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The musings and pains of a loudspeaker designer
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Offline Simon Briggs  
#41 Posted : 12 December 2019 17:40:10(UTC)
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Originally Posted by: Simon Briggs Go to Quoted Post


So I have 4 number 18" JBL 2245H bass units, these need new surrounds do I go with them using two drivers per side or look for new more modern 18" units?


At the present time I am researching three or 4 alternative 18" drivers to the JBL units.

Crossover points will be 250 Hz Bass 2700 Hz mid to treble.

Simon



Not much movement with this project, as the JBLs need new surrounds fitted so may look for a modern alternative, plus a diversion with designing a largish 2 way for a friend.

As this will be active I have some flexibility.

Two drivers are under consideration.

I have not ruled out 'Isobaric' mounting to reduce enclosure size.

Will be sealed box low Q=0.5

Drivers under consideration are by UK firm Precision Devices

PD186/2

and PDN.2151

simply because ears I trust attest to excellent sound performance.



SJB



EDIT 27/06/2020

Searching the forum in details two of the best pieces of advice recieved to date, maybe he should look at these options?

Originally Posted by: Martin Colloms Go to Quoted Post
for speedy bass , not necessarily the most bass, I favour Qtc at 0.5 to 0.6 for a sealed box.

Thus I would trade , for a given allowable box volume a 12inch for a 15 inch to achieve it.

I am wary of too much equalisation and electronics ahead of it as with more supplies, power noise, extra ground routes

immediacy and fidelity may be impaired in favour of a notional text book frequency response.

The box size implies lots of panel area, so massive bracing and damping is a prerequisite if the journey is to be worth the effort and expense.

Martin Colloms




Originally Posted by: Martin Colloms Go to Quoted Post


DM will have to work hard to define the design and try to exclude the noise from all our suggestions.

Thiel and KEF have been working towards coincident, time aligned driver systems with proprietary drivers. The Quad gets there as of right.

Avalon is more time coherent than most with low diffraction narrow enclosure forms , tilted back to align the bass mid and treble start positions relative to the listener.

The resulting system CSD is particularly good, thanks to careful control of the effective driver working ranges. With these designs it is the attention to such detail which impresses.


My instinct for an enthusiast is a sealed box three way with a form narrowing with height, a true 8ohm impedance, , ie two of the '5ohm' bass drivers in series probably 220mm SEAS , .

probably the 160 mm Scan pulp cone wide range mid and a DXT soft dome tweeter.

We could try and firm up device type numbers from this broad suggestion.

Martin C



Noting the above project in bold highlighted mentioned elsewhere!!

Edited by user 27 June 2020 11:37:50(UTC)  | Reason: Not specified
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Offline Simon Briggs  
#42 Posted : 28 June 2020 11:54:46(UTC)
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Well one thing is sure, I have been very indecisive over several years, and, rambling on here, trying and failing to select a project to progress with and build.

I have been looking at many different options over the years, since my late 90s SLAMM build. Searching for fulfilling my deep curiosity, solace in good full range sound reproduction, mainly of classical organ and electronic music, the hunger for knowledge, desire for learning (must be my autism) which has resulted in many notebooks full of sketches, designs, calculations, ideas some unique? and over the years, have purchased quite a few technical books, recent buys include the new edition of HPL by our esteemed host, and Beranek’s detailed analysis revised reprint of Acoustics.

So, what do I want?

A/ I am looking for a replacement for my SLAMM type project of the mid-90s. I realise however things and my own ideas have moved on.

One individual has recently questioned me with “You don’t really know what you want” perhaps that is a bit disingenuous, but this is correct, as I cannot decide which single project to build.

My better half also asked the same type of question recently but was even more blunt and more direct than my recent inquisitor!!

So now that my Spouse has waged in and questioned me in detail. I have sat down, took time out and thought about it. She is very bright, knows good designs and sound quality, is not afraid of telling manufacturers and dealers when things are not right, and rang rings around one Audio reviewer during a Q&A session at a FHN/RR show some years ago!!. (as a retired dancer, she knows just a thing or two about rhythm and timing)

So what do I really want?

My answer, being honest with myself, (I will not go into the technical details here, 000s of words needed) in brief, is to look at building more than one of my designs.

Well she said “You are very bright, driven, not afraid to try and fail and have the technical design skills, better than what many manufacturers have access too!! But alas not the monetary resources. She added “Stop asking silly questions on forums that you already know the answers to! be confident in your own abilities and focus on three of your designs then”, She said carefully, looking through my notes (ignoring the deeper maths) and as a result, has advised me to look at.

