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Impulse H5 restoration

grazie

pfm Member
I have another set of speakers to restore. I think they'll sound great when finished. The first problem is that the foam surrounds on the 8.5" SEAS (corrected) woofers have perished. I was considering doing replacements myself, but I believe it's a bit tricky and I'm clumsy. Both are reading 6 Ohms on a DVM, so I'm hopeful a re-surround would be worthwhile. Falcon has told me that original driver is unobtainable, but they do have a replacement. I'll need to contact Falcon again to get the driver model details.

I haven't actually used the speaker as I removed the drivers to check and get more info about them, but their markings are unreadable. If I replace the drivers and use the speaker, is there any way to determining if the units are faulty by listening or other methods?

Also, I'm sure the XOs will need re-capping. They appear to be mounted to a panel which is part of the top of the cabinet. Anybody, familiar with these speakers know how to get the XOs out? I can provide photos later if that helps.
 
Martin Clark (acoustica) may be along in a while as he has H2's and according to his website http://www.acoustica.org.uk/ the H2, Ta'us and H5 share the same unit. Ought to be possible to refoam them (I did some Heybrook HB1 woofers recently -first attempt, not difficult, just requires patience) plenty of refs on here.
AP
 
Paul at Reference Fidelity Components refurbishes customers speakers and has just done two pairs of Impulse. He can tackle all aspects of refurbishment and has developed replacement upgraded crossovers.
 
Thanks for the Reference Fidelity Components tip. Paul is a great bloke. No chance of NOS units, so I'll give re-foaming a try. I've got a pair of AR18s's that need doing too, so I'll practice with those. If there are 8.5" drop in replacements available I certainly can't find them.
 
Re-foaming these bass drivers isn't hard:

http://www.pinkfishmedia.net/forum/showthread.php?t=134619

When I last looked for comparable replacement drivers iirc there was a Vifa bass unit that used a chassis that would physically fit, chassis and bolt fixing centres identical; but the Thiele-Small params were all quite different - markedly lower sensitivity for one - so not actually 'drop-in replacement.'
 
Grazie/anyone.

I wonder if you would do me a big big favour, I'm in the process of building a pair of H2's but incorporating some modern theories and need some measurements/dimensions at various points just to clarify I'm not pissing in the wind and in right ball park.

I can/will post a drawing out lining what I need.



TIA

Graham
 
I don't think I can help Graham. Although the H5 cabinet is similar to the H2, but missing the horn box, the width and depth are slightly different. Your drawings makes it look like the horn section is a separate box, but to me the photos seem to show a single cabinet. However, the photos I've looked at aren't great.

If you think my H5 cabinets are close enough, I can supply measurements for D to H. Incidentally, how come you know the base width is 270mm and not know the other measurements?
 
grazie,

thanks for the reply....I was just hoping some one with an interest might pick up on this thread (please forgive the intrution) and I will start a new one. The measurments shown are from the original advertisment and published tests off of Martins site. There is very little info on the net regards to spec as I can rather cant find.

The dims of the mouth of the MID horn and the overal dimensions are at this point in time, a best guess. I just need to get the Bass enclosure and MID dimensions confirmed. And I'll be away on the build.

Yes, My drawing is not an exact copy of the orginal rather an improvement. (with luck) De-coupling and damping, separate MID enclouser again de-coupled from the Bass enclosure.

The Tweeter is also de-coupled and damped on a suspension system, again to de-couple from the bass enclosure.

In affect I'm trying to achieve a (sort of) cross between the H2 and the Ta'us. Both are good but both could be better.
 
Graham
- I think the long story short version is that you'll be doing the design over complete. providing the few dims wont actually help.

Reason being - the original bass driver isn't available: so the bass loading will need dsigning for the driver you do choose, inc choosing appropriate volume (compliance volume) before the throat to get the low-pass filter effect, and tailoring the expansion you need thereafter to suit the driver you 've picked (try Hornresp for modelling horns and mass-loaded transmission lines...)

Then the bass driver you choose will set the point at which you cross to a horn mid (again, new driver needs to be chosen), and the crossover point will set how large the mid horn mouth perimeter and length needs to be (depends on expansion rule chosen); and finally, you have to pick a tweeter to top it all off.

And finesse a crossover to suit.

Summary: while I applaud the idea - take the H2 as inspiration as you like - but anything moving forward is inherently and fundamentally a different beast in all aspects. Perhaps take a look how Brian Taylor followed it up with the Aspara H1 for other ideas, too :)



(I really need to find space and time to buld-up the upscale derivative I scribbled a few years ago..)
 
I agree with Martin, as soon as you have to change a driver in almost all speakers you are having to redisgn, but especially in a speaker like this.

Stefan
 
Hi Martin/Stefan

Thanks for your input, the main driver for this, is the thread on Trade Discussion. Paul of RFC has restored H2’s and Taus using new drive units and a complete redesign of the xover using the original enclosures.

I’ve had many discussions with Paul (who has expressed a keen interest) and Jerry of Falcon A with regards to suitable drivers and xover design to facilitate a build. I will take another look and confirm that what I’m trying to achieve is ‘achievable’.

