All this being said I do find there's perhaps a very slight veiling in the midrange. Maybe some crossover adjustment is needed, or maybe it's nothing to do with the speakers at all. I will keep tinkering anyway.
Regarding the foam trick. This was something mentioned by Dr. Geddes in his thread "Geddes on Waveguides". He uses the idea on his commercial range of speakers which, by the few accounts available, sound superb. He claims the foam absorbs HOMs (High Order Modes I think) so you get more of the direct/in-phase sound and less of the sound that has been deflected around the waveguide's throat causing harshness and unnaturalness in the compression driver's sound. He uses a chunk of foam and EQs the top end back out.
It just so happens a big chunk of foam EQs my tweeters back down to being quite flat so no EQ is needed. So the foam on these 8" waveguides loaded with APT-50s is a double-whammy upgrade. I sometimes feel the treble doesn't sound "direct" as a result but I can't argue with the overall musicality. There's a nice lack of spittiness or any peakiness. Sibilants picked up by microphones are there but not exaggerated by the tweeters, and they would be if the tweeters were left standard!
Regarding the foam trick. This was something mentioned by Dr. Geddes in his thread "Geddes on Waveguides". He uses the idea on his commercial range of speakers which, by the few accounts available, sound superb. He claims the foam absorbs HOMs (High Order Modes I think) so you get more of the direct/in-phase sound and less of the sound that has been deflected around the waveguide's throat causing harshness and unnaturalness in the compression driver's sound. He uses a chunk of foam and EQs the top end back out.
It just so happens a big chunk of foam EQs my tweeters back down to being quite flat so no EQ is needed. So the foam on these 8" waveguides loaded with APT-50s is a double-whammy upgrade. I sometimes feel the treble doesn't sound "direct" as a result but I can't argue with the overall musicality. There's a nice lack of spittiness or any peakiness. Sibilants picked up by microphones are there but not exaggerated by the tweeters, and they would be if the tweeters were left standard!
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I'm experimenting with some foam damping of the rear wave behind the mid drivers. Some A/B testing shows it's easier to localise instruments/vocals with foam - they get locked to the speaker, more like with a boxed speaker. There's also an increase in the "body" of the piano, vocal, guitar etc. In particular, piano sounds more real so I think I need to use some foam permanently. I even got my girlfriend to listen blind and she preferred the sound of a piano recording with the foam. She described it as "less harsh and brash". I'd not have described it as harsh myself but, to be fair, it was rather loud!
I used big, quality corner absorbers for this. I could sacrifice one and cut it up to fit neatly... I'm just not sure how to cut foam!
I knew I had to try foam because Mr Loesch specifically recommended it for dipoles in a small room. He also recommended running one woofer boxed but that was just not practical with my woofers in this room.
I used big, quality corner absorbers for this. I could sacrifice one and cut it up to fit neatly... I'm just not sure how to cut foam!
I knew I had to try foam because Mr Loesch specifically recommended it for dipoles in a small room. He also recommended running one woofer boxed but that was just not practical with my woofers in this room.
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If possible, please try pulling the speakers forward somewhat to avoid the desk. The 2 corners of the desk seem too close to and in front of the mids and tweeters, which may cause some refections/diffractions.
Maybe the space wouldn't be practically allowed, but you may try it temporarily to see how it's going. 😉
Maybe the space wouldn't be practically allowed, but you may try it temporarily to see how it's going. 😉
That foam trick works like magic. It cuts off the peak above 10khz and leaves the rest alone... very very nice, and handy.
In listening it does sound smoother, you want to turn it up. But there is a kind of delayed quality... it gives away some coherence. Also found it a little muffled, but only a little. I did reduce the thickness of the foam by half, maybe some more work is required.
In listening it does sound smoother, you want to turn it up. But there is a kind of delayed quality... it gives away some coherence. Also found it a little muffled, but only a little. I did reduce the thickness of the foam by half, maybe some more work is required.
Stanley knife is usually the way to go. If the foam is around 1" thick, you could use scissors for a neater edge.
Edit - if it's really thick, a bread knife works, because of the similarities between bread and foam.
CLS - I hear you, but it's pretty impractical. I need this desk here 🙁 I could try temporarily to see what it does for the sound though. I can't wait to get into a bigger room.
ra7 - I'm glad you tried the foam, are you also using it on the APT-50? I agree with your listening impressions 100%. There is a slight muffled/indirect quality but it's probably overwhelmed by the smoother sound and lack of tizz/resonance I was hearing on some sounds. Obviously the tweeter now wants MUCH less attenuation. If Geddes and his disciples are enjoying their foam inserts then there's hope for perfecting it but I seem to recall there was some debate about possible degradations (along with the clear improvements). Of course I could be using the wrong foam and very badly. Perhaps it would work better if it was more nearly cut to fill the waveguides properly.
Chris - The foam is REALLY thick I would say. Bread knife sounds terrific, nice one!
Cheers,
Simon
ra7 - I'm glad you tried the foam, are you also using it on the APT-50? I agree with your listening impressions 100%. There is a slight muffled/indirect quality but it's probably overwhelmed by the smoother sound and lack of tizz/resonance I was hearing on some sounds. Obviously the tweeter now wants MUCH less attenuation. If Geddes and his disciples are enjoying their foam inserts then there's hope for perfecting it but I seem to recall there was some debate about possible degradations (along with the clear improvements). Of course I could be using the wrong foam and very badly. Perhaps it would work better if it was more nearly cut to fill the waveguides properly.
Chris - The foam is REALLY thick I would say. Bread knife sounds terrific, nice one!
