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Thread: My Devon Dilemma - the boxes are too small

  1. #11
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 2,551
    I'm Alex.

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    Another thought, at the other end of the frequency scale, treble, the Tannoys are merciless in revealing roughness in the top end. A lot of class D amps are optimised for 4 Ohm speakers, that is a flat frequency response in to a 4 Ohm load. If used with a higher impedance load, top end treble is likely to be emphasised.

    In this case the output filter capacitors should be changed. I sometimes run a Class D TPA3116, it's pretty good, but this treble emphasis can be heard. I should really change the filter capacitors as mentioned.

    I generally run Rogers BBC LS3/6, which have a tapped auto transformer on their input. This would allow me to change the input impedance to something lower and around 4 Ohms if I wanted. I have not tried this as yet. My favourite amp with these speakers in a Radford STA25 III.
    Spendorman

  2. #12
    Join Date: Dec 2015

    Location: vancouver

    Posts: 515
    I'm danilo.

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    Yup.. tannoys ARE merciless on low quality upstream gear.
    Also respond marvelously to even the tiniest quality improvements.. A double edged sword.
    I tried an Ta2020 'amp 6' for a short while.. before it died it proved a decent gizmo, for a wee chip device.
    But tripath chips are Extinct these days
    LM3886 chip amp device can be actually a pleasingly good amp.
    IF of first world design and parts
    MY 3116 chip amp (bought because of much internet babble praise) proved Horrid to my ears.
    Not surprised you are displeased with it
    Screechy with ugly speaker threatening extraneous on off noises
    Another Chi-Fi Ebay item..Immediately for the trashbin.
    My audio bits: Thorens / diy phono, CD/dvd player(s), diy pre, F6, Tannoy Golds in my boxes / my xovers, and of course all strung together with basic diy Wires
    Lots of Cd's, yet more audio files, a couple of hundred semi worn Lps.

  3. #13
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 2,551
    I'm Alex.

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    TPA 3116 amps are very much variable depending on how they were built, mine was built by a class D expert (not me), and is totally silent, no switch on / off thump, no other extraneous noises, just a very slight upper treble lift as mentioned, because it's used in to higher impedance speakers than it was designed for. I am far from displeased with it. At some point I may change the output filer capacitors to suit higher impedance speakers.

    I think Geoff heard my TPA3116 in to my home built LS3/5a clones. I don't think he complained too much.
    Spendorman

  4. #14
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 22,576
    I'm Geoff.

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    Quote Originally Posted by spendorman View Post
    I think Geoff heard my TPA3116 in to my home built LS3/5a clones. I don't think he complained too much.
    Yes. I thought it sounded very good. Actually, it was the best I've heard LS3/5a type speakers.
    Mr. Tact!

    Main system: MMs/ADCs/Low output MC's/One rare Japanese SUT/One scarce British phono stage/various tonearms/hefty Japanese DD TT and hefty Japanese BD TT and small British BD TT/Swiss Idler jobs. 4 CD players/2 jitter buster/2 DACs/Valve buffer. TVC, stepped attenuator or valve pre-amp/Class A SS power-amp or Class A EL34 valve monos or big Japanese (part Class A) integrated. Big and smaller dual concentric speakers and full range speakers, amongst others. And too much more to list!

  5. #15
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 22,576
    I'm Geoff.

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    Quote Originally Posted by danilo View Post
    Yup.. tannoys ARE merciless on low quality upstream gear.
    Also respond marvelously to even the tiniest quality improvements.. A double edged sword.
    That is very true.
    Mr. Tact!

    Main system: MMs/ADCs/Low output MC's/One rare Japanese SUT/One scarce British phono stage/various tonearms/hefty Japanese DD TT and hefty Japanese BD TT and small British BD TT/Swiss Idler jobs. 4 CD players/2 jitter buster/2 DACs/Valve buffer. TVC, stepped attenuator or valve pre-amp/Class A SS power-amp or Class A EL34 valve monos or big Japanese (part Class A) integrated. Big and smaller dual concentric speakers and full range speakers, amongst others. And too much more to list!

  6. #16
    Join Date: Aug 2009

    Location: Staffordshire, England

    Posts: 14,928
    I'm Martin.

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    Quote Originally Posted by spendorman View Post
    Actually, I think the infinite baffle will give a slower roll off, will go down lower. But less output at upper bass frequencies.
    Depth of bass is dependant on the overall design of the speaker, If it is ported in a way designed to augment bass then FR will roll off steeply below the tuning point but that point could be very low indeed. Before that there should be no roll off so bass would be plus or minus 3db to the lowest frequency the speaker is able to produce. If a sealed cab it will roll off slowly but gradually reducing in level.

    I think the problem here is the speaker is able to reproduce a bass frequency that excites the room, If they were producing that frequency at a low level this would not happen. I suggest that the first step is to find out at exactly what frequency this is happening at and see if it cannot be cured by simply recalculating port size and length so that the response rolls off steeply before it reaches this frequency. Changing the port size would seem the easiest fix. And easily reversible if you move to a larger room or sell them.

