What's with the sharp edges on speaker boxes these days?

[tvrgeek]

Harbeth has focused on cabin damping, as well as (vibration-wise) decouple front and rear baffle from the four remaining side panels. Both strategies are following results from published BBC studies .

George

Do you have a reference to those studies? I think I understand a rational for the baffle, but not the rear.

 

[forr]

An externally hosted image should be here but it was not working when we last tested it.

Sometimes ago, I built a loudspeaker with this front baffle for the medium and the tweeter with the idea to minimise the secondary emissions at the edges, the aim being to get the most stable position of instruments as possible. I was influenced by photos of Kef Maidstone and Sonus Faber Stradivari.

Overall width was about 50 cm. Drivers were a 170 mm ScanSpeak Discovery and a 27 mm aluminum (shown here), crossover at about 1700 Hz, which was soon replaced by a 25 Vifa (crossover at 2300 Hz).

I was rather satisfied.

I then bought second hand 17 cm ScanSpeak Revelators and ScanSpeak D2905-970000 tweeters. I mounted them in a conventionnal rectangular box, 33 cm wide, top edge at 20 cm of the tweeter apex.

I very much prefered these last speakers and did not find that the general stereo image had suffered at all from what it was with my previous "low diffraction" baffles.

I am now on the way of thinking that provided that the baffle width is sufficiently large, let's say more than 32 cm, diffraction with a rectangular box may not be an issue for good stereo rendition.

 

[Melo theory]

Well, lett me tell you Yoke, those look amazing! Especially for a first build.

Edit: I am not psychic, Yoke's original post was before mine 😉
It was deleted and posted after this!
🙂

 

[yoke]

well,please be gentle with me...😉
Those are my first loudspeakers I ever build...or Lets say try to build...

I have read some articles about building loudspeakers but I'am more like practical then theoretic type so I first like to build and then figure what's wrong...

Ok I know that's not the right way...but...

So here is the measurements taken from my loudspeakers and you can see that I have diffraction problem
And now I need advice what to do...the plan is to cut cabinet as on picture...
Would that help ? Or should I just apply some felt on buffe ?

The thing is that my PC is dead and I can't play with measurment right now...I useing mobile phone to open forum 😉

Whell maybe my problem would help some else 😉

 

[gpapag]

Do you have a reference to those studies? I think I understand a rational for the baffle, but not the rear.

It will take me some time to find them as I am away from my pc.
But meanwhile, feel free to run through the jungle (start from the last pages, it is more fun)

BBC Research and Development Reports : Free Texts : Download & Streaming : Internet Archive



George

 

[Remlab]

Years ago, I owned Dunlavy SC-1's. They(The entire line) had an interesting way of dealing with edge diffraction by wrapping perforated sheet metal around a perimeter of 1/2" thick acoustic felt and then covering it with grill cloth(The perforated metal was not in front of the drivers). With the grilles in place, it looked like a typical beveled mdf based grille frame, but it only used perforated metal and wool felt(Come to think of it, it also had small rounded plastic corners). It was a very "clean" way of using felt and by far the best way of eliminating diffractive effects. You can just make out the underside in this photo..
Dunlavy SC 1 speakers

 

[studiotech]

Grimm Audio

Maybe either of you guys could check them out while in SF?

A couple guys from the studio are there. They are going to try to hear them tomorrow with our edited demo disc, but it's just a booth on the show floor, so....

Greg

 

[puppet]

Yoke ... tell us what your xo settings are on the behringer. Doesn't look like you've done any prior EQ or time alignment.

I'd be looking at eq for each band to get the individual responses looking good ,within reason anyway ... more appropriate slopes for the drivers and time alignment to improve transitions.

Hard to tell what's going on right now. The response is a mess.

 

[yoke]

@puppet....

A s I mention,my PC is dead,and it will take some time to put it together. So right now I can't play with slopes or anything, can't acces dcx... I have those images on net,but don't really know at what setting I take them... So don't know if there's point talking about it.

