G, sounds like....
open cell foam to me.
"so maybe best to insert an absorbent strip instead to quell reflections back through the driver and ~transparent to the WLs of interest." but I suppose there are a number of ways to impliment such an "absorbent strip" but open cell foam is probably as easy a solution as I can think of. A layer of open weave wool from an old blanket or knitted scarf might work just as well. a layer of 3M scrubbie material might also work or a length wise row of tooth brush heads (bristle) might just do. I think the idea is to restrict things for higher frequencies and let the lower ones push through. Regards Moray James.
open cell foam to me.
"so maybe best to insert an absorbent strip instead to quell reflections back through the driver and ~transparent to the WLs of interest." but I suppose there are a number of ways to impliment such an "absorbent strip" but open cell foam is probably as easy a solution as I can think of. A layer of open weave wool from an old blanket or knitted scarf might work just as well. a layer of 3M scrubbie material might also work or a length wise row of tooth brush heads (bristle) might just do. I think the idea is to restrict things for higher frequencies and let the lower ones push through. Regards Moray James.
Greets!
Right, open cell foam, and since Earl Geddes chose 300 ppi density after extensive testing to quell higher order modes (HOMs) in his waveguide (WG), it seems as good a starting point as any.
Seems a good plan to me, just like designing in too much gain and dialing it back to suit beats not having it when needed, so goes having too much HF response and damping it rather than an audible dip in our acute hearing BW IMO.
GM
Right, open cell foam, and since Earl Geddes chose 300 ppi density after extensive testing to quell higher order modes (HOMs) in his waveguide (WG), it seems as good a starting point as any.
Seems a good plan to me, just like designing in too much gain and dialing it back to suit beats not having it when needed, so goes having too much HF response and damping it rather than an audible dip in our acute hearing BW IMO.
GM
As always, thanks for the suggestions and advice Greg, it's much appreciated.
Got a couple of ideas are throat adjustments, but until I get time to build a pair of the stepped cabinets I won't be able to dial them in right to avoid the potential problems you describe -all three run up to a similar frequency at present. I'm toying with the idea of using complete twin throats at the moment, rather than splitting at the end of the first path, but I suspect that could cause some additional crosstalk / turbulence issues, as well as probably increased friction? Any thoughts on that one?
Cheers
Scott
Got a couple of ideas are throat adjustments, but until I get time to build a pair of the stepped cabinets I won't be able to dial them in right to avoid the potential problems you describe -all three run up to a similar frequency at present. I'm toying with the idea of using complete twin throats at the moment, rather than splitting at the end of the first path, but I suspect that could cause some additional crosstalk / turbulence issues, as well as probably increased friction? Any thoughts on that one?
Cheers
Scott
Greets!
Well, judging by these WE/JBL/Altec multi-cell designs there's some advantages, but then these were trying to squeeze all the HF they could out of a driver that rolled off fairly low: http://www.google.com/patents?vid=USPAT1992268&id=KOB5AAAAEBAJ&dq=1992268
GM
Well, judging by these WE/JBL/Altec multi-cell designs there's some advantages, but then these were trying to squeeze all the HF they could out of a driver that rolled off fairly low: http://www.google.com/patents?vid=USPAT1992268&id=KOB5AAAAEBAJ&dq=1992268
GM
Hello,
I am looking at building a set of Harveys. Thing is, being a poor student, the fostex drivers are a bit out of reach. What do people think about the Visaton FR10 (8 ohm)? They cost about £7.50 +p+p+VAT each.
They are cheap enough that I may buy 4 and play with some mods (damar, de-whizzer, phase plugs, duct seal...)
They would be driven by an RH84 built out of a radiogram's amp. The room is fairly small, and althoug I like some bass, I like 'tuneful' bass, not a one-note-boom. I tend to listen at fairly low levels.
I am not looking for anyone to run off and spend lots of time doing the sims, just a general comment on how they might work as a stop gap.
thanks,
James
EDIT- looking at the frugal-horn site, the driver does not seem to affect the cabinet's response much. Perhaps they will be Ok.
I am looking at building a set of Harveys. Thing is, being a poor student, the fostex drivers are a bit out of reach. What do people think about the Visaton FR10 (8 ohm)? They cost about £7.50 +p+p+VAT each.
They are cheap enough that I may buy 4 and play with some mods (damar, de-whizzer, phase plugs, duct seal...)
They would be driven by an RH84 built out of a radiogram's amp. The room is fairly small, and althoug I like some bass, I like 'tuneful' bass, not a one-note-boom. I tend to listen at fairly low levels.
I am not looking for anyone to run off and spend lots of time doing the sims, just a general comment on how they might work as a stop gap.
thanks,
James
EDIT- looking at the frugal-horn site, the driver does not seem to affect the cabinet's response much. Perhaps they will be Ok.
