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Offline Simon Briggs  
#41 Posted : 12 December 2019 17:40:10(UTC)
Simon Briggs

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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.


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


and PDN.2151

simply because ears I trust attest to excellent sound performance.


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

Offline Simon Briggs  
#42 Posted : 28 June 2020 11:54:46(UTC)
Simon Briggs

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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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