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gen0me View Drop Down
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    Posted: 15 January 2017 at 11:11pm
Here is what I have:
That goes to horn:


That is a speaker side:


As you see the gaps are so small. Around 2mm wide. The speaker is 8"(little bigger then outer circle on pic). The gaps are so small so their cross surfaces be around the starting cross-surface of a horn I am designing.

As you see on the photos this phase plug just makes differences in distances from membrane bigger than without it but the front chamber volume should be smaller.
Do I understand it right?
Red - front chamber volume
Blue, green - cross-surfaces

So what is wrong with mine phase plug?
Why every phase plug I see has bigger gaps than mine?


I saw some phase plugs for 8" speakers going higher than 2.5khz.
Does this phase plug has any right of existance or will it cause some distortions etc?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 15 January 2017 at 11:34pm
Looks like a very high compression ratio, compression drivers tend to use upto about 10:1.
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gen0me View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 16 January 2017 at 12:24am
Yes around 15:1.
1" HF drivers don't have phase plug and 2" has gaps similar widtch to fills in phase plug.
Hmm.. Should I than take example from 1"?
The problem is without phase plug I will go to 1khz.

I thought even about this minitweeter shape phase plugs but the gaps still will be small.
Is there some another shape?

Should I even try this phase plug on photo?
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Centauri View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Centauri Quote  Post ReplyReply Direct Link To This Post Posted: 16 January 2017 at 1:51am
Depending on what the lower frequency limit is, a 15:1 compression is likely to tear the paper cone to shreds.  Also, unlike a metal diaphragm which acts more like a piston at high frequencies, higher frequencies from a paper cone tend to propagate along the cone from the centre, so the sound from the centre will lead the sound from the edge - a single opening near the edge of the cone works better.  Sometimes takes a lot of experimentation to get it right.  I got an Eminence Beta8 out to 2.5kHz without such a high compression as detailed here.

Edited by Centauri - 16 January 2017 at 1:52am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 16 January 2017 at 1:23pm
Omg! I just read http://www.centauriaudio.com.au/diy/plugs.html before.
So I think the best option wold be like in Round throat = 142cm^2 with round phase plug. I will check hornresp if it will allow me to change horn this way. This peak at 350hz you had on simulation?

I'm wondering one more thing. In Round throat = 142cm^2 with round phase plug you positioned phase plug 5mm in front of the cone. 5mm x Sd ~= 100cm^3. That's similar to my simulation which gives me around 1khz. Do you think I shouldn't make lower volume and hope in practise it will give me higher cutoff?

The horn should be going very low. 100hz, but I don't know how low I would like to cut it. Depends on how I would feel the lowest delay peak. I like to cut bands with weak filters. At Rms power its excursion is around 2.5mm.

Edit:
OK so very easy way is to change Sthroat=30cm^2 what gives compression ratio around 22:7 ~ 1:7.
Is membrane in danger?

Edit2:
After simulations and "fun" with exponential/conical beginning of horn I think maximum reasonable Sentry will be 40cm^2. Later characteristic starts loosing smoothness. On higher bandwidth appears mountains. So obvious question is if thats only simulation as you noticed not accurate higher bandwitch.
Nevertheless 4:22 ~ 1:5.5. Should be fine.


Edited by gen0me - 16 January 2017 at 9:32pm
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Centauri View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Centauri Quote  Post ReplyReply Direct Link To This Post Posted: 16 January 2017 at 11:32pm
Generally, if your throat geometry is good, you can get about an octave higher than Hornresp predicts.  

I don't think you will be very successful getting down to 100Hz - any more bandwidth than 3 octaves is doing well, and will usually result in lower efficiency. Arguably the most efficient midrange box made - the Martin Philishave (which I still use) - had a maximum bandwidth of 2.5 octaves.  100Hz will require a long horn with a low flare rate, which is detrimental to high frequencies (and their dispersion).  Sometimes having a faster initial flare rate at the throat can extend bandwidth, and if you need to fold the horn due to length, a large radius smooth bend is required to keep the top end - both these methods were used in Bill Fitzmaurice's DR boxes, which are a complex build.  Another way to increase bandwidth is to port the rear chamber - design the horn to go down to 200Hz & let the port fill in the lower octave, although this does increase group delay and excursion.

Ultimately, you will have to go beyond simulations & experiment to get the results you want.


Edited by Centauri - 16 January 2017 at 11:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2017 at 12:17am
I don't want ported horn. It will just move delay mountain higher and add another from port.
Can't find much info about those DRs. Are they bend 90°?

Edit:
Which one sounds better? Narrow higher efficient or wider? Not looking at whole Soundsystem.

Edited by gen0me - 17 January 2017 at 1:00am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Centauri Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2017 at 1:08am
8" version of DR box (DR200) here : http://billfitzmaurice.net/DR200.html
He only sells plans.
A build thread on his forum can be seen here : http://billfitzmaurice.info/forum/viewtopic.php?f=30&t=18414 which gives an idea of the arrangement - the speaker faces rear of box with fast expansion to top / bottom of box, horn path then splits each side via smooth curves.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Centauri Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2017 at 1:21am
Originally posted by gen0me gen0me wrote:


Which one sounds better? Narrow higher efficient or wider? Not looking at whole Soundsystem.

I prefer to keep the bandwidth narrower - easier to get flatter response & keep distortion down.  My current rig runs 15" ported horns 30Hz to 90Hz, 12" horns 90Hz to 500Hz.  Using Philishaves & 2" horns above that as temporary measure until I finish developing top boxes, which will be dual 6" 500Hz - 4kHz plus 2x 1" HF on one flare.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 21 January 2017 at 5:03pm
So looks like I will aim for 100Hz - 1kHz. Anyway HF driver is good enough for that. So no more experiments. Always leave me possibility to change HF driver on BMS coaxials for 4 way in case I dont like mids.

Edit:
Still dispersion bothers me.

Edited by gen0me - 21 January 2017 at 5:06pm
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