Hi James
The Harvey's are tuned a touch low for these drivers -for BVR horns you don't want to go below 0.707Fs or the midrange is going to go walkabout. There's not a lot in it, but I'd be a little careful, especially as I'm increasingly cynical about the claimed Fs of many drivers. Lowther state 36Hz for their DX4 for example. Martin has measured his at ~60Hz. That said, for £7.50 each for the Visatons, it's not much of a gamble, especially as they're a solid company, so as ever YMMV.
Might I suggest though that you save a few more pennies and go for the Monacor SPH-60X? Wilmslow Audio can supply a pair, delivered, for £46, or you can get them a bit cheaper from spectrum audio, albeit there'll be VAT to pay on top of that. It'll be a better match, and I can vouch for the quality of the Monacor unit, which really is a bargin. Better IMO than buying 4 of the Visatons, plus materials to modify them.
The Harvey's are tuned a touch low for these drivers -for BVR horns you don't want to go below 0.707Fs or the midrange is going to go walkabout. There's not a lot in it, but I'd be a little careful, especially as I'm increasingly cynical about the claimed Fs of many drivers. Lowther state 36Hz for their DX4 for example. Martin has measured his at ~60Hz. That said, for £7.50 each for the Visatons, it's not much of a gamble, especially as they're a solid company, so as ever YMMV.
Might I suggest though that you save a few more pennies and go for the Monacor SPH-60X? Wilmslow Audio can supply a pair, delivered, for £46, or you can get them a bit cheaper from spectrum audio, albeit there'll be VAT to pay on top of that. It'll be a better match, and I can vouch for the quality of the Monacor unit, which really is a bargin. Better IMO than buying 4 of the Visatons, plus materials to modify them.
Scott, sorry to mess with your design fore the second time, and hopefully dont get offended by this 
I think you have said earlier that it really is more like a BR with big mouth
So I wonder if you complicate the design a bit, around the "horn" mouth
Hopefully picture will exsplain better
Also, I think optional bracing in hornmouth looks very strange to me, the way its placed - but maybe that dont matter so much
edit... ahhhh, yes, I see now your latest Calhoun/Shadow is actually similar
so I guess you have thought about it allready
I think you have said earlier that it really is more like a BR with big mouth
So I wonder if you complicate the design a bit, around the "horn" mouth
Hopefully picture will exsplain better
Also, I think optional bracing in hornmouth looks very strange to me, the way its placed - but maybe that dont matter so much
edit... ahhhh, yes, I see now your latest Calhoun/Shadow is actually similar
so I guess you have thought about it allreadyAttachments
The more input the better IMO.
In re the vent profile, nope -it's deliberate. Although they're BRs, the vent flare is carefully chosen. The abrupt final expansion is end-correction -it helps kill peaking at Fc in-room. The Shadow / Calhoun are approached from a different design perspective (effectively a Fonken variation combined with a waveguide), and don't require correction as the alignment is different -Ebs in the case of Calhoun.
The brace in the BVRs was designed by Dave actually to kill mouth vibrations as these cabinets go lower than a lot. It shouldn't affect the response as the wavelengths involved are greater than usual, and the angle is linked to the final expansion / flare a la some Fostex designs.
Best
Scott
In re the vent profile, nope -it's deliberate. Although they're BRs, the vent flare is carefully chosen. The abrupt final expansion is end-correction -it helps kill peaking at Fc in-room. The Shadow / Calhoun are approached from a different design perspective (effectively a Fonken variation combined with a waveguide), and don't require correction as the alignment is different -Ebs in the case of Calhoun.
The brace in the BVRs was designed by Dave actually to kill mouth vibrations as these cabinets go lower than a lot. It shouldn't affect the response as the wavelengths involved are greater than usual, and the angle is linked to the final expansion / flare a la some Fostex designs.
Best
Scott
It's borrowed from full-length horns to be honest & isn't something that really shows up on sims (not well anyway). I learned about it from GM. When I built my test mules this was one of the things I wanted to look at, and it appears to work in this case too -the published design sounded smoother in the bass. I'm not sure if I'm surprised or not. Given that it works for full-length designs, it seems reasonable, but as these are basically BRs I wasn't sure if it would still be applicable.
Hey, that was actually my thoughts - if optimum mouth fore the BR(BVR) actually should be a genuine horn mouth, or something a bit different, tighter with better "grip" of the air - I might have an idea that it also could be related to the width the mouth, in terms how much it needs to exspand
I might think that optimum could be a less angled conical shape with a rounding at the end
edit ... but that I guess would be better made with double width instead of building tall double-mouths
I might think that optimum could be a less angled conical shape with a rounding at the end
edit ... but that I guess would be better made with double width instead of building tall double-mouths
