more like £3,800 when I got them (with stands) but they seem to have come down a bit. I think you will find the £3,000 only gets you the speakers, the custom stands are another £200.

The rest og my kit is...

Cambridge Audio DiscMagic transport
Behringer DEQ2496 for digital room correction and built in DAC
Ming Da (same as Edenlake and Icon Audio) MC-7R pre-amp
AML1 speakers
and a ton of room conditioning.

Next upgrade is either a subwoofer or a DAC (hence my interest in the Benchmark). Kevin and I are planning to meet up and try his Audio Aero DAC in my system at some point but I don't know when it will happen! Despite the cheapish front end it sounds damn good

 

[3DSonics]

Hi,

Oh, comments?!

Over the years I have had many speakers that had some sort "device" in front of the tweeter. They invariably sounded WAY better after removal and if neccesary re-adjusting the tweeter level. Any such device I have come across always added a certain "whispy", "hissy" quality to sibilants, among other things.

I would be interested in hearing what the current MEG's would sound like with the protective mesh and the little acoustic device removed.... I guess I'd have to buy them first.

Oh, while we are at it, I also found that the best domes are inverted. Maybe one day I'll semi-clone the MEG's using Focal inverted dome tweeters, Seas paper cone midrange, a suitable 15" woofer and a Behringer DCX2496 as crossover, with a nice 6-channel Amp.

Ciao T

 

[Tenson]

You could just buy a pair

For what they do I think they seem like a high-end audio bargain.

 

[3DSonics]

Hi,

You could just buy a pair

Where'se the fun in that. I want to experiment (again) with current feed on the midrange & tweeter (possibly even woofer, considering the more or less open enclosure).

I might even have the ideal midrange driver for that, a yet "top secret" project of a friend that I have peripheral involvement with, a Fullrange 5" Driver with aluminum cone, neodymium magnet, aerodynamic basket and a rather even response from whever the enclosure's LF cutoff ends up being to around 15KHz....

Might be fun to just add supertweeter at very high frequencies and add an active time aligned subwoofer, "Gainclone" derived transconductance amplifiers and such fun... ;-)

For what they do I think they seem like a high-end audio bargain.

Yes, if I hear that they are only twice the cost of these AML1's....

Ciao T

 

[Tenson]

Ahh but you haven't heard the AML1's in a proper environment yet, they come very close to the 901K's and at only half the price! It just depends which way you look at it... and if you have a large or small room hehe!

 

[Stereo Mic]

I thought the acoustic lens was employed to modify the directionality of the tweeter as it crosses over so low down on the AML-1?

If that's the case, surely taking it away creates the worst example of the problem Thorsten refers to when he chastizes domestic two ways, namely widely different dispertion patterns at the crossover frequency.

NB. Tenson, according to your measurements, you have also lost a substantial amount of bass by taking the speaker apart. Why would that be?

 

[dcathro]

Hi,



Over the years I have had many speakers that had some sort "device" in front of the tweeter. They invariably sounded WAY better after removal and if neccesary re-adjusting the tweeter level. Any such device I have come across always added a certain "whispy", "hissy" quality to sibilants, among other things.

I would be interested in hearing what the current MEG's would sound like with the protective mesh and the little acoustic device removed.... I guess I'd have to buy them first.

Oh, while we are at it, I also found that the best domes are inverted. Maybe one day I'll semi-clone the MEG's using Focal inverted dome tweeters, Seas paper cone midrange, a suitable 15" woofer and a Behringer DCX2496 as crossover, with a nice 6-channel Amp.

Ciao T

Apparently, the new B&W diamond tweeter sounds much worse with its protective grill on. However, if you touch the diaphram, it shatters and turns to dust!

Dave

 

[Tenson]

I thought the acoustic lens was employed to modify the directionality of the tweeter as it crosses over so low down on the AML-1?

If that's the case, surely taking it away creates the worst example of the problem Thorsten refers to when he chastizes domestic two ways, namely widely different dispertion patterns at the crossover frequency.

NB. Tenson, according to your measurements, you have also lost a substantial amount of bass by taking the speaker apart. Why would that be?

I can't tell much difference in the dispersion pattern when moving about. I can put them back with a little effort anyway so it doesn't really matter.

I think the loss of bass is because I re-tuned it on the DEQ. After changing quite a bit of my acoustic treatment recently I had to re-tune it and I think it was too bassy before. I'm not sure why it looks more 'jagged' though

 

[3DSonics]

Hi,

I thought the acoustic lens was employed to modify the directionality of the tweeter as it crosses over so low down on the AML-1?

I doubt it has much functionality in that particular application, it may slightly broaden the very high frequency dispersion (just look at the dimensions and the wavelength involved). Also, the low crossover point in the AML1 keeps the dispersion pretty even, if too wide IMHO for far field use.

If that's the case, surely taking it away creates the worst example of the problem Thorsten refers to when he chastizes domestic two ways, namely widely different dispertion patterns at the crossover frequency.

The AML1 is really a nearfield monitor (and Simon uses it as one IIRC) and in the region of the crossover frequency has a pretty even (wide) directivity. I suspect the narrowing dispersion pattern higher up is not as much of an issue in nearfield applications anyway.

Ciao T

 

[Tenson]

Simon,
I'll call you, I'm currently spending a lot of time in Northern France house hunting so times at a premium at the moment


K

No problem my time is stretched pretty tight at the moment as well. There is no rush!

 

[Tenson]

Where did the post I just replied to go?!