audio-talk

I suppose if the path length from the rear driver, out of the H-frame cavity, and round the sides to the front driver, is 0.6m or so, then it would cancel at 260Hz. Something like that.

Here you go straight from rhe

Sorry for sausage fingers .. Martin explains it better.
http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

Thank you Steve and thank you Martin King.

So you can make your H frame deeper to lower the bass response but in doing so you decrease the quarter wavelength resonance meaning the steeper roll off of the H frame occurs at a lower frequency. So mine are 500mm deep which equates to a quarter wavelength resonance of c170Hz.

That's a bummer, I was planning on taking the 285s up to c400Hz to meet the 208s, as Mark suggested. Rethink required!

500mm deep H frame... so it’s overall depth is 1000mm? They will be more like organ pipes... different set of challenges all together.

Well this just illustrates why the Quasars were designed the way they were. The Lower driver is only suppose to run up to approx 200Hz and then roll off, as it's in a U-baffle with some depth However the U-baffle bit is also slanted, so that the depth is not a fixed value - to help reduce colouration ( resonance ) effects in that range and higher up.

vinylnvalves wrote: ↑Thu Jan 14, 2021 12:08 pm 500mm deep H frame... so it’s overall depth is 1000mm? They will be more like organ pipes... different set of challenges all together.

500mm deep, so 1m from front to back of the speaker, radius = 0.5m.

f = v / 2.pi.r = 343 / 2 x 3.142 x 0.5 = 109Hz ish.

Except it seems it's not that simple! Your point about the Quasars is well made Mark.

IslandPink wrote: ↑Thu Jan 14, 2021 1:12 pm Well this just illustrates why the Quasars were designed the way they were. The Lower driver is only suppose to run up to approx 200Hz and then roll off, as it's in a U-baffle with some depth However the U-baffle bit is also slanted, so that the depth is not a fixed value - to help reduce colouration ( resonance ) effects in that range and higher up.

Colouration was still pretty evident
Mark, Sloping baffles do help to slow the cancellation effect. But like all colouration once heard it's hard to dismiss, I have pieter to thank for that imprinted in my head.


I did read the link to martin kings artical, i found it interesting.

He appears to me to very much 'measurist' more than a listener, the reason for me saying that ( on top of the low end gear he loves) is the part about damping not being required in u & h frames, in my experence it makes a big difference, regardless of length even on a flat baffle its effect was obvious to me.... But clearly not to everyone !

Acoustic damping of the H frames for sub <200 Hz will have no benefit... the physics say so. Maybe mechanical damping of the frame to stop it vibrating could have some benefit.. like a CLD.

vinylnvalves wrote: ↑Fri Jan 15, 2021 8:23 am Acoustic damping of the H frames for sub <200 Hz will have no benefit... the physics say so. Maybe mechanical damping of the frame to stop it vibrating could have some benefit.. like a CLD.

On a flat baffle all the drivers are on it steve.
On top of that there are reflections from the wall or corner behind the baffle which I've always found to have an impact on the sound

theres always some transmission of sound, a sheet of ply or chipboard is not totally soundproof, theres always some (quite alot !) transmission through it, H frames and 'open box' frames still suffer. But as always how it's made has an influence too.

My view is to get good sound, its about getting the speakers wood work as dead and damped as you can and sufficiently braced.


To my ears it results in a cleaner sound.

Loudspeakers to me are like amplifiers.
It's easy to contaminate the sound, it's just more physical, and like amplifiers that results in both cancellation and spurious sound (colouration)

This may be one reason why I liked Vic’s creations- there is no baffle.

Perhaps thats why those little subs i knocked up sound as clean as they do, theres virtually nothing to vibrate.

I think that the "cancellation" expectations from a calculator are misleading. Not "all" of the sound creeps around the edge to phase cancel. For sure, the calculations would show where the null on the side would show up. Having spent time with Quad ELS 57s proves to me that dipoles can have decent base without 10 inches of XMAX. Maybe not enough bass for heavy rock or rap, but certainly enough for acoustic music.
I think the critical number is NOT the depth of an H frame, rather the distance from the back wall. OB seem to be best when we simply let them breathe. That being said, I have great doubts about naked drivers suspended. The improvements by having 2 opposing LF drivers (Like a Ripole - or even in sealed boxes) just have always been too great to ignore.

rowuk wrote: ↑Fri Jan 15, 2021 4:05 pm Maybe not enough bass for heavy rock or rap, but certainly enough for acoustic music.

Ah, a -3dB point of 80Hz, then.
IMO, when it comes to domestic listening, flat to 40Hz is the minimum target, with 30Hz usually being adequate.

Chris

rowuk wrote: ↑Fri Jan 15, 2021 4:05 pm Having spent time with Quad ELS 57s proves to me that dipoles can have decent base without 10 inches of XMAX. Maybe not enough bass for heavy rock or rap, but certainly enough for acoustic music.

nearly 20 years with large electrostatics and I completely agree.