The fact that Paul has successfully replaced all the original drive units all beit needing a revised xover gives one hope or maybe not. 
 
Well he definately know what he is doing and has probably spent a very very long time making sure it all calculates properly.
 
Just to be clear chaps, I have not replaced the woofer which as Martin suggests may require a change of horn loading to suit the new woofer. Hornresp is really the best piece of software available from what I can see to model the chosen driver and cabinet layout. That does not preclude a truncated horn arrangement a la H2 design, but I agree, it likely will affect the horn dimensions,

The mid driver replacement is in fact a direct drop in replacement for the mid-horn since it uses identical throat loading/compression, a very similar acoustic and electrical response and is within 0.5dB on sensitivity. There there are differences in the bandpass crossover necessary for several reasons, not least of which is that the original is lifted wrt the woofer and the tweeter.

The tweeter can be replaced for what you like. The cabinet has no impact at all but the crossover for the tweeter will require re-design for the offset placement and wrt the mid horn bandpass filter transfer function.

Regarding the H6, the Lali, the H2 and the Taus, I used the original bass drivers for each project but re-measured every driver RAW in cabinet (including replacement mids/tweeters) and initially simulated the crossover before the iterative process of building prototype circuits, re-measuring using the mic, and refining (and recalibrating the model). The end result in each case was pretty seamless.

I think that the drivers you have Graham are very suited to the design you have in mind, but I would strongly recommend that you download Hornresp and use that initially to model your woofer enclosure based on a similar truncated horn design. The H2 mid horn design WILL work as-is with the mid drivers that you already have so this sort of determines the cabinet width if you want it to look the same as the H2.

Hope this clarifies things a little!
 
Not that I know of: probably because once you head down the horn-load-everything route it's pretty much shit-or-bust: just go big, and reap the whirlwind properly :D

I dont think it's a coincidence the Aspara designs (Brian Taylor's follow-up project ) started with a 12" bass driver, creating a two-way with bi-radial mid-teble horn - not unlike JBL Everests in some respects: Pick a big, beefy driver, for high dynamics/sensitvity; select route to optimal mid/hi output to match; and the whole limited only by 'vaguely domestically acceptable' cabinet volume.

If it were higher priority, I would too...
 
I confess, I've had some odd hybrid thoughts too.

For example - why not buy a new minimonitor that does the mid-treble integration thing beautifully, saving hours of diy messing about, and drive that as the top two-thirds of a three-way; replacing the hooty bottom-end with something of effortlessly higher quality to taste.

Picture a Kef LS50 sat on/integrated to a bass cab that might start with 10" driver that only goes up to 3-500Hz. The minimonitor fares better, runs far cleaner/cooler and will go loud cleaner because you've fundamentally unloaded it. And semi-active operation then overcomes the moderate sensitivity gap to the bass units - very simple four channel active crossover and 4x mono power amps'd do the lot.

Could be a direct route to a very fine result...
 
There are plenty of diy horn bass cabinets out there Martin. Some of them don't even look that hard/expensive to build and I do have a big table saw.......
 
I confess, I've had some odd hybrid thoughts too.

For example - why not buy a new minimonitor that does the mid-treble integration thing beautifully, saving hours of diy messing about, and drive that as the top two-thirds of a three-way; replacing the hooty bottom-end with something of effortlessly higher quality to taste.

Picture a Kef LS50 sat on/integrated to a bass cab that might start with 10" driver that only goes up to 3-500Hz. The minimonitor fares better, runs far cleaner/cooler and will go loud cleaner because you've fundamentally unloaded it. And semi-active operation then overcomes the moderate sensitivity gap to the bass units - very simple four channel active crossover and 4x mono power amps'd do the lot.

Could be a direct route to a very fine result...

Not as easy to integrate as you might think (if only proper loudspeaker design was that easy!) and would require modelling for the integration with the horn in any event. You would have to consider the field lobing and phase too. Better imho to design something integrated from scratch. You would also have to consider directivity with frequency and sensitivity maching too. It can be done but you'd be working backwards. Just as easy to design from scratch and probably better off doing it that way. There are few easy wins I'm afraid. I've seen and heard it done the way you describe and not once has it sounded right or integrated. It's far more complex than using a satellite and sub set up and getting a sub to properly integrate and anyone who's tried that knows the challenges there.
 
Did you get the measurements you wanted? I wasn't quite sure what you were after. If it is from the H2 I can measure mine.
Have you seen the acoustica site about the Impulse horn speakers? It's really useful with information and modifying tips, although I have found the information is worth double checking.
As well as the H2s I have a pair of H6s. The smaller is a superb speaker and would make a good basis for a DIY horn project. They are a two-way and have a much simpler cabinet design.
I found the H6s worked superbly with a Musical Fidelity 3a pre-amp and MA50 monoblocks. The amp combo is designed to roll off in the bass, which the H6s don't need. When I bought my H2s I realised I would need an amp capable of driving the bass properly. I bought a Cayin 500MK which I am more than happy with.
 


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