Visceral impact of Jon's M8a vs 850490 ???

**Paul H** · 28 December 2006, 09:19 Thursday

Originally posted by jquin

Hi all Newbie here

I have looked at Jon's M8a/XT25 design and wondering how it would perform
against my amateurishly devised three way of 850490 and maybe 821615 & XT25.

Knowing nothing about you, your skill set or available design & building tools, my money's on the M8a design being in a completely different better class from whatever you might hammer together. Of course, this is the internet, so you might be a famous speaker designer known exclusively thoughout the southern hemisphere for all I know

The Peerless HDS have a reputation for being very good drivers that are reasonably easy to work with - they don't have any resonances or peaks that make crossover design extra-difficult.

The XT30 has measured well above 2000 Hz, and somewhat poorly below that, so it's a good 3-way tweeter but not so great for a low crossover. I've confirmed this with my own listening tests with the XT30 swapped out for a SS9800 - the SS9800 is much 'smoother' (to be fair, it's also much harder on the wallet). I'd look at the Seas 27TDFC for your use - it's been getting good reviews from the diy crowd here and is very reasonably priced.

I jumped into a massive speaker design as a relative newb (the one in my avatar) and can only reiterate what many others have said - keep it simple at first. I was/am pleased with the final result but the frustration along the way almost made me quit - and I'm very stubborn and never quit anything.

If you're new to this, and want to do something from scratch, the 8" HDS and the Seas 27TDFC as a two-way will give you drivers that are easy to work with and that can produce very excellent sound - with the right box and crossover.

**JonMarsh** · 28 December 2006, 12:07 Thursday

Anyone considering building the M8a two way or something similar would be advised to change drivers over to the M8ta design, which ever combination of tweeter with the RS225 woofer you prefer, and build it in whatever enclosure size is feaible or desirable for you- from a small sealed desig to the M8a woodstyle project or something larger.

Now, I wouldn't discourage the idea of a three way system instead (has a fair amount to recommend it), but doing a good working three way crossover takes a bit more skill and care than a two way.

What's your idea/concept for managing the baffle step, what crossover frequencies do you have in mind, what slopes, and how do you plan to handle the relative phase between the drivers?

Use SPL-MAX spreadsheet or something similar to model the output capability of the Peerless midrange (2 mm Xmax) before deciding on how to use it in a speaker.

The 850490 is not the best candidate for a three way with higher crossover points, as it's first cone issues show up around 600-700 Hz. Xmax is OK at 5.5 mm. Would be a lot better off with two 850439 than the 8". Even the 830884 has a dip-flex mode at 900 Hz, I wouldn't use it in a three way crossed higher than 400 Hz or so, depending on slopes.

For some ruminations on three way design issues, see CJD's three way designs in the Mission Accomplished section; for some theoretical transfer function ruminations, have a lood at the recent three way design study thread.

Good luck, and by all means, have fun!

**jquin** · 28 December 2006, 17:34 Thursday

Thanks all.

What about the issue of Visceral impact. While I still want the system to be very musical I was hoping it would have some special effects.

Also without taxing you too much what books would you recommend. I have read Loudspeaker Cookbook to death but where do I go from there?

Regards
John Q

**JonMarsh** · 28 December 2006, 18:09 Thursday

Viscreal impact, I think your're looking for higher SPL's than an 8" two way or three way provide.

Look to CJD's three way designs in the Missions accomplished sections.

If you're familiar with and understand V7 of the Loudspeaker Design Cookbook (which is a mixed bag in my opinion), Speaker Building 201 by Ray Alden is a good bet; I'd also suggest getting a copy of Testing Loudspeakers by Joseph D'appolito.

OTOH, you might learn more ueseful stuff doing a lot of reading on Sigfried Linkwitz's site, and MarkK's. I'm of a mind with them that linear distortion testing using shaped sine bursts is quite important to identify cone issues, and multi-tone harmonic distortion testing is also very useful and necessary, thoug being the lazy butt that I am I'm often quite happy to settle for swept sine tests. D'Appolito's book is no more a comprehensive bible for speaker testing than, say, Douglas Self's "Audio Power Amplifier Design Handbook" is the end all for solid state amplifier design, but a lot of guys who fancy themselves hotshot amplifier designers obviously didn't learn or don't understand some of the basic and details which Self covers quite well.

Beyond that, there are probably more than a few nuggest buried here and there on this forum (clipping to notebook software is useful for capturing and organizing online info, but curiously that's not a popular type of software on the PC side of the world, though it is on Mac's), undoubtedly in others, too, but most don't have the information archived nicely like our Missions Accomplished sections. Have you been through all of those references and links?

good luck, and by all means, have fun doing it.

~Jon

Visceral impact of Jon's M8a vs 850490 ???

Visceral impact of Jon's M8a vs 850490 ???

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