1/ A reasonably large two or three way, to replace the KEF BBC LS5/1AEs in out bedroom cum A/V system. (I’ll be keeping the KEFs as they are a collector’s item) or go for the Troels The Loudspeaker kit? Link here.
2/ A big sealed system rather like a three-way NS1000 on steroids, she likes in her words their tight rhythmic bass. (she also liked the Linn Isobarik’s bass but not the mid/treble!!)

Wait 5 years or so and then work on
3/ Finally, my endgame!! A SLAMM replacement, my all-out assault retirement speaker probably will be M9 or a WAMM Chronosonic sized behemoth of all my own creation.

Well she said over the next couple of years, look through your notes, refine the designs and build the two smaller!! systems by using drivers you already have. She prefers tight low(ish) Q sealed box rhythmic bass.

With her keen mind, her counsel and blunt honesty, she has given me the most logical advice to date.

I have now taken a time out and have realised that what I am searching for, is not achievable with just one single loudspeaker build.

So if I ramble again, kindly refer me to this post!!

Now it is over to me!........
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Offline Simon Briggs  
#43 Posted : 08 July 2020 14:04:57(UTC)
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Well I am happy, this is the bass response of the main design I am going with.

I am not going to say too much more about it at this stage, but it models well in several programmes.


÷ñÒ339389773êÖ2õæ÷Bass Response÷ñÒ339389773êÖ3õæ÷

Edited by user 10 July 2020 09:19:24(UTC)  | Reason: Not specified
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Offline Simon Briggs  
#44 Posted : 19 July 2020 13:39:50(UTC)
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Things are taking shape, I now have all the drivers, the bass units are amazing

More thoughts on my Bass enclosure, which will be heroic, the approx. 10 cu ft bass enclosure will probably use constrained layer damping in the main walls which will be twice the thickness of my SLAM build of the late 1990s and twice the bass volume.

Weight restrictions will not be a consideration and will be disregarded.

One thing I will have to look at very carefully at (from Martin's recent experience with the M2 review), and a thread here is Loudspeaker isolation which will be carefully considered too, with lessons gleaned from Magico M series floor couplers as well.

This 'Man in a shed' will fight back, with higher level Engineering and Science qualifications, experience in Loudspeaker system design, various construction techniques, a keen intellectual curiosity and willingness to keep learning too, I am therefore better equipped than some companies to succeed!! My late 90's SLAM type project bears testament to this success. ThumpUp

Edited by user 19 July 2020 14:02:15(UTC)  | Reason: Not specified
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Offline en1omb  
#45 Posted : 19 July 2020 17:36:16(UTC)
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Loving the gusto you are employing! The level of anticipation as we finally get close the pictures of the final thing may be too much to bare!

I wish I had the patience to learn enough And then the bravery to commit to a build.
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Offline Simon Briggs  
#46 Posted : 07 August 2020 10:05:48(UTC)
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Originally Posted by: en1omb Go to Quoted Post
Loving the gusto you are employing! The level of anticipation as we finally get close the pictures of the final thing may be too much to bare!

I wish I had the patience to learn enough And then the bravery to commit to a build.



Thanks, this process has certainly been interesting. This reinforces my view that, having gained a reasonable level of expertise, I have many 1000s of hours of experience, that one will always continue to learn, and I find new discoveries exciting, and look forward to many more 😊
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Offline Simon Briggs  
#47 Posted : 03 April 2021 14:46:46(UTC)
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Originally Posted by: Simon Briggs Go to Quoted Post
Things are taking shape, I now have all the drivers, the bass units are amazing

More thoughts on my Bass enclosure, which will be heroic, the approx. 10 cu ft bass enclosure will probably use constrained layer damping in the main walls which will be twice the thickness of my SLAM build of the late 1990s and twice the bass volume.

Weight restrictions will not be a consideration and will be disregarded.

One thing I will have to look at very carefully at (from Martin's recent experience with the M2 review), and a thread here is Loudspeaker isolation which will be carefully considered too, with lessons gleaned from Magico M series floor couplers as well.

This 'Man in a shed' will fight back, with higher level Engineering and Science qualifications, experience in Loudspeaker system design, various construction techniques, a keen intellectual curiosity and willingness to keep learning too, I am therefore better equipped than some companies to succeed!! My late 90's SLAM type project bears testament to this success. ThumpUp


System design update 03/04/2021

I am continuing to refine the alignment of the bass enclosure, crossovers are more or less there (basic electrical filter shapes modelled allowing for baffle position and driver characteristics) but will need tweaking when the system is built, to fine tune any anomalies.

Once the main system is built (at test stage) careful measurements will need to be taken. Fortunately measurement kit is now reasonably priced and within reach.

The crossovers have been designed to be external and care will be taken to mount and isolate from the main speaker.