    However if the offending frequency is quite high, and it may be, it largely depends on the room volume, this may be impossible; or possible, but make the speaker sound very bass shy.

    A room calculator would be a start. Input the room dimensions and see what frequencies excite the room nodes. That should give a rough idea where the problem lies.

    You could also potentially solve it with bass traps but they would be large and from what you say, domestically unacceptable.
    Martin



    Current Lash Up:

    Technics SL1200 with Sumiko h/s & Nagaoka MP50 * Firebottle valve MM phono stage * Parasound CDPi1000 * NVA P90SA passive pre / Krell KSA50S Power amp * JM Lab Electra 926 loudspeakers *


  7. #17
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 2,551
    I'm Alex.

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    Quote Originally Posted by walpurgis View Post
    Yes. I thought it sounded very good. Actually, it was the best I've heard LS3/5a type speakers.
    Praise indeed, thank you. I built those LS3/5a clones about 1976. They sound quite similar to my Chartwell 15 Ohm LS3/5a's, but with slightly more extended and firmer bass, due to marginally larger/ more rigid cabinet with slightly more damping.

    It also shows that TPA3116 amps can be pretty good. Although, I'm not sure that I would build one, even though I've had a good part of my working life dealing with electronics.
    Spendorman

  8. #18
    Join Date: Mar 2012

    Location: Gloucestershire

    Posts: 3,911
    I'm Paul.

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    A few points of note:

    1. It is unwise to consider varying alterations to a properly designed port in a vented enclosure. The port is calculated to work for a specific enclosure size, so altering the point of resonance will have a marked effect on system efficiency can can lead to damage to both driver and driving amplifier if got wrong. Better to plug it completely and see how that goes.

    2. Tannoy didn't always get their port dimensions correct and the Cheviots used a port length resulting in EBS tuning, to a point way too low to be of any use at all, and allowing excessive cone excursions, especially with vinyl replay.

    Quote Originally Posted by Macca View Post
    D... I suggest that the first step is to find out at exactly what frequency this is happening at...
    +1

    however, it is not generally recommended that a port is retuned to try and solve the problem unless it is wrong to start with. The port is designed to work in conjunction with the enclosure's specific volume and the driver specific parameters. It is not a movable feast without consequence.


    I would start by assessing (as Martin points out) room response at the listening position. Beg, borrow or steal a calibrated mic and run a set of pink noise bursts and assess room response from listening position. Failing this, just use your ears, and try moving speakers to reduce standing waves. It is important not to have them positioned so that they are equi-distant from rear or side walls as this will double output at certain frequencies with standing wave reinforcement.

    12 inch drive units won't have any real disadvantages over 10 inch. Both will result in the same room excitement of the 40-60Hz room modes when the levels are matched.

    The cabinets are no doubt adding to colouration. Most vintage Tannoy factory cabs benefit from internal damping and bracing. A shaped or corner style narrow unit, made taller to get the correct internal volume, would work well because such shapes are inherently stiffer than regular rectangular boxes as well as less prone to internal standing wave formation.

    Chatsworth style cabs do have a little lift in the 40-60 Hz range partially due to internal standing waves, partly due to cabinet resonance and partly due to volume and how that works with the drive unit T&S parameters. As you can't do too much about the volume in this case, any improvements are limited to minimising internal waves, stiffening the cabinets and increasing mass to sink and damp resonances. To do this effectively, even where you may not wish to add a lot of panel mass, you need to break up the resonant frequency of the panels such that no two sub panels share the same harmonic frequencies. This means avoiding equi-spaced internal bracing. Use something like sound-clear internal damping poly-elastomer damping compounds for car panels (available from Ebay) to damp internal surfaces. Add a sloped base panel made from MDF set onto sloped battons and fill the annulus with sand or grout. The slope only needs to be 5 or 10 degrees. This will aid the avoidance of standing waves long the length of the cabinet. Finally, rip out the old mattress foam and use higher efficiency acoustic wedges to rear/top/base and sides.

    If plugging ports, then system "Q" needs working out to maintain a Q of .707 for a Butterworth response (B2), and if this proves too boomy, the stuffing can be altered (lowered) to provide a gradually lower Q to a point of say 0.5 which is usually considered over-damped (although in theory it is critically damped) but in your case, such tuning could lower the bass output in the problem area enough to make it worthwhile experimenting with this. This of course assumes a closed box (plugged port and use a substantial air tight plug). You can approximate a Q of around .71 with most cabinets by stuffing the boxes with damping compounds until about a 70 to 75% by volume is achieved as a rule of thumb (not with vented speakers). This ideally needs measured though using something like DATS (dayton audio test system) which will provide a value for Q when measuring impedance with frequency response. Then work back, removing a little at a time until the response matches the best compromise for your circumstances.

