Speakerplans.com Homepage
Forum Home Forum Home > Plans > Other plans
  New Posts New Posts RSS Feed - B2F
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

B2F

 Post Reply Post Reply Page  <1 456
Author
Message
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10520
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 12:41am
Excellent work! That's more in line with what I'd expect from a design with this much thought into it. <6 dB from >100 Hz won't win any medals in PA land, but it'll probably get you a couple hours extra fun off a battery with some friends in a field.

I'm curious what led you to the measurements with the horn facing the floor? It's not a technique I've seen before.
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 2814
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 9:26am
Originally posted by toastyghost toastyghost wrote:

Excellent work! That's more in line with what I'd expect from a design with this much thought into it. <6 dB from >100 Hz won't win any medals in PA land, but it'll probably get you a couple hours extra fun off a battery with some friends in a field.

I'm curious what led you to the measurements with the horn facing the floor? It's not a technique I've seen before.


I'm going to use it as a mobile system with 360deg dispersion. top unit will be 360deg too. going to try a wheelboard with a hole in it next. thinking it will provide some loading and increase the effective horn length too. will be using 8" wheels so will have space underneath to put a lot of bracing on the wheelboard.

I was hoping the speaker pointed down would have performed a bit better even without the wheelboard. 22cm (red) was better than 11cm (purple). maybe even slightly higher would be okay. I've found some nice 8" castors so will get those and then try the BC style loading and see if I can get any extra low extension.

EDIT: 8" castors have a height of 26cm, 10" castors have a height of 32cm. so I will do some more measurements before deciding which to try.








Edited by snowflake - 31 July 2021 at 9:48am
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 2814
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 14 August 2021 at 1:58pm
weighed the finished speaker yesterday - cab is 72kg but will probably go up to 75kg with some paint and a few handles added. It is mostly poplar which is lighter than birch and not quite as stiff but it is well braced where it matters and doesn't seem to resonate (except for the rear access hatch which I am going to replace with aluminium). for it's weight the max output is pretty impressive.

battery is 15.5kg
amp is 5kg
wheelboard is 12.5kg (still playing with this to get flat response by adjusting opening size)
top box will be about 20kg

it rolls very easily on the 8" castors I got, even on rough ground, and they don't rattle too badly

Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10520
Post Options Post Options   Thanks (1) Thanks(1)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 14 August 2021 at 3:46pm
Just a heads up if you’re going to try the ‘choke’ of a BC style opening - there needs to be significant space in front of the cabinet for the modified wavefront to develop. It’s about 45 centimetres for the BC415.

The rest is all down to the expansion and CSA of the internal horn so that it can ‘see’ the opening and the ‘virtual horn’ on the boundary.

I’m not sure it’s a good idea if you’re after 360 coverage, since the entire point of the BC design is to improve on axis sensitivity through focusing of the sound output via the ‘cancellation donut’? There’s an install of a BC415 in Anomalie in Berlin that’s flown central aiming down, and I’m told that it was tricky to integrate with the four point mains since there is almost no bass once you get close to the edge of the dance floor.

If you want omnidirectional output then perhaps inspiration from the Apple HomePod’s horn loading would be a good thing to include in the wheelboard?
https://www.diyaudio.com/forums/multi-way/308654-apples-homepod-bottom-firing-horn-provides-directivity-control.html

Lots of drawings in the patents.

Edited by toastyghost - 14 August 2021 at 3:48pm
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 2814
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 14 August 2021 at 4:19pm
yeah I could tell it wasn't quite working as hoped.

I have got more output below 55Hz from a hole that is 1/3 of the horn mouth - dropped the f3 from 55Hz to 42Hz. but it comes at the cost of ~3dB sensitivity from 60-120Hz. running off battery I would rather have the sensitivity.

could have gone up to the 32cm wheels - Will try that and see what happens. I'm not sure the dimensions of the cab are big enough to get an effect though, even using the ground as a boundary.

I think if I make the hole bigger I might find a sweet spot at about 60% of the horn mouth where it smooths out the 2dB peaks in the response and gives me a few Hz extra bottom end whilst only losing <1dB sensitivity.

will also try and find a brick corner somewhere I can use to measure 1/8th space response and see how low it goes. I think a stack of four or more of these FLH could be quite impressive for PA use. I haven't tried venting the rear chamber yet either.


Edited by snowflake - 14 August 2021 at 5:09pm
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10520
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 14 August 2021 at 5:49pm
Originally posted by snowflake snowflake wrote:

I have got more output below 55Hz from a hole that is 1/3 of the horn mouth - dropped the f3 from 55Hz to 42Hz. but it comes at the cost of ~3dB sensitivity from 60-120Hz. running off battery I would rather have the sensitivity.



That suggests the ratios aren’t correct for the BC loading, and instead you’ve got an ‘inverse horn’ effect where the throat is larger than the mouth. That type of design gets much broader frequency response at the expense of sensitivity, but that’s the opposite of the boundary loading effect you observe when going from ‘normal’ FLH to BC mode in adaptable boxes like the BC218 and BC215.




Still nice to have the option though, depending on the event / music type. Personally I prefer a lower playing system at lower level than one that’s hammering it out with no LF.

Edited by toastyghost - 14 August 2021 at 5:51pm
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 2814
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 14 August 2021 at 6:16pm
I really need to do some impedance measurements because the lower sensitivity I am measuring doesn't necessarily mean lower efficiency which is what will drain the battery. I will try some Hornresp sims to see if I can get an idea how impedance changes.

I also have the option of using a Waves Maxxbass 102 processor - its lower setting is 60Hz which is where the speaker starts to roll off.
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10520
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 14 August 2021 at 6:30pm
Hornresp can’t simulate diffraction so as yet I haven’t seen anyone get boundary sims out of it in a meaningful manner. You can export the data and combine it manually with something like Edge Tolvan or Jeff Bagby’s spreadsheet if you’re clever about it.

Or it’s Akabak time…
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 2814
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 15 August 2021 at 2:26pm
Originally posted by toastyghost toastyghost wrote:

Hornresp can’t simulate diffraction so as yet I haven’t seen anyone get boundary sims out of it in a meaningful manner. You can export the data and combine it manually with something like Edge Tolvan or Jeff Bagby’s spreadsheet if you’re clever about it.

Or it’s Akabak time…

oh yeah I've used Bagby's spreadsheet before. but any diffraction will change the directivity but not the impedance won't it? and as you say I'm possibly not even getting a diffraction effect here - so could just model the hole and the external horn path in hornresp.
Back to Top
 Post Reply Post Reply Page  <1 456
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.078 seconds.