I still believe that crossovers should be mounted externally, and the performance compromises of mounting crossovers inside the ‘box’ are too much of a compromise I cannot accept.
I have researched this area very carefully over the years, having built like for like systems crossovers inside and out; and the advantages of external crossovers offer performance advantages that are too big for me to ignore.

I have been looking and researching the effects of group delay and reducing it to reasonable levels balancing the bass alignment carefully with this. Generally my alignments thus far have resulted in GP of well below 20ms at 20 Hz and below 8ms at 40hz in one case an alternative using the same enclosure tuned by playing around with Rg offers GP of below 8 at 20Hz and 3,5 ms at 40hz.

One thing I would like is the future possibility of reducing GP further inspired by the recent review of the KIM system and the roon tuning method used.

Nest phase will be to investigate how to best alter levels of Rg one way will be to look at the inductors used in series with the bass driver but also small levels of high performance series resistance and tune using different values until the best is found then wither use the best resistor I can find or a high performance inductor with the right parameters to suit.
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Offline en1omb  
#48 Posted : 03 April 2021 19:44:27(UTC)
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Sounds like you have been busy! I hope you can reach a point where you don’t feel the need to tweak any further and then enjoy it. I get the impression DIY projects are never finished!
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Offline Simon Briggs  
#49 Posted : 03 April 2021 22:50:06(UTC)
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Originally Posted by: en1omb Go to Quoted Post
Sounds like you have been busy! I hope you can reach a point where you don’t feel the need to tweak any further and then enjoy it. I get the impression DIY projects are never finished!


Indeed DIY projects I am involved with have a habit of extended periods of development!! but with purchasing some newer measuring kit, I hope to shorten the tweaking period considerably to just enjoy them.

The only issue with this project is that I will not be starting construction until later in the year when I can get access to my Dad's workshop

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Offline Simon Briggs  
#50 Posted : 07 July 2021 12:07:12(UTC)
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Hopefully Boris will allow us some more but sensible measured freedom.

Will need access to a workshop.

Crossovers designed and modelled taking into account driver placement and baffle size / layout.

Bass enclosure is to be a sealed box, not inconsiderable in size but with an alignment which will make room placement sensible.

20Hz bass will be within reach maybe a touch lower as the anticipated f10 point is about 10Hz lower than my old Spendor S100

See what freedom we get?


Edited by user 18 November 2021 15:06:17(UTC)  | Reason: Not specified
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Offline Simon Briggs  
#51 Posted : 18 November 2021 15:48:27(UTC)
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This is the anticipated in room bass response of my design using a series cap around 1000-1300uF to equalise the bass.

Extending down to about 16Hz in room -4dbs and 13Hz -6dbs approx

UserPostedImage

Edited by user 18 November 2021 15:55:09(UTC)  | Reason: Not specified
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Offline Simon Briggs  
#52 Posted : 17 December 2021 17:00:04(UTC)
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Projects temporarily on hold due to unavailability of materials

Edited by user 31 December 2021 22:21:24(UTC)  | Reason: Not specified
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Offline en1omb  
#53 Posted : 19 December 2021 18:56:03(UTC)
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Hopefully it will just make the pay off all that much sweeter!
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Offline Simon Briggs  
#54 Posted : 22 December 2021 13:41:37(UTC)
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Originally Posted by: en1omb Go to Quoted Post
Hopefully it will just make the pay off all that much sweeter!


This setback will make me more determined, will regroup and hopefylly 2022 will bring better?
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Offline Simon Briggs  
#55 Posted : 31 December 2021 22:58:33(UTC)
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As we go forward into 2022 I will continue to refine the design, but only on paper.
The structural form is taking shape, but the crossovers I have modelled restrict the baffle size and driver layout.
Think of a Yamaha NS1000 on steroids (But in a much larger low Q sealed box) with decoupled mid and treble modules.
The curve below is an rough indication of approximate bass extension in-room.
Using a very high performance 18" Bass driver, this system will be able to take huge inputs in the bass whereas most domestic speakers even some real big ones can handle a few 10s or maybe near 100 watts at 20Hz, mine will be able to take bass inputs upwards of 500 watts!!


The Bass response

UserPostedImage


Power handing Curve

Note 1.5Kw at the lowest note of a 4 string bass and even 400 watts at 10Hz

I describe power handling as sufficient!!

Bass Power Handling


Edited by user 31 December 2021 23:00:53(UTC)  | Reason: Not specified
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Offline Simon Briggs  
#56 Posted : 05 January 2022 17:14:24(UTC)
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All projects on hold, my family unit received some bad news this morning

Edited by user 08 February 2022 09:36:32(UTC)  | Reason: Not specified
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