Dilemmas, as always -- BLH vs BVR - diyAudio
Go Back   Home > Forums > Loudspeakers > Full Range

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 7th February 2009, 12:24 AM   #1
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Default Dilemmas, as always -- BLH vs BVR

Hello there,

A friend of mine was hooked by Lowther recently. I'm now helping him on the cabinet design...

As I've seen various measured data, many of the Lowthers have a rising response begins at 1kHz. Huge peaks above that, and relatively much lower SPL between 100 ~ 1kHz is commonly seen. So I think a short front horn (or WG) should be needed to help on the mid-midbass, otherwise the boosted bass by BLH might overwhelm the mid. Together with the HF peaks, it'd be an unbalanced response.

So, here they are.

The 1st version is based on PM2A. With the real measured parameters I occasionally got from the web, I ran some sims on hornresp. Finally I got a result which is satisfying -- a 'real' horn instead of a pipe with ragged response:

Data of BLH:
Click the image to open in full size.

SPL of BLH:
Click the image to open in full size.
(grey is at corner)

Phase of BLH:
Click the image to open in full size.

Followings are for the short front horn:

Phase:
Click the image to open in full size.

SPL:
Click the image to open in full size.

Data:
Click the image to open in full size.


The screen shots above are arranged in such a way that you may compare the phase with ease -- that's what I'm concerning. On the frequencies which front and back's phase are 180 degree apart, they should cancel each other out.

According to the sims, when the front and back are out of phase, the SPLs they produce are also very different. So they more or less dominate on their own range indivdually, thus there'd be no obvious cancellation, which is of course a good thing.

Bad thing is, this cab is HeeeEEEUUUUGE !! When finished, the total volume exceeds 500 Lt -- more or less like a refrigerator
  Reply With Quote
Old 7th February 2009, 12:40 AM   #2
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Default Part- II, the BVR

So, a smaller version is needed. Here are the sims based on PM6A in a BVR, also with front loaded short horn:

BVR data:
Click the image to open in full size.

BVR SPL:
Click the image to open in full size.
(grey is at corner)

BVR phase:
Click the image to open in full size.

Front horn phase:
Click the image to open in full size.

Front horn SPL:
Click the image to open in full size.

Front horn data:
Click the image to open in full size.

As can be seen on the screen shots, at 100Hz, front and back are almost perfectly out of phase. While their SPLs are simular, so a severe dip may happen here.


I don't worry about the far more humble performance of this BVR version, and the much more reasonable size is welcome, but the midbass hole would probably a real problem.


Did I miss anything? How accurate are the sims? And the most important, how do other BVRs perform in real life?

According to the short paths of BVR (related to the real horn), midbass cancellation seem unavoidable. How do you guys resolve this?

Any comments?


PS. Sorry for the long posts and thanks for reading.
  Reply With Quote
Old 7th February 2009, 05:07 AM   #3
diyAudio Member
 
Join Date: Jun 2007
Default Re: Part- II, the BVR

Quote:
Originally posted by CLS
Here are the sims based on PM6A in a BVR, also with front loaded short horn.
Hi CLS,

Hornresp Version 21.00 can model conical and/or exponential compound horns. The attached screenprint shows the input parameter values for your design assuming radiation into half-space, but with the oblate spheroidal waveguide approximated by a conical horn.

The Combined Response tool can be used to show the overall output from the front and rear horns.

Kind regards,

David
Attached Images
File Type: jpg lowther.jpg (59.4 KB, 621 views)
__________________
www.hornresp.net
  Reply With Quote
Old 7th February 2009, 11:11 AM   #4
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Hi David,

Thanks a lot for your input.

I modified it somewhat (enlarge the duct and chamber to boost up more bass):
Click the image to open in full size.


And the 'thing' will look like this:
Click the image to open in full size.


And I got the response as:
Click the image to open in full size.

It looks pretty good, I guess. As long as the midhigh resonance peaks are well damped.

I set the path length difference as -80cm because I plan to put the mouth of BVR to the rear of cabinet and let it faces the wall or even corner. 80cm is more or less the depth of cabinet plus some of the width.

I'll play with the models some more.

Thanks again
  Reply With Quote
Old 7th February 2009, 11:27 AM   #5
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
I modeled this thing:
Click the image to open in full size.


And got this if I set the BLH mouth facing forward:
Click the image to open in full size.


This if I set the BLH mounth on the back and facing a corner:
Click the image to open in full size.


TBH this case looks worse, to me.

So it turns out quite the opposite of my previous expectation.
  Reply With Quote
Old 7th February 2009, 12:12 PM   #6
hm is offline hm  Europe
diyAudio Member
 
hm's Avatar
 
Join Date: Feb 2004
Location: near Hamburg Germany
Hello,
forget the front horn, you canīt get enough bass,
take a second driver, most 8" need support below ~800 Hz,
my SAXOPHON is with 34 Hz, under 200 L, 100 dB 1 W, 1mm
measurement with AN8"
Attached Images
File Type: jpg saxfront2.jpg (39.4 KB, 635 views)
__________________
http://www.hm-moreart.de
  Reply With Quote
Old 7th February 2009, 01:22 PM   #7
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
Assuming you design sufficient gain into the back-horn, & the driver selected has a reasonably low mass-corner, going compound to lift the lower midband makes perfect sense, although the trick is always to get the crossover between them right.
  Reply With Quote
Old 8th February 2009, 12:13 AM   #8
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Thanks for the comments

Hi hm,

Actually I've looked into some of your designs, they are very interesting indeed.

However, when a 'horn' is largely narrowed, it's character tends to a "pipe", that is, a zig-zag response and lower efficiency.

I back-engineered an Acousta (with PM6A), and got this:
Click the image to open in full size.
(placed at 1/4 space -- 1 pi )

Like very many other "commercial products", the CSA's along the 'horn' are highly reduced, thus a bad looking response and lower effeciency.

Getting into such 'trouble' of making a horn, I really hope a good result and don't want such a compromise.

I also thought of helper woofer or clear 2 way. Although those are technically correct, it's still somewhat disappointing to an enthusiast of single driver fullrange speaker ( -- especially a Lowther lover, I guess). This decision is not mine, as mentioned in the very beginning -- this is for a friend.


Hi Scottmoose,

Thanks for the advice. I thoght the same. I've listened to a pair of PM4A with Oris 150 horn. I like the sound very much. Tonal balace is excellent (for my taste, a little bit warm).

Without front loaded section, Lowthers sound too thin. It grabs attentions at first but becomes fatiguing quickly.

So I'll stick to the compound design and see what can be done.
  Reply With Quote
Old 8th February 2009, 09:39 AM   #9
diyAudio Member
 
Scottmoose's Avatar
 
Join Date: Mar 2005
Location: UK
Right, if you're going to back load, they need a big horn to damp that HF / midband sufficiently.
  Reply With Quote
Old 8th February 2009, 11:50 AM   #10
hm is offline hm  Europe
diyAudio Member
 
hm's Avatar
 
Join Date: Feb 2004
Location: near Hamburg Germany
Hello,

simulations are not all,
AFAIK Hornresponse shows the horn mouth not the sum driver with horn,
in AJhorn it looks different,
so you need experience to get an idea what happens in real
and the room.
__________________
http://www.hm-moreart.de
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 11:26 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2