Doc modding Marantz imperial 7

[karatestu]

When I convert those oak boozing tables into speakers the interior volume is going to be too big for a 6.5" and 5.25" inch combo. I will do it anyway but try two 6.5" first as the increased volume (25 litres rather than the 20 litres I have now) and the better materials and construction might just tip the balance in their favour.

The bottom baffle and down firing 6.5" mid bass can go in straight off but I will make temporary top baffles out of birch ply for the up firing driver so I can swap between the 6.5" and 5.25" to see which is best. That will mean I can save the oak for when I am certain what the up firing driver will be.

If the enclosures end up too big then I can add steel and braces and sand bags until the optimum is found. Better to be too big than too small as you can't add more volume whereas it's easy to take volume away.

[karatestu]

I am having second thoughts about using solid oak for the whole thing. I got carried away with using as much of the table as possible for cost and recycling purposes.

Thinking more about it, solid wood doesn't always lead to best sound and has it's problems from a construction point of view. Solid wood expands and contracts across the grain with humidity. This movement has to be allowed for in the construction otherwise cracking results. That is no problem for a piece of furniture which doesn't have to be airtight and doesn't have to deal with vibration, pressure etc.

It seems like making the speaker air tight and not prone to rattles whilst allowing for movement will be a major undertaking and one that is probably above my skill level.

The other option is to just use the Oak legs and make the rest of it from baltic birch which doesn't move.

Any experienced wood workers here that could chime in ?

[karatestu]

Don't worry, I have had some very good advice from the fine folk who frequent TAS. Apart from Slinger that is who obviously knows bugger all about wood

P.S - I will know if he bothers to look at this blog

[karatestu]

I found a couple of speakers using bipole bass drivers. They seem to becoming more popular and stuffed full of class D amplification and dsp trickery.

https://www.bowerswilkins.com/en-gb/home-audio/pv1d

This one I think uses opposing drivers which share a magnet

https://uk.kef.com/products/referenc ... bwoofer

[karatestu]

Quote from diyaudio

System Q influences both time domain, which is buried in the reverberation of the room (so it cannot be examined anymore), and frequency domain, which is altered by the room (so a different system Q in the same round still sounds different). So if you compare different system Q's, you are comparing their frequency domain performance.

A comparison can be done. Lower Q means less bass. If you happen to have a room which amplifies bass, this bass reduction can be a good thing. If you live in a room which does the opposite, a higher Q is better. Therefore, determining which alignment is 'best' in room X is meaningless for room Y.

This quote deals with the design choice I am about to make. Increasing box volume lowers Q which reduces bass but the roll off is less steep which results in a bigger box producing more deep bass than the smaller one. But I am not that bothered about deep bass anyway. What I am more interested in is the reduced bass at resonance and above.

I have a room which "amplifies" bass, I am pretty sure of that. So the good thing about diy is I can try and offset this by designing my speakers to be leaner in the bass. So, a bigger enclosure for a certain driver is how this can be achieved.

The recent bipole configurations I have tried were (A) two 5.25" in a 17.5 litre box (B) two 6.5" drivers in a 20 litre box (C) 6.5" down firing and 5.25" up firing. I expect the double 6.5" version was too high Q for my room and taste because the box was too small (I suspected this). The double 5.25" version was super clean down below because the Q was lower due to the boxbeing oversized. The 6.5" and 5.25" seems to be roughly correct for a 20 litre box but I still yearn for the super tight bass of the double 5.25" version.

My final build is going to be roughly 25 litres and so I am hoping that trying the double 6.5" in that oversized volume will bring back the super tight bass I remember of the double 5.25" version in an oversized box. My room's seem to be complete bastards as far as bass goes. At least I know what to do to get the best result with what I have ( no I don't mean buying some dsp or putting ugly and totally ridiculous room treatments in my living room).

[Ordinaryman]

I quite often think that the rooms we listen in have one of the biggest effects on what we hear and imo more so than speakers, amps,,source etc. For me some of the best stuff I've ever owned sounded crap in my current room. Just happy with what I have now

[antonio66]

"Don't worry, I have had some very good advice from the fine folk who frequent TAS. Apart from Slinger that is who obviously knows bugger all about wood "

Wonder if he can remember anything about the morning sort?

[karatestu]

Placing my speakers across a corner has brought some changes in how things are presented. The band seems further away now. As semi omni speakers are so dependent on reflections off boundaries then that is probably why ? Or it is a visual Jedi mind trick

It got me thinking again . How about angling the top and bottom baffles to project more sound in to the room. The legs of these tables I am using are splayed by 5 degrees. I could tilt the top and bottom baffles from horizontal by 5 degrees as well. That would make the rear edge of the top baffle 3 cm higher and the rear edge of the bottom baffle 3 cm nearer the floor.

Any more than 5 degrees and it starts to look odd. It makes construction even harder but might be worth it. Will the force cancellation of the bipolar design still work as well with the drivers now being 10 degrees out of line. There would be no internal walls parallel which is said by standing wave believers to be a good thing..

[karatestu]

Did some more terrible quality DIY today. I got a pair of 30 cm cubes going with bipolar 5" to compare with the 6,5' down and 5" up firing jobbie. Whilst I was doing that I thought I might as well try and see what a bit of steel lining would do for the sound with these crap chipboard monstrosities.

I found some left over 3mm steel from when I steel lined the marantz imperial 7 cabs. Yes, remember them I had enough to do every wall of both cabs and it was even hammerited as well I never listened to the marantz cabs without the 6mm of steel I put in only listened after.

Well blow me down. Even with only 3mm the bass is transformed in tightness . It just goes to prove what a difference the cabinet makes. It makes me wonder that maybe everything I have done previously with crap chipboard has been a total waste of time. But it was cheap and quick to do when all you had to do was cut it, glue and screw.

I knew chipboard was crap but this has really emphasised how shite it really is for bass.

[karatestu]

And whilst I was basking in the sound from the steel lined 5"bipole I decided to revist isobaric Thecube with 6.5" and 5"mid bass was taken apart and another down firing 6.5" added in clamshell fashion. I wired them in series and in parallel to the 5" up firer.

I was sat waiting to be amazed when I pressed play on the remote. But I wasn't. The bass was really tight, infact it was so tight it had almost completely funked off. Well not quite. It did go noticeably lower but obviously the box was much too large for this configuration and the Q must be sub bessel level. Nevermind.

The most annoying thing was a resonance in the mid range. Totally ruined it. Must be caused by the chamber between the two 6.5 inchers although it never happened with the two 12 inchers I had in clamshell isobaric.

You live and learn