Cheers,
Simon
SimonY, are you using open-cell foam?
Closed-cell doesn't work properly.
Earl Geddes uses about 30 pores per inch.
I'm using it, but I found better results if the foam comes right forward to the baffle.
David
Closed-cell doesn't work properly.
Earl Geddes uses about 30 pores per inch.
I'm using it, but I found better results if the foam comes right forward to the baffle.
David
David,
I'm using something random I found that was probably used for packaging originally. If I can do it neatly enough I could sacrifice some of one of my bass traps. They will be open-cell foam. I'm getting some furniture stuff from a friend too, but we don't know what types those off-cuts will be.
I'm using something random I found that was probably used for packaging originally. If I can do it neatly enough I could sacrifice some of one of my bass traps. They will be open-cell foam. I'm getting some furniture stuff from a friend too, but we don't know what types those off-cuts will be.
I'm using it on a audio nirvana full range driver on OB. Only the whizzer area. There are plenty of nasties beyond 2khz, but this is such a wonderful driver that I'm not about to give up on it just yet. The foam does help, but yes, it has some issues. Perhaps we are using the wrong kind.
David any links of where to get the right kind? Pics?
David any links of where to get the right kind? Pics?
Sorry, don't have any links.
I'll post some pics tomorrow.
The open-cell foam I have seen has been either blue 😱 20mm 15 ppi (pores per inch) which doesn't meet the criteria, black 20mm 20 ppi, and the one I am using, black 25mm 30 ppi.
I got some from a roll at the local foam suppliers.
Some fish tank filters are 20 ppi, but are usually too small to fit a waveguide to the mouth.
I've cut discs and laminated them with a super-glue that specifically glues polypropylene and foam (and fingers!), putting only about three dabs around the circumference of each layer.
One test for open-cell foam is that you can see through it, say, 30mm of 30ppi.
David
I'll post some pics tomorrow.
The open-cell foam I have seen has been either blue 😱 20mm 15 ppi (pores per inch) which doesn't meet the criteria, black 20mm 20 ppi, and the one I am using, black 25mm 30 ppi.
I got some from a roll at the local foam suppliers.
Some fish tank filters are 20 ppi, but are usually too small to fit a waveguide to the mouth.
I've cut discs and laminated them with a super-glue that specifically glues polypropylene and foam (and fingers!), putting only about three dabs around the circumference of each layer.
One test for open-cell foam is that you can see through it, say, 30mm of 30ppi.
David
Interesting... The bass absorber foam I have here is not very see-through! I'd say it's much too dense.
Here are the pics as promised.
1. "see-through" (25mm 30ppi)
2. My application in the Audiosyncrasies:
12" Parts Express Dayton waveguide.
5 or 6? layers of 25mm to bring the foam flush with the baffle, and then a final disc on top for neatness.
EQd flat digitally.
I found that leaving the first 20 or 30mm or so of the throat clear of foam sounded the best.
BTW it cuts beautifully with an electric carving knife (can bevel the edges).
David
1. "see-through" (25mm 30ppi)
2. My application in the Audiosyncrasies:
12" Parts Express Dayton waveguide.
5 or 6? layers of 25mm to bring the foam flush with the baffle, and then a final disc on top for neatness.
EQd flat digitally.
I found that leaving the first 20 or 30mm or so of the throat clear of foam sounded the best.
BTW it cuts beautifully with an electric carving knife (can bevel the edges).
David
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The cleanest way to cut foam is with a hot wire. Usually the wire is mounted vertically, pulled really tight and you move the foam along the wire to cut it. I have seen people use a fret saw, a wire to replace the saw blade (resistance wire, electrically isolated from the saw) and an adjustable toy train power supply for that.
Or you could go to a shop where they sell foam and have it cut to size there.
Or you could go to a shop where they sell foam and have it cut to size there.
Great tips guys! Thank you for the pictures David, those speakers look really unique and interesting. Now to source some foam of the required spec... 🙂
Hi,
I took a measurement of the Beta 8A on the baffle nearfield - 10cm from the dustcap. The full crossover is in place, the other drivers are disconnected. There seems to be a bit of a resonance at about 1500hz.
Simon
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I intend to follow Bud Purvine's advice on treating the Beta 8a and go all the way with EnABL pattern rings, gloss painting and "two way glue".
Bud's advice:
http://www.diyaudio.com/forums/mult...ng-impressions-techniques-26.html#post1821202
And his photos of a treated Eminence Beta 8A: Picasa Web Albums - Bud - Emminance Bet...
Also see his more recent comments:
http://www.diyaudio.com/forums/mult...ng-impressions-techniques-51.html#post2287679
Bud's advice:
http://www.diyaudio.com/forums/mult...ng-impressions-techniques-26.html#post1821202
And his photos of a treated Eminence Beta 8A: Picasa Web Albums - Bud - Emminance Bet...
Also see his more recent comments:
http://www.diyaudio.com/forums/mult...ng-impressions-techniques-51.html#post2287679
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Hi Simon
Is it possible that the unconnected XO parts are causing this strange behaviour ?
Or did you replace the other drivers by equivalent loads ?
Hi Ricardo,
No I don't think that's possible, I think it's an acoustic/physical phenomenon rather than an electrical one. Also I'm not sure it's strange. A big un-braced baffle should probably have significant resonances, unfortunately.
Ra7 - I see you deleted your last post. I was about to say that I thought the frequency response shown at 0ms looked like a good match for the steady-state response graph I also posted, it just looks different because one is on a 100dB range and the other a 25dB range and has the low frequencies cut off (not sure why, something to do with the way the system works?).
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