All measurements a taken in room...and as you can se I have naked walls...and floor... So there is lot of reflections that mess with response...

Here is another one...i take couple images,some with crossover filters off, and some with cut for mid/high from to 2 to 2.8kHz...bass from 200 to 300Hz...2.5 sistem...based od edgars and tony eveII...but with some changes 😉...

The mic is not calibrated so...those measurements were taken just to give me some idea what is going on.. Will try to calibrate it...and will try to learn how to use arta...

But for now what bugs me is deep at around 3.8kHz which is from baffle as it stay even if I measure off axis...

I didn't play with EQ and time...

 

[yoke]

Could someone point me to some felt which can be placed on baffle ? As it would be easy start po play with 😉

...some picture... 😉

Thanks

 

[tinitus]

try google search on sub carpet, and go to pictures 😱😛

 

[Remlab]

try google search on sub carpet, and go to pictures 😱😛

A high grade wool felt would be much more appropriate.
FilzFelt 10mm Wool Design Felt - Textiles - Modenus Catalog
The "Where to buy" button lists Croatia, but it may be a faux list. The felt company is German though. Close enough to find a distributor..

 

[DrDyna]

See, there you have it......
They look good DrDyna.

Thanks 🙂 It wasn't a really expensive speaker that I built just for fun, but I figured..hey, why not. It only takes about 2 minutes to put on a roundover, lol.

 

[puppet]

Yoke ... the dip @3.8Khz ... did you ever measure that driver on a baffle by itself?
Is that dip the driver or the enclosure?

 

[Pallas]

***Many of you know my devotion to using felt on any baffle. I made many a test combining baffle edge radii/chamfer with felt. In almost all cases, surprising to me, I found that a square edge provided the best result.

You wrote a really great article about use of felt with measurements showing fairly dramatic measured improvements, as well as comparative measurements of different felt configurations (if memory serves) that you previously shared. I thought I had saved it, but alas I can't find it.

Would you mind re-sharing it?

 

[tvrgeek]

In practice, at least MY practice, 1/2 bevel did not help at all. 1/2 round over helped some. 3/4 helped IMMENSELY. A 2 inch bevel did not help at all either. Theory? The round means it is distributing the incidence angle over a broader frequency range. One would need to do a series of pure tone tests to verify this. I just know how well it both sounds and measures to my ears in my rooms.

 

[Remlab]

David Ralph's Speaker Pages - Felt Effects on Baffle Diffraction

http://www.speakerdesign.net/audioXpress/diffraction/diffraction.html

http://www.speakerdesign.net/felt/felt_ring_vs_blocks.html

 

[tvrgeek]

Ah, those two papers from audioXp were ones I was thinking about.

 

[Remlab]

I'd like to know Dr. Geddes opinion on using felt for diffraction control, since he uses a foam plug for HOM control(Somewhat similar approach, even though they are unrelated)

 

[yoke]

try google search on sub carpet, and go to pictures 😱😛

Thanks titinus 😉

A high grade wool felt would be much more appropriate.
FilzFelt 10mm Wool Design Felt - Textiles - Modenus Catalog
The "Where to buy" button lists Croatia, but it may be a faux list. The felt company is German though. Close enough to find a distributor..

Thanks Remlab, will try to contact someone, or order from USA..will give it a try...

Yoke ... the dip @3.8Khz ... did you ever measure that driver on a baffle by itself?
Is that dip the driver or the enclosure?

No I never measure...I know, I did this in a wrong way...I should first measure then build...but then I would not build anything 😀 ... Now I have build, I like the results...think it have potentials 😀

The drivers are 2904/7000 , 18W8545, 21W8555...
The 2904/7000 have some dip in that area, but it's like -1db and I have like -5db...As I don't have experience, I don't know how bad it is...I see some graphs from other loudspeakers and most of them have those dips...

Well I have to put my PC back together as without it's hard to make any progress 😉

This is dinemsions of front buffle, for 2904/7000 and 18W8545...