Peter ,
take care and i hope you’ll feel better soon 
(the best vaccine)
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I have just managed to get the sweep tone to play through Roon…this is great as I can now test the filters results in Roon. I found my little minimal filter was 8hz out…re tweaked it and bingo…brilliant…nice flat response down to 40hz 
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2 x 5.5 inch Woofers do not equal 1 x 8 inch Driver they equal 2 x 5.5 inch Drivers.
The important thing is not your system can reach 25hz it is the output else your spk would
sound like a pair of Tannoys.
If you have ever played speakers in the open air you would find out the room is the strongest
part of a audio system.
You may not have worked out the length of your Piece of String !
But you can work out the dimensions of your room herein lies the answer to the problem!
I have no doubt about that, and that’s the reason I started this thread.
Sorry what do you mean by “Piece of String” and “working out the dimensions”? I’m afraid I’m lost in translation 
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2 x 5.5 drivers matically do equal 1 x 8 inch…what matters is the amount of air you can excite…to get the lower tones involves more excursion … thats why big speakers with large cone areas are easily able to maintain low frequency at sensible spls. In theory it would be possible to go down to 20hz with a 100mm driver…but the rest of the frequency range would need to suppressed by the crossover to match the output…which would mean you would have a speaker of about 60dB efficiency for 1 watt… and a speaker with no headroom as the bass would require massive excursion…
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To transfer the same amount of energy into the air, smaller cones require larger excursions at all frequencies, that is true and a simple physical fact. Relative to larger cones, they require simply greater movement to transfer the same amount of energy into the air at any given frequency.
As the frequency increases (provided the speaker system’s lower resonance point for that driver is well below frequency being reproduced) that energy is transferred with less movement, but the energy is still transferred with approximately the same efficiency, so the cone moves less and no compensation is required from the crossover. This is true for all driver units for all speakers, it applies irrespective of the size of the driver.
Yes true but speakers are not linear…show me a 100mm driver capable of delivering a frequency response from 20hz to 5khz flat… I am guessing now but you probably need about a 50mm excursion for that. Mark audio produce a driver that’s pretty good down to 40hz… that has pretty good excursion.
They are within reason: typically about 5% THD at VLF falling (due to limitations of the suspension and spider and the asymmetric acoustic suspension effect on the cone itself), falling to about 0.5% THD at higher frequencies.
Note: ^^^ I didn’t specify 4" or any other speaker dimension or specific frequency, the principle I gave (based on energy coupling analysis) applies to ALL speaker drivers irrespective of size or excursion limits. it even applies to tweeters!
[quote=“Richieroo, post:1323, topic:5761, full:true”]
2 x 5.5 drivers matically do equal 1 x 8 inch…what matters is the amount of air you can ex
[You are not arguing your own statement of how many drivers equal a bigger driver.
Which as i said is wrong. The rest is a ramble of little if any consequence.
One you are making multiple meaningless arguments which are as relevant as the age old argument about how long is a piece of string.
Two if you do not understand working out dimensions i question your ability to be posting any of your reasoning.
Could you please clear something up. Are you trying to promote/ prove someone else’s view
of things?- or do you have a question of you own you wish to put to the Forum?
I can only comment on the latter.
I assume that the volume is attenuated by means of a resistor change so it will alter the whole frequency range handled by the driver/drivers in question. I can do the same with my speakers as they are DIY. It is very handy and can really help to achieve a non fatiguing sound in any location. I really think more speakers need the feature, if only on the tweeter. I’m sure there would be many less threads about systems sounding thin and bright.
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I will explain it this way.
The static radiating area on a 250mm woofer is far more than that of 3 x 125mm units equalling a combined figure of 375mm.
But that is NOT my point which is.
If a 150mm woofer has a freq response of 45hz to 5khz and you add 10 of them the Bass will
never be lower than 45hz as this is the driver limit.
When you go from 1 unit to 2 units the overall volume will increase by 3db - 2 units to 4 units
likely another 3db.
A larger woofer of the same construction of ANY size will produce a lower Bass frequency
at a different roll off to the smaller units.
Regardless of the so called benefits of smaller drive units this fad of designing speakers by Fashion has created a situation where there is no such thing as a 8ohm spk very few 6ohm
ones and plenty that in use drop to 2 to 3ohms requiring large outputs of current from the Amplifier if a level frequency response is to be maintained.
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This explains alot when I think about my own speakers.
One of the pet hates I have is with speakers with multiple bass drivers…you seem to get a slight blurring effect on bass transients which I think is caused by small variations in driver tolerances…I think this is particularly noticeable when they are mounted close on a baffle…for that reason I prefer a single bigger cone for bass…aka DBL…
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There are a couple of misconceptions here:
When adding bass drivers, the diameter is irrelevant, the ability to drive pressure waves in the air is the product of:
total area x throw
200mm bass driver typically has a cone of about 165mm diameter; area = 0.027sq m
150mm bass driver typically has a cone of about 115mm diameter; area = 0.013sq m
2 x 150mm bass driver typically give an area of 0.026sq m, so essentially the same as a single 200mm driver.
However a it’s easier to make a 115mm cone more rigid (than a 165mm cone) and therefore work well with a lower strength suspension (i.e. spider and terminating roll) and have a longer throw, so achieving the same Fs(0) as a 200mm driver. However the 115mm cone is also likely to have a higher first break up mode frequency allowing the tweeter crossover to be higher.
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Thank you Xanthe 
Best Peter
No wonder @Mitch has such an extensive booze selection. He must need it to drown his sorrows when he listens to the dreadful bass on his speakers 
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Thanks for that…that is an extreme example…and it probably sounds just fine as the units are quite small and the blurring is summed across them all… Judging by Mitches Whisky collection I think he is a happy chappy!
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