    Of course, it is better to design such things accounting for the correct internal volumes, and not always possible to effect all such improvements in smaller cabinets. The 315 requires a closed cabinet of some 75 to 100 litres or a vented cabinet from 100 to 155 litres net volume, tuned accordingly. Correct tuning if using a vented design is critical, not variable by choice without consequences. There's an article which may help explain things linked HERE


    There is no unforgiving HF response if the crossovers are properly implemented or the originals set at -1 (energy) and flat (rolloff) which is the true flat electrical setting (albeit, there is still a slight voltage lift from the autoformer). They can be very revealing but only if every other area is got right to provide that clarity. Some people mistakenly think that the revealing nature comes from using a lifted response but this is just boosting HF response to provide the detail and is painful ion the ears from the midrange upwards! The clarity comes from a balance of sorted cabinet design and sorted crossover. Then they can deliver in spades without any lift in response.

    Happy to help further and best way might be to call for a chat and take it from there. You can get 315s to work in surprisingly small spaces but it is all down to getting the cabinet right.

    There is one final trick that you can play once the port dimensions are checked and proved to be correct: Introduce a resistive plug of dense open-cell foam or similar of about an inch thick into the port. This modulates the speaker’s impedance characteristics, reducing and smoothing bass output as it creates a semi-aperiodic loading. Part-stuffing the ports or using bunches of straws as was popularised some years ago is NOT recommended.
    Last edited by Reffc; 23-12-2016 at 06:44.

  9. #19
    Join Date: Jan 2008

    Location: Forest of Dean, Glos & Cambrian mountains, Wales

    Posts: 8,157
    I'm Jerry.

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    If you have a ported speaker and room-boom, then it is definitely worth experimenting with stuffing the port with material. I use speaker wadding in mine and the amount of wadding used can be tuned to quite significantly vary the bass output.

    I actually started experimenting using socks, and that encouraged me to go further with the idea!

    I see that Paul is against the idea ...

    Quote Originally Posted by Reffc View Post
    Part-stuffing the ports or using bunches of straws as was popularised some years ago is NOT recommended.
    ... but I find it can work surprisingly well!
    I'm a let's-just-try-it empiricist and Paul likes to get the techie stuff right!
    Jerry

    Main systems:
    Spotify Premium streaming, Xiang Sheng DAC-01A. Alternating amp setups: Little Bear P8 valve pre / Nobsound NS-02G power amp & Philips Black Tulip 270 pre / Philips 380 power amp. Speakers: MBL 116F. Atratus3 i/c & Western Electric 16GA spkr cables. Missing Link Cryo Ref and Nordost Magus power cables

    Analog rig Turntable: Technics SL-150mk2 & AT-1010 arm, ADC XLM1 Integra / Linn Asak - VdH retip cartridges.

    Headphones: B&O H6, PSB M4U-1,Beyerdynamic DT-150, B&O Form 2 & 2a B&O U70, and Sony XBA-H1 & SoundMagic E10 IEM headphones

    2nd system: Pioneer DVD transport, Rotel RP-3000 tt / Goldring Eroica LX, SMSL Q5 Pro DAC/Pre-power amp, Klegg Symphony 102 speakers

  10. #20
    Join Date: Mar 2012

    Location: Gloucestershire

    Posts: 3,911
    I'm Paul.

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    Quote Originally Posted by jandl100 View Post
    If you have a ported speaker and room-boom, then it is definitely worth experimenting with stuffing the port with material. I use speaker wadding in mine and the amount of wadding used can be tuned to quite significantly vary the bass output.

    I actually started experimenting using socks, and that encouraged me to go further with the idea!

    I see that Paul is against the idea ...



    ... but I find it can work surprisingly well!
    I'm a let's-just-try-it empiricist and Paul likes to get the techie stuff right!
    I'm not against stuffing a port Jerry but part stuffing is definitely a BAD idea for the health of the loudspeaker and possibly even the driving amplifier. I am not against empirical trials but I'd like to think that an intelligent chap like yourself would appreciate that I speak from a standpoint of hard earned knowledge and experience, not from guessing! . I've given the reasoning and if you actually read the link that was posted, you'll perhaps appreciate why I gave it. It's a basic fact that tuning ports too high or low diminishes system efficiency and can cause damage. I can only give advice though and if someone chooses to ignore it, at least others reading it who might wish to learn more about it have the information . It's a science, not a guessing game where ported enclosures are concerned. As you suggest, using different materials but COMPLETELY and NOT partly stuffing the port is worth the experimentation but if one is to do that, then to get the best effect, it's often found by either closing the port completely with a hard plug OR creating an aperiodic loading whilst maintaining the port, so a dense foam about an inch thick will be better than using a sock stuffed willy-nilly into a port and at least means that you'll have something left to wear under your shoes...

    How a ported enclosure loads a room is dependent upon where the ports are positioned, their cross sectional area and the tuned frequency. Often, two different but same volume enclosures tune to the same frequency but one using ports located rear instead of front, or one using choked port tuning and too small a cross section, can ave appreciably different effects on the room response. Rear loading can lead to more boom problems for example.

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